Macroinvertebrate Communities in Ephemeral

Ponds: Effects of Competition, Landscape, and Hydroperiod

on Species Richness

Edmund HartUniversity of Vermont

ESA 2007

What is an Ephemeral Pond?

• A landscape depression regularly filling in either the fall or the spring.

• Rarely hold water for more than 4 - 5 months after spring ice out, but can be flooded for multiple years.

• Range in size from 68 – 2941 m2

• Regular drying and no inflow or outflow prevents the establishment of fish populations.

Ponds Undergo Regular Drying

Common Ephemeral Pond Taxa

Community assembly

Communities reform each year with some taxa overwintering, and others colonizing in the early spring.

• Only certain taxa can exploit ephemeral habitats.(Wiggins et al 1980, Williams 1997).

• Have resting eggs (cladocerans, Branchiopods) or dessicant resistant life stages.

• Rapid development (mosquitoes, other Diptera).• Early colonizers from nearby permanent habitat (Hemiptera,

Dytiscidae).

• Wissinger and Gallagher (1999) found between 63 and 71% of post-drought insect taxa were from dessicant resistant stages.

Schematic of community structure.

.2

.4

.9

.6

.7

.1

.3 .2

.5

Hydroperiod

.8 .3

.3

.1

.1

.5

.2

.1.8

.9

.4 .6

.2

= Taxa that can utilize ephemeral habitat

= Taxa already presentIn habitat

= Potential colonizerModel drawn after Schnieder and Frost (1996)

Study question

Do competitive interactions with salamander larva Or abiotic habitat variables determine invertebrate species richness?

Study LocationDelaware Water GapNational Recreation Area

• 67,000 acres in New Jersey and Pennsylvania bordering 40 miles of the Delaware river.

• Includes two large ridges on either side of the river valley and numerous tributaries.

I. Two independent factors crossed, third added post-hoc

a) Open or closed canopy

b) Ambystoma spp. larva present or absent

c) Third factor added, late or early drying

d) One site for each of the initial factors, 4 total sites

Experimental Design

II. Sites sampled every other week from 3/25/04 to

6/25/04 or until dry

a) Three 1-Meter dipnet sweeps taken and then pooled, and picked for 10 minutes to make 1 composite sample

b) Three composite samples taken per visit.

c) All three samples pooled into a single species richness count per sampling date

Experimental Design

Model Development and Analysis

Data was analyzed using the lmer function for mixed models in the lme4 package (Bates and Sarkar 2007) of R

(R Development Core Team 2007).

• Calculated Aikake’s Information for small sample sizes (AICc) (Burnam and Anderson 2002)

• Calculated Aikake weights,

• Calculated model selection frequencies and 95% confidence intervals using 10,000 bootstrap replicates

Model Interpretation

Null No biological interactions at work

Habitat Non-forested sites have greater abundance or species richness

Hydroperiod Sites with longer hydroperiod have greater abundance or species richness

Competition Competition with salamander larva structures species richness or abundance

Habitat and Hydroperiod

Ponds with open habitat and long drying period will have the highest abundance or species richness

Habitat and Competition

Salamander competition and habitat together determine species richness

Competition and Hydroperiod

Salamander competition and hydroperiod together determine species richness

Since design was not fully crossed, a saturating likelihood results when too many factors are added into the model. Therefore interaction terms could not be considered, only additive effects of two parameters.

Candidate Models

ResultsSpecies Richness by Treatment

Results

Individual based rarefaction curves generated by EstimateS (Colwell 2005). Open sites have higher species diversity.

The model with habitat and hydroperiod predictors best fits the data, also having the highest AICc weight and bootstrap frequency.

Model Results

Model Log-Likelihood AICc Lower 95% CI

Upper 95% CI

Delta AICc

AICc Weights

Bootsrap Selection Frequencies

Null -21.68 47.9 33.34 53.46 3.1 0.091 0.013 Habitat -19.31 45.76 29.59 52.06 0.96 0.265 0.153 Hydroperiod -21.25 49.64 34.89 55.17 4.84 0.038 0 Competition -21.46 50.06 35.56 55.46 5.26 0.031 0 Habitat and Hydroperiod -17.4 44.8 26.24 51.79 0 0.429 0.68 Habitat and Competition -18.57 47.14 30.84 53.82 2.34 0.133 0.154 Competition and Hydroperiod -20.96 51.92 37.33 57.21 7.12 0.012 0

• The strongest predictor of species richness was abiotic habitat variables.

• Open habitat was a strong predictor on its own.•Open habitats could be better quality habitat (Tarr et al 2005)•Open habitats are more detectable by aerial colonizers (My own wild rank speculation)

• Competitive interactions with Ambystoma larva have little impact on macroinvertebrate species richness.

•Agrees with Corti et al’s (1997) prediction of low effects of predation on highly disturbed systems•Also larval densities probably didn’t reach high enough levels

Conclusions

Questions? Worms sure are tastier than bugs

Thanks DEWA staff,Rich Evans,USGS BRD

Brian Beckage,Nick Gotelli