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Snorkel surveys are frequently used to monitor stream-dwelling fish. Inferring local abundance from snorkel surveys is complicated by two primary factors: variable fish detection probabilities and the relative abundance of fish in habitat types below the recommended minimum depth for snorkeling. We examine these factors across three salmonid species (Oncorhynchus spp.), 4 years, and 113 location-years in Oregon coastal streams. We calibrate snorkel counts to mark-recapture estimates and develop mathematically explicit expressions that convert a new snorkel count into a probability density of abundance for streams containing mixed habitat types that were and were not snorkeled. Snorkelers detected 63%, 47%, and 39% of juvenile coho salmon (Oncorhynchus kitsutch), steelhead trout (Oncorhynchus mykiss), and cutthroat trout (Oncorhynchus clarkii clarkia) estimated by mark-recapture, respectively, but uncertainty within and among sampling units was high. Further, analytics developed here can be used to infer abundance and uncertainty for habitat types that were not snorkeled. Our quantification of uncertainty arising from using snorkel counts as a proxy for abundance will help managers balance biological risks with available resources. [ABSTRACT FROM AUTHOR]

Major disturbances can temporarily remove factors that otherwise constrain population abundance and distribution. During such windows of relaxed top‐down and/or bottom‐up control, ungulate populations can grow rapidly, eventually leading to resource depletion and density‐dependent expansion into less‐preferred habitats. Although many studies have explored the demographic outcomes and ecological impacts of these processes, fewer have examined the individual‐level mechanisms by which they occur. We investigated these mechanisms in Gorongosa National Park, where the Mozambican Civil War devastated large‐mammal populations between 1977 and 1992. Gorongosa's recovery has been marked by proliferation of waterbuck (Kobus ellipsiprymnus), an historically marginal 200‐kg antelope species, which is now roughly 20‐fold more abundant than before the war. We show that after years of unrestricted population growth, waterbuck have depleted food availability in their historically preferred floodplain habitat and have increasingly expanded into historically avoided savanna habitat. This expansion was demographically skewed: mixed‐sex groups of prime‐age individuals remained more common in the floodplain, while bachelors, loners, and subadults populated the savanna. By coupling DNA metabarcoding and forage analysis, we show that waterbuck in these two habitats ate radically different diets, which were more digestible and protein‐rich in the floodplain than in savanna; thus, although individuals in both habitats achieved positive net energy balance, energetic performance was higher in the floodplain. Analysis of daily activity patterns from high‐resolution GPS‐telemetry, accelerometry, and animal‐borne video revealed that savanna waterbuck spent less time eating, perhaps to accommodate their tougher, lower‐quality diets. Waterbuck in savanna also had more ectoparasites than those in the floodplain. Thus, plasticity in foraging behavior and diet selection enabled savanna waterbuck to tolerate the costs of density‐dependent spillover, at least in the short term; however, the already poorer energetic performance of these individuals implies that savanna occupancy may become prohibitively costly as heterospecific competitors and predators continue to recover in Gorongosa. Our results suggest that behavior can provide a leading indicator of the onset of density‐dependent limitation and the likelihood of subsequent population decline, but that reliable inference hinges on understanding the mechanistic basis of observed behavioral shifts. [ABSTRACT FROM AUTHOR]

Many large herbivore populations are partially migratory, in which the population is comprised of both non-migratory (resident) and migratory individuals. Density-dependence contributes to regulating the dynamics of partially migratory populations by altering habitat selection, vital rates, or rates of behavioral switching between migratory tactics. Studies of mechanisms leading to these shifts have focused mainly on their behavior on summer range, overlooking the potential for density-dependent effects during winter that may influence decisions to migrate. We hypothesized that competition for food and safety from wolf predation risk on winter ranges would differentially affect habitat selection, movements, and grouping behavior of migrant and resident female North American elk (Cervus canadensis) on their sympatric winter range. We used GPS locations from 92 adult female elk in 155 elk-winters at Ya Ha Tinda, Alberta, Canada, over a 14-year period when the elk population declined by ∼70% to test our hypotheses. Elk showed consistently strong selection for areas of high forage biomass that corresponded to longer residence times and shorter return times to areas of high forage biomass. The strength of the selection diminished at high elk population size as did the extent to which elk traded off forage for safety from wolf predation risk. Elk increased movement rates and extended return times only to the riskiest areas. Median group size and mean sociality among elk increased at low population size, with resident elk groups being larger and more cohesive than migrant groups. Similar density-dependent responses by migrant and resident female elk on sympatric winter range indicate resident elk do not alter foraging behaviors to compensate for exposure to low nutritional resources in summer, implicating seasonal differences in nutrition are not mediated by winter densities in this system. We discuss the implications of competition on winter ranges for the maintenance of partial migration in ungulates in montane systems.

