Key Habitat Features Research Articles

Influence of environmental parameters on movements and habitat utilization of humpback whales (Megaptera novaeangliae) in the Madagascar breeding ground.

Assessing the movement patterns and key habitat features of breeding humpback whales is a prerequisite for the conservation management of this philopatric species. To investigate the interactions between humpback whale movements and environmental conditions off Madagascar, we deployed 25 satellite tags in the northeast and southwest coast of Madagascar. For each recorded position, we collated estimates of environmental variables and computed two behavioural metrics: behavioural state of ‘transiting’ (consistent/directional) versus ‘localized’ (variable/non-directional), and active swimming speed (i.e. speed relative to the current). On coastal habitats (i.e. bathymetry < 200 m and in adjacent areas), females showed localized behaviour in deep waters (191 ± 20 m) and at large distances (14 ± 0.6 km) from shore, suggesting that their breeding habitat extends beyond the shallowest waters available close to the coastline. Males' active swimming speed decreased in shallow waters, but environmental parameters did not influence their likelihood to exhibit localized movements, which was probably dominated by social factors instead. In oceanic habitats, both males and females showed localized behaviours in shallow waters and favoured high chlorophyll-a concentrations. Active swimming speed accounts for a large proportion of observed movement speed; however, breeding humpback whales probably exploit prevailing ocean currents to maximize displacement. This study provides evidence that coastal areas, generally subject to strong human pressure, remain the core habitat of humpback whales off Madagascar. Our results expand the knowledge of humpback whale habitat use in oceanic habitat and response to variability of environmental factors such as oceanic current and chlorophyll level.

Forty years of seagrass population stability and resilience in an urbanizing estuary

Summary Coasts and estuaries contain among the most productive and ecologically important habitats in the world and face intense pressure from current and projected human activities, including coastal development. Seagrasses are a key habitat feature in many estuaries perceived to be in widespread decline owing to human actions. We use spatio‐temporal models and a 41‐year time series from 100s of km of shoreline which includes over 160 000 observations from Puget Sound, Washington, USA, to examine multiscale trends and drivers of eelgrass (Zostera spp.) change in an urbanizing estuary. At whole estuary scale (100s of km), we find a stable and resilient eelgrass population despite a more than doubling of human population density and multiple major climactic stressors (e.g. ENSO events) over the period. However, the aggregate trend is not reflected at the site scale (10s of km), where some sites persistently increase while others decline. Site trends were spatially asynchronous; adjacent sites sometimes exhibited opposite trends over the same period. Substantial change in eelgrass occurred at the subsite (0·1 km) scale, including both complete local loss and dramatic increase of eelgrass. Metrics of local human development including shoreline armouring, upland development (imperviousness) and human density provide no explanatory power for eelgrass population change at any spatial scale. Our results suggest that the appropriate scale for understanding eelgrass change is smaller than typically assumed (approximately 1‐ to 3‐km scale) and contrasts strongly with previous work. Synthesis. Despite ongoing conservation concern over seagrasses world‐wide, eelgrass in Puget Sound has been highly resilient to both anthropogenic and environmental change over four decades. Our work provides general methods that can be applied to understand spatial and temporal scales of change and can be used to assess hypothesized drivers of change.

Under ice habitats for Antarctic krill larvae: Could less mean more under climate warming?

AbstractOverwintering of larvae underneath Antarctic pack ice is a critical stage in the life cycle of Antarctic krill. However, there are no circumpolar assessments of available habitat for larval krill, making it difficult to evaluate how climate change may impact this life stage. We use outputs from a circumpolar sea ice model, together with a set of simple assumptions regarding key habitat features, to identify possible regions of larval krill habitat around Antarctica during winter. We assume that the location and suitability of habitat is determined by both food availability and three‐dimensional complexity of the sea ice. A comparison of the combined area of these regions under current conditions with a warm climate scenario indicates that while total areal sea ice extent decreases, there is a consistently larger area of potential larval krill habitat under warm conditions. These findings suggest that decreases in sea ice extent may not necessarily be detrimental for krill populations.

