Reflect Habitat Quality Research Articles

On the marine feeding behavior and activity budgets of Belted Kingfishers (Megaceryle alcyon) during the post-fledging period

Belted Kingfishers (Megaceryle alcyon) are widely distributed across aquatic environments in North America, but their behavior in marine habitats remains understudied, especially during the post-fledging period. We recorded daily activity budgets of adult and fledgling Belted Kingfishers on San Juan Island, Washington, and investigated the effects of tides and age class on feeding behaviors. Feeding attempt rate was highest at high tide, but strike success was highest at low tide. Adults foraged more successfully than juveniles and caught fish almost twice as large, consistent with juvenile inexperience during the post-fledging period. Strike success rates also varied between study sites for both adults and juveniles, potentially reflecting habitat quality. These results improve our understanding of how Belted Kingfishers behave in marine environments, and to our knowledge provide the first study of marine Belted Kingfishers during the post-fledging period. Follow-up studies quantifying prey availability and comparing seasonal behaviors of kingfishers in freshwater and marine habitats may help clarify the mechanisms behind the patterns we observed.

Suitability and Transferability of the Resource-Based Habitat Concept: A Test With an Assemblage of Butterflies

A functional definition of the habitat-concept based on ecological resources incorporates three interconnected parameters: composition, configuration and availability of the resources. The intersection of those parameters represents the functional habitat of a given population or species. Resource composition refers to the co-occurrence of the resources required by each individual to complete its life cycle. Resource configuration refers both to the way individual resources are spatially distributed within the habitat and the way all the resources are organized in the habitat space. Resource availability refers to the accessibility and procureability of resources. Variation in these variables is predicted to influence the demography of the population. To test the suitability of this definition and its transferability across landscapes, we first conducted a very detailed study on habitat and resource use of five butterfly species within a large nature reserve. Second, we conducted a larger-scale study, focusing on metapopulations of two species. We monitored demography for each species and tested whether its variation can be explained by (1) the vegetation type, (2) the vegetation composition or (3) the availability and configuration of the species-specific ecological resources. To confirm that resource availability and configuration reflect habitat quality, we also assessed their impacts on individual morphology. Whatever the investigated spatial scale, our results quantitatively demonstrate the overall better performance of the resource-based habitat approach compared to other most commonly used approaches. Our analysis allowed us to assess the relative importance of each ecological resource in terms of both their availability and organization relative to the species’ abundance, demography and individual fitness measures. Resource availability did not play the predominant role in defining habitat quality as it was in most cases overruled by resource organization. Finally, we confirmed the between-population transferability of the habitat definition and quality estimates while adopting a resource-based habitat approach. Our study clearly demonstrates the suitability of the resource-based definition of the habitat. Therefore, we argue that this approach should be favored for species of conservation concern. Although most conclusions so far have emerged from butterfly studies, the resource-based definition of the habitat should also be ecologically relevant to many other organisms.

PERFIL DOS FRAGMENTOS DE MATA ATLÂNTICA COM REGISTROS DO MUTUM-DO-SUDESTE

Avaliar os efeitos das mudanças no uso da terra sobre a biodiversidade se tornou uma questão-chave para conservação das espécies. Para isso, é necessário analisar a configuração e composição da paisagem em que determinada espécie ocorre. O objetivo foi traçar um perfil dos remanescentes florestais de Mata Atlântica localizados no sul da Bahia que apresentam registros atuais e históricos de Crax blumenbachii. Analisaram-se quatorze áreas utilizando diferentes escalas espaciais (escala de mancha, 500 m, 1 e 2 km) para calcular a quilometragem total e a distância mais próxima de estradas e rios até a borda da mancha, porcentagem de área ocupada por: floresta, floresta com cabrucas, pastagem e agricultura; densidade de fragmentos e a proximidade desses fragmentos até a borda de cada mancha, a área ocupada por casas e a distância dessas até a borda da mancha. Selecionou-se a escala de 2 km por melhor descrever a configuração e composição da paisagem. Há dois perfis de áreas com registros de mutum: (1) áreas com paisagens mais florestadas, com mais rios e estradas, pouca pastagem/agricultura e casas próximas, e (2) áreas distantes de casas, com estradas e fragmentos florestais próximos. Estas são caracteristicas de áreas com registros recentes ou históricos de mutum, e não necessariamente refletem qualidade de habitat para a espécie.