According to the ideal‐free distribution (IFD), individuals within a population are free to select habitats that maximize their chances of success. Assuming knowledge of habitat quality, the IFD predicts that average fitness will be approximately equal among individuals and between habitats, while density varies, implying that habitat selection will be density dependent. Populations are often assumed to follow an IFD, although this assumption is rarely tested with empirical data, and may be incorrect when territoriality indicates habitat selection tactics that deviate from the IFD (e.g. ideal‐despotic distribution or ideal‐preemptive distribution).When territoriality influences habitat selection, species' density will not directly reflect components of fitness such as reproductive success or survival. In such cases, assuming an IFD can lead to false conclusions about habitat quality. We tested theoretical models of density‐dependent habitat selection on a species known to exhibit territorial behaviour in order to determine whether commonly applied habitat models are appropriate under these circumstances.We combined long‐term radiotelemetry and census data from grey wolves Canis lupus in the Upper Peninsula of Michigan, USA to relate spatiotemporal variability in wolf density to underlying classifications of habitat within a hierarchical state‐space modelling framework. We then iteratively applied isodar analysis to evaluate which distribution of habitat selection best described this recolonizing wolf population.The wolf population in our study expanded by >1,000% during our study (~50 to >600 individuals), and density‐dependent habitat selection was most consistent with the ideal‐preemptive distribution, as opposed to the ideal‐free or ideal‐despotic alternatives.Population density of terrestrial carnivores may not be positively correlated with the fitness value of their habitats, and density‐dependent habitat selection patterns may help to explain complex predator–prey dynamics and cascading indirect effects. Source–sink population dynamics appear likely when species exhibit rapid growth and occupy interspersed habitats of contrasting quality. These conditions are likely and have implications for large carnivores in many systems, such as areas in North America and Europe where large predator species are currently recolonizing their former ranges. [ABSTRACT FROM AUTHOR]

Habitat selection is a process that spans space, time and individual life histories. Ecological analyses of animal distributions and preferences are most accurate when they account for inherent dynamics of the habitat selection process. Strong territoriality can constrain perception of habitat availability by individual animals or groups attempting to colonize or establish new territory. Because habitat selection is a function of habitat availability, broad-scale changes in habitat availability or occupancy can drive density-dependent habitat functional responses. We investigated density-dependent habitat selection over a 19-year period of grey wolf (Canis lupus) recovery in Michigan, USA, using a generalized linear mixed model framework to develop a resource selection probability function (RSPF) with habitat coefficients conditioned on random effects for wolf packs and random year intercepts. In addition, we allowed habitat coefficients to vary as interactions with increasing wolf density over space and time. Results indicated that pack presence was driven by factors representing topography, human development, winter prey availability, forest structure, roads, streams and snow. Importantly, responses to many of these predictors were density-dependent. Spatio-temporal dynamics and population changes can cause considerable variation in wildlife–habitat relationships, possibly confounding interpretation of conventional habitat selection models. By incorporating territoriality into an RSPF analysis, we determined that wolves' habitat use in Michigan shifted over time, for example, exhibiting declining responses to winter prey indices and switching from positive to negative responses with respect to stream densities. We consider this an important example of a habitat functional response in wolves, driven by colonization, density-dependence and changes in occupancy during a time period of range expansion and population increase.

