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:
2.6 Changes: Population Dynamics
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.
Population Dynamics Changespopulation sizefactors regulate Changes in population size and the factors that regulate populations over time.
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.
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)
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
Dispersion individuals geographical population boundaries The distribution of individuals within geographical population boundaries. Three examples of dispersion patterns: 1.Clumped 2.Uniform 3.Random
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
Dispersion Patterns 2.Uniform a.individuals are evenly distributed b.interactions among individuals of a population Example: Example: creosote bushes in the desert
Dispersion Patterns 3.Random a.unevenly distributed b.random dispersion is rare Example Example: clams in a mud flat
Understanding Population Growth 1. Exponential Growth Model Exponential growth: Exponential growth: The rate of expansion (growth) of a population under ideal conditions.
Exponential Growth – J Curve Example: bacteria Number of individuals (N) Time J-shaped produces a J-shaped curve
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)
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).
Logistic Growth: S-Curve Example: turtles in a pond Number of individuals (N) Time S-shaped produces a S-shaped curve K
Draw an s-curve and draw a j-curve Label each
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
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
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
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
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
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)
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
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
Life History Examples R-strategist species: 1.Garden weeds 2.Insects 3.Desert flowers K-strategist species: 1.Humans 2.Apes 3.Elephants
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?
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
Survivorship Curves Type 2 survivorship curve: Intermediateextremes Intermediate between the extremes. % of survivors % of maximum life span Example squirrel
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
Age Structure Pre-reproductiveReproductivePost-reproductive
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/
Question: human population What are the reasons for the increase in human population? Answer: 1.Improved health 2.Technology 3.Decreased death rates
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
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)
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