Abstract
When data are limited it is difficult for conservation managers to assess alternative management scenarios and make decisions. The natterjack toad (Bufo calamita) is declining at the edges of its distribution range in Europe and little is known about its current distribution and abundance in Poland. Although different landscape management plans for central Poland exist, it is unclear to what extent they impact this species. Based on these plans, we investigated how four alternative landscape development scenarios would affect the total carrying capacity and population dynamics of the natterjack toad. To facilitate decision-making, we first ranked the scenarios according to their total carrying capacity. We used the software RAMAS GIS to determine the size and location of habitat patches in the landscape. The estimated carrying capacities were very similar for each scenario, and clear ranking was not possible. Only the reforestation scenario showed a marked loss in carrying capacity. We therefore simulated metapopulation dynamics with RAMAS taking into account dynamical processes such as reproduction and dispersal and ranked the scenarios according to the resulting species abundance. In this case, we could clearly rank the development scenarios. We identified road mortality of adults as a key process governing the dynamics and separating the different scenarios. The renaturalisation scenario clearly ranked highest due to its decreased road mortality. Taken together our results suggest that road infrastructure development might be much more important for natterjack toad conservation than changes in the amount of habitat in the semi-natural river valley. We gained these insights by considering both the resulting metapopulation structure and dynamics in the form of a PVA. We conclude that the consideration of dynamic processes in amphibian conservation management may be indispensable for ranking management scenarios.
Highlights
Due to human impact many species are threatened with extinction
Based on the case study of natterjack toad, we show that despite sparse local data, a meaningful ranking of management scenarios is possible by combining landscape information and a population viability analysis, which can be based on demographic parameters extracted from the literature
Metapopulation Structure and Carrying Capacity Natterjack toad habitats are distributed throughout the study area, with the biggest patches located in the area of the national park (Figure 1a and b)
Summary
Due to human impact many species are threatened with extinction. Because of the scale and speed of species extinctions conservationists require methods that facilitate decision making in the light of scarce data. Important tools often used by policy makers include habitat models [1] and population viability analysis (PVA) which are used to assess threats and to identify the most suitable management scenarios for a given species [2]. It is often challenging to decide which tool is most appropriate for a particular problem and to what extent the ranking of management scenarios depends on the choice of the tool. We contrast scenario ranking resulting from habitat modelling with that from population dynamic modelling
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