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Habitat Availability (habitat + availability)
Selected AbstractsSpatio-temporal patterns of fish assemblages in a large regulated alluvial riverFRESHWATER BIOLOGY, Issue 7 2009RENAUD RIFFLART Summary 1. The River Durance, the last alpine tributary of the River Rhône, is a large, braided alluvial hydrosystem. Following large-scale regulation, flow downstream of the Serre-Ponçon dam has been maintained at 1/40th of previous annual mean discharge. To assess the effects of historical disturbances, fish assemblages and habitat use were analysed during five summers in a representative reach of the middle Durance. 2. Habitat availability and use were assessed with a multi-scale approach including the variables water depth, current velocity, roughness height of substratum, amount of woody debris and lateral/longitudinal location. Eighteen fish species were sampled by electrofishing in 289 habitat sample units. 3. Partial least square (PLS) regression showed that taxa were mainly distributed according to relationships between their total length and water depth/velocity variables. Fish assemblage composition was also related to roughness height as well as distance from the bank or to the nearest large woody debris. However, PLS regression revealed no significant differences in habitat selection between two periods of varying hydromorphological stability. 4. Fish distribution patterns and density were related to proximity to the bank and cover, indicating that local scale variables need to be considered in conservation and restoration programmes. [source] Dynamics of mutualist populations that are demographically openJOURNAL OF ANIMAL ECOLOGY, Issue 6 2006ANDREW R. THOMPSON Summary 1Few theoretical studies have examined the impact of immigration and emigration on mutualist population dynamics, but a recent empirical study (A.R. Thompson Oecologia, 143, 61,69) on mutualistic fish and shrimp showed that immigration can prevent population collapse, and that intraspecific competition for a mutualistic partner can curb population expansion. To understand in a theoretical context the implications of these results, and to assess their generality, we present a two-species model that accounts explicitly for immigration and emigration, as well as distinguishing the impacts of mutualism on birth rates, death rates and habitat acquisition. 2The model confirms that immigration can stabilize mutualistic populations, and predicts that high immigration, along with enhanced reproduction and/or reduced mortality through mutualism, can cause population sizes to increase until habitat availability curbs further expansion. 3We explore in detail the effects of different forms of habitat limitation on mutualistic populations. Habitat availability commonly limits the density of both populations if mutualists acquire shelter independently. If a mutualist depends on a partner for habitat, densities of that mutualist are capped by the amount of space provided by that partner. The density of the shelter-provider is limited by the environment. 4If a mutualism solely augments reproduction, and most locally produced individuals leave the focal patch, then the mutualism will have a minimal effect on local dynamics. If the mutualism operates by reducing rates of death or enhancing habitat availability, and there is at least some immigration, then mutualism will affect local dynamics. This finding may be particularly relevant in marine systems, where there is high variability (among species and locations) in the extent to which progeny disperse from natal locations. 5Overall, our results demonstrate that the consequences of immigration and emigration for the dynamics of mutualists depend strongly on which demographic rate is influenced by mutualism. 6By relating our model to a variety of terrestrial and aquatic systems, we provide a general framework to guide future empirical studies of the dynamics of mutualistic populations. [source] Habitat availability, hunting or poaching: what affects distribution and density of large mammals in western Tanzanian woodlands?AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009Matthias Waltert Abstract Game reserves (GR) in Tanzania have been found to support similar or lower densities of large mammals compared with National parks (NP). But as these areas usually differ considerably not only in regard to management but also to environmental factors, we assessed the relative importance of vegetation cover, species-specific habitat preferences and legal (trophy hunting) and illegal off-take for observed differences in species-specific densities. In the Katavi ecosystem, open habitats were characteristic elements of Katavi NP, while Rukwa GR was dominated by miombo forest. In an inter-specific comparison, density differences were moderately correlated with preferences for open habitats, and with estimates of combined legal and illegal off-take but not with one of these separately. In a multiple linear regression, open habitat preference was found to explain 39.6% of the density differences between the two protected areas. This analysis suggests that the broad-scale pattern of most species' distributions is governed by differing vegetation cover but that several species are overexploited by illegal (elephant, giraffe, buffalo, bush pig, warthog) or combined off-take (hippopotamus, eland, waterbuck), thus emphasizing the need for quota readjustments and a more efficient anti-poaching control. Résumé En Tanzanie, on a découvert que les réserves de chasse, comparées aux parcs nationaux, abritaient des densités semblables ou inférieures de grands mammifères. Mais étant donné que ces zones diffèrent d'habitude considérablement, en termes non seulement de gestion mais aussi de facteurs environnementaux, nous avons évalué l'importance relative de la couverture végétale, des préférences spécifiques des espèces en matière d'habitat, et des prélèvements légaux (chasse aux trophées) et illégaux dans les différences constatées des densités spécifiques. Dans l'écosystème de Katavi, les habitats ouverts sont des éléments caractéristiques du Parc National de Katavi (PN) alors que la Réserve de Chasse de Rukwa (RC) est dominée par la forêt à miombo. Dans une comparaison interspécifique, les différences de densitéétaient modérément liées à la préférence pour des habitats ouverts et aux estimations de prélèvements légaux et illégaux combinés, mais pas avec les estimations séparées des uns ou des autres. Dans une régression linéaire multiple, on a découvert que la préférence pour un habitat ouvert expliquait 39.6% des différences de densité entre les deux aires protégées. Cette analyse