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Habitat Variables (habitat + variable)
Selected AbstractsEffects of herbivore species richness on the niche dynamics and distribution of blue sheep in the Trans-HimalayaDIVERSITY AND DISTRIBUTIONS, Issue 6 2009Tsewang Namgail Abstract Aim, To understand the community structure of mountain ungulates by exploring their niche dynamics in response to sympatric species richness. Location, Ladakh and Spiti Regions of the Western Indian Trans-Himalaya. Methods, We used the blue sheep Pseudois nayaur, a relatively widely distributed mountain ungulate, as a model species to address the issue. We selected three discrete valleys in three protected areas with similar environmental features but varying wild ungulate species richness, and studied blue sheep's diet and habitat utilization in them. Habitat variables such as slope angle, distance to cliff and elevation at blue sheep locations were recorded to determine the habitat width of the species. Faecal pellets were collected and microhistological faecal analysis was carried out to determine the diet width of blue sheep in the three areas with different ungulate species richness. Blue sheep's niche width in terms of habitat and diet was determined using the Shannon's Index. Results, The habitat width of blue sheep had a negative relationship with the number of sympatric species. However, contrary to our expectation, there was a hump-shaped relationship between blue sheep's diet width and the sympatric species richness, with the diet width being narrower in areas of allopatry as well as in areas with high herbivore species richness, and the greatest in areas with moderate species richness. Main conclusions, We suspect that the narrow diet width in allopatry is out of choice, whereas it is out of necessity in areas with high herbivore species richness because of resource partitioning that enables coexistence. We suggest that interactions with sympatric species lead to niche adjustment of mountain ungulates, implying that competition may play a role in structuring Trans-Himalayan mountain ungulate assemblages. Given these results, we underscore the importance of including biotic interactions in species distribution models, which have often been neglected. [source] Stream macroinvertebrate occurrence along gradients in organic pollution and eutrophicationFRESHWATER BIOLOGY, Issue 7 2010NIKOLAI FRIBERG Summary 1.,We analysed a large number of concurrent samples of macroinvertebrate communities and chemical indicators of eutrophication and organic pollution [total-P, total-N, NH4,N, biological oxygen demand (BOD5)] from 594 Danish stream sites. Samples were taken over an 11-year time span as part of the Danish monitoring programme on the aquatic environment. Macroinvertebrate communities were sampled in spring using a standardised kick-sampling procedure whereas chemical variables were sampled six to 24 times per year per site. Habitat variables were assessed once when macroinvertebrates were sampled. 2.,The plecopteran Leuctra showed a significant negative exponential relationship (r2 = 0.90) with BOD5 and occurred at only 16% of the sites with BOD5 above 1.6 mg L,1. Sharp declines with increasing BOD5 levels were found for the trichopteran families Sericostomatidae and Glossosomatidae although they appeared to be slightly less sensitive than Leuctra. Other plecopterans such as Isoperla showed a similar type of response curve to Leuctra (negative exponential) but occurred at sites with relatively high concentrations of BOD5 up to 3,4 mg L,1. In contrast, the response curve of the isopod Asellus aquaticus followed a saturation function reaching a plateau above 3,4 mg L,1 BOD5 and the dipteran Chironomus showed an exponential increase in occurrence with increasing BOD5 concentration. 3.,Macroinvertebrate occurrence appeared to be related primarily to concentrations of BOD5, NH4,N and total-P whereas there were almost no relationships to total-N. Occurrence of a number of taxa showed a stronger relationship to habitat conditions (width and substrate) than chemical variables. 4.,Important macroinvertebrate taxa are reduced at concentrations of BOD5 that are normally perceived as indicating unimpacted stream site conditions. Our results confirmed sensitivity/tolerance patterns used by existing bioassessment systems only to some degree. [source] Factors influencing Willow Tit Poecile montanus site occupancy: a comparison of abandoned and occupied woodsIBIS, Issue 2007ALEX J. G. LEWIS The British Willow Tit Poecile montanus kleinschmidti underwent a decline of 85% between 1970 and 2003. The cause of this decline is unknown. However, several hypotheses have been put forward to account for it: competition from other tit species, predation by Great Spotted Woodpeckers Dendrocopos major and habitat change. In order to test these, woods that are currently occupied by Willow Tits were paired with woods (within 50 km) that had been abandoned by Willow Tits five or more years previously. Point counts for other tit species (potential competitors) and woodpecker species (potential predators) were carried out at ten evenly spaced points throughout each wood. Habitat variables were collected within a 50-m radius of where a Willow Tit was located (in the occupied woods) or where maps showed a Willow Tit had been located (for abandoned woods). No evidence was found for differences in numbers of potential competitor or potential predator species in abandoned and occupied woods. Soil water content was found to be higher at occupied sites. No other habitat features differed between the two categories of site. The drying up of British woods could therefore be implicated in the Willow Tit decline and this warrants further investigation. [source] The use of teak (Tectona grandis) plantations by large mammals in the Kilombero Valley, southern TanzaniaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2009C. Bonnington Abstract The establishment of plantations is impacting the large mammal populations of the Kilombero Valley, Tanzania. Animal spoors were used as a proxy for activity to determine the influence of teak stand age on mammals. Habitat variables were compared between different aged stands to investigate the relationship between mammal activity and vegetation characteristics. Vegetation surveys found plantation composition to differ with age; with young stands characterized by slender teak trees, limited leaf litter, abundant grass layer and substantial bare ground. Older plantations contained a high leaf litter layer and dead