We assessed the effect of habitat heterogeneity and predator density on the European hare (Lepus europaeus), a declining farmland specialist, in intensive farmlands in Central Europe. Using spotlight surveys we explored population density and habitat preference of the European hare in spring and autumn during 2014–2015 in seven farmland regions, of which six were located in the Czech Republic and one in Austria. The average population density of European hares significantly differed between study regions in the Czech Republic and Austria, however, we found no differences in population density between autumn and spring. In particular, the average European hare population density in study regions in the Czech Republic varied between 6.8–17.0 individuals/100 ha, whereas in Austria the population density reached 65.3 individuals/100 ha. Differences between spring and autumn population densities were not significant. European hare population density was significantly negatively affected by mean patch size and positively by area of arable land. We did not find a significant effect of red fox (Vulpes vulpes) presence on the numbers of European hares in individual regions. Habitat preferences differed among regions with contrasting population densities and field sizes, hares in regions of high density and small fields were more equally distributed among available habitats compared to regions of low or intermediate density and large fields. To conclude, conservation measures focusing on enhancing habitat heterogeneity by reducing field size may be an effective tool to support populations of European hares in arable farmland landscapes. [ABSTRACT FROM AUTHOR]

The spatial distribution of marine fishes can change for many reasons, including density-dependent distributional shifts. Previous studies show mixed support for either the proportional-density model (PDM; no relationship between abundance and area occupied, supported by ideal-free distribution theory) or the basin model (BM; positive abundance-area relationship, supported by density-dependent habitat selection theory). The BM implies that fishes move towards preferred habitat as the population declines. We estimate the average relationship using bottom trawl data for 92 fish species from six marine regions, to determine whether the BM or PDM provides a better description for sea-bottom-associated fishes. We fit a spatio-temporal model and estimate changes in effective area occupied and abundance, and combine results to estimate the average abundance-area relationship as well as variability among taxa and regions. The average relationship is weak but significant (0.6% increase in area for a 10% increase in abundance), whereas only a small proportion of species-region combinations show a negative relationship (i.e. shrinking area when abundance increases). Approximately one-third of combinations (34.6%) are predicted to increase in area more than 1% for every 10% increase in abundance. We therefore infer that population density generally changes faster than effective area occupied during abundance changes. Gadiformes have the strongest estimated relationship (average 1.0% area increase for every 10% abundance increase) followed by Pleuronectiformes and Scorpaeniformes, and the Eastern Bering Sea shows a strong relationship between abundance and area occupied relative to other regions. We conclude that the BM explains a small but important portion of spatial dynamics for sea-bottom-associated fishes, and that many individual populations merit cautious management during population declines, because a compressed range may increase the efficiency of harvest. [ABSTRACT FROM AUTHOR]

We investigated the impact of forest harvest and tree masting on the abundance and habitat selection of yellow-necked mice ( Apodemus flavicollis ) and bank voles ( Myodes glareolus ). Our study was conducted in managed European beech ( Fagus sylvatica ) forest, in four closed-canopy and four shelterwood stands, during two mast and two non-mast years. We predicted that (1) forest harvest will positively affect vegetation cover, resulting in increased abundance of yellow-necked mice; (2) abundance of bank voles will not be affected by forest harvest; (3) the increased abundance of yellow-necked mice in shelterwood vs. closed-canopy stands will be more pronounced after non-mast (low rodent abundance) than after mast years (high rodent abundance), and (4) both species of rodents will select microhabitats with protective cover (provided by coarse woody debris or dense vegetation), but this preference will be stronger after non-mast than after mast years. In agreement with the first prediction, the abundance of yellow-necked mice tended to be higher in shelterwood than in closed-canopy stands, and was positively associated with average vegetation cover (generally denser in shelterwood than in closed-canopy stands). The second prediction was partially supported: while there was no clear effect of forest harvest on bank vole abundance, it was negatively affected by soil scarification conducted at two shelterwood stands. In concurrence with predictions (3) and (4), habitat associations of both rodent species were considerably weaker after mast years at both stand and microhabitat scales. Unexpectedly, after mast years, there was a negative association between bank vole abundance and vegetation cover, perhaps resulting from interference competition with yellow-necked mice. Our findings demonstrate that masting-related fluctuations in rodent abundance strongly influence their patterns of habitat selection. [ABSTRACT FROM AUTHOR]

