Conservation Biology

Through effects on the spatiotemporal distribution of individuals in the environment and population extinction probability, habitat selection behaviors have strong implications for conservation biology.

Small and fragmented populations

Threatened populations are usually small and subdivided within fragmented habitats. Habitat choice behaviors are critical for conservation issues because: (1) habitat choice strategies affect individual exploratory and prospecting movements between isolated habitat patches, which can lead to increased mortality risk depending on the degree of fragmentation; (2) the distribution and movements of individuals among habitat patches directly affect the dynamics and viability of the small subpopulations and thus the metapopulation; (3) individuals may end up settling on low-quality habitat because of constraints on mobility and information gathering, or on sites of decaying quality because of human activity. The study of breeding habitat choice is thus critical for the monitoring and management of threatened, reintroduced, or reinforced

Figure 12 The ideal free distribution. (a) Individuals start occupying the highest quality patch (patch A). As population density on patch A increases, fitness return decreases as a result of a negative density-dependence function (e.g., due to competition). When density on patch A reaches level D1, expected fitness on patch A is equal to expected fitness on patch B, which is of lower quality but still empty. The next individuals to arrive should thus start occupying patch B, as well as continuing to occupy patch A. The same applies for patch C (level D2on patch B and D3on patch A), etc. At equilibrium (dashed line), individuals are distributed among patches (densities DA, DB, and DC) so that their fitness is equal on all patches (Fe). (b)This mechanism can also operate in a closed population when local densities of individuals change as a result of demographic or environmental stochasticity. Unbalanced local densities will generate different fitness gains on different patches, due to the overexploitation of rich patches (patch A, case b1) or poor patches (patches B and C, case b2). In this case, some individuals should move to a less exploited patch, so that individual fitness as equilibrium is equal on all patches again (b3). Adapted from Fretwell SD and Lucas HL (1970) On territorial behavior and other factors influencing habitat distribution in birds. Theoretical developments. Acta Biotheoretica 19: 16-36.

1987 1988 1989 Spiders

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Sites row 1

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Site quality (row)



Figure 13 Testing the predictions of the ideal free and ideal dominant distribution (IFD/IDD) models in a population of prothonotary warblers. Habitat and breeders characteristics were compared between sites of varying quality. Sites differed in their relative location with respect to shoreline, with increasing distance to the shore for increasing row level. (a) Prey abundance (thus intrinsic site quality) gradually decreased with increasing site row. Breeding male (b) wing length and (c) body mass (measuring male quality), and (d) breeding densities decreased with increasing row level, i.e., decreasing site quality (no differences in females). (e) Females initiated breeding earlier in high-quality (row 1) sites compared to low-quality (row 3) sites. Finally, breeding success measured by (f) mean fledgling number and (g) percentage of eggs that produced fledglings decreased with decreasing site quality. Thus the spatial distribution of prothonotary warblers in this population followed an IDD, with higher-quality males excluding lower-quality ones from the preferred, highest-quality areas, and thereby achieving higher reproductive success. Data 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.

populations. Knowledge of factors affecting habitat choice has direct implications in such situations, and may greatly influence the design and monitoring of protected areas as well as the assessment of subdivided populations' viability.

Environments under human influence

Human activities can alter habitat structure and quality, and in particular break the natural correlations among habitat components. Thus, naturally selected habitat choice strategies may become maladaptive in environments modified by human activity: individuals may be lured to unsuitable patches because cues no longer reveal habitat quality when some habitat characteristics affecting fitness deteriorated but do not affect the cues used by individuals to assess site quality. Such a mismatch defines an ecological trap. Because small and subdivided

□ Random o Philopatry

Quality ♦ Presence Success

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Quality ♦ Presence Success

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0.2 0.4 0.6 0.8 Autocorrelation coefficient

0.2 0.4 0.6 0.8 Autocorrelation coefficient

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Figure 14 An illustration of population consequences of individual habitat selection behavior. (I) Spatial aggregation of individuals. Strategies of breeding habitat selection based on different types of information lead to different levels of spatial aggregation of individuals among patches (a). In particular, the use of the presence of conspecifics generates spatial aggregation far above the IFD. (b) Individuals aggregate on the best patches as environmental predictability (and thus the value of information) increases. However, when breeding success is negatively density dependent, individuals using the presence of conspecifics pay a cost via decreased success, which limits the efficiency of this strategy. (II) Population regulation via site quality. A negative feedback can be created via individual habitat selection behavior. In small populations, individuals occupy the best patches, leading to a high growth rate (year 1). When population increases, individuals start settling on sites of decreasing quality, thus mean occupied site quality decreases (years 2 and 3). Consequently, population growth is slowed (year 4). As population declines again, mean quality of occupied sites, and thus population growth, increases again (year 5). (I) From Doligez B, Cadet C, Danchin E, and Boulinier T (2003) When to use public information for breeding habitat selection? The role of environmental predictability and density dependence. Animal Behaviour 66: 973-988. (II) From Rodenhouse NL, Sherry TW, and Holmes RT (1997) Site-dependent regulation of population size: A new synthesis. Ecology 78, 2025-2042.

populations have often greatly decreased in size in the recent past, a large proportion of potentially suitable patches may be unoccupied, but may nevertheless need to be preserved to allow individuals to move. Such situations require managing habitat in terms of metareserves aiming at protecting a habitat type independently from the current occupation by the species of interest.

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