Orthopteran insect species are a major taxonomic group in natural and disturbed ecosystems of temperate and subtropical Eurasia (Sergeev 1998). These species occur in both natural (particularly grasslands) and anthropogenic landscapes
Department of Ecology, Zoological Institute, University of Mainz, P.O. Box 3980, D-55099 Mainz, Germany e-mail: [email protected]
Centre for Nature Conservation, University of Göttingen, von-Siebold-Str. 2, D-37075 Göttingen, Germany e-mail: [email protected]
J.C. Habel and T. Assmann (eds.), Relict Species: Phylogeography and Conservation Biology, 385 DOI 10.1007/978-3-540-92160-8_23, © Springer-Verlag Berlin Heidelberg 2010
(meadows, pastures, agricultural fields, etc.). They are very sensitive to temperature, are especially characteristic of hot and sunny regions and are in general no food specialists. Populations of grasshoppers and bush crickets are declining in Central Europe (Ingrisch and Köhler 1998). More than half of these species are already considered endangered since many of their habitats are rapidly being destroyed, fragmented and changed (Ingrisch and Köhler 1998). However, over the past decade there has been increasing evidence that several orthopterans are able to shift their ranges towards the North as a consequence of present global warming (Kleukers et al. 1996; Cannon 1998; Widgery 2000).
Small population sizes are often the consequence of recent habitat fragmentation or loss. However, they also characterize highly ecologically specialized organisms restricted to scarce habitats such as relict species. Such species show highly localized ranges and are pre-dominantly found in regions where past climate changes have not resulted in major extinction events. Although it is widely acknowledged that population persistence greatly depends on population size and temporal fluctuations, the long historical persistence of many relict and endemic taxa as small populations contradicts this relationship. However, anthropogenic habitat fragmentation, alteration and loss are threats to any species. Thus, assessing the chance of species survival under current and future environmental conditions is especially important for species inhabiting patchy and scarce habitats.
The thermophilic grey bush cricket Platycleis albopunctata (Orthoptera: Tettigoniidae) is distributed throughout Europe. Because dry grassland has a patchy distribution in Central Europe, populations of this cricket inhabit habitat islands. During the last century, habitat fragmentation has increased due to changes in land use. The species is considered threatened in Germany (category three, Ingrisch and Köhler 1998) because of the ongoing loss of dry grasslands which results in relict populations. Over the past decades, there has been increasing evidence that P. albopunctata is shifting its range towards the North as the result of present global warming (Widgery 2000). Field studies on this cricket have shown that temperature conditions and vegetation density of habitats strongly differ (Gottschalk et al. 2003). It has been suggested that such differences in habitat conditions affect population dynamics of this species and that this may consequently have an impact on its extinction risk (Gottschalk et al. 2003). Although warmer habitats (e.g. dry grasslands) allow for higher reproduction rates and faster development of life stages (Köhler 1999), they have sparser vegetation than colder habitats (e.g. semi-dry grasslands) and a lower rate of primary production which causes food limitation.
In order to better understand the mechanisms that determine the vulnerability of this cricket under current and future thermal conditions in habitats of different food availability, we utilized an individual-based model (IBM) from a previous publication (Griebeler and Gottschalk 2000a). IBMs have been successfully applied to various species (DeAngelis and Mooij 2005) including orthopterans (Wagner and Berger 1996; Griebeler and Gottschalk 2000a,b) to assess their degree of endangering. We test the hypothesis of differing population dynamics generated by differences in temperature conditions and in food availability that was proposed by Gottschalk et al. (2003) based on field observations and laboratory experiments. Therefore, we apply it to the two populations experimentally studied in this paper (in contrast to Griebeler and Gottschalk 2000a,b; Gottschalk et al. 2003), and additionally consider a broader number of habitat conditions by varying temperature profiles and food availability of habitats. Furthermore, we perform a sensitivity analysis for mortalities of life stages and the length of egg diapause, as these may also be altered under global change as a result of simultaneously affected abiotic conditions and/ or species interactions.
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