Dynamics and trophic interactions of small rodents: landscape or regional effects on spatial variation?

Geographically varying rodent dynamics may be due to specific landscape effects or to regional variation. Two common vole species (Clethrionomys glareolus and Microtus agrestis), their main predators and their impact on some important food items were monitored in Sweden on forest clearcuts in two different landscape types, situated in two different regions with different climatic conditions. Censuses, with 10-16 clearcuts in each landscape and both landscapes in the two regions, were designed to permit analyses of variance of the effects of landscape composition and region on dynamics and species interactions. Region had a far greater influence than landscape on vole numbers, on the proportions of generalist and specialist predators and on the winter browsing of bark of indigenous and experimental woody plants as well on seed consumption in experimental supplies. The findings indicated an influence of the depth and quality of the snow cover on the predation rates by generalist and specialist predators. However, there were also clear signs of food limitation in the snow-rich areas. Such areas had fewer generalist predators, which probably meant less directly density-dependent predation. Thus, lack of high-quality food may put a brake on population growth in climatically harsh regions, permitting increasing populations of specialist predators such as small mustelids to subsequently over-utilise their main prey and potentially cause prolonged low densities. Snow conditions may affect numbers and interactions both within habitats, landscapes and regions. Thus, to more fully understand rodent dynamics, small-scale movements and interactions of individuals in relation to the main large-scale factor(s) of various regions need to be examined.     

Habitat quality and population density drive occupancy dynamics of snowshoe hare in variegated landscapes

The influence of habitat quality and population density on occupancy dynamics may surpass that of traditional metrics of area and isolation, but often this is not considered explicitly in studies of spatially structured populations. In landscapes that are not easily characterized as binary habitat/non‐habitat (e.g. variegated landscapes), this influence may be even more important and occur at both local and landscape levels. It follows that occupancy dynamics may be driven by disparate processes depending on how extinction or colonization relate to habitat quality and population density. We examined the relative influence of area, structural isolation, habitat quality, local population density, and neighborhood population density (i.e. population density in the landscape around a site) on the probability of extinction and colonization of snowshoe hare Lepus americanus across an expansive forest mosaic landscape (encompassing the northern third of Idaho). Habitat quality and population density were highly influential in determining extinction and colonization, whereas patch area and isolation were much less important. Sites with heavier vegetative cover at the site or landscape‐level were more likely to be colonized and less likely to go extinct, and sites with greater local population density in the previous time step had lower probability of extinction. Sites embedded in high density neighborhoods also were less likely to go extinct, but not more likely to be colonized. We found a significant interaction between local and neighborhood population density on extinction in 1 yr, suggesting that the strength of demographic rescue may vary dependent on local site densities. Our results add to a growing literature showing that factors outside of structural metrics of area and isolation are important drivers of occupancy dynamics. Given the multi‐scaled influence of habitat quality and population density on occupancy dynamics, our work also indicates that research on snowshoe hare must extend beyond simply assessing local factors to understand the spatial dynamics of populations.     

The influence of landscape structure on occurrence, abundance and genetic diversity of the common frog, Rana temporaria

Human‐caused habitat destruction and modification constitute one of the largest threats to population persistence and biodiversity, and are also suspected to be the major cause behind the global decline of amphibian populations. We assessed the potential role of agriculture‐related habitat fragmentation on population size and genetic variability in the common frog (Rana temporaria) by recording the occurrence, population density and genetic diversity in three geographically disparate regions in Sweden – each containing landscapes of high and low agricultural activity – and related these to landscape variables extracted from digital maps. We found a highly significant region‐by‐landscape interaction in occurrence, population density and genetic diversity revealing a reversed response to agriculture from south to north: while the effects of agriculture on R. temporaria populations were negative in the south, there were no effects in the central region, whereas positive effects were observed in the north. Spatial autocorrelation analyses of genetic data revealed that populations in high agricultural activity areas were more isolated than populations in low activity areas both in the southern and central regions of Sweden. Landscape diversity showed a strong positive correlation with both density and occurrence of frogs in Sweden as a whole, as well as in the southern region. Also, negative effects of roads and positive effects of ditches on genetic diversity were found in the south. Overall, these results suggest clear but regionally opposite effects of habitat structure on the population size and genetic diversity of amphibian populations. This means that the management strategy aiming to maximize the size and genetic diversity of local common frog populations, and perhaps also those of other amphibian populations, should account for regional differences in existing land‐use patterns.     

