Showing papers by "Volkmar Wolters published in 2006"

Habitat loss, trophic collapse, and the decline of ecosystem services.

Abstract: The provisioning of sustaining goods and services that we obtain from natural ecosystems is a strong economic justification for the conservation of biological diversity. Understanding the relationship between these goods and services and changes in the size, arrangement, and quality of natural habitats is a fundamental challenge of natural resource management. In this paper, we describe a new approach to assessing the implications of habitat loss for loss of ecosystem services by examining how the provision of different ecosystem services is dominated by species from different trophic levels. We then develop a mathematical model that illustrates how declines in habitat quality and quantity lead to sequential losses of trophic diversity. The model suggests that declines in the provisioning of services will initially be slow but will then accelerate as species from higher trophic levels are lost at faster rates. Comparison of these patterns with empirical examples of ecosystem collapse (and assembly) suggest similar patterns occur in natural systems impacted by anthropogenic change. In general, ecosystem goods and services provided by species in the upper trophic levels will be lost before those provided by species lower in the food chain. The decrease in terrestrial food chain length predicted by the model parallels that observed in the oceans following overexploitation. The large area requirements of higher trophic levels make them as susceptible to extinction as they are in marine systems where they are systematically exploited. Whereas the traditional species-area curve suggests that 50% of species are driven extinct by an order-of-magnitude decline in habitat abundance, this magnitude of loss may represent the loss of an entire trophic level and all the ecosystem services performed by the species on this trophic level.

Relationship among the species richness of different taxa.

Abstract: Spatially explicit forecasting of changes in species richness is key to designing informative scenarios on the development of diversity on our planet. It might be possible to predict changes in the richness of inadequately investigated groups from that of groups for which enough information is available. Here we evaluate the reliability of this approach by reviewing 237 richness correlations extracted from the recent literature. Of the 43 taxa covered, beetles, vascular plants, butterflies, birds, ants, and mammals (in that order) were the most common ones examined. Forests and grasslands strongly dominated the ecosystem types studied. The variance explanation (R 2 ) could be calculated for 152 cases, but only 53 of these were significant. An average correlation effect size of 0.374 (95% CI ¼ 60.0678) indicates positive but weak correlations between taxa within the very heterogeneous data set. None of the examined explanatory variables (spatial scale, taxonomic distance, trophic position, biome) could account for this heterogeneity. However, studies focusing on 10-km 2 grid cells had the highest variance explanation. Moreover, within-phylum between- class comparisons had marginally significantly lower correlations than between-phylum comparisons. And finally, the explanatory power of studies conducted in the tropics was significantly higher than that of studies conducted in temperate regions. It is concluded that the potential of a correlative approach to species richness is strongly diminished by the overall low level of variance explanation. So far, no taxon has proved to be a universal or even particularly good predictor for the richness of other taxa. Some suggestions for future research are inclusion of several taxa in models aiming at regional richness predictions, improvement of knowledge on species correlations in human dominated systems, and a better understanding of mechanisms underlying richness correlations.

Impact of summer drought on forest biodiversity: what do we know?

Abstract: To date, very few studies have assessed the impact of summer droughts on forest biodiversity and ecosystem functioning. Decreased ecosystem productivity and increased mortality are general consequences of drought on biodiversity. Competitive species, species adapted to cold and wet conditions as well as species with low reproduction rates and/or limited mobility seem the more affected. However, species-specific effects are regulated by mechanisms allowing for resistance to drought. The short-term consequences of drought on biodiversity depend on species abilities to resist, and to recover after, drought, and on competitive interactions between species. Although the abundance of many species generally decreases during drought, some taxa may increase in number during drought or shortly after. The effects of recurrent droughts must be evaluated in the wider context of global climate and habitat change. Considering the predicted increase in drought frequency and intensity, interdisciplinary research initiatives on this issue are needed urgently.

