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<br />during the preparation of this article.
<br />Genetics and Demography in
<br />Biological Conservation
<br />
<br />Predicting the extinction of single populations or species
<br />requires ecological and evolutionary information. Pri-
<br />mary demographic factors affecting population dynamics
<br />include social structure, life history variation caused by
<br />environmental fluctuation, dispersal in spatially heteroge-
<br />neous environments, and local extinction and coloniza-
<br />tion. In small populations, inbreeding can greatly reduce
<br />the average individual fitness, and loss of genetic variabili-
<br />ty from random genetic drift can diminish future adapt-
<br />ability to a changing environment. Theory and empirical
<br />examples suggest that demography is usually of more
<br />immediate importance than population genetics in deter-
<br />mining the minimum viable sizes of wild populations. The
<br />practical need in biological conservation for understand-
<br />ing the interaction of demographic and genetic factors in
<br />extinction may provide a focus for fundamental advances
<br />at the interface of ecology and evolution.
<br />DESTRUCTION AND FRAGMENTATION OF NATURAL AREAS,
<br />especially tropical rain forests with their high species
<br />diversity', is now causing extinction of species at a rate that
<br />is orders of magnitude as high as normal background rates of
<br />exnn rion (1). If there are anv paleontologists in the distant future,
<br />our "modem age"-the 20th and 21st centuries-will likeiv be
<br />u V,
<br />i;
<br />U
<br />recorded as a period of one of the greatest mass extinctions of all
<br />time, comparable to the event 65 million years ago in which it can be
<br />estimated that the majority of species then living on Earth perished
<br />(1, 2). In addition to the ethical problem of extirpating life forms
<br />that evolved over millions of years, there arc practical reasons for
<br />conserving wild areas containing species of potential medical,
<br />agricultural, recreational, and industrial value (3). Ultimately, suffi-
<br />cient alteration of natural ecosystems may destabilize regional and
<br />global climate and biogeochemical evcles, with potentially disastrous
<br />effects (4).
<br />Awareness of the benefits of conserving biological diversity is
<br />growing rapidly in many countries, but it remains to be seen
<br />whether conservation efforts will increase fast enough in relation to
<br />the rate of destruction to preserve much of the natural diversity that
<br />existed in the last century. As the remaining natural areas become
<br />smaller and more fragmented, it is increasingly important to under-
<br />stand the ecological and evolutionary dynamics of small populatipps
<br />in order to effectively manage and preserve them for a time when
<br />future restoration of natural areas may allow expansion of their
<br />ranges. Propagation of endangered species in captivity, for example,
<br />in zoos and arboreta, can contribute significantly to global conserva-
<br />tion ctlorts; this alone, however, is not a viable alternative because
<br />limited facilities are available and because inevitable genetic changes
<br />from random genetic drift and selection in artificial environments
<br />The author is in the Department of Ecology and Evolution. Umversxty of Chicagci,
<br />Chicago. IL 60637.
<br />ARTICLES tics
<br />Th :1 Tree,.,,,-n ,.,,2V
<br />RUSSELL LANDE
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