Persistence in the longitudinal distribution of lotic insects in a changing climate: a tale of two rivers

The longitudinal distribution of many taxa in rivers is influenced by temperature. Here we took advantage of two older datasets on net-spinning caddisflies (Hydropsychidae) from contrasting European rivers to assess changes in species occurrence and relative abundance along the river by resampling the same sites, postulating that an increase in river temperature over the intervening period should have resulted in cool-adapted species retreating into the headwaters and warm adapted species expanding upstream. Distributional changes in the Welsh Usk were slight between 1968/69 and 2010, one rare species appearing at a single headwater site and one warm-adapted species disappearing from the main river. Distributional changes in the French Loire, between 1989–93 and 2005, were similarly modest, with no consistent movement of species up- or downstream. We estimate that the decadal rate of increase in the mean summer daily maximum in the Usk was only 0.1°C at one ‘summer cool’ headwater site, while a neighbouring ‘summer warm’ tributary increased by 0.16°C per decade, and the main river by 0.22°C. The Loire is warmer than the Usk and the mean decadal rates of increase, over the period 1989–2005, at three sites along the lower reaches were 0.39, 0.48 and 0.77°C. Increases in stream and river temperature, therefore, were spatially variable and were not associated with consistent upstream movement of species in either of these (very different) rivers. We conclude that either the temperature increases have hitherto been insufficient to affect species distribution or, more speculatively, that it may not be possible for river organisms (that do not respond only to temperature) to move upstream because of a developing spatial mismatch between key habitat characteristics, some of them changing with the climate but others not.

Spontaneous succession on spoil banks supports amphibian diversity and abundance

The ecological value and conservation potential of post-mining areas have been increasingly recognized by scientists and conservationists during recent decades. Especially valuable are sites left to spontaneous succession, which constitute habitats with high species diversity, or habitats that serve as refuges for threatened species. In contrast to several other taxa, there is a lack of such evidence for amphibians, despite the assumption that primary succession leads to a more suitable environment for amphibians than does technical reclamation. Therefore, we compared the effects of technical reclamation and spontaneous succession on amphibian presence, species richness, and abundance of the model species Rana dalmatina in technically reclaimed and unreclaimed sections of spoil banks in the Czech Republic's North Bohemian brown coal basin. We found that most recorded amphibian species, and R. dalmatina in particular, occurred predominantly within successional spoil bank sections. Apart from reclamation status, amphibians preferred partially vegetated ponds (5–75% vegetation cover) having gently sloping shores (<30°) and lower water conductivity. Mean species richness per pond (1.95 vs. 1.20), the proportion of ponds occupied by amphibians (88.5% vs. 69.4%), and the mean numbers of R. dalmatina clutches per pond (9.05 vs. 1.65) were significantly higher at unreclaimed sites compared to technically reclaimed sites. This study confirms the conservation value of post-mining sites for amphibians and evidences that sites left to spontaneous succession provide more suitable habitats for amphibians compared to technically reclaimed sites. Key habitat characteristics driving amphibian assemblages within post-mining sites are identified and guidelines for effective protection of amphibians in post-mining areas are proposed.

An evaluation of rapid methods for monitoring vegetation characteristics of wetland bird habitat

