Manipulating Individual Decisions and Environmental Conditions Reveal Individual Quality in Decision-Making and Non-Lethal Costs of Predation Risk

Robert L. Thomson,Jukka T. Forsman,Mikko Mönkkönen,Gustavo Tomás,Claudia Mettke-Hofmann

doi:10.1371/journal.pone.0052226

Abstract

Habitat selection is a crucial decision for any organism. Selecting a high quality site will positively impact survival and reproductive output. Predation risk is an important component of habitat quality that is known to impact reproductive success and individual condition. However, separating the breeding consequences of decision-making of wild animals from individual quality is difficult. Individuals face reproductive decisions that often vary with quality such that low quality individuals invest less. This reduced reproductive performance could appear a cost of increased risk but may simply reflect lower quality. Thus, teasing apart the effects of individual quality and the effect of predation risk is vital to understand the physiological and reproductive costs of predation risk alone on breeding animals. In this study we alter the actual territory location decisions of pied flycatchers by moving active nests relative to breeding sparrowhawks, the main predators of adult flycatchers. We experimentally measure the non-lethal effects of predation on adults and offspring while controlling for effects of parental quality, individual territory choice and initiation of breeding. We found that chicks from high predation risk nests (<50 m of hawk) were significantly smaller than chicks from low risk nests (>200 m from hawk). However, in contrast to correlative results, females in manipulated high risk nests did not suffer decreased body condition or increased stress response (HSP60 and HSP70). Our results suggest that territory location decisions relative to breeding avian predators cause spatial gradients in individual quality. Small adjustments in territory location decisions have crucial consequences and our results confirm non-lethal costs of predation risk that were expressed in terms of smaller offspring produced. However, females did not show costs in physiological condition which suggests that part of the costs incurred by adults exposed to predation risk are quality determined.

Highlights

Habitat selection is an important decision in the life of any organism
Reproductive investment may be altered in terms of offspring number and invested resources resulting in reduced reproductive success in terms of smaller and fewer offspring when predation risk is greater [12,13,14]
We previously found that pied flycatchers (Ficedula hypoleuca) show fine-tuned territory location decisions relative to predator nests [35,36]

Summary

Introduction

Habitat selection is an important decision in the life of any organism. Individual survival and future reproductive output are largely dependent on the quality of the habitat in which an individual exists. Breeding habitat selection can be important because choices strongly influence reproductive success and fitness [1]. Predation risk can alter breeding habitat selection by individuals of many taxa [5,6,7,8], and thereby alter the spatial structure and diversity of communities [9,10]. A poor choice in breeding habitat relative to ambient predation risk will have negative consequences, either through decreased survival or subtly via non-lethal costs [11]. Stress protein induction relative to risk of predation has only recently been investigated in different taxa, including insects [18], crustaceans [19], amphibians [22], mammals [17], and birds [20]

Methods

Results

Conclusion