SREL Reprint #0792




Effects of Density on Growth, Metamorphosis, and Survivorship in Tadpoles of Scaphiopus holbrooki

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.

Key words:  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.

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