Seven forms of rarity in mammals

Abstract

Conservation biologists have identified threats to the survival of about a quarter of the mammalian species; to identify patterns of rarity and commonness of mammals, we studied a global sample of 1212 species (about 28% of the mammals) using the ‘7 forms of rarity’ model (in which species are roughly divided into above and below the median for local population density, species’ range area, and number of habitat types). From a niche‐based hypothesis of abundance and distribution, we predicted that mammals would exhibit a bimodal pattern of rarity and commonness, with an overabundance of species in the relatively rarest and most common categories; and just such a significant bimodal pattern emerged, with over a quarter of the species classified as exceedingly rare and a further quarter very common, supporting the niche‐based hypothesis. Orders that include large mammals, including perissodactyls, primates, diprotodonts, and carnivores, exhibited significantly high proportions of relatively rare species; and tropical zoogeographic regions, especially Indomalaya, had relatively high proportions of species in the rarest category. Significant biases in the available data on mammals included under‐sampling of small species like rodents and bats, and a relative paucity of data on zoogeographic regions outside of North America and Australia. Mammalian species listed as of conservation concern by the IUCN occurred in all cells of the model, indicating that even relatively common species can be listed as threatened under some conditions; but we also found that sixty‐three species were relatively rare in all three criteria of the 7‐forms model but were not listed as threatened, indicating potential candidates for further study. Mammals may be a group of animals where rarity or commonness is a natural aspect of species biology, both confirming and perhaps partly explaining the large proportion of mammals assigned threatened status.

New records of Uroderma magnirostrum Davis (Mammalia, Chiroptera) from southeastern Brazil, with comments on its natural history

“…Discussions on the rarity in mammals have taken into account biological characteristics such as local population density, range of distribution, and flexibility in habitat use (YU & DOBSON 2000). As previously reported, U. magnirostrum has a large geographical distribution and had been sampled in a wide Revista Brasileira de Zoologia 20 (4): 691-697, dezembro 2003 variety of habitat types.…”

Resistance and resilience: quantifying relative extinction risk in a diverse assemblage of Australian tropical rainforest vertebrates

“…This model has been discussed in detail elsewhere (e.g. Kattan, 1992;Yu & Dobson, 2000). Briefly, the model uses geographical range size, local abundance and habitat specificity.…”

“…Kattan (1992) extended the rarity model to explore vulnerability of Colombian birds to extinction and the model has since been applied by a number of other studies to determine rarity and extinction risk (e.g. Pitman et al ., 1999;Yu & Dobson, 2000;Harcourt et al ., 2002). However, as outlined above, these three traits probably give little information about the potential of a species to recover following environmental change.…”

Niche conservatism above the species level

“…This is important because, although most studies of niche conservatism focus on the distribution of species and links to climate, geographic ranges do reflect the entire suite of a taxon's ecological requirements and its interactions with other organisms (20). For example, the size, shape, and distribution of a geographic range results from a characteristic abundance distribution of individuals, which is determined by both intrinsic properties of the species, and extrinsic, or environmental, parameters (16,30,31). In theory, intrinsic properties such as population growth rates, dispersal ability, litter size, etc., as opposed to extrinsic factors such as climate alone, may heavily influence a species' realized niche.…”