Wetland managers benefit from monitoring data of sufficient precision and accuracy to assess wildlife habitat conditions and to evaluate and learn from past management decisions. For large-scale monitoring programs focused on waterbirds (waterfowl, wading birds, secretive marsh birds, and shorebirds), precision and accuracy of habitat measurements must be balanced with fiscal and logistic constraints. We evaluated a set of protocols for rapid, visual estimates of key waterbird habitat characteristics made from the wetland perimeter against estimates from (1) plots sampled within wetlands, and (2) cover maps made from aerial photographs. Estimated percent cover of annuals and perennials using a perimeter-based protocol fell within 10 percent of plot-based estimates, and percent cover estimates for seven vegetation height classes were within 20 % of plot-based estimates. Perimeter-based estimates of total emergent vegetation cover did not differ significantly from cover map estimates. Post-hoc analyses revealed evidence for observer effects in estimates of annual and perennial covers and vegetation height. Median time required to complete perimeter-based methods was less than 7 percent of the time needed for intensive plot-based methods. Our results show that rapid, perimeter-based assessments, which increase sample size and efficiency, provide vegetation estimates comparable to more intensive methods.

Building an indigenous evidence-base for tribally-led habitat conservation policies

Habitat conservation is a priority for many tribes, and indigenous local experts develop environmental policy goals based on their traditional knowledge of animal habitat use and habitat change. An indigenous evidence-base for ice seal and walrus habitat conservation in the Bering Strait region of Alaska was built by using qualitative methods to document the knowledge of 82 local expert seal and walrus hunters. Local experts produced detailed descriptions of seal and walrus habitat use and drivers of change in key habitat features, as well as policy goals based on indigenous evidence. These indigenous habitat policy goals are compared to U.S. government policies and differences are explored in terms of the indigenous evidence-base.

Long term thinning and logging in Australian cypress pine forest: Changes in habitat attributes and response of fauna

The manipulation of habitat through thinning and logging activities may have cascading effects on fauna because of direct and indirect changes to key habitat features. However, the combined effect of thinning and logging on fauna has not been investigated for Australian forests, despite the widespread use of thinning as a silvicultural management tool in selectively logged forests, and the emerging interest in thinning for biofuels. We therefore surveyed reptiles, birds and key habitat variables at sites selected to sample four management classes reflecting categories of thinning and/or logging activity in cypress pine Callitris glaucophylla forests of the Brigalow Belt bioregion of Australia. Habitat structure and assemblages of reptile and bird species were distinct across the four management classes, reflecting long-term cumulative impacts of small- and/or large-diameter tree removal in a dynamic system, but the response of various functional groups of species was mixed. Recovery of some habitat elements (e.g. small trees) to a state that maintains densities of most fauna species appears to be relatively rapid, but depends on the combined effect of thinning and logging. Other habitat elements, such as large cypress trees which were reduced by logging and unaffected by thinning, require longer time frames to mature and therefore will be critical resources to maintain during future management activities in cypress forests. Overall, it appears that thinning activities affect fauna and therefore must be considered when making decisions about forest management. We suggest management of production forests aims for a mosaic of thinning and/or logging combinations across the landscape, but emphasise the importance of retaining or restoring unthinned and unlogged areas.

Interactive effects of source and recipient habitats on plant invasions: distribution of exotic species in Chile

AbstractAimMost studies on invasibility consider the characteristics of the habitats colonized. However, the success of the establishment of exotic species can be conditioned by the characteristics of the donor communities. In this study, we analyse the extent to which the distribution of exotic herbaceous species in Chile is conditioned either by the climatic characteristics of the recipient area or by the environmental features of the source areas on the Iberian Peninsula.LocationChile and the Iberian Peninsula (Portugal and Spain).MethodsFor Chile, we characterized the exotic species according to their current Chilean distribution and their region of origin. For the Iberian Peninsula, we compiled the floristic composition of 11,702 relevés. We classified each relevé according to key habitat characteristics (bioclimate, soil nutrient status and type of community associated with human activities) and calculated the percentage of species in common with Chile in different climatic regions therein.ResultsOver half of Chile's exotic species exhibited a geographic distribution related to the climate of the recipient area. The main donor communities were those associated with ruderal and arable land habitats, although their importance depended upon the climate in the recipient area. Correspondence was observed between the climatic characteristics of the communities in the source area and those of the recipient areas.Main conclusionsThe results highlight the influence of the characteristics of habitats in the source area on the successful establishment of exotic species in Chile. The relationships between source and recipient area are scale dependent, climate constituting the main driver at broad scale. Within each climatic region, the communities associated with habitats presenting greater anthropic influence act as the main donors. Both features indicate the existence of filters that select species pre‐adapted to the climatic and habitat conditions in the recipient area.

