Environmental variables associated with the distribution and occupancy of habitat specialist tadpoles in naturally acidic,oligotrophic waterbodies

Environmental factors play an integral role, either directly or indirectly, in structuring faunal assemblages. Water chemistry, predation, hydroperiod and competition influence tadpole assemblages within waterbodies. We surveyed aquatic predators, habitat refugia, water height and water chemistry variables (pH, salinity and turbidity) at 37 waterbodies over an intensive 22‐day field survey to determine which environmental factors influence the relative abundance and occupancy of two habitat specialist anuran tadpole species in naturally acidic, oligotrophic waterbodies within eastern Australian wallum communities. The majority of tadpoles found were of Litoria olongburensis (wallum sedge frog) and Crinia tinnula (wallum froglet) species, both habitat specialists that are associated with wallum waterbodies and listed as Vulnerable under the IUCN Red List. Tadpoles of two other species (Litoria fallax (eastern sedge frog), and Litoria cooloolensis (cooloola sedge frog)) were recorded from two waterbodies. Tadpoles of Litoria gracilenta (graceful treefrog) were recorded from one waterbody. Relative abundance and occupancy of L. olongburensis tadpoles were associated with pH and water depth. Additionally, L. olongburensis tadpole relative abundance was negatively associated with turbidity. Waterbody occupancy by C. tinnula tadpoles was negatively associated with predatory fish and water depth and positively associated with turbidity. Variables associated with relative abundance of C. tinnula tadpoles were inconclusive and further survey work is required to identify these environmental factors. Our results show that the ecology of specialist and non‐specialist tadpole species associated with ‘unique’ (e.g. wallum) waterbodies is complex and species specific, with specialist species likely dominating unique habitats.     

Spatial and temporal variability of aquatic habitat use by amphibians in a hydrologically modified landscape

1. Habitat loss is a major driver of biodiversity decline worldwide. Temporary waterbodies are especially vulnerable because they are sensitive both to human impact and to climatic variations. Pond‐breeding amphibians are often dependent on temporary waterbodies for their reproduction, and hence are sensitive to loss of temporary ponds. 2. Here we present the results of a 5‐year study regarding the use of temporary aquatic habitats by amphibians in a hydrologically modified area of Eastern Europe (Romania). The annual number of aquatic habitats varied between 30 and ～120. Each aquatic habitat was characterised by a number of variables such as: ‘type’ (pond, drainage ditch and archaeological ditch), ‘hydroperiod’ (number of weeks the ponds were filled in a given year), ‘depth’ (cm), ‘area’ (m²) and the density of predatory insects (‘predation’). The turnover rate for each amphibian species for each wetland was calculated based on the pond occupancy. 3. Eight amphibian species were recorded from the aquatic habitats. Hydroperiod was the most important variable, positively influencing wetland use by amphibians and their reproductive success. Most species preferred drainage ditches for reproduction, and the reproductive success was highest in this habitat type every year. For most of the species, the local extinction rate was higher than the colonisation rate in the first 4 years, but the situation reversed in the last year of the study when wetland use by amphibians sharply increased because of high rainfall. 4. This study confirms the importance for amphibians of maintaining and managing aquatic habitat diversity at small spatial scales. Man‐made aquatic habitats such as drainage ditches may be important habitats for amphibians, and this should be considered in restoration activities.     

The roles of landscape context, niche breadth, and range boundaries in predicting species responses to habitat alteration