Habitat selection in a dynamic seasonal environment: Vegetation composition drives the choice of the breeding habitat for the community of passerines in floodplain grasslands

The conservation of grasslands is a concern worldwide as they are threatened by climate change and the expansion of intensive agricultural practices. The management of these areas must take into account the decisional process of habitat selection by individual organisms to identify potential ecological traps or underused habitats. Organisms that live in heterogeneous environments must select their breeding habitat based on cues that reflect habitat quality. In dynamic ecosystems such as grasslands, environmental cues used by individuals should show a strong temporal autocorrelation, such that their characteristics during breeding can be predicted earlier in the season. Our objective was to test if habitat features that explain grassland birds' distribution during the nesting and chick-rearing period could be predicted from the habitat features available on territory settlement. In western France, we analysed the relationships between the occurrence, richness and abundance of four passerine species, and vegetation structure and composition during chick-rearing period. We then analysed the temporal autocorrelation of vegetation features to determine whether the cues used during the settlement period reliably predicted the vegetation features encountered at later stages of breeding. We found that birds selected habitats characterized by a low cover of grasses, but did not respond to the physical structure of vegetation. The composition of vegetation was also the only variable that exhibited temporal autocorrelation over the course of the season, suggesting that individuals may rely on this feature to select optimal breeding habitats. Our results suggest that in dynamic environments, and in the absence of breeding experience or public information, animals can choose their breeding habitat based on a simple assessment of vegetation composition. A detailed knowledge of the underlying drivers of habitat selection is essential to manage habitats, identify potential ecological traps, and enhance the attractiveness of areas especially those under agri-environmental schemes.

Drivers of local densities of endangeredLycaena hellebutterflies in a fragmented landscape

AbstractDue to their specialised habitat requirements, butterflies are particularly vulnerable to habitat loss and fragmentation. Understanding the drivers of local abundances of species is essential for their effective conservation in fragmented landscapes. We investigated factors affecting population densities of an endangered European butterfly, the Violet Copper (Lycaena helle), occurring in a small metapopulation near the city of Kraków, southern Poland. The environmental parameters tested as predictors of the local densities of the species included both the variables associated with spatial structure of habitats such as patch sizes, their isolation and fragmentation as well as those potentially reflecting habitat quality. Patch area and vegetation height turned out to be the only factors significantly influencingL. helledensities, both having a positive effect. The positive impact of patch area is a bit surprising, since its relationship with population densities is typically negative in butterflies. In our study system it is likely to derive from source‐sink dynamics as the smaller habitat patches are apparently too small to sustain viable local populations. In turn, the positive influence of vegetation height implies that the ongoing succession does not deteriorate the quality of the recently abandoned meadows yet, whereas higher turf may provide better sheltering places. The loss of almost half ofL. hellehabitat patches in the study area in recent years is alarming. However, its inclusion into the Natura 2000 system should help to conserve the species as long as this act is followed by proper management of its habitats.

Species Diversity, Abundance and Brood Numbers of Breeding Waterbirds in Relation to Habitat Properties in an Agricultural Watershed

Land-use changes and the resulting habitat degradation have been regarded as the most important known causes of waterfowl population declines. We assessed the habitat requirements of waterbirds, including waterfowl, in a hemiboreal, agricultural watershed in southern Finland. We related the birds' species diversity, abundance and brood numbers on ten lakes to environmental variables, including land use characteristics as well as topographic and local biotic features. Both species diversity and pair numbers responded to land use characteristics, such as the area of agricultural land surrounding the lakes. Our results suggest that land use may reflect habitat quality, possibly in terms of resource availability and predation risk. The pair numbers of waterbirds grew along with the availability of invertebrates, an important food resource. The abundance of gulls affected the diversity, abundance and reproductive success of waterfowl positively in our study area, probably because they provided shelter from pre...

