Showing papers by "Volkmar Wolters published in 2005"

Local vs. landscape controls on diversity: a test using surface‐dwelling soil macroinvertebrates of differing mobility

Abstract: Aim A better understanding of the processes driving local species richness and of the scales at which they operate is crucial for conserving biodiversity in cultivated landscapes. Local species richness may be controlled by ecological processes acting at larger spatial scales. Very little is known about the effect of landscape variables on soil biota. The aim of our study was to partly fill this gap by relating the local variation of surface-dwelling macroarthropod species richness to factors operating at the habitat scale (i.e. land use and habitat characteristics) and the landscape scale (i.e. composition of the surrounding matrix). Location An agricultural landscape with a low-input farming system in Central Hesse, Germany. Methods We focused on five taxa significantly differing in mobility and ecological requirements: ants, ground beetles, rove beetles, woodlice, and millipedes. Animals were caught with pitfall traps in fields of different land use (arable land, grassland, fallow land) and different habitat conditions (insolation, soil humidity). Composition of the surrounding landscape was analysed within a radius of 250 m around the fields. Results Factors from both scales together explained a large amount of the local variation in species richness, but the explanatory strength of the factors differed significantly among taxa. Land use particularly affected ground beetles and woodlice, whereas ants and rove beetles were more strongly affected by habitat characteristics, namely by insolation and soil characteristics. Local species richness of diplopods depended almost entirely on the surrounding landscape. In general, the composition of the neighbouring landscape had a lower impact on the species richness of most soil macroarthropod taxa than did land use and habitat characteristics. Main conclusions We conclude that agri-environment schemes for the conservation of biodiversity in cultivated landscapes have to secure management for both habitat quality and heterogeneous landscape mosaics.

The response of carabids to landscape simplification differs between trophic groups

Abstract: We studied the response of carabid species richness and density to landscape simplification (measured as percentage cover of non-crop habitat surrounding each study site) in 36 wheat fields using pitfall traps. Carabids were divided to trophic groups following the literature. The number of species from different trophic groups declined with increasing landscape simplification in the order: carnivores > phytophages > omnivores. Density compensation of both carnivores and phytophages suggests that species decline is caused by the loss of specific resources rather than by an overall reduction in food availability. Increasing evenness indicates that a greater share of phytophagous species contributes to density compensation at poorer sites. A comparison with data from complementing studies shows that marked differences in species numbers (carnivores > omnivores > phytophages) are due to a different sensitivity of trophic groups to agricultural management. Since our findings seem to be partly due to increasing sensitivity to landscape changes with trophic rank, and partly to decreasing sensitivity of depauperate communities to local environmental stress, species loss can best be explained by the co-action of factors at local and regional scales. Species richness decline might significantly alter the role of carabids as biocontrol agents.

Food Web Ecology: Playing Jenga and Beyond

Abstract: De Ruiter et al. argue that the old notion of a food web as a static arch, with a critical keystone species (whose removal would cause collapse of the arch), is outdated. Instead, they see ecosystems as dynamic, both spatially and temporally, and explain how describing them in this way reveals the basis of unexpected stabilities that occur in response to even large environmental perturbations.

Sex-related differences in roost-site selection by Daubenton's bats Myotis daubentonii during the nursery period

Abstract: 1 We investigated sex-related differences in roost-site selection by Daubenton's bats Myotis daubentonii in their summer habitat in central Germany. We studied whether the location of and landscape structure around nine nursery roosts and seven male-only roosts differed during the nursery period (15 May−31 July). Roosts were located by radio-tracking, and animal numbers and group composition were obtained by trapping and counting at roosts. Landscape structure was evaluated by a GIS-based habitat analysis. 2 Marked variation in animal numbers was observed both in nursery roosts (range: 6–144 individuals) and male roosts (range: 1–51 individuals). The surroundings of nursery and male roosts varied significantly in the proportion of areas belonging to different landscape elements. The areas covered by ponds, lakes and rivers, as well as the area covered by coppices were larger in the surroundings of nursery roosts. Moreover, nursery roosts lay closer to a river and at lower altitudes than male roosts. Male Daubenton's bats used more distant foraging sites than gravid or lactating females. 3 The differences in roost-site location between the two sexes are suggestive of intraspecific competition for access to productive foraging areas in the surroundings of the summer roosts, with females being dominant over males. We assume that breeding females defend climatically favourable areas with good food supply in order to increase the survival of their offspring.

