Dealing with extinction is forever: understanding the risks faced by small populations

ABSTRACT

Despite its importancefor ecology, extinction was often neglected by this science until the present environmental crisis brought the subject to the fore in the early eighties. Important theoretical developments, mainly island biogeography, metapopulation theory and geneticas contributed to build a set of theories on the genetic and ecological processes which threaten the persistence of small populations. Two of the greatest contributions of this paradigm were to show the propabilistic nature of extinction, and to make clear the point how a small population can be extinguished by stochastic processes even if protected from further human intervention. Four such processes can be distinguished demographic, environmental and genetic stochasticities, and loss of adaptive flexibility. undestanding and modeling these processes resulted in the development of Population viability analysis (PVA), a family of simulation models employed to quantify the future risk of extinction of a small population. The complexity of the extinction processes poses serious problems for the reliability of the predictions; however, PVA has had considerable heuristic value in fostering improvements in understanding extinction. In addition to the scientific and technical aspects, there are also complex economic considerations involved. Nevertheless the small population paradigm and PVA have allowed great advancements in our capacity of devising scientifically sound conservation and management actions to diminish extincion.