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Ecotones as diversity centers: Richness and rarity patterns in New World passerines.
Kark, Salit*,1, Alnutt, Tom2, Brooks, Tom3, Manne, Lisa4, 1 Stanford University, Stanford, CA2 World Wildlife Fund-US Conservation Science Program, Washington, DC3 Conservation International Center for Applied Biodiversity Science, Washington, DC4 Natural History Museum, London
ABSTRACT- Substantial work has been directed towards identifying areas with especially high richness and endemism (i.e. hotspots). This has focused substantial attention towards a comparison of ecological communities and ecoregions. However, recent work is suggesting that areas of transition between these regions may actually serve as within-species diversity centers at the genetic and morphological levels. We here test the hypothesis that ecotones between ecoregions are hotspots of richness and rarity at the multi-species level. We predict that richness and rarity (i.e. narrow endemism) will be higher closer to the boundary between ecoregions. We also predict that the relationship will become stronger closer to areas where multiple ecoregions coincide. We tested these hypotheses using data for the New World native Passeriformes (~2300 breeding songbirds). We calculated the distance of each of 4998 1-degree grid cells (longitude x latitude) to the nearest 1-5 boundaries between the terrestrial ecoregions of the New World, as classified by WWF. The same was done for biomes. Our results support the hypotheses: both richness and range size rarity significantly increase with decreasing distance to the nearest boundary. Thus, grid cells that are located closer to the transition between ecoregions and biomes maintain higher diversity and rarity. The relationship becomes stronger with distance to multiple boundaries. These findings suggest that ecotones have an important role in the maintenance and possibly in the generation of biodiversity. They may serve as hotpsots of richness and of rare species and should receive much more research and conservation attention.
KEY WORDS: richness, rarity, ecotone, birds