Extant species in human‐dominated landscapes differ in their sensitivity to habitat loss and fragmentation, although extinctions induced by environmental alteration reduce variation and result in a surviving subset of species with some degree of ‘resistance’. Here, we test the degree to which variable responses to habitat alteration are (1) essentially an inherent property of a taxon subject to constraints imposed by its geographical range, as suggested by Swihart et al. (2003), (2) a function of the landscape in which a species occurs, or (3) a function of spatial trends occurring on large scales. We used data collected on 33 vertebrate species during 2001–04 across the upper Wabash River basin, Indiana, in 35 square ‘landscapes’, each 23 km² in size. Six species of forest rodent, six species of grassland rodents, seven species of bats, eight species of aquatic turtles, and six species of amphibians were sampled at 504, 212, 590, 228, and 625 patches, respectively. The fraction of patches of primary habitat (e.g. forests for tree squirrels, wetlands for aquatic turtles) occupied by a target species was used as a response variable. On a basin‐wide scale, 47% of variation in proportional occupancy among species could be explained by taxon‐specific variables; occupancy rates were related positively to niche breadth and negatively to the proximity of a geographical range boundary. After controlling for species effects, landscape‐level occupancy rates varied significantly for 16 of 33 species, with variation partitioned among landscape variables alone (mean = 11% of variation), spatial trend variables alone (26%), and both variable sets jointly (8%). Among landscape variables, percentage forest cover positively affected occupancy rates of three bat species and a tree squirrel. Variation in occupancy rates among landscapes was consistent with large‐scale spatial trends for 13 species. Our findings demonstrate the general importance of niche breadth as a predictor of species responses to habitat alteration and highlight the importance of viewing the effects of habitat loss and fragmentation at multiple spatial scales.     

Persistence at distributional edges: Columbia spotted frog habitat in the arid Great Basin,USA

A common challenge in the conservation of broadly distributed, yet imperiled species is understanding which factors facilitate persistence at distributional edges, locations where populations are often vulnerable to extirpation due to changes in climate, land use, or distributions of other species. For Columbia spotted frogs (Rana luteiventris) in the Great Basin (USA), a genetically distinct population segment of conservation concern, we approached this problem by examining (1) landscape‐scale habitat availability and distribution, (2) water body‐scale habitat associations, and (3) resource management‐identified threats to persistence. We found that areas with perennial aquatic habitat and suitable climate are extremely limited in the southern portion of the species’ range. Within these suitable areas, native and non‐native predators (trout and American bullfrogs [Lithobates catesbeianus]) are widespread and may further limit habitat availability in upper‐ and lower‐elevation areas, respectively. At the water body scale, spotted frog occupancy was associated with deeper sites containing abundant emergent vegetation and nontrout fish species. Streams with American beaver (Castor canadensis) frequently had these structural characteristics and were significantly more likely to be occupied than ponds, lakes, streams without beaver, or streams with inactive beaver ponds, highlighting the importance of active manipulation of stream environments by beaver. Native and non‐native trout reduced the likelihood of spotted frog occupancy, especially where emergent vegetation cover was sparse. Intensive livestock grazing, low aquatic connectivity, and ephemeral hydroperiods were also negatively associated with spotted frog occupancy. We conclude that persistence of this species at the arid end of its range has been largely facilitated by habitat stability (i.e., permanent hydroperiod), connectivity, predator‐free refugia, and a commensalistic interaction with an ecosystem engineer. Beaver‐induced changes to habitat quality, stability, and connectivity may increase spotted frog population resistance and resilience to seasonal drought, grazing, non‐native predators, and climate change, factors which threaten local or regional persistence.     

Human disturbance and stage‐specific habitat requirements influence snowy plover site occupancy during the breeding season

Habitat use has important consequences for avian reproductive success and survival. In coastal areas with recreational activity, human disturbance may limit use of otherwise suitable habitat. Snowy plovers Charadrius nivosus have a patchy breeding distribution along the coastal areas on the Florida Panhandle, USA. Our goal was to determine the relative effects of seasonal human disturbance and habitat requirements on snowy plover habitat use. We surveyed 303 sites for snowy plovers, human disturbance, and habitat features between January and July 2009 and 2010. We made multiple visits during three different sampling periods that corresponded to snowy plover breeding: pre‐breeding, incubation, and brood‐rearing and used multi‐season occupancy models to examine whether human disturbance, habitat features, or both influenced site occupancy, colonization (probability of transition from an unoccupied site to an occupied site), and extinction (probability of transition from an occupied site to an unoccupied site). Snowy plover site occupancy and colonization was negatively associated with human disturbance and site extinction was positively associated with human disturbance. Interdune vegetation had a negative effect on occupancy and colonization, indicating that plovers were less likely to use areas with uniform, dense vegetation among dunes. Also, dune shape, beach debris, and access to low‐energy foraging areas influenced site occupancy, colonization, and extinction. Plovers used habitat based on beach characteristics that provided stage‐specific resource needs; however, human disturbance was the strongest predictor of site occupancy. In addition, vegetation plantings used to enhance dune rehabilitation may negatively impact plover site occupancy. Management actions that decrease human disturbance, such as symbolic fencing and signage, may increase the amount of breeding habitat available to snowy plovers on the Florida Panhandle and in other areas with high human activity. The specific areas that require this protection may vary across snowy plover life history stages.     