Effect of historic landscape change on the genetic structure of the bush-cricket Metrioptera roeseli

Abstract: This study investigates the impact of past and present landscape structure on the current genetic structure of the bush-cricket Metrioptera roeseli (Orthoptera, Tettigoniidae) in a rural landscape in Germany. Assuming that land-use types, such as grassland, arable land and forest, as well as linear structures, mainly roads, differentially affect the connectivity of the bush-cricket's habitat and therefore migration and gene flow, we correlated landscape parameters between sampling locations as derived from GIS-maps with genetic similarities between individual bush-crickets as estimated by RAPD-PCR. Fifty bush-crickets were sampled with distances between sampling locations varying between 15 m and 2 km. Corresponding landscape configurations were recorded in 8 years between 1945 and 1998. Landscape configuration 50 years ago appeared to have influenced the present genetic structure of the bush-cricket (R 2 = 0.18). Crossing roads and land use other than grassland along the transect between sampling locations tended to decrease genetic similarity, whereas grassland and parallel roads tended to increase genetic similarity between bush-crickets. Following shifts in land use during 1953–1973 the correlation between landscape and present genetic structure decreased gradually. Our study suggests that it needs time for the landscape to build a visible effect on the genetic structure of the bush-cricket population, and that this effect cannot be detected if the landscape changes faster than the genetic structure responds to it.

Dynamic food webs

Abstract: Food webs are special descriptions of biological communities focusing on trophic interactions between consumers and resources. They have become a central issue in population, community, and ecosystem ecology. They provide a way to analyze the interrelationships among community dynamics and stability and ecosystem functioning, and how these are influenced by environmental change and disturbance. Population dynamics of interacting predators and prey are difficult to predict, and many ecosystems are known to contain hundreds or thousands of these interactions arranged in highly complex networks of direct and indirect interactions. Approaching food web structure and dynamics from environmental characteristics shows that environmental heterogeneity may create subsystems, especially at the lower trophic levels in food webs, with organisms at the higher trophic levels that act as “integrators” across this variability in space and time and stabilize dynamics of their resources via density-dependent adaptive foraging. Approaching food web structure from dynamics in populations shows that the evolution of realistic food web structures can be explained on the basis of simple rules regarding population abundance and species occurrence. The analyses of biological properties of individuals within populations show a strong explanatory power of body size to population abundance scaling rules in understanding the dynamics and persistence of trophic groups in food webs. Resource availability and use may govern the structure and functioning of food webs; in turn, food web interactions are the basis of ecosystem processes and govern important pathways in the global cycling of matter, energy, and nutrients.

Increased density of honeybee colonies affects foraging bumblebees

Abstract: Avec l'augmentation du nombre d'especes d'abeilles sauvages en danger la question de la concurrence possible entre especes due a une forte densite locale d'abeilles domestiques (Apis mellifera) est interessante pour la protection de la nature et l'apiculture, et pas seulement en Europe. Dans les etudes effectuees jusqu'a present les consequences possibles d'une augmentation de la densite d'abeilles domestiques sur les bourdons ont surtout ete considerees au niveau du genre Bombus, mais cela ne tient pas compte des exigences ecologiques tres variees des differentes especes de bourdons. C'est pourquoi nous avons etudie les effets possibles de la concurrence au niveau des groupes d'especes de bourdons dans un paysage agricole (bassin d'AmoneBurg, Allemagne). Les surfaces experimentales comprenaient un champ d'1,1 ha de Phacelia tanacetifolia ainsi que des surfaces voisines plus petites ayant une vegetation naturelle soit de Polygonum persicaria, Epilobium angustifolium, Centaura jacea, soit de Lotus uliginosus. Ont ete installees dans le champ de phacelie soit aucune, soit 10 colonies d'A. m. ligustica. Les densites de butineuses ont ete comptees durant 4 a 5 j. L'introduction experimentale des colonies d'A. m. ligustica a provoque une nette augmentation de la densite totale d'abeilles domestiques non seulement sur le champ de phacelie, mais aussi sur les parcelles de vegetation naturelle (Tab. 1). Si l'on exploite les comptages sur phacelie uniquement pour le genre Bombus, il n'y a pas de correlation significative. Si on les exploite au niveau des groupes d'especes, on trouve pour le groupe B. terrestris des modifications spatiales faibles mais significatives sur la phacelie (Tab. II). Les butineuses du groupe B. terrestris se sont concentrees sur les parcelles ayant une faible densite florale et qui etaient plus eloignees des colonies d' A. m. ligustica. Sur les parcelles de vegetation naturelle, les densites d'abeilles domestiques ont ete multipliees par trois sur toutes les plantes, y compris sur Lotus des l'apport d'une colonie d'A. m. ligustica (Tab. I, Fig. 3). L'analyse des resultats au niveau de l'espece montre des oppositions nettes entre les divers groupes de bourdons : le groupe B. terrestris n'a montre aucune reaction a l'augmentation de la densite des abeilles domestiques, alors que le groupe B. lapidarius, ainsi que les especes a langue longue (B. muscorum, B. sylvarum et B. pascuorum) ont reagi en butinant plus intensement les parcelles de Lotus sans abeilles domestiques. Des modifications temporelles dans le comportement de butinage afin d'eviter la concurrence n'ont pu etre observees dans un perimetre restreint que pour B. lapidarius sur Epilobium et pour les bourdons a langue longue sur Lotus (Fig. 4). Pour les bourdons a langue longue qui ont un rayon d'action reduit, des effets negatifs de fortes densites locales d'abeilles domestiques ne sont pas a exclure meme sur des ressources en masse, si une concentration sur les plantes alternatives des prairies, jacheres ou zones de bordure voisines n'est pas possible. Puisqu'en cas de forte concurrence alimentaire non seulement les especes d'abeilles sauvages mais aussi la sante des colonies d'abeilles domestiques en souffrent, l'effort pour maintenir des paysages fleuris mais avant tout riches et varies en plantes represente un but important et commun aux groupements d'apiculteurs et aux associations de protection de la nature.

