ASSESSING THE CONTRIBUTION OF ABIOTIC NICHES AND DISPERSAL LIMITATIONS TO SPECIATION AND EXTINCTION UNDER CLIMATE CHANGE USING SIMULATION STUDIES

Species’ geographic distributions are constrained by three main factors: abiotic niche requirements, biotic interactions, and dispersal constraints. Interactions among these factors during times of environmental change impact patterns of speciation, extinction, and distributional dynamics. However, determining the relative contribution of each factor is challenging. We applied simulation studies to assess feedbacks between abiotic niche breadth, dispersal capacity, and environmental change to isolate their impacts on patterns of speciation and extinction. Specifically, we tested three hypotheses: 1) species with narrow niche breadths have higher rates of speciation and extinction; 2) species with rapid and far-reaching dispersal capacity (relative to the rate of climate change) have reduced speciation and extinction potential; and 3) increased rate and frequency of environmental change inhibits evolutionary change. Species with large and small niche breadths were chosen from a phylogenetically and ecologically diverse group of 1710 extant plants with known physiological climate tolerances. Dispersal capacity was manipulated as maximum search distance. Climate fluctuated between warm intervals equivalent to the last interglacial and cold intervals equivalent to the last glacial maximum mapped onto Eurasia. Rate, frequency, and length of climate stability were varied to produce fast, medium, and slow climate change scenarios. Speciation and extinction events were documented by building a virtual phylogeny for each simulation. Preliminary results suggest that speciation and extinction are indeed damped in taxa with greater dispersal capacity, even under differing rates of climate change. Under the most rapid climate change scenario, however, species with poor dispersal capacity experienced particularly high rates of speciation and extinction. Interestingly, in all simulations, speciation and extinction rates varied in tandem, which matches observations throughout much of the fossil record. These results support expectations from macroevolutionary theory, where species with higher dispersal capacity are less likely to experience speciation via allopatry, and specialist species are more sensitive to extinction and speciation pressures than generalists.