Habitat use by five sympatric Australian freshwater crayfish species (Parastacidae)

1. The Grampians National Park in Victoria is a ‘hot spot’ for freshwater crayfish diversity, with seven species from six genera occurring in sympatry. Few studies have examined how multiple species of freshwater crayfish co‐exist across landscapes consisting of a mosaic of perennial and seasonal habitats. Despite their endemicity and likely key role in freshwaters, the ecology and biology of these crayfish remains unknown. 2. This study determined the distribution and habitat use of five crayfish species (Euastacus bispinosus, Cherax destructor, Geocharax falcata, Gramastacus insolitus and Engaeus lyelli). Seasonal sampling surveys ascertained whether crayfish distribution was related to habitat type, environmental or physicochemical variables, catchment or season. 3. Distribution was directly related to habitat type and the environmental and physicochemical variables that characterised habitats. Engaeus lyelli, G. falcata and G. insolitus occurred predominantly in floodplain wetlands and flooded vegetation habitats, E. bispinosus occurred only in flowing soft‐sediment channels and C. destructor was found in all catchments and habitat types studied. Gramastacus insolitus co‐occurred with G. falcata at all sites except two, so no distinct habitat separations were apparent for these two species. 4. A high percentage cover of boulders was the best indicator of crayfish absence, and discriminated between habitat types and crayfish species: it was probably a surrogate for a larger range of environmental and physicochemical variables. Catchment and season did not affect crayfish distribution. 5. These crayfish species varied in their degree of habitat specialisation from strongly generalist (C. destructor) to occupying only a specific habitat type (E. bispinosus). Some species appeared specialised for seasonal wetlands (G. insolitus and G. falcata). Overlap in site occupancy also varied: G. insolitus and G. falcata distributions were strongly associated, whereas C. destructor appeared to occur opportunistically across habitats, both alone and co‐occurring with all the other species. 6. Management strategies to conserve multiple species of crayfish co‐existing within landscapes will need to incorporate a range of perennial and seasonal habitat types to ensure sufficient space is available for species to maintain different occupancy patterns. Given that water resources are under increasing pressure and are strongly regulated within the Grampians National Park, this may present a conservation challenge to water managers in this location.     

American pika in a low‐elevation lava landscape: expanding the known distribution of a temperature‐sensitive species

In 2010, the American pika (Ochotona princeps fenisex) was denied federal protection based on limited evidence of persistence in low‐elevation environments. Studies in nonalpine areas have been limited to relatively few environments, and it is unclear whether patterns observed elsewhere (e.g., Bodie, CA) represent other nonalpine habitats. This study was designed to establish pika presence in a new location, determine distribution within the surveyed area, and evaluate influences of elevation, vegetation, lava complexity, and distance to habitat edge on pika site occupancy. In 2011 and 2012, we conducted surveys for American pika on four distinct subalpine lava flows of Newberry National Volcanic Monument, Oregon, USA. Field surveys were conducted at predetermined locations within lava flows via silent observation and active searching for pika sign. Site habitat characteristics were included as predictors of occupancy in multinomial regression models. Above and belowground temperatures were recorded at a subsample of pika detection sites. Pika were detected in 26% (2011) and 19% (2012) of survey plots. Seventy‐four pika were detected outside survey plot boundaries. Lava complexity was the strongest predictor of pika occurrence, where pika were up to seven times more likely to occur in the most complicated lava formations. Pika were two times more likely to occur with increasing elevation, although they were found at all elevations in the study area. This study expands the known distribution of the species and provides additional evidence for persistence in nonalpine habitats. Results partially support the predictive occupancy model developed for pika at Craters of the Moon National Monument, another lava environment. Characteristics of the lava environment clearly influence pika site occupancy, but habitat variables reported as important in other studies were inconclusive here. Further work is needed to gain a better understanding of the species’ current distribution and ability to persist under future climate conditions.     

