Pg. Demaynadier et Ml. Hunter, Forest canopy closure and juvenile emigration by pool-breeding amphibians in Maine, J WILDL MAN, 63(2), 1999, pp. 441-450
For amphibians that breed in temporary pools, juvenile emigration is an imp
ortant life-history movement linking the aquatic habitat of larvae to the s
urrounding upland habitats occupied by maturing animals and adults. However
, little is known regarding the habitat preferences and sensitivity to dist
urbance of newly metamorphosed amphibians. We examined whether selection oc
curs for closed-canopy forest conditions during emigration by using pitfall
traps and drift fences to sample naturally occurring populations of wood f
rogs (Rana sylvatica) and spotted salamanders (Ambystoma maculatum) along r
ecently created forest-clearcut edges in central Maine. Habitat preferences
during emigration were further investigated via an experimental approach t
hat quantified movements of newly metamorphosed wood frogs cultured in arti
ficial pools located along an abrupt forest-power line edge. Among natural
populations, the abundance of juveniles and adults of both species declined
sharply across a gradient running from relatively mature forest-interior h
abitat (70-90 yr old) to recently clearcut habitat (2-11 yr old). Similarly
, in the power line experiment, juvenile wood frogs showed an emigration pr
eference for closed-canopy habitat immediately upon metamorphosis, with the
highest capture rates occurring in microhabitats characterized by dense fo
liage in both the understory and canopy layers. Our results suggest populat
ions of wood frogs, spotted salamanders, and other amphibian species breedi
ng in temporary pools are likely to benefit from efforts to maintain connec
tivity between upland forest habitats and aquatic breeding sites. Seminatur
al field experiments provide a valuable manipulative approach for studying
the potential effects of habitat fragmentation on populations of migratory
amphibians.