Biodiversity Unhinged: Assessing measures of biodiversity in a Pleistocene shell bed

Gwen M. Daleydaleyg@winthrop.edu

I was sitting in the ________________ __________________ when Richard

Bambach came by. He had been ____________________ and had an idea

about my ___________. After discussing this _____________ idea for _____

_________ , I decided that the idea was ________! I decided to ___________

the idea.

RKB Mad Libs

research space research verb

verb

research activity/topic/product adjective number

unit of timedescriptive

phraseverb

lab sorting shells

watching

counting annoying 20

minutes nuts disregard

Yorktown Samples

WAIT!Why not count all the fragments?

19952014

Why not count al l of the fragments?

COUNTING BIVALVES

A bivalve shell has two valves. Each valve has only one umbo, so a fragment of the valve that contains the umbo indicates the presence of one valve of that species.

The umbo is attached to the hinge structures of the shell, which is usually the most durable part of the valve.

The hinge contains essential morphologic information for identifying bivalve taxa.

Caloosa Shell Quarry Fort Thompson Formation

SAMPLING B-FRAGMENTS

A sample of the Fort Thompson Formation (Pleistocene) from the Caloosa Shell Quarry in Florida was chosen to process.

The sample had previously been processed for paleoecologic material and bivalve hinge fragments (and other material) were removed.

The remaining “picked” material was re-picked. All fragments were classified to the lowest taxonomic level possible. To avoid confusion, non-hinge fragments will be called b-fragments.

sieves

2 kg

Sample Processing

> 4 mm

fragments

> 4 mm1-4 mm>1 mm

~900 g ~330 g ~770 g = 2,000 g

HingeFragment

s

OtherFragment

s

Specimens

Taxa

3,200 6,400 9,600 12,80000

10

20

30

40

RAREFIED DIVERSITY

Caloosa Shell Quarry Fort Thompson Bivalve Hinge Fragment Data

45

Hammer, Ø., Harper, D.A.T., Ryan, P.D. 2001. PAST: Paleontological statistics software package for education and data analysis. Palaeontologia Electronica 4(1): 9pp. http://palaeo-electronica.org/2001_1/past/issue1_01.htm

BIVALVE DIVERSITY

A total of 45 species of bivalves were recovered from the >4 mm sediment size fraction of the 12 Caloosa Shell Quarry samples of the Fort Thompson Formation using hinge fragment data.

500 1000 1500 2000 2500 3000 3500 400000

4

8

12

16

20

24

28

32

36

This sample

RAREFIED DIVERSITY

All FTT samples

3230

Caloosa Shell Quarry Fort Thompson Bivalves

Specimens

Taxa

The species richness as determined by hinge fragments for the specific sample that was re-picked for fragments was 30 species.

The rarefied diversity for the 12 combined Fort Thompson (FTT) samples at 1,100 specimens was somewhat higher.

BIVALVE DIVERSITY

Caloosa Shell Quarry Fort Thompson Formation

SAMPLING B-FRAGMENTS

Chione elevata

gastropodsshell cheese

Anadara transversa

Other bivalves

unsorted

Although other taxa were separated (e.g., barnacles, corals and gastropods), low level classification was only practical for bivalve fragments.

Too Many B-Fragments

Chione elevata (2,070)

Anadara transversa (520)

Anomia simplex (198) Other bivalves

Ostrea equestris (95)

Trachycardium egmontonium

Parvilucina nasula

Mercenaria campechiensis

Dosinia acetabulum

Chione elevata

COUNTING B-FRAGMENTS

Taxa were scored based on how many different bivalve species they would be easily confused with if a hinge fragment were not present:

One: Shell structure and sculpture sufficient to confidently identify taxa

Two: Species easily confused with one other taxon

Three: Species easily confused with two other taxa

Four: Species easily confused with at least three other taxa

Brachidontes exustus

SPECIES FOUND AS HINGE FRAGMENTS

11/30 species (37%) found as hinge fragments were missing from the B-fragment-only portion of the sample.

