环境科学概论教学课件（第四讲）.ppt

1,Population CharacteristicsA Population Growth CurveCarrying CapacityHuman Population Growth,CHAPTER FOURPopulation Characteristics and Issues,2,Background,Thomas Malthus,An Essay on the Principle of Population (1798),at some point in time an expanding population must exceed supply of prerequisite natural resources, i.e., population increases exponentially resulting in increasing competition for means of subsistence, food, shelter, etc. This concept has been termed the Struggle for Existence.,Demography,3,Charles Darwin,The origin of species (1859),Survival of the Fittest,4,Define the following characteristics of a population: natality, mortality, sex ratio, age distribution, reproductive potential, and spatial distribution.Describe how a growing population goes through lag, exponential growth, and stable equilibrium phases.Describe how the carrying capacity for a population in a region is determined by environmental resistance.List the four categories under which limiting factors can be classified.Explain why humans are subject to the same forces of environmental resistance as are other organisms.Explain how human population growth is influenced by social, theological. philosophical, and political thinking.,OBJECTIVES,5,Population: a group of individuals of the same species inhabiting a particular area at a specific time.,6,How can we recognize so many individuals crowded in an area?,zebra,butterfly,Population,7,Population Characteristics,Natality: refers to the number of individuals added to the population through reproduction.,Mortality: refers to the number of deaths in a population over a particular time period.,8,population,births,immigrants,deaths,emigrants,gains,losses,9,age structure and sex ratio,Age distribution: the number of individuals in each age class as a ratio of one class to another.,Growing stationary declining,10,Label the three age structure graphs shown below. One is (a)slow growth, one is (b)no growth, one is(c) fast growth.,11,Sex ratio: refers to the relative numbers of males and females.,12,Population density: is the number of organisms per unit area.,13,absolute density,鼠洞-相对指标,鼠夹 - 直接指标,relative density,14,Population Growth Curve,Typical population growth tends to follow a particular pattern, consisting of a lag phase, an exponential growth phase, and a stable equilibrium phase.,Four periods:a lag phasean exponential growth phasea stable equilibrium phasea death phase,15,Growth as normally seen under artificial conditions, e.g. lab populationsLimits to population size are: Food Waste product elimination Disease control Space,16,Most populations are limited in growth at some carrying capacity (K) (the maximum population size a habitat can accommodate),Logistic growth,17,Environmental resistance to growth may be because of: Food and shelter llimitations Competition and predation by other organisms Unfavorable physical conditions,18,19,Carrying Capacity,The carrying capacity of an area is the number of individuals of a species that can survive in that area over time.,20,Limiting Factor: a particular condition or factor that limits the size of a population.,eg:Oxygen supplyFood supplyDiseasePredatorsLimited space,21,Species can be divided into two broad categories based on their reproductive strategies: K-strategists are usually large organisms that have relatively long lives, produce few offspring, and provide care for their offspring. R-strategist is typically a small organism that has a short life, produces many offspring, and does not reach a carrying capacity.,Reproductive Strategies,22,Time (generations),K-selection,R-selection,23,The human population growth curve has a long lag phase followed by a sharply rising exponential growth phase that is still rapidly increasing.,Human Population= 6,339,110,260,Growth will slow down either due to decreased births or increased deaths.,Human Population Growth,24,Exponential growth since Industrial Revolution: better nutrition, medical care and sanitation. Growth rates ( r ) 1963: 2.2%(0.022), 1990: 1.6%, 2003: 1.3% (200,234/day), 2015: 1%,25,e.g The population of China was 0.45 billion in 1949, and 0.95 billion in 1978. Then, how much r value is in the 29 years, according exponential growth model?,26,Available raw materials,27,Available energy,28,Waste disposal,29,Social factors influence human population,War,Convulsion,30,Summary,Populationbirthrate (natality) death rate (mortality)Population growth is determined by the combined effects of the birthrate and death rate.sex ratioAge distributiontypical population growth curvecarrying capacityfour major categoriesK-strategistsr-strategists are generally small, short-living organisms that reproduce very quicklyThe human population is increasing at a rapid rate. The earths ultimate carrying capacity for humans is not known. The causes for human population growth are not just biological but also social, political, philosophical, and theological.,。