wood, low grass abundance and minimal bare ground. Spoor transects revealed that mammal species number decreased as the teak matured. Of those vegetation variables tested, grass and bare ground abundance explained significantly the variation in species number and in individual species' habitat use between differently aged stands; therefore this habitat use was influenced by the foraging value of the plantation. This study showed that several species (some of which warrant conservation attention, such as elephant) use plantations <6 years old to a greater extent than plantations >6 years. Thus, there is a need for conservation measures, such as wildlife corridors and staggered teak planting to be continued, allowing large mammal movements in the valley. Résumé L'installation de plantations a un impact sur les populations de grands mammifères de la Vallée de Kilombero, en Tanzanie. Les traces des animaux ont été utilisées comme signes d'activité pour déterminer l'influence de l'âge des bosquets de teck sur les mammifères. On a comparé les variables de l'habitat entre des bosquets d'âge différent pour étudier la relation entre l'activité des mammifères et les caractéristiques de la végétation. Des études de la végétation ont montré que la composition des plantations varie avec leur âge : les jeunes plantations sont caractérisées par des troncs de teck plus minces, une litière de feuilles plus restreinte, une couche herbeuse abondante et une partie non négligeable de sol nu. Les plantations plus anciennes présentent une litière de feuilles plus épaisse et du bois mort, peu d'herbes et très peu de sol nu. Les traces ont révélé que le nombre d'espèces de mammifères diminuait quand la plantation vieillissait. Parmi les variables de la végétation testées, l'abondance de l'herbe et la quantité de sol nu expliquaient de manière significative la variation du nombre d'espèces et celle de l'utilisation de l'habitat par chaque espèce en fonction de l'âge des plantations. L'utilisation de cet habitat était donc influencée par la valeur alimentaire de la plantation. Cette étude a montré que plusieurs espèces (dont certaines, comme l'éléphant, garantissent l'attention de la conservation) fréquentent les plantations de moins de six ans plus souvent que celles de plus de six ans. Il faut donc poursuivre les mesures de conservation, comme des corridors pour la faune sauvage et des plantations de teck décalées, qui permettent les déplacements des grands mammifères dans la vallée. [source] Comparison of three expert elicitation methods for logistic regression on predicting the presence of the threatened brush-tailed rock-wallaby Petrogale penicillataENVIRONMETRICS, Issue 4 2009Rebecca A. O'Leary Abstract Numerous expert elicitation methods have been suggested for generalised linear models (GLMs). This paper compares three relatively new approaches to eliciting expert knowledge in a form suitable for Bayesian logistic regression. These methods were trialled on two experts in order to model the habitat suitability of the threatened Australian brush-tailed rock-wallaby (Petrogale penicillata). The first elicitation approach is a geographically assisted indirect predictive method with a geographic information system (GIS) interface. The second approach is a predictive indirect method which uses an interactive graphical tool. The third method uses a questionnaire to elicit expert knowledge directly about the impact of a habitat variable on the response. Two variables (slope and aspect) are used to examine prior and posterior distributions of the three methods. The results indicate that there are some similarities and dissimilarities between the expert informed priors of the two experts formulated from the different approaches. The choice of elicitation method depends on the statistical knowledge of the expert, their mapping skills, time constraints, accessibility to experts and funding available. This trial reveals that expert knowledge can be important when modelling rare event data, such as threatened species, because experts can provide additional information that may not be represented in the dataset. However care must be taken with the way in which this information is elicited and formulated. Copyright © 2008 John Wiley & Sons, Ltd. [source] Effects of habitat disturbance and food supply on population densities of three primate species in the Kakamega Forest, KenyaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2009Christos Mammides Abstract While habitat disturbance and food availability are major factors thought to determine the abundance of primates, evidence for their importance is uneven. We assessed the effects of these factors on three monkey species, guerezas (Colobus guereza), blue monkeys (Cercopithecus mitis) and redtails (Cercopithecus ascanius), in four areas of the Kakamega Forest, Kenya. Group densities of guerezas and blue monkeys were higher in areas where disturbance levels were also higher. Food availability measured as basal area density of food trees did not correlate significantly with the group densities of any of the three monkeys. The diversity of food trees, another potential measure of food abundance did, however, correlate with group densities of guerezas and blue monkeys suggesting that food availability may positively influence monkey density, and may sometimes increase with disturbance. Group densities of redtails did not correlate with any habitat variable examined, suggesting that factors other than those we considered may have influenced the abundance of this species particularly. Résumé Alors qu'on pense que ce sont les perturbations de l'habitat et la disponibilité de la nourriture qui déterminent l'abondance des primates, les preuves de cette importance sont mitigées. Nous avons étudié les effets de ces facteurs sur trois espèces de singes, le colobe guereza (Colobus guereza), le cercopithèque à diadème (Cercopithecus mitis) et le cercopithèque ascagne (Cercopithecus ascanius), dans quatre zones de la forêt de Kakamega, au Kenya. La densité des troupes de guerezas et de cercopithèques à diadème était plus forte dans les zones où le niveau de perturbation était plus élevé. La disponibilité de la nourriture, mesurée par la densité d'arbres alimentaires par unité de surface, ne montrait pas de corrélation positive avec la densité des troupes d'aucune des trois espèces de singes. La diversité des arbres alimentaires, autre mesure potentielle de l'abondance de nourriture, montrait une corrélation avec les troupes de guerezas et de mitis, suggérant que la disponibilité de la nourriture