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2006

Limnological And Landscape Factors Affecting Use Of Limnological And Landscape Factors Affecting Use Of

Manufactured Ponds By The Invasive Cuban Treefrog (Osteopilus Manufactured Ponds By The Invasive Cuban Treefrog (Osteopilus

Septentrionalis) Septentrionalis)

Terina Nusinov University of Central Florida

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STARS Citation STARS Citation Nusinov, Terina, "Limnological And Landscape Factors Affecting Use Of Manufactured Ponds By The Invasive Cuban Treefrog (Osteopilus Septentrionalis)" (2006). Electronic Theses and Dissertations, 2004-2019. 753. https://stars.library.ucf.edu/etd/753

LIMNOLOGICAL AND LANDSCAPE FACTORS AFFECTING USE OF MANUFACTURED PONDS BY THE INVASIVE CUBAN TREEFROG (OSTEOPILUS SEPTENTRIONALIS)

by

TERINA McEACHERN NUSINOV B.S. University of Central Florida, 2001

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science

in the Department of Biology in the College of Arts and Sciences at the University of Central Florida

Orlando, Florida

Spring Term 2006

ii

© 2006 Terina McEachern Nusinov

iii

ABSTRACT

Exotic amphibians are often detrimental to native biotas. In Florida, the exotic Cuban

Treefrog (Osteopilus septentrionalis) eats native frogs and may outcompete them for resources.

Cuban Treefrogs thrive in disturbed areas and around buildings, and often breed in manufactured

wetlands such as retention ponds and borrow pits. This study identified limnological, landscape,

and biotic characteristics that discouraged pond use by Cuban Treefrogs and promoted use by

native amphibian species. I sampled natural and manufactured ponds in Orange County, Florida,

for one year, using standard methods to estimate the species richness and relative abundance of

amphibians and their potential fish and macroinvertebrate predators. I determined the

relationship between the presence of Cuban Treefrogs and twelve limnological (% vegetation,

slope, pond age, pH, % dissolved oxygen, air temperature, water temperature, turbidity,

conductivity, depth, perimeter, and area) and seven landscape characteristics (% canopy closure

over ponds, building density, distance to nearest building, road density, distance to nearest road,

distance to nearest forest stand, and % forest cover), plus five biotic factors (native amphibian

richness and abundance, fish richness and abundance, and macroinvertebrate abundance). No

relationship existed between native amphibian abundance or species richness and the presence or

absence of Cuban Treefrogs. Ponds with a greater percentage of vegetation, large perimeters,

and low pH and turbidity had greater native amphibian species richness. Cuban Treefrogs were

more likely to be found in ponds with a greater percentage of aquatic vegetation and small

perimeters. My results show that building large retention ponds containing low-turbidity water

will restrict colonization by Cuban Treefrogs and maintain species richness of native

amphibians.

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ACKNOWLEDGMENTS

I thank Dr. John Fauth for serving as my advisor and providing help and guidance during

my graduate career. I also thank Drs. David Jenkins and John Weishampel for being on my

committee and providing support. Gary, my husband, deserves many thanks for being my rock

and helping me with field work and technical aspects. My parents, James and Teresa

McEachern, spurred my love of nature long ago and also assisted with call censuses. I also want

to thank my sisters Jamie, Joy, and Heather, for interest and support of my research. Orange

County Roads and Drainage gave me permission to sample retention ponds under their

jurisdiction. I am grateful to land owners who allowed me to sample their ponds: Ray Poli,

Destiny and Josh Wallen, Mr. and Mrs. Marsh, Eleanor Widows, Kevin Davis, Conni Dickinson,

Judy Mack, and the staff at Heritage Golf, Jefferson Lofts, Polos East, and High Point Club. My

fellow graduate students and friends, especially Kristine Schad and Shireen Alemadi, deserve a

great deal of thanks for providing support and feedback on papers. Those who helped with field

work deserve much gratitude: Kristine Schad, Jesse Abelson, Stephenie Alvarado, Mary Beth

Manjerovic (and for statistics help), Alaina Bernard, and Mike Piatak. Special thanks go to Julia

Noran and Lisa McCauley for helping me with my GIS map. I also want to thank the UCF

Biology Department for the Graduate Student Research Enhancement Award, which provided

financial support.

v

TABLE OF CONTENTS

LIST OF FIGURES ...................................................................................................................... vii

LIST OF TABLES......................................................................................................................... ix

LIST OF ABBREVIATIONS......................................................................................................... x

CHAPTER ONE: INTRODUCTION............................................................................................. 1

CHAPTER TWO: METHODS....................................................................................................... 6

Sampling Sites ............................................................................................................................ 6

Valencia Islands .................................................................................................................... 10

Econ Trail.............................................................................................................................. 10

Union Park Church ............................................................................................................... 10

Cypress Glen......................................................................................................................... 10

Golf Shop .............................................................................................................................. 12

High Point Club .................................................................................................................... 12

Polos...................................................................................................................................... 12

Jefferson Lofts ...................................................................................................................... 12

Bonneville ............................................................................................................................. 12

Poli ........................................................................................................................................ 13

Fairways Inverary ................................................................................................................. 13

Deerwood.............................................................................................................................. 13

Fairways Firestone ................................................................................................................ 13

Cypress Lakes Retention....................................................................................................... 13

Flowers Natural..................................................................................................................... 17

vi

Challenger Parkway Natural ................................................................................................. 17

Lake Circe Natural ................................................................................................................ 17

Fairways Natural ................................................................................................................... 17

South Tanner Natural ............................................................................................................ 19

Cypress Lakes Natural .......................................................................................................... 19

Limnological and Landscape Sampling.................................................................................... 19

Amphibian Sampling ................................................................................................................ 21

Statistical Methods.................................................................................................................... 22

CHAPTER THREE: RESULTS................................................................................................... 26

Limnological and Landscape Factors ....................................................................................... 26

Amphibian Sampling ................................................................................................................ 26

Fishes, Macroinvertebrates, Reptiles, and Birds....................................................................... 50

CHAPTER FOUR: DISCUSSION............................................................................................... 56

APPENDIX: DATA...................................................................................................................... 61

REFERENCES ............................................................................................................................. 66

vii

LIST OF FIGURES

Figure 1: Sampling sites in Orange County, Florida, USA. .......................................................... 8

Figure 2: Manufactured pond study sites, western area................................................................ 11

Figure 3: Manufactured pond study sites, central area. ................................................................ 15

Figure 4: Manufactured pond study sites, eastern area................................................................. 16

Figure 5: Natural pond study sites. ............................................................................................... 18

Figure 6: Flow chart showing variable selection for logistic regression model. This procedure

was followed for analyses of both pond types combined and for manufactured ponds only.

............................................................................................................................................... 25

Figure 7: Mean (± 1 S. E.) by pond type for statistically significant (p < 0.05) limnological

variables. ............................................................................................................................... 31

Figure 8: Mean (± 1 S. E.) species richness of native amphibians by pond type. ........................ 34

Figure 9: Significant linear regressions for log10 native amphibian species richness versus %

vegetation, log10 perimeter, pH, and log10 turbidity.............................................................. 35

Figure 10: Native amphibian species abundance (± 1 S. E.) was not significantly higher when

Cuban Treefrogs were absent or present............................................................................... 36

Figure 11: Logistic plot of the probability Cuban Treefrogs were present as a function of

turbidity, measured as nephelometric turbidity units (NTU)................................................ 38

Figure 12: Logistic plot of the probability Cuban Treefrogs were present as a function of

conductivity in millisiemens. ................................................................................................ 39

Figure 13: Logistic plot of probability Cuban Treefrogs were present as a function of native

amphibian abundance............................................................................................................ 40

viii

Figure 14: Logistic plot of probability Cuban Treefrogs were present as a function of

macroinvertebrate abundance. .............................................................................................. 41

Figure 15: Logistic plot of probability Cuban Treefrogs were present as a function of area. ...... 42

Figure 16: Receiver operating characteristic (ROC) curve for perimeter and % vegetation........ 43

Figure 17: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a

function of turbidity. ............................................................................................................. 44

Figure 18: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a

function of conductivity........................................................................................................ 45

Figure 19: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a

function of native amphibian abundance. ............................................................................. 46

Figure 20: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a

function of macroinvertebrate abundance............................................................................. 47

Figure 21: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a

function of perimeter............................................................................................................. 48

Figure 22: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a

function of fish species richness. .......................................................................................... 49

ix

LIST OF TABLES

Table 1: Number of study pond, map datum, and National Wetlands Inventory Description. ...... 9

Table 2: Mean (± 1 S. E.), t values, degrees of freedom, and p values of normally-distributed

limnological factors for manufactured (N = 14) versus natural (N = 5) ponds. ................... 28

Table 3: Mean (± 1 S. E.), t values, degrees of freedom, and p values of normally-distributed

landscape factors for manufactured (N = 14) versus natural (N = 5) ponds......................... 29

Table 4: Wilcoxon Tests for nonparametric variables.................................................................. 30

Table 5: Amphibians recorded using all sampling methods......................................................... 32

Table 6: Fishes recorded using all sampling methods. ................................................................. 51

Table 7: Bird species observed in and along ponds during sampling........................................... 52

Table 8: Macroinvertebrates and reptile species recorded using all sampling methods............... 55

x

LIST OF ABBREVIATIONS

Abbreviation Scientific Name Common Name

Amphibians AGRY Acris gryllus Southern Cricket Frog AMEA Amphiuma means Two-toed Amphiuma BTER Bufo terrestris Southern Toad EPLA Eleutherodactylus planirostris Greenhouse Frog‡ GCAR Gastrophryne carolinensis Eastern Narrowmouth Toad HCIN Hyla cinerea Green Treefrog HFEM Hyla femoralis Pine Woods Treefrog HSQU Hyla squirella Squirrel Treefrog OSEP Osteopilus septentrionalis Cuban Treefrog‡ RCAT Rana catesbeiana Bullfrog RGRY Rana grylio Pig Frog RSPH Rana sphenocephala Southern Leopard Frog SINT Siren intermedia Lesser Siren SLAC Siren lacertina Greater Siren

Fishes ANEB Ameiuris nebulosus Brown Bullhead EAME Esox americanus Redfin Pickerel EEVE Elassoma evergladeii Everglades Pygmy Sunfish EFUS Etheostoma fusiforme Swamp Darter EGLO Enneacanthus gloriosus Blue Spotted Sunfish EOKE Elassoma okefenokee Okefenokee Pygmy Sunfish FCHR Fundulus chrysotus Golden Topminnow GHOL Gambusia holbrooki Mosquitofish HFOR Heterandria formosa Least Killifish HLIT Haplosternum littorale Brown Hoplo‡ LGUL Lepomis gulosus Warmouth LMAC Lepomis macrochirus Bluegill LMAR Lepomis marginatus Dollar Sunfish LMIC Lepomis microlophis Redear Sunfish MSAL Micropterus salmoides Largemouth Bass NCRY Notemigonus crysoleucas Golden Shiner PLAT Poecilia latipinna Sailfin Molly

Macroinvertebrates BELO Belostoma sp. Water Bug CYBI Cybister sp. Diving Beetle DRAG Dragonfly (Anisoptera) DYTS Dysticid Beetle

xi

HYDS Hydrophilus sp. Water Scavenger Beetle LAME Lethocerus americanus Giant Water Bug NAIA Dragonfly Naiad (Anisoptera) NAUC Creeping Water Bug (Naucorid) PROC Procambarus sp. Crayfish RANA Ranatra sp. Water Scorpion

Reptiles AFER Apalone ferox Florida Softshell Turtle AMIS Alligator mississippiensis American Alligator CCON Coluber constrictor Black Racer EOBS Elaphe obsoleta Yellow Rat Snake KBAU Kinosternon baurii Striped Mud Turtle NFAS Nerodia fasciata Banded Watersnake NFLO Nerodia floridana Florida Green Watersnake SODO Sternotherus odoratus Common Musk Turtle

Birds AALB Ardea alba Great Egret AANH Anhinga anhinga Anhinga AFUL Anas fulvigula Mottled Duck AHER Ardea herodius Great Blue Heron APHO Agelaius phoeniceus Red-winged Blackbird APLA Anas platyrhynchos Mallard BVIR Butorides virescens Green Heron EALB Eudocimus albus White Ibis ECAE Egretta caerulea Little Blue Heron ETHU Egretta thula Snowy Egret ETRI Egretta tricolor Tricolor Heron GCAN Grus canadensis Sandhill Crane GCHL Gallinula chloropus Common Moorhen MAME Mycteria americana Wood Stork PAUR Phalacrocorax auritus Double-crested Cormorant PFAL Plegadis falcinellus Glossy Ibis PHAL Pandion haliaetus Osprey PPOD Podilymbus podiceps Pied-billed Grebe ‡ Non-native species

1

CHAPTER ONE: INTRODUCTION

Exotic species are defined as any introduced organisms that are not native to an area and

may be considered a nuisance: for example, exotic species contribute to the endangered or

threatened status of 42% of animals and plants on the U.S. endangered species list (Bryant 2002).

