Integrated modeling of insect population dynamics at two temporal scales

1. Population size of species with birth-pulse life-cycles varies both within and between seasons, but most population dynamics models ignore the former and assume that a population can be characterised adequately by a single number within a season. However, within-season dynamics can be too substantial to be ignored when modelling dynamics between seasons. Typical examples are insect populations or migratory animals. Numerous models for only between-season dynamics exist, but very few have combined dynamics at both temporal scales.

2. We extend the models of Dennis et al. (2016b) in two directions: we adapt them for a generation time >1 year and fit them as an integrated population model for multiple data types, by maximising a joint likelihood for time-series of population counts of unmarked individuals and capture-recapture data from a smaller sample of sites with marked individuals. We analyse annual monitoring data for the endangered flightless beetle Iberodorcadion fuliginator from 17 populations in the Upper Rhine Valley for 1998–2016, with a 2-year life cycle. Standard tools of classical statistics are used for model fitting and comparison and a concentrated likelihood approach provides computational efficiency.

3. The additional information introduced by the capture-recapture data makes the population model more robust and also enables true, rather than relative, abundance to be estimated. Fitting a dynamic stopover model provides estimates of survival and phenology parameters within a season, as well as productivity between seasons. For I. fuliginator, we demonstrate a population decline since 1998 and how this links with productivity, which is affected by temperature. A delayed mean emergence date in recent years is also shown.

4. A main point of interest in our work is the focus on the two temporal scales at which perhaps most animal populations vary: in the short-term, a population is seldom ever truly closed even within a single season, and in the long term (between seasons) it never is. Hence models such as ours may serve as a template for a very general description of population dynamics in many species. This includes rare species with limited data sets, for which there is a general lack of population dynamic models, yet conservation actions may greatly benefit from this kind of models.