Clutch Overlap and Clutch Size: Alternative and Complementary Reproductive Tactics

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Abstract
A clutch is a group of offspring more or less in the same developmental phase which are being invested in simultaneously. When 2 successive clutches are invested in simultaneously, they can be said to overlap. The reproductive tactic of overlapping clutches can be used in conjunction with, or as an alternative to, altering clutch size. The utility of clutch overlap resides in the imbalances in demand that offspring place upon their parents. There are 2 such sorts of demand: larger clutches (at some point) require disproportionate amounts of energy (cost-expansion hypothesis), and some periods of the offspring developmental interval are more demanding than others (variant-energy hypothesis). These 2 phenomena interact to set upper limits to clutch size (limit hypothesis). When clutch size can no longer be augmented, organisms will find other ways to increase relative reproductive success (circumvention hypothesis). One such way is to optimally space clutches, overlapping them in time so that parents rear more than 1 clutch during non-demanding phases of offspring development. This increases the number of offspring development. This increases the number of offspring reared per unit time. In ecological time, clutch overlap should vary inversely with clutch size and even when clutches are not overlapped, within a breeding season the interval between successive clutches should be greater for large clutches than for small clutches. The amount of clutch overlap should increase as organisms gain reproductive experience. Clutch overlap patterns are examined in the pigeon Columba livia, which has a constant clutch size of 2.