Coastal Wetland Support of Great Lakes Fisheries: Progress from Concept to Quantification

AbstractFishery support is recognized as a valuable ecosystem service provided by aquatic systems, but it is harder to quantify than to describe conceptually. In this paper, we combine data on fish inhabiting Great Lakes coastal wetlands (GLCWs) with information on commercial and recreational harvest and the piscivore forage base to develop quantitative understanding of the multiple species involved in direct and indirect fishery support of this complex fishery. We then examine patterns of species co‐occurrence and life history and relationships to GLCW conditions in order to identify fishery support metrics useful in aggregating species patterns and evaluating management outcomes. Our criteria for wetland prevalence (≥10% occurrence) and fishery importance (≥1% of recreational or commercial harvest in one or more of the Great Lakes or having a major forage fish role) yielded 21 wetland‐using, fishery‐relevant species representing multiple taxonomic groups and life history attributes. Wetland‐using species are estimated to make up half the biomass and 60% of the dollar value of the fish landed commercially and ∼80% of the fish numbers harvested recreationally. All of the GLCWs studied supported species of interest to recreational and commercial fishers but with widely varying composition. A few key habitat characteristics (e.g., vegetation structure) are broadly predictive of the types of sport and panfish present, with more degraded GLCWs generally supporting abundant but lower‐value taxa (rough‐fish species) and less degraded GLCWs supporting fewer but higher‐value taxa (sport and panfish species). No single taxonomic or functional metric seems adequate to capture the diversity of fishery‐relevant species supported by GLCWs; fishery support needs to be understood and managed in a multimetric context.Received May 16, 2014; accepted October 15, 2014

Cavity characteristics, but not habitat, influence nest survival of cavity-nesting birds along a gradient of human impact in the subtropical Atlantic Forest

Cavity-nesting vertebrates are an important component of biodiversity in tropical and subtropical forests, but their persistence will increasingly depend on remnant trees in logged forest and agricultural areas. To identify key habitat features for conservation, we examined the factors that influenced daily nest survival for a community of cavity-nesting birds along a gradient of human impact, from primary Atlantic Forest through logged forest to farms. We used logistic-exposure models to determine how characteristics of the habitat, nest tree, cavity, and timing influenced daily nest survival. Overall, predation and/or usurpation caused 92% of nest failures. Daily survival rates ranged 0.961–0.992 for five species of birds that could be studied best, giving probabilities of 0.19–0.62 of survival from laying to fledging. The top models predicting nest survival included cavity and tree characteristics but no habitat variables (canopy cover, forest condition, or distance to forest edge). Small birds (12–128g) experienced higher nest survival in cavities with smaller entrance diameters, higher above the ground. Large birds (141–400g) experienced higher nest survival in living trees than in dead trees. Birds experienced similar nest survival in primary forest, logged forest, and farms. Our results highlight the conservation value of cavity-bearing trees in anthropogenic habitats. A pressing policy issue for tropical and subtropical forests is to move beyond minimum diameter cutting limits and instead focus on retention of large old trees.

Riders on the Storm: Selective Tidal Movements Facilitate the Spawning Migration of Threatened Delta Smelt in the San Francisco Estuary

