POPULATION-DENSITY AND AREA - THE ROLE OF BETWEEN-PATCH AND WITHIN-PATCH PROCESSES

The relationship between population density and the size of host plant patches was investigated for the red milkweed beetle Tetraopes tetrao phthalmus inhabiting unmanipulated patches of Asclepias syriaca. The r esource concentration hypothesis proposes that density-area patterns, specifically that of increasing herbivore density with patch size, are primarily a function of movement between host plant patches. This res earch investigated the degree to which movement accounted for density- area patterns. Poisson regression analysis of beetle abundance versus milkweed patch size revealed that beetle density tended to increase wi th patch size. The pattern of density and patch size resulted from loc al reproduction and residence time. The density of emerging beetles te nded to increase with patch size while emigration rates were unrelated to patch size. Immigration rates were constant with patch size for ma le beetles, and decreased with patch size for female beetles. Net flux of beetles (immigration - emigration) did not vary with patch size fo r male beetles and decreased with patch size for female beetles. Compa risons are made between this system and previously studied systems whe re movement plays a significant role in forming density area patterns. Additionally, several hypotheses are presented which may account for greater in situ recruitment and residence time in large patches.