Estimating appropriate mowing timing for the population of an endangered butterfly inhabiting grassland patches in an agricultural landscape

Abstract

It has been recognized that the timing of disturbance, in addition to its intensity and frequency, is important for the population dynamics of organisms because the impact of the disturbance depends on the life history stage at which it occurs (i.e., egg, larva, or adult). However, the effects of disturbance timing on consumer population dynamics have not been explored. This study simultaneously estimated the effects of mowing frequency and timing on the subpopulation dynamics of the endangered grassland butterfly, Plebejus argyrognomon. A two-year investigation of a metapopulation of P. argyrognomon consisting of approximately 150 habitat patches revealed that subpopulation size decreased with increasing mowing frequency, in addition to the positive effect of patch area and habitat connectivity. With the mowing frequency fixed at once per year, subpopulation size maximized when mowing occurred during the adult period in the previous generation, presumably due to reduced impact in the high-mobility adult stage. By mowing during this period, subpopulation size was maintained at several times higher than mowing during the larval period. It is suggested that disturbance timing should be incorporated into the conservation of metapopulations in human-managed landscapes. Implications for insect conservation Reducing mowing frequency is important for the conservation of P. argyrognomon. In addition, mowing during the adult stage is best suited for maintaining subpopulations.