Responses of oribatid mite communities to summer drought: The influence of litter type and quality

Abstract: A litterbag experiment was used to study the impact of extended periods of summer drought on the structure of oribatid mite communities (Acari, Oribatida) developing in two litter types (beech, spruce) of two qualities (fresh, pre-incubated). Within each litter type, litter quality determined species composition and densities and, in turn, this determined the impact of drought upon the oribatid mite communities. In both litter types, drought had a greater impact on community development in the pre-incubated compared to the fresh litter. In the short-term perspective of the present study, oribatid mite communities in beech litter were less sensitive to summer drought than those in spruce litter. This was partly due to the presence of site-specific, drought-tolerant species but seemed also strongly related to differences in the decomposition patterns between the litter types. Marked changes in densities and composition of oribatid communities after only one period of summer-drought suggest that there is a potential for a significant alteration of oribatid community structure in both litter types if climatic changes persist.

The microfood web of grassland soils responds to a moderate increase in atmospheric CO2

Abstract: The response of the soil microfood web (microflora, nematodes) to a moderate increase in atmospheric CO2 (120%) was investigated by means of a free air CO2 enrichment experiment. The study was carried out in a seminatural temperate grassland for a period of 4 consecutive years (1 year before fumigation commenced and 3 years with fumigation). Several soil biological parameters showed no change (microbial biomass, bacterial biomass) or decline (microbial respiration) in the first year of elevated CO2 treatment as compared with controls. Each of these parameters were higher than controls, however, after 3 years of treatment. The relative abundance of predaceous nematodes also decreased in year 1 of the experiment, increased in year 2, but decreased again in year 3. In contrast, the relative abundance of root hair feeding nematodes, at first, increased under elevated CO2 and then returned to the initial level again. Increased microbial biomass indicates enhanced C storage in the labile carbon pool of the active microfood web in subsequent years. According to measurements on the amounts of soil extractable C, changes in resource availability seem to be key to the response of the soil microfood web. We found a strong response of bacteria to elevated CO2, while the fungal biomass remained largely unchanged. This contrasts to findings reported in the literature. We hypothesize that this may be because of contrasting effects of different levels of CO2 enrichment on the microbial community (i.e. stimulation of bacteria at moderate levels and stimulation of fungi at high levels of CO2 enrichment). However, various CO2 effects observed in our study are similar in magnitude to those observed in other studies for a much higher level of atmospheric carbon. These include the particular sensitivity of predaceous nematodes and the long-term increase of microbial respiration. Our findings confirm that the potential of terrestrial ecosystems to accumulate additional carbon might be lower than previously thought. Furthermore, CO2-induced changes of temperate grassland ecosystems might emerge much earlier than expected.

The Effects of Spatial Scale on Trophic Interactions

Abstract: Food chain models have dominated empirical studies of trophic interactions in the past decades, and have lead to important insights into the factors that control ecological communities. Despite the importance of food chain models in instigating ecological investigations, many empirical studies still show a strong deviation from the dynamics that food chain models predict. We present a theoretical framework that explains some of the discrepancies by showing that trophic interactions are likely to be strongly influenced by the spatial configuration of consumers and their resources. Differences in the spatial scale at which consumers and their resources function lead to uncoupling of the population dynamics of the interacting species, and may explain overexploitation and depletion of resource populations. We discuss how changed land use, likely the most prominent future stress on natural systems, may affect food web dynamics by interfering with the scale of interaction between consumers and their resource.

Effects of management practices on ant species richness and community composition in grasslands (Hymenoptera: Formicidae)

Abstract: The aim of our study was to evaluate the impact of four types of grassland management (silage meadows, hay meadows, meadow pastures and cattle pastures) on species richness and composition of ant communities. No impact of management type on ant species richness and community composition could be revealed. In contrast, moisture and total nitrogen content of the soil had a strong influence on the number of ant species. We could not find a relationship between species richness of ant communities and plant diversity. It is concluded that differences in intensity between the four management types were probably not strong enough for affecting ant communities differentially. Thus, assuming the maintenance of low intensity agriculture, a mosaic of different regimes of grassland management seems not to be imperative for maintaining ant diversity in mesic grasslands of marginal regions of Central Europe. In contrast, environmental conditions are important and should be considered in grassland management schemes aiming at protecting ant diversity.