Soil fauna modifies the recalcitrance-persistence relationship of soil carbon pools

Abstract: Traditional models of soil organic matter decomposition predict that soil carbon pools with high chemical stability and large physical structure are more resistant against degradation than chemically labile and fine-grained material. We investigated whether soil fauna, by its direct and indirect effects on carbon turnover, would reinforce or counteract this general trend. The effects of four major faunal groups on carbon pools of differing recalcitrance were studied in an extensive microcosm experiment. Ninty-six microcosms were inoculated with nematodes, enchytraeids, collembola, and lumbricids in three densities, including combinations of groups. 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 60 days. At the end of the experiment, soil particles were separated into size classes ( 250 μm) and carbon pools were separated into solubility fractions (K 2 SO 4 -soluble, pyrophosphate-soluble, insoluble), by means of ultrasonic dispersion and subsequent stepwise solubilisation. Both in bare soil and in soil with litter, the carbon pools with the highest chemical stability (insoluble) and the larger particle sizes (>63 μm) were degraded more intensively than all other pools in the presence of lumbricids. The pools of intermediate chemical stability (pyrophosphate-soluble) underwent simultaneous degradation and neoformation brought about by different animal groups. The chemically most labile pool (K 2 SO 4 -soluble) remained largely unaffected by the fauna. Fixation of carbon in microbial biomass was increased by nematodes in bare soil and by enchytraeids in soil with litter. The results illustrate in detail how, under the influence of soil fauna, soil carbon pools are decomposed in a cascade-like process where carbon is transferred from the stable to the more labile pools, while simultaneously a proportion is fixed in microbial biomass and another part is lost as CO 2 . Thereby, the relationship between a substrate's persistence and its chemical stability and physical size is substantially modified. We summarize the mechanisms that most likely are responsible for the different effects of the investigated faunal groups.

Landscape effects on the genetic structure of the ground beetle Poecilus versicolor STURM 1824

