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Population Cycle - PowerPoint PPT Presentation


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Population Cycle. H. Biology. Population Ecology. Population ecology = study of populations in an environment, including environmental influences on density and distribution, age structure, and population size

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Population Ecology

Population ecology = study of populations in an environment, including environmental influences on density and distribution, age structure, and population size

Population = group of same individuals of a single species living in the same general area at the same time and can interbreed

populations
Populations
  • Three key features of populations:
    • Size – number of individuals in an area
    • Density – measurement of population per unit area or unit volume
    • Dispersion - describes their spacing relative to each other
      • Clumped, even/uniform, random
measuring density
Measuring Density
  • Population Density = individuals

unit area

  • Unit area= length x width

Ex: What is the density of trees in 1 km2 in there are 1000 trees in 50 km2?

1000 trees = 20 trees

50 km2 km2

factors that affect populations
Factors that Affect Populations
  • Available resources (ex. food, water, shelter)
  • Activities of other organisms (ex. predators, disease-causing parasites)
  • Organism's own characteristics (ex. gestation period, number of young produced, nurturing of young, migratory)
  • Time of day or year (ex. tides, seasons, nocturnal or diurnal)
  • Weather (ex. amount of rainfall, cyclone, drought)
size depends on
Size depends on…

Growth Rate:

Birth Rate – Death Rate = Rate of natural increase (b - d = r)

density
Density
  • Population density = number of individuals / unit of area
    • Dp=N/s
density1
Density
  • Density is affected by…

1. Immigration- movement of individuals into a population

2. Emigration- movement of individuals out of a population

3. Density-dependent factors- Bioticfactors in the environment that have an increasing effect as population size increases

  - Ex. Disease, competition, parasites

4. Density-independent factors-Abioticfactors in the environment that affect populations regardless of their density

- Ex. Temperature, storms, habitat destruction,

drought

population density growth
Population Density (Growth)
  • Immigration and births cause an INCREASE in population
  • Emigration and death cause a DECREASE in population
dispersion
Dispersion

clumped

even (uniform)

random

what is dispersion
What is Dispersion?
  • Clumped Dispersion
    • Populations found in tight clusters, dispersed across a large landscape.
    • In between very few to no individuals are usually found.
    • Grouped possibly for protection or survival
  • Random Dispersion
    • Populations found randomly about their habitat.
    • In immobile species, this is usually caused by their ability to live anywhere in a given habitat, except, they are limited to growing wherever they are first set root.
    • In motile populations, individuals are able to move about their habitat, so that at any given instance, they can be found anywhere about their environment.
  • Uniform Dispersion
    • Populations found evenly distributed about their habitat.
    • This is generally caused by a species ability to survive anywhere in their habitat - they use the resources found immediately around them, and spread out as to use all of the available resources.
population growth
Population Growth
  • Exponential Growth =
    • population grows as if there are no limitations to how large it can get (biotic potential)
    • J-curve
    • A population increases slowly at first (the "lag phase") and then grows increasingly rapidly with time ("log phase”)
    • IN NATURE, NOT LIKELY…
    • Ex: HUMAN POPULATION, ELEPHANTS
what are other factors that affect population growth
What are Other Factors That Affect Population Growth?

Limiting factor-any biotic or abiotic factor that restricts the existence of organisms in a specific environment.

EX.- Amount of water, Amount of food, Temperature

carrying capacity
Carrying Capacity
  • Carrying Capacity - the maximum population size that can be supported by the available resources
    • There can only be as many organisms as the environmental resources can support
population curves
Population curves

Exponential Growth (J-shaped)

Logistic (S-shaped)

factors that affect the carrying capacity
Factors That Affect the Carrying Capacity
  • Limiting Factor - any biotic or abiotic factor that restricts the existence of organisms in a specific environment

- Ex: Amount of water, Amount of food, Temperature

  • Two types:
  • Density-dependent limiting factor
  • Density-independent limiting factor
density dependent limiting factors
Density-dependent limiting factors
  • Factors that are affected by the number of individuals in a given area
  • Include:
    • Competition
    • Predation
    • Parasitism/disease
density independent limiting factors
Density-independent limiting factors
  • Aspects of the environment that limit a population’s growth regardless of population density
  • Include:
    • Unusual weather
    • Natural disasters
    • Human activities (chopping down a forest)
limiting factors control population sizes
Limiting Factors Control Population Sizes
  • Density-dependent factors come into play when population approaches and/or passes the carrying capacity
    • Food supplies, waste, population-crowding diseases, H2O, mates, predators
  • Density-independent factors have nothing to do with the population size
    • THINK: NATURE
    • Floods, droughts, earthquakes, other natural disasters and weather conditions
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