V. V. Krishnan

The Effects of Edge Permeability and Habitat Geometry on Emigration from Patches of Habitat

Using computer simulations, we investigated two factors that may affect emigration from insular patches of habitat, where emigration is the proportion of dispersing individuals that leave the habitat patch. The first factor, edge permeability,

THE EFFECTS OF CONSPECIFIC ATTRACTION AND HABITAT QUALITY ON HABITAT SELECTION IN TERRITORIAL BIRDS (TROGLODYTES AEDON )

\phi

SEARCH COSTS AND HABITAT SELECTION BY DISPERSERS

, reflects the tendency of a disperser reaching the edge of a habitat patch to cross the boundary and emigrate; edge permeability is positively related to emigration for any given habitat patch. The second factor is the edge-to-size ratio (ESR), the proportion of home ranges at the edge of a habitat patch; for any degree of edge permeability greater than zero, the ESR is positively related to emigration. When habitats have relatively hard edges (e.g., 0

How Territorial Animals Compete for Divisible Space: A Learning‐Based Model with Unequal Competitors

\leq \phi \leq

Territory acquisition in lizards. IV. Obtaining high status and exclusive home ranges

0.1), edge permeability is a more important determinant of emigration than is the ESR. Conversely, when habitats have relatively soft edges (

Functions Of Fights in Territory Establishment

\phi

Nonintuitive cue use in habitat selection

> 0.1), the ESR is the more important determinant of emigration. These interactions between the effects of edge permeability and patch size and shape have important implications for field biology. In particular, investigators should be cautious when comparing hard- and soft-edged habitats, since patch size and shape may have important ecological effects in soft-edged, but not in hard-edged, insular patches of habitat. Field studies of phytophagous insects and of vertebrates in fragmented or insular habitats tend to support the predictions of these models. Hence, these models may be relevant to both conservation and control policies.

Buffered Development: Resilience after Aggressive Subordination in Infancy

When animals choose habitats and territories in which to live or reproduce, their preferences can be affected by two sets of factors: habitat quality and conspecifics. There is general agreement among theoreticians and empiricists that animals should prefer to settle in habitats with high ‘‘intrinsic quality,’’ for example, in areas that offer high resource densities, protection from predators and parasites, or other features that enhance growth, survivorship, or offspring production (Fretwell and Lucas 1970; Rosenzweig 1985, 1991; Ens et al. 1992; Schieck and Hannon 1993; Yosef and Grubb 1994; Sutherland 1996). There is much less agreement, however, in either the theoretical or the empirical literature with respect to the effects of conspecifics on habitat selection (review in Stamps 1994). One large and influential body of theory holds that, because conspecifics are competitors, individual fitness should monotonically decline as a function of conspecific density (Brown 1969; Fretwell and Lucas 1970; Fretwell 1972; Maynard Smith 1974; Rosenzweig 1985, 1991; Parker and Sutherland 1986; Halama and Dueser 1994; Morris 1995, 1996; Ovadia and Abramsky 1995; Sutherland 1996). Such models imply that the presence of previous settlers in a habitat should discourage newcomers from settling in that habitat. However, others have suggested that settlers might benefit by settling or living near conspecifics, in which case newcomers should be attracted to conspecifics while settling (review in Stamps 1988; see also following paragraph).

The Relationship between Selectivity and Food Abundance in a Juvenile Lizard

The effects of search costs on habitat selection by dispersers are largely unknown. We explore how habitat selection behavior is affected by the risk of mortality en route and by deferred search costs (i.e., costs incurred during search that reduce fitness after arrival in the new habitat), using a model designed for long-distance natal dispersers searching for scarce patches of suitable habitat embedded within a matrix of unsuitable habitat. In this situation, increases in the risk of mortality during search reduce disperser selectivity, where selectivity is reflected by the period during search when dispersers are only willing to accept a high-quality habitat. However, the effects of deferred costs on selectivity depend on other factors with pronounced effects on selectivity, including en- counter rates with high-quality habitats, relative habitat quality, and total search time. Surprisingly, under some sets of conditions, increases in deferred costs lead to increases in disperser selectivity. Overall, the effects of mortality and deferred costs on selectivity are small relative to the effects of other factors on selectivity. For instance, our model suggests that selectivity is much more strongly affected by total search time than by search costs, and it predicts a positive relationship between total search time and disperser selec- tivity across individuals in the same population, even in the face of considerable inter- individual variation in risk of mortality or deferred search costs.

How Different Types of Natal Experience Affect Habitat Preference

It is widely assumed that aggressive behavior affects space acquisition in territorial species, but to date most workers have focused on competition for indivisible space, that is, space that cannot be divided or shared. We present a learning‐based model that investigates the effects of aggressive interactions on space acquisition when unequal competitors arrive and settle in patches of divisible space. This model assumes that aggressive interactions act as punishment, in the sense that previous aggressive interactions in a given area reduce an individual’s likelihood of returning to that area. Individually based, spatially explicit simulations incorporating this and other assumptions were used to investigate the effects of different types of aggressive interactions on the space use of individuals and dyads settling in divisible space. At the individual level, final space use was related to the amount of punishment that individuals inflicted on their opponents during aggressive interactions; in general, highly aggressive individuals acquired larger, more exclusive home ranges than less aggressive individuals. At the dyadic level, the division or sharing of space between competitors depended on both the relative and absolute punishment that competitors inflicted on one another during aggressive interactions. Aggressive interactions in which both participants strongly punished one another (e.g., escalated fights) produced mutually exclusive home ranges, interactions with intermediate levels of punishment produced asymmetrical space use patterns proportional to asymmetries in punishment levels, and interactions involving little punishment for either participant generated large home ranges with extensive home range overlap. Overall, our model implies that territorial animals need not “win” aggressive interactions to win divisible space, that repeatedly “nagging” an opponent may also be a viable strategy for gaining space, and that a learning‐based approach can account for puzzling patterns in the territorial literature, for example, observations of individuals who acquire space by initiating aggressive interactions that they never win.