Shifts in breeding habitat selection behaviour in response to population density

Abstract

We tested whether mountain pine beetles Dendroctonus ponderosae, an insect herbivore that exhibits outbreak population dynamics, modifies its habitat selection behaviour in response to density-dependent environmental shifts. Using an individual-based habitat selection model, we formulated predictions of how beetle population density will influence breeding habitat selectivity. Our model predicted that beetles should be more selective at intermediate densities than at low or high densities. The mechanisms influencing optimal selectivity differed between low and high density populations. In low density populations, breeding site availability was the primary factor affecting selectivity, whereas intraspecific competition and the reliability of habitat quality cues were important in high density populations. We tested our model predictions in natural populations that encompassed a range of beetle population densities. Our empirical findings supported the two key predictions from our model. First, habitat quality was more variable in high density populations. Second, individuals in high density populations were less selective compared to beetles from intermediate density populations. Our results demonstrate that beetles alter their habitat selection behaviour in response to density-dependent shifts. We propose that the behavioural changes we identified may influence the rate at which beetle populations transition between density states.