SY408 Lecture Notes - Net Reproduction Rate, Guppy, Exponential Growth
Document Summary
Ecologists usually measure the densities of organism in terrestrial environments as the number of individuals per unit of area. For species whose members differ markedly in size, such as plants and animals, the percentage of ground covered or the total mass of individuals may be more useful measures of density than the number of individuals. Most accurate way to determine the density and structure of a pop"n is to count every individual and note its location. Estimating pop"n densities is easiest for sedentary organisms. Estimates of total pop"n size will be inaccurate if marked individuals learn to avoid traps or leave study area. High death rates of young individuals are followed by high survival rates. As the # of individuals in a pop"n increases, the # of new individuals added per unit of time accelerates, even if the rate of increase expressed on a per individual basis-per capita growth rate-remains constant- exponential growth.
