Spatially explicit null models in biogeography: Toward a multi-scale understanding of the niche.

摘要

In general, most ecologists envision the "niche" as a central organizing tenet, and that particular parameters of the niche help structure biogeographic patterns of diversity, distribution and abundance. The major emergent alternative to the niche concept requires the inference of background stochasticity, and its application through null models. For example, rather than competitive interactions of species shaping the coexistence of species, "historical accidents of dispersal" have been suggested. In this thesis I explore, in some detail, the concept of niche using of null models.;Results can be regarded as representing intermediate states between the extremes of continua of which niche and neutral models form the ends. With respect to the relative strengths of stochastic and deterministic processes, this thesis has characterized the attributes of groups of species. For example, large-ranged NA tree species are influenced by the MDE more than small-ranged species; moreover, regional, null species distribution models performed best for birds, insects, reptiles, sedges, as well as for aquatic and terrestrial plants. It seems most likely that real species distributions are the product of variation in relative strength of stochastic and deterministic processes.;In this thesis, two detailed and quite different null models are presented. The first, based on the "Mid-Domain Effect" (MDE), explores the influence of continental geometry on patterns in species richness and range size frequency distributions. I compared the MDE predictions first to observations on tree species richness in continental North America (n = 417 species), and then to amphibian, bird and mammal species richness across North and South America (n = 2216, 3771 and 1605 species, respectively) contrasting the relative contributions of null model results and environmental correlates. I have developed a novel null methodology to predict the niche of a species, or a group of species; I applied this at local and regional scales to examine null spatial distribution predictions for a single, endangered species at the local scale ( Opuntia humifusa at Point Pelee National Park), and for groups of rare species at a regional scale (based on reported occurrences across south-western Ontario).