Exotic species often outcompete native species for resources and cost the United States an

estimated $138 billion in environmental damage and loss each year. Control of exotic reptiles

and amphibians alone cost $604,000 per year at the end of the last century in the United States

(Pimentel et al. 1999). About 32% of amphibians are globally threatened (Stuart et al. 2004),

and introduction of exotic amphibians and non-native fishes are cited among the many causal

factors (Wilson and Porras 1983, Barinaga 1990, Wake 1991, Blaustein 1994, Blaustein et al.

1994, Fisher and Shaffer 1996, Adams 1999, Collins and Storfer 2003, Kats and Ferrer 2003).

Deliberate and accidental introductions enable increasing numbers of exotic amphibians and

fishes to colonize and spread into non-native areas. For example, Marine Toads (Bufo marinus)

were introduced in Hawaii, Australia, and Florida to control beetles in sugar cane fields, but

quickly became a dangerous invasive (Pemberton 1933, Riemer 1958, Punzo and Lindstrom

2001, The State of Queensland 2003). Bullfrogs (Rana catesbeiana), which are not native to the

western United States, eat and outcompete native amphibians and contributed to the decline of

many western species (Moyle 1973, Bury and Luckenbach 1976, Hayes and Jennings 1986, Pearl

et al. 2004). Bullfrogs also were introduced to northwestern Europe, where they pose a potential

threat to native amphibians (Stumpel 1992).

Introduced fish can have similar negative effects on native salamanders and frogs.

Introduced trout significantly reduced larval densities of Long-toed Salamanders (Ambystoma

2

macrodactylum) in high-elevation lakes in Washington (Tyler et al. 1998), and introduced

goldfish (Carassius auratus) can eat enough native Eastern Long-toed Salamander (Ambystoma

macrodactylum) eggs to threaten the salamander population’s survival (Monello and Wright

2001). Introduced mosquitofish (Gambusia holbrooki) and crayfish (Procambarus clarkii) in the

Santa Monica Mountains, California, can consume enough California Newt (Taricha torosa)

eggs to potentially inhibit the newt’s reproductive success (Gamradt and Kats 1996). Introduced

mosquitofish and trout (Oncorhynchus sp.) prey heavily on Pacific Treefrogs (Hyla regilla) in

the Santa Monica Mountains and in the Sierra Nevada, California (Goodsell and Kats 1999,

Matthews et al. 2001), and introduced sunfish (Lepomis sp.) reduced survival to near zero for

Pacific Treefrogs and Red-legged Frogs (Adams 2000). Introduced fish also eliminated

Mountain Yellow-legged Frogs (Rana mucosa) in Sequoia and Kings Canyon National Parks in

California (Bradford et al. 1993), and likely caused declines in other protected areas (Knapp and

Matthews 2000). Invasive species have been implicated in the decline of many amphibian

species (Kats and Ferrer 2003), and without management many invasive species will continue to

expand their ranges.

My study identified characteristics of manufactured ponds that promote native amphibian

species instead of the Cuban Treefrog (Osteopilus septentrionalis), which is an exotic species in

Florida and several Caribbean islands (Joglar and Lopez 1995, Meshaka 2001). Cuban Treefrogs

probably arrived in the Florida Keys in cargo imported from Cuba in 1931 (Barbour 1931). The

habitats of central and southern Florida are very similar to those within their native range, which

allowed Cuban Treefrogs to colonize much of Florida (Meshaka 2001), with deleterious effects

on native species. In Everglades National Park (ENP), Cuban Treefrogs ate five species of

native frogs including Southern Toads (Bufo terrestris), Eastern Narrowmouth Toads

3

(Gastrophryne carolinensis), Southern Leopard Frogs (Rana sphenocephala), Green Treefrogs

(Hyla cinerea), and Squirrel Treefrogs (Hyla squirella) (Meshaka 2001). In laboratory

experiments, Cuban Treefrogs also ate Green Treefrogs (Wyatt and Forys 2004), and Cuban

Treefrog tadpoles reduced growth and development rates of Green Treefrog and Southern Toad

larvae (Smith 2005). By the mid 1990’s the range of Cuban Treefrogs extended to central

Florida (Meshaka 1996a) and Cuban Treefrogs now are common in the Orlando area, and along

Florida’s east coast as far north as New Smyrna Beach, Volusia County (Campbell 1999).

Seven life-history traits make Cuban Treefrogs a successful colonizer (Meshaka 2001):

1. High fecundity (mean clutch size: 3961 ± 2211.8, S. D.) and a long breeding season.

Cuban Treefrogs can breed year-round, although most breeding occurs from May to

October (Florida Wildlife Extension 1995, Meshaka 2001).

2. Short generation time. Cuban Treefrogs undergo metamorphosis within about 27 d post-

hatching; for females, the shortest estimated time to maturity is 7 - 9 months after

transformation (Meshaka 2001).

3. Wide physiological tolerance range, including to pond temperatures of 12-41° C (Meshaka

2001).

4. Larger body size than other hylids, which enables Cuban Treefrogs to have large clutches

of eggs, exploit large prey, and avoid some predators. Average adult snout-vent length

(SVL) is 45-50 mm, with a maximum SVL of 165 mm for females and 112 mm for males

(Mittleman 1950, Meshaka 1996b).

5. Potentially superior competitive ability compared to native species for resources such as

food, especially within disturbed areas such as human developments (Meshaka 2001).

4

6. A broad range of prey sizes, which includes invertebrates, vertebrates, and conspecifics. In

ENP, female Cuban Treefrogs consumed prey that were 12.2 ± 7.8 mm (mean and standard

deviation), while males, females, and juveniles combined consumed prey that were 10.9 ±

7.5 mm (mean and standard deviation: Meshaka 2001).

7. Ability to coexist well with humans (Meshaka 1996c, d, Meshaka 2001).

Human-altered landscapes often create aquatic habitats for amphibians (Ostergaard and

Richter 2001), including Cuban Treefrogs. All Florida anurans except the introduced

Greenhouse Frog (Eleutherodactylus planirostris) lay their eggs in water and most will breed in

manufactured ponds such as borrow pits, retention ponds and ornamental ponds (Babbitt and

Tanner 1997, Kent and Langston 2000). Cuban Treefrogs also deposit eggs in swimming pools,

sewers, cisterns, culverts, ponds, ornamental ponds and bird baths (Florida Wildlife Extension

1995, Meshaka 2001). Within ENP, abundance of Cuban Treefrogs was positively correlated

with presence of disturbed areas, buildings and lighting (Meshaka 2001, Rice et. al 2002), which

often are located near manufactured ponds. Therefore, suburban ponds have potential to become

source populations that accelerate the spread of Cuban Treefrogs.

Currently, design and placement of manufactured ponds are left to the developer, with

guidelines dictating only that manufactured ponds be aesthetically pleasing to the community

and provide a place for wildlife (Urban Design Element 1998). Typical manufactured-pond

design, which places ponds in disturbed areas and in close proximity to buildings, appears to

favor Cuban Treefrogs, but could be altered to favor native amphibians. Meshaka (2001)

identified several landscape types in ENP that were difficult for Cuban Treefrogs to invade. For

example, no Cuban Treefrogs were found in sawgrass marsh or in high water. Areas that were

too dry, too wet, burned frequently, or lacked vertical structure (e. g., vegetation or buildings) or

5

refugia also were not used by Cuban Treefrogs, but had larger populations of native frogs; more

Green Treefrogs and Squirrel Treefrogs than Cuban Treefrogs were found in marsh habitat

(Meshaka 2001).

My study tested three null hypotheses about the relationship between amphibian diversity

in natural and manufactured ponds.

1. Ho1: Native amphibian abundance and richness is independent of Cuban Treefrog

presence.

2. Ho2: Cuban Treefrog presence and absence is independent of limnological and landscape

characteristics, and biotic factors.

3. Ho3: Native species richness is independent of limnological, landscape, and biotic

characteristics.

The purpose of my research is to provide guidelines for pond construction that discourages

expansion of Cuban Treefrog populations and promotes use of manufactured ponds by native

amphibians.

6

CHAPTER TWO: METHODS

Sampling Sites

I sampled fourteen manufactured and six natural ponds in eastern Orange County,

Florida, using State Road 50 as the center of a 15 km long belt transect (Figure 1). Ponds were

within a band approximately 2 km north and south of State Road 50, with State Road 419

(Chuluota Road) and State Road 50 forming the eastern boundary and State Road 551

(Goldenrod Road) and State Road 50 as the western boundary. Originally, I intended this as an

urban-rural transect, but rapid development on the eastern border of my study site prevented this

comparison. I numbered all manufactured ponds within the transect, and used a random number

generator to select fourteen of them (Haahr 2000). Doing so minimized bias in pond selection

and provided a random sample. When I was unable to gain access to ponds, I selected another

using the random number generator. I paired six manufactured ponds with the nearest natural

pond to minimize spatial variation and facilitate comparison of pond characteristics. I also

planned to compare each manufactured pond to a nearby natural pond, but I was unable to

acquire permission to sample equal numbers of manufactured and natural ponds. Mean distance

between paired ponds was one kilometer (S. D. = 627 m). One natural pond located off

Challenger Parkway was demolished in August 2005, five months into my study so data from

this pond were not included in any analyses.

All 14 manufactured ponds (Table 1) were classified as permanent, excavated ponds by

the National Wetlands Inventory (NWI) classifications (United States Fish and Wildlife Service

2006). The six natural ponds were classified as having unconsolidated, scrub-shrub or deciduous

bottoms, and being in seasonally or semipermanently flooded habitat. I verified that Flowers

7

Natural was a natural pond from a 1947 aerial photograph (Record 101, Flight FIPS 12095,

Flight # 4D, Tile # 7 (State University System of Florida 2004)), despite being misclassified by

NWI as excavated. The discrepancy arose because a small section of the pond was excavated at

one point in the past. All ponds contained enough water to set traps throughout the study except

Fairways Natural and Fairways Firestone, which were mostly dry in March 2006. Manufactured

ponds are described below, in order from west to east, followed by natural ponds described west

to east.

