Increasing frequency of low summer precipitation synchronizes dynamics and compromises metapopulation stability in the Glanville fritillary butterfly

Abstract

Climate change is known to shift species' geographical ranges, phenologies and abundances, but less is known about other population dynamic consequences. Here, we analyse spatio-temporal dynamics of the Glanville fritillary butterfly (Melitaea cinxia) in a network of 4000 dry meadows during 21 years. The results demonstrate two strong, related patterns: the amplitude of year-to-year fluctuations in the size of the metapopulation as a whole has increased, though there is no long-term trend in average abundance; and there is a highly significant increase in the level of spatial synchrony in population dynamics. The increased synchrony cannot be explained by increasing within-year spatial correlation in precipitation, the key environmental driver of population change, or in per capita growth rate. On the other hand, the frequency of drought during a critical life-history stage (early larval instars) has increased over the years, which is sufficient to explain the increasing amplitude and the expanding spatial synchrony in metapopulation dynamics. Increased spatial synchrony has the general effect of reducing long-term metapopulation viability even if there is no change in average metapopulation size. This study demonstrates how temporal changes in weather conditions can lead to striking changes in spatio-temporal population dynamics.

Predictable allele frequency changes due to habitat fragmentation in the Glanville fritillary butterfly

“…1), where it has a large metapopulation in a network of 4,000 dry meadows (16,25). Although the extinction risk of small local populations is increased by inbreeding (26), along with many demographic processes, the metapopulation as a whole has shown no declining trend for the past 25 y (25), although the amplitude of fluctuations in the metapopulation as a whole has increased, probably due to climate change (27). In contrast, an isolated population on a small island, Pikku Tytärsaari, in the northern Baltic, shows great loss of genetic diversity and reduction of fitness due to accumulation of genetic load (9).…”

Spatial and temporal genetic structure at the fourth trophic level in a fragmented landscape

“…Additionally, there is strong yearly (generation) fluctuation and spatial variation of population sizes owing to the environmental variation and the host metapopulation dynamics [19,54]. This scenario can lead to loss of genetic variability, especially when the population size is small [55,56].…”

“…However, there are also global (the whole Å land islands) fluctuations in the butterfly population size primarily owing to weather. Large fluctuations are occurring increasingly frequently [54] and affect the overall resource availability to the wasp. Over the four years of the study, the hyperparasitoid population size decreased, both independent of the host population (years 2009-2010 and 2011-2012) and in association with the host population size (year 2010-2011; figure 1a).…”

Weather explains high annual variation in butterfly dispersal

“…Nevertheless, there is currently no consensus on the effects of exceptional weather conditions on the colonization process, as was recently pointed out by Malinowska et al [49]. Thus, more empirical case studies are needed in documenting the effects of extreme weather conditions [50].…”

“…Alternatively, such an effect could be counteracted if average cloudiness would simultaneously increase, especially for heliothermic insects [31]. The results of several recent studies have emphasized the potentially high ecological importance of the variability and extreme weather events compared with average weather conditions [53][54][55][56] and the difficulty of predicting the consequences on population dynamics of such climatic changes [50]. Improving our knowledge on the role that average and extreme weather conditions have in governing the annual dispersal rates of ectotherm animals, such as insects, requires further attention.…”