Population dynamics of Great Bittern (Botaurus stellaris) in the Netherlands: interaction effects of winter weather and habitat fragmentation

The increased variability in weather as a manifestation of climate change is expected to have negative impacts on population survival in wildlife species, because it will likely lead to increased variation in vital demographic rates (mortality and reproduction) in these populations. For the effective protection of biodiversity, adaptation measures are needed to compensate for the expected increase in weather variability and the negative interaction with habitat fragmentation. As a case study, we studied the fluctuations in Great Bittern numbers (Botaurus stellaris) from 28 monitoring plots scattered over the Netherlands to explore the interaction between the effect of weather and possible remediating effects of the landscape structure. Great Bittern habitat surrounding these plots differs with respect to area, quality, and degree of isolation of this habitat. In western Europe, Great Bitterns are found to be susceptible to continuous loss of suitable habitat due to vegetation succession and fragmentation. Moreover, year-to-year fluctuations in local Great Bittern populations can be caused by severe winter weather or other weather extremes. Our results show that severe winter weather has indeed a significant negative impact on Great Bittern population growth rates. Furthermore, we found that an increased carrying capacity and spatial cohesion (i.e. inverse of habitat fragmentation) contribute to an increase in mean growth rates over the years. As growth rates are higher in large, well-connected habitats, we argue that recovery from negative effects of, e.g. severe winters on Great Bittern population numbers is enhanced in these less-fragmented habitats. We derived generic adaptation measures for enhancing the recovery rate of populations of species in general: one should invest in more large, well-connected nature areas, not only to diminish the negative effects of habitat fragmentation on wildlife populations, but additionally to reduce the impacts of climatic variability.     

Strategies of environmental organizations in the Netherlands with regard to the acidification problem

Summary It is usually assumed that a strategy should be considered to be a quality of an environmental organization. The organization would either employ a characteristic strategy with respect to a problem over time or at least it would use the same strategy regarding different problems at a certain point in time.The purpose of this study was to investigate whether strategies of environmental organizations concerning acidification change over time; and are the same as those in respect of ozone depletion. The results show that strategies regarding acidification changed over time and that they were different from those concerning ozone depletion (obtained from an earlier case study). In the ozone depletion case only environmentally-oriented organizations were actively involved with the problem. The definition in society of acidification as a dying forest issue attracted, however, attention from nature-oriented organizations as well. The resulting broad spectrum of organizations mutually influenced each other's strategies. These findings indicate that the definition of a problem in society is very important for determining the strategies pursued by environmental organizations. This conclusion has not merely academic value, but it can also serve as a boundary condition when defining future strategies of environmental organizations.Ruud Pleune is a Research Associate in the Department of Science, Technology and Society at Utrecht University.