8

http://mappoint.msn.com

Figure 1: Sampling sites in Orange County, Florida, USA. Solid line indicates northern and southern boundaries of a 4 km-wide belt transect centered on State Road 50 (Colonial Drive). Natural (circles) and manufactured (triangles) ponds were identified using an aerial photograph (DOQ, 2002) (www.terraserver.microsoft.com). Inset shows study-site location in Orange County, Florida.

9

Table 1: Number of study pond, map datum, and National Wetlands Inventory Description. National Wetlands Inventory Description for Palustrine Wetlands

# Pond Name N Latitude W Longitude Code Bottom Habitat 1 Valencia Islands 81°15’29.83” 28°33’21.59” PUBHx† Unconsolidated Permanently flooded, excavated 2 Econ Trail 81°15’17.05” 28°34’25.95” PUBHx † Unconsolidated Permanently flooded, excavated 3 Union Park Church 81°14’35.86” 28°34’31.14” PUBHx Unconsolidated Permanently flooded, excavated 4 Cypress Glen 81°14’39.25” 28°33’35.54” PUBHx † Unconsolidated Permanently flooded, excavated 5 Golf Shop 81°13’29.54” 28°34’02.96” PUBHx † Unconsolidated Permanently flooded, excavated 6 High Point Club 81°13’15.36” 28°33’34.91” PUBHx † Unconsolidated Permanently flooded, excavated 7 Polos 81°11’43.46” 28°33’43.29” PUBHx † Unconsolidated Permanently flooded, excavated 8 Jefferson Lofts 81°12’11.14” 28°34’11.14” PUBHx † Unconsolidated Permanently flooded, excavated 9 Bonneville 81°11’23.94” 28°34’07.14” PUBHx † Unconsolidated Permanently flooded, excavated 10 Poli 81°10’43.31” 28°34’35.83” PUBHx Unconsolidated Permanently flooded, excavated 11 Fairways Inverary 81°10’23.22” 28°34’22.05” PUBHx † Unconsolidated Permanently flooded, excavated 12 Deerwood 81°10’19.23” 28°33’23.85” PUBHx † Unconsolidated Permanently flooded, excavated 13 Fairways Firestone 81°09’39.91” 28°34’14.83” PUBHx Unconsolidated Permanently flooded, excavated 14 Cypress Lakes Retention 81°07’34.79” 28°34’03.51” PUBHx † Unconsolidated Permanently flooded, excavated 15 Flowers Natural 81°14’21.78” 28°33’50.76” PUBG Unconsolidated Permanently flooded, excavated 16 Challenger Pkwy. Natural* 81°12’18.07” 28°34’26.82” PSS1C Scrub-shrub Broad-leaved deciduous, seasonally flooded 17 Lake Circe Natural 81°11’02.59” 28°34’04.80” PEM1F Emergent Persistent, Semipermanently flooded 18 Fairways Natural 81°10’21.79” 28°33’56.73” PEM1F Emergent Persistent, Semipermanently flooded 19 South Tanner Natural 81°08’28.52” 28°33’47.08” PEM1F Emergent Persistent, Semipermanently flooded 20 Cypress Lakes Natural 81°07’03.16” 28°34’00.04” PFO6F Forested Deciduous, Semipermanently flooded *Pond demolished early August 2005. †PUBHx code assumed, no NWI data available for recently-built ponds

10

Valencia Islands Valencia Islands (Figure 2a) was a retention pond located in the middle of the Valencia

Islands neighborhood and maintained by Orange County Roads and Drainage. The pond was

surrounded by mowed grass, had some torpedo grass (Panicum repens) and road grass

(Eleocharis baldwinii) present and lacked canopy cover.

Econ Trail Econ Trail (Figure 2b) was a retention pond located south of Econ River Estates and

maintained by Orange County Roads and Drainage. The pond was surrounded by mowed grass,

had some road grass and water pennywort (Hydrocotyle umbella), and no canopy cover.

Union Park Church Union Park Church (Figure 2c) was a borrow pit located east of the church and

maintained by it. This pond was surrounded by sweet gum (Liquidambar styraciflua), oaks

(Quercus spp.), greenbrier (Smilax sp.) and muscadine grape (Vitis rotundifolia), contained

torpedo grass and fragrant water lily (Nymphaea odorata), and had moderate canopy cover.

Cypress Glen Cypress Glen (Figure 2d) was a retention pond located west of the Cypress Glen

neighborhood and maintained by Orange County Roads and Drainage. The pond was

surrounded by mowed grass and had steep slopes on the east, south, and west sides. Some water

pennywort and algae were present but the pond had minimal canopy cover. The pond also had a

fountain, which rarely was on during my study.

11

(a) (b)

(c) (d)

(e) (f)

Figure 2: Manufactured pond study sites, western area. Valencia Islands, taken May 4, 2005, facing north (a), Econ Trail, taken May 4, 2005, facing northwest (b), Union Park Church, taken April 30, 2005, facing northeast (c), Cypress Glen, taken on May 5, 2005, facing east (d), Golf Shop, taken May 3, 2005, facing northwest (e), and High Point Club, taken on May 3, 2005, facing southwest (f).

12

Golf Shop Golf Shop (Figure 2e) was a retention pond located about 20 m west of the Heritage Golf

Retail Center and was maintained by it. The pond was surrounded by mowed grass, had cattail

(Typha sp.), Carolina willow (Salix caroliniana) and giant duckweed (Spirodela polyrhiza)

around its border, and some canopy cover.

High Point Club High Point Club (Figure 2f) was a retention pond located west of the High Point Club

apartments and was maintained by the apartments. The pond was mostly surrounded by mowed

grass and had cypress (Taxodium sp.) on the west side. Carolina willow and giant duckweed

were present and the pond had some canopy cover.

Polos Polos (Figure 3a) was a retention pond located south of Polos East apartment complex

and maintained by the community. The pond was surrounded by mowed grass on three sides and

had a wooded area on the south side, which consisted of red maple (Acer rubrum), pine (Pinus

sp.) and cypress. Cattails and torpedo grass were present, and it had little canopy cover. The

fountain was on throughout my study.

Jefferson Lofts Jefferson Lofts (Figure 3b) was a retention pond surrounded by the Jefferson Lofts

apartments and maintained by the community. The pond was surrounded by mowed grass, had

some road grass and fragrant water lily, and no canopy cover. The fountain (visible in the upper

left corner of Figure 3b) was on throughout my study.

Bonneville Bonneville (Figure 3c) was a retention pond located west of the Pine Creek housing

development and maintained by Orange County Roads and Drainage. The pond was surrounded

by mowed grass and had a wooded area nearby, comprised of secondary-growth pine, cypress,

13

red maple, and saw palmetto (Serenoa repens). Some torpedo grass and water pennywort were

present and the pond had no canopy cover.

Poli Poli (Figure 3d) was a borrow pit located toward the east side of Naomi Poli’s property.

The pond was surrounded by mowed grass, some pine, red maple, loblolly bay (Gordonia

lasianthus) and netted chain fern (Woodwardia areolata). Some torpedo grass and pickerelweed

(Pontederia cordata) were present and the pond had well-developed canopy cover.

Fairways Inverary Fairways Inverary (Figure 3e) was a retention pond located south of the Fairways golf

course and housing community and was maintained by the community. The pond was

surrounded by mowed grass, had a minimal amount of road grass, and no canopy cover.

Deerwood Deerwood (Figure 3f) was a retention pond located west of the Deerwood housing

development and maintained by the community. The pond was surrounded by mowed grass, had

a small amount of water pennywort, and no canopy cover. The nearest wooded area consisted of

pine and sweet gum (Liquidambar styraciflua).

Fairways Firestone Fairways Firestone (Figure 4a) was a retention pond adjacent to the Fairways golf course

and housing community and was maintained by the community. The pond was surrounded by

mowed grass, had 3-4 pine trees about 5 m from the northern and southern pond edges, a small

amount of water pennywort, and no canopy cover.

Cypress Lakes Retention Cypress Lakes Retention (Figure 4b) was a retention pond located west of the Cypress Lakes

housing development and maintained by the community. It was surrounded by mowed grass,

14

had 3-4 pine trees about 5 m from the pond edge, a small amount of torpedo grass present and no

canopy cover. The fountain was on throughout my study.

15

(a) (b)

(c) (d)

(e) (f)

Figure 3: Manufactured pond study sites, central area. Polos, taken May 1, 2005, facing south (a), Jefferson Lofts, taken March 10 2006, facing southwest (b), Bonneville, taken on March 10, 2006, facing northwest (c), Poli, taken May 1, 2005, facing northeast (d), Fairways Inverary, taken on May 3, 2005, facing east (e), and Deerwood, taken on May 4, 2005, facing northeast (f).

16

(a) (b)

Figure 4: Manufactured pond study sites, eastern area. Fairways Firestone, taken May 3, 2005, facing northwest (a), and Cypress Lakes Retention, taken on May 5, 2005, facing northwest (b).

17

Flowers Natural

Flowers Natural (Figure 5a) was a natural pond with cypress trees (Taxodium sp.) in the

center and surrounded by three homes. Cypress, red maple (Acer rubrum) and elephant ear

(Xanthosoma sagittifolium) around the periphery provided moderate canopy cover. The pond

had torpedo grass, giant duckweed and water lettuce (Pistia stratiotes) in it.

Challenger Parkway Natural Challenger Parkway Natural (Figure 5b) was a natural pond near the intersection of State

Road 434 (Alafaya Trail) and Challenger Parkway, and was filled for commercial development

in August 2005. The pond was surrounded by some small trees and shrubs and was adjacent to a

retention pond and a small wooded area comprised mostly of pine. Bog buttons (Lachnocaulon

sp.), rushes and water pennywort were present and the pond had some canopy cover. The pond

contained water from the start of the study until it was destroyed.

Lake Circe Natural Lake Circe Natural (Figure 5c) was a donut-shaped natural cypress pond located

southwest of Lake Pickett Manor. The pond was surrounded by mowed grass and some saw

palmetto. Fragrant water lily, pickerelweed, bog buttons, and maidencane (Panicum hemitomon)

were present in the center. Cypress around the edges provided canopy cover over approximately

40 % of the pond.

Fairways Natural Fairways Natural (Figure 5d) was a natural pond located north of State Road 50 at the

entrance to the Fairways community and maintained by it. The pond was mostly surrounded by

mowed grass and had Carolina willow (Salix caroliniana) and St. John’s- wort (Hypericum sp.)

on its periphery. The east end of the pond was dominated by cattails (Typha sp.) and a small

amount of canopy cover, provided by pines and oaks, on its northern and western sides.

18

(a) (b)

(c) (d)

(e) (f)

Figure 5: Natural pond study sites. Flowers Natural, taken June 14, 2005, facing northwest (a), Challenger Parkway Natural before it was destroyed, taken May 1, 2005, facing northeast (b), Lake Circe Natural, taken May 1, 2005, facing northwest (c), Fairways Natural, taken May 3, 2005, facing southeast (d), South Tanner Natural, taken April 30, 2005, facing north (e), Cypress Lakes Natural, taken March 5, 2006, facing north (f).

