SIZE-DEPENDENT REPRODUCTIVE OUTPUT IN AGRICULTURAL WEEDS

Data on reproductive and vegetative weights of individuals from five species of agricultural weeds (Apera spica-venti L., Datura stramonium L., Abutilon theophrasti Medic., Sorghum halepense (L.) Pers., and Panicum miliaceum L.) were used to test Weiner's (1988) model of linear size-dependent reproductive output in plants. In general, the populations showed strong evidence (P < 0.001) of linear relationships between reproductive and vegetative weight. Linearity was most pronounced in cases where size differences were primarily due to competition. Generally, the linear relationships were consistent from population to population within a species. Many of the populations also showed positive x-intercepts, indicating a threshold size for reproduction. However, there were a number of populations with no apparent relationship between reproductive and vegetative weight, with departures from linearity, or with positive y-intercepts (negative x-intercepts).