suggère que le schéma, à grande échelle, de la distribution de la plupart des espèces est régi par une différence de couverture végétale, mais que plusieurs espèces semblent être surexploitées par les prélèvements illégaux (éléphants, girafes, buffles, potamochères, phacochères) ou combinés (hippopotames, élands, waterbucks), ce qui souligne la nécessité de réajuster les quotas et d'exercer des contrôles anti-braconnage plus efficaces. [source] Dynamic distribution modelling: predicting the present from the pastECOGRAPHY, Issue 1 2009Stephen G. Willis Confidence in projections of the future distributions of species requires demonstration that recently-observed changes could have been predicted adequately. Here we use a dynamic model framework to demonstrate that recently-observed changes at the expanding northern boundaries of three British butterfly species can be predicted with good accuracy. Previous work established that the distributions of the study species currently lag behind climate change, and so we presumed that climate is not currently a major constraint at the northern range margins of our study species. We predicted 1970,2000 distribution changes using a colonisation model, MIGRATE, superimposed on a high-resolution map of habitat availability. Thirty-year rates and patterns of distribution change could be accurately predicted for each species (, goodness-of-fit of models >0.64 for all three species, corresponding to >83% of grid cells correctly assigned), using a combination of individual species traits, species-specific habitat associations and distance-dependent dispersal. Sensitivity analyses showed that population productivity was the most important determinant of the rate of distribution expansion (variation in dispersal rate was not studied because the species are thought to be similar in dispersal capacity), and that each species' distribution prior to expansion was critical in determining the spatial pattern of the current distribution. In future, modelling approaches that combine climate suitability and spatially-explicit population models, incorporating demographic variables and habitat availability, are likely to be valuable tools in projecting species' responses to climatic change and hence in anticipating management to facilitate species' dispersal and persistence. [source] Consistent spatial patterns across biogeographic gradients in temperate reef fishesECOGRAPHY, Issue 1 2008Maren Wellenreuther Biogeographic gradients may facilitate divergent evolution between populations of the same species, leading to geographic variation and possibly reproductive isolation. Previous work has shown that New Zealand triplefin species (family Tripterygiidae) have diversified in habitat use, however, knowledge about the consistency of this pattern throughout their geographic range is lacking. Here we examine the spatial habitat associations of 15 New Zealand triplefin species at nine locations on a latitudinal gradient from 35°50,S to 46°70,S to establish whether distant populations differ in habitat use. Triplefin diversity and density varied between locations, as did habitat variables such as percentage cover of the substratum, onshore-offshore location, microposition, depth and exposure. Canonical discriminant analysis identified specific species-habitat combinations, and when habitat was statistically partialled from location, most species exhibited consistent habitat associations throughout their range. However, the density of a few species at some locations was lower or higher than expected given the habitat availability. This indicates that the habitat variables recorded were not the sole predictors of assemblage structure, and it is likely that factors influencing larval dispersal (e.g. the low salinity layer in Fiordland and geographic isolation of the Three Kings Islands) play an additional role in structuring assemblage composition. Together these results suggest that New Zealand triplefin species show strong and consistent habitat use across potential biogeographical barriers, but this pattern appears to be modified by variation in larval supply and survival. This indicates that species with broad geographic distributions do not necessarily show phenotypic variation between populations. [source] Assessing the influence of environmental heterogeneity on bird spacing patterns: a case study with two raptorsECOGRAPHY, Issue 2 2006Thomas Cornulier Testing for aggregation or regularity in point patterns is difficult in the presence of spatial variation in abundance due to environmental heterogeneity. Using a recently developed method generalizing Ripley's K function for non homogeneous point patterns, we test the aggregation of the nests in two species of birds (little owl and Montagu's harrier) exhibiting heterogeneous distributions in response to landscape structure. We compare the results obtained under different null models accounting for environmental heterogeneity at large and/or small spatial scales. Whereas both species were initially found to form clusters at some scale, taking spatial heterogeneity into account revealed that 1) territorial little owls showed no clustering of territories when habitat availability was considered; 2) semi-colonial harriers still formed significant clusters, but part of the aggregation in this species could be explained by landscape structure alone. Our results highlight that it is feasible and highly recommended to account for non-stationarity when testing for aggregation. Further, provided that sufficient knowledge of the study system is available, this approach helps to identify behavioural and environmental components of spatial variation in abundance. Additionally, we demonstrate that accounting for large or small-scale heterogeneity affects the perception of spacing behaviours differently, so that both need to be considered. [source] Modelling and analysing evolution of dispersal in populations at expanding range boundariesECOLOGICAL ENTOMOLOGY, Issue 5 2007CLARE L. HUGHES Abstract 1.,Species would be expected to shift northwards in response to current climate warming, but many are failing to do so because of fragmentation of breeding habitats. Dispersal is important for colonisation and an individual-based spatially explicit model was developed to investigate impacts of habitat availability on the evolution of dispersal in expanding populations. Model output was compared with field data from the speckled wood butterfly Pararge aegeria, which currently is expanding its range in Britain. 