pourrait influencer positivement la densité des singes, et qu'elle peut parfois augmenter avec les perturbations. La densité des troupes d'ascanius ne montrait de corrélation avec aucune des variables de l'habitat étudiée, ce qui suggère que d'autres facteurs que ceux que nous avons étudiés pourraient avoir influencé particulièrement l'abondance de cette espèce. [source] Bird responses to fire severity and time since fire in managed mountain rangelandsANIMAL CONSERVATION, Issue 3 2010P. Pons Abstract Broom matorrals are subjected to extensive burning in the Pyrenees to improve grazing value, despite being a habitat of conservation interest in Europe. Our aim here is to evaluate the impact of such management practices over the long term, and of fire severity over the short term, on avifauna. Bird-habitat stations were distributed in broom shrublands from a few months to 51 years after fire, at 1400,2100 m a.s.l. Overall, shrub cover was the main habitat variable affecting the bird community composition. The abundance trends of bird species for half a century after fire were varied, but population recovery seemed slower (especially in the Dartford warbler Sylvia undata) than it had been reported at a lower altitude. Three species of European conservation concern (Alauda arvensis, Lullula arborea and Lanius collurio) showed abundance peaks at 10,19 years after fire. This time interval showed the highest species richness, abundance and conservation value, whereas shrub cover continued to increase afterwards. The bird assemblage tended to impoverish with increasing fire severity in the first year after a fire. Our results emphasize: (1) the slow recovery of bird community of burnt mountain shrublands; (2) the need for long-term biodiversity assessments to help improve planning of fire intervals at different altitudes; (3) the relevance of reducing fire severity due to its impact on fauna. [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] Bilby distribution and fire: a test of alternative models of habitat suitability in the Tanami Desert, AustraliaECOGRAPHY, Issue 6 2007Richard Southgate The distribution of the bilby Macrotis lagotis was assessed in the Tanami Desert using stratified random plots, repetitively sampled transects, aerial survey transects, and ground truth plots. Compared to a previous assessment of distribution, the extent of occurrence has changed little in the last 20 yr. However, the area of occupancy is small relative to the extent of occurrence and <25% of the current geographic range has bilby sign <20 km apart. Generalised linear modelling was used to determine the strength of association between bilby occurrence and habitat variables and identify refugia characteristics. Four competing candidate models were examined to determine whether bilby occurrence associated significantly with productive substrates and introduced herbivores, the distribution of key predator species, the pattern of fire, and climatic gradients including rainfall and temperature. For the entire study area, bilby presence associated most strongly with variables of mean annual rainfall, substrate type and the probability of dingo occurrence. Proximity to recently burnt habitat formed a significant predictor of bilby occurrence in a model derived for a reduced part of the study area where most sign was found. The work suggested that the current frameworks underpinning understanding of biotic distributions in arid Australia are deficient, and that climatic gradients, lateritic and rocky systems, and predators need to be incorporated into our thinking in the future. The extent of occurrence based on outlier records from opportunistic reports provided a misleading indication of the true status of the bilby. [source] To what extent can management variables explain species assemblages?ECOGRAPHY, Issue 6 2004A study of carabid beetles in forests Studies concerning the influence of forest management on invertebrate communities often focus on a limited set of chosen variables and rarely quantify the importance of management as opposed to other influences. We aimed at: 1) comparing the importance for species assemblages of habitat variables defined by management with those independent of it; 2) understanding the ecological significance of the variation remaining when both management and non-management variables are used. We caught carabid beetles according to a stratified pitfall sampling based on forest structure, tree composition and stand age. Forty-nine habitat variables were measured using three spatial scales. We decomposed the variation of species assemblages with successive constrained ordinations based on sets of variables, and studied the life traits of the species least and best explained by the model including all of the variables. Forest structure, composition and stand age showed important effects but explained a relatively small part of the overall variation in species assemblages. Management accounted for ca 30% of the variation, but non-management variables had a significant impact and the interaction between management and non-management sets resulted in significant influences. Most species for which the variation was highly explained by the model were generally large and with inefficient wings, while the least explained species were small. Our study suggests that: 1) even with highly controlled samples, the influence of management on species assemblages should not be studied by a limited set of categorical variables; 2) management variables may interact with factors outside of the manager's control; 3) a significant part of the variation cannot be explained by habitat variables and needs taking ecological processes into account; 4) rules to optimise constrained ordination techniques applied to species-habitat studies can be proposed. [source] Spatial correlations of Diceroprocta apache and its host plants: evidence for a negative impact from Tamarix invasionECOLOGICAL ENTOMOLOGY, Issue 1 2002Aaron R. Ellingson Abstract 1. The hypothesis that the habitat-scale spatial distribution of the Apache cicada Diceroprocta apache Davis is unaffected by the presence of the invasive exotic saltcedar Tamarix ramosissima was tested using data from 205 1-m2 quadrats placed within the flood-plain of the Bill Williams River, Arizona, U.S.A. Spatial dependencies within and between cicada density and habitat variables were estimated using Moran's I and its bivariate analogue to discern patterns and associations at spatial scales from 1 to 30 m. 2. Apache cicadas were spatially aggregated in high-density clusters averaging 3 m in diameter. A positive association between cicada density, estimated by exuvial density, and the per cent canopy cover of a native tree, Goodding's willow Salix gooddingii, was detected in a non-spatial correlation analysis. No non-spatial association between cicada density and saltcedar canopy cover was detected. 