Can we predict the expansion rate of a translocated butterfly population based on a priori estimated movement rates?

Abstract

Conservation translocation is a controversial, yet sometimes the only applicable, conservation tool in the face of the human-induced environmental change. One important aspect often neglected in translocation experiments is predicting the spatial expansion potential of the translocated population in the release area. In this study, we used a spatially explicit movement model to project the expansion rate of a translocated clouded Apollo (Parnassius mnemosyne) population. The model was parameterised with data collected from the source population inhabiting an open landscape with well-connected habitat patches. We then used these parameter estimates to simulate the spread of the translocated population in the new area, which was a forested landscape with more fragmented habitat. We tested the model predictions by comparing them to the observed expansion rate between 2000 and 2016. Additionally, we tested whether including annually varying weather conditions would increase realism in the projections. Model predictions were qualitatively correct and quantitatively most accurate for flight seasons with prevailing weather conditions similar to those of the season when the data for parameter estimation was collected. We conclude that spatially explicit movement models are potential tools to improve the planning of future conservation translocations in terms of choosing the optimal release area, as they enable the comparison of functional connectivities even between structurally different landscapes. However, our results suggest that a model fitted based on movement data from a single year may not be representative for the overall dispersal rates due to temporal variation in dispersal.