The Paradox of Forest Fragmentation Genetics
ANDREA T. KRAMER,
JENNIFER L. ISON,
MARY V. ASHLEY,
AND HENRY F. HOWE
Department of Biological Sciences (M/C 066), University of Illinois at Chicago, 845 W. Taylor Street, Chicago, IL 60607, U.S.A.
Chicago Botanic Garden, Division of Plant Science and Conservation, 1000 Lake Cook Road, Glencoe, IL 60022, U.S.A.
Department of Zoology, Field Museum of Natural History, 1400 S. Lake Shore Drive, Chicago, IL 60605, U.S.A.
Abstract: Theory predicts widespread loss of genetic diversity from drift and inbreeding in trees subjected to
habitat fragmentation, yet empirical support of this theory is scarce. We argue that population genetics theory
may be misapplied in light of ecological realities that, when recognized, require scrutiny of underlying evolu-
tionary assumptions. One ecological reality is that fragment boundaries often do not represent boundaries for
mating populations of trees that benefit from long-distance pollination, sometimes abetted by long-distance
seed dispersal. Where fragments do not delineate populations, genetic theory of small populations does not
apply. Even in spatially isolated populations, where genetic theory may eventually apply, evolutionary ar-
guments assume that samples from fragmented populations represent trees that have had sufficient time to
experience drift, inbreeding, and ultimately inbreeding depression, an unwarranted assumption where stands