PARENT SESSION
Contributed Oral Session 18: Avian Communities and Populations
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 524 C, Level 5, Palais des congrès de Montréal
The challenge of statistically identifying species-resource relationships on an uncooperative landscape.
Smith, Barry*,1, Goodinson, Clive2, Martin, Kathy1, 2, 1 Canadian Wildlife Service, Delta, BC, Canada2 Department of Forest Sciences, Vancouver, BC, Canada
ABSTRACT- Point-counts in combination with vegetation plots have been used to collect data in bird studies exploring species-habitat relationships. In an ideal world, analysis of the resulting data would yield correct and significant correlations between point-count detections and various putative habitat attributes. However, in practice the data are invariably noisy and their interpretation inconclusive, perhaps even misleading. In order to explore possible causes of such analytical failures, we constructed a spatially explicit model which simulates the sampling of a territorial species on a landscape characterized by a number of habitat resources. The spatial distribution of each resource and the distribution of territories across the landscape, given known species-habitat relationships, were defined a priori. The point-count and vegetation plot regime was then superimposed on the landscape and sample data generated. For a given set of simulation parameters, sample data were generated and analyzed repeatedly, as in power analysis, in order to determine the minimum sampling effort required to correctly detect the true species-habitat relationships. The results of our simulations showed that only under highly simplified conditions were the true species-habitat relationships detectable for a realistic sampling effort. Disturbingly, often statistically significant, but incorrect, relationships were identified. In addition to previously acknowledged sources of variance in the data, such as species detectability and density, we determined that the synchrony of the spatial periodicity of the habitat resources, the average territory size, and the radii of both point-counts and vegetation plots, were critical factors influencing the success of a sampling effort.
Key words: point counts, vegetation plots, species-habitat relationships, power analysis