Population Dynamics at Prappach and Hammelburg Between and

The trend in annual population size estimated by our model for Prappach was in overall agreement with field data when carrying capacities between 1,000 and 10,000 adults were assumed (Spearman rank correlation r between observed and predicted sizes: r=0.786, N=7, p = 0.05 for all capacities between 1,000 and 10,000, Fig. 1). Population sizes steadily increased from 1993 until 1995, and the maximum size was reached in 1995. In the following 4 years, the sizes steadily decreased again, but the population never went extinct. The decline between 1995 and 1999 was much weaker in the simulations than observed in the field. Contrary to the natural population, the population frequently went extinct within the simulated time period for carrying capacities (K) below 1,000 adults (extinction probabilities p t; K<400: p t = 1, K = 500: p t = 0.644, K = 750: p t = 0.216).

The rather constant population sizes observed at Hammelburg were only reproduced by the model for capacities between 200 and 500 adults (marginal significant Spearman rank correlation r between observed and predicted sizes due to the smaller number of years, Sachs 1992: r=0.600, N= 6, p = 0.15 for capacities between 200 and 500 adults, Fig. 1). The simulated course in population size became similar to the course observed at Prappach for capacities higher than 500 adults. For these capacities, a maximal size was observed in 1995 (Fig. 1). However, the population always went extinct for the lowest capacity studied (K = 100).

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