Intermediate pond sizes contain the highest density, richness, and diversity of pond-breeding amphibians.

Raymond D. Semlitsch,Dana L. Drake,William E. Peterman,Brittany H. Ousterhout,Thomas L. Anderson,Francisco Moreira

doi:10.1371/journal.pone.0123055

Abstract

We present data on amphibian density, species richness, and diversity from a 7140-ha area consisting of 200 ponds in the Midwestern U.S. that represents most of the possible lentic aquatic breeding habitats common in this region. Our study includes all possible breeding sites with natural and anthropogenic disturbance processes that can be missing from studies where sampling intensity is low, sample area is small, or partial disturbance gradients are sampled. We tested whether pond area was a significant predictor of density, species richness, and diversity of amphibians and if values peaked at intermediate pond areas. We found that in all cases a quadratic model fit our data significantly better than a linear model. Because small ponds have a high probability of pond drying and large ponds have a high probability of fish colonization and accumulation of invertebrate predators, drying and predation may be two mechanisms driving the peak of density and diversity towards intermediate values of pond size. We also found that not all intermediate sized ponds produced many larvae; in fact, some had low amphibian density, richness, and diversity. Further analyses of the subset of ponds represented in the peak of the area distribution showed that fish, hydroperiod, invertebrate density, and canopy are additional factors that drive density, richness and diversity of ponds up or down, when extremely small or large ponds are eliminated. Our results indicate that fishless ponds at intermediate sizes are more diverse, produce more larvae, and have greater potential to recruit juveniles into adult populations of most species sampled. Further, hylid and chorus frogs are found predictably more often in ephemeral ponds whereas bullfrogs, green frogs, and cricket frogs are found most often in permanent ponds with fish. Our data increase understanding of what factors structure and maintain amphibian diversity across large landscapes.

Highlights

One of the most fundamental questions in ecology is what maintains species diversity [1]
Species were predictably found in different pond types; Hylid frogs, comprised of Hyla chrysoscelis/versicolor, Pseudacris crucifer and P. maculata, and the salamanders Ambystoma maculatum and Notophthalmus viridescens louisianensis were detected at the highest proportion of ephemeral sites (> 62%), while Rana catesbeiana and R. clamitans were detected at > 92%, and Acris blanchardi were detected at > 69% of the permanent sites with fish (Table 1)
Our results show a consistent and predictable pattern of peak larval density, richness, and species diversity of amphibians at intermediate pond area that partially supports the hypothesis of a balance between pond drying and predation

Summary

Introduction

One of the most fundamental questions in ecology is what maintains species diversity [1]. Understanding that multiple gradients of disturbance and productivity likely all interact with species traits to generate patterns of diversity we see in the real world is critical [7,11] This is especially important because natural or anthropogenic environmental disturbances such as wildfire, flooding, grazing, invasive species or droughts due to climate change can alter the frequency, intensity, duration, and timing of disturbance regimes making a mechanistic understanding critical for future management and conservation of species communities. Examining a range of pond environments with different probabilities of drying across a large landscape inhabited by a diversity of amphibian species can yield insight into the mechanisms driving species success, predict the structure of communities, and help develop management and protection guidelines for maintaining biodiversity. Our ultimate goal is to provide an analysis of a largescale pattern based on extensive field surveys and provide general mechanistic inferences regarding the balance between hydroperiod and predation pressure that can be used to develop management and conservation guidelines

Ethics Statement

Results

Discussion