evolutionary rescue

Bell G 2013 Evolutionary rescue and the limits of adaptation. Phil Trans R Soc Lond B 368:20120080.

• the role of relative fitness in adaptation is well understood
• evolutionary rescue emphasizes the need to recognize explicitly the importance of absolute fitness

• the gradualist view of evolution is that natural selection is almost always very weak
• field and laboratory studies of selection are likely to be fruitless
• extreme gradualism uncouples evolution from ecology
• ecological processes can be studied without reference to natural selection
• genetic variation is inadequate to fuel appreciable change in the short term of a few dozen generations

• the success of field studies of natural selection subsequent to the 1950s, however, made it clear that selection was often much stronger than had been expected, and could cause rapid modification in response to environmental change
• the dynamics of a population exposed to a stress, or a stimulus, will have both ecological and evolutionary components
• an overall shift in abundance and a change in composition

• populations may adapt to conditions that would have been lethal to their ancestors, allowing the population to persist when in the absence of genetic variation it would have become extinct
• this is the phenomenon of evolutionary rescue

• population size usually becomes a major player in evolutionary theory only for neutral processes of genetic drift, where selection is excluded or ineffective
• one distinctive feature of evolutionary rescue is that it brings population size back as an essential element in the dynamics of adaptation
• adaptation in animals and plants with relatively small populations will often depend on the quantity of standing genetic variation