环境生态学教学课件：Chapter 3-1-Population

1、Population EcologyWhat Is Population? A group of individuals of a single species inhabiting a specific area. In other words, a group of interbreeding individuals of the same species.Population is made up by individuals. And it is more than addition of separate individuals, but actually organized by

2、interactional relationships internally.Population is the basic unite of species, as well as the basic unite of communityConcept of PopulationCommunity VS Species A population is the collection of inter-breeding organisms of a particular speciesz Different subjects concept: A species is a taxonomic g

3、roup whose members can interbreed, while a population is a ecological group.z Particular: Particular time and particular space outlining in populationWhat Is Population Ecology? The science that describes how and why populations changePopulations may stay the same, increase, or decreaseConcept of Po

4、pulation ecologyWhat Are Characteristics for Population? Gray Whales rounding the point of land on their way feeding grounds off the coasts of Alaska and Siberia in which the calves(仔) were born. They travel a distance of about 18,000km with the entire population of over 20,000 gray whales. (a) The

5、bright orange and black monarch butterflies gives no hint of their capacity to migrate. After mating, the male die, however, the female begin migrate to inland and north, meanwhile lay eggs until they encounter milkweeds. Then the kids will continue migrating following with their mothers direction.

6、(b)Population in Nature(b)Monarch butterflies fly thousands of kilometers from the Rocky Mountains to reach their winter roost(栖木）.(a) The populations of gray whales migrate from subtropical waters off Baja California to the Arctic and back again.What Are Characteristics for Population? We can chara

7、cterize individual populations in terms of there Size (average vs. variation) Density (impacts on size; density dependence) Patterns of Dispersion Demographics (age structure, sex ratios) Rates of growth (or decline) Limits on population growthCommon Characteristics for PopulationDensity : the measu

8、re of how crowded organisms are in their environment.Because organisms compete for resources, keeping a balance is important. If the population is too high, some organisms will die.Population density declines with increasing organism size.Climate, topography and all kinds of the physical environment

9、 may limit the distribution of a population ( Natural Selection).Distribution : a description of how organisms are distributed within their community. Distributed Patterns Why Different Types?Recognize Different Patterns The first step toward testing statistically between these three types of distri

10、butions is to sample the population to estimate the mean(m) and variance(方差)1/)(222nnXXSiiNumbers of sample sample sizePopulation variance if s2/m =0, then regular distribution if s2/m =1, then random distribution if s2/m1, then clumped distributionThe Patterns of Space Utilization Dispersing Utiliz

11、ation: Individuals, maybe families, get gather in a tiny space (realm), additionally, there are no other individuals of the same species living at the same time. It prevails at animals, e.g. panda, 3.9-6.4km2 Aggregating Utilization: Individuals aggregate in areas where the environment is favorable,

12、 What might be the pattern of distribution in all kinds of species. The Patterns of Space UtilizationThe Allee lawGregarious animals have an advantage on the survivor, therefore, they enjoy a low mortality rate.Population has its own proper density, less than or more then that value would cause an i

13、nhibiting influence to their existence.Population DynamicsBasic Population Ecology AttributeBirth rate & Death rate Birth rate: Generally means the ability of reproduction for per female.Narrowly means ratio of the number of young born out of the gross in one population. Maximum Birth rate:The b

14、irth rate of one population merely restrained by its physical factors is out of control of any type of limiting factors, namely, access to abundant resources. Birth rate refers to the average ability of reproduction for each individuals in one population rather than partly certain numbers of individ

15、uals attribute.Population DynamicsPopulation Statistics ParametersAge Distribution (Structure) distribution of males and females in each age group of a population used to predict future population growth Individuals are categorized by three physical phrase: Pre-reproductive age Reproductive age Post

16、-reproductive ageAge distribution Age-Structure Pyramids is plotted by proportion of each period of age in the gross. X-axis is the proportion Y-axis is the age period Age structure related to growth ratePyramid shape is rapid growth, many young (Rwanda)Kettle(壶) shape is declining population (Hunga

17、ry)Rectangular shape is zero growth, stable population (Sweden)Major reproductive ages Life TablesAn age-specific summary of a survivor pattern of a populationIt best constructed by following the fate of a cohort.Two estimating patterns: A cohort life table: The most reliable way is to identify a la