Agricultural intensification alters marbled newt genetic diversity and gene flow through density and dispersal reduction

Recent agricultural intensification threatens global biodiversity with amphibians being one of the most impacted groups. Because of their biphasic life cycle, amphibians are particularly vulnerable to habitat loss and fragmentation that often result in small, isolated populations and loss of genetic diversity. Here, we studied how landscape heterogeneity affects genetic diversity, gene flow and demographic parameters in the marbled newt, Triturus marmoratus, over a hedgerow network landscape in Western France. While the northern part of the study area consists of preserved hedged farmland, the southern part was more profoundly converted for intensive arable crops production after WWII. Based on 67 sampled ponds and 10 microsatellite loci, we characterized regional population genetic structure and evaluated the correlation between landscape variables and (i) local genetic diversity using mixed models and (ii) genetic distance using multiple regression methods and commonality analysis. We identified a single genetic population characterized by a spatially heterogeneous isolation-by-distance pattern. Pond density in the surrounding landscape positively affected local genetic diversity while arable crop land cover negatively affected gene flow and connectivity. We used demographic inferences to quantitatively assess differences in effective population density and dispersal between the contrasted landscapes characterizing the northern and southern parts of the study area. Altogether, results suggest recent land conversion affected T. marmoratus through reduction in both effective population density and dispersal due to habitat loss and reduced connectivity.     

Population dynamics of tundra voles in relation to configuration of willow thickets in southern arctic tundra

The areal extent and configuration of thickets of willow shrubs are currently changing in the Arctic both as an effect of global warming and changed browsing pressure of reindeer. These changes have been predicted to impact the distribution and abundance of wildlife species relying on willow thickets as habitat. We assessed the relation between variables quantifying willow thicket configuration and population dynamics of tundra voles (Microtus oeconomus) in three riparian regions in Finnmark, northern Norway, which were subject to intense browsing by semi-domesticated reindeer. The tundra vole, which exhibits 5-year population cycles in Finnmark, is the dominant small rodent species in riparian landscape elements in southern arctic tundra. In the course of a 4-year trapping study, tundra vole populations went through the cyclic phases of increase, peak and crash, however, with distinct differences between the three regions in the population dynamics. Within regions, the occupancy pattern during the increase phase was positively related to willow thicket configuration (in particular edge density and willow height) only in the region attaining the highest abundance and occupancy. However, local abundance was not clearly related to habitat features within any regions. The lack of consistency in the response of tundra vole populations to willow thicket configuration, as well as the positive relation between the degree of thicket shredding and tundra vole habitat occupancy in one of the regions, indicates that tundra voles will not be much affected by climate or browsing induced changes in the shrubbiness of the tundra in the future.     

Saproxylic beetles in artificially created high-stumps of spruce and birch within and outside hotspot areas

Artificially created high-stumps (snags) are created regularly during forest felling operations in Swedish coniferous production forests. The saproxylic beetle fauna in high-stumps of spruce and birch, on 20 clearcuts in Southern Sweden, were sampled by bark sieving. Ten of the clearcuts were located in hotspot areas with documented occurrence of many red-listed saproxylic beetle species. The other ten clearcuts were located in a typical production forest landscape (i.e. the matrix). Our aim was to investigate whether the benefit of creating high-stumps differs if the clearcuts is located in a hotspot area or in the matrix. In total 4,179 saproxylic beetles were found, belonging to 66 species, 9 of which were red-listed. Birch high-stumps hosted more species, on average, than spruce high-stumps. In an ordination analysis, tree species had the strongest explanatory effect among the environmental variables. No difference in beetle fauna could be found between the hotspot and matrix clearcuts, for neither birch nor spruce, according to all parameters: species numbers, species composition and red-listed species. The study does not indicate that conservation efforts in coniferous production forests should be concentrated to hotspot areas.     

