Abstract
An animal’s home-range can be expected to encompass the resources it requires for surviving or reproducing. Thus, animals inhabiting a heterogeneous landscape, where resource patches vary in size, shape and distribution, will naturally have home-ranges of varied sizes, so that each home-range encompasses a minimum required amount of a resource. Home-range size can be estimated from telemetry data, and often key resources, or proxies for them such as the areas of important habitat types, can be mapped. We propose a new method, Resource-Area-Dependence Analysis (RADA), which uses a sample of tracked animals and a categorical map to i) infer in which map categories important resources are accessible, ii) within which home range cores they are found, and iii) estimate the mean minimum areas of these map categories required for such resource provision. We provide three examples of applying RADA to datasets of radio-tracked animals from southern England: 15 red squirrels Sciurus vulgaris, 17 gray squirrels S. carolinensis and 114 common buzzards Buteo buteo. The analyses showed that each red squirrel required a mean (95% CL) of 0.48 ha (0.24–-0.97) of pine wood within the outermost home-range, each gray squirrel needed 0.34 ha (0.11–1.12) ha of mature deciduous woodland and 0.035–0.046 ha of wheat, also within the outermost home-range, while each buzzard required 0.54 ha (0.35–0.82) of rough ground close to the home-range center and 14 ha (11–17) of meadow within an intermediate core, with 52% of them also relying on 0.41 ha (0.29–0.59) of suburban land near the home-range center. RADA thus provides a useful tool to infer key animal resource requirements during studies of animal movement and habitat use.
Highlights
That an animal’s home range contains vital resources for survival and reproduction seems obvious, but identifying and quantifying resource requirements is less so
We introduce Resource-Area-Dependence Analysis (RADA), a new method that uses a sample of tracked animals and a categorical map depicting resource distribution to infer where important resources are accessible and to estimate the minimum area required for such resource provision
Red squirrels on Furzey Island had their resources distributed in fragmented pine woodland in little-used grassland around tarmac areas, the whole being surrounded by sea
Summary
That an animal’s home range contains vital resources for survival and reproduction seems obvious, but identifying and quantifying resource requirements is less so. Visual observations of bird territories showed that territory size could correlate inversely with food supply [1,2]. These observations were followed by a similar and growing body of relationships between range size and habitats from elusive species, for which locations could be collected systematically only by tracking, including raptors [3,4], large cats [5,6], squirrels [7], lagomorphs [8], deer [9,10,11], bears [12,13], and moose [14]. There are several difficulties with this approach, including (i) the unit-sum constraint, by which one strongly avoided habitat (e.g. water for a squirrel) tends to make all others seem preferred, (ii) pseudo-replication, if locations from the same animal are treated as independent observations, and (iii) the definition of what is available or (iv) used
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