What drives (meta)population dynamics of the bog frittilary? The relative importance of habitat quality, climate and parasitism

The bog fritillary (Boloria eunomia) is a specialist butterfly inhabiting wet meadows and peat bogs, originally chosen as a model system to study metapopulation dynamics because, for this species, the landscape can be easily defined by a clearcut but meaningful “habitat vs matrix” dichotomy. It has been intensively studied in Belgium since 1992, becoming a landmark study system for (meta)population dynamics and viability. Here, we show how we refined our understanding of its population dynamics, in its density-dependent and density-independent aspects, by adding levels of detail in the quantification of its habitat quality, as well as considering the impact of parasitism and climate. We replaced the simplified black and white view (“habitat quality is constant, only habitat size and configuration in the matrix matters”) by a more detailed “shades of grey” view (“habitat quality varies in space and time according to resource availability”). We present how we synthesized data collected on the species over 30 years to reconstruct spatiotemporal changes in habitat quality, filling data gaps via interpolation, proxy variables or expert assessment. These habitat quality data, combined with relevant climatic parameters covering each life stage of the butterfly, were used to revisit what drives population growth rate of the bog fritillary. This confirmed the strong density-dependence previously observed, uncovered strong influence of parasitism as well as climate during larval stages, but did not indicate a direct effect of habitat quality. Eventually, we discuss the consequences for species viability and conservation under climate change