Population Growth：人口增长.pptVIP

Changes in Population Size Text p. 660-669 Population Dynamics Populations always changing in size Deaths, births Main determinants (measured per unit time): Natality = number of births Mortality = number of deaths Emigration = # of individuals that move away Immigration = # of individuals that move into an existing population Effect on Determinants The determinants vary from species to species Environmental Conditions Fecundity Potential for a species to produce offspring in one lifetime vs. Limits on Fecundity Fertility often less than fecundity Food availability Mating success Disease Human factors Immigration/Emigration 1. Population Change (?N) = [(births + immigration) – (deaths + emigration)] - just plug in the values as determined. 2. To calculate the rate of population growth: gr = ?N/?t eg. Snail population in Banff Springs is 3800 in 1997, but falls to 1800 in 1999. Calcluate the growth rate. gr = 1800-3800 2 years = - 1000 snails/year the population declined at a rate of 1000 snails per year. Calculating Changes in Population Size Calculating Changes in Population Size 3. Calculating the per capita growth rate (cgr): ?N/N (N= initial pop. size) cgr = [(birth + immigration) – (deaths + emigration)] x 100 (%) initial population size (n) Positive Growth: Birth + Immigration Death + Emigration Negative Growth: Birth + Immigration Death + Emigration Calculate: a) the change in a population in which there were 20 births, 25 immigrants, 10 deaths, and 5 emigrants. b) What is the per capita growth if the original population was 75?. + 30 + 40% Open/Closed Population Growth can depend on type of population Open: influenced by natality, mortality and migration Closed: determined by natality and mortality alone Population Growth in Unlimited Environments Under ideal conditions – no predators and unlimited resources… A species can reach its biotic potential - the highest possible per capita growth rate fo