世界人口分布.ppt
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1、Lecture 10: Population Growth,http:/ 起重机 立体停车设备 电动葫芦 http:/ 衬塑复合管 涂塑复合管 钢塑复合管 消防涂覆钢管,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 clo
2、sed 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 lab
3、oratory. 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 cl
4、osed 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 popul
5、ation 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 2
6、000,Whooping crane, an endangered species recovered 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, increase in population size.,
7、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, whats the population size? N(5)=N(0)Exp(rt)=300*exp(0.5*5)=3655 (495, 815, 1344, 2216, 3655) t=10, ?,Prediction of
8、population growth,44524,10.2 Life table,Life table is an age-specific account of mortality. Purpose of life table: to provide a clear and systematic picture of mortality and survival within a population,How to construct a life table?,1. start with a cohort: a group of individuals born in the same pe
9、riod of time; 2. Add a column of lx as the probability at birth of surviving to any given age;,How to construct a life table (cont.)?,3. calculate dx, a measure of age-specific mortality 4. Calculate age-specific mortality rate, qx,10.3 Different types of life table,Two types Cohort or dynamic life
10、table as the above gray squirrel Time-specific life table,Elf opine,10.4 Life tables provide data for mortality and survivorship curves,Table is better than words, but a graph is worth one thousand words. Mortality curve and survivorship curve.,Mortality curves,Survivorship curves,Log scale for Y ax
11、is,Three basic types of survivorship,Type I (convex) Humans and other mammals and some plants (k-selection) Type II (survival rates do not vary with age) Adult birds, rodent, and reptiles, perennial plants Type III. Concave Mortality rate high in the beginning (r-selection) Oysters, Fish, many plant
12、 species (most trees),10.5 Birthrate is age-specific,Crude birthrate (demographers): # of birth over a period of time divided by population size at the beginning of the period*1000 Age-specific birthrates, bx Mean # of females birth to a female in each age group. (Only females give birth; birth rate
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