Ecological scale and species-habitat modeling: studies on the Northern flying squirrel.




Wheatley, Matthew Thompson

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Although scale is consistently identified as the central problem in ecology, empirical examinations of its importance in ecological research are rare and fundamental concepts remain either largely misunderstood or incorrectly applied. Due to the mobile and wide-ranging nature of wildlife populations, species-habitat modeling is a field in which much proliferation of multi-scale studies has occurred, and thus provides a good arena within which to test both scale theory and its application. Insufficient examination of a relevant breadth of the scale continuum could be an important constraint in all multi-scale investigations, limiting our understanding of scalar concepts overall. Here I examine several concepts of ecological scale by studying free-ranging populations of northern flying squirrels (Glaucomys sabrinus), purported to be a keystone species in northern forests. Coarse-grain digital forest coverage revealed that flying squirrels in the boreal and foothills of Alberta were not conifer specialists, rather forest generalists regarding stand type and age. Lack of coarse-grain scale effects led me to examine fine-grain data, including an assessment of scale domains using a novel continuum approach. Fine-grain data revealed important scale-related biases of trapping versus telemetry, namely that, at fine-grain scales, different habitat associations could be generated from the same data set based on methods alone. Then, focusing on spatial extent, I develop a true multi-scalar approach examining scale domains. First, I quantify only forest attributes across multiple extents, and demonstrate unpredictable scale effects on independent variables often used in species-habitat models. Second, including both independent (habitat) and dependent (squirrel telemetry) variables in the same approach, I demonstrate that the relative ranking and strength-of-evidence among different species-habitat models change based on scale, and this effect is different between genders and among life-history stage (i.e., males, females, and dispersing juveniles). I term this the “continuum approach”, the results of which question the validity of many published species-habitat models. Lastly, I attempt to clarify why existing models should be scrutinized by reviewing common rationales used in scale choice (almost always arbitrary), outlining differences between “observational scale” and the commonly cited “orders of resource selection”, and making a clear distinction between multi-scale versus multi-design ecological studies.



Northern flying squirrel, Glaucomys sabrinus, Alberta, ecology