2.,During range expansion, models simulated positive linear relationships between dispersal and distance from the seed location. This pattern was observed regardless of quantity (100% to 10% habitat availability) or distribution (random vs. gradient distribution) of habitat, although higher dispersal evolved at expanding range margins in landscapes with greater quantity of habitat and in gradient landscapes. Increased dispersal was no longer evident in any landscape once populations had reached equilibrium; dispersal values returned to those of seed populations. However, in landscapes with the least quantity of habitat, reduced dispersal (below that of seed populations) was observed at equilibrium. 3.,Evolutionary changes in adult flight morphology were examined in six populations of P. aegeria along a transect from the distribution core to an expanding range margin in England (spanning a latitudinal distance of >200 km). Empirical data were in agreement with model output and showed increased dispersal ability (larger and broader thoraxes, smaller abdomens, higher wing aspect ratios) with increasing distance from the distribution core. Increased dispersal ability was evident in populations from areas colonised >30 years previously, although dispersal changes were generally evident only in females. 4.,Evolutionary increases in dispersal ability in expanding populations may help species track future climate changes and counteract impacts of habitat fragmentation by promoting colonisation. However, at the highest levels of habitat loss, increased dispersal was less evident during expansion and reduced dispersal was observed at equilibrium indicating that, for many species, continued habitat fragmentation is likely to outweigh any benefits from dispersal. [source] On the relationship between niche and distributionECOLOGY LETTERS, Issue 4 2000H.R. Pulliam Applications of Hutchinson's n -dimensional niche concept are often focused on the role of interspecific competition in shaping species distribution patterns. In this paper, I discuss a variety of factors, in addition to competition, that influence the observed relationship between species distribution and the availability of suitable habitat. In particular, I show that Hutchinson's niche concept can be modified to incorporate the influences of niche width, habitat availability and dispersal, as well as interspecific competition per se. I introduce a simulation model called NICHE that embodies many of Hutchinson's original niche concepts and use this model to predict patterns of species distribution. The model may help to clarify how dispersal, niche size and competition interact, and under what conditions species might be common in unsuitable habitat or absent from suitable habitat. A brief review of the pertinent literature suggests that species are often absent from suitable habitat and present in unsuitable habitat, in ways predicted by theory. However, most tests of niche theory are hampered by inadequate consideration of what does and does not constitute suitable habitat. More conclusive evidence for these predictions will require rigorous determination of habitat suitability under field conditions. I suggest that to do this, ecologists must measure habitat specific demography and quantify how demographic parameters vary in response to temporal and spatial variation in measurable niche dimensions. [source] Challenges in developing fish-based ecological assessment methods for large floodplain riversFISHERIES MANAGEMENT & ECOLOGY, Issue 6 2007J. J. DE LEEUW Abstract, Large European floodplain rivers have a great diversity in habitats and fish fauna, but tend to be heavily modified. The complexity of these river systems and their multiple human impacts pose considerable challenges for assessment of their ecological status. This paper discusses: (1) the application of historical information on fish fauna and habitat availability to describe reference conditions; (2) responses of fish assemblages to human disturbance by comparing various rivers and river segments with different impacts and/or time series within rivers; (3) the role of floodplain water bodies in ecological assessment; and (4) monitoring of large rivers using different gears and sampling designs for main channels and floodplain habitats. The challenge for the future is to standardise and calibrate sampling methods and data to enhance the potential for ecological assessment of large rivers. [source] Between-year variations in Little Bustard Tetrax tetrax population densities are influenced by agricultural intensification and rainfallIBIS, Issue 3 2010ANA DELGADO The Little Bustard is suffering a widespread population decline mainly due to agricultural intensification. This study evaluates the effects of intensification level, habitat availability and rainfall on the population dynamics of this species. The population density of males was monitored for 7 years (2002,2008) at 184 points located within three sites with contrasting levels of agricultural intensification in southern Portugal. Densities decreased along the intensification gradient from 8.2 to 2.3 males,/,km2. Overall, there was an approximately 50% population decline during the period 2002,2008, driven by a decline observed in one of the less intensive sites, whereas in the other two sites densities remained fairly constant. Yearly variations in male densities were influenced by intensification level, amount of grassland habitat and rainfall patterns. Thus, agricultural intensification is having a negative effect on population densities of this threatened species, particularly through the loss of grasslands (fallow fields and pastures) suitable for displaying males. The results also suggest a positive impact of rainfall on male densities, although this is more likely in grasslands within less intensive agricultural regions of poorer soil quality, where higher breeding male densities occur. Grassland habitat quality, driven by both climate and human management, probably plays a major role in the population dynamics of this threatened steppe bird in its strongholds. [source] Information needs to support environmental impact assessment of the effects of European marine offshore wind farms on birdsIBIS, Issue 2006A.D. FOX European legislation requires Strategic Environmental Assessments (SEAs) of national offshore wind farm (OWF) programmes and Environmental Impact Assessments (EIAs) for individual projects likely to affect birds. SEAs require extensive mapping of waterbird densities to define breeding and feeding areas of importance and sensitivity. Use of extensive large scale weather, military, and air traffic control surveillance radar is recommended, to define areas, routes and behaviour of migrating birds, and to determine avian migration corridors in three dimensions. EIAs for individual OWFs