Scales of Variation in Habitat Suitability and Quality

The importance of a given factor for habitat choice varies with its spatiotemporal variability. Local habitat quality can vary at different scales, both spatially (e.g., between

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Figure 2 Illustration of the spatiotemporal variation of habitat quality from several field studies. (a) Mean fecundity (number of young fledged per reproductive event ±1 SE) of collared flycatchers (Ficedula albicollis) in a series of 11 forest patches over 6 years. The relative quality of a patch differs between years: for example, the patch indicated by an arrow has the lowest mean fecundity in the first year, but the second highest fecundity 2 years later. (b) Mean prey abundance per 2 m2 leaf surface in a flooded vegetation along shores that constitutes breeding habitat of prothonotary warblers (Protonotaria citrea) over 3 years, according to the localization of breeding site within patch. Sites are located in rows parallel to shoreline, with row 1 closest to, and row 4 farthest from, the shore (stars indicate significant differences). (c) Temporal autocorrelation of mean fledgling number and condition as measures of patch quality in collared flycatchers in a series of 20 forest patches over 20 years (closed symbols: significant coefficients). The autocorrelation fades after a time lag of 1 year. (d) Conversely, the temporal autocorrelation of patch reproductive success (mean number of fledged young per nest) for black-legged kittiwakes (Rissa tridactyla) stays significant for 3 years. (a) From Doncaster CPD, Clobert J, Doligez B, Gustafsson L, and Danchin E (1997) Balanced dispersal between spatially varying local populations: An alternative to the source-sink model. American Naturalist 150:425-445. (b) Reproduced from Petit LJ and Petit DR (1996) Factors governing habitat selection by prothonotary warblers: Field tests of the Fretwell-Lucas models. Ecological Monographs 66:367-387, with permission. (c) Data from Doligez B, Part T, Danchin E, Clobert J, and Gustafsson L (2004) Availability and use of public information and conspecific density for settlement decisions in the collared flycatcher. Journal of Animal Ecology 73: 75-87. (d) Data from Danchin E, BoulinierT, and Massot M (1998) Conspecific reproductive success and breeding habitat selection: Implications for the study of coloniality. Ecology 79: 2415-2428.

and within habitat patches) and temporally (Figure 2). Detecting spatial heterogeneity and temporal predictability is tightly linked with the scale considered. The environment may be homogeneous at a given spatial or temporal scale (e.g., within patches or hours), but heterogeneous at another scale (e.g., among patches or years). Habitat selection can involve a cascade of nested scales: individuals can first choose among habitat types, then a general area within a habitat type, and then within this area, a patch that may comprise several sites. The relevant spatial and temporal scales at which habitat choice needs to be investigated thus have to be identified. These scales are constrained by habitat heterogeneity itself, but also by the ability of individuals to detect heterogeneity. Individuals may choose between habitats only if they are aware of habitat or patch quality variation. The scales at which an individual perceives spatial heterogeneity (depending, e.g., on its movement ability) constrain habitat selection and define the upper scales of possible habitat choice. Only environmental factors affecting fitness and varying in time and space at the scales individuals can explore are therefore relevant to habitat choice.

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