Spatial Distribution of Individuals and Evolutionary Consequences

Habitat choice directly affects the distribution of individuals in the environment and their use of habitat patches through movement and dispersal. Individual habitat choice is thus linked to spatial aggregation patterns at the population level, and the choice of each individual may have important consequences for the rest of the population (Figure 14). Different habitat selection decisions, in particular foraging and breeding, will affect the dynamics of individuals' distribution in the environment, but at different timescales: foraging habitat selection is linked to short-term use of the environment, while breeding habitat choice will be directly linked to long-term persistence of local populations via reproduction and exchanges of individuals (thus genes) between populations, that is, dispersal.

Habitat choice strategies based on different information sources may generate different individuals' distributions among patches and temporal dynamics (Figure 14). In particular, social attraction (i.e., use of conspecifics' presence) will progressively strongly aggregate individuals on the highest-density patch, and the whole population may end up in a single patch, independently from the relative

Equilibrium

qualities of the different patches. The presence of individuals prevented from breeding because of the lack of available sites on highly occupied patches while breeding sites are available on other suitable patches can be explained by the use of social attraction for breeding habitat selection. Breeders will indeed aggregate on a fraction of suitable patches rather than colonizing empty patches, and on these occupied patches, only a fraction of the individuals manage to secure a breeding site, the rest remaining nonbreeders because of patch saturation. Constraints in habitat selection may therefore lead to the evolution of floating and queuing strategies.

Effect of habitat choice on population regulation

Simple habitat choice decision rules can also participate in site-dependent regulation of populations, through the sequential occupation of sites of decreasing quality (Figure 14). When the population increases due to high fitness on good-quality patches, an increasing proportion of individuals start settling on patches of lower quality. Thus average fitness at the population scale decreases, which reduces the overall population growth rate, and may lead the population to start decreasing. This regulatory effect is obtained simply through the variation in the mean quality of chosen and occupied sites, even in the absence of local crowding effects (i.e., negative density dependence at the individual level), that is, no decrease in fitness is observed for individuals occupying the best sites: the population growth rate varies simply because of the variation in the mean quality of occupied sites.

Habitat choice and local population viability

Individual choices are constrained by the accessibility of reliable information, and the use of suboptimal information sources may increase individuals' spatial aggregation. In a metapopulation (i.e., a set of populations connected by dispersal), individuals' aggregation on some patches leaving others empty may increase the overall extinction probability of the metapopulation by increasing the probability of simultaneous extinction of all subpopulations. In addition, if individual fitness negatively depends on local density, aggregated distributions further increase local extinction probabilities. Mixed strategies of habitat choice, using a combination of cues, or condition-dependent habitat selection strategies, may minimize extinction probability.

Evolution of sociality and coloniality

Individual strategies based on conspecific cues have also been suggested to lead to the evolution of group living. By affecting spatial distribution of individuals in the environment and thus population structure, habitat selection can lead to selective pressures favoring the evolution of group living behaviors. The use of social information for habitat choice may have led to different forms of group living, such as coloniality, since individuals using conspe-cifics' presence or performance for breeding site choice settle on already-occupied patches and thus aggregate breeding sites. Furthermore, feeding or breeding close to conspecifics may favor the gathering of social information on habitat quality, thus individuals may actively seek spatial aggregation to gather social information.

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