Severe recent decrease of adult body mass in a declining insectivorous bird population.

Migratory bird species that feed on air-borne insects are experiencing widespread regional declines, but these remain poorly understood. Agricultural intensification in the breeding range is often regarded as one of the main drivers of these declines. Here, we tested the hypothesis that body mass in breeding individuals should reflect habitat quality in an aerial insectivore, the tree swallow (Tachycineta bicolor), along a gradient of agricultural intensity. Our dataset was collected over 7 years (2005-2011) and included 2918 swallow captures and 1483 broods. Analyses revealed a substantial decline of the population over the course of the study (-19% occupancy rate), mirrored by decreasing body mass. This trend was especially severe in females, representing a total loss of 8% of their mass. Reproductive success was negatively influenced by intensive agriculture, but did not decrease over time. Interestingly, variation in body mass was independent of breeding habitat quality, leading us to suggest that this decline in body mass may result from carry-over effects from non-breeding areas and affect population dynamics through reduced survival. This work contributes to the growing body of evidence suggesting that declines in migratory aerial insectivores are driven by multiple, complex factors requiring better knowledge of year-round habitat use.

Effects of management legacies on stream fish and aquatic benthic macroinvertebrate assemblages.

Fish and benthic macroinvertebrate assemblages often provide insight on ecological conditions for guiding management actions. Unfortunately, land use and management legacies can constrain the structure of biotic communities such that they fail to reflect habitat quality. The purpose of this study was to describe patterns in fish and benthic macroinvertebrate assemblage structure, and evaluate relationships between biota and habitat characteristics in the Chariton River system of south-central Iowa, a system likely influenced by various potential management legacies (e.g., dams, chemical removal of fishes). We sampled fishes, benthic macroinvertebrates, and physical habitat from a total of 38 stream reaches in the Chariton River watershed during 2002-2005. Fish and benthic macroinvertebrate assemblages were dominated by generalist species tolerant of poor habitat quality; assemblages failed to show any apparent patterns with regard to stream size or longitudinal location within the watershed. Metrics used to summarize fish assemblages and populations [e.g., presence-absence, relative abundance, Index of Biotic Integrity for fish (IBIF)] were not related to habitat characteristics, except that catch rates of piscivores were positively related to the depth and the amount of large wood. In contrast, family richness of benthic macroinvertebrates, richness of Ephemeroptera, Trichoptera, and Plecoptera taxa, and IBI values for benthic macroinvertebrates (IBIBM) were positively correlated with the amount of overhanging vegetation and inversely related to the percentage of fine substrate. A long history of habitat alteration by row-crop agriculture and management legacies associated with reservoir construction has likely resulted in a fish assemblage dominated by tolerant species. Intolerant and sensitive fish species have not recolonized streams due to downstream movement barriers (i.e., dams). In contrast, aquatic insect assemblages reflected aquatic habitat, particularly the amount of overhanging vegetation and fine sediment. This research illustrates the importance of using multiple taxa for biological assessments and the need to consider management legacies when investigating responses to management and conservation actions.

Phenotypic differentiation of Ponto-Caspian gobies during a contemporary invasion of the upper Danube River

Evolution is known to act on contemporary timescales and invasive organisms are often used to study rapid evolutionary changes of geno- and phenotypes under natural conditions. The ability and speed of local adaptation is discussed as a key character triggering successful invasions. Variation of body shape among populations of two highly invasive, sympatric Ponto-Caspian goby species (Teleostei: Gobiidae) with a comparable invasion history in the upper Danube River, i.e. Neogobius melanostomus and Ponticola kessleri, was assessed using geometric morphometric methods. Phenotypic variation established within less than 15 generations was evident in both species. It was mainly correlated with geographical location, but in N. melanostomus also with substrate type, an ecological variable reflecting habitat quality. The two species differed in their degree of intraspecific variation which was more pronounced in N. melanostomus, the numerically dominant invader in the upper Danube. Body shape variation significantly correlating with geographical rather than ecological variables suggests a heritable component and renders phenotypic plasticity as a lone explanation unlikely. Patterns of body shape similarity among upper Danubian goby populations suggest a stepping-stone rather than a continuous expansion model for both species, where multiple introductions, possibly from various origins, may have shaped differentiation.

