Density Dependence and Adult Survival Drive Dynamics in Two High Elevation Amphibian Populations

Amanda M Kissel,Erin Muths,Simone Tenan

doi:10.3390/d12120478

Abstract

Amphibian conservation has progressed from the identification of declines to mitigation, but efforts are hampered by the lack of nuanced information about the effects of environmental characteristics and stressors on mechanistic processes of population regulation. Challenges include a paucity of long-term data and scant information about the relative roles of extrinsic (e.g., weather) and intrinsic (e.g., density dependence) factors. We used a Bayesian formulation of an open population capture-recapture model and >30 years of data to examine intrinsic and extrinsic factors regulating two adult boreal chorus frogs (Pseudacris maculata) populations. We modelled population growth rate and apparent survival directly, assessed their temporal variability, and derived estimates of recruitment. Populations were relatively stable (geometric mean population growth rate >1) and regulated by negative density dependence (i.e., higher population sizes reduced population growth rate). In the smaller population, density dependence also acted on adult survival. In the larger population, higher population growth was associated with warmer autumns. Survival estimates ranged from 0.30–0.87, per-capita recruitment was <1 in most years, and mean seniority probability was >0.50, suggesting adult survival is more important to population growth than recruitment. Our analysis indicates density dependence is a primary driver of population dynamics for P. maculata adults.

Highlights

Progress in mitigating declines in animal populations depends on moving beyond the identification of causes and towards the determination of mechanism—how a particular cause affects whole populations
Genetic connectivity in boreal chorus frogs is associated with landscape complexity, and migration/colonization is facilitated by stepping-stone habitats [49]
We explored the relative contribution of intrinsic and extrinsic factors regulating two populations of P. maculata using data from two relatively stable populations

Summary

Introduction

Progress in mitigating declines in animal populations depends on moving beyond the identification of causes and towards the determination of mechanism—how a particular cause affects whole populations. A prerequisite for making sense of such mechanisms is to understand how populations are regulated (e.g., intrinsically or extrinsically) and to understand how regulation is affected by cause(s) of decline (e.g., a system perturbed by disease or invasive species). The past three decades of amphibian declines illustrate a progression in conservation efforts from identifying a phenomenon [1], to identifying potential causes [2,3,4], to searching for mechanisms [5,6] and identifying mitigation strategies [7,8,9]. Regulation is likely a combination of the effects of intrinsic (e.g., density dependence, [12,13]) and extrinsic (e.g., environmental [14,15]) factors and their interactions.

Methods

Results

Conclusion