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. 2009 Jun 9;106(23):9322-7.
doi: 10.1073/pnas.0810306106. Epub 2009 May 21.

A global assessment of endemism and species richness across island and mainland regions

Gerold Kier  1 , Holger Kreft, Tien Ming Lee, Walter Jetz, Pierre L Ibisch, Christoph Nowicki, Jens Mutke, Wilhelm Barthlott
Affiliations

A global assessment of endemism and species richness across island and mainland regions

Gerold Kier et al. Proc Natl Acad Sci U S A. .

Abstract

Endemism and species richness are highly relevant to the global prioritization of conservation efforts in which oceanic islands have remained relatively neglected. When compared to mainland areas, oceanic islands in general are known for their high percentage of endemic species but only moderate levels of species richness, prompting the question of their relative conservation value. Here we quantify geographic patterns of endemism-scaled richness ("endemism richness") of vascular plants across 90 terrestrial biogeographic regions, including islands, worldwide and evaluate their congruence with terrestrial vertebrates. Endemism richness of plants and vertebrates is strongly related, and values on islands exceed those of mainland regions by a factor of 9.5 and 8.1 for plants and vertebrates, respectively. Comparisons of different measures of past and future human impact and land cover change further reveal marked differences between mainland and island regions. While island and mainland regions suffered equally from past habitat loss, we find the human impact index, a measure of current threat, to be significantly higher on islands. Projected land-cover changes for the year 2100 indicate that land-use-driven changes on islands might strongly increase in the future. Given their conservation risks, smaller land areas, and high levels of endemism richness, islands may offer particularly high returns for species conservation efforts and therefore warrant a high priority in global biodiversity conservation in this century.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Global patterns of endemism richness (ER; range equivalents per 10,000 km2) for (A) vascular plants, (B) terrestrial vertebrates, (C) amphibians, (D) reptiles, (E) birds, and (F) mammals across 90 biogeographic regions. Map legends were classified using quantiles, i.e., each color class contains a comparable number of regions. Box-and-whisker plots illustrate rank-based differences in endemism richness between mainland (n = 76; white boxes) and island regions (n = 14; gray boxes). Boxes mark second and third quartiles; whiskers mark the range of the data.
Fig. 2.
Fig. 2.
Cross-taxon congruence of endemism richness (ER; range equivalents per 10,000 km2) of vascular plant and terrestrial vertebrate classes. Ranked values of (A) amphibians, (B) reptiles, (C) birds, and (D) mammals are plotted against vascular plants. Red dots indicate island regions, gray dots mainland regions. Values of Spearman's rank correlation coefficient (rs) are shown for each relationship (all P < 0.001).
Fig. 3.
Fig. 3.
Performance of a prioritization ranking on the basis of vascular plants. (A) Two different rankings are compared: For ranking 1 (blue), regions were ranked in descending order according to their total number of range equivalents. Ranking 2 (red) ranked regions in descending order on the basis of their endemism richness per 10,000 km2. Curves indicate the accumulation of range equivalents (solid lines) and area (dotted lines) across the rankings and are contrasted against a random expectation (gray lines; mean values and 95% confidence intervals for 10,000 random rankings). Islands are highlighted by orange circles. (B) Cross-taxon performance of plant-based ranking 2 (red) for terrestrial vertebrates. The ranked regions appear on the x axis; values on the y axis indicate the proportion of all range equivalents covered.
Fig. 4.
Fig. 4.
Comparison of key conservation features for mainland (green) and island regions (orange). (A) Variation in area sizes, (B) past land-cover loss (year 2000), (C) human impact (year 2000), (D) future land-cover loss (projections for the year 2100 according to ref. 52) because of land-use change and, (E) because of climate change, (F) current protection status (proportion covered by protected areas). Values in B–F represent ranks. Significance codes indicate differences (Mann-Whitney U-test) between mainlands and islands: ***, P < 0.001; **, P < 0.01; *, P < 0.1; ns, not significant.
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