Importance of scalar and riparian habitat effects for assessment of ecological status using littoral diatoms

The classification of waterbodies under the Water Framework Directive is dependent on the ability of monitoring programmes to reflect habitat quality using biotic elements including benthic diatom communities. This study investigated the influence of specific riparian habitats, of mixed woodland, grassland and lake artificial structures such as jetties and slipways, on benthic diatom assemblages in nine lakes across gradients of total phosphorus, alkalinity and in the presence or absence of Dreissena polymorpha. The heterogeneity of the benthic diatom assemblages at riparian and lake scale was assessed by taking three replicates per site category per lake, following standard European Union protocols. Canonical correspondence analysis (CCA) and mixed effect modelling was used to investigate the main environmental controls on assemblage structure. Non-metric Multidimensional Scaling (NMDS) was used to examine patterns in assemblage structure. No single environmental gradient was found to control benthic diatom composition, with differences among assemblages influenced both by riparian habitat type within lakes and interaction of multiple environment gradients, including presence of D. polymorpha. Greater control was exerted on community structure at the lake than local riparian scale. The influence of scalar factors on diatom assemblages increased with increasing scale. We recommend that for effective monitoring and assessment of ecological status, standard sampling protocols should include localised littoral habitats with individual samples pooled across riparian habitat types, thereby accounting for both multiple environmental and spatial controls on community structure.

Distribution and individual condition reveal a hierarchy of habitat suitability for an area-sensitive passerine

The identification of environmental factors linked to increased risk of local extinction often relies on inference from patterns of distribution. Yet for declining populations, the assumption of population equilibrium that underlies species distribution models is violated. Measures such as individual condition can provide a more direct indication of extinction risk, and can start to be detected before declines commence. We compared distribution-based and condition-based approaches to identifying factors affecting habitat suitability for an area-sensitive passerine, the eastern yellow robin Eopsaltria australis, in eastern Australia. We compared patterns of individual condition between robins and several common, more mobile species (Meliphagid honeyeaters and yellow thornbills Acanthiza nana). Robin presence was not affected by landscape context, but robins avoided sites with a more grassy ground layer. However, robins inhabiting landscapes with less remnant woodland had higher ratios of heterophils to lymphocytes in peripheral blood, indicating higher long-term stress. No clear spatial patterns of condition were detected for the more mobile species. Our findings suggest a hierarchical model of habitat suitability, whereby robins avoid grassy sites, but where they do occur are in poorest condition when inhabiting less-vegetated landscapes. We predict greater rates of local extinction of robins from such landscapes. The use of indicators of individual condition, in addition to distribution data, can unveil otherwise cryptic factors as important influences on habitat quality. As habitat occupancy does not always reflect habitat quality, exploring patterns in condition indices can complement species distribution modelling, potentially revealing threats to persistence before population declines have commenced.

Assessing habitat quality of farm-dwelling house sparrows in different agricultural landscapes

Having historically been abundant throughout Europe, the house sparrow (Passer domesticus) has in recent decades suffered severe population declines in many urban and rural areas. The decline in rural environments is believed to be caused by agricultural intensification, which has resulted in landscape simplification. We used giving-up densities (GUDs) of house sparrows feeding in artificial food patches placed in farmlands of southern Sweden to determine habitat quality during the breeding season at two different spatial scales: the landscape and the patch scale. At the landscape scale, GUDs were lower on farms in homogeneous landscapes dominated by crop production compared to more heterogeneous landscapes with mixed farming or animal husbandry. At the patch level, feeding patches with a higher predation risk (caused by fitting a wall to the patch to obstruct vigilance) had higher GUDs. In addition, GUDs were positively related to population size, which strongly implies that GUDs reflect habitat quality. However, the increase followed different patterns in homogeneous and heterogeneous landscapes, indicating differing population limiting mechanisms in these two environments. We found no effect of the interaction between patch type and landscape type, suggesting that predation risk was similar in both landscape types. Thus, our study suggests that simplified landscapes constitute a poorer feeding environment for house sparrows during breeding, that the population-regulating mechanisms in the landscapes differ, but that predation risk is the same across the landscape types.

