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Current behaviour-based interference models assume that the predator population is infinitely large and that interference is weak. While the realism of the first assumption is questionable, the second assumption conflicts with the purpose of interference models. Here, we tested a recently developed stochastic version of the Beddington–DeAngelis functional response—which applies to a finite predator population without assuming weak interference—against experimental data of shore crabs (Carcinus maenas) foraging on mussels (Mytilus edulis). We present an approximate maximum likelihood procedure for parameter estimation when only one focal individual is observed, and introduce ‘correction factors’ that capture the average behaviour of the competing but unobserved individuals. We used the method to estimate shore crab handling time, interaction time, and searching rates for prey and competitor. Especially the searching rates were sensitive to variation in prey and competitor density. Incorporating constant parameter values in the model and comparing observed and predicted feeding rates revealed that the predictive power of the model is high. Our stochastic version of the Beddington–DeAngelis model better reflects reality than current interference models and is also amenable for modelling effects of interference on predator distributions.

Trade-offs play a central role in life history theory. This article explains why they exist, how they arise, how they can be measured, and briefly discusses their evolution. Three important trade-offs are discussed in detail: the trade-off between current reproduction and survival, between current and future reproduction, and between offspring size and number.

Ecological and evolutionary population changes are often interlinked, complicating the understanding of how each is affected by environmental change. Using a male dimorphic mite as a model system, we studied concurrent changes in the expression of a conditional strategy and in the population in response to harvesting over 15 generations. We found evolutionary divergence in the expression of alternative male reproductive morphs—fighters and defenceless scramblers (sneakers)—caused by the selective harvesting of each male morph. Regardless of which morph was targeted, the direction of evolution of male morph expression in response to harvesting was always towards scramblers, which, in case of the harvesting of scramblers, we attributed to strong ecological feedback (reduced cannibalism opportunities for fighters) within the closed populations. Current evolutionary theory, however, predicts that the frequency of a morph always decreases when selected against: to understand phenotypic trait evolution fully, evolutionary theory would benefit from including ecological interactions, especially if traits have ecological consequences that in turn feedback to their evolutionary trajectory.