Density‐dependent home‐range size revealed by spatially explicit capture–recapture
The size of animal home ranges often varies inversely with population density among populations of a species. This fact has implications for population monitoring using spatially explicit capture–recapture (SECR) models, in which both the scale of home‐range movements σ and population density D usually appear as parameters, and both may vary among populations. It will often be appropriate to model a structural relationship between population‐specific values of these parameters, rather than to assume independence. We suggest re‐parameterizing the SECR model using kp = σ p √Dp , where kp relates to the degree of overlap between home ranges and the subscript p distinguishes populations. We observe that kp is often nearly constant for populations spanning a range of densities. This justifies fitting a model in which the separate kp are replaced by the single parameter k and σ p is a density‐dependent derived parameter. Continuous density‐dependent spatial variation in σ may also be modelled, using a scaled non‐Euclidean distance between detectors and the locations of animals. We illustrate these methods with data from automatic photography of tigers Panthera tigris across India, in which the variation is among populations, from mist‐netting of ovenbirds Seiurus aurocapilla in Maryland, USA, in which the variation is within a single population over time, and from live‐trapping of brushtail possums Trichosurus vulpecula in New Zealand, modelling spatial variation within one population.
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Document Type: Research Article
Publication date: July 1, 2016