should define the key avian species present; as well as assess the hazards presented to birds in terms of avoidance behaviour, habitat change and collision risk. Such measures, however, are less helpful in assessing cumulative impacts. Using aerial survey, physical habitat loss, modification, or gain and effective habitat loss through avoidance behaviour can be measured using bird densities as a proxy measure of habitat availability. The energetic consequences of avoidance responses and habitat change should be modelled to estimate fitness costs and predict impacts at the population level. Our present ability to model collision risk remains poor due to lack of data on species-specific avoidance responses. There is therefore an urgent need to gather data on avoidance responses; energetic consequences of habitat modification and avoidance flights and demographic sensitivity of key species, most affected by OWFs. This analysis stresses the importance of common data collection protocols, sharing of information and experience, and accessibility of results at the international level to better improve our predictive abilities. [source] Role of larval host plants in the climate-driven range expansion of the butterfly Polygonia c-albumJOURNAL OF ANIMAL ECOLOGY, Issue 3 2007BRIGITTE BRASCHLER Summary 1Some species have expanded their ranges during recent climate warming and the availability of breeding habitat and species' dispersal ability are two important factors determining expansions. The exploitation of a wide range of larval host plants should increase an herbivorous insect species' ability to track climate by increasing habitat availability. Therefore we investigated whether the performance of a species on different host plants changed towards its range boundary, and under warmer temperatures. 2We studied the polyphagous butterfly Polygonia c-album, which is currently expanding its range in Britain and apparently has altered its host plant preference from Humulus lupulus to include other hosts (particularly Ulmus glabra and Urtica dioica). We investigated insect performance (development time, larval growth rate, adult size, survival) and adult flight morphology on these host plants under four rearing temperatures (18,28·5 °C) in populations from core and range margin sites. 3In general, differences between core and margin populations were small compared with effects of rearing temperature and host plant. In terms of insect performance, host plants were generally ranked U. glabra U. dioica > H. lupulus at all temperatures. Adult P. c-album can either enter diapause or develop directly and higher temperatures resulted in more directly developing adults, but lower survival rates (particularly on the original host H. lupulus) and smaller adult size. 4Adult flight morphology of wild-caught individuals from range margin populations appeared to be related to increased dispersal potential relative to core populations. However, there was no difference in laboratory reared individuals, and conflicting results were obtained for different measures of flight morphology in relation to larval host plant and temperature effects, making conclusions about dispersal potential difficult. 5Current range expansion of P. c-album is associated with the exploitation of more widespread host plants on which performance is improved. This study demonstrates how polyphagy may enhance the ability of species to track climate change. Our findings suggest that observed differences in climate-driven range shifts of generalist vs. specialist species may increase in the future and are likely to lead to greatly altered community composition. [source] Dynamics of mutualist populations that are demographically openJOURNAL OF ANIMAL ECOLOGY, Issue 6 2006ANDREW R. THOMPSON Summary 1Few theoretical studies have examined the impact of immigration and emigration on mutualist population dynamics, but a recent empirical study (A.R. Thompson Oecologia, 143, 61,69) on mutualistic fish and shrimp showed that immigration can prevent population collapse, and that intraspecific competition for a mutualistic partner can curb population expansion. To understand in a theoretical context the implications of these results, and to assess their generality, we present a two-species model that accounts explicitly for immigration and emigration, as well as distinguishing the impacts of mutualism on birth rates, death rates and habitat acquisition. 2The model confirms that immigration can stabilize mutualistic populations, and predicts that high immigration, along with enhanced reproduction and/or reduced mortality through mutualism, can cause population sizes to increase until habitat availability curbs further expansion. 3We explore in detail the effects of different forms of habitat limitation on mutualistic populations. Habitat availability commonly limits the density of both populations if mutualists acquire shelter independently. If a mutualist depends on a partner for habitat, densities of that mutualist are capped by the amount of space provided by that partner. The density of the shelter-provider is limited by the environment. 4If a mutualism solely augments reproduction, and most locally produced individuals leave the focal patch, then the mutualism will have a minimal effect on local dynamics. If the mutualism operates by reducing rates of death or enhancing habitat availability, and there is at least some immigration, then mutualism will affect local dynamics. This finding may be particularly relevant in marine systems, where there is high variability (among species and locations) in the extent to which progeny disperse from natal locations. 5Overall, our results demonstrate that the consequences of immigration and emigration for the dynamics of mutualists depend strongly on which demographic rate is influenced by mutualism. 6By relating our model to a variety of terrestrial and aquatic systems, we provide a general framework to guide future empirical studies of the dynamics of mutualistic populations. [source] Hydrological disturbance benefits a native fish at the expense of an exotic fishJOURNAL OF APPLIED ECOLOGY, Issue 5 2006F. LEPRIEUR Summary 1Some native fish in New Zealand do not coexist with introduced salmonids. Previous studies of disjunct distributions of exotic brown trout Salmo trutta and native galaxiids demonstrated native extirpation except where major waterfalls prevented upstream migration of trout. In the Manuherikia River system, we predicted that water abstraction might be a further factor controlling the spatial distribution of both the invader and a native fish. 2We applied multiple discriminant function analyses to test for differences in environmental conditions (catchment and instream scales) at sites with roundhead galaxias Galaxias anomalus and brown trout in sympatry and allopatry. We then used a supervised artificial neural network (ANN) to predict the presence,absence of G. anomalus and brown trout (135 sites). The quantification of contributions of environmental variables to ANN models allowed us to identify factors controlling their spatial distribution. 