Population ecology


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  • Unfortunately, it is usually impractical to attempt to count individuals in a population.
    One sampling technique that researchers use is known as the mark-recapture method.
    Individuals are trapped, captured, tagged, recorded, and then released.
  • Population ecology

    1. 1. Population Ecology Grade: 11 By: T G TsoTeTsi
    2. 2. What is population ecology? -Science that deals with measuring changes in population size and composition -Identify the factors that cause the changes
    3. 3. Studying Populations • A population consists of all the individuals of a species in a given area. • Population structure describes the age distribution of individuals, and how those individuals are spread over the environment.
    4. 4. Why is it important for scientist to describe natural populations?
    5. 5. • To assess the health of population • To determine the endangered or threatened status •To predict the population dynamics
    6. 6. What is population ? A group of individual of the same species of organisms that occupy the same area, using the same resources and acted upon by the same environmental factors
    7. 7. Population dynamics • Study how and why population size changes over time • Study the factors affecting growth, stability and decline of populations (birth rate, mortality, survivorship, migration) • All populations undergo 3 phases in life cycle : - growth, stability, decline
    8. 8. Population Dynamics •Characteristics of Dynamics •Size •Density •Dispersal •Immigration •Emigration •Births •Deaths •Survivorship
    9. 9. • Populations have size and geographical boundaries. – The density of a population is measured as the number of individuals per unit area. – The dispersion of a population is the pattern of spacing among individuals within the geographic boundaries – The size of a population The characteristics of populations are shaped by the interactions between individuals and their environment
    10. 10. DENSITY
    11. 11. MEASURING DENSITY Density Number of individuals per unit of area at a given time • Expressed in terms of items or organisms per unit area • For example: the number of paddy plants per square meter of a paddy field • Population density varies due to limiting factors
    12. 12. • Measuring density of populations is a difficult task. – We can count individuals; we can estimate population numbers.
    13. 13. Mark and recapture method One way to estimate the size of a population is to capture and mark individuals from the population, release them, and then resample to see what fraction of individuals carry marks.
    14. 14. DISPERSION
    15. 15. Three general patterns:Three general patterns: clumping, uniformclumping, uniform distribution, and random dispersiondistribution, and random dispersion Most species live in clumps or groupsMost species live in clumps or groups.. Population DistributionPopulation Distribution
    17. 17. Clumped dispersion • Also known as aggregated distribution • Individuals aggregate in patches • Caused by : environment where the resources concentrated in patches • Other factors : mating, limited seed dispersal • Importance : for protection, reducing competition, increasing feeding efficiencies
    18. 18. Clumped Dispersion
    19. 19. Uniform dispersion • Pattern of equally spaced individuals • Caused by the ability to survive anywhere in the habitat • Used the resources found immediately around them • Importance : able to set up the zone of territories for feeding, nesting, breeding
    20. 20. Uniform Dispersion
    21. 21. Random dispersion • Spacing pattern based on total unpredictability • Individual in a population are spaced all over an area in a way that in unrelated to the presence of others • Caused by the ability to live anywhere in a given area except, they are limited to grow wherever they are first set root (for plants)
    22. 22. Random Dispersion
    23. 23. SIZE
    24. 24. Changes in a Population • 3 factors determine population changes –births –deaths –migration • immigration • emigration
    25. 25. Continues… Population of organism able to change over time Increase in population size usually due to natality (birth rate) Decrease in population size as a result of mortality
    26. 26. Determining the rate of changes in population. • Changes in time must taken into thought ΔN / Δt = N (b-d) Δ = change in equations N = number of individuals t = time b =natality d = mortality
    28. 28. Population growth can be describe by using a growth curves.
    29. 29. • Logistic growth: Exponential growth when resources are unlimited and slowed growth as species approach carrying capacity of environment. – Growth curve called an S-curve because of its shape. • Environmental resistance: factors that tend to reduce population growth rates.
    30. 30. Exponential growth • The growth rate is always positive • NO upper limit to population size
    31. 31. Exponential growth curve • Mode of population that assume birth rate and death rate remain constant over time • Describing an idealized population in an unlimited population • Ignoring immigration and emigration • The result in exponential growth is that if b > d, r > 0
    32. 32. • Typically, unlimited resources are rare. –Population growth is therefore regulated by carrying capacity (K), which is the maximum stable population size a particular environment can support. The logistic model of population growth incorporates the concept of carrying capacity
    33. 33. LOGISTIC GROWTH RATE Assumes that the rate of population growth slows as the population size approaches carrying capacity, leveling to a constant level. S-shaped curve CARRYING CAPACITY The maximum sustainable population a particular environment can support over a long period of time. POPULATION GROWTH RATE
    34. 34. Factors influencing population density Population density can be affected by the interaction of density-dependent factors and density-independent factors
    35. 35. Density-Dependent Factors • limiting resources (e.g., food & shelter) • production of toxic wastes • infectious diseases • predation • stress • emigration
    36. 36. Density-Independent Factors • Severe storms and flooding • Sudden unpredictable severe cold spells • Earthquakes and volcanoes • Catastrophic meteorite impacts
    37. 37. List of reference Choudyhury. S. (2009). Population Ecology. Available from: http://www.slideshare.net/Shohail/population-ecology-1968004?v=default&b=&from_search=1 Pointer. K. (2011). Community Ecology: Populations. Available from: http ://www.slideshare.net/coachpointer/population-ecology-9976847? v=default&b=&from_search=2 Tnewberry. (2008). Ecology 1: Population Ecology. Available from: http://www.slideshare.net/tnewberry/population-ecology-514438? v=default&b=&from_search=3 Sojhk. (2010). Population Ecology. Available from: http://www.slideshare.net/sojhk/chapter-54-4835841 Faranany. (2013). Population Ecology. Available from: http://www.slideshare.net/faranany/population-ecology-16591693