Recognizability Score

Hing

e Fr

agm

ent C

ount

(n

=1,1

08)

11

2 3 4

10

100

1,000

x2 (2)

1,0000

x2 (2)

x4 (2)

x2 (2)

x2 (1) x3

x2

Timoclea grus (1)Crassinella lunulata (1)Parvilucina amianta (10)

Diplodonta punctata (3)Acar domingensis (1)Macrocallista nimbosa (1)

Abra aequalis (3)Nearomya floridana (3)Transennella stimpsoni (3)Noetia ponderosa

Semele proficula (1)

1

2

3

45/7 bivalves with recognizability scores of 3 or 4 are missing from the B-fragment-only sample.

8 of the missing species have very small adult shell sizes.

Species not found as B-fragments

1 10 100 1000 100001

10

100

1000

Hin

ge F

ragm

ent C

ount

(N=1

,108

)

B-Fragment Count (N=3,088)

Caloosa Shell Quarry Fort Thompson Bivalves

SPECIES MORE ABUNDANT AS HINGE FRAGMENTS

The three species found at least 3x more abundantly as hinge fragments than B-fragments are species with small adult body size.

P. nassula (13,80)

Mulinia (8,32)

P. multilineata(3,10)

Hin

ge F

ragm

ent C

ount

(N=1

,108

)

B-Fragment Count (N=3,088)1 10 100 1000 10000

1

10

100

1000

Caloosa Shell Quarry Fort Thompson Bivalves

SPECIES MORE ABUNDANT AS B-FRAGMENTS

Most of the species found at least 9x more abundantly as B-fragments than hinge fragments are (not surprisingly) fragile. They also lack large hinge teeth.

Ostreola (95,7)Brachidontes (56,6)

Argopecten (35, 2)Dosinia (17, 1)

Dosinia elegans is a large bivalve.

Recognizability Score

B-Fr

agm

ent C

ount

(n=3

,088

)

11

2 3 4

10

100

1,000

10,000

x2 (2)

Trachycardium egmontonium

SPECIES FOUND AS B-FRAGMENTS

19 of 22 species found in the B-fragments were also identified as hinge fragments within the same sample.

Two of the three species are large and relatively fragile compared to most FTT bivalves.

All three species are found in other FTT samples.

1

Chama congregata

1

Spisula solidissima

1

Trachycardium egmontonium

Caloosa Shell Quarry Fort Thompson Formation

BIAS IN THE B-FRAGMENT SUB-SAMPLE

Smaller bivalve species

Bivalve species that were less readily identifiable without an attached hinge fragments.

Easily fragmented bivalve species

Bivalve species with more readily identifiable shell structure

Larger bivalve species

500 1000 1500 2000 2500 3000 3500 400000

4

8

12

16

20

24

28

32

36

B-fragments

hinge fragmentsall fragments

RAREFIED DIVERSITY

All FTT samples

19

24

3230

Caloosa Shell Quarry Fort Thompson Bivalves

Specimens

Taxa

Hammer, Ø., Harper, D.A.T., Ryan, P.D. 2001. PAST: Paleontological statistics software package for education and data analysis. Palaeontologia Electronica 4(1): 9pp. http://palaeo-electronica.org/2001_1/past/issue1_01.htm

SPECIES FOUND AS FRAGMENTS

The non-hinge fragment portion of the sample contains only a sub-sample of the bivalve diversity.

Including all of the fragments in the count lowers the measured diversity.

Caloosa Shell Quarry Fort Thompson Bivalve Species Richness

This Study

12 bulk, 33 cm intervals of 4 sections

2 kg of sediment/sample processed

1

Portell et al. 1995

Portell, R.W., K.S. Schindler and D. Nichol. 1995. Biostratigraphy an paleoecology of the Pleistocene invertebrates from the Leisey Shell Pits, Hillsborough Country, Florida. Bulletin of the Florida Museum of National History 37 Pt. I: 127-164.

6 bulk, 1 m intervals of 3 sections

5-7 kg of sediment/sample processed

2Localities

Sampling

Processing

Sieve Size

Hunt and pick? No Yes

specimens >4 mm identified specimens >1 mm identified

45 species 49 species

3 species missing from Portell et al.’s list were very rare (12, 4, 3 specimens) in this study7 species missing from Portell et al.’s Fort Thompson list were found in lower strata

Species Richness:

35 species are found on both lists

10 species 14 speciesNot on other list:

2 species missing from this study’s Fort Thompson list were found in lower strata2 species from this study are too small to be retained on a 4 mm sieve. 10 species, including several large and easily identified species, were on Portell et al.’s list but not present in the samples of this locality from this study

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