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“Introduction Most species are rare (Brown et al. 1996) and almost all species are rare at some point during their existence. Rarity usually precedes extinction and new species often begin as rare individuals in the landscape (Brown 1984). Some species maintain this rarity over the course of their existence while a few species become common (Murray and Lepschi 2004). Species abundance and distribution is a foundational discipline within ecology (Andrewartha 1961; Brown 1984; Krebs 1985), thus the causes and consequences of rarity fundamentally affect many ecological theories. While it is obvious how common species can persist, it is less obvious how rare species can maintain their population sizes when demographic challenges

are so apparent. In order to gain a more mechanistic view of these challenges, Rabinowitz (1981) proposed a more specific classification Etomoxir in vivo of rarity in order to accurately describe species distribution and abundance patterns. She pointed out that species with specific habitat requirements (specialists) Amylase might have different ecological and biological properties

than EPZ015666 in vivo uncommon but generalist species and that local abundance (LA) (dense populations vs. sparse populations) and geographic range (GR) (large vs. small) might also shed light on the causes and consequences of rarity. This identification matrix yields eight categories (23 = 8), with seven of these categories reflecting some sort of rarity. The eighth species type in this matrix (Fig. 1), wide-ranging generalist species with dense populations, is a type that is not rare but common. The seven types of rarity have been widely utilized to describe patterns of species distribution: in a Web of Science search in June of 2009, 365 research papers cited this matrix. Fig. 1 Distribution of rarity types within the dataset of 101 species. Numbers indicate number of species per category included in the meta-analysis. Black areas of pie charts indicate the percent of the dataset each rarity type represents. Common species were not included (N = 0). Species identified on only two of the three rarity axes (N = 6, Appendix 1) are not included in this figure Investigation of species distribution and abundance patterns is a primary concern of ecological research, yet the majority of papers citing the Rabinowitz rarity matrix comes from the conservation literature.