The life history and decline of the threatened Australian frog,Litoria raniformis

A popular idea amongst ecologists last century was that animals which exploit dynamic environments often display ‘fast’ life history strategies (high fecundity, rapid growth and maturation, and low or variable adult survival rates) relative to those which occupy more stable environments. Whilst the underlying theory has been discredited, the categorization remains of interest, because species with ‘fast’ life history traits are thought to be more robust to human‐induced environmental change than those with ‘slow’ life history traits. We examined the life history traits of the endangered Australian frog Litoria raniformis, to determine whether it displays ‘fast’ life history traits (like its sister species L. aurea and L. castanea), and to assess the role of these traits in the decline of this species. Mark‐recapture data confirmed that L. raniformis displays rapid growth and maturation. The data also suggest that L. raniformis displays relatively low adult survival rates. We propose that the ‘fast’ life history traits of this species are adaptive to metapopulation dynamics. In turn, we suggest that the rapid decline of L. raniformis may have resulted from metapopulation collapse, driven ultimately by habitat loss, degradation and fragmentation, and proximately by severe stochastic perturbations.     

Fish recruitment in a large,temperate floodplain: the importance of annual flooding,temperature and habitat complexity

1. Large river floodplains are considered key nursery habitats for many species of riverine fish. The lower Volga River floodplains (Russian Federation) are still relatively undisturbed, serving as a suitable model for studying the influence of flooding and temperature on fish recruitment in floodplain rivers. 2. We examined the interannual variability in recruitment success of young‐of‐the‐year (YOY) fish in the lower Volga floodplain in relation to flood pulse characteristics and rising water temperatures in the spring. We sampled four areas with different flooding regimes, in three consecutive years (2006–2008). 3. Extensive areas with a long duration of flooding accommodated high densities of young fish. This suggests that extended inundation improves the recruitment success of river fish. In areas with extensive flooding, the biomass of YOY of most fish species was about three times higher in 2006 and 2007 than in 2008. We hypothesise that low spring temperatures in 2008 may have caused this reduced recruitment and that a flood synchronised with rising temperature enhances recruitment success. 4. Extensive flooding was particularly favourable for species characterised by large body size, delayed maturation, high fecundity and low parental investment, such as pike Esox lucius, roach Rutilus rutilus and ide Leuciscus idus. Gibel carp Carassius gibelio, a species tolerant of high temperature and hypoxia, did particularly well in small waterbodies in the driest parts of the floodplain. 5. Structural characteristics of floodplain waterbodies explained much of YOY fish density. These species–environment associations varied from year to year, but some species such as common bream Abramis brama, roach and gibel carp showed consistent relationships with structural habitat characteristics in all years, despite large interannual fluctuations in flood pulse and spring temperature.     

Effects of Tamarix removal on the community dynamics of riparian birds in a semiarid grassland

Invasion of riparian habitats by non‐native plants is a global problem that requires an understanding of community‐level responses by native plants and animals. In the Great Plains, resource managers have initiated efforts to control the eastward incursion of Tamarix as a non‐native bottomland plant (Tamarix ramosissima) along the Cimarron River in southwestern Kansas, United States. To understand how native avifauna interact with non‐native plants, we studied the effects of Tamarix removal on riparian bird communities. We compared avian site occupancy of three foraging guilds, abundance of four nesting guilds, and assessed community dynamics with dynamic, multiseason occupancy models across three replicated treatments. Community parameters were estimated for Tamarix‐dominated sites (untreated), Tamarix‐removal sites (treated), and reference sites with native cottonwood sites (Populus deltoides). Estimates of initial occupancy (ψ₂₀₀₆) for the ground‐to‐shrub foraging guild tended to be highest at Tamarix‐dominated sites, while initial occupancy of the upper‐canopy foraging and mid‐canopy foraging guilds were highest in the treated and reference sites, respectively. Estimates of relative abundance for four nesting guilds indicated that the reference habitat supported the highest relative abundance of birds overall, although the untreated habitat had higher abundance of shrub‐nesters than treated or reference habitats. Riparian sites where invasive Tamarix is dominant in the Great Plains can provide nesting habitat for some native bird species, with avian abundance and diversity that are comparable to remnant riparian sites with native vegetation. Moreover, presence of some native vegetation in Tamarix‐dominated and Tamarix‐removal sites may increase abundance of riparian birds such as cavity‐nesters. Overall, our study demonstrates that Tamarix may substitute for native flora in providing nesting habitat for riparian birds at the eastern edge of its North American range.     

