Variation In Habitat Associations Research Articles

Intraspecific variation in habitat relationships for pygmy rabbits: Implications for conservation of habitat specialists

AbstractEnvironmental relationships can differ across the geographic range of species, especially for widespread generalists. Because habitat specialists are more vulnerable to environmental changes, incorrect assumptions about consistent habitat associations could hinder strategic conservation efforts. We used species distribution models (SDMs) to evaluate intraspecific variation in habitat associations for a habitat specialist of conservation concern, the pygmy rabbit (Brachylagus idahoensis), which is endemic to the sagebrush biome of the western United States. Our goal was to model habitat associations for pygmy rabbits across a portion of their range to evaluate regional variation and contrast predictions with results from a model developed at the rangewide extent. We created inductive SDMs using maximum entropy methods within five ecological regions that encompassed about 20% of the species rangewide distribution and spanned diverse environmental gradients. We included a suite of environmental predictor variables representing topography, vegetation, climate, and soil characteristics. Results of the regional models identified substantial variation in habitat associations across the five regions, with each retaining a unique set of environmental predictors. Bioclimatic variables were the most influential environmental parameters in all five regions, but the specific variables differed. The models developed at regional extents predicted smaller areas of habitat (an average of 15% less for suitable habitat and 80% less for primary habitat) than predictions generated from a model developed at the rangewide extent. Because bioclimatic variables were effective in discriminating areas used by pygmy rabbits, they also provided an opportunity to assess potential changes in habitat distribution by incorporating future climate projections. Distributions modeled under two mid‐century emission scenarios projected substantial reductions in suitable habitat for pygmy rabbits across most regions and pronounced variation among regions in the magnitude and direction of the climate effects. Collectively, results of this work underscore the need to incorporate regional variation in habitat associations into planning for current and future conservation and management strategies.

Accounting for geographic variation in species-habitat associations during habitat suitability modeling.

Range-wide species conservation efforts are facilitated by spatially explicit estimates of habitat suitability. However, species-environment relationships often vary geographically and models assuming geographically constant relationships may result in misleading inferences. We present the first range-wide habitat suitability model (HSM) for the federally threatened eastern indigo snake (Drymarchon couperi) as a case study illustrating an approach to account for known latitudinal variation in habitat associations. Specifically, we modeled habitat suitability using interactive relationships between minimum winter temperature and several a priori environmental covariates and compared our results to those from models assuming geographically constant relationships. We found that multi-scale models including interactive effects with winter temperature outperformed single-scale models and models not including interactive effects with winter temperature. Our top-ranked model had suitable range-wide predictive performance and identified numerous large (i.e., ≥1000 ha) potential habitat patches throughout the indigo snake range. Predictive performance was greatest in southern Georgia and northern Florida likely reflecting more restrictive indigo snake habitat associations in these regions. This study illustrates how modeling interactive effects between temperature and environmental covariates can improve the performance of HSMs across geographically varying environmental gradients.

Resource selection functions based on hierarchical generalized additive models provide new insights into individual animal variation and species distributions

Habitat selection studies are designed to generate predictions of species distributions or inference regarding general habitat associations and individual variation in habitat use. Such studies frequently involve either individually indexed locations gathered across limited spatial extents and analyzed using resource selection functions (RSFs) or spatially extensive locational data without individual resolution typically analyzed using species distribution models. Both analytical methodologies have certain desirable features, but analyses that combine individual‐ and population‐level inference with flexible non‐linear functions may provide improved predictions while accounting for individual variation. Here, we describe how RSFs can be fit using hierarchical generalized additive models (HGAMs) using widely available software, providing a means to explore individual variation in habitat associations and to generate species distribution maps. We used GPS tracking data from golden eagles Aquila chrysaetos from across eastern North America with four environmental predictors to generate monthly distribution models. We considered three model structures that assumed different amounts of individual variation in the functional relationship between predictors and habitat use and used k‐fold cross‐validation to compare model performance. Models accounting for individual variability in shape and smoothness of functional responses performed best. Eagles exhibited the least amount of individual variation in response to land cover variables during winter months, with most individuals more closely adhering to the population‐level trend. During the summer months, eagles exhibited more substantial individual variation in shape and smoothness of the functional relationships, suggesting some need to account for individual variation in eagle habitat use for both inferential and predictive purposes, during this time of year. Because they allow users to blend flexible functions with random effects structures and are well‐supported by a variety of software platforms, we believe that HGAMs provide a useful addition to the suite of analyses used for modeling habitat associations or predicting species distributions.

