Using landscape history to predict biodiversity patterns in fragmented landscapes.
Bottom Line: The model predicts that community similarity declines with terragenetic distance, and that local endemics are more likely to be found in terragenetically distinctive fragments than in large fragments.We derive equations to quantify the variance around predictions, and show that ignoring the spatial structure of fragmented landscapes leads to over-estimates of local extinction rates at the landscape scale.We argue that ignoring the shared history of habitat fragments limits our ability to understand biodiversity changes in human-modified landscapes.
Affiliation: Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot, SL5 7PY, UK.Show MeSH
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Mentions: As expected under the terragenetic model, we found a positive correlation between predicted and observed community similarity ( = 0.25, 95% CI = −0.07 to 0.54; Fig.6a) and a strong, negative correlation between observed community similarity and terragenetic distance ( = −0.28, 95% CI = −0.51 to −0.01; Fig.6c). Contrary to the terragenetic predictions, we found a positive correlation between community similarity and geographical space ( = 0.52, 95% CI = 0.28 to 0.72; Fig.6d), although the slope was near-zero (slope = 0.003) and, with just four fragments, we were unable to reject the hypothesis that the observed slope was zero (linear regression: F1,4 = 1.66, P = 0.27). Furthermore, this pattern may have been an artefact of a weak negative correlation between geographical distance and the log-ratio of fragment sizes for the four fragments in this analysis (Mantel test: r = −0.08, P = 0.58). We also detected a negative correlation between observed and predicted local endemic species richness ( = −0.92, 95% CI = −0.96 to −0.87; Fig.6b). However, the slope of this relationship was also near-zero (slope = −0.002) and observed numbers of endemic species were several orders of magnitude higher than the predictions, likely an artefact of sampling just four fragments incompletely. Many species deemed locally endemic in our empirical data will be shared with fragments that were not sampled, and this undersampling of fragments will greatly inflate the observed number of local endemics. Undersampling of the beetle communities within the fragments probably also contributes to the inflated estimates of endemic species. This interpretation is supported by the low values of observed community similarity in the beetle data (Didham. 1998b), with observations being consistently lower than the values predicted under the terragenetic model.
Affiliation: Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot, SL5 7PY, UK.