3Brown trout can reach most locations in the Manuherikia catchment, and often occur upstream of G. anomalus. Their largely disjunct distributions in this river are mediated by water abstraction for irrigation, together with pool habitat availability and valley slope. Trout are more susceptible than the native fish to stresses associated with low flows, and seem to be prevented from eliminating galaxiid populations from sites in low gradient streams where there is a high level of water abstraction. 4Synthesis and applications. In contrast to many reports in the literature, our results show that hydrological disturbance associated with human activities benefits a native fish at the expense of an exotic in the Manuherikia River, New Zealand. Water abstraction is also known to have negative impacts on native galaxiids, therefore we recommend restoring natural low flows to maintain sustainable habitats for native galaxiids, implementing artificial barriers in selected tributaries to limit trout predation on native fish, and removing trout upstream. [source] Loop migration in adult marsh harriers Circus aeruginosus, as revealed by satellite telemetryJOURNAL OF AVIAN BIOLOGY, Issue 2 2010Raymond H. G. Klaassen Loop migration among birds is characterized by the spring route lying consistently west or east of the autumn route. The existence of loops has been explained by general wind conditions or seasonal differences in habitat distribution. Loop migration has predominantly been studied at the population level, for example by analysing ring recoveries. Here we study loop migration of individual marsh harriers Circus aeruginosus tracked by satellite telemetry. We show that despite a generally narrow migration corridor the harriers travelled in a distinct clockwise loop through Africa and southern Europe, following more westerly routes in spring than in autumn. We used the Normalized Difference Vegetation Index (NDVI) to identify potential feeding habitat in Africa. Suitable habitat seemed always more abundant along the western route, both in spring and autumn, and no important stopover site was found along the eastern route. Observed routes did thus not coincide with seasonal variation in habitat availability. However, favourable habitat might be more important during spring migration, when the crossing of the Sahara seems more challenging, and thus habitat availability might play an indirect role in the harriers' route choice. Grid-based wind data were used to reconstruct general wind patterns, and in qualitative agreement with the observed loop marsh harriers predominantly encountered westerly winds in Europe and easterly winds in Africa, both in autumn and in spring. By correlating tail- and crosswinds with forward and perpendicular movement rates, respectively, we show that marsh harriers are partially drifted by wind. Thus, we tentatively conclude that wind rather than habitat seems to have an overriding effect on the shape of the migration routes of marsh harriers. General wind conditions seem to play an important role also in the evolution of narrow migratory loops as demonstrated for individual marsh harriers. [source] Phylogeographical structure in the coastal species Senecio rodriguezii (Asteraceae), a narrowly distributed endemic Mediterranean plantJOURNAL OF BIOGEOGRAPHY, Issue 7 2009Arántzazu Molins Abstract Aim, Our goals were (1) to assess the levels of chloroplast DNA variation in a narrowly distributed plant restricted to continental islands, (2) to ascertain whether a phylogeographical structure is present in plants restricted to coastal linear systems, and (3) to interpret the results in the light of the known palaeogeography of these islands. Location, The Eastern Balearic Islands (Majorca and Minorca) in the Western Mediterranean Basin. Methods, Sampling included 134 individuals from 28 populations of Senecio rodriguezii covering the entire range of the species. Sequences of the chloroplast genome (trnT,trnL spacer) were obtained and parameters of population genetic diversity and substructure were determined (hsht, Gst). The geographical structure of genetic variation was assessed by an analysis of molecular variance (AMOVA). Additionally, a spatial AMOVA (SAMOVA) was used to identify groups of populations that were geographically homogeneous and maximally differentiated from each other. Finally, a pattern of isolation by distance was assessed by testing the correlation between the matrix of pairwise ,ST values and the matrix of geographical distances between pairs of populations using a Mantel test. Results, Seven haplotypes were detected in S. rodriguezii. Only two of them were shared between islands; all of the others were restricted to Majorca (two) or Minorca (three). Overall, we found high levels of genetic diversity and significant geographical structuring of cpDNA markers. Most of the variation detected can be attributed to differences among populations (84.6%), but there was also a significant differentiation between the islands. Main conclusions, Our results support the view that the Balearic Islands constitute a reservoir of genetic diversity, not only for widespread Mediterranean taxa, but also for endemic ones. The intraspecific genetic structure found in S. rodriguezii suggests that its population history was dominated by both expansion and contraction events. This has resulted in a species that is highly structured genetically, showing very few shared haplotypes between islands, and a high number of haplotypes restricted to small geographical areas within the islands. Changes in habitat availability and dynamic processes of population fragmentation and connectivity due to repeated cycles of sea-level changes during the Quaternary are the possible underlying factors that have shaped the cpDNA pool of this endemic species on a regional scale. [source] Thermal tolerance and geographical range size in the Agabus brunneus group of European diving beetles (Coleoptera: Dytiscidae)JOURNAL OF BIOGEOGRAPHY, Issue 2 2008P. Calosi Abstract Aim, Within clades, most taxa are rare, whilst few are common, a general pattern for which the causes remain poorly understood. Here we investigate the relationship between thermal performance (tolerance and acclimation ability) and