CONCEPTS OF RARITY IN VASCULAR PLANT SPECIES, WITH SPECIAL REFERENCE TO THE GENUS CALOCHORTUS PURSH (LILIACEAE)

Abstract

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Rare canopy species in communities within the Atlantic Coastal Forest in Rio de Janeiro State, Brazil

“…Rarity can have many causes, which include terrestrial history, the history of previous land-use, the age of the taxa, the ecology of the species, evolutionary history, population dynamics, reproductive biology, as well as stochastic events (Kubitzki 1976;Fiedler 1986;Fiedler and Ahouse 1992). Additionally, problems related to taxonomic identiWcation or inappropriate sampling techniques may lead to apparent rarity or abundance (Gaston 1994).…”

Evolutionary age and risk of extinction in the global avifauna

“…Two patterns are possible: older taxa might have more threatened species if extinction probability increases through time, or fewer threatened species if greater taxon age reflects better survival abilities (Stanley, 1979;Fiedler, 1986;Smith, 1994). The former pattern is the more likely, because all species must *Address all correspondence to Kevin J.…”

Genetic divergence among and diversity within two rare Banksia species and their common close relative in the subgenusIsostylis R.Br. (Proteaceae)

“…Although this does not follow the general trend for plants, there are a number of studies that have also shown no association between geographic distribution and levels of genetic diversity (Gitzendanner and Soltis 2000). This example emphasises a number of general issues raised by various authors in relation to the causes of rarity and restricted geographical distribution (Fiedler 1986;Fiedler and Ahouse 1992;Kunin and Gaston 1993). Rarity has multiple origins and therefore the genetic consequences of rarity cannot be generalized in a simplistic fashion.…”