Migration strategies in estuarine fishes typically include behavioral adaptations for reducing energetic costs and mortality during travel to optimize reproductive success. The influence of tidal currents and water turbidity on individual movement behavior were investigated during the spawning migration of the threatened delta smelt, Hypomesus transpacificus, in the northern San Francisco Estuary, California, USA. Water current velocities and turbidity levels were measured concurrently with delta smelt occurrence at sites in the lower Sacramento River and San Joaquin River as turbidity increased due to first-flush winter rainstorms in January and December 2010. The presence/absence of fish at the shoal-channel interface and near the shoreline was quantified hourly over complete tidal cycles. Delta smelt were caught consistently at the shoal-channel interface during flood tides and near the shoreline during ebb tides in the turbid Sacramento River, but were rare in the clearer San Joaquin River. The apparent selective tidal movements by delta smelt would facilitate either maintaining position or moving upriver on flood tides, and minimizing advection down-estuary on ebb tides. These movements also may reflect responses to lateral gradients in water turbidity created by temporal lags in tidal velocities between the near-shore and mid-channel habitats. This migration strategy can minimize the energy spent swimming against strong river and tidal currents, as well as predation risks by remaining in turbid water. Selection pressure on individuals to remain in turbid water may underlie population-level observations suggesting that turbidity is a key habitat feature and cue initiating the delta smelt spawning migration.

Identifying the key habitat characteristics of threatened European mudminnow (Umbra krameri, Walbaum 1792)

Identifying the key habitat characteristics of threatened European mudminnow (Umbra krameri, Walbaum 1792)

Habitat use and selection of black scoters in southern New England and siting of offshore wind energy facilities

ABSTRACTThe southern New England continental shelf is an important region for black scoters (Melanitta americana) during winter and migratory staging periods and a priority area for developing offshore wind energy facilities. However, little is known about the migration phenology and habitat use of black scoters in this portion of their range and this information is necessary to assess potential risks to black scoters during the marine spatial planning process. In this regional black scoter study over 2 winters, we used satellite telemetry and spatial modeling techniques to estimate migratory timing and length of stay, quantify winter home range size and site fidelity between winters, examine key habitat characteristics associated with core‐use areas, and map relative probabilities of use across a 3,800‐km2 marine spatial planning area for 2 proposed offshore renewable energy facilities. Black scoters spent nearly 5 months in southern New England, with wide variation among individuals in the size of winter utilization distributions (range 16–12,367 km2). Approximately 50% of the tagged birds returned to southern New England during the subsequent winter and had variable fidelity to core‐use areas occupied the previous winter. During both winters, black scoter core‐use areas were located closer to shore, at shallower water depths, with coarser sediment grain size and higher probability of hard‐bottom occurrence relative to available areas. Resource selection functions classified the majority of a nearshore 5‐turbine, 34‐km2 renewable energy zone off Block Island as high probability of use by black scoters, whereas an offshore 200‐turbine, 667‐km2 federal lease block zone was classified as low to medium‐low probability of selection. Wind energy facilities, such as the Block Island site, constructed in relatively shallow (&lt;20 m deep), nearshore habitats (&lt;5 km) over hard‐bottomed or coarse‐sand substrate could displace some foraging black scoters wintering in this region, whereas the larger federal lease block zone located farther offshore is more likely to affect scoters dispersing among core‐use areas and during migration between wintering and breeding grounds. © 2014 The Wildlife Society.

Resource selection and space use by sea ducks during the non-breeding season: Implications for habitat conservation planning in urbanized estuaries

Wide-ranging marine birds rely on multiple habitats for wintering, breeding, and migrating, and their conservation may be dependent on protecting networks of key areas. Urbanized estuaries are critical wintering and stopover areas for many declining sea ducks in North America; however, conservation measures within estuaries are difficult to establish given lack of knowledge about habitat use by these species and the variety of competing human interests. We applied hierarchical modeling to evaluate resource selection of sea ducks (surf scoters, Melanitta perspicillata) wintering in San Francisco Bay, California, USA, a large and highly urbanized estuary. We also examined their distribution, home range, and movements with respect to key habitat features and regions within the estuary. Herring roe was the strongest predictor of bird locations; however, eelgrass, water depth and salinity were also highly-ranked, with sea ducks using deeper areas of higher salinity associated with herring roe and eelgrass presence during mid-winter. Sea ducks were also strongly associated with ferry routes, suggesting these areas may contain resources that are too important to avoid and emphasizing the need to better understand water traffic effects. Movements and home range size differed between males and females in early winter but became more similar in late winter. Birds traveled farther and used several sub-bays in early winter compared to mid-winter when herring roe availability peaked in the Central Bay. Our findings identified key environmental variables, highlighted core use areas, and documented critical periods for consideration when developing conservation plans for sea ducks in urbanized estuaries.