19

South Tanner Natural

South Tanner Natural (Figure 5e) was a natural pond located on the north side of Destiny

and Josh Wallen’s property. The pond was surrounded on three sides by a wooded area

comprised of red maple (Acer rubrum), pine (Pinus sp.) and sweet gum (Liquidambar

styraciflua). Some fragrant water lily (Nymphaea odorata) and canopy cover were present.

Cypress Lakes Natural Cypress Lakes Natural (Figure 5f) was a natural cypress dome in the middle of the

Cypress Lakes neighborhood. The pond was surrounded by mowed grass and had two retention

ponds nearby. A large amount of submerged vegetation (e. g., bladderworts, Utricularia sp.) and

emergent vegetation (e. g., St. John’s-wort, Bog buttons, and maidencane) were present and most

of the pond had canopy cover.

Limnological and Landscape Sampling

At each site, I measured eleven limnological variables that often affect the suitability of

ponds as amphibian breeding sites and might influence Cuban Treefrogs. I determined the

percent vegetation cover at each pond, including submerged and emergent vegetation which

provides potential habitat for tadpoles, using twelve 1 m2 PVC quadrats. I placed quadrats at the

cardinal positions of the pond (about 0.25 m from the pond edge), four midway between them

(e.g. northwest, southeast, southwest, and northwest), and four toward the pond center, diagonal

from the northwest, northeast, southeast, and southwest positions. I measured pond slope as the

mean value of four cardinal measurements with a clinometer. I determined pond age by

consulting landowners and county records. During each sampling period, I measured standard

abiotic factors such as pH, air temperature, dissolved oxygen, water temperature (instantaneous,

20

maximum and minimum), turbidity, conductivity, and morphological characters such as pond

depth, perimeter, and area. I used an Orbeco-Hellige Model 966 Portable Turbidimeter (Orbeco

Analytical Systems, New York) to measure turbidity and a YSI 556 Multiprobe System (YSI

Incorporated, Yellow Springs, Ohio) to measure dissolved oxygen, pH, conductivity, and water

temperature. I calibrated the meter before sampling each pond.

I measured seven landscape variables that could affect amphibian diversity. I measured

% canopy openness with hemispherical photographs and analyzed them with Gap Light Analyzer

software (Frazer et al. 1999). I took a hemispherical photograph in the center of the eleven

ponds with canopy cover and trimmed out surrounding trees using the Gap Light Analyzer

software. I did not take hemispherical photographs at Valencia Islands, Econ Trail, Jefferson

Lofts, Bonneville, Fairways Inverary, Deerwood, Fairways Firestone, and Cypress Lakes

Retention ponds because there were no trees overhanging these ponds. I later converted %

canopy openness to % canopy closure by subtracting % canopy openness from 100. Available

light influences habitat quality and thereby growth rates of some larval amphibians (Werner and

Glennemeier 1999, Skelly et al. 2002, Halverson et al. 2003, Skelly et al. 2005). I determined

building density, road density, and % forest cover from aerial photographs (Digital Orthophoto

Quadrangles, DOQs) and ArcGIS 9 (ESRI, Redlands), and directly measured or used a

rangefinder or Geographical Information Systems (GIS) to determine distance to the nearest

building, forest, and road. I counted all buildings and roads and estimated % forest cover within

a 250 m buffer zone from each pond edge. This distance is suggested as the minimum required

terrestrial buffer zone for amphibians (Semlitsch 1998, Semlitsch and Bodie 2003). I defined

forest as a wooded area > 5000 m2 (> 0.5 hectares).

21

Amphibian Sampling

I determined the species richness and abundance of native and exotic amphibians using

three standard methods: trapping, dipnetting, and calling censuses. I used unbaited plastic

minnow traps to estimate the relative abundance of amphibians, as well as fishes and

macroinvertebrates. I used a random number generator to determine the order I visited ponds

during all sampling sessions, which were conducted in March, June, July, and September, 2005,

and in March 2006. During each session, I set four traps at each of the cardinal points for a total

of sixteen traps (as in Eason and Fauth 2001). Plastic fish traps (model MT1) were purchased

from Aquatic Eco-Systems, Inc. (Apopka, Florida) and had a mesh size of 4.8 mm and an

entrance diameter of 22 mm. The four groups of traps were equidistant from each other and set

in water shallow enough (< 15 cm) for animals with lungs to breathe. Traps remained in ponds

for 24 hours, and then I identified, staged, sexed, and released all animals captured. I also used

dipnetting and visual censuses to detect Cuban Treefrogs and other amphibian, fish, and

macroinvertebrate species. I walked around each pond with the dipnet and made one meter

sweeps at 4-5 sites at each cardinal direction and recorded any species not captured previously in

minnow traps. I determined the abundance of fish and macroinvertebrates by their inadvertent

capture in minnow traps and dipnet sweeps for amphibians. I recorded relative abundance of

fishes, macroinvertebrates, and presence of reptiles and birds because they were potential

predators of amphibian larvae, as well as potential indicators of pond quality.

I censused chorusing amphibians during and immediately after rainfall or in the evening.

Calling censuses are useful for determining the relative abundance, species composition,

breeding habitat, and presence of anurans that otherwise are difficult to observe (Heyer et. al

22

1994). I censused amphibians for at least 5 min at each site, usually from 2030 to 2300 h, and

visited 10 ponds a night. I recorded the number of males calling, species, weather conditions,

and air temperature at the beginning and end of each session. I censused on April 7, May 21,

May 31, June 30, August 25, and September 7, 2005, and January 13 and February 3, 2006, for a

total of eight sessions.

Statistical Methods

I used a t-test to test the null hypotheses that mean abundance and richness of native

amphibian species were independent of Cuban Treefrog presence, and whether mean

limnological, landscape, and biotic factors were independent of manufactured or natural ponds. I

log-transformed turbidity and native amphibian species richness to meet t-test assumptions.

Conductivity, slope, % canopy closure, nearest forest, and reptile richness did not meet the

assumption of normality so I used a Wilcoxon signed-rank test to examine differences in

medians.

I used logistic regression to test the null hypothesis that the presence and absence of

Cuban Treefrogs were independent of continuous limnological and landscape variables, richness

of native amphibians, and the relative abundance of amphibians, fishes and macroinvertebrates.

After evaluating each factor individually to identify those that were significant (limnological,

landscape, or biotic variables), a backward stepwise logistic regression determined which

variables were most important in predicting the presence and absence of Cuban Treefrogs

(Figure 6). The critical probability to remove a variable was 0.10. Due to multicollinearity, I

excluded slope, % dissolved oxygen, minimum temperature, and area, but retained % vegetation,

23

pH, air temperature, pond temperature, maximum pond temperature, turbidity, conductivity, and

perimeter. I excluded depth because I did not receive permission to measure it in one pond

(Jefferson Lofts). To determine if pond perimeter scaled with pond area, I used linear regression

with perimeter as my dependent variable and the square root of area as my independent variable.

I fit a line to the data and saved the residuals, which I used in logistic regression and linear

regression plots that originally had perimeter in them. I found that perimeter is not independent

of area. I decided to use perimeter instead of area because perimeter was measured more

accurately. For landscape variables, I excluded road density and nearest road due to

multicollinearity, but retained distance to nearest building, building density/250 m buffer zone,

nearest forest, forest density/250 m buffer zone, and % canopy closure. I considered variables to

be multicollinear if the pair of variables had a r > 0.6, and a p value < 0.05. I then analyzed all

significant variables from the three initial logistic regressions (perimeter, % vegetation, and

macroinvertebrate abundance) using one final, backward stepwise logistic regression (Figure 6).

Next, because manufactured and natural ponds differed significantly in some parameters,

I analyzed data with logistic regression only on manufactured ponds to identify factors that

affected the distribution of Cuban Treefrogs in them. I followed the same procedure as above: I

determined which parameters were important individually, then ran the three groups in a

backward stepwise logistic regression model (minus the multicollinear variables mentioned

above), and then combined significant parameters from all groups in a final backward stepwise

model to determine a final model.

I used linear regression to test the null hypothesis that native amphibian species richness

was independent of limnological, landscape, and biotic factors. I log-transformed native

amphibian species richness, turbidity and perimeter to meet the assumptions of normality. I used

24

G-tests of independence to test the null hypothesis that presence of amphibian, fish,

macroinvertebrate (the five most common taxa), bird, and reptile species, were independent of

pond type. I also used G-tests of independence to test the null hypothesis that presence of native

amphibian and fish species were independent of presence and absence of Cuban Treefrogs. I

used JMP version 5.1 (SAS Institute 2003) to perform statistical analyses, with α = 0.05 for all

hypothesis tests.

25

Figure 6: Flow chart showing variable selection for logistic regression model. This procedure was followed for analyses of both pond types combined and for manufactured ponds only.

Excluded limnological variables that

were multicollinear.

Entered remaining

variables into backward stepwise logistic

regression.

Kept significant

limnological variables.

Excluded landscape

variables that were

multicollinear.

Entered remaining landscape

variables into backward stepwise logistic

regression.

No variables were

significant.

No biotic variables were multicollinear.

Entered biotic variables into

backward stepwise logistic

regression.

Entered remaining limnological and biotic variables into backward

stepwise logistic regression.

Kept remainingsignificant variables.

Kept significant

biotic variables.

26

CHAPTER THREE: RESULTS

Limnological and Landscape Factors

Manufactured and natural ponds differed significantly in six limnological metrics and one

landscape metric (Tables 2 and 3). Mean percent vegetation was significantly higher in natural

ponds than in manufactured ponds, while mean pH, dissolved oxygen, log10 turbidity, pond

temperature and depth were significantly higher in manufactured ponds than in natural ponds

(Figure 7). Among the landscape parameters, only percent canopy closure was significantly

higher in natural ponds than manufactured ponds (Table 4). On average, natural ponds had 27%

higher % vegetation and 31% more canopy cover than manufactured ponds, but had a mean pH

that was 1.1 units lower. Manufactured ponds also averaged 37.5% greater % dissolved oxygen,

turbidity that was 5.27 nephelometric turbidity units higher and pond temperatures that were 2º C

warmer. Manufactured ponds also were about twice as deep as natural ponds. No other

limnological or landscape factors differed significantly between manufactured and natural ponds.

Amphibian Sampling

I recorded a total of 1088 amphibian individuals comprising 14 amphibian species (Table

5) in the 19 ponds that remained undestroyed during my study. This is 63% (14 of 22) of the

number of amphibian species recorded in Orange County (United States Geological Survey

2006). I did not find Oak Toads (Bufo quercicus), Barking Treefrogs (Hyla gratiosa), Spring

Peepers (Pseudacris crucifer), Chorus Frogs (Pseudacris nigrita), Little Grass Frogs (Pseudacris

ocularis), Gopher Frogs (Rana capito), Bronze Frogs (Rana clamitans), and Eastern Spadefoots

27

(Scaphiopus holbrookii). Southern Toads (Bufo terrestris) were the most common amphibian

species recorded, followed by Leopard Frogs (Rana sphenocephala), and Green Treefrogs (Hyla

cinerea). Greenhouse Frogs (Eleutherodactylus planirostris) and Pine Woods Treefrogs (Hyla

femoralis) were the rarest. Ranids were absent from four ponds and hylids were absent from five

ponds. The only salamander species detected were Lesser Sirens (Siren intermedia), Greater

Sirens (Siren lacertina) and Amphiumas (Amphiuma means), which in total were trapped in

seven ponds. The most species-rich pond was Fairways Natural (S = 10), followed by

Challenger Parkway Natural (S = 9), and High Point Club (S = 8). Deerwood had the lowest

species richness (S = 1), followed by six other retention ponds: Union Park Church, Cypress

Glen, Jefferson Lofts, Poli, Fairways Inverary, and Cypress Lakes Retention (all S = 2). Pig

Frogs (Rana grylio), Greater Sirens (Siren lacertina) and Lesser Sirens (Siren intermedia) were

significantly more common in natural ponds than manufactured ponds (all three had χ2 > 3.69, d.

f. = 1, p < 0.05). No other amphibian species was significantly more common in one pond type

than the other. Leopard Frogs were the only native amphibian that were significantly more

common in ponds when Warmouth were absent (χ2 = 10.2, d. f. = 1, p < 0.00).

