Population ecology
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Population ecology






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

Population ecology Population ecology Presentation Transcript

  • Population Ecology Grade: 11 By: T G TsoTeTsi
  • What is population ecology? -Science that deals with measuring changes in population size and composition -Identify the factors that cause the changes
  • 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.
  • Why is it important for scientist to describe natural populations?
  • • To assess the health of population • To determine the endangered or threatened status •To predict the population dynamics
  • 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
  • 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
  • Population Dynamics •Characteristics of Dynamics •Size •Density •Dispersal •Immigration •Emigration •Births •Deaths •Survivorship
  • • 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
  • 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
  • • Measuring density of populations is a difficult task. – We can count individuals; we can estimate population numbers.
  • 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.
  • 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
  • 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
  • Clumped Dispersion
  • 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
  • Uniform Dispersion
  • 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)
  • Random Dispersion
  • SIZE
  • Changes in a Population • 3 factors determine population changes –births –deaths –migration • immigration • emigration
  • 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
  • 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
  • Population growth can be describe by using a growth curves.
  • • 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.
  • Exponential growth • The growth rate is always positive • NO upper limit to population size
  • 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
  • • 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
  • 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
  • Factors influencing population density Population density can be affected by the interaction of density-dependent factors and density-independent factors
  • Density-Dependent Factors • limiting resources (e.g., food & shelter) • production of toxic wastes • infectious diseases • predation • stress • emigration
  • Density-Independent Factors • Severe storms and flooding • Sudden unpredictable severe cold spells • Earthquakes and volcanoes • Catastrophic meteorite impacts
  • 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