. Animal Ecology. Animal ecology. OT200 < I 150 Z '00 o £ 50 CD ^ 0 Instantaneous percentage. Asymptote i -40 i ( [ Cumulative growth rote ( ..--Absolute growth rate -| g I ? 10 I I X 6 0° |FEB|MAR|APR|MAY| JUN|JUL|AUG|SEP| FIG. I Annual ecesis of the Invertebrate connmuni herb and shrub strata of a deciduous forest. 223 + 266 + 218 + 273 + 272 5 K ; log e (20) 250; ; N = (*) l + e not fully expressed, even though its trend is present inherently. The sigmoid curve shows that a population grows slowly at first, then at an accelerating
. Animal Ecology. Animal ecology. OT200 < I 150 Z '00 o £ 50 CD ^ 0 Instantaneous percentage. Asymptote i -40 i ( [ Cumulative growth rote ( ..--Absolute growth rate -| g I ? 10 I I X 6 0° |FEB|MAR|APR|MAY| JUN|JUL|AUG|SEP| FIG. I Annual ecesis of the Invertebrate connmuni herb and shrub strata of a deciduous forest. 223 + 266 + 218 + 273 + 272 5 K ; log e (20) 250; ; N = (*) l + e not fully expressed, even though its trend is present inherently. The sigmoid curve shows that a population grows slowly at first, then at an accelerating rate which is at maximum at the point of inflection, after which the population continues to increase but at a decelerating rate, finally becoming stabilized at the upper asymp- tote. Most growth curves are symmetrical, and the point of inflection is one-half the value of the asymp- tote. The lower concave part of the curve is called the accelerating phase oj growth and the upper convex part of the curve, the inhibiting phase of groivth. If the number of new individuals added during each unit of time, absolute growth rate, is plotted against time midway in each period, a bell-shaped curve is obtained, the peak of this curve coinciding with the point of inflection on the sigmoid curve. However, the number of individuals involved in the absolute growth rate varies with the length of the time unit used, and the time unit of greatest signifi- cance varies from one species to another. Compari- sons of growth rate of different populations are diffi- cult unless instantaneous growth rates are obtained. The instantaneous groivth rate is the rate of growth at a point on a time scale and is usu- ally expressed in terms of increase per individual or unit biomass per unit of time. It cannot be measured, but it can be calculated from the logistic curve by the differential equation (Park 1939, Andrewartha and Birch 1954) dN ,, K-N dt k where jV is the size of the populations at any time t
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Keywords: ., bookcentury1900, bookcollectionbiodive, booksubjectanimalecology