the size of a species' geographical range for an assemblage of four ecologically similar European diving beetles (the Agabus brunneus group) to examine whether thermal physiology relates to latitudinal range extent, and whether Brown's hypothesis and the environmental variability hypothesis apply to these taxa. Location, Europe. Methods, In order to determine the species tolerances to either low or high temperatures we measured the lethal thermal limits of adults, previously acclimated at one of two temperatures, by means of thermal ramping experiments (± 1°C min,1). These measures of upper and lower thermal tolerances (UTT and LTT respectively) were then used to estimate each species' thermal tolerance range, as total thermal tolerance polygons and marginal UTT and LTT thermal polygons. Results, Overall, widespread species have higher UTTs and lower LTTs than restricted ones. Mean upper lethal limits of the Agabus brunneus group (43 to 46°C), are similar to those of insects living at similar latitudes, whilst mean lower lethal limits (,6 to ,9°C) are relatively high, suggesting that this group is not particularly cold-hardy compared with other mid-temperate-latitude insects. Widespread species possess the largest thermal tolerance ranges and have a relatively symmetrical tolerance to both high and low temperatures, when compared with range-restricted relatives. Over the temperature range employed, adults did not acclimate to either high or low temperatures, contrasting with many insect groups, and suggesting that physiological plasticity has a limited role in shaping distribution. Main conclusions, Absolute thermal niche appears to be a good predictor of latitudinal range, supporting both Brown's hypothesis and the environmental variability hypothesis. Restricted-range species may be more susceptible to the direct effect of climate change than widespread species, notwithstanding the possibility that even ,thermally-hardy', widespread species may be influenced by the indirect effects of climate change such as reduction in habitat availability in Mediterranean areas. [source] A regional impact assessment of climate and land-use change on alpine vegetationJOURNAL OF BIOGEOGRAPHY, Issue 3 2003Thomas Dirnböck Abstract Aim, Assessing potential response of alpine plant species distribution to different future climatic and land-use scenarios. Location, Four mountain ranges totalling 150 km2 in the north-eastern Calcareous Alps of Austria. Methods, Ordinal regression models of eighty-five alpine plant species based on environmental constraints and land use determining their abundance. Site conditions are simulated spatially using a GIS, a Digital Terrain Model, meteorological station data and existing maps. Additionally, historical records were investigated to derive data on time spans since pastures were abandoned. This was then used to assess land-use impacts on vegetation patterns in combination with climatic changes. Results, A regionalized GCM scenario for 2050 (+ 0.65 °C, ,30 mm August precipitation) will only lead to local loss of potential habitat for alpine plant species. More profound changes (+ 2 °C, ,30 mm August precipitation; + 2 °C, ,60 mm August precipitation) however, will bring about a severe contraction of the alpine, non-forest zone, because of range expansion of the treeline conifer Pinus mugo Turra and many alpine species will loose major parts of their habitat. Precipitation change significantly influences predicted future habitat patterns, mostly by enhancing the general trend. Maintenance of summer pastures facilitates the persistence of alpine plant species by providing refuges, but existing pastures are too small in the area to effectively prevent the regional extinction risk of alpine plant species. Main conclusions, The results support earlier hypotheses that alpine plant species on mountain ranges with restricted habitat availability above the treeline will experience severe fragmentation and habitat loss, but only if the mean annual temperature increases by 2 °C or more. Even in temperate alpine regions it is important to consider precipitation in addition to temperature when climate impacts are to be assessed. The maintenance of large summer farms may contribute to preventing the expected loss of non-forest habitats for alpine plant species. Conceptual and technical shortcomings of static equilibrium modelling limit the mechanistic understanding of the processes involved. [source] Habitat use, abundance, and persistence of Neotropical migrant birds in a habitat matrix in northeast BelizeJOURNAL OF FIELD ORNITHOLOGY, Issue 3 2010Camila Gómez-Montes ABSTRACT To ensure adequate protection of nonbreeding habitats used by Neotropical migratory landbirds, we must first address questions about habitat use and quality. On the Yucatan peninsula, migrants use many habitats, several of which remain unstudied, and methodological differences preclude interhabitat comparisons based on studies to date. We used distance sampling along line transects in six habitats in northeast Belize to examine use of previously unstudied habitats (e.g., salt marsh) by Neotropical migrants and to permit comparison across habitats. We calculated unadjusted and adjusted (for detectability) density estimates for individual migrant species and for all species combined to generate hypotheses about habitat quality based on the assumption that density and quality are positively correlated. Adjusted density estimates for all migrants were highest in black mangrove habitat (1799 ± 110 ind/km2), intermediate in three forest types and milpa (range 598,802 ind/km2), and lowest in salt marsh (207 ± 32.3 ind/km2). By combining density estimates with habitat availability in our study region, we estimated that evergreen forest and black mangrove supported 70% and 9% of the region's migrant population, respectively. At the species level, five of the 10 most common species had habitat preferences (>50% detections in one habitat). Given the diversity of habitat preferences among species and apparent seasonal movements, our results indicate that Neotropical migrants in northeast Belize are dependent on a matrix of interconnected habitats. RESUMEN Para asegurar la protección adecuada del hábitat no- reproductivo utilizado por aves migratorias Neotropicales terrestres, debemos responder preguntas sobre el uso y la calidad del hábitat. En la península de Yucatán, lasaves migratorias utilizan muchos hábitats, varios de los cuales aún continúan sin ser estudiados. Además las diferencias metodológicas evitan hacer comparaciones inter-hábitat basadas en los estudios que se han hecho hasta ahora. Utilizamos unmuestreo a lo largo de transectos de