Cross-scale habitat selection by terrestrial and marine mammals




Fisher, Jason Thomas

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Ecology has been devoted to defining the content of a species’ environment. Defining the extent, or size, of a species’ environment is also pivotal to elucidating species-habitat relationships. More than a home range, this extent integrates an individual’s lifetime experiences with resources, competition, and predators. I theorised that a species’ habitat extent is identifiable from its characteristic spatial scale of habitat selection, which in turn is predicted by body size. I reviewed scale-dependent mammalian habitat selection studies and found that a characteristic scale was typically not identified, but identifiable. Of several ecological predictors tested, only body mass was a significant predictor of the relative size of a species’ characteristic habitat selection scale. Tests of existing data are confounded by differing approaches, so I empirically tested the scale-body mass hypothesis using a standardised survey of 12 sympatric terrestrial mammal species from the Canadian Rocky Mountains. For each species, support for habitat models varied across 20 scales tested. For six species, I found a characteristic selection scale, which was best predicted by species body mass in a quadratic relationship. Occurrence of large and small species was explained by habitat measured at large scales, whereas medium- sized species were explained by habitat measured at small scales. The relationship between body size and habitat selection scale is congruent with the textural-discontinuity hypothesis, and implies species’ evolutionary adaptation to landscape heterogeneity as the driver of scale-dependent habitat selection. I applied this principle to examine wolverine habitat selection, and found that anthropogenic fragmentation of the landscape influences that species’ occurrence in space at large spatial scales. Finally, I contended that the prevailing paradigm equating habitats to resources omits interspecific interactions that are key predictors of a species’ occurrences. I examined habitat selection of martens and fishers in terrestrial environments, and sea otters in marine coastal environments, and tested whether the presence of heterospecifics could explain spatial occurrence beyond landscape structure and resources. In both cases, the presence of heterospecifics explained species occurrence beyond simple resource selection. Interspecific interactions are key drivers of a species’ distribution in space; this is the spatial expression of the concepts of fundamental and realized niches. Body size interacts with landscape structure to determine the scale of a species’ response to its environment, and within this habitat extent, interspecific interactions affect the species’ pattern of occurrence and distribution.



habitat relationships, spatial scale, scaling, allometry, landscape, competition, interspecific, martens, fishers, sea otters