Habitat selection models are the basis of an increasing number of conservation and management programs. Decision-makers rely on accurate models to assess animal distribution over space and time, and to recommend suitable actions that can alleviate human-wildlife conflicts. Despite a rapidly growing number of field studies on habitat selection, there remains a paucity of empirical evidence that selection is a density-dependent process that can impact males and females differently. Based on 11 years of monitoring, we demonstrate that the response of African elephants (Loxodonta africana) to land-cover types varied with population size, and that density-dependent adjustments differed between sexes. Specifically, our longitudinal follow-up of GPS-collared elephants revealed that elephants gradually decrease their selection for open woodlands and forests, as the population increased and the availability of palatable browse species decreased. Both sexes – though males more strongly – increased their travel rate together with their relative probability of selection of roads for travel. Also, elephants displayed a density-dependent increase in their selection of infrastructures, a response that was stronger for males than females. The risk of human-elephant conflicts thus increased with population size, with males being particularly prone to be involved in such conflicts. Overall, we provide rare empirical evidence that density-dependence in fine-grain habitat selection can differ between sexes. This information can be critical to accurately forecast potential human-wildlife conflicts, and for taking targeted and effective conservation and management actions. • Fine-grain habitat selection of elephants varies with density and between sexes. • Males and females differ in density-dependent responses to human infrastructures. • Habitat selection makes males more likely involved in human-wildlife conflicts. • Sex- and density-dependent selection can give critical info to orient conservation. [ABSTRACT FROM AUTHOR]

A review of population and community dynamics and habitat selection of rodents in complex desert landscapes is presented. Population dynamics of rodents in all deserts are driven mainly by resource pulses induced by rainfall events. In a long-term perspective, this pattern is sometimes interrupted by rare extreme weather events and by habitat transformation due to wildfire or climate change. Rainfall-population density relations were found to be modified by intrinsic (population autoregulation, habitat selection) and extrinsic (interspecific competition, predation) processes, but the relative importance and geographic specificity of these processes are unclear. Density-dependent habitat selection was found in all studied desert rodent species inhabiting more than one habitat. Density-dependent habitat selection was expressed in different types of population regulation, resulting in density-dependent or density-independent habitat distribution. However, processes of density-dependent habitat selection have been studied in only one region; there are no data yet to analyze how different strategies of habitat selection vary among different desert regions. Dynamics of community composition include one widely distributed pattern, an increase in species richness with density. Another pattern, zero-sum community dynamic, was found in North American deserts. Dynamics of the niche community structure is expressed in the increase of niche overlap with density growth. In Palaearctic deserts, this increase in niche overlap was accompanied by stronger aggregation of niches in spatial guilds. The last phenomenon was not recorded in North American deserts, which reflects differences in expression of spatial guilds between Palaearctic and Nearctic rodent communities. [ABSTRACT FROM AUTHOR]

The dynamics of fish behavior, migration, and habitat use following stock enhancement will influence the outcome of recovery programs and indicate the ecological limits of the system. This study tested the effect of release density on emigration, activity patterns, and space utilization by releasing juvenile mulloway (Sciaenidae:Argyrosomus japonicus) at low and high densities and monitoring movement intensively for 336 h post release. Mulloway released at high densities had faster emigration and greater overall emigration rates than low density releases. Also, mulloway released at high densities used sub-optimal habitats at a greater frequency. Released fish dispersed into habitat patches at densities proportional to the quality of the habitat patch, consistent with density-dependent habitat selection. Targeting releases of small numbers of fish to the carrying capacity of individual patches of habitat will contribute to the success and economic viability of release programs in open systems. Releases of high densities of individuals or repeated releases at the same site may lead to increased emigration and losses from the stocked system. The capacity of a target habitat to support released fish can be rapidly assessed using pilot releases and intensive monitoring of acoustically tagged fish, prior to the implementation of large-scale release programs. [ABSTRACT FROM PUBLISHER]