distancia variable, en seis hábitats, algunos previamente no estudiados (ej. ciénagas salobres), en el noreste de Belize para examinar y comparar el uso por parte de las migratorias Neotropicales, Calculamos estimados de densidad, ajustados y no ajustados (para detectabilidad), para especies particulares de migratorias y para todas las especies combinadas para generar una hipótesis sobre la calidad del hábitat basándonos en la presunción que la densidad estaría positivamente correlacionada con la calidad del hábitat. Los estimados de densidad ajustados para todos los migratorios fueron más altos en mangle negro (1799 ± 100 ind/km2), intermedios en tres tipos de bosque y milpa rango 598,802 ind/km2) y menores en ciénagas salobres (207 ± 32.3 ind/km2). Combinando los estimados de densidad con la disponibilidad de hábitats en nuestra región de estudio, estimamos que el bosque siempreverde y el mangle negro sostienen el 70% y 9% de los migratorios en la región, respectivamente. A nivel de especies, cinco de las 10 especies más comunes tienen preferencias de hábitat (>50% de las detecciones en un hábitat). Dada la diversidad de preferencias de hábitat entre especies y el aparente movimiento estacional, nuestros resultados indican que las aves migratorias Neotropicales en el noreste de Belize dependen de una matriz de hábitats interconectados. [source] Habitat preferences of European grayling in a medium size stream, the Ain river, FranceJOURNAL OF FISH BIOLOGY, Issue 6 2000J. P. Mallet The three grayling Thymallus thymallus age-classes had strong preferences for their local habitat in the Ain river. All age-classes preferred high water velocities between 70 and 110 cm s -1, confirming that grayling is a typical rheophilic species. An important intraspecific segregation regarding depth occurred, as large individuals preferred deeper water than small ones (optimal ranges=50,60, 80,120 and 100,140 cm for 0+, 1+ and adults respectively). The three age-classes had similar preferences for small substratum articles, with optimal values between 0·5 and 16·0 mm. Preference curves were generally comparable between the two sites, despite important differences in habitat availability. It is emphasized that grayling needs various habitat conditions to achieve its entire life cycle. The increasing scarcity of this species underlines the urgency of protecting lotic habitat integrity and diversity. [source] Plant functional group composition and large-scale species richness in European agricultural landscapesJOURNAL OF VEGETATION SCIENCE, Issue 1 2008Jaan Liira Abstract Question: Which are the plant functional groups responding most clearly to agricultural disturbances? Which are the relative roles of habitat availability, landscape configuration and agricultural land use intensity in affecting the functional composition and diversity of vascular plants in agricultural landscapes? Location: 25 agricultural landscape areas in seven European countries. Methods: We examined the plant species richness and abundance in 4 km × 4 km landscape study sites. The plant functional group classification was derived from the BIOLFLOR database. Factorial decomposition of functional groups was applied. Results: Natural habitat availability and low land use intensity supported the abundance and richness of perennials, sedges, pteridophytes and high nature quality indicator species. The abundance of clonal species, C and S strategists was also correlated with habitat area. An increasing density of field edges explained a decrease in richness of high nature quality species and an increase in richness of annual graminoids. Intensive agriculture enhanced the richness of annuals and low nature quality species. Conclusions: Habitat patch availability and habitat quality are the main drivers of functional group composition and plant species richness in European agricultural landscapes. Linear elements do not compensate for the loss of habitats, as they mostly support disturbance tolerant generalist species. In order to conserve vascular plant species diversity in agricultural landscapes, the protection and enlargement of existing patches of (semi-) natural habitats appears to be more effective than relying on the rescue effect of linear elements. This should be done in combination with appropriate agricultural management techniques to limit the effect of agrochemicals to the fields. [source] Critical habitat during the transition from maternal provisioning in freshwater fish, with emphasis on Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)JOURNAL OF ZOOLOGY, Issue 4 2006J. D. Armstrong Abstract In freshwater fish, the transition from dependence on maternal yolk reserves to independent foraging can be an early critical period, with survival during this stage having a strong influence on population abundance and cohort strength. Information concerning Atlantic salmon Salmo salar and brown trout Salmo trutta as model species is reviewed to show how population dynamics are influenced by habitat use during the transitional stage and illustrate the role of maternal provisioning along with density-dependent and -independent factors. The allocation of resources in yolk and timing and position of spawning strongly influence the biotic and abiotic environments of juveniles and their subsequent performance. Vulnerability to predators, adverse environmental conditions and restricted conditions over which they can successfully forage result in specific habitat requirements for newly independent juveniles. The availability of slow-flowing habitats at stream margins during the first month of independence is crucial. Alteration of natural flow regimes and physical habitat structure, associated with a wide range of anthropogenic influences, can have significant deleterious effects on the availability of critical juvenile habitat. A model combining habitat structure and the relationship between density-dependent and -independent mortality is presented to explore the range of conditions under which the transitional period would have a strong influence on population abundance. This model provides a framework for establishing thresholds or optima for habitat availability that will favour sufficient recruitment out of the transitional stage. Using the modelling framework, managers can make informed decisions on the utility and cost effectiveness of fisheries and habitat management activities designed to increase juvenile survival during the transition to independence. A range of management options is outlined for improving habitat quality and increasing juvenile survival during the transitional period, including restoration of structural complexity, provision of suitable flow regimes, and tailoring stocking and reintroduction strategies to mimic natural dynamics. [source] Distribution and density of Callimico goeldii in the Department of Pando, BoliviaAMERICAN JOURNAL OF PRIMATOLOGY, Issue 3 2006Leila M. Porter Abstract A survey of the distribution and density of Callimico goeldii was conducted at five sites across northwestern Bolivia, in the Department of Pando. C. goeldii was found at two sites north of the Manuripi River, with high densities at one site located along the Acre River. Estimates of habitat availability at these sites suggest that C. goeldii reaches high densities in areas with low human density and well established and extensive bamboo forests. These results, when reviewed with those of prior studies, indicate that the patchy distribution of C. goeldii in Pando is a result of both riverine barriers and the availability of bamboo habitat. Am. J. Primatol. 