Aim To describe rarity and elucidate its biology in a tropical mammalian order, the Primates.
Location Africa, Central and South America, Asia, Madagascar.
Methods A review of the literature, with some additional analyses using data from the literature. A variety of definitions of rarity are used in order to describe it and to investigate its biology by correlating the degree of rarity with a variety of biological traits indicative of resource use (e.g. size of annual home range), reproductive rate (e.g. birth interval)and specialization (e.g. number of habitat types used).
Results Few primate taxa occur outside the tropics, and most taxa are rare (small geographical range size or latitudinal extent, low density or both). Latitudinal extent is narrower at lower latitudes in Africa and Asia, but the potential resultant packing of taxa appears not to explain the taxonomic diversity gradient. Whilst primate species do not show the common, positive density by range size relationship, primate genera show a significant shallow slope, and primate families/subfamilies a strongly positive slope. Rare taxa are specialized, but neither use more resources nor breed more slowly than common taxa. The correlation of rarity and specialization is via geographical range: taxa with small ranges, or small ranges for their density, are specialized, but not taxa at low density. Common taxa are generalized because they consist of more differently specialized subtaxa, not because each subtaxon is generalized.
Main conclusions Most primate taxa are rare, in which case most are presumably likely to go extinct. Rare primates are specialized, but do not necessarily use more resources, nor breed more slowly. Specialization as an explanation for rarity appears to work via constriction of range size, not of density. Common primates might be common (large range size) not because subtaxa or individuals are generalized, but because they are composed of more subtaxa. A consequence could be that persistence of even common taxa will depend on conservation of several populations scattered across the taxon's geographical range.