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Population Ecology Population ecology is the study of populations in relation to environment –Including environmental influences on population density.

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Presentation on theme: "Population Ecology Population ecology is the study of populations in relation to environment –Including environmental influences on population density."— Presentation transcript:

1 Population Ecology Population ecology is the study of populations in relation to environment –Including environmental influences on population density and distribution, age structure, and variations in population size

2 Levels of Organization OrganismOrganism PopulationPopulation CommunityCommunity EcosystemEcosystem BiomeBiome

3 Describing populations

4 SizeSize: total # of individuals in a pop (N) DensityDensity : # / unit area Describing populations

5 Estimation of Population Size Sampling technique Mark and recapture Describing populations

6 Mark and Recapture Orgs are captured, tagged, and then released. Some time later, the same process is repeated and the following is used: Describing populations

7 Ex: –Suppose that 50 zebra mussels are captured, marked, and released. One week later, 100 zebra mussels are captured and 10 are found to have markings already. The estimated population would then be N= (50·100) / (10) = 5000/10 = 500 N=500 Describing populations

8 Dispersion Describes how individuals in a population are distributedDescribes how individuals in a population are distributed 1.Clumped 2.Uniform 3.Random Describing populations

9 Clumped dispersion Clumped dispersion (most common) –Individuals aggregate in patches resource availabilitybehavior –May be influenced by resource availability & behaviorExample: For many animals, such as these wolves, living in groups 1.increases the effectiveness of hunting. 2.spreads the work of protecting and caring for young. 3.helps exclude other individuals from their territory. Fish travel in schools – safety in numbers Describing populations

10 Uniform dispersion -Individuals are evenly distributed social interactionsterritoriality -May be influenced by social interactions such as territoriality Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors. Some plants secrete toxins that keep others away Describing populations

11 Random dispersion –The position of each individual is independent of other individuals Dandelions grow from windblown seeds that land at random and later germinate. Describing populations

12 Biotic potential of a population= –max rate at which a population could increase under ideal conditions Influenced by several factors: –Age at which reproduction begins –Life span during which the organisms are capable of reproducing –Number of reproductive periods in the lifetime –Number of offspring the organism is capable of having Changes in Population Size Describing populations

13 Age Structure Description of the abundance of individuals of each age in a population. Describing populations

14 Age Structure Diagrams Describing populations

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16 China India United States 2004

17 Zero population growth

18 1954 Animation Describing populations

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20 Survivorship Curves Describes how the mortality of individuals in a species varies during their lifetime The survivorship curve for Belding’s ground squirrels –Shows that the death rate is relatively constant Number of survivors (log scale) Age (years) Males Females Describing populations

21 Type I, Type II, and Type IIISurvivorship curves can be classified into three general types : Type I, Type II, and Type III I II III ,000 Percentage of maximum life span Number of survivors (log scale) Type I A species in which most survive to middle age Parenting Type II Length of survivorship is random. Death rate is constant.

22 Type III Most individuals die young. Few reach reproductive maturity. Fish release 1000s of eggs. No parenting I II III ,000 Percentage of maximum life span Number of survivors (log scale) Animation

23 Factors Affecting Population

24 Limiting Factors  Things that prevent a population from attaining its biotic potential –2 categories 1.Density-dependent 2.Density-independent Density Dependent Density Independent Factors Affecting Population

25 Density Dependent number Populations regulated by density-dependent factors are affected by the number of organisms present. a)Predation b)Parasitism c)Disease d)Competition - the more organisms crowd together, the more damaging are food shortages, parasites, and predators. Intraspecific Competition = the struggle between members of a population for scarce resources Factors Affecting Population

26 Density Independent The number of organisms present does not affect the influence of the factor. –Fire, earthquakes, storms, floods Density-independent factors show no correlation with the size of the population. Factors Affecting Population

27 Describing Population Growth Population ecologists describe two general patterns of populations growth: 1.Exponential 2.Logistic

28 The growth of a population can be described by the following equation: r= reproductive rate (or growth rate) N= population size at the beginning of the interval for which the births and deaths are counted. r =. births-deaths N Net increase of individuals Can r be negative? Zero? Types of Population Growth

29 r = Ex: –A–A population of 1000 had 60 births and 10 deaths over a one year period. What is the growth rate? –0–0.05 per year births-deaths N Types of Population Growth

30 If the rate of reproduction per individual remains constant through time, then the rate at which the population increases is a multiple of the number of individuals in the population. In a population showing exponential growth the individuals a aa are not limited by food, disease, predation or competition. Exponential growth r>0 Types of Population Growth

31 Exponential population growth –Results in a J-shaped curve –Usually short lived in nature- not sustainable ,000 1,500 2,000 Number of generations Population size (N) dN dt  1.0N dN dt  0.5N Population size (N) r>0 Types of Population Growth

32 Carrying Capacity (K) Populations usually reach a carrying capacity. Upper limit to the number of individuals the environment can support. the real world Types of Population Growth

33 Logistic growth short periods of timeA population can grow exponentially only for short periods of time, because it would very quickly deplete all the resources necessary for its survival. Over long periods of time, populations tend to attain an equilibrium population size which is determined by the available resources. In most real populations both food and disease become important as conditions become crowded. dN dt  r max N Animation Types of Population Growth

34 Zero population growth –Occurs when the birth rate equals the death rate The population growth equation can be expressed as dN dt  rN Types of Population Growth

35 Logistic and exponential growth are associated with 2 kinds of life-history strategies 1.R-selected species (strategists) organisms are opportunistic; they reproduce rapidly when the environment is uncrowned and resources are vast 2.K-selected species (strategists) operate at a density near K Life-history strategies

36 R-selected species a. Opportunistic species, which tend to be colonizers. b. Grasses, many insects -Usually quickly invade, reproduce many offspring and die -Offspring mature quickly and require very little parental care c. Strategies for continued existence is based on individuals having the following traits: 1) small size 2) short life span 3) mature fast 4) produce many offspring 5) engage in little care of offspring Life-history strategies

37 K-selected species Such populations are equilibrium species, tend to be specialists rather than colonizers, and may become extinct when their evolved way of life is disrupted (e.g., the grizzly bear, Florida panther, etc.). Overall strategy for continued existence is based on having the following traits: 1) large size 2) long life span 3) slow to mature 4) produce few offspring 5) expend considerable energy in care – sensitive to population density Life-history strategies

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39 Human Population Growth The following made exponential growth possible 1.Increases food supply 2.Reduction in disease 3.Reduction in human waste 4.Expansion of habitat As of 28 April 2010, the human population of the world is estimated by the United States Census Bureau to be 6,817,500,000.

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41 Countries Ranked by Population: 2010 Source: U.S. Census Bureau, International Data Base. 6,817,500,000

42 Map of countries by population for the year 2007

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