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1、1 Populations and population structure,Population A population is a group of organisms of the same species which occupies a given area.,Mortality,The death rate, or mortality rate, is the number of individuals dying during a given time interval divided by the average population size over that time i
2、nterval. This is an instantaneous rate and can be estimated for the population as a whole or for specific age classes to give the age specific mortality rate. The probability of dying is the number dying per individual present at the start of the time period.,example,A population with 1000 individua
3、ls at the beginning of the time interval and 600 by the end of the period. average size = (1000+600) / 2 = 800 Mortality rate = (1000-600) / 800 = 0.5 Probability of dying = (1000-600) / 1000 = 0.4,Density-dependent growth- the logistic equation,The logistic equation describes the growth of a simple
4、 population in a confined space, where resources are not unlimited. In the early stages resources are abundant, the death rate is minimal and reproduction can take place as fast as possible allowing the individuals to attain their intrinsic rate of increase.,the logistic growth,The population increa
5、ses geometrically until the maximum number of individuals the environment can sustainably support is approached. This maximum number is called the carrying capacity (K). The population growth rate declines to zero as the population becomes more crowded and the population size stabilizes.,the logisti
6、c equation (2),Where the density dependent factor, approaches zero as the population approaches the carrying capacity and intraspecific competition becomes more intense. This equation predicts growth of a population over time to be sigmoidal, as is commonly observed in real populations.,Discussion,2
7、005年末全国总人口为13亿。1996年中国政府发表中国的粮食问题白皮书，预测2030年人口达到16亿，粮食总需求量为6.4亿吨。 我国耕地18亿亩，以世界7%的耕地养活22%的人口，但也付出了沉重的环境代价。 以我国的自然资源条件，你认为最大能承载多少人口？理由是什么？,茅于轼的争议,中国“自由市场派”的领军人物。 替富人说话，为穷人办事。 设置扶贫基金、保姆学校。,茅于轼的解释,替富人说话的人很少，因为明着替富人说话要挨骂；而替富人办事的人很多，因为肯定会有好处。 帮穷人说话的人很多，因为太容易了；而为穷人办事的人很少，因为太麻烦了。,Discussion,茅于轼领导的天则研究所最近发布“
8、18亿亩耕地红线没有必要”的研究成果，遭到很多反对，骂他是“汉奸”、“卖国贼”。 老先生亲自出面，写文章辩驳：“反对我们的研究成果”的人，或者是“因为非法利益被揭穿”了，或者就是“对粮食问题缺乏认真的思考”。总之，不是坏蛋，就是傻瓜。 你认为18亿亩耕地红线有必要吗？为什么？,Total population,Since the total number of marked animals is known an estimate of the total population can be obtained from the following equation: Total number
9、in population = Number originally marked,Number trapped Number recaptured,Exercise,Given the data as follow: number trapped is 60, number recaptured is 20, number originally marked is 50, then what is the total number of the population?,Density dependence,Population parameters such as birth and deat
10、h rates which vary with density are said to be density dependent. Birth and death rates that do not change with density are density independent.,Compensation and density dependence,There are three types of density dependence: overcompensating, undercompensating and exactly compensating. If a decline
11、 in numbers due to density dependence does not outweigh or balance the initial increase in numbers, density dependence is undercompensating.,Compensation,Overcompensating density dependence occurs where the effect of increased density more than outweighs the initial augmentation. If the decline in n
12、umbers exactly balances the initial increase in density, density dependence is said to be exactly compensating.,Forms of density dependence,Density dependence in the flour beetle Tribolium confusum. In region 1 there is undercompensating density-dependent mortality. In region 2 density dependence is
13、 overcompensating,1 2,Exactly compensating density dependence in the field grasshopper, Chorthippus brunneus（褐色雏蝗）.,Eggs,Nymph,Adults,Population fluctuation (1),Populations may fluctuate for a number of reasons: A time lag between a change in density and its effect on the population size, or delayed
14、 density dependence. The population can overshoot the carrying capacity and then show gradually diminishing, dampened oscillations before eventually stabilizing at equilibrium. This delayed density dependence may also produce cycles in predator and prey abundance;,Population fluctuation (2),Overcomp
15、ensating density dependence. This can lead to dampened oscillations, stable limit cycles (regular cycles that do not damp down) or chaotic fluctuations that appear random; Environmental stochasticity. This is a nondeterministic, unpredictable variation in the environmental conditions, resulting in a
16、 changing equilibrium density.,Cycles of abundance of the larch bud moth（灰线小卷蛾） in response to larch quality (needle length),Theoretical predator-prey oscillations,Damped oscillations,Carrying capacity,Stable limit cycles,Carrying capacity,Chaotic dynamics,Carrying capacity,Variation in the number of algae in Green Bay, Wisconsin in response to changes in the environment,
