Ecological niche conservatism spurs diversification in response to climate change.

Lengthy debate has surrounded the theoretical and empirical science of whether climatic niche evolution is related to increased or decreased rates of biological diversification. Because species can persist for thousands to millions of years, these questions cross broad scales of time and space. Thus, short-term experiments may not provide comprehensive understanding of the system, leading to the emergence of contrasting opinions: niche evolution may increase diversity by allowing species to explore and colonize new geographic areas across which they could speciate; or, niche conservatism might augment biodiversity by supporting isolation of populations that may then undergo allopatric speciation. Here, we use a simulation approach to test how biological diversification responds to different rates and modes of niche evolution. We find that niche conservatism promotes biological diversification, whereas labile niches-whether adapting to the conditions available or changing randomly-generally led to slower diversification rates. These novel results provide a framework for understanding how Earth-life interactions produced such a diverse biota.

Spatio-temporal climate change contributes to latitudinal diversity gradients.

The latitudinal diversity gradient (LDG), where the number of species increases from the poles to the Equator, ranks among the broadest and most notable biodiversity patterns on Earth. The pattern of species-rich tropics relative to species-poor temperate areas has been recognized for well over a century, but the generative mechanisms are still debated vigorously. We use simulations to test whether spatio-temporal climatic changes could generate large-scale patterns of biodiversity as a function of only three biological processes-speciation, extinction and dispersal-omitting adaptive niche evolution, diversity-dependence and coexistence limits. In our simulations, speciation resulted from range disjunctions, whereas extinction occurred when no suitable sites were accessible to species. Simulations generated clear LDGs that closely match empirical LDGs for three major vertebrate groups. Higher tropical diversity primarily resulted from higher low-latitude speciation, driven by spatio-temporal variation in precipitation rather than in temperature. This suggests that spatio-temporal changes in low-latitude precipitation prompted geographical range disjunctions over Earth's history, leading to high rates of allopatric speciation that contributed to LDGs. Overall, we show that major global biodiversity patterns can derive from interactions of species' niches (fixed a priori in our simulations) with dynamic climate across complex, existing landscapes, without invoking biotic interactions or niche-related adaptations.

Impacts of Niche Breadth and Dispersal Ability on Macroevolutionary Patterns.

We describe a spatially explicit simulation experiment designed to assess relative impacts of macroecological traits on patterns of biological diversification under changing environmental conditions. Using a simulation framework, we assessed impacts of species' niche breadth (i.e., the range of their abiotic tolerances) and dispersal ability on resulting patterns of speciation and extinction and evaluated how these traits, in conjunction with environmental change, shape biological diversification. Simulation results supported both niche breadth and dispersal ability as important drivers of diversification in the face of environmental change, and suggested that the rate of environmental change influences how species interact with the extrinsic environment to generate diversity. Niche breadth had greater effects on speciation and extinction than dispersal ability when climate changed rapidly, whereas dispersal ability effects were elevated when climate changed slowly. Our simulations provide a bottom-up perspective on the generation and maintenance of diversity under climate change, offering a better understanding of potential interactions between species' intrinsic macroecological characteristics and a dynamic extrinsic environment in the process of biological diversification.

Sharks that pass in the night: using Geographical Information Systems to investigate competition in the Cretaceous Western Interior Seaway.

One way the effects of both ecology and environment on species can be observed in the fossil record is as changes in geographical distribution and range size. The prevalence of competitive interactions and species replacements in the fossil record has long been investigated and many evolutionary perspectives, including those of Darwin, have emphasized the importance of competitive interactions that ultimately lead one species to replace another. However, evidence for such phenomena in the fossil record is not always manifest. Here we use new quantitative analytical techniques based on Geographical Information Systems and PaleoGIS tectonic reconstructions to consider this issue in greater detail. The abundant, well-preserved fossil marine vertebrates of the Late Cretaceous Western Interior Seaway of North America provide the component data for this study. Statistical analysis of distributional and range size changes in taxa confirms earlier ideas that the relative frequency of competitive replacement in the fossil record is limited to non-existent. It appears that typically, environmental gradients played the primary role in determining species distributions, with competitive interactions playing a more minor role.