3. Tests for spatial cross-correlation using the bivariate IYZ indicated the presence of a broad-scale negative association between cicada density and saltcedar canopy cover. This result suggests that large continuous stands of saltcedar are associated with reduced cicada density. In contrast, positive associations detected at spatial scales larger than individual quadrats suggested a spill-over of high cicada density from areas featuring Goodding's willow canopy into surrounding saltcedar monoculture. 4. Taken together and considered in light of the Apache cicada's polyphagous habits, the observed spatial patterns suggest that broad-scale factors such as canopy heterogeneity affect cicada habitat use more than host plant selection. This has implications for management of lower Colorado River riparian woodlands to promote cicada presence and density through maintenance or creation of stands of native trees as well as manipulation of the characteristically dense and homogeneous saltcedar canopies. [source] Feeding, growth and nutritional status of restocked salmon parr along the longitudinal gradient of a large European river: the AllierECOLOGY OF FRESHWATER FISH, Issue 2 2009A. Descroix Abstract,,, The feeding, growth and nutritional status of salmon parr (0+) released at fry stage in different riffles were studied in a large temperate river (Allier, France) throughout the active feeding period. Significant differences were observed along the upstream,downstream gradient. Parr growth performance and energy storage were higher in downstream riffles and low in the most upstream one. These longitudinal growth variations are discussed in the context of diet and food availability differences, habitat variables and intra- and inter-species competition. The most favourable site for optimum growth and nutritional status appeared to be the intermediary riffle located in the grayling zone. [source] EVOLUTION OF MOUTHBROODING AND LIFE-HISTORY CORRELATES IN THE FIGHTING FISH GENUS BETTAEVOLUTION, Issue 4 2004Lukas Rüber Abstract The origin of and evolutionary transitions among the extraordinary diverse forms of parental care in teleost fish remain largely unknown. The "safe harbor" hypothesis predicts that the evolution from a "guarding" to a "brooding" form of care in teleost fish is associated with shifts in reproductive and life-history features such as reduced fecundity, and increased egg volume with higher parental investment. Robust phylogenetic hypotheses may help to identify evolutionary changes in key traits associated with differences in the form of parental care. Here, we used reconstruction of ancestral character states to study the evolution of the two forms of parental care, bubble nesting and mouthbrooding in the fighting fish genus Betta. We also applied a comparative analysis using the phylogenetic generalized least-squares method to test the "safe harbor" hypothesis by evaluating differences between the two forms of parental care in standard length, life-history traits, and three habitat variables. Evolutionary hypotheses were derived from the first molecular phylogeny (nuclear and mitochondrial DNA sequence data; 4448 bp) of this speciose group. Ancestral character state reconstructions of the evolution of the form of parental care in the genus Betta, using the methods of unweighted parsimony and maximum likelihood, are uncertain and further indicate a high rate of evolutionary transitions. Applying different weights for the suspected directionality of changes, based on the consistent phenotypic and behavioral differences found between bubble nesters and mouthbrooders, recurrent origin of mouthbrooding in the genus Betta is favored using parsimony. Our comparative analyses further demonstrate that bubble nesters and mouthbrooders do not have a consistent set of life-history correlates. The form of parental care in Betta is correlated only with offspring size, with mouthbrooders having significantly bigger offspring than bubble nesters, but is not correlated with egg volume, clutch size, and broodcare duration, nor with any of the three habitat variables tested. Our results thus challenge the general predictions of the "safe harbor" hypothesis for the evolution of alternative brood care forms in the fighting fish genus Betta. [source] ASYMMETRY IN STRUCTURAL DEFENSES: INSIGHTS INTO SELECTIVE PREDATION IN THE WILDEVOLUTION, Issue 9 2003C. A. Bergstrom Abstract Assessment of geographical patterns in fluctuating asymmetry (small, random differences between sides of bilateral characters) among populations shows promise as a tool to resolve the relative biomechanical importance of traits, in addition to being a possible indicator of habitat quality. We used 115 endemic freshwater populations of threespine stickleback (Gasterosteus aculeatus) from Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada, to explore the degree of concordance between geographical variation of asymmetry in a predator defense structure (bony lateral plates) and geographical variation in several indirect measures of predation regime as well as several abiotic habitat variables. We found a geographical cline in the population frequency of lateral plate asymmetries, with reduced asymmetry in the southern clear-water regions of the archipelago characterized by long reaction distances and greater chance of capture by predators, and elevated asymmetry in the northern stained-water regions with poor visibility and low chances of capture. Lateral plate asymmetry was strongly correlated with expression of several defensive armor traits, including total plate numbers among populations, mean cross-sectional diameter of stickleback with the dorsal and pelvic spines erect, and mean degree of overlap between the plates and spine supports. There were no significant correlations between frequency of asymmetric fish and any of our abiotic habitat variables. Stickleback with structural plate asymmetries had fewer trout-induced scars than symmetric fish in the significant majority of populations, and there was a decrease in structural plate asymmetry with age in stained-water habitats, suggesting that trout predators may be selectively removing asymmetric fish in some lakes. This study provides evidence that