Individual Quality Explains Variation in Reproductive Success Better than Territory Quality in a Long-Lived Territorial Raptor

Iñigo Zuberogoitia,Jabi Zabala,Antoni Margalida

doi:10.1371/journal.pone.0090254

Abstract

Evolution by natural selection depends on the relationship between individual traits and fitness. Variation in individual fitness can result from habitat (territory) quality and individual variation. Individual quality and specialization can have a deep impact on fitness, yet in most studies on territorial species the quality of territory and individuals are confused. We aimed to determine if variation in breeding success is better explained by territories, individual quality or a combination of both. We analysed the number of fledglings and the breeding quality index (the difference between the number of fledglings of an individual/breeding pair and the average number of fledglings of the monitored territories in the same year) as part of a long term (16 years) peregrine falcon (Falco peregrinus) monitoring program with identification of individuals. Using individual and territory identities as correlates of quality, we built Generalised Linear Models with Mixed effects, in which random factors depicted different hypotheses for sources of variation (territory/individual quality) in the reproductive success of unique breeding pairs, males and females, and assessed their performance. Most evidence supported the hypothesis that variation in breeding success is explained by individual identity, particularly male identity, rather than territory. There is also some evidence for inter year variations in the breeding success of females and a territory effect in the case of males. We argue that, in territorial species, individual quality is a major source of variation in breeding success, often masked by territory. Future ecological and conservation studies on habitat use should consider and include the effect of individuals, in order to avoid misleading results.

Highlights

That individuals differ in their ability to survive and reproduce is a central issue of selection theory
Our results supported the hypothesis of an individual effect rather than a territory effect on variation in reproductive success
Including an individual identity as the random factor improved the model with no random factors in every case, whereas including territory identity did not

Summary

Introduction

That individuals differ in their ability to survive and reproduce is a central issue of selection theory. Fitness is an individual measure, several authors combined the concepts of habitat and fitness into the notion that habitat confers fitness to its occupants, and this has been regarded as the habitat fitness potential [7] This concept is well supported by studies reporting differences in reproductive success in birds and other groups using different environments [4,8,9]. Several studies report higher reproductive success in preferred habitat territories [5,10,15], and long-lived raptors have been reported to move from low–quality to high–quality areas as they age [15] This rule is not always followed and other factors, such as individual quality, are invoked in order to explain results This rule is not always followed and other factors, such as individual quality, are invoked in order to explain results (e.g. [16,17])

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