Butterflies and environmental change
Butterflies are a model taxon for studying the effects of environmental change, as demonstrated by large body of research results. Below are some of the recent highlights (since 2010) and a more extensive list of publications using data from the scheme is available here:
Warming temperatures have been shown to have both positive and negative effects on populations of British butterflies. Species at the northern limit of their ranges have been able to expand their ranges, moving northwards throughout the UK. Species such as Orange-tip and Peacock have become common in Scotland as the climate has become suitable. Silver-spotted Skipper has been able to colonise new habitats on north facing slopes, having previously been mainly restricted to south facing slopes. Similarly, temperature rises have also been associated with increases in Adonis Blue populations. Recent research has also shown that warming temperatures have facilitated the spread of the Brown Argus throughout England through increased use of host plants it previously only rarely used.
Migrant species have also increased in number in response to recent warming. Red Admiral, in particular, and Clouded Yellow to a lesser extent, now regularly over-winter in the UK to produce resident populations due to increasingly favourable conditions.
The story is likely to be the reverse for those species at their southern range limit in the UK with evidence to suggest that their ranges are contracting at the southern edge and/or at lower elevations, a result echoed in studies elsewhere in Europe. Population responses of these species are mixed, however, as numbers of Scotch Argus and Large Heath have both increased on monitored sites, whilst Northern Brown Argus has declined.
In addition, most species have started to appear progressively earlier in the year, and this has been strongly linked with increased temperatures. A number of species are now able to produce more than one brood in warm years, and this is increasingly observed at monitored sites. For example, Wood White now regularly produces a second brood at most sites where it is monitored, whereas at the start of monitoring this was a much rarer occurrence. Meta-analyses have shown that butterflies and other primary consumers may be advancing at different rates to both their hosts and their predators leading to concerns over potential temporal mismatching in trophic interactions.
Recent rapid range expansion in the Brown Argus is associated with increased use of geranium species as host plants brought about by climatic suitability with recent warming: Pateman et al. (2012) in Science (doi: 10.1126/science.1216980)
Community composition changes are rapid but different between birds and butterflies. Both groups do not keep up with temperature increases and suggest a climatic debt at national and continental scales. Devictor et al. (2012) in Nature Climate Change (doi:10.1038/nclimate1347)
Population density but not stability can be predicted from species distribution models. Oliver et al. (2012) in Journal of Applied Ecology (doi: 10.1111/j.1365-2664.2012.02138.x)
Diet breadth, overwintering stage and range size affect butterfly phenology. Species with narrow larval diet breadths and more advanced overwintering stages, as well as those with smaller ranges, have shown the greatest advancements in their date of first appearance. Diamond et al. (2011) in Global Change Biology (doi:10.1890/10-1594.1)
Predicting insect phenology across space and time. Hodgson et al. (2011) in Global Change Biology (doi: 10.1111/j.1365-2486.2010.02308.x)
Differences in the rate of advance of biological events between plants and consumers suggests potential for temporal mis-matching in key trophic interactions. Meta-analyses have shown that many biological events across multiple taxa and ecosystems are occurring earlier in the year consistent with recent climate warming. However, the rate of these advances are not equal across different trophic levels, being greatest in plants and least in secondary consumers Thackeray et al. (2010) in Global Change Biology (doi: 10.1111/j.1365-2486.2010.02165.x)
Habitat loss and changes in habitat management have been the greatest drivers of change in UK butterfly populations. Numerous studies on butterfly ecology have helped conservationists to restore suitable habitat, and subsequent monitoring through the UKBMS has enabled us to determine how successful this has been. In recent years some of our most threatened species, including the Pearl-bordered Fritillary and Heath Fritillary have started to show recovery across sites where habitat conservation has been put in place. The Large Blue has been successfully re-introduced into England and has now spread naturally into other suitable areas, whilst populations on monitored sites have significantly increased. However, many species are still strongly affected by management of habitats; biodiversity indicators using UKBMS data show that both woodland and farmland butterflies are declining.
Colonisation of newly restored habitats has been shown to take several years, and is related to a species’ mobility and diet, with less mobile species and those with localised host plants taking longest. Models have shown the potential importance of –landscape- versus site-scale conservation. Habitat heterogeneity has been show to be important for enhancing and stabilising butterfly populations. The habitat connecting butterfly populations affects species’ ability to disperse to new sites and their ability to recovery after population crashes (e.g. caused by extreme events such as drought).
Many species have shown significant declines despite the predicted positive effects of climate warming. Those that have increased have generally done so because conservation management has been put in place, for example the Adonis Blue and Silver-spotted Skipper where grazing is essential. Research has also shown that contrary to the expectation that more habitats will be used by butterflies as they move northwards with climate warming, many species’ habitat associations have reduced over time. The likely cause of this is the deleterious effects of habitat degradation.
In addition to direct habitat loss there are other factors which may be contributing to butterfly declines. Future and ongoing research into the effects of pesticides, for example, is a new area of research for which monitoring data is likely to help determine to what extent butterflies are affected by farmland chemicals.
Landscape structure affects the recovery of butterfly populations after extreme events. The Ringlet butterfly shows population crashes after severe droughts. These crashes are reduced, and the recovery thereafter increased, in larger and more connected patches of woodland habitat. Oliver et al. (2012) in Ecography (doi: 10. 1111/j.1600-0587.2012.07665.x)
In warmer years butterflies use a greater range of habitats, yet habitat breadth has decreased over time for most species. Habitat degradation continues to be a major driver of reductions in habitat breadth and population density of butterflies. Oliver et al. (2012) in Global Change Biology (doi:10.1111/j.1365-2486.2012.02737.x)
Host plant and mobility affect speed of colonisation by butterflies on restored grasslands. There is a time lag between arable reversion and colonisation which should be accounted for when assessing restored grassland habitats. Low mobility species and those with localised host-plants take the longest to colonise. Woodcock et al. (2012) in Biological Conservation (doi: 10.1016/j.biocon.2012.05.013)
Butterfly dispersal is related to habitat quality between sites. Populations separated by more suitable habitat tend to show increased similarity in the yearly fluctuations in butterfly population counts. Powney et al. (2011) in Methods in Ecology and Evolution (doi: 10.1111/j.2041-210X.2011.00098.x) + video? (http://www.youtube.com/watch?v=aXP14wM1hLc )
Butterfly populations benefit from having a mixture of habitats available. Populations of butterflies are more stable, and thus more likely to persist, in heterogeneous landscapes: Oliver et al. (2010) in Ecology Letters (doi: 10.1111/j.1461-0248.2010.01441.x)