Showing papers by "Volkmar Wolters published in 2004"

Edge effects on ant community structure and species richness in an agricultural landscape

Abstract: The effect of sharp edges between three different types of land use on the species richness and structure of ant communities was examined in an agricultural landscape within Central Hesse, Germany. Species richness and nest densities of ants at the centres and the edges of meadows, crop fields, and fallow land were recorded by hand sampling during 1997 and 1998. Edges between different land-use types did not increase ant species richness at the landscape scale, nor were they unique habitats for a specialised ant fauna. Nonetheless, most species shared ‘ecotonal effects’ in the way that their relative abundance either decreased (e.g. Myrmica scabrinodis) or increased (e.g. Lasius niger, Lasius flavus) at the edges, resulting in different community structure between edges and centres of the land-use types. This was influenced by two major factors: (i) the boundary contrast between the neighbouring habitats (i.e. in terms of disturbance caused by agricultural practices), and (ii) the response of different species to changing abiotic conditions. High nest densities of aggressive species with large colonies occurred along edges. We hypothesise that this can significantly reduce edge permeability for surface-dwelling arthropods.

Response of different decomposer communities to the manipulation of moisture availability: potential effects of changing precipitation patterns

Abstract: The potential impacts of changes in precipitation patterns associated with global climate change on the relationship between soil community diversity and litter decomposition were investigated. For a period of ca. 5 months, two decomposer communities in litterbags (1000 and 45 mum mesh size) containing spruce litter were subjected to two irrigation treatments: constant and fluctuating (drying/rewetting) moisture conditions. The latter were expected to induce moisture stress on the decomposer communities. The two mesh sizes were used to exclude different faunal components from the decomposer communities. The 1000 mum mesh excluded only the macrofauna, whereas the 45 mum mesh excluded both the macro- and mesofauna. In the short-term perspective of the present study, mesofauna abundance showed no response to imposed fluctuating moisture conditions. Irrespective of the presence of mesofauna, mass loss, microbial biomass and the control mechanisms, regulating carbon mineralization appeared unaffected by fluctuating moisture conditions. The reduction in the functional/structural diversity of the decomposer communities in the 45 mum litterbags resulted in strongly increased Nematoda abundance but it did not alter the response of Nematoda to fluctuating moisture conditions. Processes in the nitrogen (N)-cycle and mass loss were sensitive indicators of changes in the structural and functional complexity of decomposer communities. However, a negative effect of fluctuating moisture conditions on extractable N was coupled to the presence of mesofauna. Extremes in rainfall patterns, generated by climate change, may have a negative impact on the availability of nutrients, particularly N, for plants. This effect could be amplified by an additional impoverishment in the structural and functional complexity of the respective decomposer communities.

Limitations of faunal effects on soil carbon flow: density dependence, biotic regulation and mutual inhibition

Abstract: Soil animals are known to stimulate soil microbial activity and thereby to accelerate decomposition of soil organic matter. In this paper, we investigate potential limitations of soil animal effects on soil carbon flow by analysing how animal effects relate to the density of four major faunal groups. Specifically, we analyse the extent to which faunal effects are subject to biotic regulation or to mutual inhibition between groups under different levels of resource supply. In an extensive laboratory experiment, 96 microcosms established in three consecutive blocks were inoculated with nematodes, enchytraeids, microarthropods, and lumbricids. Each faunal group was inoculated in three densities, including combinations of groups. Introduced animal densities were within the natural range of densities in fallow soil. Bare agricultural soil and soil covered with maize litter were used as substrates. The microcosms were kept under constant conditions at 12 °C and 50% water holding capacity for 8 weeks. Soil CO 2 evolution was measured daily by means of gas chromatography. Animal effects were on an average relatively stronger in bare soil (+95% CO 2 ; R 2 =0.76) than in soil with litter (+14% CO 2 ; R 2 =0.40), where organic matter decomposition was seven times more intense. Higher animal densities generally led to accelerated decomposition up to three times that of the controls. However, beyond a specific density, decomposition rates stopped increasing or even declined, depending on the faunal group. In addition, animal effects were limited by mutual inhibition between groups in bare soil where effects were strong, while stimulatory interactions were prominent in the litter treatments where effects were generally weak. We interpret the limitation of soil faunal effects on soil carbon flow in terms of incomplete habitat exploitation and biotic regulation. Under conditions of substrate homogeneity, such as in the bare soil treatments, animal effects were stronger, but they were limited by overexploitation. Under conditions of substrate heterogeneity, such as in the litter treatments, animal effects were limited by incomplete habitat utilisation. We assume that complementary habitat colonisation by different faunal groups in the litter treatments gave rise to positive diversity effects, but that these effects did not compensate for reduced overall habitat utilisation. We infer that a knowledge of faunal resource utilisation and of mutual inhibition of faunal groups can be exploited for ecological soil management towards stabilisation of soil organic matter.

Body mass changes in male Daubenton's bats Myotis daubentonii (Chiroptera, Vespertilionidae) during the seasonal activity period

Abstract: Les variations de la masse corporelle des mâles, adultes et juveniles, du Murin de Daubenton pendant la saison active ont ete etudiees en Hesse (Allemagne) de 1998 a 2001. D'avril a octobre, des captures regulieres d'animaux de la population locale ont ete effectuees lors de leurs deplacements et la masse corporelle de chaque individu a ete determinee a l'aide d'une balance digitale. La masse corporelle des individus mâles varie significativement entre quinzaines successives (Test de Kruskal-Wallis : H = 141,75, p < 0,001). La masse corporelle augmente significativement de la derniere quinzaine d'avril (mediane: 7,0 g) a la premiere quinzaine de mai (mediane: 7,8 g). Entre la seconde moitie de mai et la premiere quinzaine d'aout, la mediane de la masse corporelle a oscille entre 7,8 et 8,3 g. De la derniere quinzaine de juillet (mediane: 7,9 g) a fin aout (mediane: 8,4 g), puis a la seconde moitie de septembre (mediane: 9,3 g), la masse corporelle a significativement augmente. La mediane la plus elevee (9,6 g) correspond a la derniere quinzaine d'octobre. La mediane de la masse corporelle des mâles juveniles s'echelonne de 6,5 g pour la premiere quinzaine de juillet a 8,5 g pour la derniere quinzaine d'aout. Les differences de masses corporelles au cours de la periode d'etude sont significatives (H = 21,70, p < 0,01). Au cours des mois de juillet, aout et septembre, la masse corporelle des adultes est significativement superieure a celle des juveniles, cette difference s'estompant des le mois d'octobre. Il est suggere que la perte de poids de certains mâles adultes en septembre est liee avec l'activite d'accouplement.