68:235,243, 2006. © 2006 Wiley-Liss, Inc. [source] Applying a continua landscape approach to evaluate plant response to fragmentation: Primula vulgaris in the Cantabrian mountainsAPPLIED VEGETATION SCIENCE, Issue 4 2009Alicia Valdés Abstract Question: Continua landscape approaches conceptualize the effects of habitat fragmentation on the biota by considering fragmented landscapes as continuous gradients, departing from the view of habitat as either suitable (fragment) or unsuitable (matrix). They also consider the ecological gradients or the ,Umwelt' (species-specific perception of the landscape) to represent the processes that ultimately limit organisms' ability to colonize and persist within habitat remnants. Are these approaches suitable for evaluating the response of plant species to fragmentation? Location: Fragmented mid-elevation temperate forests, Cantabrian range, Spain. Methods: The presence, abundance and demographic structure of populations of the perennial herb Primula vulgaris were sampled across a continuous extent of 100 ha, subdivided into 400 50 m × 50 m sampling units. These variables were related to forest availability, forest subdivision and edge density, topography and the spatial clumpiness of populations (a measure of plant dispersal constraints and, hence, a major surrogate of plant Umwelt). Results: Fragmentation processes, especially habitat loss, negatively affect P. vulgaris, with a stronger effect on presence than on abundance and demography. Despite the importance of habitat availability, P. vulgaris does not occupy all potentially suitable forest habitat, mostly owing to dispersal constraints. A positive effect of slope on plant presence also suggests some effect of habitat quality in determining establishment and occupancy of forest landscape. Conclusions: Within-habitat dispersal constraints are as important as forest fragmentation in determining the landscape-scale distribution of P. vulgaris. By assessing the relative role of the diverse fragmentation processes, and of the species' landscape perception, a continua landscape approach proves to be a valuable tool for predicting plant response to landscape change. [source] Fading of the last giants: an assessment of habitat availability of the Sunda gharial Tomistoma schlegelii and coverage with protected areasAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2010Dennis Rödder Abstract 1.The Sunda gharial Tomistoma schlegelii is, with 2500,3000 remaining specimens, one of the least studied and at the same time most endangered crocodile species. Inhabiting peat swamps in Southeast Asia, threats affecting the species are mainly associated with habitat loss and illegal hunting. 2.The effectiveness of the existing reserve network in Southeast Asia for the protection of the Sunda garial was assessed by combining spatially explicit habitat analyses derived from land cover information with species distribution modelling. Subsequently, possible improvements of the existing reserve network are derived from the habitat availability analyses. 3.The results of the spatially explicit analyses indicate that suitable habitats for the Sunda gharial in Southeast Asia, i.e. peat swamps and riverine forests, are highly fragmented. Spatial coverage of remaining habitats with protected areas fulfilling IUCN standards generally varies among regions and is best in Indonesia. However, large, currently unprotected suitable areas remain in Sumatra. Establishment of 10 additional, already proposed reserves may improve the protection of major parts of the remaining suitable habitats of the Sunda gharial. 4.According to the results of this study, the reserve network protecting this species could be significantly improved by expanding it to include seven national reserves not currently listed by the IUCN and an additional 10 reserves that have recently been proposed. Improvements and extensions of the existing reserve networks in Southeast Asia are pivotal to guarantee the long-term survival of the Sunda gharial. Copyright © 2010 John Wiley & Sons, Ltd. [source] A geomorphological framework for river characterization and habitat assessmentAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 5 2001J.R. Thomson Abstract 1.,Methods to assess the physical habitat available to aquatic organisms provide important tools for many aspects of river management, including river health monitoring, determination of river restoration/rehabilitation strategies, setting and evaluating environmental flows and as surrogates for biodiversity assessment. 2.,Procedures used to assess physical habitat need to be ecologically and geomorphologically meaningful, as well as practicable. A conceptual methodological procedure is presented that evaluates and links instream habitat and geomorphology. 3.,The heterogeneity of habitat potential is determined within geomorphic units (such as pools, runs, riffles) by assessing flow hydraulics and substrate character. These two variables are integrated as hydraulic units , patches of uniform flow and substrate. 4.,This methodology forms a logical extension of the River Styles framework that characterizes river form and behaviour at four inter-related scales: catchments, landscape units, River Styles (reaches) and geomorphic units. As geomorphic units constitute the basis to assess aquatic habitat availability, and they form the building blocks of river and floodplain systems, intact reaches of a particular River Style should have similar assemblages of instream and floodplain habitat. 5.,An application of the hydraulic unit procedure is demonstrated in gorge, partly-confined and alluvial River Styles from the Manning catchment in northern New South Wales, Australia. Copyright © 2001 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||