We use metapopulation models based on a classic competition-colonization trade-off in order to (1) study community responses to spatially structured habitat loss on dynamic landscapes when species are assembled by ecological (biogeographic) processes; and (2) to study how species are assembled into communities by evolutionary mechanisms. In the first part of our study we show how the response of species richness to habitat destruction in dynamic landscapes can be driven by the existence of either the spatial structure of habitat dynamics or by life-history trade-offs among species. In the second part of our study we confirm that competitive trade-off models predict runaway evolution towards stochastic extinction, making it impossible for stable multispecies assemblages to evolve. We demonstrate that by relaxing the strict deterministic nature of competitive exclusion in such models species can avoid selection towards extinction, allowing for the possibility of species co-evolution resulting in stable multispecies assemblages.

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A trait based approach was used to assess impacts of overstory density and thinning on understory vegetation components related to wildlife habitat. The relationship between overstory basal area and understory vegetation for species grouped by traits, such as production of flowers, fleshy-fruit and palatable leaves, was characterized in thinned and unthinned stands at seven Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests in western Oregon six years following harvests. The ranges of overstory densities within thinned and unthinned stands represent gradients of resource availability and thinning disturbance. Lower overstory densities and thinnings were associated with improved ecosystem functions, specifically the provision of wildlife habitat, as evident by higher cover of flowering and fleshy-fruit and palatable leaf producing species. Greater cover of drought, fire and heat tolerant species in low density stands and after thinnings suggested that these ecosystem functions are more likely to be maintained under climate change conditions, indicating higher resilience. The response of specific functions and response types reflect the traits characteristic for each species group and the impact of these traits on sensitivity to resource availability and disturbances. Thus, the correlation between grouping criteria and the main gradients created by management activities can provide an indication of the expected vegetation response, and therefore the impact of management practices on resilience. / Graduation date: 2012