Fragments are not islands: patch vs landscape perspectives on songbird presence and abundance in a harvested boreal forest

The boreal mixed-wood forest of northern Alberta. Canada is characterized by a mosaic of deciduous and coniferous forest patches. Recently, the deciduous portion of the forest was allocated for industrial logging. Widespread habitat loss and fragmentation may negatively affect birds and other wildlife. Most research on the effects of habitat loss on bird abundance has focussed on the forest as a patch or island in a matrix of non-habitat, but some species of songbird may use both the forest patch and the matrix. We hypothesized that some species of songbird might be able to compensate for a loss of deciduous forest by moving into other habitat types (termed "habitat compensation"). We report on a replicated field investigation in which we assessed the response of songbirds to commercial timber harvest by first examining their abundance within deciduous forest only, and then adding the clearcuts and coniferous forest in the surrounding areas to the analysis for a broader, landscape view of the system. Bird communities in deciduous and coniferous habitats had significant overlap in species composition: there was less overlap between forest and clearcuts. The shift from patch-centred to landscape sampling altered our interpretation of over half of the most common species' responses to logging in at least one year, suggesting that habitat compensation may have been occurring. However, significant variation in responses of species was observed between the two study areas. Our past reliance on island biogeographic and other single habitat approaches may be inappropriate for this system, and we stress that a broad, landscape view is required to properly assess and interpret species' responses to habitat loss and fragmentation.     

Spatial Models of Northern Bobwhite Populations for Conservation Planning

Abstract: Since 1980, northern bobwhite (Colinus virginianus) range-wide populations declined 3.9% annually. Within the West Gulf Coastal Plain Bird Conservation Region in the south-central United States, populations of this quail species have declined 6.8% annually. These declines sparked calls for land use change and prompted implementation of various conservation practices. However, to effectively reverse these declines and restore northern bobwhite to their former population levels, habitat conservation and management efforts must target establishment and maintenance of sustainable populations. To provide guidance for conservation and restoration of habitat capable of supporting sustainable northern bobwhite populations in the West Gulf Coastal Plain, we modeled their spatial distribution using landscape characteristics derived from 1992 National Land Cover Data and bird detections, from 1990 to 1994, along 10-stop Breeding Bird Survey route segments. Four landscape metrics influenced detections of northern bobwhite: detections were greater in areas with more grassland and increased aggregation of agricultural lands, but detections were reduced in areas with increased density of land cover edge and grassland edge. Using these landscape metrics, we projected the abundance and spatial distribution of northern bobwhite populations across the entire West Gulf Coastal Plain. Predicted populations closely approximated abundance estimates from a different cadre of concurrently collected data but model predictions did not accurately reflect bobwhite detections along species-specific call-count routes in Arkansas and Louisiana. Using similar methods, we also projected northern bobwhite population distribution circa 1980 based on Land Use Land Cover data and bird survey data from 1976 to 1984. We compared our 1980 spatial projections with our spatial estimate of 1992 populations to identify areas of population change. Additionally, we used our projection of the spatial distribution and abundance of bobwhite to predict areas of population sustainability. Our projections of population change and sustainability provide guidance for targeting habitat conservation and rehabilitation efforts for restoration of northern bobwhite populations in the West Gulf Coastal Plain.     

Linking density,productivity and trends of an endangered species: The Bonelli's eagle in Spain

Whether regional population density is a good indicator of environmental quality according to demographic variables such as breeding success or short-term population trends is controversial. In this paper we analyze the interrelationships among regional population density, breeding success and recent population trends of an endangered species, Bonelli's eagle in the Iberian Peninsula. We also analyze the different influence of geographical, climatic, landscape structure and human impact variables on regional variation in those demographic variables. Breeding success was higher and population decrease was lower in those areas where the population density of Bonelli's eagle was greater. Breeding success, density and recent population trends of Bonelli's eagle were tightly related, increasing from northern to southern Iberian Peninsula (with highest figures at intermediate latitudes), and as sun radiation increased, and altitude decreased. Breeding success and population density were significantly lower in the periphery of the distribution range than in core areas in the Iberian Peninsula. Population trends between 2000 and 2005 were also more negative (decreasing) in the periphery. Overall, these results suggest that population density in this endangered species of large home-range is a good indicator of environmental quality and reproductive output, and that peripheral populations occupy low-suitability areas with lower breeding success, where negative short-term population trends are more likely.     

