Macroinvertebrate Communities in Ephemeral Ponds: Effects of Competition, Landscape, and Hydroperiod on Species Richness

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Macroinvertebrate Communities in Ephemeral Ponds
Effects of Competition, Landscape, and
Hydroperiod on Species Richness
Edmund Hart University of Vermont ESA 2007
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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.

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Ponds Undergo Regular Drying
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Common Ephemeral Pond Taxa
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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.

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Schematic of community structure.
Hydroperiod
.2
.6
.2
.3
.5
.4
.7
.3
.9
.2
.1
Taxa that can utilize ephemeral habitat
.1
.1
.4
.6
.8
.3
.1
.8
.2
Taxa already present In habitat
.9
.5
Potential colonizer
Model drawn after Schnieder and Frost (1996)
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Study question
Do competitive interactions with salamander larva
Or abiotic habitat variables determine
invertebrate species richness?
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Study Location
Delaware Water Gap National 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.

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Experimental Design

• I. Two independent factors crossed, third added
  post-hoc
• Open or closed canopy
• Ambystoma spp. larva present or absent
• Third factor added, late or early drying
• One site for each of the initial factors, 4 total
  sites

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Experimental Design

• II. Sites sampled every other week from 3/25/04
  to
• 6/25/04 or until dry
• Three 1-Meter dipnet sweeps taken and then
  pooled, and picked for 10 minutes to make 1
  composite sample
• Three composite samples taken per visit.
• All three samples pooled into a single species
  richness count per sampling date

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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 Aikakes 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

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Candidate Models
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.
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Results
Species Richness by Treatment
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Results
Individual based rarefaction curves generated by
EstimateS (Colwell 2005). Open sites have higher
species diversity.
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Model Results
The model with habitat and hydroperiod predictors
best fits the data, also having the highest AICc
weight and bootstrap frequency.
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Conclusions

• 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 als (1997) prediction of
  low effects of predation on highly disturbed
  systems
• Also larval densities probably didnt reach high
  enough levels

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Questions?
Worms sure are tastier than bugs
Thanks DEWA staff, Rich Evans, USGS BRD Brian
Beckage, Nick Gotelli