1,720,973 research outputs found
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
Effects of vineyard management on biodiversity at three trophic levels
No full textIn annual crops, where disturbance intensities are generally high, numerous investigations demonstrated beneficial effects of organic and other extensive farming practices on biodiversity. It is however unclear if organic farming has the same beneficial effect in perennial crops (e.g. vineyards) because of a generally reduced background disturbance level. Moreover, the impact of farming practices on biodiversity may differ between trophic levels. We tested the effect of farming practices differing in disturbance intensity on the abundance, species richness and community composition of three trophic levels (plants, grasshoppers and spiders) in Swiss vineyards. Organic and conventional vineyards were compared, and within the latter different options of weed control (mowing vs. mulching) and pest management (hand spraying vs. helicopter spraying) were investigated. In contrast to findings in annual crops, organic farming promoted neither diversity nor abundance at any trophic level. Grasshopper diversity was even significantly lower in organic compared to conventional vineyards. Weed control as well as pest management differed in their effects, depending on the trophic level. Within conventionally managed vineyards, spider and grasshopper diversity were enhanced by mulching, while plants benefited from the lower disturbance of mowing. The greater disturbance of fungicide spraying by hand than by helicopter was disadvantageous for grasshoppers, but did not affect spiders and plants. Thus, different taxa respond differently not only to an increase in disturbance but also to different types of disturbance and local site conditions. We conclude that disturbance in organically farmed vineyards appears to be too low to be beneficial for biodiversity
Bees increase seed set of wild plants while the proportion of arable land has a variable effect on pollination in European agricultural landscapes
No full textBackground and aims – Agricultural intensification and loss of farmland heterogeneity have contributed to population declines of wild bees and other pollinators, which may have caused subsequent declines in insect-pollinated wild plants. Material and methods – Using data from 37 studies on 22 pollinator-dependent wild plant species across Europe, we investigated whether flower visitation and seed set of insect-pollinated plants decline with an increasing proportion of arable land within 1 km. Key results – Seed set increased with increasing flower visitation by bees, most of which were wild bees, but not with increasing flower visitation by other insects. Increasing proportion of arable land had a strongly variable effect on seed set and flower visitation by bees across studies. Conclusion – Factors such as landscape configuration, local habitat quality, and temporally changing resource availability (e.g. due to mass-flowering crops or honey bee hives) could have modified the effect of arable land on pollination. While our results highlight that the persistence of wild bees is crucial to maintain plant diversity, we also show that pollen limitation due to declining bee populations in homogenized agricultural landscapes is not a universal driver causing parallel losses of bees and insect-pollinated plants.Background and aims – Agricultural intensification and loss of farmland heterogeneity have contributed to population declines of wild bees and other pollinators, which may have caused subsequent declines in insect-pollinated wild plants. Material and methods – Using data from 37 studies on 22 pollinator-dependent wild plant species across Europe, we investigated whether flower visitation and seed set of insect-pollinated plants decline with an increasing proportion of arable land within 1 km. Key results – Seed set increased with increasing flower visitation by bees, most of which were wild bees, but not with increasing flower visitation by other insects. Increasing proportion of arable land had a strongly variable effect on seed set and flower visitation by bees across studies. Conclusion – Factors such as landscape configuration, local habitat quality, and temporally changing resource availability (e.g. due to mass-flowering crops or honey bee hives) could have modified the effect of arable land on pollination. While our results highlight that the persistence of wild bees is crucial to maintain plant diversity, we also show that pollen limitation due to declining bee populations in homogenized agricultural landscapes is not a universal driver causing parallel losses of bees and insect-pollinated plants
Structural versus functional habitatconnectivity measures to explain bird diversity in fragmented orchards
No full textNon-crop habitats in the landscape enhance spider diversity in wheat fields of a desert agroecosystem
No full textSpiders (Araneae) are an important group of generalist predators in arable land. In temperate climates, spiders recolonise cropland annually from the surrounding landscape. In arid climates however, irrigated crops and the surrounding landscape matrix offer sharply different habitat conditions and this might negatively affect spider migration into crops. We studied whether the spider fauna in desert crops is influenced by the surrounding landscape in a similar way to that found in temperate climates. Spiders were sampled with pitfall traps in 13 wheat fields (Triticum aestivum L.) in the Negev Desert (Israel). The fields were situated along a gradient from crop- to non-crop-dominated landscapes (1–72% non-crop habitats). Species richness of spiders in wheat fields increased with the percentage of non-crop habitats in the landscape. In addition, activity-densities of crab spiders (Thomisidae) and cobweb spiders (Theridiidae) were enhanced by high percentages of non-crop habitats in the surrounding landscape. Activity-densities of the dominant sheetweb spiders (Linyphiidae) showed no significant response to landscape composition. As the immigrant spider families employ different foraging strategies than the dominant sheetweb spiders, they functionally enriched the spider fauna in crops and potentially increase the range of prey types consumed by spiders. Thus, non-crop habitats can be expected to increase the potential for biological control by spiders in nearby crops
Body size determines the outcome of competition for webs among alien and native sheetweb spiders (Araneae: Linyphiidae)
No full textAre spider assemblages in fragmented, semi-desert habitat affected by increasing cover of agricultural crops?
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