Local habitat patch pattern of the Siberian flying squirrel in a managed boreal forest landscape

We examined how the structure of a boreal forest landscape is related to the occurrence of the Siberian flying squirrel Pteromys volans in northern Finland. The flying squirrel inhabits mature spruce-dominated ( Picea abies ) mixed forests and is categorised as vulnerable species due to habitat loss and change. We classified a landscape of 374.5 km² into potential habitat patches, potential dispersal areas, and areas incapable of being inhabited using national forest inventory data, and surveyed all 136 potential habitat patches for the presence of the species. Different landscape variables were defined, and also connections by the shortest distances to neighbouring habitat patches along both straight lines and least-cost distances based on specific movement costs were measured. Occupied patches were larger in size, contained more deciduous trees for food and nesting cavities, and were in closer proximity to the nearest occupied patches. Occupied patches were mainly located below 300 m a.s.l. The occurrence of flying squirrels was correctly predicted for 88% of the habitat patches using landscape variables. This modelling result proved to be rather general. In addition, the configuration of occupied patches was mainly clustered across the landscape, and distant occupied patches seemed to be linked to other patches via forested connections. We suggest that maintaining a clustered arrangement of good quality habitat patches and regenerating new potential habitat as well as dispersal areas between the habitat patches seem to be appropriate goals for long-term forest management planning to sustain populations of the flying squirrel in the landscape.     

Habitat selection by Ortolan Buntings Emberiza hortulana in post-fire succession in Catalonia: implications for the conservation of farmland populations

The Ortolan Bunting Emberiza hortulana is a long-distance migrant that has suffered major population declines across much of its European breeding range. While northern populations are bound largely to farmland, Mediterranean populations are largely confined to habitats subject to recurrent wildfires. Habitat selection of the Ortolan Bunting was assessed in a recently burnt area in Catalonia at landscape and habitat scales. A Zero-inflated Poisson procedure was used to model the abundance of birds in relation to landscape and habitat variables. The most parsimonious landscape model predicted the highest abundance on south-facing slopes, with a gradient above 10°. The most parsimonious habitat model showed a positive quadratic effect of bare ground and regenerating oak Quercus spp., with predicted optima for abundance around 20–30% and 20% cover, respectively. There was a clear relationship between predicted abundance of the Ortolan Bunting and post-fire regenerating oak shrubs. South-facing, moderately sloping areas were favoured and bare ground was a key feature of the species' habitat. A matrix combining patches of sparse oak shrubs and patches of bare ground appears to be the optimal breeding habitat in the Mediterranean. The maintenance or provision of similar habitat features, especially patches of bare ground, may prove crucial for the conservation of rapidly declining Ortolan Bunting populations on farmland across temperate Europe.     

Relationships between survival and habitat suitability of semi‐aquatic mammals

Spatial distribution and habitat selection are integral to the study of animal ecology. Habitat selection may optimize the fitness of individuals. Hutchinsonian niche theory posits the fundamental niche of species would support the persistence or growth of populations. Although niche‐based species distribution models (SDMs) and habitat suitability models (HSMs) such as maximum entropy (Maxent) have demonstrated fair to excellent predictive power, few studies have linked the prediction of HSMs to demographic rates. We aimed to test the prediction of Hutchinsonian niche theory that habitat suitability (i.e., likelihood of occurrence) would be positively related to survival of American beaver (Castor canadensis), a North American semi‐aquatic, herbivorous, habitat generalist. We also tested the prediction of ideal free distribution that animal fitness, or its surrogate, is independent of habitat suitability at the equilibrium. We estimated beaver monthly survival probability using the Barker model and radio telemetry data collected in northern Alabama, United States from January 2011 to April 2012. A habitat suitability map was generated with Maxent for the entire study site using landscape variables derived from the 2011 National Land Cover Database (30‐m resolution). We found an inverse relationship between habitat suitability index and beaver survival, contradicting the predictions of niche theory and ideal free distribution. Furthermore, four landscape variables selected by American beaver did not predict survival. The beaver population on our study site has been established for 20 or more years and, subsequently, may be approaching or have reached the carrying capacity. Maxent‐predicted increases in habitat use and subsequent intraspecific competition may have reduced beaver survival. Habitat suitability‐fitness relationships may be complex and, in part, contingent upon local animal abundance. Future studies of mechanistic SDMs incorporating local abundance and demographic rates are needed.     