Habitat Use Does not Reflect Habitat Quality for Henslow's Sparrows (Ammodramus Henslowii) Wintering in Fire-Managed Longleaf Pine Savannas

Interpreting habitat quality requires an understanding of the consequences of habitat use because bird density alone may not reflect habitat quality. Although habitat use can be readily quantified, subsequent effects remain elusive for most species, especially for migrants on the wintering grounds. Wintering Henslow's Sparrow (Ammodramus henslowii) densities in Longleaf Pine (Pinus palustris) savannas are fire-dependent, with highest bird densities in the first winter after a fire, but reduced density in subsequent winters without fire. We determined habitat characteristics associated with variation in bird density in the first and second winters following fire and then followed birds' diet, condition, and survival in 10 plots over two winters. Habitat structure and seed energy availability, but not plant species composition, were equally important for explaining bird density, except for two outlier plots with extremely high seed production and fewer birds than expected. Henslow's Sparrows consumed a variety of seeds and arthropods, which indicates that they are generalists capable of responding to fire-mediated changes in seed composition. Body condition decreased in midwinter, associated with a decrease of arthropods in the birds' diet. Although Henslow's Sparrow densities responded strongly to ephemeral savanna conditions, consequences of habitat use were negligible because survival and three measures of body condition did not vary with years since fire or among age and sex classes. These aspects of the winter ecology of sexually monochromatic Henslow's Sparrows are consistent with tenets of the ideal free distribution, whereby differences in bird density between habitats result in equal fitness.

Putting Density Back into the Habitat‐Quality Equation: Case Study of an Open‐Nesting Forest Bird

Ecological traps and other cases of apparently maladaptive habitat selection cast doubt on the relevance of density as an indicator of habitat quality. Nevertheless, the prevalence of these phenomena remains poorly known, and density may still reflect habitat quality in most systems. We examined the relationship between density and two other parameters of habitat quality in an open-nesting passerine species: the Ovenbird (Seiurus aurocapilla). We hypothesized that the average individual bird makes a good decision when selecting its breeding territory and that territory spacing reflects site productivity or predation risk. Therefore, we predicted that density would be positively correlated with productivity (number of young fledged per unit area). Because individual performance is sensitive to events partly determined by chance, such as nest predation, we further predicted density would be weakly correlated or uncorrelated with the proportion of territories fledging young. We collected data in 23 study sites (25 ha each), 16 of which were located in untreated mature northern hardwood forest and seven in stands partially harvested (treated) 1-7 years prior to the survey. Density explained most of the variability in productivity (R(2)= 0.73), and there was no apparent decoupling between density and productivity in treated plots. In contrast, there was no significant relationship between density and the proportion of territories fledging >or=1 young over the entire breeding season. These results suggest that density reflects habitat quality at the plot scale in this study system. To our knowledge this is one of the few studies testing the value of territory density as an indicator of habitat quality in an open-nesting bird species on the basis of a relatively large number of sizeable study plots.

Distribution patterns of free-living nematodes in differently degraded river reaches of the River Wien, Austria

