SREL Reprint #1874






Peter H. Niewiarowski and Arthur E. Dunham
Department of Biology, Leidy Labs, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6018

Abstract. -We evaluated Shine and Schwarzkopf's (SS) model of the evolution of reproductive effort (RE) in squamate reptiles. They suggested that fecundity trade-offs were unimportant in the evolution of RE in most squamate reptiles and that only survival trade-offs needed to be considered. However, we show that by assuming no variation in offspring size exists, and that adult mortality is episodic, the results of the SS model are not general. By extension, we argue that conclusions drawn about factors important in the evolution of RE in squamate reptiles are premature. Using a modified version of the SS model, we demonstrate that variation in the form of trade-offs relating offspring size and survival substantially affect relationships among clutch size, relative clutch mass, and lifetime reproductive success. We also demonstrate that the way in which adult mortality is simulated drastically affects conclusions about the potential fecundity trade-offs experienced by populations of squamate reptiles. Finally, we suggest that a complete understanding of the evolution of RE will come from theory that incorporates trade-offs between offspring size and quality, as well as other system-specific constraints on the allocation of energy to growth, maintenance, storage, and reproduction.

Key words. - Clutch size, fecundity, offspring size, reproductive cost, reproductive effort, reptiles.

SREL Reprint #1874

Niewiarowski, P.H. and A.E. Dunham. 1994. The evolution of reproductive effort in squamate reptiles: costs, trade-offs and assumptions reconsidered. Evolution 48:137-145.

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