# 2.6 Changes: Population Dynamics

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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 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.

Population Dynamics Changes in population size and the factors that regulate populations over time.

Population Density The number of individuals per unit area/volume.
Example: The number of oak trees per km2 in a forest.

Estimation of Population Size
1. Individual counts (not always practical) 2. Transects or Quadrats 3. Mark-recapture method: Lincoln Index N= marked individual X total catch second time recaptured marked individuals Example: pond turtles 1992: 18 1993: 34 (12) 1994: 30 (18)

Estimation of Population Size
Example: pond turtles 1992: 18 1993: 34 (12) 1994: 30 (18) : N = 18(34) = 51 turtles 12 _________________________________________ : N = 34(30) = 56.7 turtles 18 So: = = 53.9 turtle estimation 2

Dispersion 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: trees around a lake or pond

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

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

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

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

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

K: Carrying Capacity 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 K Number of individuals (N) Time produces a S-shaped curve

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 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 (abiotic) whose occurrence is not affected by pop density. Increases death rate & decreases birth rate Affects depend on severity of the event Examples: 1. Earthquakes 2. Fires 3. Hurricanes 4. Freeze in the fall

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

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

Survivorship 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)

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 until old age. K or r strategist? K % of survivors % of maximum life span Example? humans

Survivorship 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 span r Examples? turtles oysters frogs insects

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

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

Age Structure Post-reproductive Reproductive Pre-reproductive

Human 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.

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

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

Question: What are two ways the human population can reach Zero Population Growth? 1. Limit the # of offspring per couple a. Reduces family size b. Voluntary contraception c. Family planning 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