OPTIMUM BROOD SIZE: TESTS OF ALTERNATIVE HYPOTHESES

Area of Science:

• Ecology
• Evolutionary Biology
• Mammalogy

Background:

• Understanding factors influencing litter size is crucial in population dynamics.
• White-footed mice (Peromyscus leucopus) exhibit variation in litter size.
• The most productive litter size is not always the most common in natural populations.

Purpose of the Study:

• To investigate hypotheses explaining the observed distribution of litter sizes in free-living white-footed mice.
• To determine the primary drivers behind the prevalence of smaller-than-optimal litters.

Main Methods:

• Evaluation of four competing hypotheses for litter size distribution.
• Analysis of reproductive costs, annual recruitment variation, and parental resource investment.
• Testing the 'cliff-edge hypothesis' related to asymmetric survival in large litters.

Main Results:

• Reproductive costs and annual recruitment variation were insufficient explanations.
• Optimal reproductive investment showed partial support but was not universally applicable.
• Asymmetric survival in large litters (cliff-edge effect) partially explained the abundance of smaller litters.

Conclusions:

• No single hypothesis fully explains the litter size distribution in white-footed mice.
• Multiple mechanisms, including survival biases, interact to shape average brood size.
• The most productive litter size may not be favored due to ecological and survival constraints.