Size–Logging Interactions and Population Dynamics in Tropical Understorey Birds

Demographic vital rates (e.g., fecundity and survival) determine population size and viability. However, how anthropogenic habitat change differentially influences these dynamic population processes for species with different traits remains unknown. Crucially, this limits a mechanistic understanding of species- and community- level patterns in response to intensity of habitat change, and therefore, impedes robust prediction of future species responses. We investigated how size (across 26 forest birds, spanning almost an order of magnitude in body mass) and habitat modification (logging intensity, from intact forest to a 2.5-fold reduction in tree density) might interact to influence survival, reproduction and dispersal. Data were collected over five sessions under the robust design in a capture-mark-recapture framework and analysed using reverse time capture–recapture models. We found that smaller species were more fecund with increased logging intensity, and dispersed from more heavily logged to more intact forest. With increasing size, species reproduced better in progressively more intact forest, and dispersed from intact forest into more logged forest. These results indicate important trait-linked differences in the relative significance of various demographic processes in influencing species responses to varying intensities of habitat change. Separating the mechanistic processes underlying observed patterns is crucial to understanding and predicting anthropogenic impacts on biodiversity.