PARENT SESSION
Oral Session # 5: Biogeography I: Community Structure and Diversity.
Presiding: B Enquist
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 104.
Functional diversity along climatic gradients: A spatial model.
Schwilk, Dylan*,1, Ackerly, David1, 1 Stanford University, Stanford, CA
ABSTRACT- In heterogeneous environments, the distribution of plant species is the outcome of a series of biotic and abiotic filters: the community assembly process. Recent developments in neutral models emphasize the importance of incorporating non-equilibrial processes (e.g., ecological drift) in models of niche-structured community assembly. Here, we examine community diversity of sessile organisms in response to spatial variation in habitat. Our framework combines the potential for ecological drift with non-neutral competition for space in a heterogeneous environment. We constructed a spatially explicit model to simulate the distribution of species in a one-dimensional spatial landscape with an underlying gradient in environmental conditions. Our objective is to examine the influence of niche breadth, dispersal distances, community size (total number of individuals) and the breadth of the environmental gradient on levels of species and functional trait diversity. In our model, organisms' response to the environmental condition is described by a Gaussian fitness function and species vary in the location of their fitness mode along the gradient. As expected, equilibrium diversity decreased with increasing niche breadth. Increasing dispersal distance, however, increased diversity. Diversity increased linearly with increasing community size, consistent with neutral theory. Increasing the range of the environmental gradient, however, also increased diversity and niche-packing. The effect of environmental range is not linear: diversity levels off as environmental range approaches zero and stochastic processes become more prominent. Apparent limiting similarity emerges from the effect of niche breadth and the stochastic effect of finite populations.
Key words: similarity, theory, niche, gradient