Developing a habitat connectivity indicator for the UK: examining potential change in model landscapes

Indicators are increasingly relied upon to monitor performance against predefined targets and to aid the development of policy. Rather than provide absolute measures, indicators are intended to summarise and distil complex information into simple, robust, relative indices which can be used to assess relative change or trends over time. An indicator of habitat connectivity is one of eighteen biodiversity indicators proposed for the UK (UK Biodiversity Partnership 2007). This indicator is intended to allow the assessment of change in habitat connectivity and to monitor progress towards 2010 biodiversity targets. Fragmentation is the process of changing landscape structure by physically breaking-up large areas of habitat into smaller pieces. Connectivity, or functional connectivity, is the degree to which landscape structures facilitate or impede movement of organisms among habitat patches (Taylor et al. 1993; With et al., 1997). This paper examines the suitability of various connectivity measures, including species-based metrics, graph theory, buffer radius and least-cost approaches (e.g. Calabrese & Fagan 2004), as the basis for the UK connectivity indicator, by assessing their ability to detect change in UK model landscapes at different scales. The model landscapes are created by applying conceptual, plausible landscape change options (e.g. add/enlarge patches, remove patches, change matrix) to actual landscapes using an expert knowledgebase. These selected landscape change options alter landscape structure and have the potential to affect habitat connectivity (e.g. spatial location of new/removed patches, reduced/increased isolation, changes to landscape permeability).