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Population Cycle

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 Cycle

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  1. Population Cycle H. Biology

  2. 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

  3. 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

  4. 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

  5. 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)

  6. Size depends on… Growth Rate: Birth Rate – Death Rate = Rate of natural increase (b - d = r)

  7. Density • Population density = number of individuals / unit of area • Dp=N/s

  8. 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

  9. Population Density (Growth) • Immigration and births cause an INCREASE in population • Emigration and death cause a DECREASE in population

  10. Dispersion clumped even (uniform) random

  11. 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.

  12. 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

  13. 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

  14. 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

  15. Population curves Exponential Growth (J-shaped) Logistic (S-shaped)

  16. 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

  17. Density-dependent limiting factors • Factors that are affected by the number of individuals in a given area • Include: • Competition • Predation • Parasitism/disease

  18. 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)

  19. 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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