Practice question

Caenorhabditis elegans leaving a depleted food patch illustrates the marginal value theorem’s core prediction. The nematode commonly feeds on bacteria. As local bacteria are consumed, encounter rate and marginal food gain decline; continued residence eventually yields less than the expected return from dispersing and locating another patch. Sensory information about food concentration, recent intake, and environmental cues can regulate roaming and dwelling states, allowing departure behavior to track diminishing returns. The theorem predicts departure when current marginal gain falls to the habitat-wide average gain rate after travel costs are included. Paramecium growth with Didinium concerns predator–prey dynamics, not optimal patch residence. Tadpole cannibalism is a trophic interaction, and random diet change provides no evidence for an optimization rule. Strong support would require quantitative agreement between observed leaving times and manipulated patch quality or travel cost, not merely movement away from food. Nevertheless, leaving an experimentally depleted bacterial patch is the listed behavior most directly aligned with marginal-value reasoning.