Amphibian Biomass Export from Geographically Isolated Wetlands: Temporal Variability, Species Composition, and Potential Implications for Terrestrial Ecosystems

Julia E Earl,Sean M Blomquist,Elizabeth B Harper,David A Patrick,Jarrett R Johnson,Tracy A G Rittenhouse,Daniel J Hocking,Viorel D Popescu,Malcolm L Hunter,Betsie B Rothermel,Michael S Osbourn

doi:10.3390/d14030163

Abstract

Recently metamorphosed amphibians transport substantial biomass and nutrients from wetlands to terrestrial ecosystems. Previous estimates (except 1) were limited to either a subset of the community or a single year. Our goal was to examine temporal variability in biomass export of all amphibians within breeding ponds and the composition of that export. We completely encircled ponds with drift fences to capture, count, and weigh emerging recently metamorphosed individuals in Maine (four wetlands, six years) and Missouri (eight wetlands, 2–4 years). We estimated total amphibian biomass export, export scaled by pond surface area, species diversity, and percentage of biomass from anurans. Biomass export and export composition varied greatly among ponds and years. Our estimates were of similar magnitude to previous studies. Amphibian biomass export was higher when species diversity was low and the proportion of anurans was higher. Biomass estimates tended to be highest for juvenile cohorts dominated by a single ranid species: green frogs (Missouri) or wood frogs (Maine). Ranid frogs made up a substantial proportion of amphibian biomass export, suggesting that terrestrial impacts will likely occur in the leaf litter of forests. Future studies should examine the impacts of ranid juveniles on terrestrial ecosystem dynamics.

Highlights

Spatial subsidies occur when one ecosystem provides resources to another [1]
The goal of this study was to expand on previous work by estimating amphibian biomass export for 12 geographically isolated wetlands monitored for 2–6 years
We examined total amphibian biomass export, amphibian biomass export scaled by pond surface area, species diversity of the amphibians contributing to biomass export, and proportion of export coming from anurans to better identify potential effects on the recipient terrestrial ecosystem

Summary

Introduction

Spatial subsidies occur when one ecosystem provides resources to another [1]. This resource transfer can have large effects on recipient ecosystems, including both bottom-up effects through the movement of nutrients and energy [2,3] and top-down effects through movements of animal consumers [4,5]. Estimates from multiple wetlands over multiple years for the whole amphibian community would provide important information on variability among years and sites These data could be used to determine what environmental factors affect amphibian biomass export. Understanding which taxonomic or functional groups tend to dominate amphibian biomass export would inform future studies of terrestrial ecosystem effects. The goal of this study was to expand on previous work by estimating amphibian biomass export for 12 geographically isolated wetlands monitored for 2–6 years. These data allowed us to better understand the magnitude, characteristics, and temporal and spatial variability of amphibian biomass export. We predicted that total amphibian biomass export would increase with pond area, but that biomass scaled by pond area would be highest for the smallest ponds [17]

Study Sites

Data Collection

Data Analysis

Amphibian

Species Composition and Diversity

Discussion