Increasing density leads to generalization in both coarse-grained habitat selection and fine-grained resource selection in a large mammal.
Abstract: Density is a fundamental driver of many ecological processes including habitat selection. Theory on density-dependent habitat selection predicts that animals should be distributed relative to profitability of habitat, resulting in reduced specialization in selection (i.e. generalization) as density increases and competition intensifies. Despite mounting empirical support for density-dependent habitat selection using isodars to describe coarse-grained (interhabitat) animal movements, we know little of how density affects fine-grained resource selection of animals within habitats [e.g. using resource selection functions (RSFs)]. Using isodars and RSFs, we tested whether density simultaneously modified habitat selection and within-habitat resource selection in a rapidly growing population of feral horses (Equus ferus caballus Linnaeus; Sable Island, Nova Scotia, Canada; 42% increase in population size from 2008 to 2012). Among three heterogeneous habitat zones on Sable Island describing population clusters distributed along a west-east resource gradient (west-central-east), isodars revealed that horses used available habitat in a density-dependent manner. Intercepts and slopes of isodars demonstrated a pattern of habitat selection that first favoured the west, which generalized to include central and east habitats with increasing population size consistent with our understanding of habitat quality on Sable Island. Resource selection functions revealed that horses selected for vegetation associations similarly at two scales of extent (total island and within-habitat zone). When densities were locally low, horses were able to select for sites of the most productive forage (grasslands) relative to those of poorer quality. However, as local carrying capacity was approached, selection for the best of available forage types weakened while selection for lower-quality vegetation increased (and eventually exceeded that of grasslands). Isodars can effectively describe coarse-grained habitat selection in large mammals. Our study also shows that the main predictions of density-dependent habitat selection are highly relevant to our interpretation of RSFs in space and time. At low but not necessarily high population size, density will be a leading indicator of habitat quality. Fitness maximization from specialist vs. generalist strategies of habitat and resource selection may well be apparent at multiple spatial extents and grains of resolution.
© 2013 The Authors. Journal of Animal Ecology © 2013 British Ecological Society.
Publication Date: 2013-08-09 PubMed ID: 23931034DOI: 10.1111/1365-2656.12115Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This study suggests that as population density increases in large mammals, their selection behavior tends to generalize from specific preferences to more broad-based selection. The study was carried out using the rapidly growing population of feral horses on Sable Island, Canada, and puts the spotlight on the fundamental role of population density in ecological processes like habitat selection.
Understanding the Study
- The research is based on the theory of density-dependent habitat selection. It posits that as the population density of a species increases, the animals diversify their habitat preferences due to increased competition.
- They use isodars, a tool that measures how animals distribute themselves based on habitat profitability, and resource selection functions (RSFs) that help understand how animals choose resources within a certain habitat.
- The case study for this research is the population of feral horses on Sable Island, Nova Scotia, the population of which grew by a hefty 42% from 2008 to 2012.
Habitat Zones and Selection
- Sable Island for this study was divided into three distinct habitat zones (west, central, and east), each with different resource availability. It was found that horses were adapting their habitats as their density increased. When the population was relatively low, their preferred habitat was the west. However, as the population increased, they generalized and began to include the central and east habitats.
Resource Selection Function
- The researchers observed how horses selected for certain vegetation associations across the island and within specific habitat zones. When population density was low, they were able to choose their prefered, most productive forage, the grasslands. With increased density and resources, they began to select for lower-quality vegetation in higher quantities.
Conclusions Drawn
- The main conclusions drawn from this study bolster the relevance of density-dependent habitat selection to interpret resource selection functions. The researchers found that when population sizes are low, density can be a leading indicator of habitat quality. However, this correlation may not hold with high population size.
- Furthermore, the generalization of habitat and resource preferences as density increases underlines the trade-off between achieving maximum fitness and optimal resource utilization. This correlation is visible across multiple spatial extents and grains of resolution.
Cite This Article
APA
van Beest FM, Uzal A, Vander Wal E, Laforge MP, Contasti AL, Colville D, McLoughlin PD.
(2013).
Increasing density leads to generalization in both coarse-grained habitat selection and fine-grained resource selection in a large mammal.
J Anim Ecol, 83(1), 147-156.
https://doi.org/10.1111/1365-2656.12115 Publication
Researcher Affiliations
- Department of Animal and Poultry Science, College of Agriculture and Bioresources, University of Saskatchewan, 51 Campus Drive, Saskatoon, SK, S7N 5E2, Canada.
MeSH Terms
- Animals
- Demography
- Ecosystem
- Female
- Horses / physiology
- Islands
- Male
- Nova Scotia
- Population Density
- Population Growth
Citations
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