28

Table 2: Mean (± 1 S. E.), t values, degrees of freedom, and p values of normally-distributed limnological factors for manufactured (N = 14) versus natural (N = 5) ponds.

Manufactured

Ponds Natural Ponds

Limnological Factor Mean Mean t d. f. p % Vegetation 59.3 ± 5.23 86.8 ± 11.3 2.51 17 0.02Pond Age (as of 2006) 13.4 ± 2.2 NA NA NA NApH 6.1 ± 0.21 5.0 ± 0.28 -2.92 17 0.01Dissolved Oxygen (%) 98.7 ± 7.05 61.2 ± 8.3 -2.91 17 0.01Air Temperature (°C) 28.0 ± 0.49 28.2 ± 0.28 0.35 17 0.73Pond Temperature (°C) 25.9 ± 0.25 23.9 ± 0.41 -4.20 17 <0.00Max. Pond Temperature 29.5 ± 0.37 28.4 ± 0.74 -1.46 17 0.16Min. Pond Temperature 23.7 ± 0.47 22.3 ± 0.71 -1.53 17 0.14Turbidity (NTU) 8.0 ± 1.46 2.73 ± 0.39 -3.38 17 < 0.00Depth (m) 3.0 ± 0.40 1.31 ± 0.48 -2.33 16 0.03Perimeter (m) 300 ± 47 410 ± 107 0.99 17 0.34Area (ha) 0.6 ± 0.2 0.7 ± 0.3 0.23 17 0.82

29

Table 3: Mean (± 1 S. E.), t values, degrees of freedom, and p values of normally-distributed landscape factors for manufactured (N = 14) versus natural (N = 5) ponds.

Manufactured Ponds

Natural Ponds

Landscape Factor Mean Mean t d. f. p Building Density (#/250 m buffer zone) 126 ± 25.6 125 ± 30.1 0.24 17 0.82 Nearest Building (m) 39.3 ± 6.3 56.1 ± 15.9 1.20 17 0.24 Road Density (m/250 m buffer zone) 2151.5 ± 231 2602.2 ± 316 1.04 17 0.31 Nearest Road (m) 49.1 ± 7.7 65.5 ± 20.5 0.94 17 0.36 Forest Density (%) 18.9 ± 4.5 15.2 ± 4.7 -0.46 17 0.65

30

Table 4: Wilcoxon Tests for nonparametric variables.

Manufactured Ponds Natural Ponds

Variable 25 % Quantile Median

75 % Quantile

Score Mean

25% Quantile Median

75% Quantile

Score Mean p

Conductivity (mS) 0.106 0.118 0.145 10.9 0.069 0.108 0.125 7.4 0.25 Slope (°) 13.6 16.1 17.8 10.8 2.25 8.5 27.8 7.8 0.33 Canopy Closure (%) 0 0 43.8 8.3 33.3 53.7 64.9 14.8 0.02 Nearest Forest (m) 27.7 67.5 150.8 10.7 0 43.1 178 8.0 0.38 Reptile Richness 0 0 1 8.7 0.5 1 1.5 13.6 0.06

31

Natural Retention40

50

60

70

80

90

100

Pond Type

% V

eget

atio

n

Natural Retention40

50

60

70

80

90

100

Pond Type

% V

eget

atio

n

Natural Retention4.0

4.5

5.0

5.5

6.0

6.5

Pond Type

pH

Natural Retention4.0

4.5

5.0

5.5

6.0

6.5

Pond Type

pH

(a) (b)

Natural Retention2030405060708090

100110120

Pond Type

Dis

solv

ed O

xyge

n (%

)

Natural Retention2030405060708090

100110120

Pond Type

Dis

solv

ed O

xyge

n (%

)

Natural Retention

0.4

0.6

0.8

1.0

Pond Type

Log 1

0Tu

rbid

ity

Natural Retention0.4

0.6

0.8

1.0

Pond Type

Log 1

0Tu

rbid

ity

(c) (d)

Natural Retention20

21

22

23

24

25

26

27

Pond Type

Pond

Tem

pera

ture

(°C

)

Natural Retention20

21

22

23

24

25

26

27

Pond Type

Pond

Tem

pera

ture

(°C

)

Natural Retention

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Pond Type

Dep

th (m

)

Natural Retention0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Pond Type

Dep

th (m

)

(e) (f) Figure 7: Mean (± 1 S. E.) by pond type for statistically significant (p < 0.05) limnological variables. Percent vegetation (a), pH (b), % dissolved oxygen (c), log10 turbidity (d), pond temperature (e) and depth (f) versus pond type.

32

Table 5: Amphibians recorded using all sampling methods. Species codes are explained in the Abbreviations section.

Species

# Pond Name AG

RY

AM

EA

BTE

R

EPLA

GC

AR

HC

IN

HFE

M

HSQ

U

OSE

P

RC

AT

RG

RY

RSP

H

SIN

T

SLA

C

Tota

l

1 Valencia Islands X X X 3 2 Econ Trail X X X X X X 6 3 Union Park Church X X 2 4 Cypress Glen X X 2 5 Golf Shop X X X X X X 6 6 High Point Club X X X X X X X X 8 7 Polos X X X X X X 6 8 Jefferson Lofts X X 2 9 Bonneville X X X X X 510 Poli X X 2 11 Fairways Inverary X X 2 12 Deerwood X 1 13 Fairways Firestone X X X 3 14 Cypress Lakes Retention X X 2 15 Flowers Natural X X X X X X X 7 16 Challenger Pkwy. Natural* X X X X X X X X X 9 17 Lake Circe Natural X X X X X X X 7 18 Fairways Natural X X X X X X X X X X 10 19 South Tanner Natural X X X 3 20 Cypress Lakes Natural X X X X X X X 7 Total 4 4 20 1 7 10 2 5 6 7 8 11 6 2 *Pond demolished early August 2005.

33

Mean log10 native amphibian species richness was significantly higher in natural ponds

than in manufactured ponds (t = 3.0, d. f. = 17, p < 0.01; Figure 8). On average, I recorded seven

amphibian species in natural ponds and three species in manufactured ponds. Native amphibian

species richness (S) was significantly positively related to % vegetation and log-transformed

pond perimeter. The species-area relationship was S = 2.03A1.12. Species richness of native

amphibians also declined significantly with increasing pH and turbidity (Figure 9).

I found Cuban Treefrogs in six (32%) ponds, including four manufactured and two

natural ponds. I trapped Cuban Treefrog larvae at one manufactured and one natural pond

(Fairways Firestone and Fairways Natural), trapped an adult at one manufactured pond (Golf

Shop), and heard chorusing in low numbers (1-3 males) at three manufactured and one natural

pond (Fairways Firestone, Fairways Inverary, Bonneville, and Flowers Natural). Abundance of

native amphibians tended to be higher when Cuban Treefrogs were present, but the relationship

was not significant statistically (t = -1.87, d. f. = 17, p < 0.08; Figure 10). No native amphibian

species (or hylids or ranids alone) were significantly more common or rare than expected in

ponds with Cuban Treefrogs.

34

Natural Retention1

10

Pond Type

Nat

ive

Am

phib

ian

Spec

ies

Ric

hnes

s

2

3

4

5

6

789

Natural Retention1

10

Pond Type

Nat

ive

Am

phib

ian

Spec

ies

Ric

hnes

s

2

3

4

5

6

789

Figure 8: Mean (± 1 S. E.) species richness of native amphibians by pond type. Species richness was significantly higher in natural ponds than in manufactured ponds.

35

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Log 1

0N

ativ

e Am

phib

ian

Ric

hnes

s

20 30 40 50 60 70 80 90 100% Vegetation

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Log 1

0N

ativ

e Am

phib

ian

Ric

hnes

s

20 30 40 50 60 70 80 90 100% Vegetation

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Log 1

0N

ativ

e Am

phib

ian

Ric

hnes

s

2.0 2.2 2.4 2.6 2.8 3.0Log10 Perimeter

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Log 1

0N

ativ

e Am

phib

ian

Ric

hnes

s

2.0 2.2 2.4 2.6 2.8 3.0Log10 Perimeter

(a) (b)

-0.2

0

0.2

0.4

0.6

0.8

1.0

Log 1

0 N

ativ

eAm

phib

ian

Ric

hnes

s

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5pH

-0.2

0

0.2

0.4

0.6

0.8

1.0

Log 1

0 N

ativ

eAm

phib

ian

Ric

hnes

s

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5pH

-0.2

0

0.2

0.4

0.6

0.8

1.0

Log 1

0 N

ativ

eAm

phib

ian

Ric

hnes

s

0.4 0.6 0.8 1.0 1.2 1.4Log10 Turbidity

-0.2

0

0.2

0.4

0.6

0.8

1.0

Log 1

0 N

ativ

eAm

phib

ian

Ric

hnes

s

0.4 0.6 0.8 1.0 1.2 1.4Log10 Turbidity

(c) (d) Figure 9: Significant linear regressions for log10 native amphibian species richness versus % vegetation, log10 perimeter, pH, and log10 turbidity. Log10 native amphibian species richness regressed positively on % vegetation (R2 = 0.67, n = 19, p < 0.001) (a), log10 area (R2 = 0.23, n = 19, p < 0.04) (b), and negatively with pH (R2 = 0.27, n = 19, p < 0.02) (c), and log10 turbidity (R2 = 0.24, n = 19, p < 0.04) (d).

36

Absent Present1

10

100N

ativ

e A

mph

ibia

n Sp

ecie

s A

bund

ance

2

4

68

20

40

6080

Absent Present1

10

100N

ativ

e A

mph

ibia

n Sp

ecie

s A

bund

ance

2

4

68

20

40

6080

Figure 10: Native amphibian species abundance (± 1 S. E.) was not significantly higher when Cuban Treefrogs were absent or present.

37

Cuban Treefrogs were more likely to be found in ponds with high turbidity, high

conductivity, high native amphibian abundance, and high macroinvertebrate abundance. In

contrast, Cuban Treefrogs were less likely to be present in ponds with large area (Figures 11 -

15). Perimeter and % vegetation remained significant predictors in the final backward stepwise

logistic regression model. Cuban Treefrogs were more likely to be present when perimeters

were small and % vegetation was high. The resulting equation was

Logit (probability) = 6.37 + 0.021*(perimeter in meters) – 0.169*(% vegetation).

