دانلود رایگان مقاله تغییرات آب و هوایی در مقابل رانش زیست محیطی

Abstract

Various studies document the ecological impacts of climate change on many species and environments, ecosystem processes and species interactions (e.g. the timing of host-plant flowering and butterflies’ phenology). However, what is usually overlooked is that populations drift even in the absence of environmental stress. Ecological drift can lead to changes in community composition that can easily be mistaken for an environmental trend. We demonstrate how the neutral model of biodiversity can be used to simulate ecological drift and thus assess the significance of observed changes. We apply this method to the butterfly community of Dadia National Park, Greece, for which there is indication of a community shift due to temperature rise. We found that the observed turnover in the sampled habitats is greater than the expected neutral turnover. This has a probability of less than 2.5% to have occurred by chance (Wilcoxon signed-rank test). We also found a significant increase of the population of warm-adapted species, confirming the results of an earlier study of the same community. Nevertheless, neutral turnover still explains much of the observed variability. We argue that null models are essential to the interpretation and attribution of observed changes in species composition in the presence of regional or global environmental change.

Discussion

A large number of papers reported changes in ecological communities and attributed them to climate change. However, that these observed trends might simply be due to ecological drift is not usually tested. In this paper we used the implicit-space neutral model of biodiversity to assess the observed temporal turnover in a butterfly community that had been studied earlier using statistical methods (Zografou et al. 2014). Although statistical tests can reveal significant changes in community composition, they cannot exclude the possibility that these changes are due to ecological drift. Our approach, which estimates natural community drift, refines the null hypothesis: natural (non-climatic) processes can produce the observed turnover. Indeed, we found that neutral drift explains most of the observed variation in abundance; still there is a considerable number of species whose change in abundance is not explained by drift and a significant community turnover in four out of seven habitats studied. Thus, the null hypothesis is rejected. The drift model revealed a significant increase in abundance of warm-adapted species(i.e.species with high Species Temperature Index), consistent with the temperature rise recorded in Dadia NP since 1990 (Zografou et al. 2014). The above isin agreement with the study of Zografou et al.(2014), which reported an increased alpha-diversity of warm-adapted species and an increase of the Community Temperature Index. At the level of species, we found that the observed trends of 11 species could not be attributed to drift, because eight of them showed significant turnover in forest habitats, where the observed community turnover is also higher than expected by drift. Zografou et al. (2014) reported species with significant change in abundance. However, we found that many of these species trends are actually explained by neutral drift, while we found a few more species, not reported by Zografou et al. (2014), whose change in abundance was greater than expected by drift.