Contrasting habitat use of morphologically similar bat species with differing conservation status in south‐eastern Australia

The east‐coast free‐tailed bat Mormopterus norfolkensis Gray, 1839 is a threatened insectivorous bat that is poorly known and as such conservation management strategies are only broadly prescribed. Insectivorous bats that use human‐modified landscapes are often adapted to foraging in open microhabitats. However, few studies have explored whether open‐adapted bats select landscapes with more of these microhabitat features. We compared three morphologically similar and sympatric, molossid bats (genus Mormopterus) with different conservation status in terms of their association with vegetation, climate, landform and land‐use attributes at landscape and local habitat element scales. We predicted that these species would use similar landscape types, with semi‐cleared and low density urban landscapes used more than forested and heavily cleared landscapes. Additionally, we explored which environmental variables best explained the occurrence of each species by constructing post‐hoc models and habitat suitability maps. Contrary to predictions, we found that the three species varied in their habitat use with no one landscape type used more extensively than other types. Overall, M. norfolkensis was more likely to occur in low‐lying, non‐urban, riparian habitats with little vegetation cover. Mormopterus species 2 occupied similar habitats, but was more tolerant of urban landscapes. In contrast, Mormopterus species 4 occurred more often in cleared than forested landscapes, particularly dry landscapes with little vegetation cover. The extensive use of coastal floodplains by the threatened M. norfolkensis is significant because these habitats are under increasing pressure from human land‐uses and the predicted increase in urbanization is likely to further reduce the amount of suitable habitat.     

Preliminary evidence for a two‐for‐one deal: Wetland restoration for a threatened frog may benefit a threatened bat

Habitat restoration is an integral feature of wildlife conservation. However, funding and opportunities for habitat restoration are limited, and therefore, it is useful for targeted restoration to provide positive outcomes for non‐target species. Here, we investigate the possibility of habitat creation and management benefitting two threatened wetland specialists: the Green and Golden Bell Frog (Litoria aurea) and the Large‐footed Myotis (Myotis macropus). This study involved two components: (i) assessing co‐occurrence patterns of these species in a wetland complex created for the Green and Golden Bell Frog (n = 9) using counts, and (ii) comparing foraging activity of Large‐footed Myotis in wetlands with low and high aquatic vegetation (n = 6 and 7, respectively) using echolocation metres. Since Large‐footed Myotis possesses a unique foraging behaviour of trawling for aquatic prey, we hypothesised that foraging activity of this species would be higher in wetlands with low aquatic vegetation coverage. Additionally, we provide observations of its potential prey items. We identified one created wetland where both species were found in relatively high numbers, and this wetland had a permanent hydrology, was free of the introduced fish Gambusia (Gambusia holbrooki) and had low aquatic vegetation coverage. We also found that Myotis feeding activity was significantly higher in low aquatic vegetation coverage wetlands (x? = 65.72 ± 27.56 SE) compared to high (x? = 0.33 ± 0.33 SE, P = 0.0000). Although this is a preliminary study, it seems likely that Green and Golden Bell Frog and Large‐footed Myotis would gain mutual benefit from wetlands that are constructed to be permanent, that are Gambusia free, low in aquatic vegetation coverage, and are located in close to suitable roosting habitat for Large‐footed Myotis. We encourage adaptive aquatic vegetation removal for Green and Golden Bell frog as this may have benefits for Large‐footed Myotis. The evidence suggests that the former may be a suitable umbrella species for the latter.     

Fire,landscape change and models of small mammal habitat suitability at multiple spatial scales

