AICME II abstracts Individual-Based Spatial Simulations of Ecological Systems

Implications for conservation from an individual based model of the grey bush cricket, Platycleis albopunctata Eva Mar´ıa Griebeler1 and Eckhard Gottschalk2 . The grey bush cricket Platycleis albopunctata (Orthoptera: Tettigoniidae) is a thermophilic species that is distributed throughout Europe. In Germany, it mostly inhabits semi-arid grasslands. However, due to the loss of its natural habitat the species is considered threatened. In order to better understand those mechanisms which determine the vulnerability of the bush cricket, we developed a stochastic individual based model [1,2]. Population dynamics of the species is implemented as a day-degree model. The model is based on the assumption that individuals of a population accumulate temperatures daily during their development. At each simulated day, a temperature value is taken sequentially from a database which contains daily mean temperatures registered for a meteorological station close to an area under study. To mimic climatic conditions of the habitat, values obtained from the database are modified according to the mean temperature observed at a study area. We distinguish three life-stages in our model: eggs, larvae and adults. During simulation, the temperature sum input received by an egg or larva is summed and updated daily. Both stages pass to the next stage if their temperature sum input exceeds a specific limit. The number of eggs laid per adult each day also depends on temperature. Additionally a mortality rate at each life-stage is assumed. We applied our model to two populations that we studied during a period of ten years in Baden-W¨ urttemberg, Southern Germany. Study areas

Individual-Based Spatial Simulations of Ecological Systems AICME II abstracts

differed in vegetation cover resulting in remarkable differences in daily mean temperatures. For both populations, annual population sizes calculated by the model were in overall agreement with sizes observed in field. Phenologies of larvae and adults that we recorded during two years in the field resembled results of the model. At the warmer study site, the population size remained relatively constant over the period, while the other showed strong fluctuations in size. For both populations, MVP (Minimum Viable Population size) estimates calculated by our model were highly different due to different climatic conditions of habitats. Our results demonstrate that habitat characteristics that negatively influence temperature conditions for xerothermophilic species increase their extinction risk but may be also subject to population management. Consequently, for such species MVP estimates found in literature should be interpreted carefully.

References [1] Griebeler, E. M. and E. Gottschalk (2000) The influence of temperature model assumptions on prognosis accuracy of extinction risk. Ecological Modelling 134: 343-356. [2] Griebeler, E. M. and E. Gottschalk (2000) An individual based model of the impact of suboptimal habitats on survival of the grey bush cricket, Platycleis albopunctata (Orthoptera: Tettigoniidae). Journal of Insect Conservation 4: 225-237.

1 Department of Ecology, Institute of Zoology, University of Mainz, P.O. Box 3980, D-55099 Mainz, Germany (e-mail: [email protected]). 2 Centre for Nature Conservation, University of Gttingen, von-Siebold-Str. 2, D37075 Gttingen, Germany (e-mail: [email protected]).

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