Population regulation throughout a complex life cycle

Research Highlight: McIntosh, A. R., Greig, H. S., & Howard, S. (2022). Regulation of open populations of a stream insect through larval density dependence. Journal of Animal Ecology. https://doi.org/10.1111/1365-2656.13696. Despite decades of research on population regulation through density dependence, it remains challenging to identify and understand the relative importance of mechanisms governing open populations of organisms with complex life cycles. McIntosh et al. (2022) manipulated density of aquatic invertebrates in the field, and then followed populations for 2 years to track the effects on abundance through multiple life-history stages. The authors found that their density manipulation, performed on larvae that were about to pupate, had minimal effects on the number of emergent adults collected several months later. The manipulation had a similarly negligible influence on the number of egg masses laid at study locations. The authors attribute this to stochasticity around dispersal of flying adults through the terrestrial environment. However, later in the study, the authors found evidence of density-dependent population regulation among larval stages, seemingly controlled by resource availability. These results suggest that population dynamics depend on multiple mechanisms operating at different points in organisms' life history, which could either help or hinder population persistence with disturbance or environmental change.