Metrioptera

Abstract: The bush cricket, Metrioptera bicolor Philippi (Orthoptera, Tettigoniidae) lives in a restricted area with grassland patches separated by mainly pine forest. The regional population dynamics can be described as a metapopulation with local extinctions and col- onizations. I used inventory data in order to test the following hypotheses: (1) temporal variability of local population size should be negatively correlated with habitat heteroge- neity, when habitat quality changes in relation to fluctuating weather conditions; (2) ex- tinction risk should be higher on homogeneous habitat patches than on heterogeneous patches. Both hypotheses are convincingly corroborated and I find a compensatory effect between patch area and heterogeneity. Local extinctions may occur on large, but homo- geneous patches, and local populations can survive quite well on small patches that contain a mosaic of several types of grassland vegetation with different humid conditions. I discuss the implications of these findings for the preservation of endangered species that are sus- ceptible to regional stochasticity.

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.

Abstract: The bush cricket, Metrioptera roeseli (Orthoptera, Tettigoniidae), occurs in patchy and heterogeneous agricultural landscapes. Such a mosaic of different types of grassland habitats causes spatial variation in local population density. Low population densities may result in fewer mating opportunities that can give rise to an Allee effect, possibly leading to a population decline or extinction. This experimental study shows that individuals can avoid an Allee effect by adjusting their movement behaviour in sparse populations. Even at a population density of five individuals per hectare, i.e. approximately one percent of normal population densities, no reduction of mating frequencies was detected. Observed net displacements made by different individuals in high and low population densities could successfully be predicted by a simple model of animal movement.

Abstract: Whereas the classification of plant communities has a long tradition that of animal assemblages remains poorly developed. Here we propose a classification scheme for orthopteran communities based on regional "character species", "differential species" and "attendant species" at different levels of habitat complexity, which is also applicable to other insect groups. In this context there are three main points of special importance: (i) the geographical reference area, (ii) the hierarchical spatial level (e.g. habitat complex, habitat and microhabitat) and (iii) precise constancy criteria for the definition of character species and differential species. We develop this new approach using a study on orthopteran communites of central German semi-dry calcareous grasslands. Within this habitat, we describe seven structural types that are characterized by specific orthopteran communities. For the arrangement of the structural types several environmental parameters (e.g. height and density of vegetation) were collected. Orthopteran densities were sampled at 80 sites using a biocoenometer (box quadrat). Regional character species of semi-dry grasslands include Myrmeleotettix maculatus, Metrioptera brachyptera, Stenobothrus lineatus and Tetrix tenuicornis. Within this habitat, Chorthippus parallelus, Metrioptera roeselii, Omocestus viridulus, Pholidoptera griseoaptera and Tettigonia viridissima were designated as differential species for particular structural types. Furthermore, Tettigonia cantans and Tettigonia viridissima act as altitudinal differential species. Chorthippus biguttulus is the only attendant species with high constancy values in all structural types. This classification is a powerful tool for arthropod conservation, since it allows one to determine community completeness of very important and threatened habitats, like semi-dry calcareous grasslands.