Spatial aspects of food webs

Abstract: Spatial distributions of trophic interactions define the spatial heterogeneity of food webs and differences between local and macroecological food webs. The concept of co-occurrence has to be given up when larger spatial scales are considered that integrate different local community food webs into a metacommunity food web. This chapter provides two examples. First, some large-bodied predators are too low in numerical abundance to invade all local community food webs simultaneously. Second, not all potential resource species in a metacommunity can persist under strong top-down pressure by their consumer species and thus avoid coexistence in the same local communities. Food webs consist of organisms that vary in their taxonomic identity, body size, trophic interactions, and trophic position and thus might have very different spatial scales of interactions. Recognition of the importance of spatial scale in food web studies has several implications for food web theory. In particular, the potential food webs that are frequently described by ecologists will often differ from how food webs are realized in actual space and time. Clearly, choosing the right spatio-temporal scale for a food web study depends on the species studied and the study objective. Integrating spatial processes such as extinction and colonization by dispersal in food web models is an important step towards understanding population dynamics in complex communities, and understanding the consequences of habitat loss for the community structure and food web dynamics.

Root associated organisms modify the effectiveness of chemically induced resistance in barley

Abstract: Induced resistance (IR) offers a lasting defense against a broad spectrum of diseases in various plants, but practical applicability is impaired by unpredictable effectiveness Here we present the results of two greenhouse experiments on the modification of the effectiveness of BION® (acibenzolar-S-methyl (BTH)) induced resistance against powdery mildew in barley by different levels of root infection with mycorrhizal fungi (Glomus etunicatum) and parasitic nematodes (Heterodera avenae), respectively Root infection by mycorrhizal fungi and nematodes both had a negative effect on plant growth Adverse effects of G etunicatum suggest that parasitic effects of mycorrhizal fungi outweighed positive effects under the optimal growth conditions provided by the experiment Bion® either did not affect or decreased the number of lesions caused by powdery mildew at low and medium levels of infection by G etunicatum or H avenae, but increased it at high levels of root infection This clearly proves the important role of root-associated biota in modulating the effectiveness of IR However, plant accumulation of the resistance related protein BCI-4 was not impaired by G etunicatum or H avenae Soil biota thus appear to impact later steps of the defense pathway, rather than preventing the onset of resistance

State of the Art in Simulating Future Changes in Ecosystem Services

Abstract: Coordinating Lead Author: Peter Kareiva Lead Authors: John B. R. Agard, Jacqueline Alder, Elena Bennett, Colin Butler, Steve Carpenter, W. W. L. Cheung, Graeme S. Cumming, Ruth Defries, Bert de Vries, Robert E. Dickinson, Andrew Dobson, Jonathan A. Foley, Jacqueline Geoghegan, Beth Holland, Pavel Kabat, Juan Keymer, Axel Kleidon, David Lodge, Steven M. Manson, Jacquie McGlade, Hal Mooney, Ana M. Parma, Miguel A. Pascual, Henrique M. Pereira, Mark Rosegrant, Claudia Ringler, Osvaldo E. Sala, B. L. Turner II, Detlef van Vuuren, Diana H. Wall, Paul Wilkinson, Volkmar Wolters Review Editors: Robin Reid, Marten Scheffer, Antonio Alonso

Trophic interactions in a changing world : the role of spatial scale.

Abstract: Food chain models have dominated empirical studies of trophic interactions in the past decades, and have lead to important insights into the factors that control ecological communities. Despite the importance of food chain models in instigating ecological investigations, many empirical studies still show a strong deviation from the dynamics that food chain models predict. We present a theoretical framework that explains some of the discrepancies by showing that trophic interactions are likely to be strongly influenced by the spatial configuration of consumers and their resources. Differences in the spatial scale at which consumers and their resources function lead to uncoupling of the population dynamics of the interacting species, and may explain overexploitation and depletion of resource populations. We discuss how changed land use, likely the most prominent future stress on natural systems, may affect food web dynamics by interfering with the scale of interaction between consumers and their resource.