Tzung-Su Ding

Global hotspots of species richness are not congruent with endemism or threat

Biodiversity hotspots have a prominent role in conservation biology, but it remains controversial to what extent different types of hotspot are congruent. Previous studies were unable to provide a general answer because they used a single biodiversity index, were geographically restricted, compared areas of unequal size or did not quantitatively compare hotspot types. Here we use a new global database on the breeding distribution of all known extant bird species to test for congruence across three types of hotspot. We demonstrate that hotspots of species richness, threat and endemism do not show the same geographical distribution. Only 2.5% of hotspot areas are common to all three aspects of diversity, with over 80% of hotspots being idiosyncratic. More generally, there is a surprisingly low overall congruence of biodiversity indices, with any one index explaining less than 24% of variation in the other indices. These results suggest that, even within a single taxonomic class, different mechanisms are responsible for the origin and maintenance of different aspects of diversity. Consequently, the different types of hotspots also vary greatly in their utility as conservation tools.

Global distribution and conservation of rare and threatened vertebrates

Global conservation strategies commonly assume that different taxonomic groups show congruent geographical patterns of diversity, and that the distribution of extinction-prone species in one group can therefore act as a surrogate for vulnerable species in other groups when conservation decisions are being made. The validity of these assumptions remains unclear, however, because previous tests have been limited in both geographical and taxonomic extent. Here we use a database on the global distribution of 19,349 living bird, mammal and amphibian species to show that, although the distribution of overall species richness is very similar among these groups, congruence in the distribution of rare and threatened species is markedly lower. Congruence is especially low among the very rarest species. Cross-taxon congruence is also highly scale dependent, being particularly low at the finer spatial resolutions relevant to real protected areas. ‘Hotspots’ of rarity and threat are therefore largely non-overlapping across groups, as are areas chosen to maximize species complementarity. Overall, our results indicate that ‘silver-bullet’ conservation strategies alone will not deliver efficient conservation solutions. Instead, priority areas for biodiversity conservation must be based on high-resolution data from multiple taxa.

Global Patterns of Geographic Range Size in Birds

Large-scale patterns of spatial variation in species geographic range size are central to many fundamental questions in macroecology and conservation biology. However, the global nature of these patterns has remained contentious, since previous studies have been geographically restricted and/or based on small taxonomic groups. Here, using a database on the breeding distributions of birds, we report the first (to our knowledge) global maps of variation in species range sizes for an entire taxonomic class. We show that range area does not follow a simple latitudinal pattern. Instead, the smallest range areas are attained on islands, in mountainous areas, and largely in the southern hemisphere. In contrast, bird species richness peaks around the equator, and towards higher latitudes. Despite these profoundly different latitudinal patterns, spatially explicit models reveal a weak tendency for areas with high species richness to house species with significantly smaller median range area. Taken together, these results show that for birds many spatial patterns in range size described in geographically restricted analyses do not reflect global rules. It remains to be discovered whether global patterns in geographic range size are best interpreted in terms of geographical variation in species assemblage packing, or in the rates of speciation, extinction, and dispersal that ultimately underlie biodiversity.

Spatial turnover in the global avifauna

Despite its wide implications for many ecological issues, the global pattern of spatial turnover in the occurrence of species has been little studied, unlike the global pattern of species richness. Here, using a database on the breeding distributions of birds, we present the first global maps of variation in spatial turnover for an entire taxonomic class, a pattern that has to date remained largely a matter of conjecture, based on theoretical expectations and extrapolation of inconsistent patterns from different biogeographic realms. We use these maps to test four predictions from niche theory as to the form that this variation should take, namely that turnover should increase with species richness, towards lower latitudes, and with the steepness of environmental gradients and that variation in turnover is determined principally by rare (restricted) species. Contrary to prediction, we show that turnover is high both in areas of extremely low and high species richness, does not increase strongly towards the tropics, and is related both to average environmental conditions and spatial variation in those conditions. These results are closely associated with a further important and novel finding, namely that global patterns of spatial turnover are driven principally by widespread species rather than the restricted ones. This complements recent demonstrations that spatial patterns of species richness are also driven principally by widespread species, and thus provides an important contribution towards a unified model of how terrestrial biodiversity varies both within and between the Earths major land masses.

