Comparing aquatic macroinvertebrates communities between native and invasive plant species in Mill Creek

Shelly WesnerDepartment of Biological Sciences, York College of Pennsylvania

Introduction

As invasive plant species overtake native species, the composition of plant communities can change. Researchers have suggested that the changes in forest composition could potentially affect a whole ecosystem (Rubbo and Kiesecker 2004). Most research has focused on the effect of the changing forest composition on forest ecology, but research on the effects in nearby aquatic environments is lacking with the exception of Nevin (2005). Within creeks, aquatic macroinvertebrates form communities in natural leaf packs. As leaf litter falls into nearby streams, they are swept by the current and can accumulate on large rocks and branches forming leaf packs. These packs become inhabited by a variety of aquatic macroinvertebrates as a protection from predators and as a food source (Smith 1986). By breaking down the leaf matter and exploiting essential nutrients, the macroinvertebrates play a critical role in the food web. As changes in forest composition occurs the macroinvertebrate community composition within leaf packs can be altered. I conducted a study to determine if invasive plant species have a negative impact on leaf pack communities in a Pennsylvania creek by comparing two native plant species, Box-elder (Acer negundo) and Silky Dogwood (Corunus amomum), to two invasive plant species, Japanese Knotweed (Polygonum cuspidatum) and Tree of Heaven (Ailanthus

altissima).

I hypothesize that there will be no significant difference between the native and invasive plant species concerning macroinvertebrate richness, evenness, and diversity. This hypothesis is based on prior research by Nevin (2005).

Methods

•In October leaves of Japanese Knotweed, Silky Dogwood, Tree-of-Heaven, and Box-Elder were collected at Mill Creek.

•Leaf Packs were assembled into mesh bags with fresh leaf mass in each bag (amount equivalent to 4g dry mass).

•The packs were secured into Mill Creek at 15 sites, each site containing 1 pack of each plant species.

•After 6 weeks leaf packs were retrieved from creek.

•Macroinvertebrates were separated from the leaf material and identified.

•Remaining leaf mass was dried and weighed.

Results• There were no significant differences in

taxa richness, evenness, and diversity between the plant species.

• Silky Dogwood (a native) and Tree-of-Heaven (an invasive) had much less remaining leaf matter compared to Box-Elder (a native) and Japanese Knotweed (an invasive).

• Japanese Knotweed (an invasive) had the most remaining leaf matter of the four plant species.

Discussion• My results are similar to those of Nevin

(2005) and suggests that macroinvertebrates may not be negatively impacted by invasive plant species.

• Indeed, there may be positive effects.

• Japanese Knotweed (an invasive) does not degrade as quickly as native species and therefore may provide a longer lasting source of food and protection.

• Tree-of-Heaven (an invasive) appears to be an emphermal resource and therefore may be of limited value for food and protection.

• Further studies should consider a greater sample size.

Works CitedNevin, Andrew. 2005. Impact of exotic tree species foliage on aquatic Nevin, Andrew. 2005. Impact of exotic tree species foliage on aquatic macroinvertebrate diversity in two Pennsylvania streams. York College Thesis.macroinvertebrate diversity in two Pennsylvania streams. York College Thesis.Rubbo, Michael J, Kiesecker, Joseph M. 2004. Leaf litter composition and Rubbo, Michael J, Kiesecker, Joseph M. 2004. Leaf litter composition and community structure: translating regional species changes into local dynamics. community structure: translating regional species changes into local dynamics. EcologyEcology. 85(9):2519-2525.. 85(9):2519-2525.Smith, David L. 1986. Leaf litter processing and the associated invertebrate fauna in Smith, David L. 1986. Leaf litter processing and the associated invertebrate fauna in a tallgrass prairie stream. a tallgrass prairie stream. American Midland NaturalistAmerican Midland Naturalist. 116(1):78-86.. 116(1):78-86.

Acknowledgements

I want to thank Dr. Kleiner for his continued support and advice throughout the project. I would also like to thank the Biology Department for the opportunity to conduct research.

Dogwood

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Table 1. Mean aquatic macroinvertebrate abundance per leaf pack (Japanese Knotweed and Silky Dogwood n=5, Tree-of-Heaven and Box-Elder n=4).

Figure 4. Mean (± 95%CI) diversity of aquatic macroinvertebrate communities did not differ among the 4 species of foliage (P > 0.05, Kruskal- Wallice Test), Japanese Knotweed and Silky Dogwood n = 5, Tree-of-Heaven and Box-Elder n = 4.

Figure 2. Mean (± 95%CI) taxa richness of aquatic macroinvertebrate communities did not differ among the 4 species of foliage (P > 0.05, Kruskal- Wallice Test), Japanese Knotweed and Silky Dogwood n = 5, Tree-of-Heaven and Box-Elder n = 4.

Figure 3. Mean (± 95%CI) evenness of aquatic macroinvertebrate communities did not differ among the 4 species of foliage (P > 0.05, Kruskal- Wallice Test), Japanese Knotweed and Silky Dogwood n = 5, Tree-of-Heaven and Box-Elder n = 4.

Figure 5. Mean (± 95%CI) dry weight of remaining leaf mass found within leaf packs differed among the four species of foliage ( P < 0.05, ANOVA). An initial calculated amount of fresh leaf mass equal to 4 grams of dry leaf mass was in each pack at the start of the experiment. Japanese Knotweed and Silky Dogwood n = 15, Tree-of-Heaven and Box-Elder n = 14.

Figure 1. Total weight of dogwood wet leaves per pack dependent on 4g of dry weight. Graphs were made for all four plant species.

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X-axis Figure Legend

JK: Japanese Knotweed

SD: Silky Dogwood

TH: Tree-of-Heaven

BE: Box-elder

  Japanese Knotweed Silky Dogwood Tree-of-Heaven Box-Elder

         

Horsehair worm 0.4 0.6 0.75 1.25

Muscid 0 0 0 0.25

Flatheaded mayfly larvae 0.6 0 0 0.25

Netspinner 3.2 1.8 1.75 1.25

Riffle bettle 0.6 0.2 0 0.5

Freeliving caddisfly 1.2 0 0.25 0.5

Midge 6.6 4 1 1.75

Shrimp 0 0.2 0.5 0

Riffle bettle larvae 0 0.2 0.25 0

Mayfly 0 0.2 0 0

Water mite I 0 0 0 0.25

Water mite II 0 0 0 0.25

Water mite III 0 0.2 0 0

Water mite IV 0 0.4 0.25 0

Water mite V 0 0.2 0 0

Water mite VI 0.6 0 0 0.25

Water mite VII 0.2 0 0 0