Habitat connectivity indicator
Experimental statistic: The UK biodiversity indicators project team would welcome feedback on the novel methods used in the development of this indicator.
Type: State Indicator
Connectivity is a measure of the size and distribution of patches of habitat and the relative ease with which typical species can move through the landscape between the patches. Habitat loss and fragmentation can reduce the size of populations and hinder the movement of individuals between increasingly isolated populations, threatening their long-term viability.
The indicator illustrates changes in functional connectivity – the ability of species to move between resource patches – of 33 butterfly species in the UK. The indicator is based on a measure of population synchrony, which is the level of correlation in time-series of population growth rates from different monitoring sites. Quantifying functional connectivity will allow more targeted landscape conservation management to help reduce species extinction risk.
Between 1985 and 1995, the average functional connectivity of UK butterfly species was relatively stable, the index fell to a low of 48% in 2004, and then rose. The level of functional connectivity in 2012 is 10% greater than the level in the start year of 1985 (Figure C2i).
Assessing trends for individual species, between 1985 and 2000, 62% of species declined in connectivity with only 3% showing significant increases (Figure C2ii). In the latter half of the time series between 2000 and 2012, most species increased in connectivity (72%) with only 19% of species declining. The long-term trend from 1985 to 2012 masks mixed, individual species trends, with 33% of species increasing in functional connectivity, 19% decreasing, and 48% showing no significant change.
C2i. Change in functional connectivity, 1985 to 2012, using a 10-year moving window
- The number of individual species included in each time period varies due to the availability of data: there were 27 species in the long-term period, 29 in the early short-term period and 32 in the late short-term period. In all 33 species from three habitat types (woodland, grassland, and garden and hedgerows) are included in the indicator.
- The connectivity index was calculated as the mean value of population synchrony using a 10-year moving window. The index values were extracted from a statistical (mixed effects) model which accounts for other factors known to influence population synchrony, therefore focusing the measure on functional connectivity.
- The line graph (Figure C2i) shows the unsmoothed average trend (dashed line), and the smoothed average trend (using a LOESS regression function) (solid line) of functional connectivity over time across all 33 species. The shaded area represents the 95% confidence interval around the smoothed average trend.
- The bar chart (Figure C2ii) shows the percentage of species within the indicator that have shown a statistically significant increase, statistically significant decrease, or no significant change in functional connectivity over three time periods (long term, 1985 to 2012; early short term, 1985 to 2000; and late short term, 2000 to 2012).
Source: UK Butterfly Monitoring Scheme.
As this is an experimental statistic it has not been assessed. Views on whether Figure C2i or Figure C2ii should be the headline measure would be welcome, together with comments on the value of this new indicator (is this measuring something readers feel should be measured?) and the quality of the new metric (how well does it measure connectivity?).
Last updated: July 2018
Latest data available: 2012