Abstract
BackgroundDepartures from power law group size frequency distributions have been proposed as a useful tool to link individual behavior with population patterns and dynamics, although examples are scarce for wild animal populations.Methodology/Principal FindingsWe studied a population of Lesser kestrels (Falco naumanni) breeding in groups (colonies) from one to ca. 40 breeding pairs in 10,000 km2 in NE Spain. A 3.5 fold steady population increase occurred during the eight-year study period, accompanied by a geographical expansion from an initial subpopulation which in turn remained stable in numbers. This population instability was mainly driven by first-breeders, which are less competitive at breeding sites, being relegated to breed solitarily or in small colony sizes, and disperse farther than adults. Colony size frequency distributions shifted from an initial power law to a truncated power law mirroring population increase. Thus, we hypothesized that population instability was behind the truncation of the power law. Accordingly, we found a power law distribution through years in the initial subpopulation, and a match between the power law breakpoint (at ca. ten pairs) and those colony sizes from which the despotic behavior of colony owners started to impair the settlement of newcomers. Moreover, the instability hypothesis was further supported by snapshot data from another population of Lesser kestrels in SW Spain suffering a population decline.Conclusions/SignificanceAppropriate analysis of the scaling properties of grouping patterns has unraveled the link between local agonistic processes and large-scale (population) grouping patterns in a wild bird population.
Highlights
After decades of parallel research in animal behavior and population ecology, studying the link between them is key to advance in the understanding of many natural phenomena [1,2,3,4,5]
Using appropriate multiplicativelybinned log-log plots [22,23] we found that between 1993 to 1997 colony sizes fitted well to a power law distribution (R2 between 0.96 and 0.99), colony size variation in the last three years was better fitted to a truncated power law with a breakpoint at intermediate colony sizes (Figure 3c)
This is the first study to show the ontogeny of a truncation in the power law distribution of colony sizes throughout time in a wild population
Summary
After decades of parallel research in animal behavior and population ecology, studying the link between them is key to advance in the understanding of many natural phenomena [1,2,3,4,5]. Empirical studies conducted under laboratory conditions, where both individual behavior details and statistical grouping patterns and dynamics have been studied, further support this link between small-scale processes and population patterns [7,8,9,10]. Despite the importance of this issue, empirical evidence is still scarce for wild animal populations, and for birds. This is probably due to logistic problems derived from studying simultaneously fine-scale behavioral processes and large-scale population patterns and dynamics, and because adequate analytical frameworks are still lacking. Departures from power law group size frequency distributions have been proposed as a useful tool to link individual behavior with population patterns and dynamics, examples are scarce for wild animal populations
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