BIOL1003 Study Guide - Final Guide: Exponential Growth, Ecological Succession, Semelparity And Iteroparity
Population Ecology
• Includes environmental influences on population density and distribution, age structure and
variations in population size.
• Range: population versus species range.
• Dispersion (pattern of spacing among individuals within the boundaries of the population-)
versus dispersal (organisms that may be immigrating out of a population to a new one).
• Population - groups of organisms from the same species in same general area - eat the same
thing and interbreed.
Population Growth
• The size of a population is determined by four parameters - sources of increase: birth,
immigration and sources of decrease: death and emigration.
• Growth rate (r) is determined by birth rates (b) and mortality rates (m).
• b - m = r
• If r = 0: no growth, r > 0: population increases, r < 0: population decrease.
• Intrinsic rate of growth (rmax) is the rate of growth with no extrinsic (external-limiting) factors.
• The highest rate of birth that can occur → no limiting factors and nothing interfering.
• rmax is characteristic of the species.
• Change in population size (N) during a time interval (t) = number of births (B) - number of
deaths (D)
o Δ N/Δ t = B - D = bN - mN
• B = bN and D = mN with b = offspring in a given time/indiv. in popn.
• If N is 100 and there are 5 births (B) then b = 0.05 (birth rate).
• Δ N/Δ t = ( - m)N
• Δ N/Δ t = rN
• dN/dt = rN
• If r < 0: decreasing, r = 0: no population growth, r > 0: increasing.
• b, m and r are expressed as per capital growth per year.
Exponential Growth (unlimited resources)
• dN/dt = rmaxN
• rmax = intrinsic rate of growth, expressed as per capita growth per year.
• Low fecundity does not prevent exponential growth.
• Populations cannot increase forever without limit: K = the carrying capacity of the
environment.
• At any time K - N individuals can be accommodated.
• So (K - N)/K individuals is the fraction of K that is still available for population growth.
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