Temporal variation in small nonvolant mammal (Cricetidae and Didelphidae) microhabitat associations in the Upper Paraná Atlantic Forest

Many questions concerning habitat preferences of Neotropical small mammals remain unanswered. These questions include where the animal lives within and among the available habitats, and the temporal (seasonal and interannual) variation in the habitat associations. The objectives of this research were: (1) to determine the associations of non-volant small mammal species (Rodentia and Didelphimorphia) with specific microhabitat characteristics including vegetation structure in an area near the western boundary of the Upper Paraná Atlantic Forest, and (2) to evaluate seasonal and interannual variation in those associations. Three grids were sampled in three seasons (Dry, Wet, Variable) during two years (2015-2017). The four predominant small mammal species (Gracilinanus agilis, Akodon montensis, Hylaeamys megacephalus, and Oligoryzomys nigripes) were evaluated for seasonal and interannual variation in habitat preferences. Each of the four exhibited seasonal and/or interannual variation in microhabitat preferences for three to six of the 17 environmental variables analyzed. This is the first study to explicitly evaluate temporal variation in habitat associations of small mammals in the Atlantic Forest ecoregion. The temporal patterns of habitat association among these four predominant species reveal a complex spatially and temporally dynamic composition and structure in this small mammal community.

Lower altitudinal variation in habitat associations, tree diversity and co-dominant population structures along moist deciduous forests dominated by sal (Shorea robusta) in Northeast India

We used line transects of 10 × 500 m size to analyze the patterns of sal associations, diversity and population structure at lower elevation (<100 meters above mean sea level) of moist deciduous forests dominated by sal (Shorea robusta) in Tripura, Northeast India. Overall 216 woody species with 898.56 ha−1 mean density and 33.21 m2 ha−1 mean basal area were recorded using 32 line transects of 0.5 ha size sampled by measuring sal forests at ≥10 cm girth at breast height. Five different sal associations were recognized by cluster analysis, where sal typically associated with Terminalia bellirica, Careya arborea and Schima wallichii in moist deciduous habitats. Rare associations of sal with Artocarpus chama and Dipterocarpus turbinatusa were also identified. Species diversity (p < 0.001) and dominance (p < 0.0001) was significantly different across the sal associations; species richness was recorded higher in S. robusta – S. wallichii association with 152 species than in S. robusta – T. bellirica association with 85 species. Existing habitat disturbances and intensity of sal effects on diversity and structure were significant (p ≤ 0.05), as observed by the changes in species richness and abundance of most abundant, least abundant and unique species along the associations. Population trends and regeneration potential of sal and its most associated trees were predicted using steepness and negative slope values in regression of size class distributions of tree density per hectare at 10 girth classes for each sal association. The present investigation helps in the understanding of broad ecological aspects in lowland sal habitats, particularly when this ecosystem is shifting to these regions in relatively wetter and plain areas due to climate change.

Diversity, Seasonal Activity and Habitat Associations of Robber Flies (Diptera: Asilidae) in West-Central Illinois

Robber fly diversity, seasonal activity and habitat associations were studied in prairie and forest habitats in west-central Illinois from May to Oct. 2005. The greatest numbers of individuals and species were collected in recently burned prairie and forest habitats, although richness in the recently burned prairie was lower than expected based on rarefaction. Six of the eight most abundant species had primarily mid-season or earlier flight activity patterns; the other two species were mid- to late or late season fliers. There was significant variation in robber fly species composition among habitats. Forest habitats had greater within-habitat variation in species composition than did prairie habitats. Three indicator species (Cerotainia macrocera Say, Nerax aestuans (L.) and Promachus hinei Bromley) were found, all for prairie habitats. Two species (Ommatius ouachitensis Bullington & Lavigne and P. hinei) showed significant sex-related variation in habitat associations. These results show that significant variation in robber fly assemblages can occur over relatively small geographic areas and that fire may affect robber fly abundance and diversity.

