DELAYED DENSITY-DEPENDENCE IN A SMALL-RODENT POPULATION

The role of delayed density-dependent processes in the dynamics of ani mal populations poses a problem for ecologists; although generally ass umed important in populations that show cyclic or chaotic fluctuations , little experimental evidence for such processes exist. Through manip ulation of vole densities within enclosed areas it was shown that repr oduction, recruitment, and body growth rate in introduced populations were negatively affected by high previous density. In addition, female movement patterns shifted, and territoriality as well as home-range s ize was increased after high density. The observed changes in female s pacing-behaviour suggested that negative effects of previous density w ere partly mediated by social interactions, and agreed with the findin g that smaller (less competitive) females were the ones suffering most from increased competition. Contrary to expectations from recent work , predation could be excluded as the cause of delayed density-dependen ce in this study. Instead, chemical analyses of a dominating food plan t suggested that herbivory at high vole-density had delayed negative e ffects on food quality.