The role of transitional areas as avian biodiversity centres

Salit Kark*, Thomas F. Allnutt, Noam Levin, Lisa L. Manne, Paul H. Williams

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


Aim: With the ever-increasing threats to biodiversity, efforts are being directed towards identifying hotspots of special importance for conservation. In particular, there has been an effort to identify irreplaceable regions that are especially rich in rare species. Areas of transition between ecological systems in which multiple species coincide are expected, almost by definition, to be species-rich. Here, we examine whether this is simply a result of an overlap between two communities in boundary regions, or whether boundary areas also hold concentrations of rare (e.g. range-limited) species. We ask whether an analysis that includes areas of transition may be a useful contribution to the identification of biodiversity centres. Location and methods: To address these questions, we examined the relationship between passeriform richness and range size rarity of approximately 2300 bird species in 4889 1° New World grid cells, and the distance of the cells to boundaries between adjacent plant-based ecoregions. Results: Areas nearer to boundary regions between ecoregions not only had more bird species, but also scored more highly in terms of species rarity. The range centres of the rarest 10% of species were distributed significantly closer to boundaries between ecoregions than were species in general. This pattern persisted for rarity when we divided the New World into three latitudinal belts and analysed each separately, and when we excluded the Andes. It also persisted when compared with randomly generated ecoregion polygons. Main conclusions: The findings of this work suggest that transitional environments harbour many rare species, in addition to high richness. Consequently areas of biotic transition should be highly valued as biodiversity centres and need to be included in future global conservation analyses and decisions.

Original languageAmerican English
Pages (from-to)187-196
Number of pages10
JournalGlobal Ecology and Biogeography
Issue number2
StatePublished - Mar 2007
Externally publishedYes


  • Biodiversity
  • Birds
  • Boundaries
  • Conservation
  • Ecoregions
  • Ecotones
  • New World
  • Passeriforms
  • Range-size rarity
  • Transitional areas


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