Climate change versus ecological drift: Assessing 13 years of turnover in a butterfly community

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 drill. even in the absence of environmental stress. Ecological drilll 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.