A Comparative Measure of Biodiversity based on Species Composition

In conservation planning, species richness and species endemism are most often used as metrics to describe the biodiversity importance of areas. But when it comes to prioritizing regions for conservation actions these measures alone are insufficient because they do not reveal how similar or different the actual composition of species may be from one area to another. For comparative analysis an additional useful metric would be one that indicates the degree to which the species assemblage in one area also represents—or is distinct from—species assemblages of other areas.

In this project, a method for quantifying the compositional representativeness (CR) of species assemblages among geographic regions is being developed and tested. This metric generates asymmetric pairwise values for a Bray-Curtis type of similarity coefficient resulting in different measures for representation and distinctiveness. A proof of concept was demonstrated first with fish species assemblages in ecoregions of the Mississippi Basin and the patterns of fish species composition were compared with patterns of species richness. Later it was tested with fish species compositions among the small hydrological units of two separate freshwater ecoregions, showing its application at multiple scales.

At local and regional scales the CR metric reveals biodiversity patterns that differ from patterns of species richness alone. This project also shows that gradients of representativeness and distinctiveness are not just the inverse of each other. CR data can guide conservation planning processes to ensure that the most representative species assemblage is considered as well as the most distinctive or unique one.

Jennings, M. et al. 2008. A comparative measure of biodiversity based on species composition. Biodiversity Conservation.  DOI 10.1007/s10531-008-9322-7

Global Estimates of Terrestrial Habitat Loss and Fragmentation

Habitat loss and fragmentation are widely recognized as the primary causes of biodiversity loss in terrestrial ecosystems. But how fragmented is the world? How does the degree of fragmentation change with the extent of habitat loss? Do relationships between habitat loss and fragmentation suggest processes that conservationists could manipulate to reduce the threat of fragmentation?

To answer these questions, a global land cover dataset having a 1 km2 resolution was analyzed to quantify: (a) the extent of habitat loss, and (b) the distribution of remaining habitat. Geographic data on the amount and distribution of habitat lost and habitat remaining were produced globally as well as for each of the world’s terrestrial ecoregions. Then, for each ecoregion, detailed analyses of landscape fragmentation were completed. This resulted in quantification of 30 different fragmentation parameters for each ecoregion of the world. These parameters include, for example, measures of the largest intact patch, the overall amount of patch isolation, and the dispersion and contiguity of natural land patches within each ecoregion.

The observed relationship between the distribution of habitat block sizes and the total extent of habitat loss in ecoregions suggests a predictive model for the functional linkage between habitat loss and fragmentation. This relationship was compared among different biomes to explore whether processes of habitat loss and fragmentation differ systematically. These findings improve our understanding of the threats posed by ongoing habitat loss and fragmentation around the world, and suggest potential conservation strategies for minimizing adverse consequences for biodiversity.

Global Estimates of Effective Conservation

One way of evaluating the current status of conservation is simply to calculate the area under some form of legal protection. However, because “legal protection” means quite different things in different parts of the world (e.g., “paper parks”), it is more useful to consider current status in terms of “effective conservation.”

The Nature Conservancy assesses “effective conservation” by considering three factors—biodiversity health, conservation management and threat status. When all three conditions are satisfied (i.e., conservation management is in place, biodiversity is viable, and threats are adequately abated or mitigated) we are more confident that our conservation efforts are indeed effective.

In order to measure effective conservation at a global scale, we combine three publicly available GIS layers: a modified global land cover layer – based on the GLC 2000, an updated version of the World Database on Protected Areas (WDPA 2006), and Wildlife Conservation Society’s Human Footprint. Using ArcInfo GRID, we combined the layers in such a way, that while all the original information remains intact, it can be still be assessed to give us not only the effective conservation and derivatives thereof, but also can be easily summarized by ecoregion and used for later analyses.

Using this analysis, we found that at most 7.0% of the land area could be considered to have high effective conservation. This fell to 2.5% when a stricter version of protection was adopted. Also, when the data was analyzed using WWF’s ecoregions, it was found that this varies greatly amongst Biomes and Biogeographic Realms.

View a presentation on Global Estimates of Effective Conservation

For more information, please contact the team at conservationgateway@tnc.org