A stochastic, evolutionary model for range shifts and richness on tropical elevational gradients under Quaternary glacial cycles

Abstract

Quaternary glacial-interglacial cycles repeatedly forced thermal zones up and down the slopes of mountains, at all latitudes. Although no one doubts that these temperature cycles have left their signature on contemporary patterns of geography and phylogeny, the relative roles of ecology and evolution are not well understood, especially for the tropics. To explore key mechanisms and their interactions in the context of chance events, we constructed a geographical range-based, stochastic simulation model that incorporates speciation, anagenetic evolution, niche conservatism, range shifts and extinctions under late Quaternary temperature cycles along tropical elevational gradients. In the model, elevational patterns of species richness arise from the differential survival of founder lineages, consolidated by speciation and the inheritance of thermal niche characteristics. The model yields a surprisingly rich variety of realistic patterns of phylogeny and biogeography, including close matches to a variety of contemporary elevational richness profiles from an elevational transect in Costa Rica. Mountaintop extinctions during interglacials and lowland extinctions at glacial maxima favour mid-elevation lineages, especially under the constraints of niche conservatism. Asymmetry in temperature (greater duration of glacial than of interglacial episodes) and in lateral area (greater land area at low than at high elevations) have opposing effects on lowland extinctions and the elevational pattern of species richness in the model-and perhaps in nature, as well.

Biological diversity in a changing world

“…In contrast, never before has a single species driven such profound changes to the habitats, composition and climate of the planet. To deal with the challenges raised by these large-scale and intense modifications of the planet, we need to develop quantitative tools to quantify (Chao et al 2010;Gotelli et al 2010;Magurran & Henderson 2010) and understand (Colwell & Rangel 2010;Dornelas 2010) change; we must document change at multiple scales of space, time and organizational levels (Morris 2010;White et al 2010;Womack et al 2010); and we must develop management tools that take change into account (Mace et al 2010;MacNeil et al 2010).…”

“…Colwell & Rangel (2010) develop a model to explore the relative roles of ecological and evolutionary processes in range shifts and species richness patterns on tropical elevational gradients along Quaternary glacial and inter-glacial cycles. This model can generate a diverse array of patterns, which a comparison with empirical data reveals are realistic.…”

Density compensation, species composition, and richness of ants on a neotropical elevational gradient

“…As sites of strong ecological pattern, elevational gradients can provide insights into the historical and contemporary forces that shape life on the planet (Lomolino 2001, Rahbek 2005, McCain 2009, Colwell and Rangel 2010. Elevational gradients are of small enough spatial scale that all species in the regional species pool potentially have access to all parts of the gradient, minimizing effects of behavioral dispersal limitation.…”

Inferring responses to climate dynamics from historical demography in neotropical forest lizards

“…If idiosyncratic responses to common landscape changes characterize ecological communities in the tropics (17,18) and beyond (19,20), their incorporation in phylogeographic methods can significantly improve our understanding of the impacts of former environmental shifts on regional species pools. Methods that build upon coalescent theory to account for historical heterogeneity across taxa under a single statistical framework (21,22) provide increased power to test concerted demographic responses at the level of ecological assemblages.…”