18、rge number of individuals that are born at about the same time and keep records on them from birth to death. (However) A static life table: to record the age at death of a large number of individuals. Or from the age distribution, consisting of the proportion of individuals of different ages within

19、a population.Life-history Traits from Life TableSurvivorship curve: Type I , Type II , Type III Proposed by Deevey (1947), plotting age on the X-axis and lg(survivors) on the y-axis creates a survivorship curveMortality curves: show how quickly individuals die.life Expectancy: ex is known as the ave

20、rage lifetime to each age x 藤壶的生命表（动态）l x = nx / n0qx = dx / nxdx = (nx - nx+1 ) Lx =( nx + nx+1 ) /2ex= Tx / nxTx = LxThree Types of Survivor ship curvesPopulation GrowthPopulation Growth access to abundant resourcesGeometric Growth: It is an annual plant, populations of few kinds of trees grow in

21、discrete annual pulses. Populations of insects that produce a single generation a year also grow in pulses.Four Assumptions: Get rid of resources and space limiting Grow in discrete annual pulses Neglect immigration and emigration Lack of age distributionsPopulation GrowthNt+1=Nt Nt=N0tN0= initial n

22、umber of individualsNt=number of individuals at any time t=geometric rate of increaseT=number of time intervals of generationsPopulation GrowthPopulation Growth access to abundant resourcesExponential Growth: Anatomy (分解）of equations of exponential population growth Population GrowthPopulation Growt

23、h under impact of limitsLogistic Population Growth: Assumptions: The population growth stops is generally called carrying capacity, represented by K. At carrying capacity, dK/dt=0. Population density increases as the per capita rate of increase decreases instantly and immediately. The pattern of dec

24、line of the rate of population growth is simplest one, which increase with the growth of density by ratio, e.g. one number increase, then decline of the rate of population growth is 1/k. Neglect immigration and emigration and lack of age distributionsEnvironmental ResistanceN/K = “Environmental Resi

25、stance”Logistic Growth Equation G = rmax N (K-N/K)G = population growth per unit timermax = maximum population growth rate per unit timeN = number of individualsK = carrying capacity Logistic growth produces S-shaped curve; population growth rate decreases as N approaches KLogistic Growth CurveTime

26、(t)KPopulation size (N)Exponential Growth vs. Logistic GrowthK NKis close to 1, so population grows exponentiallyTime (t)dNdt rNK NK(1)Population GrowthWhen N is very small (imagine N is 1 and K is 1000).How does logistic growth model work?Population size (N)How does logistic growth model work?Popul

27、ation GrowthK NKGets closer and closer to 0, so population growth slowly approaches 0Population size(N)Time (t) When N approaches K (imagine N is 500, 600, .900 and K is 1000).How does logistic growth model work?Population Growth When N approaches K (imagine N is 1000 and K is 1000).K NKis 0, so pop

28、ulation growth is 0Population size(N)Time (t) N=k/2，dN/dt reaches the maximum value, the break point on plotBefore break point, dN/dt increases with N, the positive increase periodAfter break point, dN/dt decrease with N, the negative increase period Population GrowthFive periods: commence period ac

29、celeration period transition period deceleration period saturation period lagexponential growthdecelerationStable equilibrium phrase It serves as a foundation of two interacted populations growth model.It determines maximum production in various fields, e.g. fishing, agriculture, and forestry. Two p

30、arameters, r and k, have been recognized as two important concept in Biological generation of game theory.Significance of Population Growth ModelsTwo outstanding characteristics: Apply simple mathmatics Meet reality However, it fails to provide some of limiting hypotheses.Environment is stable enoug

31、h to assure birthrate and death get rid of influence.Crowded impact is equal to each individual.Influence caused by birthrate and death rate is immediate Per capita rate of increase is restrained by density, even though it is very low.Stable age distribution In sexual reproduction population, any female can find mate. Significance of Population Growth ModelsVariation in Pop. Size J-shaped curve and S-shaped curve both appear in nature, but they are not smooth as the math model. Sometimes, they mingle each other, called medium shaped curve. Seasonal variation. Environmental factors