The area under the receiver operating characteristic (ROC) curve (Figure 16) showed the model

had good predictive power. Using a prediction profiler, I determined that ponds with a perimeter

<225 m and having >66.5% vegetation had a 50% or greater chance of having Cuban Treefrogs

present.

Cuban Treefrogs were significantly more likely to be found in manufactured ponds with

high turbidity, high conductivity, high native amphibian abundance, and high macroinvertebrate

abundance. Ponds with a small perimeter or low species richness of fishes (Figures 17 - 22) also

were significantly more likely to harbor Cuban Treefrogs. Redear Sunfish and Warmouth were

significantly associated with Cuban Treefrog absence (both had χ2 > 4.9, n = 19, p < 0.03).

Brown Hoplos were significantly associated with Cuban Treefrog presence (χ2 = 4.2, n = 19, p <

0.04). Using a prediction profiler, I determined that manufactured ponds with turbidity >10.3

NTU, >0.162 mS conductivity, >12.4 individual native amphibians per trap-night, >6 individual

macroinvertebrates per trap-night, perimeter <198 m and <3.2 fish species per pond had a 50%

or greater chance of having Cuban Treefrogs present. However, none of these parameters

remained significant when they were evaluated together using backward stepwise logistic

regression.

38

.

0.00

0.25

0.50

0.75

1.00

0 5 10 15 20 25Turbidity (NTU)

Absent

Present

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 5 10 15 20 25Turbidity (NTU)

Absent

Present

Pro

babi

lity

Figure 11: Logistic plot of the probability Cuban Treefrogs were present as a function of turbidity, measured as nephelometric turbidity units (NTU). The likelihood Cuban Treefrogs were in ponds increases with higher turbidity (χ2 = 3.8, d. f. = 1, p < 0.05). The probability that Cuban Treefrogs were absent is represented by the height of the curve above the x-axis. For example, the probability of Cuban Treefrogs being absent from ponds with a turbidity of 5 and 20 NTU is 77% and 10%, respectively. The probability Cuban Treefrogs were present in ponds is represented by the distance from the curve to the 1.00 line, and is equal to (1-probability that Cuban Treefrogs were absent).

39

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0.05 0.1 0.15 0.2 0.25Conductivity (mS)

Absent

Present

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0.05 0.1 0.15 0.2 0.25Conductivity (mS)

Absent

Present

Figure 12: Logistic plot of the probability Cuban Treefrogs were present as a function of conductivity in millisiemens. The likelihood Cuban Treefrogs were in ponds increases with higher conductivity (χ2 = 5.0, d. f. = 1, p < 0.03). See Figure 11 for figure explanation.

40

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 50 100 150 200 250 300Native Amphibian Abundance(total # of individuals recorded)

Absent

Present

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 50 100 150 200 250 300Native Amphibian Abundance(total # of individuals recorded)

Absent

Present

Figure 13: Logistic plot of probability Cuban Treefrogs were present as a function of native amphibian abundance. X-axis units include total number of individuals recorded by all sampling methods and all trap nights. The likelihood Cuban Treefrogs were in ponds increases as native amphibian abundance increases (χ2 = 5.6, d. f. = 1, p < 0.02). See Figure 11 for figure explanation.

41

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 20 40 60 80 100Macroinvertebrate Abundance(total # of individuals recorded)

Absent

Present

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 20 40 60 80 100Macroinvertebrate Abundance(total # of individuals recorded)

Absent

Present

Figure 14: Logistic plot of probability Cuban Treefrogs were present as a function of macroinvertebrate abundance. X-axis units include total number of individuals recorded by trapping and dipnetting and all trap nights. The likelihood Cuban Treefrogs were in ponds increases with higher macroinvertebrate abundance (χ2 = 8.9, d. f. = 1, p < 0.00). See Figure 11 for figure explanation.

42

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 0.5 1.0 1.5 2.0 2.5 3.0Area (ha)

Absent

Present

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 0.5 1.0 1.5 2.0 2.5 3.0Area (ha)

Absent

Present

Figure 15: Logistic plot of probability Cuban Treefrogs were present as a function of area. The likelihood Cuban Treefrogs were in ponds decreases as area increases (χ2 = 4.0, d. f. = 1, p < 0.04). See Figure 11 for figure explanation.

43

Tr

ue P

ositi

veS

ensi

tivity

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

1-SpecificityFalse Positive

True

Pos

itive

Sen

sitiv

ity

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

1-SpecificityFalse Positive

Figure 16: Receiver operating characteristic (ROC) curve for perimeter and % vegetation. The ROC curve is a graphical representation of the relationship between false-positive and true-positive rates. Sensitivity is the probability that a given x value correctly predicts an existing condition. Specificity is the probability that a test correctly predicts that a condition does not exist. The closer the area under the curve is to 1.0, the greater the discriminating ability (SAS Institute, Inc. 2003). The area under this curve = 0.96, showing the model had good predictive power.

44

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 5 10 15 20 25

Turbidity (NTU)

Absent

Present

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 5 10 15 20 25

Turbidity (NTU)

Absent

Present

Figure 17: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a function of turbidity. The likelihood Cuban Treefrogs were in manufactured ponds increased with higher turbidity (χ2 = 6.1, d. f. = 1, p < 0.01). See Figure 11 for figure explanation.

45

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0.1 0.15 0.2 0.25Conductivity (mS)

Absent

Present

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0.1 0.15 0.2 0.25Conductivity (mS)

Absent

Present

Figure 18: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a function of conductivity. The likelihood Cuban Treefrogs were in manufactured ponds increased with higher conductivity (χ2 = 5.7, d. f. = 1, p < 0.02). See Figure 11 for figure explanation.

46

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 50 100 150 200 250 300Native Amphibian Abundance(total # of individuals recorded)

Absent

Present

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 50 100 150 200 250 300Native Amphibian Abundance(total # of individuals recorded)

Absent

Present

Figure 19: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a function of native amphibian abundance. X-axis units include total number of individuals recorded by all sampling methods and all trap nights. The likelihood Cuban Treefrogs were in ponds increased with higher native amphibian abundance (χ2 = 6.6, d. f. = 1, p < 0.01). See Figure 11 for figure explanation.

47

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 10 20 30 40 50 60 70Macroinvertebrate Abundance(total # of individuals recorded)

Absent

Present

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0 10 20 30 40 50 60 70Macroinvertebrate Abundance(total # of individuals recorded)

Absent

Present

Figure 20: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a function of macroinvertebrate abundance. X-axis units include total number of individuals recorded by trapping and dipnetting and all trap nights. The likelihood Cuban Treefrogs were in ponds increased with higher macroinvertebrate abundance (χ2 = 16.8, d. f. = 1, p < 0.00). See Figure 11 for figure explanation.

48

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

100 200 300 400 500 600 700 800 900

Perimeter (m)

Absent

Present

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

100 200 300 400 500 600 700 800 900

Perimeter (m)

Absent

Present

Figure 21: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a function of perimeter. The likelihood Cuban Treefrogs were in ponds decreased with larger perimeters (χ2 = 5.4, d. f. = 1, p < 0.02). See Figure 11 for figure explanation.

49

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0.0 2.5 5.0 7.5 10.0 12.5 15.0Fish Richness

Absent

Present

Pro

babi

lity

0.00

0.25

0.50

0.75

1.00

0.0 2.5 5.0 7.5 10.0 12.5 15.0Fish Richness

Absent

Present

Figure 22: Logistic plot of probability Cuban Treefrogs were present in manufactured ponds as a function of fish species richness. The likelihood Cuban Treefrogs were in ponds increased with lower fish richness (χ2 = 5.5, d. f. = 1, p < 0.02). See Figure 11 for figure explanation.

50

Fishes, Macroinvertebrates, Reptiles, and Birds

Fishes were present in all study ponds (Table 6), with Mosquitofish (Gambusia

holbrooki) being the most common fish species, followed by Warmouth (Lepomis gulosus),

Bluegill (Lepomis macrochirus) and Redear Sunfish (Lepomis microlophus). Brown Bullheads

(Ameiurus nebulosus), Redfin Pickerel (Esox americanus), Everglades Pygmy Sunfish

(Elassoma evergladeii) and Golden Shiner (Notemigonus crysoleucas) were present in one pond

each. Centrarchids were absent from four manufactured ponds. I detected Brown Hoplos

(Haplosternum littorale), which is an exotic species native to eastern South America, in four

ponds. Polos pond had the most species (S = 13), followed by Deerwood and Cypress Lakes

Natural with S = 9, but species richness and abundance of fishes did not differ significantly

between pond types (both t > 0.571, d. f. = 17, p > 0.58). Bluegill (Lepomis macrochirus) (χ2 =

5.46, d. f. = 1, p < 0.02) were significantly more common in manufactured ponds than in natural

ponds. I found Bluegill in eleven manufactured ponds (79%), but just one (20%) natural pond.

In contrast Golden Topminnows (Fundulus chrysotus) (χ2 = 6.74, d. f. = 1, p < 0.01) and Least

Killifish (Heterandria formosa) (χ2 = 8.04, d. f. = 1, p < 0.005) were significantly more common

in natural ponds than manufactured ponds. I found Golden Topminnows and Least Killifish in

all five natural ponds (100%), but just six and five manufactured ponds (43 and 36%),

respectively.

51

Table 6: Fishes recorded using all sampling methods. Species codes are explained in the Abbreviations section.

# Pond Name AN

EB

EAM

E

EEV

E

EFU

S

EGLO

EOK

E

FCH

R

GH

OL

HFO

R

HLI

T

LGU

L

LMA

C

LMA

R

LMIC

MSA

L

NC

RY

PLA

T

Tota

l

1 Valencia Islands X X X X X 5 2 Econ Trail X X X X 4 3 Union Park Church X X X X X X X X 8 4 Cypress Glen X X X 3 5 Golf Shop X X X X 4 6 High Point Club X X X X X X X 7 7 Polos X X X X X X X X X X X X X 13 8 Jefferson Lofts X X X X 4 9 Bonneville X 1 10 Poli X X X X X X 6 11 Fairways Inverary X X X X X 5 12 Deerwood X X X X X X X X X 9 13 Fairways Firestone X X 2 14 Cypress Lakes Retention X X X X 4 15 Flowers Natural X X X X X X 6 16 Challenger Pkwy. Natural* X 1 17 Lake Circe Natural X X X X X X 6 18 Fairways Natural X X X X X 5 19 South Tanner Natural X X X X X 5 20 Cypress Lakes Natural X X X X X X X X X 9 Total 1 1 1 2 6 2 11 20 10 4 13 12 4 12 4 1 3

*Pond demolished early August 2005

52

Table 7: Bird species observed in and along ponds during sampling. Species codes are explained in the Abbreviations section.

# Pond Name AA

LB

AA

NH

A

FUL

AH

ER

APH

O

APL

A

BV

IR

EALB

ECA

E

ETH

U

ETR

I

GC

AN

GC

HL

MA

ME

PAU

R

PFA

L

PHA

L

PPO

D

Tota

l

1 Valencia Islands X X X X 4 2 Econ Trail X 1 3 Union Park Church X 1 4 Cypress Glen X 1 5 Golf Shop X X X X X 5 6 High Point Club X X X X X X 6 7 Polos X X X X 4 8 Jefferson Lofts X 1 9 Bonneville X X X X 4 10 Poli X X 2 11 Fairways Inverary X X X 3 12 Deerwood X 1 13 Fairways Firestone 0 14 Cypress Lakes Retention X X 2 15 Flowers Natural X 1 16 Challenger Pkwy. Natural* X X X 3 17 Lake Circe Natural X X X X X 5 18 Fairways Natural X 1 19 South Tanner Natural 0 20 Cypress Lakes Natural X X 2 Total 9 3 2 6 2 3 3 2 3 1 1 4 2 2 1 1 1 1 *Pond demolished early August 2005

53

Birds were present at most ponds while I was sampling them (Table 7). Great Egrets

(Ardea alba) were the most common species, followed by Great Blue Herons (Ardea herodius).