geographical variation in developmental stability of threespine stickleback, as seen in the frequencies of asymmetry, reflects differences among populations in the importance of structural defenses to fitness rather than differences in habitat quality, and that asymmetry may be a target of selection by predators in wild populations. [source] Habitat-mediated size selection in endangered Atlantic salmon fry: selectional restoration assessmentEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 4 2010Michael M. Bailey Abstract Preservation of adaptive variation is a top priority of many species restoration programs, but most restoration activities are conducted without direct knowledge of selection that might foster or impair adaptation and restoration goals. In this study, we quantified geographic variation in selection on fry size of endangered Atlantic salmon (Salmo salar) during the 6-week period immediately following stocking in the wild. We also used a model selection approach to assess whether habitat variables influence patterns of such selection. We found evidence for significant size-selection in five out of six selection trials. Interestingly, the strength and pattern of selection varied extensively among sites, and model selection suggested that this variation in phenotypic selection was related to geographic variation in the presence of large woody debris and the slope of the stream gradient. The strong selection differentials we observed should be a concern for endangered salmon restoration, whether they reflect natural processes and an opportunity to maintain adaptation, or an indicator of the potentially deleterious phenotypic consequences of hatchery practices. [source] Local and ecoregion effects on fish assemblage structure in tributaries of the Rio Paraíba do Sul, BrazilFRESHWATER BIOLOGY, Issue 12 2009BENJAMIN CARVALHO TEIXEIRA PINTO Summary 1.,We examined the effects of physical and chemical habitat variables and ecoregions on species occurrence and fish assemblage structure in streams of the Paraíba do Sul basin, in southeast Brazil. 2.,Fish and environmental data were collected from 42 sites on 26 first to fourth order streams (1 : 50 000 map scale) in three ecoregions. The sites occurred in one valley and two plateau ecoregions at altitudes of 40,1080 m and distances of 0.1,188 km from the main channel of the Rio Paraíba do Sul. Physical habitat (substratum, riparian cover, habitat types) and water quality (dissolved oxygen, pH, temperature and conductivity) variables were measured at each sampling site. 3.,A total of 2684 individuals in 16 families and 59 species were recorded. 4.,Ecoregion was a better predictor of the fish assemblage than the other environmental variables, according to the differences between the mean within-class and mean between-class similarities in assemblage data. 5.,Differing landscape characteristics were associated with differing local variables and thereby with differing fish assemblage structures. Riffles, shrub, grass, dissolved oxygen, conductivity and temperature were closely related to fish assemblage structure. 6.,Fish assemblages in sites far from the main river and at higher altitudes also differed from those near the Paraíba do Sul main channel, presumably as a result of differences in connectivity, covarying environmental factors and anthropogenic influence. 7.,These results reinforce the importance of understanding how stream communities are influenced by processes and patterns operating at local and regional scales, which will aid water resource managers to target those factors in their management and rehabilitation efforts. [source] Habitat selection by Ortolan Buntings Emberiza hortulana in post-fire succession in Catalonia: implications for the conservation of farmland populationsIBIS, Issue 4 2009MYLES H. M. MENZ 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. [source] Predicting the population consequences of human disturbance for Ringed Plovers Charadrius hiaticula: a game theory approachIBIS, Issue 2007DURWYN LILEY Human disturbance and its potential impacts upon bird populations are currently topical and contentious issues for conservationists. Although many studies have revealed a behavioural impact, or even direct effect on breeding success or survival, these cannot usually be extended to predict the impact on population size. Here we present a population model that allows predictions of the effect that changes in human numbers, visiting a 9-km-long section of the coastline, may have upon the size of a Ringed Plover Charadrius hiaticula population. Human disturbance affects Ringed Plovers in our study area through birds avoiding areas of high disturbance and, in addition, through the accidental trampling of a small number of nests by people walking on the beach. Using the level of human disturbance and habitat variables (which define territory quality) it is possible to predict which areas of beach are occupied and therefore the sites available to the population. Breeding success, for a given area of beach, can be predicted from habitat data. Incorporating known, density-independent, adult mortality allows the equilibrium population size to be predicted. This provides a model that predicts population size. This model is then used to predict the population that the site would support with different, hypothetical, levels of disturbance. If nest loss from human activity was prevented, for example by fencing nests, we predict the Plover population size would increase by 8%. A complete absence of human disturbance would cause a population increase of 85%. If the numbers of people were to double, we predict the population would decrease by 23%. [source] Factors influencing territorial occupancy and reproductive output in the Booted Eagle Hieraaetus pennatusIBIS, Issue 4 2006JOSÉ E. MARTÍNEZ During a 7-year research project in a forested area of southeastern Spain, we studied territorial occupancy and reproductive success in a Booted Eagle Hieraaetus pennatus population. We monitored 65 territories, gathering information on 406 occupancy events and 229 breeding attempts, including those of two potential competitors, the Northern Goshawk Accipiter gentilis and the Common Buzzard Buteo buteo. Generalized linear mixed models were used to explain occupancy and productivity, by evaluating the relative contribution of three different types of variables (habitat, competition and past events) and considering territory as a random effect. We examined a set of a priori hypothesized models, together with a number of additional models, and