Eva Rossmanith

Changes in arthropod diversity along a land use driven gradient of shrub cover in savanna rangelands: identification of suitable indicators

Shrub encroachment linked to heavy grazing has dramatically changed savanna landscapes, and is a major form of rangeland degradation. Our understanding of how shrub encroachment affects arthropod communities is poor, however. Here, we investigate the effects of shrub encroachment on abundance and diversity of ground-dwelling (wingless) arthropods at varying levels of shrub cover in the southern Kalahari. We also ascertain if invertebrate assemblage composition changes with habitat structure and identify which aspects of habitat structure (e.g., grass cover, herbaceous plant cover, shrub density) correlate most strongly with these changes. Ant, scorpion and dung beetle abundance increased with shrub cover, whereas grasshoppers and solifuges declined. Spider and beetle abundance exhibited hump-shaped relationships with shrub cover. RTU richness within orders either mirrored abundances, or exhibited no trend. Shrub density was the habitat component most correlated with similarities between invertebrate assemblages. Ground-dwelling arthropods showed clear shifts in species assemblage composition at a similarity level of 65% according to shrub density. Changes in indicator species showed that within the Tenebrionidae (darkling beetles), certain species respond positively to shrub thickening, replacing other species within the Family. Small-bodied, wingless Scarabaeidae (dung beetles) tended to increase with increased shrub density and three species emerged as significant indicators of more thickened habitats, although this might be a response to greater dung availability, rather than habitat structure itself. We conclude that because ground-dwelling invertebrates showed such clear responses in species assemblage composition, they present excellent candidates for use as indicator species in further studies into bush encroachment.

Reproductive success and nestling diet in the Lesser Spotted Woodpecker (Picoides minor): the early bird gets the caterpillar

Populations of Lesser Spotted Woodpecker (Picoides minor) are decreasing in size, necessitating management strategies. However, data on the reproductive biology of this species are scarce. The aim of this study was to investigate the influence of timing of breeding and nestling diet on the reproductive success of the Lesser Spotted Woodpecker and thereby contribute to an understanding of the determinants influencing its reproductive success. During 6 study years between 1996–2003, we investigated various variables of reproductive success in a Lesser Spotted Woodpecker population in the Taunus low mountain range, Germany. We observed nestling feeding at breeding holes to assess the composition of nestling diet and how it changes during the season. Clutch size, number of fledglings as well as body mass of the nestlings declined with the start of egg laying. Pairs composed of individuals that had breed together in previous years started egg laying earlier than newly established pairs. Nestling diet consisted mainly of aphids, caterpillars, craneflies and wood-living larvae. The composition changed considerably within the breeding season in both early and late broods. However, early broods were provided with caterpillars more frequently, whereas late broods received wood-dwelling larvae more often. Our results suggest that Lesser Spotted Woodpeckers time their breeding so as to coincide with the early nestling stage with the highest availability of caterpillars, since this is the time of highest energy demand. Moreover, food availability declines during the breeding season, and the decline in reproductive performance seems to be an effect of this development.

THE CONFLICTING IMPORTANCE OF SHRUBBY LANDSCAPE STRUCTURES FOR THE REPRODUCTIVE SUCCESS OF THE YELLOW MONGOOSE (CYNICTIS PENICILLATA)

Abstract Shrub encroachment as a result of heavy grazing is assumed to affect species diversity negatively. However, shrubs may be important for animals because they provide shelter and nesting sites. In this study we analyzed the importance of shrubs as habitat structures at 3 spatial scales for yellow mongooses (Cynictis penicillata) in southern Kalahari rangelands. At burrow location we assumed shrubs reduce predation risk for occupants of burrows under shrubs and that shrubs protect burrows from trampling by larger herbivores. To investigate this, at microhabitat scale, we recorded the location of 24 reproductive and 112 sheltering burrows. However, in shrub-encroached areas prey availability is low. We surveyed vegetation cover and the spatial distribution of shrubs at mesoscale (1 ha) and compared it to random surveys. Group size and reproductive success were determined for 18 groups and related to shrub cover at territory scale (macroscale, 250 ha). Our results show that yellow mongooses prefer reproductive burrows under large Acacia shrubs if the distance to the next shrub was greater than 10 m. At mesoscale, areas with lower vegetation cover were favored. Shrub encroachment at territory scale (macroscale) affected group size negatively. A range of shrub cover between 15% and 17.5% indicates a critical upper threshold limiting reproduction. For yellow mongooses territory selection represents a trade-off between abundance of suitable shrubs for burrows (protection service) and the proportion of shrub cover at large spatial scales (reduced prey availability).