2Assessment Statements 2.6.1 Explain the concepts of limiting factors and carrying capacity in the context of population growth.2.6.2 Describe and explain S- and J- population curves.2.6.3 Describe the role of density-dependent and density-independent factors, and internal and external factors, in the regulation of populations.2.6.4 Describe the principles associated with survivorship curves including, K- and r-strategists.
3Population DynamicsChanges in population size and the factors that regulate populations over time.
4Population Density The number of individuals per unit area/volume. Example: The number of oak trees per km2 in a forest.
5Estimation of Population Size 1. Individual counts (not always practical)2. Transects or Quadrats3. Mark-recapture method: Lincoln IndexN= marked individual X total catch second time recaptured marked individualsExample: pond turtles1992: 181993: 34 (12)1994: 30 (18)
6Estimation of Population Size Example: pond turtles 1992: 181993: 34 (12)1994: 30 (18): N = 18(34) = 51 turtles12_________________________________________: N = 34(30) = 56.7 turtles18So: = = 53.9 turtle estimation2
7DispersionThe distribution of individuals within geographical population boundaries.Three examples of dispersion patterns:1. Clumped2. Uniform3. Random
8Dispersion Patterns1. Clumped a. individuals are aggregated in patches b. unequal distribution of resources in the environment. Example: trees around a lake or pond
9Dispersion Patterns 2. Uniform a. individuals are evenly distributed b. interactions among individuals of a populationExample: creosote bushes in the desert
10Dispersion Patterns 3. Random a. unevenly distributed b. random dispersion is rareExample: clams in a mud flat
11Understanding Population Growth Exponential Growth ModelExponential growth: The rate of expansion (growth) of a population under ideal conditions.
17Question What if? N, the number of individuals = almost 0: exponential growthN, the number of individuals = almost K (carrying capacity):growth rate is approaching zero Zero Population Growth
18Factors That Limit Population Growth 1. Density-Dependent Factors: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. Disease3. Predation/parasitism4. War
19Factors That Limit Population Growth 2. Density-Independent Factors:Population-limiting factors (abiotic) whose occurrence is not affected by pop density.Increases death rate & decreases birth rateAffects depend on severity of the eventExamples: 1. Earthquakes2. Fires3. Hurricanes4. Freeze in the fall
20number of individuals in pop. Boom and Bust SpeciesA rapid increase (boom) in a population followed by a sharp decline (bust).Examples:a. Daphnia in a pondnumber of individuals in pop.Timeboombust
21Boom and Bust SpeciesSometimes species (carnivore) depend on other species (prey) for food.Example: Snowshoe hare and lynxnumber of individuals in pop.Years
22Survivorship Curves Life History: 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)
23Opportunistic life history (r-strategist species) Characteristics:1. maturing time: short2. life span: short3. mortality rate: often high4. times female is reproductive: usually once5. age at first reproduction: early6. size of offspring: small7. parental care: none8. Size of organism: small
24Equilibrial life history (K-strategist species) Characteristics:1. maturing time: long2. life span: long3. mortality rate: often low4. times female is reproductive: often many5. age at first reproduction: late6. size of offspring: large7. parental care: often extensive8. Size of organism: tend to be large
26Survivorship Curves Type 1 survivorship curve: High survival rates until old age.K or r strategist?K% of survivors% of maximum life spanExample?humans
27Survivorship Curves Type 3 survivorship curve: High mortality rates as young but decreased mortality at later ages.K or r strategist?% of survivors% of maximum life spanrExamples?turtlesoystersfrogsinsects
28Survivorship Curves Type 2 survivorship curve: Intermediate between the extremes.Example% of survivors% of maximum life spansquirrel
29Human Population Growth Age structureProportions of individuals of a population in different age groups.A typical population has three main age groups (age structure).1. Pre-reproductive (youth)2. Reproductive3. Post-reproductive
31Human Population Growth Today Human population as a whole is growing exponentially.Has doubled (doubling-time) three times in the last three centuries (doubled the carrying capacity several times).Is now 7 billion, might reach ~8 billion by 2020.
32Question: What are the reasons for the increase in human population? Answer:1. Improved health2. Technology3. Decreased death rates
33Question: What is Zero Population Growth (ZPG)? Answer: a. birth rate equals death rate.b. intrinsic growth (r) = 0
34Question:What are two ways the human population can reach Zero Population Growth?1. Limit the # of offspring per couplea. Reduces family sizeb. Voluntary contraceptionc. Family planning2. Delay reproduction(late 20’s instead of early 20’s)
35Question: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