Human impacts and the global distribution of extinction risk

Understanding the global geographical distribution of extinction risk is a key challenge in conservation biology. It remains controversial, however, to what extent areas become threat hotspots simply because of high human impacts or due to predisposing ecological conditions. Limits to the taxonomic and geographical extent, resolution and quality of previously available data have precluded a full global assessment of the relative roles of these factors. Here, we use a new global database on the geographical distributions of birds on continents and continental islands to show that, after controlling for species richness, the best predictors of the global pattern of extinction risk are measures of human impact. Ecological gradients are of secondary importance at a global scale. The converse is true for individual biogeographic realms, within which variation in human impact is reduced and its influence on extinction risk globally is therefore underestimated. These results underline the importance of a global perspective on the mechanisms driving spatial patterns of extinction risk, and the key role of anthropogenic factors in driving the current extinction crisis.

Using stable isotopes to unravel and predict the origins of great cormorants (Phalacrocorax carbo sinensis) overwintering at Kinmen

The Food and Agricultural Organization of the United Nations and the World Organization for Animal Health have called for a better understanding of the role that migrating birds may play in spreading H5N1 highly pathogenic avian influenza (HPAI). Bird banding, traditionally used in studies of migration, is limited by low recapture rates. Telemetry can only be applied to larger species and a limited number of birds. We show that analyses of multiple stable isotopes (delta(13)C, delta(15)N, delta(18)O and deltaD) can provide an understanding of the number of breeding populations represented at large congregations of wintering birds, probable locations of these breeding populations, and which breeding populations do not contribute migrants to a wintering site. As Asia is thought to be the origin of many HPAI strains and the center of their evolution, and as bird migration is poorly understood in this part of the world, we recommend that, in addition to banding, satellite, and VHF telemetry, the stable isotope analysis of migration patterns should become a part of long-term surveillance studies.

Colony site choice of blue-tailed bee-eaters: influences of soil, vegetation, and water quality

All bee‐eaters (Family Meropidae) are cavity nesters, excavating terrestrial burrows in sites ranging from flat ground, to small mounds of soil, steep earthen banks seen in road clearings, eroded cliff faces, and river gorges. However, very little is known concerning the environmental factors that influence nest site selection in bee‐eaters. We addressed abiotic and biotic issues associated with colony site choice in blue‐tailed bee‐eaters (Merops philippinus) nesting on Kinmen Island, off mainland China, from 2000 to 2002. About 89% of the colonies were located on slopes with soils of sandy loam and the other 11% on sandy clay loam. No colony was found on clay loam, which covered 20% of the island. The sandy loam and sandy clay loam had lower soil pressure, density and moisture, which, presumably, were easier for bee‐eaters to excavate and provided better drainage and ventilation for nest cavities. Bee‐eaters avoided placing nest cavities in areas with dense vegetation and abandoned colony sites when they became overgrown. Vegetation would impede excavation and decrease the detectability of predators. Bee‐eaters may prefer colony sites near water bodies showing water chemistries indicative of more biological productivity, especially in relation to the diversity and abundance of their major prey, dragonflies.

Erratum: Global distribution and conservation of rare and threatened vertebrates

This corrects the article DOI: 10.1038/nature05237

Male pheasant‐tailed jacanas commit infanticides to avoid cuckoldry when paternity of eggs is doubtful

Many hypotheses have been proposed to explain infanticide, killing the young or destruction of eggs by conspecific adults. We report cases of infanticide in the polyandrous pheasant‐tailed jacana (Hydrophasianus chirurgus) of Taiwan. In 2004, three males and one female bred at our study site. The female mated with the three males sequentially and laid clutches for all of them. Infanticidal behaviour was observed in all males and in all but one clutch, the first clutch of the breeding season. The infanticidal males threw out the first one or two eggs of a clutch, but then accepted replacement eggs and incubated normally. Because the intervals between copulation with different males were short (1–10 days) and sperm can remain viable within the female reproductive tract for at least 4–5 days, sperm competition among the males may have been intense, and the paternity of the first few eggs in each clutch was doubtful. We suggest that male pheasant‐tailed jacana may use infanticide as a strategy to avoid cuckoldry when the paternity of eggs is in doubt.

Grenyer et al. reply

Replying to: A. S. L. Rodrigues 450, 10.1038/nature06374 (2007)Rodrigues criticizes our demonstration of low congruence in the global distributions of rare and threatened vertebrates on the grounds that we excluded locations where species counts were zero from our analyses. In practice, this makes no substantive difference to our conclusions. Some sample locations are not inhabited by any organisms of interest: such locations can inflate measures of covariation and association because their values for parameters of interest (in this case, zero counts of species) are identical. This bias has long been known (as ‘the double-zero problem’); many ecological techniques and studies exclude double-zero data for this reason.