Abstract
Most studies dealing with home ranges consider the study areas as if they were totally flat, working only in two dimensions, when in reality they are irregular surfaces displayed in three dimensions. By disregarding the third dimension (i.e., topography), the size of home ranges underestimates the surface actually occupied by the animal, potentially leading to misinterpretations of the animals' ecological needs. We explored the influence of considering the third dimension in the estimation of home-range size by modeling the variation between the planimetric and topographic estimates at several spatial scales. Our results revealed that planimetric approaches underestimate home-range size estimations, which range from nearly zero up to 22%. The difference between planimetric and topographic estimates of home-ranges sizes produced highly robust models using the average slope as the sole independent factor. Moreover, our models suggest that planimetric estimates in areas with an average slope of 16.3° (±0.4) or more will incur in errors ≥5%. Alternatively, the altitudinal range can be used as an indicator of the need to include topography in home-range estimates. Our results confirmed that home-range estimates could be significantly biased when topography is disregarded. We suggest that study areas where home-range studies will be performed should firstly be scoped for its altitudinal range, which can serve as an indicator for the need for posterior use of average slope values to model the surface area used and/or available for the studied animals.
Highlights
The home-range of an animal is traditionally defined as “the area traversed by the individual in its normal activities of food gathering, mating, and caring for young” (Burt 1943)
The altitudinal ranges within each study area varied from 888 m to 2522 m (Table 1)
Five of the study areas (1, 2, 3, 4, and 7) are included in the Atlantic bioclimatic region of the Iberian Peninsula (IP) (Rivas-Martínez et al 2004), where average temperature ranges from 0.8 Æ 3.5°C to 23.9 Æ 2.5°C (Hijmans et al 2005)
Summary
The home-range of an animal is traditionally defined as “the area traversed by the individual in its normal activities of food gathering, mating, and caring for young” (Burt 1943). Some of these studies detected a variety of differences between the planimetric and topographic home-range estimates: 3.1% for white-tailed deers (Odocoileus virginianus; Campbell et al 2004); 6.4% for allegheny woodrats (Neotoma magister; Castleberry et al 2001); 9% for diamond rattlesnakes (Crotalus ruber; Greenberg and McClintock 2008); 14% for speckled rattle snakes (Crotalus mitchellii; Greenberg and McClintock 2008); 20% for yaku monkeys (Macaca fuscata; Sprague 2000); and 23% for blackand-white snub-nosed monkeys (Rhinopithecus bieti; Grueter et al 2008) For these reasons, and as topography can affect the animal’s perception of the habitat, food resources, or access to mates (Powell and Mitchell 1998), ignoring this factor can lead researchers to misinterpret the ecological needs of animals, mainly if they inhabit mountainous or rough areas. As several carnivore species inhabit mountainous regions (e.g., Nilsson and Go€tmark 1992; Powell et al 2000), taking into account terrain roughness assumes a fundamental role in management and conservation planning
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