Dynamics of fragmented populations of the sawtooth grain beetle

Date of Completion

January 1999


Biology, Ecology|Biology, Entomology




I studied the ecology of the sawtooth grain beetle, Oryzaephilus surinamensis (L.), and used O. surinamensis in conjunction with a computer simulation to understand the regulation of small populations. Many populations of organisms deplete their food resource and inevitably encounter negative population feedbacks. Eight short-term experiments differentiated the effects of food deterioration and crowding of stages on dispersal, mortality and reproduction. Metapopulations were created by connecting vials with rubber tubes. The patches of each metapopulation were arranged in rings and food was replenished at two-week intervals. The population dynamical effects of subdivision, degradation and overall system size were manipulated in five experiments. Time-series of stage-specific abundances were compared in repeated measures ANOVA. An individual-based simulation was used to explore mechanisms of population dynamics through parameter calibration and model fitting. The experiments quantified rates of birth and death in response to both the amount of food and area. Mixed stage populations of O. surinamensis respond to food deterioration by increasing in immature mortality, sharply reducing oviposition, and increasing adult dispersal. Fragmentation experiments defined the relationship between habitat size and amount of food on population dynamics. For beetle abundance in my experiments, changing the habitat size had twice the effect of changes in the amount of food. Abundance responded more rapidly to changes in habitat area than to changes in amount of food. The results of the experiments were used to calibrate and test models that forecast population abundance. I selected from among candidate models based on minimum mean square error. The selected model indicates that periodic replenishment of food causes flushes of reproduction followed by food depletion, cannibalism and inhibited oviposition. I employed the experimental model system to test metapopulation theory, and I developed the simulation to show the mechanisms that regulate the dynamics of O. surinamensis populations. ^