Ch.15 Notes

Population / Consists of all the individuals of a species that live together in one place at one time.
Examples: all the alligators living in the Everglades this year
Demography / Study of human population size and the factors that influence it
Example: largest demographic study in the US is the census
Demographer / Scientists who studies human populations
Population size / determined by births, deaths, immigration, emigration and limiting factors (biotic and abiotic) that determine carrying capacity
Emigration / Moving away
Immigration / Moving into
Why are small populations more likely to become extinct? / Can be wiped out by one disaster
Difficulty in finding a mate
Inbreeding creates a genetically uniform population that is more susceptible to disease and less able to adapt
Example: Cheetahs, Florida panthers
Population density / Number of individuals that live in a given space
Example: 5 individuals per acre
Dispersion (list the 3 types) / The way individuals are arranged (distributed) in space
  1. random distribution;
least common (example:
many plants)
  1. even distribution (example:
predators have territories)
  1. clumped distribution;
most common (example:
grazing animals, plants near
a river, nesting sites)
Population model / Researchers try to predict how a population will grow by making a model of the population, considering growth rate and resources
Growth rate of a population / The difference between the birth rate and the death rate Can be fast, slow, zero, or declining (negative growth)

Drawing of population curves:

No growth Rapid growth Slow growth Negative growth

Population increases Population decreases

Reproductive potential / The maximum number of offspring an individual can produce
Exponential growth curve (draw one into your notes) / The rate of population growth if there are no limits to growth
Is rare in nature (example: humans since the 20th century)

Logistic growth curve (once carrying capacity is reached, the population size only varies slightly) /
Carrying capacity / The population size that an environment can sustain. Growth stops once carrying capacity is reached.
Limits on carrying capacity / Density dependent and density-independent factors
Density-dependent limiting factors / Resources that become depleted as a population grows and reduce or stop population growth: food, water, hiding and nesting spaces, over-accumulation of waste, competition, predation, human-made environmental problems
Example: If the carrying capacity for the field outside of our school grounds is 8, then adding 8 more bulls would cause starvation and over-accumulation of waste
Density-independent limiting factors / Environmental conditions that limit growth:
Natural disasters (fires, floods, freezing, storms)
Affect all living organisms in a certain environment no matter whether the populations are dense or sparse
Example: I have two ponds, one with 10 fish and one with 100 fish. If the ponds freeze, the fish in both lakes will die, not just the fish in the more densely populated lake.
Predator-prey relationship / The population of predators is limited by the population of prey. The population of prey is limited by the population of predators.

How is the growth rate of a population different below and above carrying capacity? / The growth rate is exponential until carrying capacity is reached, then it plateaus until the carrying capacity changes. The plateau is not a straight line, rather it varies slightly while the population adjusts to environmental conditions
Change in carrying capacity
can occur with new environmental conditions, such as new predators, change in plant populations, man-made conditions /
K-Strategist / Organisms that live in stable environments. Species characterized by slow maturation, few young, slow population growth, reproduction late in life, care for their young
Example: tiger, whale
R-Strategists / Organisms that live in rapidly changing environments; characterized by rapid growth, high fertility, short life span
Example: roaches
Population crash / Dramatic decline in the size of a population over a short period oftime

Activities

  1. Draw an exponential growth curve. Label both the x- and the y-axis.
  2. Describe the curve (how is growth at the beginning versus the middle and the end)
  3. What causes a population to grow exponentially?
  4. Draw a logistic growth curve for an imaginary population of mice.
  5. On this logistic growth curve, draw a new line for what happens to the population of mice after 10 wolves have been introduced into the environment.
  6. What type of organisms tend to organize themselves into even distributions?
  7. Draw a population pyramid for a human population that is growing rapidly.

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