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HOME » Butterflies as indicators
Butterflies as indicators
Butterflies are increasingly being recognised as valuable environmental indicators, both for their rapid and sensitive responses to subtle habitat or climatic changes and as representatives for the diversity and responses of other wildlife.
One of the principle objectives of the UKBMS is to investigate and develop the role of butterflies as indicators of the state of biodiversity in the UK.
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Their biology and charismatic
appeal make butterflies ideal
biodiversity indicators
Butterflies have short life cycles and thus react quickly to environmental changes. Their limited dispersal ability, larval foodplant specialisation and close-reliance on the weather and climate make many butterfly species sensitive to fine-scale changes. Recent research has shown that butterflies have declined more rapidly than birds and plants emphasising their potential role as indicators.
Butterflies occur in all main terrestrial habitat types in the UK (except for dead wood), so they have the potential to act as indicators for a wide range of species and habitats. Unlike most other groups of insects, butterflies are well-documented, their taxonomy is understood and they are easy to recognise.
Because insects make up the largest proportion of terrestrial wildlife (more than 50% of species), it is crucial that we assess the fate of insect groups in order to monitor the overall state of biodiversity. Being typical insects, the responses seen in butterflies are more likely to reflect changes amongst other insect groups, and thus the majority of biodiversity, than established indicators such as those based on birds.
By monitoring we hope to have a more sensitive indicator for insects, which dominate biodiversity - accounting for more than 50% of UK species
Our goal is to produce Governmental butterfly biodiversity indicators for all of the UK countries and for the UK as a whole. Initial work has focussed on England, as the dataset is more extensive. These candidate indicators have been developed to help the Government measure progress against targets within the England Biodiversity Strategy (EBS). These are:
- Populations of butterflies in England
(Headline indicator) - Populations of butterflies on farmland in England
(Agriculture policy workstream indicator) - Populations of butterflies in English woodland
(Woodland policy workstream indicator)
It is hoped these candidate indicators will be adopted by Defra in time for inclusion in the next EBS assessment of progress report due late 2006.
The overall population of butterflies has fluctuated over the last 30 years, with peaks at six to eight year intervals, and a progressive decline over the total period. The 19 'specialist' species have fared worse than the 23 'generalist' species. Following a low point in 2001, populations of specialist species recovered slightly up to 2005. The recent trend is therefore assessed as positive.
Populations of butterflies in England 1976-2005(Number of species in indicator shown in brackets)
Trends
Butterfly numbers have fluctuated from year-to-year according to weather conditions and natural cycles. Populations peaked in 1976, 1984, 1992, 1997 and 2003. Direct comparisons with the base year in 1976 are problematic because this coincided with a population peak, following a period of warm and dry weather. However it is evident that the peaks and troughs in the all-species index have declined progressively since 1984, revealing a long term declining population trend. This decline mostly affects the 19 specialist species which fell to only 40% of the 1976 level in 2001. Since 2001 specialist species populations have recovered to 57%, though this may turn out to be a temporary recovery. Populations of generalist species have varied around the 1976 level, with no evidence of a long-term decline, but populations have fallen in the last two years.
Background
This indicator is a multi-species index that includes 42 of the 54 native resident English butterfly species, the remainder being excluded as insufficient monitoring data is available. The indicator includes a breakdown for 19 specialist (low mobility species restricted to semi-natural habitats) and 23 generalist (mobile species that occur in a wide range of habitats in the wider countryside) species, from data collected at approximately 1000 sites.