Waterfowl distribution and productivity in the Prairie Pothole Region of Canada: tools for conservation planning

Species conservation requires an understanding of the factors and interactions affecting species distribution and behavior, habitat availability and use, and corresponding vital rates at multiple temporal and spatial scales. Opportunities to investigate these relationships across broad geographic regions are rare. We combined long-term waterfowl population surveys, and studies of habitat use and breeding success, to develop models that identify and incorporate these interactions for upland-nesting waterfowl in the Prairie Pothole Region (PPR) of Canada. Specifically, we used data from the annual Waterfowl Breeding Population and Habitat Survey (1961–2009) at the survey segment level and associated habitat covariates to model and map the long-term average duck density across the Canadian PPR. We analyzed nest location and fate data from approximately 25,000 duck nests found during 3 multi-year nesting studies (1994–2011) to model factors associated with nest survival and habitat selection through the nesting season for the 5 most common upland nesting duck species: mallard (Anas platyrhynchos), gadwall (Mareca strepera), blue-winged teal (Spatula discors), northern shoveler (Spatula clypeata), and northern pintail (Anas acuta). Duck density was highly variable across the Canadian PPR, reflecting positive responses to local wetland area and count, and amounts of cropland and grassland, a regional positive response to latitude, and a negative response to local amounts of tree cover. Nest survival was affected by temporal and spatial variables at multiple scales. Specifically, nest survival demonstrated interactive effects among species, nest initiation date, and nesting cover type and was influenced by relative annual wetness, population density, and surrounding landscape composition at landscape scales, and broad geographic gradients (east-west and north-south). Likewise, species-specific probability of nest habitat selection was influenced by timing of nest initiation, population density, relative annual wetness, herbaceous cover, and tree cover in the surrounding landscape, and location within the Canadian PPR. We combined these models, with estimates of breeding effort (nesting, renesting, and nest attempts) from existing literature, in a stochastic conservation planning model that estimates nest distribution and success given spatiotemporal variation in duck density, habitat availability, and influential covariates. We demonstrate the use of this model by examining various conservation planning scenarios. These models allow estimation of local, landscape, and regional influence of conservation investments and other landscape changes on the productivity of breeding duck populations across the PPR of Canada. These models lay the groundwork for the incorporation of conservation delivery costs for full return-on-investment analyses and scenario analyses of climate, habitat, and land use change in regional and continental population models.     

Range‐wide patterns of greater sage‐grouse persistence

Aim Greater sage‐grouse (Centrocercus urophasianus), a shrub‐steppe obligate species of western North America, currently occupies only half its historical range. Here we examine how broad‐scale, long‐term trends in landscape condition have affected range contraction. Location Sagebrush biome of the western USA. Methods Logistic regression was used to assess persistence and extirpation of greater sage‐grouse range based on landscape conditions measured by human population (density and population change), vegetation (percentage of sagebrush habitat), roads (density of and distance to roads), agriculture (cropland, farmland and cattle density), climate (number of severe and extreme droughts) and range periphery. Model predictions were used to identify areas where future extirpations can be expected, while also explaining possible causes of past extirpations. Results Greater sage‐grouse persistence and extirpation were significantly related to sagebrush habitat, cultivated cropland, human population density in 1950, prevalence of severe droughts and historical range periphery. Extirpation of sage‐grouse was most likely in areas having at least four persons per square kilometre in 1950, 25% cultivated cropland in 2002 or the presence of three or more severe droughts per decade. In contrast, persistence of sage‐grouse was expected when at least 30 km from historical range edge and in habitats containing at least 25% sagebrush cover within 30 km. Extirpation was most often explained (35%) by the combined effects of peripherality (within 30 km of range edge) and lack of sagebrush cover (less than 25% within 30 km). Based on patterns of prior extirpation and model predictions, we predict that 29% of remaining range may be at risk. Main Conclusions Spatial patterns in greater sage‐grouse range contraction can be explained by widely available landscape variables that describe patterns of remaining sagebrush habitat and loss due to cultivation, climatic trends, human population growth and peripherality of populations. However, future range loss may relate less to historical mechanisms and more to recent changes in land use and habitat condition, including energy developments and invasions by non‐native species such as cheatgrass (Bromus tectorum) and West Nile virus. In conjunction with local measures of population performance, landscape‐scale predictions of future range loss may be useful for prioritizing management and protection. Our results suggest that initial conservation efforts should focus on maintaining large expanses of sagebrush habitat, enhancing quality of existing habitats, and increasing habitat connectivity.     