Abstract: The impact of landscape structure on the genetic structure of an abundant and widespread carabid beetle Poecilus versicolor was analysed in a low mountain range (Lahn-Dill-Bergland, Germany) by means of RAPD-PCR. Habitat patch and landscape characteristics were included as independent variables into a GIS oriented correlative approach. Results indicated a high overall genetic diversity of the beetle population and suggest that the mobility of P. versicolor is much higher than previously thought. An equilibrium among migration and genetic drift has not been reached yet, therefore it is very likely that revealed differences in allele frequencies reflect current pattern of genetic diversity. Landscape characteristics at a scale of 1000 × 1000 m surrounding each study site significantly affected the genetic population structure of the carabid beetle, while it is only indirect affected by patch conditions. Opposite effects of grassland and arable land on genetic diversity demonstrated that grassland in the surrounding landscape facilitates dispersal, while arable land apparently decreases successful dispersal, but both factors increase population density on the study site. We conclude that the local population genetic structure of a widespread and highly mobile species as P. versicolor is strongly affected by the amount of suitable habitat in a landscape of large habitat proportion. The inclusion of landscape characteristics offers a powerful way for analysing effects on genetic diversity. Further studies on conservation genetics should incorporate a landscape perspective in order to assess the loss of local genetic diversity.

Age-related variation in physical and reproductive condition of male Daubenton's bats (Myotis daubentonii)

Abstract: We studied age-related variation in body mass and epididymal distension in male Daubenton’s bats. Examination of data on epididymal distension in young of the year indicates that some reach sexual maturity by the year of birth, whereas others do so in their 2nd summer. Body mass and epididymal distension were positively correlated in young of the year and adults, suggesting that early sexual maturation and reproductive condition during later life are dependent on body condition. Older males tended to be heavier and in better reproductive condition than younger ones. Examination of our data suggests that physical and reproductive condition of males increase after the initial onset of fertility until 3 years of age. This late physical maturation is in line with other life-history traits characterizing long-lived bats as K-strategists among small mammals.

Seasonal variation in nocturnal activity of male Daubenton's bats, Myotis daubentonii (Chiroptera: Vespertilionidae)

Abstract: We studied nocturnal activity in adult male Myotis daubentonii from mid-May to early September of the years 1998-2003 in a male-dominated population in central Germany. Departure from roost after sunset, nocturnal activity time, time spent foraging, and return to roost before sunrise were recorded in radio-tracked animals during four observation periods (1: 14 May - 6 June, 2: 16 June - 10 July, 3: 22 July - 14 August, 4: 23 August - 2 September). Only three males (two in period 1, one in period 4) stayed in the day roost all night. The other tracked animals left their day-roost for the first time between 25 and 220 minutes after sunset, and their last arrival at the day-roost occurred between 2 and 545 minutes before sunrise. Bats spent most of their nocturnal activity time foraging (overall mean: 79.7 % of nocturnal activity time). Duration of nocturnal activity and nightly foraging time varied considerably over the four observation periods and were most extended in mid-summer (period 3). This is a time of high spermatogenetic activity and steep increase in body mass (built-up of fat reserves), which leads to a particularly high food demand of male Daubenton's bats during this period of the year. Our results of an increased foraging activity during mid-summer provide evidence in support of the view that food demand of male Daubenton's bats is indeed highest during this time of the year.

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.

Effects of age and season on body mass and reproductive condition in male Daubenton's bats (Myotis daubentonii)

Abstract: ENCARNACAO, J. A., U. KIERDORF, V. WOLTERS: Effects of age and season on body mass and reproductive condition in male Daubenton's bats (Myotis daubentonii). Vet. arhiv 76, S239-S249, 2006. ABSTRACT We analyzed the effects of age and season on body mass and reproductive condition in male Daubenton's bats (Myotis daubentonii) from a study area in central Germany, which were captured during April to October of the years 1998-2003. On first capture, animals (n=336) were banded and classified as either young of the year or adults (i.e. males ≥ 1 year of age). On recapture, animals first caught as young of the year could be assigned an exact age in years. Epididymal distension in young of the year indicated that some males had reached sexual maturity (defined as onset of spermatogenesis) already in their year of birth, while others did so in their second summer. Body mass and epididymal distension showed pronounced variation related to age and season, with highest values reached in late summer/early autumn. Generally, older males (>2 years of age) tended to be heavier and in better reproductive condition than younger ones. Our data suggest that the physical condition of male Daubenton's bats, and their reproductive condition, both increase after the initial onset of fertility (start of spermatogenesis) until three years of age. This relatively late physical maturation is in line with other life- history traits characterizing long-lived bats as K-strategists among small mammals.