Fire is an important process in many ecosystems, but inappropriate fire regimes can adversely affect biodiversity. We identified a naturally flammable heathy woodland ecosystem where the use of planned fire had increased the extent of older vegetation, and quantified the abundance of two small native mammals in this landscape (silky mouse Pseudomys apodemoides and heath rat P. shortridgei). We defined four time‐since‐fire (TSF) categories representing a 2‐ to 55‐year post‐fire sequence and, on the basis of a habitat accommodation model, predicted that both species would select younger age‐classes over older ones. We also predicted that (i) much of the variance in vegetation structure would remain unexplained by TSF and (ii) statistical models of mammal abundance and occupancy including structural variables as predictors would be better than models including TSF. Pseudomys apodemoides selected 17‐ to 23‐year‐old sites, while there was no evidence that P. shortridgei selected a particular TSF category, findings that were inconsistent with our predictions. In line with our predictions, relatively large portions of the variance in vegetation structure remained unexplained by TSF (adjustedr² for four structural variables: 0.24, 0.29, 0.35 and 0.57), and in three of four cases there was strong evidence that statistical models of mammal abundance and occupancy including structural variables were better than those including TSF. At the site scale (hectares), P. shortridgei abundance was positively related to the cover of dead material at the base of Xanthorrhoea plants and at the trap scale (metres), the trapability of both species was significantly related to vegetation volume at 0–20 cm. Our findings suggest that TSF may not be a good proxy for either vegetation structure or species abundance/occupancy.     

Management of calcareous grasslands for Nickerl’s fritillary (<Emphasis Type="Italic">Melitaea aurelia</Emphasis>) has to consider habitat requirements of the immature stages,isolation, and patch area

We analysed the habitat preferences of adult stages and oviposition electivity of Melitaea aurelia in calcareous grasslands in the Diemel Valley (central Germany) to assess the key factors for successful management. Egg-laying and adult habitats of M. aurelia were more or less congruent. Oviposition electivity at the host plant (Plantago media) was best explained by a combination of host plant quantity and vegetation structure. Habitat quality, isolation and patch area explained 86% of the current patch occupancy of M. aurelia. With M. aurelia preferentially inhabiting transitional vegetation types, management requires a balance between abandonment and disturbance. Disturbances provide open soil that facilitates germination of the host plant Plantago media. On the other hand, immature and adult stages of M. aurelia perform best on calcareous grasslands with a high amount of host plants and low disturbance intensity. Traditional rough grazing regimes seem to be the most favourable tool for developing the necessary spatial and temporal heterogeneity in patches. The best results may be achieved by rotational grazing where only a subset of inhabited patches is grazed intensively each year. Our analysis of patch occupancy indicates that it would be desirable to restore patches in close proximity to occupied sites.     

Crossing the Tasman Sea: Inferring the introduction history of Litoria aurea and Litoria raniformis (Anura: Hylidae) from Australia into New Zealand

Abstract The amphibian fauna of New Zealand consists of three native species (Leiopelma spp.), and three Litoria species introduced from Australia in the last 140 years. We conducted a molecular phylogeographical study that aimed to identify the Australian origins of two species, Litoria aurea and Litoria raniformis. We used partial sequences of the mitochondrial cytochrome oxidase I (cox1) gene from 59 specimens sampled from across the range of both species to identify the probable source populations for the New Zealand introductions, and to describe the current genetic diversity among New Zealand Litoria populations. Our genetic data suggest that L. aurea was introduced into the North Island of New Zealand from two regions in Australia, once from the northern part of coastal New South Wales and once from the southern part of coastal New South Wales. Our data indicate that L. raniformis introductions originated from the Melbourne region of southern Victoria and once established in the South Island of New Zealand, the species subsequently spread throughout both islands. In addition, we found a distinct haplotype in L. raniformis from Tasmania that strongly suggests, contrary to earlier reports, that this species was not introduced into New Zealand from Tasmania. Finally, we identified two very distinctive mitochondrial lineages of L. raniformis within the mainland Australia distribution, which may be previously unrecognized species.     

The importance of aquatic vegetation in beaver diets and the seasonal and habitat specificity of aquatic‐terrestrial ecosystem linkages in a subarctic environment