Key features for saproxylic beetle diversity derived from rapid habitat assessment in temperate forests

Managing and monitoring forest biodiversity is challenging and rapid habitat assessment protocols should be developed to provide us with general key features based on field data.A rapid habitat assessment protocol was implemented over a wide forest gradient in France to analyze surrogacy patterns and performance consistency of presumed key attributes for saproxylic beetle diversity (large trees, microhabitat-bearing trees with trunk cavities, fruiting bodies of saproxylic fungi, tree crown deadwood and sap runs, large logs and snags) and of stand openness. Data compiled in this study include standardized deadwood and window-flight trapped beetle data from 313 plots in oak, lowland and highland beech, lowland pine, highland spruce–fir and mixed temperate forests throughout France.The most structuring factors for species richness and composition of saproxylic beetles were the density of cavity- or fungus-bearing trees and of snags, as well as the degree of openness in the 1-ha surrounding the stand. These key habitat features were nevertheless inconsistent over the different types of temperate forests, and for rare species vs. all species combined. No one variable robustly explained variations in species richness in the deciduous or conifer forest types.The influence of deadwood and “habitat trees” was affected by meso- and micro-climatic features. A significant effect of stand openness on saproxylic beetles was observed both in deciduous and in conifer forests, but only in lowlands. Effects on species richness due to an interaction between substrate availability and openness were observed in montane forests only.Our results point toward the relevance of ecological attributes in tracking changes in saproxylic beetle biodiversity in specific forest contexts, but our study failed to identify any universal structural biodiversity indicators which could be surveyed in part with data from national forest inventories and used to track progress in sustainable forest management or in the protection of sensitive areas.

In search of the best local habitat drivers for saproxylic beetle diversity in temperate deciduous forests

Deadwood-associated species are increasingly targeted in forest biodiversity conservation. In order to improve structural biodiversity indicators and sustainable management guidelines, we need to elucidate ecological and anthropogenic drivers of saproxylic diversity. Herein we aim to disentangle the effects of local habitat attributes which presumably drive saproxylic beetle communities in temperate lowland deciduous forests. We collected data on saproxylic beetles in 104 oak and 49 beech stands in seven French lowland forests and used deadwood, microhabitat and stand features (large trees, openness) as predictor variables to describe local forest conditions. Deadwood diversity and stand openness were consistent key habitat features for species richness and composition in deciduous forests. Large downed deadwood volume was a significant predictor of beetle species richness in oak forests only. In addition, the density of cavity- and fungus-bearing trees had weak but significant effects. We recommend that forest managers favor the local diversification of deadwood types, especially the number of combinations of deadwood positions and tree species, the retention of large downed deadwood and microhabitat-bearing trees in order to maximize the saproxylic beetle diversity at the stand scale in deciduous forests. To improve our understanding of deadwood-biodiversity relationships, further research should be based on targeted surveys on species-microhabitat relationships and should investigate the role of landscape-scale deadwood resources and of historical gaps in continuity of key features availability at the local scale.

