Rapid evolution: from genes to communities, and back again?

1. Ecologists now recognize that ecologically important traits sometimes undergo large heritable changes on the same time-scale as ecological change ('rapid' or 'contemporary' evolution). We know much less about the meanings of 'sometimes' (how often?) and 'important' (how important?). I review some of what I and my collaborators have learned about rapid evolution and suggest some of its implications. 2. Rapid evolution is common: when conditions change, traits evolve. But the rate of change is hard to predict, even across a set of published laboratory predator–prey experiments, and very similar trait changes can result from very different molecular mechanisms, even within one species. 3. Evolutionary rescue (adaptive response to a detrimental environmental change) is common, but not always effective. The full range is observed, from little to almost complete compensation for environmental change. 4. Cases of limited compensation show that strong selection is necessary, but not sufficient for rapid adaptation. The response of the copepod Onychodiaptomus sanguineus to fluctuating predation shows that the time-scale of environmental variation is important. The response of Daphnia galeata to eutrophication shows that life-history trade-offs and constraints can prevent evolution from buffering the entire life history against environmental changes. 5. Eco-evolutionary dynamics are harder to predict when traits affecting multiple interactions evolve. Theory predicted, and experiments confirmed, a much larger range of possible evolutionary outcomes when a prey species evolves defences against two predators rather than one. These and other recent findings suggest that the devil is in the details: many subtle factors, such as how trade-offs depend on resource availability, can have large effects on eco-evolutionary dynamics. 6. Ecologists are increasingly engaged in predicting the ecological effects of human impacts such as species introductions and climate change. Forecasting evolutionary responses is part of that challenge. One implication of the 'newest synthesis' is that rapid adaptation to changing conditions is nothing new, so the past and present can tell us a lot about the future. If prediction is our goal, then developing predictive theory for eco-evolutionary dynamics, and testing it in tractable model systems, should be a priority.