|SREL Reprint #0792|
of Density on Growth, Metamorphosis, and Survivorship in Tadpoles of Scaphiopus
Raymond D. Semlitsch and Janalee P. Caldwell
Density-dependent aspects of growth, metamorphosis,
and survivorship of Scaphiopus holbrooki tadpoles were examined in
the laboratory under two experimental regimes. In the first density experiment, the growth index (W) of
tadpoles decreased exponentially with density.
Mean growth rate varied from 0.023 mL/d at the lowest density to 0.006 mL/d
at the highest density. The mean
number of days to metamorphic climax was positively associated with the initial
density treatment: 27 d at the
lowest density to 86 d at the highest density.
The body size of tadpoles at metamorphosis showed a concave curvilinear
relationship to initial density, indicating tadpoles at the highest densities
are apparently capable of growth recovery once released from density stress.
The survival of tadpoles decreased exponentially with initial density,
from 90% at the lowest density to 20% at the highest initial density.
In the second experiment a cross-classified design
was used to examine the effects of density and duration of treatment (time) on
growth and metamorphosis. Density
and time had significant effects on body size at metamorphosis and days to
metamorphosis. There was no
significant interaction between density and time.
These results indicate that the inhibitory effect of density stress
varies with the duration of the stress.
Scaphiopus holbrooki tadpoles
exhibit development traits (rapid growth, short larval period, small body size
at metamorphosis) that should be favored by natural selection in high density
habitats. “Dispersability” may
be a mechanism whereby S. holbrooki can minimize the detrimental
effects of density stress.
Amphibia; Anura; density; dispersability; growth metamorphosis; Scaphiopus
holbrooki; survivorship; tadpoles.
SREL Reprint #0792
Semlitsch, R.D. and J.P. Caldwell. 1982. Effects of
density on growth, metamorphosis, and survivorship in tadpoles
of Scaphiopus holbrooki. Ecology 63:905-911.