MIGRATORY SUCCESS OF JUVENILES: A POTENTIAL CONSTRAINT ON CONNECTIVITY FOR POND-BREEDING AMPHIBIANS
BETSIE B. ROTHERMEL
Division of Biological Sciences, University of Missouri, 105 Tucker
Hall, Columbia, Missouri 65211-7400 USA
Abstract. The persistence of pond-breeding amphibians in highly
fragmented land- scapes may be constrained by the need for connectivity
between aquatic breeding sites and suitable terrestrial habitat, an example:
of landscape complementation. Although migratory ability determines the
spatial scale at which landscape complementation operates, the factors
influencing migratory success of amphibians, especially of juveniles,
are poorly understood. This study is the first to investigate whether
juvenile amphibians possess any innate, long- distance orientation mechanisms
that might improve their chances of locating suitable terrestrial habitat.
I conducted experimental releases of spotted salamanders (Ambystoma
maculatum) and American toads (Bufo americanus) from 18
artificial 'pools in replicate pastures at distances of 5-50 m from the
nearest forest edges. Using circular drift fences with pitfall traps,
I captured, individually marked, and released metamorphosed salamanders
(n = 323) and toads (n = 203) leaving each pool. Salamanders exhibited
nonrandom orientation at nine pools, but at only one was the mean movement
direction consistent with the direction to the nearest fore$t edge. Emigrating
salamanders probably responded to microtopographic or other distinct features
of each pool, rather than to distant cues. Migratory success was determined
by recaptures of marked juveniles at drift fences along the forest edges.
I used logistic regression to model probability of recapture and evaluated
alternative models using an information-theoretic approach. Migratory
success of both species was primarily a function of distance to nearest
forest. Of salamanders and toads released from 50-m pools, < 15% reached
the forest, suggesting that few juvenile amphibians would be able to migrate
greater distances across pastures. Breeding sites lacking connectivity
to suitable terrestrial habitat may be population sinks due to high mortality
of juveniles during emigration. Additional research is needed to determine
appropriate threshold dis- tances between breeding sites and terrestrial
habitat, as' well as the potential effectivene&s of movement corridors
for migrating amphibians.
Key words: Ambystoma maculatum; American toad; Bufo
americanus; connectivity; dispersal; juvenile amphibians; landscape
complementation; mark-recapture; migration; orientation; perceptual range;
spotted salamander.
SREL Reprint #2794
Rothermel, B. B. 2004. Migratory success of juveniles: a potential constraint on connectivity for pond-breeding amphibians. Ecological Applications 14:1535-1546.
