The Functional Response of a Generalist Predator

Sophie Smout,Carmen Fernández,John Harwood,Christian Asseburg,Stephen Redpath,Jason Matthiopoulos,Simon Thirgood,Frederick R. Adler

doi:10.1371/journal.pone.0010761

Abstract

BackgroundPredators can have profound impacts on the dynamics of their prey that depend on how predator consumption is affected by prey density (the predator's functional response). Consumption by a generalist predator is expected to depend on the densities of all its major prey species (its multispecies functional response, or MSFR), but most studies of generalists have focussed on their functional response to only one prey species.Methodology and principal findingsUsing Bayesian methods, we fit an MSFR to field data from an avian predator (the hen harrier Circus cyaneus) feeding on three different prey species. We use a simple graphical approach to show that ignoring the effects of alternative prey can give a misleading impression of the predator's effect on the prey of interest. For example, in our system, a “predator pit” for one prey species only occurs when the availability of other prey species is low.Conclusions and significanceThe Bayesian approach is effective in fitting the MSFR model to field data. It allows flexibility in modelling over-dispersion, incorporates additional biological information into the parameter priors, and generates estimates of uncertainty in the model's predictions. These features of robustness and data efficiency make our approach ideal for the study of long-lived predators, for which data may be sparse and management/conservation priorities pressing.

Highlights

There is a growing realisation that management which considers only the dynamics of individual species is inadequate for conserving biodiversity [1],[2]
The Bayesian approach is effective in fitting the MSFR model to field data
Focus has shifted towards the identification of relatively measured metrics that reflect the overall status of ecosystems [8]

Summary

Introduction

There is a growing realisation that management which considers only the dynamics of individual species is inadequate for conserving biodiversity [1],[2]. This has led to calls for an ecosystem-based approach to management [3] in the fields of fisheries [4], forestry [5] and wildlife management. Focus has shifted towards the identification of relatively measured metrics that reflect the overall status of ecosystems [8]. These metrics are useful for monitoring the impacts of management but provide little biological insight. Consumption by a generalist predator is expected to depend on the densities of all its major prey species (its multispecies functional response, or MSFR), but most studies of generalists have focussed on their functional response to only one prey species

Methods

Results

Discussion

Conclusion