The extent and ecological significance of trophic linkages across ecosystem boundaries have been the subject of considerable recent research attention. North American beavers Castor canadensis engineer terrestrial influences in aquatic ecosystems by constructing terrestrial food caches near their lodges and aquatic influences in terrestrial ecosystems by building dams and flooding low lying areas. However, it is poorly resolved to what extent beavers rely on aquatic food sources and whether this reliance is greater during winter when ice cover physically confines beavers to aquatic habitats or during summer when warm, ice free water promotes the growth and accessibility of aquatic vegetation. Working in a subarctic region, we surveyed the abundance of aquatic and terrestrial food sources in and around lotic and lentic environments and estimated their contributions to beaver diets during open water and ice covered periods using carbon and nitrogen stable isotope analysis of hair samples. Ponds had four times more aquatic vegetation than streams, but terrestrial habitats around ponds had less than half as much shrub cover as habitats adjacent to streams. Beaver diets in this subarctic environment are estimated to be comprised of 60 to 80% aquatic vegetation, with beavers occupying ponds consuming more aquatic vegetation in winter than beavers occupying streams, which rely more on terrestrial shrubs cached near their lodge. Collectively, these results show how the influence of physical barriers on ecosystem linkages can be modified by habitat‐ and season‐specific abundances of preferred resources and the potential for animals to consume food in ecosystems and seasons different from where and when the food was harvested.     

What predicts the use by brook trout (Salvelinus fontinalis) of terrestrial invertebrate subsidies in headwater streams?

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Characteristics of Golden‐winged Warbler territories in plant communities associated with regenerating forest and abandoned agricultural fields

In the Appalachian portion of their breeding range, Golden‐winged Warblers (Vermivora chrysoptera) nest in shrubland and regenerating forest communities created and maintained by disturbance. Because populations of Golden‐winged Warblers have exhibited precipitous declines in population throughout their Appalachian breeding range, management activities that create or maintain early successional habitat are a priority for many natural resource agencies and their conservation partners. Within these early successional habitats, however, additional information is still needed concerning the relative importance of different vegetation features in selection of breeding territories by Golden‐winged Warblers. Our objective, therefore, was to use logistic regression to estimate the probability of territory‐level occupancy by Golden‐winged Warblers in north‐central Pennsylvania at two sites, each with its own early successional community, based on vegetation characteristics. Our communities were composed of shrublands and regenerating forest sites resulting from two disturbances: agriculture and forest fire. Despite differences in vegetation structure, portions of both study areas (regenerating forest and old field) supported territorial Golden‐winged Warblers. Probability of territory occupancy by Golden‐winged Warblers increased with percent blackberry (Rubus) cover in the regenerating forest community, and decreased as basal area and distance to microedge increased (i.e., as vegetation patchiness decreased) in both communities. These habitat features have also been found to influence other aspects of Golden‐winged Warbler breeding ecology such as nest‐site selection, pairing success, and territory abundance. Vegetation features influencing Golden‐winged Warbler territory establishment can differ among shrubland and regenerating forest communities, and management decisions and outcomes may be affected by these differences. Our study provides a starting point for a more comprehensive hypothesis‐driven occupancy survey to investigate features of the territories of Golden‐winged Warblers across a broader geographic range and in different vegetation communities.     

The social elite: Habitat heterogeneity,complexity and quality in granite inselbergs influence patterns of aggregation in Egernia striolata (Lygosominae: Scincidae)

Habitat heterogeneity, structural complexity and habitat quality are key features of the environment that drive species' distribution and patterns of biological organization. Traditionally, pattern‐based studies have focused on faunal responses to biological systems. However, the influence of non‐biological environments such as insular rock outcrops on patterns of vertebrate distribution is conceivably as important, but has received less attention. Granite inselbergs are a naturally heterogeneous and spatially‐limited habitat. As such, they provide an opportunity for investigating whether environmental attributes influence social behaviour in animals that use these kinds of habitat, particularly lizards that are well adapted to saxicoline environments. We applied ecological theory to investigate the influence of habitat heterogeneity, structural complexity and habitat quality on patterns of home‐site occupancy in the crevice skink Egernia striolata (Lygosominea: Scincidae) from insular granite outcrops located within fragmented agricultural landscapes. We compared home‐site occupancy among solitary juveniles, solitary adults and lizard aggregations. We found significant differences in home‐site occupancy between aggregations and solitary lizard outcrop attributes measured at multiple spatial scales. The probability of a home‐site being occupied by an aggregation increased where large rock masses were present, on northern aspects near the core of the outcrop and in structurally variegated landscapes. Significantly more aggregations occupied home‐sites surrounded by high boulder cover and crevice microhabitat. We provide evidence that geophysical attributes of granite inselbergs and landscape context can influence patterns of lizard aggregation. Thus, we clearly document the environmental correlations of variability in sociality among subpopulations of Egernia striolata.