POPULATION-DYNAMIC PRINCIPLES

Although the causes of population extinction, locally and globally, are many, varied and idiosyncratic when individual species are considered, there are nevertheless some basic general constraints and ground rules that make some species more extinction-prone than others. This paper reviews their implications for the ultimate and proximate causes of extinction. Phenomena reviewed include: a positive correlation between local abundance and size of geographic range, putting some populations in 'double jeopardy'; smaller average range sizes in the tropics; metapopulation dynamic processes that can spread risk, but only if the spatial correlation between fluctuations of conspecific populations is low; the influence of body size and trophic position; and phylogenetic constraints on range sizes and abundance.