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2.6 Changes: Population Dynamics. Assessment Statements  2.6.1 Explain the concepts of limiting factors and carrying capacity in the context of population.

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Presentation on theme: "2.6 Changes: Population Dynamics. Assessment Statements  2.6.1 Explain the concepts of limiting factors and carrying capacity in the context of population."— Presentation transcript:

1 2.6 Changes: Population Dynamics

2 Assessment Statements  Explain the concepts of limiting factors and carrying capacity in the context of population growth.  Describe and explain S- and J- population curves.  Describe the role of density-dependent and density-independent factors, and internal and external factors, in the regulation of populations.  Describe the principles associated with survivorship curves including, K- and r-strategists.

3 Population Dynamics  Changespopulation sizefactors regulate  Changes in population size and the factors that regulate populations over time.

4 Population Density numberindividuals per unit area/volume  The number of individuals per unit area/volume.  Example:  Example:The number of oak trees per km 2 in a forest.

5 Estimation of Population Size Individual counts 1.Individual counts (not always practical) 2.Transects or Quadrats 3.Mark-recapture method 3.Mark-recapture method: Lincoln Index N= marked individual X total catch second time recaptured marked individuals Example: pond turtles 1992: : 34 (12) 1994: 30 (18)

6 Estimation of Population Size Example: pond turtles1992: : 34 (12) 1994: 30 (18) : N = 18(34) = 51 turtles _________________________________________ : N = 34(30) = 56.7 turtles _________________________________________ So: = = 53.9 turtle estimation 2

7 Dispersion individuals geographical population boundaries  The distribution of individuals within geographical population boundaries.  Three examples of dispersion patterns: 1.Clumped 2.Uniform 3.Random

8 Dispersion Patterns 1. Clumped a.individuals are aggregated in patches b.unequal distribution of resources in the environment. Example Example: trees around a lake or pond

9 Dispersion Patterns  2.Uniform a.individuals are evenly distributed b.interactions among individuals of a population Example: Example: creosote bushes in the desert

10 Dispersion Patterns  3.Random a.unevenly distributed b.random dispersion is rare Example Example: clams in a mud flat

11 Understanding Population Growth 1. Exponential Growth Model Exponential growth: Exponential growth: The rate of expansion (growth) of a population under ideal conditions.

12 Exponential Growth – J Curve  Example: bacteria Number of individuals (N) Time J-shaped produces a J-shaped curve

13 Understanding Population Growth 2. Logistic Growth Model logistic growth: logistic growth: environmental factors that restrict the growth of a population population limiting factors (called: population limiting factors)

14 K: Carrying Capacity maximum environmentsupport time (K)  The maximum stable population size that a particular environment can support over a relatively long period of time (K).

15 Logistic Growth: S-Curve  Example: turtles in a pond Number of individuals (N) Time S-shaped produces a S-shaped curve K

16 Draw an s-curve and draw a j-curve  Label each

17 Question  What if?  N, the number of individuals = almost 0: exponential growth  N, the number of individuals = almost K (carrying capacity): growth rate is approaching zero Zero Population Growth

18 Factors That Limit Population Growth 1. Density-Dependent Factors: Population-limiting factors population density  Population-limiting factors whose effects depend on population density.  The greater the pop, the greater the effects. (negative feedback) Examples: 1. Limited food supply (competition) 2. Disease 3. Predation/parasitism 4. War

19 Factors That Limit Population Growth 2. Density-Independent Factors: Population-limiting factors notpop density  Population-limiting factors (abiotic) whose occurrence is not affected by pop density.  Increases death rate & decreases birth rate  Affects depend on severity of the event Examples: Examples: 1. Earthquakes 2. Fires 3. Hurricanes 4. Freeze in the fall

20 Boom and Bust Species (boom) (bust)  A rapid increase (boom) in a population followed by a sharp decline (bust).  Examples: Daphnia a. Daphnia in a pond number of individuals in pop. Time boom bust

21 Boom and Bust Species species(carnivore) species (prey)  Sometimes species (carnivore) depend on other species (prey) for food.  Example: Snowshoeharelynx  Example: Snowshoe hare and lynx number of individuals in pop. Years

22 Survivorship Curves  Life History: birthreproduction death Series of events from birth through reproduction to death.  Two basic types of life history strategies: 1. Opportunistic life history (r-strategist species) 2. Equilibrial life history – limited by carrying capacity(K) (K-Strategist species)

23 Opportunistic life history (r-strategist species) Characteristics: 1. maturing time:short 2. life span:short 3. mortality rate:often high 4. times female is reproductive:usually once 5. age at first reproduction:early 6. size of offspring:small 7. parental care:none 8. Size of organism:small

24 Equilibrial life history (K-strategist species) Characteristics: 1. maturing time:long 2. life span:long 3. mortality rate:often low 4. times female is reproductive:often many 5. age at first reproduction:late 6. size of offspring:large 7. parental care: often extensive 8. Size of organism: tend to be large

25 Life History Examples R-strategist species: 1.Garden weeds 2.Insects 3.Desert flowers K-strategist species: 1.Humans 2.Apes 3.Elephants

26 Survivorship Curves  Type 1 survivorship curve: High survival rates High survival rates until old age. % of survivors % of maximum life span humans K or r strategist? K Example?

27 Survivorship Curves  Type 3 survivorship curve: High mortalityyoung decreased mortality High mortality rates as young but decreased mortality at later ages. % of survivors % of maximum life span K or r strategist? r Examples? turtles oysters frogs insects

28 Survivorship Curves  Type 2 survivorship curve: Intermediateextremes Intermediate between the extremes. % of survivors % of maximum life span Example squirrel

29 Human Population Growth  Age structure individualspopulation age groups Proportions of individuals of a population in different age groups. (age structure). A typical population has three main age groups (age structure). 1.Pre-reproductive (youth) 2.Reproductive 3.Post-reproductive

30 Age Structure Pre-reproductiveReproductivePost-reproductive

31 Human Population Growth Today  Human population exponentially  Human population as a whole is growing exponentially. doubled (doubling-time) (doubled the carrying capacity several times).  Has doubled (doubling-time) three times in the last three centuries (doubled the carrying capacity several times). ~8 billion2020  Is now 7 billion, might reach ~8 billion by rld-population/

32 Question: human population  What are the reasons for the increase in human population?  Answer: 1.Improved health 2.Technology 3.Decreased death rates

33 Question: Zero Population Growth (ZPG)?  What is Zero Population Growth (ZPG)?  Answer: birth ratedeath rate a.birth rate equals death rate. b.intrinsic growth (r) = 0

34 Question:  What are two ways the human population can reach Zero Population Growth? Limit the # of offspring per couple 1.Limit the # of offspring per couple a. Reduces family size b. Voluntary contraception c. Family planning Delay reproduction 2.Delay reproduction (late 20’s instead of early 20’s)

35 Question:  What will happen to human’s if the population continues to grow at this rate?  Is there a limit to human population growth? Why/why not?  What EVS does your argument support? Explain


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