24,568 research outputs found
Effects of seminatural habitats on spiders in olive groves and their potential role against Bactrocera oleae (Rossi) (Diptera: Tephritidae)
No full textEffects of habitat isolation and predation pressure on an arboreal food-web
No full textHabitat isolation is expected to reduce population densities of animals via reduced immigration. However, altered trophic interactions in isolated habitats may modify these effects, especially since the strength of isolation effects is expected to increase with trophic rank. Here, we studied effects of habitat isolation on a food-web module consisting of herbivorous beetles, predatory spiders, spider-preying wasps and arthropod-feeding birds. We compare two systems that were studied in subsequent years: a study on 29 mature apple orchards that varied in the degree of isolation from forest, and a study on 20 groups of newly planted cherry trees that showed similar variation in their degree of habitat isolation. No birds were observed on the young fruit trees. Wasps and spiders showed the expected lower abundances in isolated habitats. On mature trees, birds were present and showed lower abundances in isolated habitats. Wasps were reduced to a similar degree by habitat isolation as on the young trees. Surprisingly, spider densities on the mature trees were higher in isolated than in connected habitat. This contrasting response of spiders to habitat isolation is likely to be due to release from bird predation in isolated mature orchards. In both study systems, beetles showed no significant effect of habitat isolation. Our results confirm that the sensitivity to fragmentation increases with trophic rank, and suggest that trophic interactions should receive more attention in fragmentation studies.Swiss National Science foundation [3100A0-114058
Taxonomic and functional differentiation of spiders in habitats in a traditional olive producing landscape in Italy
No full textAnnual crops are generally assumed to host simplifi ed arthropod communities that depend on immigration from the surrounding landscape. Perennial, low-input crops such as olive groves are likely to depend less on immigration from other habitats, however, studies on the landscape ecology of perennial crops are scarce. This paper studies the assemblages of arboreal spiders in three types of habitats adjoining olive groves: woods, garigue and other cultivated olive groves in a traditional olive producing landscape. Spiders were sampled during summer and the three types of habitats were compared in terms of species, families and functional groups in order to determine differences in diversity and the potential for spider spillover. As is often reported for annual crops, olive groves had a lower alpha and beta diversity than more natural habitats in terms of species, with a strong dominance of a single species, Frontinellina frutetorum (C.L. Koch, 1834). Differences in diversity between olive groves and natural habitats were not signifi cant at family or functional group levels. With the possible exception of orb weavers, this study indicates that the spiders that were common in olive groves did not occur at higher densities in habitats that were more natural. This indicates there is limited spillover between perennial crops and other late-successional habitats. The enhancement of spiders in olive orchards for pest control may thus depend more on local management than on the presence of semi-natural habitats as a source of immigration
Body size–climate relationships of European spiders
No full textAim: Geographic body size patterns of mammals and birds can be partly understood under the framework of Bergmann's rule. Climatic influences on body size of invertebrates, however, appear highly variable and lack a comparable, generally applicable theoretical framework. We derived predictions for body size–climate relationships for spiders from the literature and tested them using three datasets of variable spatial extent and grain. Location: Europe. Methods: To distinguish climate from space, we compared clines in body size within three datasets with different degrees of co-variation between latitude and climate. These datasets were: (1) regional spider faunas from 40 European countries and large islands; (2) local spider assemblages from standardized samples in 32 habitats across Europe; and (3) local spider assemblages from Central European habitats. In the latter dataset climatic conditions were determined more by habitat type than by geographic position, and therefore this dataset provided a non-spatial gradient of various microclimates. Spider body size was studied in relation to latitude, temperature and water availability. Results: In all three datasets the mean body size of spider assemblages increased from cool/moist to warm/dry environments. This increase could be accounted for by turnover from small-bodied to large-bodied spider families. Body size–climate relationships within families were inconsistent. Main conclusions: Starvation resistance and accelerated maturation can be ruled out as explanations for the body size clines recorded, because they predict the inverse of the observed relationship between spider body size and temperature. The relationship between body size and climate was partly independent of geographic position. Thus, the restriction of large-bodied spiders to their glacial refugia owing to dispersal limitations can be excluded. Our results are consistent with mechanisms invoking metabolic rate, desiccation resistance and community interactions to predict a decrease in body size from warm and dry to cool and moist conditions
Water limitation prevails over energy in European diversity gradients of sheetweb spiders (Araneae: Linyphiidae)
No full textAcross large spatial scales, species richness in many taxa is mainly determined by climatic variables. However, some of the mechanisms behind large-scale patterns of species richness and abundance are expected to act on the community level, and on a smaller scale than the resolution of the data commonly used for deriving these patterns. We studied the distribution of sheetweb spiders (Araneae: Linyphiidae) across Europe using both standardised samples from local habitats and large-scale inventories. In the first approach, we analysed species and individual numbers from standardised pitfall traps from 17 locations distributed from northern Sweden to Spain and Greece. We also calculated Simpson indices to correct for different activity densities. Additionally, we analysed whether diversity of sheetweb spiders is sensitive to habitat type. In the second approach, we investigated the known sheetweb spider species richness of European countries and large islands. In both datasets, species richness of sheetweb spiders reached a maximum at about 55°N and declined towards the Mediterranean and the Arctic. In addition, species richness decreased from western (maritime) to eastern (continental) regions. Also Simpson diversity showed a hump-shaped relation to latitude, and was the only variable influenced by habitat type. In contrast to species richness and diversity, activity density increased monotonously with latitude. Towards the north, sheetweb spiders are likely limited by energy availability, towards the south, water limitation as well as bottom-up and top-down community interactions may reduce sheetweb spiders. Accordingly, their diversity does not follow the pattern of vertebrates, large insects and aquatic organisms, which depend more strongly on energy availability
Large variatiion of suction sampling efficiency depending on arthropod groups, species traits and habitat properties
No full textContrasting effects of habitat fragmentation, population density, and prey availability on body condition of two orb-weaving spiders
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