Density-independent and density-dependent variables both affect the spatial distributions of species. However, their effects are often separately addressed using different analytical techniques. We apply a spatially explicit regression framework that incorporates localized, interactive and threshold effects of both density-independent (water temperature) and density-dependent (population abundance) variables, to study the spatial distribution of a well-monitored flatfish population in the eastern Bering Sea. Results indicate that when population biomass was beyond a threshold a further increase in biomass-promoted habitat expansion in a non-additive fashion with water temperature. In contrast, during years of low population size, habitat occupancy was affected positively only by water temperature. These results reveal the spatial signature of intraspecific abundance distribution relationships as well as the non-additive and non-stationary responses of species spatial dynamics. Furthermore, these results underscore the importance of implementing analytical techniques that can simultaneously account for density-dependent and density-independent sources of variability when studying geographical distribution patterns. [ABSTRACT FROM AUTHOR]

Abstract: Use of habitat is a critical component related to structure of small-mammal communities, with partitioning occurring primarily along dimensions of microhabitat, although use of microhabitat often does not explain fully use at a macrohabitat level. Through grid studies of small mammals in coastal Colima, Mexico (during January 2003–2005), we appraised influence of available habitat, species richness, abundance, and cumulative abundance of other small mammals on variation in habitat used by species. We evaluated 14 habitat variables (reflecting ground cover, slope, canopy, and vegetation density on vertical and horizontal axes) and developed a composite variable (principal component 1) reflecting general openness of habitat through which we addressed habitat use. For the four most common mammalian species (Sigmodon mascotensis, Heteromys pictus, Baiomys musculus, and Oryzomys couesi), two measures of variation in habitat used were employed to estimate niche breadth, one of which assessed variation in habitat use relative to variation present on a grid. Sigmodon mascotensis and B. musculus preferred areas that were more open, and H. pictus and O. couesi occupied less-open areas; breadth of habitat use did not differ interspecifically. Habitat use was more variable on grids with more variability in habitat, although not greater than chance expectations. Findings do not lend support to the resource-breadth hypothesis as an explanation for population densities of species at a local level or the habitat-heterogeneity hypothesis as a predictor of species richness. Variation in habitat used by S. mascotensis did not proportionally increase when diverse habitat was available but was greater when the species was more abundant. For H. pictus, when cumulative abundance of other small mammals was greater, breadth of habitat used was greater. Intraspecific density-dependent habitat selection may result in S. mascotensis selecting a greater variety of habitats, while greater interspecific abundance is related to a greater range in use of habitats by H. pictus. Baiomys musculus used a higher proportion of habitat relative to that available when more species were present on a grid. Variation in habitat used by O. couesi was unrelated to any factor examined. Overall, the four species responded in notably different ways with respect to availability of habitat, abundance, and presence of other species. [Copyright &y& Elsevier]

1. We used observational and experimental field studies together with an individual-based simulation model to demonstrate that behaviours of mottled sculpin ( Cottus bairdi) were broadly consistent with the expectations of Giving-Up Density theory and an Ideal Pre-emptive Distribution habitat selection model. 2. Specifically we found that: (i) adult mottled sculpin established territories within patches characterised by significantly higher prey densities and prey renewal rates than patches occupied by juveniles or randomly selected patches; (ii) patches abandoned by adult sculpin possessed significantly lower prey densities than newly occupied patches, although this was not true for juveniles; (iii) the observed giving-up density (GUD) for adult sculpin (i.e. average prey density in patches recently abandoned) increased linearly with increasing fish size up to the average prey density measured in randomly selected patches (i.e. 350 prey items per 0.1 m2) and decreased with increasing sculpin density and (iv) juveniles rapidly shifted their distribution towards the highest quality patches following removal of competitively dominant adult sculpin. 3. These results provide the first evidence of the applicability of GUD theory to a stream-dwelling organism, and they elucidate the underlying factors influencing juvenile and adult sculpin habitat selection and movement behaviours. Furthermore, optimal patch use, ideal pre-emptive habitat selection and juvenile ‘floating’ provide behavioural mechanisms linking environmental heterogeneity in the stream benthos to density-dependent regulation of mottled sculpin populations in this system. [ABSTRACT FROM AUTHOR]