Genetic variation and population differentiation in the lichen-forming ascomycete Xanthoria parietina on the island Storfosna, central Norway

Genetic diversity and fine-scale population structure in the lichen-forming ascomycete Xanthoria parietina was investigated using sequence variation in part of the intergenic spacer (IGS) and the complete internal transcribed spacer (ITS) regions of the nuclear ribosomal DNA. Sampling included 213 and 225 individuals, respectively, from seven populations in two different habitats, bark and rock, on the island Storfosna off the central west coast of Norway. Both markers revealed significant variation and a total of 10 IGS and 16 ITS haplotypes were found. There were no signs of significant positive spatial autocorrelation at any spatial size class down to 10% of transect length, nor did we find significant deviations from neutrality or signs of historical population expansion. Analysis of molecular variance (amova) indicated that most of the genetic variance observed was within populations, but when populations were grouped according to habitat, more than a quarter of the variance was explained among groups. Pairwise comparisons of populations (F(ST), exact tests of population differentiation) revealed significant differentiation between populations in different habitats (on bark or rock), but not between populations in the same habitat. Haplotype networks show that internal and presumably old haplotypes are shared between habitats, whereas terminal haplotypes tend to be unique to a habitat, mostly bark. We interpret the observed pattern to mean that there is no evidence of restricted gene flow between populations in the same habitat at the present spatial scale (interpopulation distances one or a few kilometres). On the other hand, differentiation between habitats is considerable, which we attribute to restricted gene flow between habitats (habitat isolation). Evidence suggests that the observed differentiation did not evolve locally. Estimates of divergence time between populations in the respective habitats indicate that an ancestral population started to diverge at least 34,000 years ago but probably much further back in time.     

Interactions between habitat heterogeneity and food affect reproductive output in a top predator

1. Habitat heterogeneity has important repercussions for species abundance, demography and life-history patterns. While habitat effects have been more thoroughly studied in top-down situations (e.g. in association with predation), their role in bottom-up situations (e.g. in association with food abundance) has been less explored and the underlying mechanism(s) behind the ecological patterns have not commonly been identified. 2. With material from 1993 to 2003, we test the hypothesis that the reproduction of Finnish northern goshawks Accipiter gentilis (L.) is bottom-up limited by habitat composition, especially in situations where the density of their main prey (grouse) is low. Special emphasis was placed on identifying the mechanism(s) behind potential habitat effects. 3. While laying date and large-scale variation in the main prey density (but not habitat composition) were related to the number of eggs goshawks laid, small-scale differences in alternative prey density between different territories later influenced how many young were fledged via the mechanism of habitat-dependent partial-brood loss. As a result of this mechanism, a difference in nestling condition also arose between goshawk territories with differing habitat compositions. 4. As the relative proportions of different landscape elements in a given landscape is a function of large-scale differences in geomorphology and land use, this means that the reproductive performance of goshawks as averaged over larger scales can be understood correctly only in respect to the fact that habitat gradients differ across landscapes. 5. In addition to being one of the first papers identifying the mechanism of partial brood loss as being primarily responsible for the habitat-specific differences in the production of young, this study further illustrates the need to identify small-scale mechanisms to correctly understand the large-scale patterns of reproductive performance in territorial species. The repercussions of the observed habitat effect for local population development are discussed.     

Novel insights into habitat suitability for Amazonian freshwater mussels linked with hydraulic and landscape drivers

Novel insights into habitat suitability for two Unionida freshwater mussels, Castalia ambigua Lamarck, 1819 (Hyriidae) and Anodontites elongatus (Swainson, 1823) (Mycetopodidae), are presented on the basis of hydraulic variables linked with the riverbed in six 500‐m reaches in an eastern Amazonian river basin. Within the reaches, there was strong habitat heterogeneity in hydrodynamics and substrate composition. In addition, we investigated stressors based on landscape modification that are associated with declines in mussel density. We measured hydraulic variables for each 500‐m reach, and landscape stressors at two spatial scales (subcatchment and riparian buffer forest). We used the Random Forest algorithm, a tree‐based model, to predict the hydraulic variables linked with habitat suitability for mussels, and to predict which landscape stressors were most associated with mussel density declines. Both mussel species were linked with low substrate heterogeneity and greater riverbed stability (low Froude and Reynolds numbers), especially at high flow (low stream power). Different sediment grain size preferences were observed between mussel species: Castalia ambigua was associated with medium sand and Anodontites elongatus with medium and fine sand. Declines in mussel density were associated with modifications linked to urbanization at small scales (riparian buffer forest), especially with percent of and distance from rural settlements, distance to the nearest street, and road density. In summary, the high variance explained in both hydraulic and landscape models indicated high predictive power, suggesting that our findings may be extrapolated and used as a baseline to test hypotheses of habitat suitability in other Amazonian rivers for Castalia ambigua and Anodontites elongatus and also for other freshwater mussel species. Our results highlight the urgent need for aquatic habitat conservation to maintain sheltered habitats during high flow as well as mitigate the effects of landscape modifications at the riparian buffer scale, both of which are important for maintaining dense mussel populations and habitat quality.     