selected the best models following an information-theoretic approach. Our best models related territorial occupancy and productivity to previous breeding success (the fledging of one or two young), which appeared to be the most important factor determining the probability of reoccupation and the reproductive output in the subsequent year. The best occupation model revealed that the probabilities of occupancy were also conditioned by a competition variable (intraspecific nearest-neighbour distance) and two habitat variables (the location of the nest on the valley slope and the distance to the nearest forest track). Unlike the best occupation model, however, the selected model for reproductive output did not incorporate any competition variable besides previous breeding success, but included another two habitat variables (the effects of trunk height and NNE orientation). [source] Structure of Macroinvertebrate Communities in Relation to Environmental Variables in a Subtropical Asian River SystemINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2010Xiao-Ming Jiang Abstract Subtropical Asian rivers support a highly diverse array of benthic macroinvertebrates. Yet, their biodiversity and functionality has been poorly investigated. We choose the Chishui River system, one of the largest un-dammed, first level branches upstream of the Yangtze River, China, to: 1) determine the spatial pattern of macroinvertebrate diversity and community structure, and 2) examine the influence of variables at local habitat and basin scales on the distribution of macroinvertebrate communities. Samples were collected from 43 sites in spring of 2007. After Canonical Correspondence Analysis, two basin and five habitat variables were found to be significant predictors of the macroinvertebrate community structure. Variance partitioning analysis showed that habitat physical variables had a greater influence than other environmental variables in macroinvertebrate community, which suggested that preserving habitat, especially upstream, should be strongly considered in biological conservation. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Can niche use in red and grey squirrels offer clues for their apparent coexistence?JOURNAL OF APPLIED ECOLOGY, Issue 6 2002Jenny Bryce Summary 1Introduced species are, world-wide, one of the most serious threats to biodiversity. Grey squirrels Sciurus carolinensis are one of many introduced species to have threatened a native congener; they are thought to have replaced red squirrels Sciurus vulgaris throughout much of the UK as a result of competition. The rate of competitive replacement may be influenced by habitat composition, with some red squirrel populations persisting for prolonged periods in the presence of greys in predominantly coniferous forest. 2Here the similarity of red and grey squirrels' pattern of habitat use was investigated in Craigvinean forest in Scotland, UK, a site that has experienced apparent coexistence for up to 30 years. Overlap was examined in several dimensions: spatial overlap of home ranges, dynamic association and niche overlap. Habitat selection was examined at three levels: selection of core home range areas, selection of tree species within the home range, and the characteristics of patches used intensively by each squirrel species in comparison with random locations within their home range. 3Although there was overlap between red and grey squirrel ranges, there were clear differences in the macrohabitats utilized, with red squirrels selecting areas of Norway spruce Picea abies and grey squirrels selecting riparian corridors of mixed woodland for their home ranges. Within their home ranges, habitat selection by individual red and grey squirrels was similar, but again with reds selecting Norway spruce and greys selecting patches of mixed conifers and broad-leaved trees. As no habitat variables consistently affected the microdistribution of red and grey squirrels within blocks or ,stands' of trees, stands that were used were thought to constitute good and relatively homogeneous habitats for squirrels of either species. 4There was no evidence to suggest that red and grey squirrels avoided using the same areas at the same time, and potential niche overlap was considerable (0·77). However, partitioning of habitats may have reduced competition between red and grey squirrels and hence have contributed to red squirrel persistence at this site. 5This work (i) reinforces earlier proposals that forest management offers a promising tool to assist the conservation of red squirrels; (ii) raises the issue of determining the spatial scale at which coexistence operates; and (iii) offers an illustration of how the management of invasive species can be mediated through the manipulation of niche availability. [source] Red-tail monkey groups in forest patches outside the protected area system in the ,Kampala area'AFRICAN JOURNAL OF ECOLOGY, Issue 2004D. Baranga Abstract This study was conducted in the ,Kampala area', a forest-savanna-agricultural mosaic, and was aimed at investigating the ecology and survival of the red-tail monkey, Cercopithecus ascanius schmidti in fragmented forest patches outside the protected area system. The relationship between habitat variables and red-tail monkeys' distribution and other demographic factors were investigated. The average group size for red-tail monkeys in the forest patches was 11.9, while that in Mpanga Forest Reserve it was 23.2. Most of the red-tail monkey groups had breeding females but there were small populations with no breeding females. The number of breeding females and young varied in different forest patches with the breeding sex ratio ranging from 0 to 1:3. The residential status of red-tails in the patches was partly influenced by the presence of the vervet monkey and the intensity of human activities in the vicinity. [source] Habitat specialization and adaptive phenotypic divergence of anuran populationsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2005J. VAN BUSKIRK Abstract We tested for adaptive population structure in the frog Rana temporaria by rearing tadpoles from 23 populations in a common garden experiment, with and without larval dragonfly predators. The goal was to compare tadpole phenotypes with the habitats of their source ponds. The choice of traits and habitat variables was guided by prior information about phenotypic function. There were large differences among populations in life history, behaviour, morphological shape, and the predator-induced plasticities in most of these. Body size and behaviour