AbstractFree-living nematode communities were investigated at four morphologically different reaches along the River Wien, Austria. A near natural (NN) reach, two impounded reaches of different size (small and large: SI, LI) and a restored reach (RR) were sampled in autumn, winter, spring and summer (2004-2005). A total of 4144 individuals were counted and comprised 78 species. Nematodes of the impounded sites contributed least (5% at SI) and most (60% at LI) to the total fauna. Mean site abundances (ind./10 cm2) were 68, 27, 10 and 1 at RR, NN, LI and SI, respectively. Species diversity ranged from 1.59 at LI to 2.16 at RR. Bacterivorous nematodes dominated all sites (>50%); only algivorous Chromadoridae represented a high percentage contribution (46%) at LI. Based on this high portion, the maturity index (MI 1-5) was highest at this site (2.61). The MI indicated status of good water quality for the NN (2.5). The relatively low MI (2.10) and the high portion of cp1 Secernentea (14%) reflect the status of critical pollution at the restored site. The patterns of average taxonomic distinctness (ATD) did not optimally reflect habitat quality; a better descriptor of degraded river habitats seems to be the variation of taxonomic distinctness (VTD) in this study. In conclusion, the MI seems to be a better descriptor of pollution and the VTD of morphological degradation.

Water Turbidity Affects the Development of Sexual Morphology in the Palmate Newt

AbstractIn theory, animal signals are designed to optimize transmission across a specific habitat. However, sexual signals characteristics often reflect habitat quality, a feature that does not necessarily match habitat structure. Besides, many species exploit a particular habitat for breeding so that the growth of sexual signals can depend on the additive effects of breeding and non‐breeding habitats. We combined field and experimental data to investigate the relative effect of terrestrial and aquatic habitat on the development of sexual ornaments in the palmate newt, Triturus helveticus. This species exploits a large ecological range of habitats. Like many amphibians, it spends the breeding season in water and the rest of year on land. We tested the influence of terrestrial (forest cover) and aquatic habitat variables (turbidity, organic matter, pH, nitrate and chloride) on male sexual morphology. Neither terrestrial nor aquatic habitat variables accounted for body size variation. In contrast, the size of male sexual traits decreased with water turbidity, suggesting that the expression of visual signals matched the local conditions of signal transmission. We provide experimental evidence that this pattern is not caused by reduced foraging efficiency in turbid water. We propose alternative mechanisms to account for the relationship between turbidity and visual sexual signals, and discuss the consequences of small scale environmental variation on mate choice.

Settlement decisions in blue tits: difference in the use of social information according to age and individual success

Dispersers are expected to assess breeding habitat quality before settlement. Although cues reflecting habitat quality are well studied, social cues have not been as well evaluated. In this paper, we studied breeding habitat selection during 3 years in a natural population of blue tits, Cyanistes caeruleus, breeding in nest-boxes. Our aim was to investigate if this species used conspecific density and/or reproductive success of con- and heterospecifics (i.e., social cues) in settlement decisions. The patterns observed were consistent with the idea that juveniles, when dispersing from their natal patches, did not react to any of the cues that we tested. In contrast, breeders that dispersed seemed to respond to both conspecific mean patch reproductive success (PRS) and breeding density of the settlement patch in the year of dispersal, their response differing according to their own reproductive success. Indeed, failed breeders moved to areas with high PRS and low density relative to source patches, while successful breeders behaved the opposite. The comparison between juveniles and adults might be modulated by the limited time available to juveniles to gather information on PRS and density at the end of the dispersing year. Adults lacking these time constraints, however, seemed to rely on these conspecific cues although limited by their own quality. Additionally, breeders were more likely to be immigrants in patches with relatively low breeding success and density the previous year, suggesting that settlement is influenced by multiple cues, which may reveal information on different aspects of habitat and be available at different moments. Collectively, our results support the importance of social cues for blue tits' settlement.

