o_19ko2dt161ng2j4e1tgnoqv1s45a.pdf

J. GREGSON, R. DE KOK, J. MOAT & S. BACHMAN (2007)
method (Schatz 2002) and Rapoport’s mean propinquity method (Willis et al. 2003), (Fig. 2c).
The cell adjacency method considers all contiguous grid cells from the AOO calculations to be
a single subpopulation. Rapoport’s mean propinquity technique is based on the mean line
length of a minimum spanning tree (a set of lines that connect all points in the minimum
possible distance). Subpopulations are separated where the limb (line) distance is greater than
twice the mean limb distance (Willis et al. 2003).
Other parameters
The above three parameters have the advantage that they can be calculated quickly, easily and
automatically from georeferenced data sets, and can be used to assign preliminary conservation
ratings to species using IUCN Criteria. For taxa that are threatened, a more detailed ‘desktop’
conservation assessment may be required and GIS can be of use here too. Habitat level data
can be used to infer declines at the species level. Remote sensing imagery including aerial
photographs and satellite images were used to see how forest cover changed over time at
Mount Oku and Ijim Ridge in Cameroon (Baena 2005).
A B C D
Fig. 2. Examples of EOO, AOO and subpopulations calculations using GIS. From Willis et al.
(2003).
Habitat fragmentation for each species distribution can also be calculated: the preferred habitat
of the species is first identified from the label, and species distributions compared to habitat
datasets. Fragmentation of habitats can be calculated using Fragstats program and Patch Analyst
in ArcView. Consideration needs to be made as to which metric of fragmentation is used;
again there may not be a ‘one size fits all’ solution. It may also be possible to develop indices
of fragmentation based on the subpopulation techniques as discussed above. Biological meaning
can be added to the distances between subpopulations, i.e., by considering dispersal ability so
that a more realistic measure of fragmentation can be obtained.
251