Martinez N.,Hintermann and Weber AG
Bird Study | Year: 2012
Capsule Amount of sparse vegetation show a direct link to reproductive success. Aims To examine the influence of sparse vegetation on clutch size of Common Redstarts Phoenicurus phoenicurus. Methods Clutch size and the amount of sparse ground vegetation within territories were measured. Results Clutch size was positively correlated with the amount of sparse vegetation. Clutches in territories with the highest amounts of sparse vegetation contained approximately one more egg than clutches in territories with the lowest amount of sparse vegetation. Conclusion The presence of sparse vegetation is correlated with clutch size and thus reproductive success. This finding suggests a direct link between habitat degradation through the loss of sparse vegetation and observed population decreases of bare-ground foraging birds. The results strengthen the argument that the implementation of sparse vegetation in agri-environment schemes is likely to improve the breeding success of bare-ground foraging birds, such as Common Redstarts. © 2012 British Trust for Ornithology.
Hanspach J.,Helmholtz Center for Environmental Research |
Hanspach J.,Luneburg University |
Schweiger O.,Helmholtz Center for Environmental Research |
Kuhn I.,Helmholtz Center for Environmental Research |
And 6 more authors.
Ecography | Year: 2014
Species ranges are shaped by both climatic factors and interactions with other species. The stress gradient hypothesis predicts that under physiologically stressful environmental conditions abiotic factors shape range edges while in less stressful environments negative biotic interactions are more important. Butterflies provide a suitable system to test this hypothesis since larvae of most species depend on biotic interactions with a specific set of host plants, which in turn can shape patterns of occurrence and distribution. Here we modelled the distribution of 92 butterfly and 136 host plant species with three different modelling algorithms, using distribution data from the Swiss biodiversity monitoring scheme at a 1 × 1 km spatial resolution. By comparing the ensemble prediction for each butterfly species and the corresponding host plant(s), we assessed potential constraints imposed by host plant availability on distribution of butterflies at their distributional limits along the main environmental gradient, which closely parallels an elevational gradient. Our results indicate that host limitation does not play a role at the lower limit. At the upper limit 50% of butterfly species have a higher elevational limit than their primary host plant, and 33% have upper elevational limits that exceed the limits of both primary and secondary hosts. We conclude that host plant limitation was not relevant to butterfly distributional limits in less stressful environments and that distributions are more likely limited by climate, land use or antagonistic biotic interactions. Obligatory dependency of butterflies on their host plants, however, seems to represent an important limiting factor for the distribution of some species towards the cold, upper end of the environmental gradient, suggesting that biotic factors can shape ranges in stressful environments. Thus, predictions by the stress gradient hypothesis were not always applicable. © 2013 The Authors.
Dorazio R.M.,U.S. Geological Survey |
Kery M.,Swiss Ornithological Institute |
Royle J.A.,U.S. Geological Survey |
Plattner M.,Hintermann and Weber AG
Ecology | Year: 2010
A variety of processes are thought to be involved in the formation and dynamics of species assemblages. For example, various metacommunity theories are based on differences in the relative contributions of dispersal of species among local communities and interactions of species within local communities. Interestingly, metacommunity theories continue to be advanced without much empirical validation. Part of the problem is that statistical models used to analyze typical survey data either fail to specify ecological processes with sufficient complexity or they fail to account for errors in detection of species during sampling. In this paper, we describe a statistical modeling framework for the analysis of metacommunity dynamics that is based on the idea of adopting a unified approach, multispecies occupancy modeling, for computing inferences about individual species, local communities of species, or the entire metacommunity of species. This approach accounts for errors in detection of species during sampling and also allows different metacommunity paradigms to be specified in terms of species-and location-specific probabilities of occurrence, extinction, and colonization: all of which are estimable. In addition, this approach can be used to address inference problems that arise in conservation ecology, such as predicting temporal and spatial changes in biodiversity for use in making conservation decisions. To illustrate, we estimate changes in species composition associated with the species-specific phenologies of flight patterns of butterflies in Switzerland for the purpose of estimating regional differences in biodiversity. © 2010 by the Ecological Society of America.
Schai-Braun S.C.,University of Natural Resources and Life Sciences, Vienna |
Weber D.,Hintermann and Weber AG |
Hacklander K.,University of Natural Resources and Life Sciences, Vienna
European Journal of Wildlife Research | Year: 2013
The number of European brown hares (Lepus europaeus) has been declining throughout much of Europe since the 1960s. Consequently, many studies have focused on analysing habitat selection of European hares in order to improve the suitability of the habitat for this species. Habitat preferences of European hares are known to be affected by hare density, but most studies have been conducted in agricultural areas where hare densities were medium to high. Finding habitat preferences at high densities is difficult as most available habitats are occupied. In addition, in agricultural areas, field size might influence the hares' habitat selection because it affects the distribution and availability of certain habitat types. However, most studies relate to areas with large field sizes. In this study, we analysed the habitat preferences of European hares in spring and autumn during the activity period, in the early hours of the night, in an agricultural area with low hare density and small average field size using Chesson's electivity index. Moreover, we focused on the question whether two different habitat classifications varying in their specificity might cause contradictory results regarding European hares' habitat preferences. Our results show that in this agricultural area with low hare density, European hares avoided several habitat types which were preferred in other study areas with higher hare densities. Therefore, we assume that hare density has an influence on the species' habitat selection. In contrast, the small average field size of our study area seemed not to have an effect on hare habitat preference. Furthermore, by pooling habitat types into broader groups, substantial information was lost in some categories. Hence, for some categories, e.g. grassland or agricultural crop land, more detail might be needed than for others, such as urban areas, when analysing hares' habitat selection. In conclusion, our results imply that studies on habitat preferences have to be conducted in areas with low hare density to be able to gain knowledge on the species' habitat requirement and hereinafter improve the suitability of the habitat for this species. © 2012 Springer-Verlag Berlin Heidelberg.
Lang A.,University of Basel |
Buhler C.,Hintermann and Weber AG
Ecological Indicators | Year: 2012
Butterflies (Lepidoptera) have been suggested for environmental monitoring of genetically modified organisms (GMO) due to their suitability as ecological indicators, and because of the possible adverse impact of the cultivation of current transgenic crops. A critical point is the sampling effort to be invested in such a monitoring. Here, we estimated the required sample size necessary to monitor potential effects of genetically modified crops on butterflies (Lepidoptera). We used data from two Swiss long-term butterfly monitoring surveys applying the common transect count method. The two monitoring surveys differed in several basic aspects such as geographical area covered, landscape context and sampling intensity. We carried out prospective power analyses in order to estimate the required sample size to detect effects of differing magnitude on mean species number, total individual abundance, mobility classes of butterflies and selected individual species. The required sample size decreased substantially when effect sizes above 10% were estimated. For example, a sample size of 79 transects would be sufficient to detect changes of 30% in total individual abundance for both survey types. Detecting effects on mean species number would need much less transects. Considerably more samples would be needed to analyze the abundance of single species. Several options are presented to increase statistical power or reduce required sample size, respectively. Also, we recommend to pool species to different mobility classes, and/or analyze patch occupancy of species instead of their individual abundance. The transect count approach is a suitable method for butterfly monitoring, both on a local as well as on a landscape scale. Consequently, both types of Swiss butterfly monitoring schemes are basically suitable for GMO monitoring. If transects are short and restricted to intensely used landscape, even non-professional field workers may yield data sufficient for effective monitoring, which might be relevant with respect to involved costs. © 2011 Elsevier Ltd.