were correlated with predation risk in the source pond, in agreement with adaptive population divergence. Tadpoles from large sunny ponds were morphologically distinct from those inhabiting small woodland ponds, although here an adaptive explanation was unclear. There was no evidence that plasticity evolves in populations exposed to more variable environments. Much among-population variation in phenotype and plasticity was not associated with habitat, perhaps reflecting rapid changes in wetland habitats. [source] Effect of wave exposure dynamics on gut content mass and growth of young-of-the-year fishes in the littoral zone of lakesJOURNAL OF FISH BIOLOGY, Issue 7 2010S. Stoll Total length, body mass and gut content mass of young-of-the-year (YOY) perch Perca fluviatilis, dace Leuciscus leuciscus and bleak Alburnus alburnus were recorded over the summer of 2006 at three littoral sites at Upper Lake Constance. In P. fluviatilis and L. leuciscus, gut content mass correlated positively with wave-induced energy flux (EF) of the respective site and sampling day, while no correlation of gut content mass with EF was found in A. alburnus. It was assumed that benthivorous P. fluviatilis and L. leuciscus profited from suspended or uncovered benthic food items generated by wave action at sites and periods with high EF. Alburnus alburnus, in contrast, feeding mainly on zooplankton in upper parts of the water column, could not profit from increased EF. In P. fluviatilis, increased gut content mass during periods of high EF resulted in higher growth rates. For L. leuciscus, no real growth rates in local fish populations could be determined, as individuals were less sedentary, and when increased growth occurred at sites during the periods of high EF, migration of fish levelled out the resulting size differences within few days. The results of this study show that dynamic habitat variables affect site profitability in the littoral zone of lakes, especially in benthivorous fishes. Therefore, dynamic habitat variables should be considered in addition to fixed habitat properties in analyses of habitat choice of fishes in the littoral zone of lakes. [source] Habitat selection by juvenile Atlantic salmon: the interaction between physical habitat and abundanceJOURNAL OF FISH BIOLOGY, Issue 4 2005R. D. Hedger The effect of physical river habitat variables on the distribution of juvenile Atlantic salmon Salmo salar L. in the Rivière de la Trinité, Québec, Canada, was examined using generalized additive modelling. A survey of Atlantic salmon fry and parr densities and habitat variables (flow velocity, water column depth and substratum size) was conducted in the summer months from 1984 to 1992. Clear patterns of habitat use existed: specific ranges of habitat variables were selected, with parr preferring greater velocities, depths and substratum sizes than fry. There was a large variation, however, in juvenile densities for given velocities, depths or substratum sizes, with this variation being greatest in optimal habitats. On examination of an individual year, interaction between the variables was found to explain some of the variation. On a year-to-year basis the juvenile Atlantic salmon population was found to exhibit an ,Ideal Free Distribution', which resulted in greatest variation in optimal habitats with year-to-year changes in population abundance. [source] Invasibility of a coastal strip in NE Spain by alien plantsJOURNAL OF VEGETATION SCIENCE, Issue 4 2002Eduardo Sobrino Castroviejo et al. (1986,1999); Tutin et al. (1968,1980) Abstract. The alien plant species and the ecological factors that facilitate their invasion to a coastal strip in the Baix Camp region (Tarragona, NE Spain) were studied. A detailed inventory of the area showed that 20% of the plant species, most of them from the American Continent, were aliens, many of which were strongly invasive. At the habitat level, the relationships between the invasive behaviour and a number of autecological, ecological and habitat variables were analysed by means of logistic analyses. In the best model five variables were related to alien plant invasions: climatic affinity, disturbance of the invaded habitat, route of introduction, soil moisture during summer, and life form. To elucidate the environmental factors that could be responsible for alien plant invasions at a regional scale, the number of alien taxa and the environmental features at 13 localities of the western Mediterranean area were analysed. The warm lowlands, subjected to low annual rainfall and high population density, exhibited the greatest reception capacity for alien plants. It is concluded that various specific environmental features , high mean temperatures, the abundance of riparian systems, the existence of biotopes with favourable water balance which harbour a great richness of alien species and the high human pressure to which the enclave is subjected, combined with the ecological requirements of the alien species and certain species attributes (biotype) can interact at different scales and have caused the over-representation of alien plants. [source] The Yellow-necked Mouse Apodemus flavicollis in Britain: status and analysis of factors affecting distributionMAMMAL REVIEW, Issue 3-4 2001Aidan C. W. Marsh ABSTRACT A national survey of the Yellow-necked Mouse (Apodemus flavicollis) in Britain was undertaken by The Mammal Society. The live-trapping study sampled small mammal populations from 168 deciduous woodlands in autumn 1998. Within their range, Yellow-necked Mice were widespread in deciduous woodland and were more abundant than Wood Mice in 15% of the woodlands sampled. These trapping records, as well as records solicited from local recorders, record centres and individuals, supplemented the existing distribution map, confirming the general pattern, but with minor extensions to some range borders. Yellow-necked Mice were found in woodland of all ages, but were more common in woods of ancient origin than in younger woodland. Woodland size was not important in determining the presence or abundance of Yellow-necked Mice, but they were more often absent from woods more than 2 km from neighbouring substantial woodland. The presence of Yellow-necked Mice did not affect the relative abundance of Wood Mice (Apodemus sylvaticus). However, the decline in the proportion of breeding male Wood Mice at the end of the main breeding season was more marked in those woods that also contained Yellow-necked Mice. Where their ranges overlapped, Bank Voles (Clethrionomys glareolus) were less abundant where