Snowy Egrets (Egretta thula), Tricolor Herons (Egretta tricolor), Double-crested Cormorants

(Phalacrocorax auritus), Glossy Ibis (Plegadis falcinellus), Osprey (Pandion haliaetus), and

Pied-billed Grebes (Podilymbus podiceps) were the rarest species, with one sighting each. Two

manufactured ponds, High Point Club and Golf Shop, had the most bird species with six and five

species, respectively. I did not observe any bird species at South Tanner Natural or Fairways

Firestone. Mean bird richness was not significantly higher in natural versus manufactured ponds

(t = -0.465, d. f. = 16, p < 0.648).

Macroinvertebrates were present in all ponds (Table 8). Water scorpions (Ranatra sp.)

and water bugs (Belostoma sp.) were encountered most often in ponds (in traps and dipnet

sweeps), while newly metamorphosized dragonflies (Anisoptera) and water scavenger beetles

(Hydrophilus sp.) were encountered less often in ponds. Macroinvertebrate richness was

significantly higher in natural than in manufactured ponds (t = 2.34, d. f. = 17, p < 0.03). I

captured an average of 5.4 macroinvertebrate species in natural ponds and 4.1 in manufactured

ponds. Challenger Parkway Natural had the most macroinvertebrate species (S = 7) and

Deerwood the least (S = 2). Crayfish (Procambarus sp.) also were significantly more common

in natural ponds than manufactured ponds (χ2 = 5.6, d. f. = 1, p < 0.02). I captured crayfish in

five (100%) natural versus seven (50%) manufactured ponds, and crayfish densities were 18.2

individuals per trap night in natural ponds and 12 individuals per trap night in manufactured

ponds, on average.

Reptile species were detected in low numbers at nine ponds (Table 8). I saw three

species of turtles, four species of snakes, and one American Alligator (Alligator

54

mississippiensis). Florida Softshell Turtles (Apalone ferox) were seen the most often, in one

manufactured and two natural ponds. Fairways Natural had the most reptiles detected (2), while

I did not observe any reptile species at eight manufactured ponds and three natural ponds:

Valencia Islands, Econ Trail, Union Park Church, Golf Shop, Bonneville, Poli, Deerwood,

Fairways Firestone, Cypress Lakes Retention, Challenger Parkway Natural, and Cypress Lakes

Natural. Reptile presence and absence did not differ significantly by pond type (χ2 = 3.0, n = 19,

p < 0.08).

55

Table 8: Macroinvertebrates and reptile species recorded using all sampling methods. Species codes are explained in the Abbreviations section.

Macroinvertebrate Species Reptile Species

# Pond Name BEL

O

CY

BI

DR

AG

DY

TS

HY

DS

LAM

E

NA

IA

NA

UC

PRO

C

RA

NA

Tota

l

AFE

R

AM

IS

CC

ON

EOB

S

KB

AU

NFA

S

NFL

O

SOD

O

Tota

l

1 Valencia Islands X X X X X 5 0 2 Econ Trail X X X 3 0 3 Union Park Church X X X 3 0 4 Cypress Glen X X X 3 X 1 5 Golf Shop X X X X X 5 0 6 High Point Club X X X X 4 X 1 7 Polos X X X X 4 X 1 8 Jefferson Lofts X X X X 4 X 1 9 Bonneville X X X X X X 6 0 10 Poli X X X X 4 0 11 Fairways Inverary X X X X X 5 X 1 12 Deerwood X X 2 0 13 Fairways Firestone X X X X X X 6 0 14 Cypress Lakes Retention X X X 3 0 15 Flowers Natural X X X X X X 6 X 1 16 Challenger Pkwy. Natural* X X X X X X X 7 0 17 Lake Circe Natural X X X X X 5 X 1 18 Fairways Natural X X X X X 5 X X 2 19 South Tanner Natural X X X X X 5 X 1 20 Cypress Lakes Natural X X X X X X 6 0 Total 16 12 2 7 2 5 13 3 13 18 3 1 1 1 1 1 1 1 Species codes are explained in the Abbreviations section. *Pond demolished early August 2005

56

CHAPTER FOUR: DISCUSSION

In my study area, Cuban Treefrogs did not have any detectable effect on the abundance or

species richness of native amphibians. If anything, the trend was toward higher native abundance

where Cuban Treefrogs were present. I did not expect this result because Cuban Treefrogs eat

and may outcompete native frogs (Meshaka 2001, Rice et al. 2002, Wyatt and Forys 2004).

Cuban Treefrogs also favored the same habitats as native amphibians: small, highly vegetated

ponds. This pattern likely occurred because predatory fish occurred in all of my study ponds.

Fishes prey on larval and adult amphibians, and many hylid species avoid ovipositing in ponds

with fish (Gamradt and Kats, 1996, Kats et al. 1998, Goodsell and Kats 1999, Binckley and

Resetarits 2002). Adult Cuban Treefrogs may have avoided ponds with fish. Alternatively,

Cuban Treefrog larvae may have been eaten by fishes; Cuban Treefrogs were encountered

significantly less often in ponds with Warmouth and Redear Sunfish. I heard Cuban Treefrogs

chorusing at three ponds but never detected their larvae. I found Cuban Treefrog larvae in two

ponds with predatory fish (mainly Mosquitofish, Bluegill, and Redear Sunfish [Lepomis

microlophis]), Cuban Treefrogs likely used pond vegetation to escape predators, and can explain

their low densities: 30.6 individuals per trap night in Fairways Firestone (67% vegetated), and

0.53 individuals per trap night in Fairways Natural (100% vegetated). In my study area, Cuban

Treefrogs bred elsewhere, such as in watering containers for livestock (T. Nusinov, personal

observation). Containers are fish-free habitats, and during the wet season in Florida usually

retain water for months at a time.

Cuban Treefrogs were more likely to be found in ponds with small perimeters because

such ponds attract and contain fewer predators (Pearman 1995), and larval amphibians may

57

experience less competition due to a larger ratio of edge to interior habitat (Pearman 1993).

Ponds with smaller perimeters also were more likely to dry out, thereby eliminating predatory

fishes. The two ponds that dried during my study, (Fairways Firestone and Fairways Natural),

had small perimeters and low predatory fish richness, and were the only places I trapped Cuban

Treefrog larvae. I recorded Cuban Treefrogs most often in highly vegetated ponds, perhaps

because aquatic macrophytes provide tadpoles with feeding habitat and places to escape

predators (Monello and Wright 1999, Welch and MacMahon 2005). Ponds with perimeters <225

m and having >66.5 % vegetation had a 50%+ probability of supporting Cuban Treefrogs. Based

on this information, ponds like Cypress Glen (which had a mean perimeter of 157 m and 66%

vegetation), may be susceptible to future invasion by Cuban Treefrogs.

While pond perimeter and % vegetation together effectively explained Cuban Treefrog

distributions, several individual parameters also were useful: turbidity, conductivity,

area/perimeter and abundance of native amphibians and macroinvertebrates. Cuban Treefrogs

were more likely to occur in ponds with high turbidity and conductivity. Fish have difficulty

detecting prey in turbid waters (Miner and Stein 1993, Rowe and Dean 1998), which may

provide a visual refuge. High conductivity is associated with runoff from urban areas (Long and

Schorr 2005), and Cuban Treefrogs often are found in urban areas (Meshaka 1996c, Meshaka

2001, T. Nusinov, personal observation). However, parameters I used to quantify urbanization

(e. g., building and forest density), did not explain the distribution of Cuban Treefrogs in my

study area. For example, the area under the ROC curve for a model with building and forest

density as independent variables was 0.53.

Cuban Treefrogs were more likely to be recorded in ponds with high abundances of

macroinvertebrates, which can prey on amphibian larvae (e. g., Werner and McPeek 1994).

58

However, macroinvertebrates also rely on vegetation for refuge from predators and food (Sharitz

and Batzer 1999), in a manner similar to larval amphibians (Monello and Wright 1999, Welch

and MacMahon 2005). Species richness of native amphibians increased with increasing %

vegetation, which is important as habitat and refugia for larval amphibians (Monello and Wright

1999, Welch and MacMahon 2005). Species richness of native amphibians also increased with

increasing perimeter, which is most likely a species-area relationship, and is widely documented

for amphibians (e.g., Dickman 1987, Findlay and Houlahan 1997, Ricklefs and Lovette 1999,

Lehtinen and Galatowitsch 2001). However, species richness of native amphibians decreased

with increasing pH, and the natural ponds I sampled had significantly lower pH than

manufactured ponds. Amphibian species native to the southeastern United States are fairly acid

tolerant (Pierce 1985), and can survive in ponds with low pH. Mean species richness of native

amphibians was also lower in ponds with higher turbidity, probably because it negatively affects

food sources such as algae, which are limited by low light, and can consequently reduce growth

and development in tadpoles (Welsh and Ollivier 1998, Henley et al. 2000, Gillespie 2002).

Distributions of several native species of amphibians and fishes varied with specific

limnological, landscape, and biotic variables. Pig Frogs (Rana grylio) were more common in

natural ponds than in manufactured ponds. This large ranid frog inhabits diverse aquatic

ecosystems and uses upland habitats less than other species (Delis et al. 1996). Pig frogs were

affected little by habitat alteration and persisted in natural wetlands surrounded by homes.

Greater and Lesser Sirens (Siren lacertina and Siren intermedia, respectively) were more

common in natural ponds than manufactured ponds. Sirens typically inhabit ponds with high

amounts of vegetation (Petranka 1998) and responded favorably to vegetation in study ponds.

Golden Topminnows (Fundulus chrysotus), Least Killifish (Heterandria formosa),

59

macroinvertebrates, and crayfish (Procambarus sp.) also were more common in natural ponds

than manufactured ponds. These species are positively associated with vegetation (Loftus and

Kushlan 1987, Jordan et al. 1996, Jordan et al. 1998). All four taxa were more common in

natural ponds, which averaged 27.6% more vegetation cover than manufactured ponds. Bluegill

(Lepomis macrochirus) was significantly more common in manufactured ponds than natural

ponds, presumably because these popular game fish were stocked for recreational fishing.

