The climatic and biotic conditions at any geographic location will change through time, for example, because of the advance of glaciers. If it is to avoid extinction, a species adapted to a moving habitat must either track its habitat spatially, or adapt genetically to the new environmental conditions. These processes of migration and evolution are important in determining continental biogeographic patterns. We develop a model to explore the relative contributions of adaptation and dispersal as alternative mechanisms whereby a population can respond to changing environmental conditions. In our model the environment to which the species is adapted moves across the landscape at a constant velocity, and a quantitative trait determines each individual's fitness as a function of the local environmental conditions. Local populations are allowed to adapt genetically to the environmental conditions at each point in space, so that a cline develops in the quantitative character. We find that if the rate of environmental movement is slow, the species will track its environment across space, otherwise it will go extinct. Additionally, the higher the genetic variance in the character, the easier it is for the species to maintain itself in a moving environment. Our results generalize previous models that predict a critical patch size of suitable habitat necessary for population persistence.

Constraints have important effects on the evolution of life history strategies, but several difficulties have been encountered in determining constraints empirically. Here we investigate methods for measuring a specific type of constraint known as a trade-off. A trade-off between two traits implies a perfect negative correlation between the traits. Trade-offs may involve more than two traits, however, and pairs of traits involved in such a higher-dimensional trade-off may be positively correlated. If some of the traits involved in a trade-off are omitted from the experimental design, the trade-off may not even be detectable. Direct measures of trade-offs are thus complicated, and indirect means of identifying trade-offs may often provide the only feasible measures.

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