Influence of mowing on the persistence of two endangered large blue butterfly species.
Abstract
Mowing influences two endangered butterfly species, Maculinea nausithous and Maculinea teleius, directly through egg destruction and larval mortality on the mown plants and indirectly through altering the abundance of their sequential resources in meadows (Sanguisorba plants for oviposition and early larval development and Myrmica ant nests for later larval development and pupation). Although conservation biologists have argued that mowing during the adult stage is detrimental to population persistence, it is not obvious how the timing and frequency of mowing impact on population dynamics. A simulation model was used to investigate how current 'traditional' mowing regimes could be altered to reconcile butterfly conservation with agriculture. The key mechanism affecting the impact of mowing on population persistence was the interaction between density-independent and density-dependent mortalities in different larval stages of each life cycle. Because of this interaction, optimal mowing regimes for butterfly conservation were sensitive to the type of density regulation displayed by each species, and to landscape attributes such as the influence of climate on resource availability and the level of parasitism. Despite this sensitivity, we were able to identify robust mowing regimes appropriate for a wide range of landscape attributes and to derive general management recommendations. Synthesis and applications. Our results showed that the 'traditional' mowing regime (twice per year with the second cut during the flight period) was always detrimental to the two butterfly species at both local (single population) and regional (metapopulation) scales. However, mowing once a year, or every second or third year, before or after the flight period, was appropriate for both species in the considered landscapes. Maculinea teleius could persist only at a regional scale, assuming dispersal among the meadows, whereas M. nausithous could persist at both local and regional scales. Thus it is essential that the recommended mowing regimes are applied across several connected meadows within reach of dispersing butterflies if both butterflies are to be conserved in a region.