Although the main purpose of retention ponds is to reduce stormwater runoff and

pollutants, diverse wildlife uses retention ponds, including amphibians (Delis et al., 1996, Bishop

et al. 2000, Bishop et al. 2000b, Ostergaard and Richter 2001, Ostergaard 2002). Current laws in

the United States require reducing the amount of pollution entering water bodies (Tsihrintzis and

Hamid 1997). Consequently, retention ponds must be built with new housing and commercial

developments, and roadways (Scheuler 1992, Scheuler et al. 1992, Mallin et al. 2002, Sparling et

al. 2004). Retention ponds in suburban Florida may be suitable breeding sites that accelerate the

spread of Cuban Treefrogs. Most retention ponds are built large and deep because this is a cost-

effective way to reduce runoff (England 2000). My results show that the current design of

retention ponds makes invasion by Cuban Treefrogs less likely, provided pond perimeters are

large and vegetation is kept to a minimum. Stocking ponds with predatory fish, especially

Warmouth and Redear Sunfish, also should reduce the likelihood that Cuban Treefrogs will

breed in ponds. Unfortunately, it may be difficult to make ponds less suitable for Cuban

Treefrogs and more suitable to native amphibian species because both groups responded

positively to similar limnological, landscape, and biotic factors. Keeping ponds large in surface

area and reducing turbidity (e. g., by controlling runoff) may increase native species richness in

manufactured ponds without a concomitant increase in Cuban Treefrogs. Perhaps more

60

important to limiting the spread of this invasive amphibian is restricting their access to container

habitats, such as ornamental ponds, fountains, and untreated swimming and wading pools.

Future Cuban Treefrog studies should focus on the use of these container habitats, which also are

breeding sites of mosquitoes - homeowners have added incentive to keep them free of pest

species.

61

APPENDIX: DATA

62

Appendix 1: Mean (± 1 S. E.) limnological factors by pond.

# Pond Name

Pond Temperature

(ºC)

Max. Pond Temperature

(ºC)

Min. Pond Temperature

(ºC)

Air Temperature

(ºC)

Turbidity (NTU) pH Conductivity

(mS)

1 Valencia Islands 26.2 ± 2.1 31.6 ± 2.5 25.1 ± 2.0 28.7 ± 2.1 4.2 ± 1.4 5.8 ± 1.0 0.084 ± 0.01 2 Econ Trail 24.6 ± 2.6 30.9 ± 2.8 23.1 ± 3.1 27.0 ± 2.5 8.4 ± 2.0 6.8 ± 0.24 0.127 ± 0.01 3 Union Park Church 25.7 ± 2.6 31.2 ± 2.5 24.5 ± 3.8 25.9 ± 2.7 9.8 ± 7.0 5.8 ± 0.25 0.107 ± 0.00 4 Cypress Glen 27.0 ± 2.1 29.6 ± 2.4 25.6 ± 2.2 29.3 ± 2.3 5.2 ± 1.3 5.7 ± 0.52 0.077 ± 0.01 5 Golf Shop 24.3 ± 2.4 28.6 ± 1.4 22.1 ± 3.8 27.5 ± 2.4 7.9 ± 2.1 6.3 ± 0.35 0.234 ± 0.06 6 High Point Club 26.4 ± 2.0 29.2 ± 3.0 25.2 ± 2.6 31.0 ± 1.5 4.2 ± 0.66 4.3 ± 0.78 0.110 ± 0.01 7 Polos 25.9 ± 2.6 28.3 ± 3.1 24.4 ± 2.5 28.6 ± 3.1 6.3 ± 2.8 5.5 ± 0.87 0.110 ± 0.01 8 Jefferson Lofts 27.5 ± 2.8 29.5 ± 2.8 22.0 ± 2.3 30.7 ± 2.4 2.7 ± 0.32 6.5 ± 1.2 0.170 ± 0.03 9 Bonneville 26.6 ± 2.2 29.8 ± 2.4 24.0 ± 2.9 30.0 ± 2.3 6.4 ± 1.5 7.2 ± 0.75 0.114 ± 0.02 10 Poli 24.9 ± 2.3 29.0 ± 2.4 23.3 ± 2.6 28.6 ± 2.0 4.4 ± 1.6 6.0 ± 0.83 0.102 ± 0.01 11 Fairways Inverary 26.2 ± 2.6 30.3 ± 3.8 25.4 ± 3.1 26.9 ± 2.2 23.4 ± 13.5 7.3 ± 0.84 0.136 ± 0.02 12 Deerwood 25.5 ± 2.1 27.0 ± 3.0 21.0 ± 2.5 25.2 ± 2.1 8.6 ± 1.4 6.6 ± 0.20 0.130 ± 0.02 13 Fairways Firestone 25.4 ± 3.1 27.4 ± 3.2 20.3 ± 4.3 25.9 ± 3.2 15. 5± 7.7 5.5 ± 0.85 0.226 ± 0.11 14 Cypress Lakes Retention 26.9 ± 2.1 31.0 ± 1.7 25.2 ± 2.3 27.2 ± 2.2 5.8 ± 3.0 6.2 ± 0.79 0.122 ± 0.01 15 Flowers Natural 22.7 ± 2.2 28.8 ± 2.7 20.4 ± 3.1 28.5 ± 1.7 3.7± 1.0 4.5 ± 0.57 0.125 ± 0.01 17 Lake Circe Natural 24.7 ± 1.8 28.4 ± 2.0 21.4 ± 3.3 28.3 ± 1.5 2.0 ± 0.71 4.5 ± 0.09 0.037 ± 0.01 18 Fairways Natural 24.6 ± 3.7 30.8 ± 1.0 24.7 ± 1.7 27.5 ± 2.4 3.0 ± 0.81 5.4 ± 0.71 0.102 ± 0.01 19 South Tanner Natural 23.2 ± 2.5 27.9 ± 3.0 22.5 ± 2.7 27.7 ± 1.6 1.6 ± 0.36 4.6 ± 0.64 0.124 ± 0.01 20 Cypress Lakes Natural 24.3 ± 1.5 26.2 ± 2.4 22.5 ± 2.2 29.1 ± 1.1 3.3 ± 1.0 5.9 ± 0.38 0.108 ± 0.03

63

Appendix 2: Mean (± 1 S. E.) limnological factors by pond.

§ Unable to gain permission to measure depth.

# Pond Name Perimeter (m) Area (ha)

% Dissolved Oxygen

Depth (m) Slope (°) Year Constructed

% Vegetation

1 Valencia Islands 411 ± 3.3 0.9 ± 0.1 94.8 ± 21.8 2.7 ± 0.08 12.00 1993 662 Econ Trail 296 ± 11 0.4 ± 0.1 92.1 ± 7.56 4.0 ± 0.10 16.00 1997 663 Union Park Church 261 ± 11 0.3 ± 0.03 91.2 ± 6.17 2.2 ± 0.09 25.50 1986 584 Cypress Glen 157 ± 2.6 0.1 ± 0.01 97.6 ± 10.7 1.6 ± 0.17 24.25 1995 665 Golf Shop 217 ± 16 0.2 ± 0.04 32.1 ± 8.22 3.1 ± 0.03 17.50 1999 926 High Point Club 828 ± 7.6 2.6 ± 0.5 97.0 ± 14.9 3.0 ± 0.20 11.25 1994 837 Polos 280 ± 16 1.1 ± 0.3 105 ± 18.5 3.6 ± 0.12 16.50 1990 668 Jefferson Lofts 336 ± 5.6 0.5 ± 0.04 143 ± 15.1 § 16.25 2003 339 Bonneville 212 ± 2.4 0.3 ± 0.01 128 ± 13.4 4.1 ± 0.08 13.75 1999 6710 Poli 200 ± 43 0.2 ± 0.01 80.4 ± 10.9 2.5 ± 0.06 13.75 1972 2511 Fairways Inverary 215 ± 1.9 0.4 ± 0.2 126 ± 22.0 1.5 ± 0.05 18.75 1985 5812 Deerwood 230 ± 2.0 0.2 ± 0.01 84.2 ± 9.93 3.7 ± 0.07 15.00 1997 2513 Fairways Firestone 115 ± 21 0.1 ± 0.03 94.1 ± 12.9 0.4 8± 0.14 13.00 1985 6714 Cypress Lakes Retention 450 ± 5.8 1.0 ± 0.2 117 ± 11.0 6.2 ± 0.06 16.25 2001 5815 Flowers Natural 374 ± 9.5 0.2 ± 0.07 34.4 ± 10.5 1.6 ± 0.08 16.75 NA 9217 Lake Circe Natural 585 ± 18 1.6 ± 0.4 83.4 ± 14.3 0.95 ± 0.08 2.25 NA 10018 Fairways Natural 232 ± 5.4 0.5 ± 0.06 73.1 ± 16.5 0.33 ± 0.05 8.50 NA 10019 South Tanner Natural 145 ± 10 0.1 ± 0.01 56.6 ± 11.6 3.0 ± 0.13 38.75 NA 4220 Cypress Lakes Natural 717 ± 4.1 0.9 ± 0.02 58.3 ± 12.9 0.62 ± 0.03 2.25 NA 100

64

Appendix 3: Landscape factors by pond.

# Pond Name

Distance to

Nearest Building

(m)

Building Density

(#/ 250 m buffer)

Distance to Nearest

Road (m)

Road Density (m paved

surface/250 m buffer zone)

Distance to Nearest

Forest (m)

Forest Density (%)

% Canopy Closure

1 Valencia Islands 53.2 377 82.7 3687 20 10 02 Econ Trail 25.3 94 14.9 3132 102 15 03 Union Park Church 83.4 50 21.0 1724 30 23 50.94 Cypress Glen 12.6 210 18.6 2801 258 0 41.55 Golf Shop 28.9 41 47.8 1745 110 10 15.26 High Point Club 76.2 117 99.1 2539 70 10 68.37 Polos 29.2 95 52.1 1330 36 16 28.18 Jefferson Lofts 10.1 27 5.9 2104 267 0 09 Bonneville 35.6 56.0 60.3 1221 9 52 010 Poli 43.6 59 93.8 1203 115 35 55.811 Fairways Inverary 34.0 235 39.6 2703 260 0 012 Deerwood 53.2 151 38.4 1835 12 44 013 Fairways Firestone 6.00 93 53.3 899 65 35 014 Cypress Lakes Retention 58.5 160 59.8 3193 48 15 015 Flowers Natural 51.8 73 63.1 1863 43 12 59.017 Lake Circe Natural 104 205 108.0 3259 0 23 49.018 Fairways Natural 44.8 135 35.1 2848 306 0 17.519 South Tanner Natural 72.9 42 113.7 1834 0 27 70.920 Cypress Lakes Natural 82.2 170 82.3 3204 50 14 53.7

65

Appendix 4: Total amphibian abundances for all sampling methods.

*Pond demolished early August 2005.

Species

# Pond Name AG

RY

AM

EA

BTE

R

EPLA

GC

AR

HC

IN

HFE

M

HSQ

U

OSE

P

RC

AT

RG

RY

RSP

H

SIN

T

SLA

C

Tota

l

1 Valencia Islands 9 1 1 112 Econ Trail 11 3 1 18 1 2 363 Union Park Church 3 1 44 Cypress Glen 2 4 65 Golf Shop 1 1 119 39 1 2 1636 High Point Club 1 13 6 7 1 1 13 5 477 Polos 2 1 1 14 2 1 218 Jefferson Lofts 8 1 99 Bonneville 11 131 3 1 142 28810 Poli 3 1 411 Fairways Inverary 1 3 412 Deerwood 8 813 Fairways Firestone 52 154 1 20714 Cypress Lakes Retention 2 1 315 Flowers Natural 2 6 1 2 5 15 3 3416 Challenger Pkwy. Natural* 22 2 1 2 2 1 1 9 2 4217 Lake Circe Natural 39 2 3 4 4 8 2 6218 Fairways Natural 1 4 2 12 8 5 3 13 6 2 5619 South Tanner Natural 1 2 1 420 Cypress Lakes Natural 25 8 13 10 2 16 5 79 Total 88 5 145 2 32 183 3 9 169 146 82 201 18 5 1088

66

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