The North Atlantic Oscillation, climate change and the ecology of British insects

Abstract

Evidence is accumulating that climate change is having a significant effect on a wide range of organisms spanning the full range of biodiversity found on this planet. This study investigates the ecological role of climate change, the North Atlantic Oscillation (NAO) and habitat change on British insect populations. Despite the NAO having a considerable effect on British weather, the role of the NAO on British insects has not previously been studied in great detail. The World's two best entomological time series datasets were used – the United Kingdom Butterfly Monitoring Scheme (UKBMS) and the Rothamsted Insect Survey of aphids – both surveys with very large sample sizes and high quality data. Summary of main findings: 1. Warm weather associated with a positive NAO index caused the spring migration of the green spruce aphid (Elatobium abietinum), a pest species of spruce trees (Picea) to start earlier, continue for longer and contain more aphids. An upward trend in the NAO index during the period 1966-2006 is associated with an increasing population size of E. abietinum. 2. The NAO does not affect the overall UK butterfly population size. However, the abundance of bivoltine butterfly species, which have a longer flight season, were more likely to respond positively to the NAO compared to univoltine species, which show little or a negative response. 3. A positive winter NAO index was associated with warmer weather and earlier butterfly flight dates. For bivoltine (two generations in a year) species, the NAO affects the phenology of the first generation, and then the timing of the second generation is indirectly controlled by the timing of the first generation. The NAO influences the timing of the butterfly flight seasons more strongly than it influences population size. 4. Butterfly data from Monks Wood National Nature Reserve in Cambridgeshire showed that the NAO does not affect the abundance of the whole butterfly community, but it does affect the population size of some species. The NAO does not affect butterfly diversity, but there were decreases in butterfly diversity and number of species with time. 5. The total number of butterflies counted at Monks Wood was constant for most of the time series. However, the population size of the ringlet (Aphantopus hyperantus) increased from very low numbers to more than half the total number of butterflies counted each year. Therefore the total population size of all the other species has decreased considerably. 6. The NAO was more important than climate change in determining the flight phenology of the meadow brown butterfly (Maniola jurtina) at Monks Wood. In conclusion, the NAO affects the abundance of some species of British butterfly, and an aphid species, with a stronger effect on the timing of flight rather than abundance. There was evidence for a long-term decrease in the biodiversity of butterflies at Monks Wood and this decrease is likely to continue.