1. Describing distribution and abundance is requisite to exploring interactions between organisms and their environment. Recently, the resource selection function (RSF) has emerged to replace many of the statistical procedures used to quantify resource selection by animals. 2. A RSF is defined by characteristics measured on resource units such that its value for a unit is proportional to the probability of that unit being used by an organism. It is solved using a variety of techniques, particularly the binomial generalized linear model. 3. Observing dynamics in a RSF – obtaining substantially different functions at different times or places for the same species – alerts us to the varying ecological processes that underlie resource selection. 4. We believe that there is a need for us to reacquaint ourselves with ecological theory when interpreting RSF models. We outline a suite of factors likely to govern ecologically based variation in a RSF. In particular, we draw attention to competition and density-dependent habitat selection, the role of predation, longitudinal changes in resource availability and functional responses in resource use. 5. How best to incorporate governing factors in a RSF is currently in a state of development; however, we see promise in the inclusion of random as well as fixed effects in resource selection models, and matched case–control logistic regression. 6. Investigating the basis of ecological dynamics in a RSF will allow us to develop more robust models when applied to forecasting the spatial distribution of animals. It may also further our understanding of the relative importance of ecological interactions on the distribution and abundance of species. [ABSTRACT FROM AUTHOR]

The general warming of the eastern Bering Sea (EBS) and the wide range of abundance exhibited by several eastern Bering Sea flatfish motivated an examination of how density-dependent and density-independent factors may influence the spatial distributions of EBS flatfish. In this study, EBS trawl survey data from 1982 to 2006 were used to examine how temporal changes in the distributions of six flatfish species groups [yellowfin sole ( Limanda aspera), rock sole ( Lepidopsetta sp.), flathead sole ( Hippoglossoides sp.), Alaska plaice ( Pleuronectes quadrituberculatus), arrowtooth flounder ( Atheresthes sp.), and Greenland turbot ( Reinhardtius hippoglossoides)] are related to temporal changes in the location of the ‘cold pool’ (bottom water < 2°C), and how the area occupied by flatfish are related to the cold pool and population abundance. Rock sole and flathead sole distributions have generally moved northwest since 1982 and are significantly correlated with the movement of the cold pool, whereas arrowtooth flounder avoid the cold pool and their area occupied is inversely related to the size of the cold pool. The area occupied by arrowtooth flounder and rock sole are also significantly related to stock abundance. Multivariate statistical models indicate that the location of rock sole is more strongly related to stock abundance than to the cold pool, whereas the area occupied by arrowtooth flounder is more strongly related to the area of the cold pool rather than abundance. The temperatures occupied by several flatfish stocks indicate a substantial variability in suitable temperatures. These results suggest that a complex suite of density-dependent and density-independent factors may determine the response of EBS flatfish spatial distributions to increasing temperatures. [ABSTRACT FROM AUTHOR]

Habitat selection by individuals is often a density-dependent process: as density increases, the quality of the habitat decreases due to resource competition and interference. These same changes in habitat quality should likewise affect the foraging efforts of individuals at the patch scale. We used density manipulations, fenced enclosures in the field, to examine patch use in two species of gerbils, Gerbillus andersoni allenbyi and G. pyramidum. At the same time, we used sand tracking to measure activity densities and confirm that gerbils show density-dependent habitat selection across the stabilized and semistabilized sand habitats. We then quantified individual patch use, using giving-up densities (GUD: the amount of food left behind in a resource patch following exploitation) in artificial food patches. Gerbils used resource patches in a density-dependent manner, showing lower GUDs at higher activity densities. Interestingly, this was not the case in both habitats. In the stabilized sand habitat, GUDs for both gerbils were high, and decreased with increasing activity density, but in the semistabilized dune habitat, GUDs remained constantly low. This led GUDs in the two habitats to converge al high activity densities. For these surprising findings we suggest two mechanistically different explanations, one that relies on the ideal despotic distribution and the other, on safety in numbers. Evidence supports the second hypothesis, in which safety is pumped from the semistabilized to the stabilized habitat with increasing activity density. [ABSTRACT FROM AUTHOR]

Theories of density-dependent habitat selection predict that competitive interference should produce curvilinear relationships when the population densities in adjacent habitats are graphed against each other. We tested the theory by manipulating population densities of brook trout (Salvelinus fontinalis) in four separate natural-stream enclosures containing flat and riffle habitats. Brook trout distributions in streams typically reflect a size-based dominance hierarchy. As predicted by theory, interference among individuals was revealed by curved regressions of density in the paired habitats (isodars). Brook trout exhibited no strong preference for either habitat at low population densities. Habitat preferences emerged clearly at higher densities, apparently reflecting the distribution of suitable sites in the habitat pairs. Predicted body size distributions between flat and riffle were mirrored consistently by those observed in the population. The isodar analysis, based only on density data. revealed the competitive behaviors that underlie brook trout distributions in real streams. [ABSTRACT FROM AUTHOR]