NONIDEAL BREEDING HABITAT SELECTION: A MISMATCH BETWEEN PREFERENCE AND FITNESS

The selection of breeding sites in heterogeneous habitats should ideally be based on cues closely reflecting habitat quality and thus predicting realized individual fitness. Using long-term population data and data on territory establishment of male Northern Wheatears (Oenanthe oenanthe), we examined whether territory characteristics linked to individual fitness (reproductive performance and survival) also were linked to territory preference. Breeding territories varied in their physical characteristics and their potential effects on reproductive performance, and this variation among territories was correlated from one year to the next. Of all measured territory characteristics (from the focal and the previous year) only territory field layer height predicted individual fitness, i.e., reproductive performance was higher in territories with permanently short rather than growing field layers. Territory preference, instead, was only linked to the size of territory aggregations, i.e., males settled earlier at territory sites sharing borders with several adjacent sites than at those with few or no adjacent sites. This mismatch between territory characteristics linked to fitness and those linked to territory preference was not explained by site fidelity or compensated for by the different fitness components measured. Because the results were not in agreement with an ecological trap scenario, where poor habitats are preferred over high-quality habitats, our results suggest a more general case of nonideal habitat selection. Whereas nonideal selection with respect to territory field layer height may be explained by its poor temporal predictability within the breeding season, the preference for territory aggregations is still open to alternative adaptive explanations. Our study suggests that nonideal habitat selection should be investigated by direct estimates of preferences (e.g., order of territory establishment) and their links to habitat characteristics and fitness components. Furthermore, we suggest that the probability of establishing a territory needs to be included as a factor influencing patterns of habitat selection.

WHAT CAN HABITAT PREFERENCE MODELS TELL US? TESTS USING A VIRTUAL TROUT POPULATION

Habitat selection (“preference”) models are widely used to manage fish and wildlife. Their use assumes that (1) habitat with high animal densities (highly selected habitat) is high quality habitat, and low densities indicate low quality habitat; and (2) animal populations respond positively to the availability of highly selected habitat. These assumptions are increasingly questioned but very difficult to test. We evaluated these assumptions in an individual‐based model (IBM) of stream trout that reproduces many natural complexities and habitat selection behaviors. Trout in the IBM select habitat to maximize their potential fitness, a function of growth potential (including food competition) and mortality risks. We know each habitat cell's intrinsic habitat quality, the fitness potential a trout in the cell would experience in the absence of competition. There was no strong relation between fitness potential and the density of fish in the IBM; cells where fitness potential was high but density low were common for all age classes, and fitness potential was not proportional to density. This result was consistent at high and low abundance and high and low overall habitat quality. We developed a statistical model of trout density observed in the IBM as a function of the four habitat variables that vary among cells. We then tested the ability of modeled mean density to predict population response to habitat changes resulting from stream flow modification. Modeled density partially explained population response to flow, but only at flows near the flow at which the density model was developed, and not for groups (e.g., juveniles) experiencing strong competition for habitat. Modeled density predicted population response opposite that observed for age‐0 trout and incorrectly predicted response of all age classes to major changes in flow. These results make sense if habitat selection is understood as an emergent property of (1) the mechanisms by which habitat affects fitness, (2) habitat availability, (3) population abundance and size structure, and (4) how individuals compete with each other. We identified eight reasons why animal density may not reflect habitat quality and several inherent limitations of habitat selection modeling.

DOES DENSITY REFLECT HABITAT QUALITY FOR NORTH AMERICAN RED SQUIRRELS DURING A SPRUCE-CONE FAILURE?

Predicting animal populations over time often is done using models of density–habitat relationships that assume animal density is a reflection of habitat quality. We explored whether this assumption was true for the North American red squirrel (Tamiasciurus hudsonicus), a species present at different densities in 3 conifer habitats: white spruce (Picea glauca; high resource quality, unstable availability), mixed conifer, and lodgepole pine (Pinus contorta; lower resource quality, stable availability). We documented density, body condition, survival, reproduction, and turnover in these 3 habitats during a failure of spruce-cone crop, when the potential for the relative importance of habitats to change was greatest. During this time squirrel densities in white spruce decreased by 66% to match with those found in pine and mixed-conifer forests. Red squirrels in spruce forests experienced lower survival and fewer females successfully weaned young, and juvenile production was lower. Adult and juvenile immigration was more important than local juvenile production in replacing squirrel mortality in spruce and mixed-conifer forests. Our results indicate that density does not always reflect habitat quality for red squirrels, and we question the historical high-quality rating of white spruce habitat for this species. Further, our findings suggest that movement of ostensibly highly territorial adults in late winter and early spring is an important mechanism in determining annual squirrel densities regardless of habitat type.