世界人口分布.ppt

World population Population growth Definition: how the number of individuals in a population increases or decreases with time Growth is controlled by rates of birth, immigration and death and emigration. Open or closed population: no immigration and emigration, or immig.=emig. In closed population, growth is determined by birth rate and death rate. 10.1 Population growth reflects the difference between rates of birth and death Model development A population of freshwater hydra growing in an aquarium in the laboratory. Population size N(t) when time is t. This is a closed population. Population size change is related to birth rate (b) and death rate (d) dN/dt=(b-d)N=rN The difference between birth rate and death rate is the intrinsic growth rate (r) (instantaneous per capita rate of growth). r=b-d In a closed population, population size change is related to birth rate (b) and death rate (d) The difference between birth rate and death rate is the intrinsic growth rate (r) (instantaneous per capita rate of growth). r=b-d Population growth is related to this intrinsic growth rate (r). Exponential population growth Equations: 1) dN/dt=rN (differential equation form) 2) N(t)=N(0) exp(rt) (exponential growth model) Conditions: Initial population is small No food or resource limitation An example Reindeer, St. Paul, Alaska. Started in 1910 with only 4 males and 22 females In 1940, there were nearly 2000 Whooping crane, an endangered speciesrecovered from near extinction in 1941 How to calculate r? Software, Excel (trendline) Aransas National Wildlife Refuge Properties of exponential growth r determines the shape of the growth. r=0, no change in population size r0, decrease in population size; r0, increase in population size. Properties of exponential growth Widely used in biology N(t)=N(0)Exp(rt) Give a time t, we can predict the population size. An Example: Deer population: N(0)=300, r=0.5, after 5 years, what’s the population size? N(5)=N