EFFECTS OF PATCH SHAPE ON THE NUMBER OF ORGANISMS

This study examined effects of habitat patch shape on the abundance of organisms. The effects of patch shape were considered in terms of (1) immigration and emigration of organisms, (2) the amount of available resources in a patch and (3) spatial and temporal heterogeneity of the organisms and environment. I hypothesized that (1) the number of orga nisms would increase as patch shape elongates because organisms are mo re likely to encounter an elongated patch, (2) the number of organisms in a patch would remain constant for all patch shapes where the numbe r of organisms in a patch was limited by the amount of resources, beca use patch shape does not change the patch area that is directly associ ated with the amount of patch resources, and (3) spatial and temporal variation of the abundance of organisms would increase as patch shape elongates because an elongated patch is more likely to interact with t he variable surrounding matrix. Common millipedes, Oxidus gracilis, an d their habitat, plywood boards of five shapes (width:length ratio; 1: 1, 1:4, 1:9, 1:36, 1:144) with an area of 900 cm(2) were placed in for est and old field and the number of millipedes appearing under the boa rds was monitored. Significantly higher mean number of millipedes unde r the boards was observed at a patch with an elongated shape in the fo rest and the old field. A significant positive correlation was observe d between perimeter length of a patch and the number of millipedes in the old field. The temporal and spatial variation of the number of mil lipedes was high in the old field. The spatial and temporal variation was higher for boards with elongated shape.