shows a landscape prioritization (zoning) for British butterflies, based on species-specific surfaces of population connectivity. Most high priority landscapes are species-rich regions in southern England, which contain core areas of the distributions of many rare species. Nonetheless, high priority areas are also found in Scotland, where the core areas of five northern species occur. The most important 10% of area (a
) included 3868 separate (usually multi-cell) blocks of land, which demonstrates a high degree of fragmentation of distributions of threatened species in modified habitats at this scale. Some of these small fragments have populations that are populations that are dynamically connected and, for conservation purposes, should be managed as part of the same landscape. To identify such landscapes, we grouped together blocks of land to reflect their natural biological affinities and proximity to one another (b
, see §2
). This procedure identified 75 landscapes that cover 4.9% of the British land surface, and could logically be identified as single landscapes with respect to long-term population dynamics and conservation management. This method provides a means by which conservation planning for British butterflies can move forward from the current focus on sites for the rarest and most threatened species (e.g. the UK Biodiversity Action Plan, UK Biodiversity Steering Group 1995
), to the conservation of landscapes that will maintain the entire butterfly fauna.
Figure 2 (a) Landscape prioritization zones for British butterflies. Colour-scale from low to high priority (cumulative percent of landscape removed when the focal cell is removed): dark blue 0–60%, light blue 60–80%, yellow 80–90%, orange (more ...)
shows a landscape prioritization for detailed regional planning at a high spatial resolution in the HCC region, based on connectivity surfaces derived from habitat models (Wintle et al. in press
). A hierarchy of solutions with significant habitat aggregation is found both for the UK butterflies and the Hunter valley even though they are based on different data at different spatial scales. The connectivity computation makes a great difference to the small-scale spatial pattern of the recommended reserve area of HCC: a 20% solution based directly on probability of occurrence includes 3915 often closely spaced distinct blocks of land (separate analysis, not shown). In contrast, calculations based on connectivity produce only 22 compact and well connected blocks (), which are well suited as starting points for local conservation planning.
Figure 3 (a) Landscape prioritization for the indicator species in Hunter Valley, eastern Australia. Colour-scale as in a. (b) Priority landscape groupings based on the top 20% zone (see §2).
We assessed the use of weights in Zonation for the British butterflies. We classified species as habitat specialists or wider-countryside species (Asher et al. 2001
) and weighted them as 10 and 1, respectively: the specialists have declined (Warren et al. 2001
) whereas the wider-countryside species survive in a multitude of rural and urban landscapes outside protected areas. a
demonstrate the success of our approach: more than 90% of the original summed connectivity of high and medium priority (Asher et al. 2001
) species is retained in a small fraction (less than 10%) of the landscape identified as high priority zones in our analysis. Low priority species lose more of their distribution (c
) because they have much larger initial distributions (d
). A higher fraction is retained for habitat specialists than for wider countryside species, as expected due to the weighting of species (b
). Even following a high proportional
loss of connectivity, the low priority species still retain higher absolute
levels of connectivity within reserve areas than the habitat specialists (d
). The situation is different in the Hunter Valley, where the top 20% fraction of the remaining forest (12.9% of the total land surface) includes only more than 25% of the distributions of all indicator species. Because the indicators have wide but mostly non-overlapping distributions, essentially none of the remaining forest cover can be lost without some predicted loss of biological value. Nonetheless, the core area of each species is covered by our solution ().
Figure 4 (a–c) Proportion of original distribution (connectivity) retained for each of the 57 British butterfly species as a function of proportion of landscape remaining as lower priority zones are removed. Habitat specialists (weight 10) and wider countryside (more ...)
Sensitivity analyses reveal that our recommended solutions are not overly dependent on dispersal abilities assumed in connectivity computations or species weights used in Zonation. Doubling or halving dispersal distances (for UK and HCC) caused the identity of ca
15% of cells in the top 10% zone to change. For the butterflies of Britain, 74.3% of the grid cells in the top 10% of our base solution (a
) were also included when all species received equal weights, the latter giving more emphasis to regions with strong occurrences of common species. The corresponding value was 98.7% when only habitat specialist species were used in the analysis, indicating that the habitat specialists are strongly driving the zoning when using our default 10