Temporal Variation in Population Size of European Bird Species: Effects of Latitude and Marginality of Distribution

In the Northern Hemisphere, global warming has been shown to affect animal populations in different ways, with southern populations in general suffering more from increased temperatures than northern populations of the same species. However, southern populations are also often marginal populations relative to the entire breeding range, and marginality may also have negative effects on populations. To disentangle the effects of latitude (possibly due to global warming) and marginality on temporal variation in population size, we investigated European breeding bird species across a latitudinal gradient. Population size estimates were regressed on years, and from these regressions we obtained the slope (a proxy for population trend) and the standard error of the estimate (SEE) (a proxy for population fluctuations). The possible relationships between marginality or latitude on one hand and slopes or SEE on the other were tested among populations within species. Potentially confounding factors such as census method, sampling effort, density-dependence, habitat fragmentation and number of sampling years were controlled statistically. Population latitude was positively related to regression slopes independent of marginality, with more positive slopes (i.e., trends) in northern than in southern populations. The degree of marginality was positively related to SEE independent of latitude, with marginal populations showing larger SEE (i.e., fluctuations) than central ones. Regression slopes were also significantly related to our estimate of density-dependence and SEE was significantly affected by the census method. These results are consistent with a scenario in which southern and northern populations of European bird species are negatively affected by marginality, with southern populations benefitting less from global warming than northern populations, thus potentially making southern populations more vulnerable to extinction.     

Predicting badger sett numbers: evaluating methods in East Sussex

Abstract. One way in which a species' numbers may be estimated without direct counting is to predict their dispersion and density from more readily available habitat measures, such as landscape variables measured from maps or vegetation variables measured in the field. We compare the power of ordination and regression techniques for predicting badger ( Meles meles L.) numbers at a local scale, using a land class system, map-read landscape variables and field-derived vegetation variables. Sett density was used as a surrogate of badger density. Multiple linear regression using vegetation and landscape variables together gave the most accurate prediction of sett density, while ordination techniques were of lesser value. The addition of vegetation variables to landscape variables did not substantially improve the power of ordination. Outlier Sett Density was predicted more accurately, and by different variables, to Main Sett Density. The relationship between badger ecology and habitat variables that were useful in predicting sett density is discussed.     

Landscape features and spatial distribution of adult northern corn rootworm (Coleoptera: Chrysomelidae) in the South Dakota areawide management site

The northern corn rootworm, Diabrotica barberi Smith & Lawrence (Coleoptera: Chrysomelidae), creates economic and environmental concerns in the Corn Belt. To supplement the population control tactics of the Areawide Pest Management Program in Brookings, SD, geographic information systems were used from 1997 to 2001 to examine the spatial relationships between D. barberi population dynamics and habitat structure, soil texture, and elevation. Using the inverse distance weighted interpolation technique, D. barberi population density maps were created from georeferenced emergence and postemergence traps placed in maize, Zea mays L., fields. For each year, these maps were overlaid with vegetation, soil, and elevation maps to search for quantitative relationships between pest numbers and landscape structure. Through visual interpretation and correlation analysis, shifts in landscape structure, such as size, number, and arrangement of patches were shown to associate with D. barberi population abundance and distribution in varying degrees. D. barberi were found in greater proportions than expected on loam and silty clay loam soils and on elevations between 500 and 509 m. An understanding of the interactions between D. barberi population dynamics and landscape variables provides information to pest managers, which can be used to identify patterns in the landscape that promote high insect population density patches to improve pest management strategies.