Ecosystem-level dynamics of soil-vegetation features, with implications for conserving a narrowly endemic reptile

Narrow endemism presents challenges to species occurrence modeling particularly when the distribution of key local habitat features changes across space and time as a function of processes operating at larger scales. One need facing conservation in such settings is a better understanding of the biogeographic dynamics of the larger features that govern occurrence of critical local habitat. The Mescalero–Monahans shinnery sands region of western North America is a dynamic landscape where sand shinnery oak interacts with wind-driven sand to establish dune habitat. This ecosystem supports several narrowly endemic dune-dwelling species including the dunes sagebrush lizard. Using near-anniversary satellite and aerial imagery from 1986, 1998, and 2011, we integrated object-based image classification and statistical analysis to develop and validate a spatially explicit estimate of the sand shinnery oak ecosystem, including dynamics associated with its attrition and emergence, at high resolution throughout an 89,849-km2 study area encompassing the range of the dunes sagebrush lizard. The spatial estimate of the distribution and extent of the sand shinnery oak soil-vegetation association validated reasonably well (overall accuracy = 0.79; sensitivity = 0.49; specificity = 0.91) and showed that the association declined 10.3 % in extent during the 25-year assessment window. The presence of sand shinnery oak, patch size, and patch isolation were dynamic across space and time; a regression model showed that smaller, isolated patches on the periphery of the system were more likely to be lost over time whereas larger, less isolated, and centrally distributed patches were more likely to persist or expand. This study details broadly applicable methods to accurately delineate landforms throughout large extents, and offers mapping tools specific to issues surrounding Mescalero–Monahans shinnery sands endemics that are readily amenable to testing, refinement, and application in efforts to focus sustainable landscape management including conservation of endemic species.

Physicochemical assessment of Unio crassus habitat quality in a small upland stream and implications for conservation

The abundance of Unio crassus (Philipsson 1788) has declined over the last decades. Despite the high conservation status of this species, knowledge on its ecological requirements is scarce. The objective of this study was to identify key habitat characteristics in areas with recent recruitment of U. crassus in a small upland stream. Furthermore, we investigated stretches where the species is presently absent. Sediment deposition, redox potential, flow velocity, water depth, nitrogen and phosphorus load were investigated. Fine sediment deposition was high with 19.4 kg m−2 month−1 at colonized and 13.3 kg m−2 month−1 at non-colonized stretches of the Sallingbach. At all study stretches, redox potentials in the interstitial zone varied around 300 mV which constitutes the boundary value between oxic and anoxic conditions. Results of chemical water analyses indicated high nitrogen loads. Nitrate nitrogen concentrations averaged between 4.1 and 6.5 mg NO3–N/l at all study stretches, significantly exceeding the currently proposed threshold value of 2.0 mg/l for functional U. crassus streams. The results in this study suggest that U. crassus is more tolerant to eutrophic habitat conditions than previously expected. Our findings show that currently considered physicochemical parameters and high fine sediment deposition cannot mechanistically explain the occurrence of U. crassus in the stream.

Spatial prediction of brushtail possum (Trichosurus vulpecula) distribution using a combination of remotely sensed and field-observed environmental data

Context In New Zealand, the introduced brushtail possum, Trichosurus vulpecula, is a reservoir of bovine tuberculosis and as such poses a major threat to the livestock industry. Aerial 1080 poisoning is an important tool for possum control but is expensive, creating an ongoing need for ever more cost-effective ways of using this technique. Aims To develop geographic information system (GIS) models to better predict spatial variation in the distribution of unmanaged possum populations, to facilitate better targeting of control activities. Methods Relative abundance of possums and their distribution among habitat types were surveyed in a dry high-country area of the northern South Island. Two GIS-based models were developed to predict the relative abundance of possums on trap lines. The first model used remotely sensed (digital) environmental data; the second complemented the remotely sensed data with fine-scale habitat and topographic data collected on the ground. Key results Digital environmental factors and habitat features proved to be key predictors of relative possum abundance. In both GIS models, height above valley floor, presence of forest cover and mean annual temperature were the strongest predictors. Conclusions Predictive maps (projections) of relative possum abundance produced from these models can provide useful decision-support tools for pest-control managers, by enabling possum control to be targeted spatially. Implications Spatially targeted pest control could allow effective control activities for invasive species or disease vectors to be applied at a lower cost for the same benefit.