We use a simple Lotka--Volterra model of interspecific competition to show that density-dependent habitat selection may play a role in the classic study of intraspecific competition among flour beetles (Tribolium spp.). Then we quantify the potential fitness advantage of rapid emigration by red-backed voles (Clethrionomys gapperi) within a field experimental facility. Results in both cases were consistent with the ideal free distribution, and yet provided an alternative explanation for interactions among flour beetles and an evaluation of the relationship between differential fitness and individual behavior in a mobile population. These results demonstrate the utility of simulation models to gain novel insights of behaviors producing patterns of differential habitat use. [ABSTRACT FROM AUTHOR]

Spatial movement models often base movement decision rules on traditional optimal foraging theories, including ideal free distribution (IFD) theory, more recently generalized as density-dependent habitat selection (DDHS) theory, and the marginal value theorem (MVT). Thus optimal patch departure times are predicted on the basis of the density-dependent resource level in the patch. Recently, alternatives to density as a habitat selection criterion, such as individual knowledge of the resource distribution, conspecific attraction, and site fidelity, have been recognized as important influences on movement behavior in environments with an uncertain resource distribution. For foraging processes incorporating these influences, it is not clear whether simple optimal foraging theories provide a reasonable approximation to animal behavior or whether they may be misleading. This study compares patch departure strategies predicted by DDHS theory and the MVT with evolutionarily optimal patch departure strategies for a wide range of foraging scenarios. The level of accuracy with which individuals can navigate toward local food sources is varied, and individual tendency for conspecific attraction or repulsion is optimized over a continuous spectrum. We find that DDHS theory and the MVT accurately predict the evolutionarily optimal patch departure strategy for foragers with high navigational accuracy for a wide range of resource distributions. As navigational accuracy is reduced, the patch departure strategy cannot be accurately predicted by these theories for environments with a heterogeneous resource distribution. In these situations, social forces improve foraging success and have a strong influence on optimal patch departure strategies, causing individuals to stay longer in patches than the optimal foraging theories predict. [ABSTRACT FROM AUTHOR]

The article identifies the core areas of six severely depleted marine fish species on the Scotian Shelf, Canada, using the theory of ideal free distribution (IFD). Many marine fish species have declined throughout the world due to overfishing, and the Scotian Shelf off eastern Canada is no exception. IFD theory had proved popular because of its efficient logic and has been developed as an evolutionarily stable strategy. The researchers tested for density-dependent distribution on both regional and local scales. At the regional scale, a density-dependent response was observed in the majority of populations. At the local scale, density was expected to remain stable in areas of high density and to change more rapidly in marginal areas, in response to changes in regional abundance. Lower local density responses were associated with areas of higher density, but deviations were evident, in part due to the magnitude of decline and in part due to fishing effects. Former areas of high density can be eroded if the population has severely declined. Fishing directed at an area of high density can cause local depletion when recolonization rates are low relative to the intensity of fishing. Thus, areas occupied during periods of low regional abundance do not of necessity reflect the historical array of core areas.

Abstract Habitat use by feral cats and dingoes was examined within a heterogeneous semi-arid woodland site in central Australia over 2 years. Density estimates of feral cats based on tracks were higher in mulga habitat than in open habitat. Isodar analysis implied that this pattern of habitat use by feral cats was consistent with the consumer-resource model of density-dependent habitat selection, which is an ideal free solution. The reason why mulga supported higher densities of feral cats was unclear. Foraging success of feral cats may be higher in the mulga because the stalk and ambush hunting tactics typically employed by felids are well suited to dense cover. Mulga may also have offered feral cats more protection from dingo predation. Dingo activity was distributed uniformly across habitats. The dingo isodar was statistically non-significant, suggesting that habitat selection by dingoes was independent of density. [ABSTRACT FROM AUTHOR]