The effects of climate and habitat on butterfly populations
Biodiveristy is threatened globally and there is a need to monitor and understand future changes. Rigourous assessment of trends in insect populations is difficult because they are a species-rich, yet little known taxa. Butterflies are among the most practical insect group to study, given their extensive long-term, large-scale datasets. The effects of climate and habitat of butterfly populations are examined to understand the implications of environmental change for these, and other, insect taxa. It is found that first appearance (phenology) of most British butterflies has advanced in the last two decades and is strongly related to climate. Further warming is predicted to advance appearance by 2 to 6 days per 1°C temperature increase. Despite this strong relationship between appearance dates and temperature over time, a comparable geographical relationship between temperature and timing was not detected for over a third of species analysed, suggesting their populations may be adapted to their local climates. A seasonal switch in egg-laying requirements of the butterfly, Polyommatus bellargus, demonstrates an interaction between niche requirements and climate determine fluctuations in populations. The effect of climate on populations of other butterflies was studied using national weather records and indices of population change since 1976. Strong associations between weather and population fluctuations were found in 28 out of 31 species studied. Models derived from these associations predict that most species will increase in abundance under warmer climates. Large scale habitat modification is known to have profoundly affected butterfly populations over the last century. Data from a farm scale evaluation ofthe effects of management for genetically modified herbicide-tolerant (GMHT) crops showed that effects on vegetation cover and flowering at this scale has marked knock-on effects for butterflies and other mobile, nectar feeding insects.