Individuals will also have to make a series of habitat choices for breeding. As for foraging, breeding requires availability of high-quality food resources necessary for offspring development, but also many other resources affecting breeding success, in particular the presence of mates and availability of safe breeding sites (Figure 6). In some species, decisions made during the course of breeding are sequential in time and space, and made independently based on different criteria. In other species, all resources have to be secured simultaneously, which may generate tradeoffs between optimal choices for each resource. In many species, the number of breeding attempts is limited over an individual's lifetime, because breeding involves longer timescales than foraging (up to several years), and/or is a seasonal activity implying yearly timescales. Thus constraints associated with breeding habitat selection often differ from foraging habitat selection. Habitat choice may vary depending on the type of breeding site and species breeding ecology, and can occur at variable spatial scales, both in absolute values (from millimeters for some parasites to hundred of kilometers for large vertebrates), and relative values, depending in particular on the spatial range used by a given species.
Time spent on the patch
Figure 5 Patch-departure decision rules in discrete foraging environments. When resources are not distributed evenly but are aggregated in patches whose size is not a priori known, individuals can adopt several simple rules for deciding when to stop exploiting their current patch and leave for another patch (black arrows). Dashed arrows indicate when resources items are found by individuals. The probability to stay in the current patch, also called responsiveness, is shown depending on time spent in the patch. When the probability to stay in the current patch drops below a critical threshold, the individual leaves the patch. (a) Incremental rule; (b) decremental rule; (c) giving-up-time rule (giving-up time: Tg); (d) fixed-number rule; (e) fixed-time rule. (a, b) Adapted from Waage JK (1979) Foraging for patchily distributed hosts by the parasitoid Nemeritis canescens. Journal of Animal Ecology 48: 353-371; and Van Alphen JJM, Bernstein C, and Driessen G (2003) Information acquisition and time allocation in insects parasitoids. Trends in Ecology and Evolution 18: 81-87. (c) From Stephens DW and Krebs JR (1987) Foraging Theory. Princeton, NJ: Princeton University Press. (d, e) From IwasaY, Higashi M, and Yamamura N (1981) Prey distribution as a factor determining the choice of optimal foraging strategy. American Naturalist 117: 710-723.
Table 1 An overview of the different rules for patch-departure decisions in the context of foraging habitat selection, and the conditions in which each rule is likely to be selected for in terms of type of environmental variation in patch quality (i.e., spatial distribution of resource items) and individuals' knowledge on the environment. All proximate rules assume that individuals cannot a priori assess patch quality upon entering the patch
Patch-departure decision rule
Ultimate mechanism Marginal value theorem Leave patch if when the instantaneous intake rate from the current patch falls below the mean intake rate in the environment
Initial probability to stay on patch depending on its quality (size); probability to stay decreases linearly with unsuccessful time on patch; each resource item found adds an increment to the current level of probability to stay; leave patch when threshold probability is met Decremental rule
Initial probability to stay on patch depending on its quality (size); probability to stay decreases linearly with unsuccessful time on patch; each resource item found subtracts a decrement to the current level of probability to stay; leave patch when threshold probability is met Giving-up time rule
Leave patch if time since last resource item found exceeds a given threshold
Fixed-number rule Leave patch when a fixed number of resource items has been found
Search patch for a fixed period of time and leave patch independent of the number of resources items found
High variability of patch quality (aggregated spatial distribution of resource items) Limited individual knowledge about patch size
Low variability of patch quality (evenly dispersed spatial distribution of resource items) Good individual knowledge about patch size
High variability of patch quality (aggregated spatial distribution)
Low variability of patch quality (constant number of resource items per patch)
Poisson distribution of number of resource items per patch
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