Yellow-necked Mice were also present. The distribution of the Yellow-necked Mouse was explored with respect to a number of climatic, soil and habitat variables. Maximum summer temperature was the most significant variable explaining distribution, although woodland cover variables also contributed. Soil moisture and pH, mean rainfall and winter temperature parameters did not predict Yellow-necked Mouse distribution. Low summer temperature may limit Yellow-necked Mouse distribution through its impact on tree seed production and diversity. Climatic change leading to a rise in summer temperature might encourage range expansion by Yellow-necked Mice, if their other habitat requirements are met. [source] Improving predictions of the location and use of warrens in sensitive rabbit populationsANIMAL CONSERVATION, Issue 5 2009I. C. Barrio Abstract The location and use of warrens is a key factor in the population dynamics of the European rabbit Oryctolagus cuniculus L., which can influence stability and persistence in the long term. Within the species' original distribution range, its numbers have declined sharply in recent decades, which is a serious problem for the conservation of Mediterranean ecosystems. Artificial warrens are commonly used to bolster rabbit populations and the characterization of natural warrens in those areas might improve their efficiency. In this study, we use binomial generalized linear models to identify the factors associated with the location and use of warrens in a low-density area and we evaluate the effect of including the spatial structure of the data in the model. In addition, we generate a map that predicts the most suitable areas for artificial warrens. Contrary to what was expected, habitat variables are only secondary factors, and the location and use of warrens is influenced mainly by spatial factors, such as proximity to nearby warrens. Furthermore, the aggregated spatial pattern of warrens suggests that, at the local scale, for example, the hunting estate, intra-specific interactions might be playing a primary role in these low-density populations. To identify the most suitable sites for artificial warrens and, thereby, improve the efficiency of artificial warren building for conservation purposes, information about spatial structures should be included in models predicting natural warrens of European rabbits. [source] Can a large metropolis sustain complex herpetofauna communities?ANIMAL CONSERVATION, Issue 5 2009An analysis of the suitability of green space fragments in Rome Abstract Urban areas are primary causes of species' range fragmentation and reduction. However, relatively few studies have attempted to describe the habitat variables influencing the diversity and conservation of amphibians and reptiles, particularly in Mediterranean Europe and in large metropolitan areas. We explored this broad conservation ecology problem by studying the richness and diversity patterns in relation to a suite of six independent habitat variables in Rome, one of the most ancient cities of the world. We considered all the green remnant areas (n=62) of Rome, ranging 1 to >1000 ha in size, which are interspersed within a sea of urbanized matrix. A total of 10 amphibian and 15 reptile species were studied. Their presence/absence patterns were assessed and the effects of the various habitat variables on each species were predicted by a logistic regression model. A total of 1261 presence records (404 amphibians and 857 reptiles) were analysed. Fragment size and wood size within each fragment did correlate significantly with the species richness of both amphibians and reptiles, and there was a clear threshold effect after 50 ha of wooded surface. The presence of water bodies positively affected the species distribution. One amphibian and three reptiles inhabited exclusively fragments >50 ha. The distance from the centre did not affect fragment species richness. The presence of most species of both amphibians and reptiles was positively influenced by the irregular versus circular shape of the wooded area. The legal protection of a given area did not influence the observed patterns but the total number of sheltered species. Overall, our study suggests that, in order to maintain the current diversity and population viability, it is necessary, in addition to water bodies' maintenance, to (1) preserve the wooded landscapes over 50 ha; (2) promote irregularly shaped increases in the wood surface; (3) maintain ecotonal boundaries. [source] Domestic dogs as an edge effect in the Brasília National Park, Brazil: interactions with native mammalsANIMAL CONSERVATION, Issue 5 2009A. C. R. Lacerda Abstract Edge effects are a well-known result of habitat fragmentation. However, little has been published on fragmentation, isolation and the intrusive influence from the surrounding matrix at the landscape level. The objectives of the present study are to evaluate the presence of dogs in the Brasília National Park (BNP) in relation to habitat type and the influence from the surrounding matrix. In addition, this study examines the response of the native mammal fauna to the presence of dogs. Track stations were built along dirt roads in the BNP and subsequently examined for the presence or absence of tracks. We used a stepwise logistic regression to model the occurrence of five mammal species relative to habitat variables, with an ,=0.05 to determine whether to enter and retain a variable in the model. A simulation of each species occurrence probability was conducted using a combination of selected habitat variables in a resource selection probability function. Results indicate a negative relationship between distance from the BNP edge and the probability of dog occurrences. From an ecological perspective, the presence of dogs inside the BNP indicates an edge effect. The occurrence of the maned wolf was positively associated with distance from a garbage dump site and negatively associated with the presence of dog tracks. The maned wolf and giant anteater seem to avoid areas near the garbage dump as well as areas with dog tracks. There is no support for the possible existence of a feral dog population inside the BNP, but the effects of free-ranging dogs on the wildlife population in such an isolated protected area must not be neglected. Domestic dog Canis familiaris populations and disease control programs should be established in the urban, sub-urban and rural areas surrounding the BNP, along with the complete removal of the garbage dump from the BNP surroundings. [source] | |||||||||||||||||||||||||||||||