INSECT ECOLOGY -- ENTOMOLOGY/BIOLOGY 127 LECTURES 3 and 4-- GEOMETRIC & EXPONENTIAL GROWTH POPULATION GROWTHI. Processes affecting population growthA. Fundamentally four processes affect population growth and decline, but we will concentrate on just two for now: birth and death.IF we assume that the population is closed (no migration) and population growth is continuous, then we can model population growth for infinitesimal small periods of time. Population growth rate: ΔN/Δt = dN/dt = B - D B = b⋅N, where bis the instantaneous birth rateof births individual-1unit time-1; a per capita rate => per individual D = d⋅N, where dis the instantaneous death rateof deaths individual-1unit time-1; a per capita rate => per individual (NOTE: dN ≠d⋅N)dN/dt = (b- d)N; assumes b and dare constant and not affected by population size = rN; ris the instantaneous rate of increase, ris also called the intrinsic rate of natural increase. B. The rate of change of size of a population is the difference between birth and death rates: r= rate of population size change = instantaneous birth rate – instantaneous death rate dN –– = rN dt C. This fundamental relation summarizes all development of descriptions about population growth and dynamics. Starting point for more complex models. II. Describing population growth:A. Populations can grow in two distinct ways. These are: Discrete generations:- non-overlapping generations e.g., insects that reproduce annually: a single generation per year Continuous generations:Lecture 3 and 4, page 1
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