ALLEE EFFECT AND POPULATION-DYNAMICS IN THE GLANVILLE FRITILLARY BUTTERFLY

The Allee effect - a decrease in population growth rate at low density - may be produced by several mechanisms including difficulty in findi ng mates at low densities. We present evidence for the Allee effect in natural populations of an endangered butterfly, the Glanville fritill ary (Melitaea cinxia) and for two mechanisms that cause it. Specifical ly, we show that emigration rate increases and the fraction of mated f emales decreases with decreasing local density. We then demonstrate a connection between mating success and population growth rate and more generally, slightly reduced reproductive success in the smallest butte rfly populations in an extensive data set gathered over four years. Th e Allee effect increases the significance of the rescue effect in meta populations, and thereby the potential for alternative stable states i n metapopulation as well as in local dynamics.