Box 2 Evolutionary invasion analysis
The evolutionary ecology of dispersal [News and Comment]
Ulf Dieckmann, Bob O'Hara and Wolfgang Weisser
Trends in Ecology & Evolution, 1999, 14:3:88-90
To assess which dispersal strategies are favored by natural selection, the potential of
invasion by mutant (or immigrant) strategies into populations of resident dispersal
strategists can be investigated. Such evolutionary invasion analyses are best based on the
population dynamics between mutant and resident individuals. If the initial growth rate of
a rare mutant within a given resident population is positive, the mutant can invade and
typically replace the former resident.
Repeated substitutions of this kind can take populations to a dispersal strategy (or to a
polymorphism thereof) that is 'unbeatable' or 'evolutionarily stable'5. The
theory of adaptive dynamics123 allows us to predict the resulting evolutionary
change in continuous adaptive traits such as dispersal rates. Also, contingent dispersal
strategies can be investigated, such as probabilities of dispersing from or into
subpopulations of given densities, or dispersal rates that are dependent on age.
How a model metapopulation is invaded by a new dispersal strategy is shown by the sequence
of illustrations below. Each graph depicts the frequency distribution of patches inhabited
by n resident and m mutant individuals. Within-patch dynamics are individual-based and
logistic, and the rate of dispersal between patches is adaptive. Initially mutant
strategists are few and far between, but they eventually take over the entire population.
Using knowledge of population dynamics to predict success or failure of such invasions
gives a theory for the evolution of dispersal that is firmly rooted in descriptions of
ecological change.
