POPULATION-DYNAMICS OF A SEED FEEDING BUG, LYGAEUS-EQUESTRIS .1. HABITAT PATCH STRUCTURE AND SPATIAL DYNAMICS

In E-central Sweden, this insect inhabits a highly patchy environment, and uses 2 kinds of habitats. In summer it breeds in patches of the host plant Vincetoxicum hirundinaria, whereas during the rest of the year it lives gregariously at hibernation sites, usually crevices in southward facing rock walls. Bugs fly from breeding to hibernation sites in late August or September and back in late April or May to feed and reproduce. Although most movements are short, at least 10% of the bugs move >1 km between breeding areas in successive years. The occupancy of both breeding and hibernation sites varies from year to year. The probability of a host plant patch being colonized is correlated with both degree of sun exposure and patch size. Winter populations have a highly aggregated structure and local stochastic events connected to snow-melting are important mortality factors. Within each year both parental and offspring population densities vary much between plant patches. However, rates of population change are more synchronized. Local population growth may, at least during certain sunny summers, be limited by shortage of seeds from the previous year. Large potential food resources are unavailable to the insect due to unfavourable microclimate conditions caused by shading. Due to high interpatch migration rates and considerable synchrony in population change in different patches population data for different patches can be pooled when analyzing temporal population changes. -from Authors