Lisa L. Manne

Relative risk of extinction of passerine birds on continents and islands

Greater numbers and higher proportions of recent species extinctions have been on islands rather than on continents. In contrast, predictions of massive future extinctions stem from the current clearing of continental, tropical forests. For instance, since 1600, 97 out of 108 bird extinctions have been on islands. However, 452 of the total 1,111 species currently considered to be threatened are continental. Island flora and fauna are uniquely vulnerable to the human introduction of previously absent predators, diseases and other menaces, whereas species on continents are not so ecologically naive. So could predictions of future continental extinctions based on island histories be exaggerated? Most threatened species have small geographic ranges, and the ranges of island species are inevitably smaller than those of continental species. For a given range size, how do the proportions of threatened island and continental species compare? Here we compile the ranges of thepasserine (perching) birds of the Americas. Corrected for range size, continental species are more—not less—likely to be threatened. We use this unexpected vulnerability of continental species with small ranges to produce a map showing where species losses might occur in the long term.

Beyond eight forms of rarity: which species are threatened and which will be next?

We tabulate three measures of rarity: local abundance, breeding range size and elevational extent for the passerine birds of the New World. We determine what fraction of species is threatened with extinction within the combinations of these three measures. Species with smaller ranges, lower abundances and narrower elevational bands suffer higher levels of threat across lowland, montane and island species. For a given range size, lowland species suffer higher levels of threat than island or montane species. (This is counter to the intuition that island species ‐ and those isolated on mountain tops ‐ might be ecologically naive.) When all three factors are considered together, there is only a slight tendency for lowland species to be disproportionately more threatened. Simply, island and montane species tend to be relatively common within their restricted ranges and their increased abundance reduces their likelihood of being threatened. Elevation is a consistent but relatively unimportant factor in determining threat; abundance and range size are much more important, and have an interactive effect on threatened status. We calculate the number of humans with which each species shares its breeding range, and find that this number does not aid in predicting threat status.

The distribution of cultural and biological diversity in Africa

Anthropologists, biologists and linguists have all noted an apparent coincidence in species diversity and human cultural or linguistic diversity. We present, to our knowledge, one of the first quantitative descriptions of this coincidence and show that, for 2° × 2° grid cells across sub–Saharan Africa, cultural diversity and vertebrate species diversity exhibit marked similarities in their overall distribution. In addition, we show that 71% of the observed variation in species richness and 36% in language richness can be explained on the basis of environmental factors, suggesting that similar factors, especially those associated with rainfall and productivity, affect the distributions of both species and languages. Nevertheless, the form of the relationships between species richness and language richness and environmental factors differs, and it is unlikely that comparable mechanisms underpin the similar patterns of species and language richness. Moreover, the fact that the environmental factors considered here explain less than half of the variation in language richness indicates that other factors, many of which are likely to be historical or social, also influence the distribution of languages.

Building indicator groups based on species characteristics can improve conservation planning

How well can indicator groups, as sets of species with well-known distributions, represent the distribution of overall biodiversity to select networks of areas for conservation? In the literature, reliable indicator groups of complementarity have proven difficult to find, with some taxon-based indicator groups resulting in no more species represented than when areas are chosen at random. We rigorously test which quantifiable characteristics of species make them better components of indicator groups of complementarity in area networks. We find that even indicator groups comprised of randomly chosen, taxonomically unrelated species perform better than randomly chosen areas, and we demonstrate the improved efficiency of protected-area networks possible when using indicator groups chosen on the basis of species’ characteristics.

The calculus of biodiversity: integrating phylogeny and conservation

We thank John Gittleman and Mike McKinney for their efforts in organizing the working group and the support of NCEAS through the NSF (Grant #DEB-94-21535), the University of California at Santa Barbara and the State of California. O.B-E. was also funded by an NSERC (Canada) postdoctoral fellowship.

Hypersingular integrals at a corner

Abstract For a smooth boundary, hypersingular integrals can be defined as a limit from the interior, the approach direction being taken, for convenience, normal to the surface. At a boundary corner, the limit process, with a necessarily non-normal approach direction, provides a valid definition of the hypersingular equation, as long as the same direction is employed for all integrations. The terms which are potentially singular in the limit are shown to cancel, provided the function approximations at the corner are consistent. The analytical formulas for the singular integrals are more complicated than for a smooth surface, but are easily obtained using symbolic computation. These techniques have been employed to accurately solve the ‘L-shaped domain’ potential considered by Jaswon and Symm (Integral Equation Methods in Potential Theory and Elastostatics, Academic Press, New York, USA, 1977).

Utility of Measuring Abundance versus Consistent Occupancy in Predicting Biodiversity Persistence

The primary goals of reserve selection are to represent all chosen units of biodiversity and to ensure their long-term persistence while minimizing costs. We considered two simple proxies of species persistence: a time series of point-count data to calculate abundance and a time series of presence-absence data to calculate permanence (a measure of consistent occupancy over time). Using two 10-year intervals of data from the North American Breeding Bird Survey, we compared the performance of each measure at predicting persistence 18 years later. For nonrare species, abundance and permanence predicted persistence similarly well. We performed complementarity-based reserve selections with data on species abundance and permanence (from 1970 to 1979) and then evaluated the effectiveness of the reserve networks at maintaining species populations and efficiency in land use (data from 1997 to 2006). Abundance proved a better predictor of future local persistence than permanence, which justifies the relatively larger financial and temporal costs of collecting a time series of point-count data to estimate abundance. If future extinction events were used as a measure of reserve-network effectiveness, the performance of abundance and permanence did not differ markedly. Nevertheless, when future abundance, which is a more sensitive measure of network effectiveness, was used, abundance was significantly better than permanence at selecting longer-term, high-quality, species-specific habitat but required larger reserves to do so.

Ecology: Engineered food webs

An important new study shows that, in a food web, the strengths and arrangement of the interactions between species are determining factors of stability of the system.