Ontogenetic variation in habitat associations for four flatfish species in the Gulf of Maine‐Georges Bank region

Multivariate ordination techniques were used to examine how size classes of four flatfish species, American plaice Hippoglossoides platessoides, winter flounder Pseudopleuronectes americanus, yellowtail flounder Limanda ferruginea and fourspot flounder Paralichthys oblongus, are related to bottom depth, bottom temperature, substratum grain size and temporal factors using a 35 year time series from autumn and spring in the Gulf of Maine‐Georges Bank region. Depth had the most explanatory value during both seasons in most cases, with fish size generally increasing with depth. One exception was yellowtail flounder in the spring for which a temporal factor explained the most variance, reflecting an increase in size over the time series due to changes in fishing pressure. Temperature was secondarily important for yellowtail flounder in the autumn and for fourspot flounder in both seasons. Substratum type was secondarily important for winter and yellowtail flounders in the spring with smaller fish associated with larger substratum types. Seasonal associations with depth, temperature and substratum are related to seasonal spawning migrations, thermal preferences and other ecological factors.

Seasonal variation in the habitat associations of Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) from the southern Gulf of St. Lawrence

We compared habitat associations of southern Gulf of St. Lawrence Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) between the summer feeding season on the Magdalen Shallows and the overwintering period in the Cabot Strait. Data were from bottom trawl surveys conducted in September 1993, 1994, and 1995 and January 1994, 1995, and 1996. Both species occupied much deeper, warmer water in winter than in summer. The effect of cod age on temperature distribution reversed between the two seasons, with younger cod occupying warmer water than older cod in summer and colder water in winter. Selection of both depth and temperature by cod tended to be more significant in September than in January. The reduced statistical significance of habitat selection by cod in winter was associated with a more aggregated distribution in this season. The contrast between seasons in habitat associations was particularly strong for plaice. The median habitats occupied by plaice were 58-67 m and -0.1 to 0.3°C in September and 374-426 m and 5.2-5.4°C in January. Habitat selection by plaice was significant in both seasons, but significance tended to be greater in January. Degree of aggregation in plaice distribution was similar between the two seasons. Female plaice occupied significantly warmer water than males in September but not in January. The ecological and practical implications of this striking seasonal variation in habitat associations are discussed.

Breeding bird communities of the western and northern Canadian boreal forest: relationship to forest type

We examined the distribution of 80 species of breeding birds across 67 census plots from a variety of sources in the boreal forest of western and northern Canada to obtain information on bird habitat associations for forest management. The sites ranged from upland black spruce (Picea mariana) to riverine deciduous forests and wet, marshy bogs. Axis 1 of an ordination (detrended correspondence analysis) demonstrated a gradient in bird communities from dry to wet sites; axis 2 may have been a black spruce (nutrient poor) to mixed deciduous forest gradient (nutrient rich). Hierarchical classification (twinspan) identified five groups of sites according to their bird communities. Despite geographical variation in bird communities and possible geographical variation in habitat associations, sites were classified according to their forest types rather than regional affinities. Yellow-rumped warblers (Dendroica coronata) and dark-eyed juncos (Junco hyemalis) showed a pronounced gradient of increased abundance from deciduous to coniferous sites. White-throated sparrows (Zonotrichia albicollis) and alder flycatchers (Empidonax alnorum) showed a reverse gradient. In 22 sites of known-age aspen (Populus tremuloides) – mixedwood forests from central Saskatchewan, an ordination indicated a strong relationship between stand age (and thus the proportion of coniferous cover) and bird community structure. The highest combined densities of Neotropical migrants occurred in old forests, whereas short-distance migrants were most abundant in young forests. The highest abundance of upper-canopy gleaners was found in old forests, whereas ground foragers were most abundant in early successional forests. These findings have important implications for management of boreal forests.