Colonial, more widely distributed and less abundant bird species undergo wider population fluctuations independent of their population trend.

Anders P Møller,José J Cuervo

doi:10.1371/journal.pone.0173220

Abstract

Understanding temporal variability in population size is important for conservation biology because wide population fluctuations increase the risk of extinction. Previous studies suggested that certain ecological, demographic, life-history and genetic characteristics of species might be related to the degree of their population fluctuations. We checked whether that was the case in a large sample of 231 European breeding bird species while taking a number of potentially confounding factors such as population trends or similarities among species due to common descent into account. When species-specific characteristics were analysed one by one, the magnitude of population fluctuations was positively related to coloniality, habitat, total breeding range, heterogeneity of breeding distribution and natal dispersal, and negatively related to urbanisation, abundance, relative number of subspecies, parasitism and proportion of polymorphic loci. However, when abundance (population size) was included in the analyses of the other parameters, only coloniality, habitat, total breeding range and abundance remained significantly related to population fluctuations. The analysis including all these predictors simultaneously showed that population size fluctuated more in colonial, less abundant species with larger breeding ranges. Other parameters seemed to be related to population fluctuations only because of their association with abundance or coloniality. The unexpected positive relationship between population fluctuations and total breeding range did not seem to be mediated by abundance. The link between population fluctuations and coloniality suggests a previously unrecognized cost of coloniality. The negative relationship between population size and population fluctuations might be explained by at least three types of non-mutually exclusive stochastic processes: demographic, environmental and genetic stochasticity. Measurement error in population indices, which was unknown, may have contributed to the negative relationship between population size and fluctuations, but apparently only to a minor extent. The association between population size and fluctuations suggests that populations might be stabilized by increasing population size.

Highlights

Temporal variability in population size, and the causes and consequences of such variability, are central topics in ecology and population biology [1,2,3,4], and, in conservation biology [5,6,7]
When species-specific parameters were analysed one at a time, the magnitude of population fluctuations was positively related to coloniality, water habitat, total breeding range, heterogeneity of distribution and natal dispersal, and negatively related to urbanisation, abundance, relative number of subspecies, parasitism and proportion of polymorphic loci (Table 1)
When both Paleartic breeding area and abundance were included in the model, population fluctuations were still negatively related to abundance, implying that populations fluctuated less with large population size and with high density

Summary

Introduction

Temporal variability in population size, and the causes and consequences of such variability, are central topics in ecology and population biology [1,2,3,4], and, in conservation biology [5,6,7]. Temporal variability in population size has been studied at both intraspecific and interspecific levels Temporal variability in population size is often estimated as inter-annual variability, which can be quantified by standard statistics such as the coefficient of variation or the standard deviation [22]. SEE provides an estimate of population fluctuations around the trend, i.e., temporal variability in population size independent of population trend. These two components of variation provide qualitatively different information and should be studied independently of each other. [26,27,28]), temporal variability in population size independent of population trend has rarely been studied Despite the large amount of research focusing on variability in total population size (see references above), or on population trends (e.g. [26,27,28]), temporal variability in population size independent of population trend has rarely been studied

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