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Population and community ecology

Population and community ecology. Population ecology. Terminology. Species Habitat Population Community Ecosystem Ecology Ecological niche. Size of a population. Definition and impact on population size: Natality Mortality Dispersal (including immigration, emigration and migration)

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Population and community ecology

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  1. Population and community ecology Population ecology J Gerber and J Goliath

  2. Terminology • Species • Habitat • Population • Community • Ecosystem • Ecology • Ecological niche J Gerber and J Goliath

  3. Size of a population Definition and impact on population size: • Natality • Mortality • Dispersal (including immigration, emigration and migration) Aspects of population fluctuation and regulation: • Carrying capacity • Environmental resistance/limiting factors and its impact on population growth • The effect of annual and seasonal fluctuations on population size J Gerber and J Goliath

  4. Size of a population Characteristics of the following growth patterns/forms: • Geometric growth form (J-shaped curve) • Logistic growth form (S-shaped curve) Methods to determine population size, demographics and population movements: • Direct technique (census) • Indirect technique – simple sampling and mark recapture J Gerber and J Goliath

  5. Activity 1- Terminology Instructions Explanation of activity on terminology. In pairs/groups define the terms on the work sheet given. After 10 minutes each pair/group give feedback. J Gerber and J Goliath

  6. Terminology • Species – Group of organisms with similar characteristicswhich can interbreed to produce fertile offspring  • Habitat – Specific type of environment (area) in which a plant or animal species normally occur • Population – Group of organisms of the same speciesthat occur in a particular areain a particular time so that interbreeding occurs J Gerber and J Goliath

  7. Terminology • Community – Group of populations  occurring in a particular area e.g. lion, zebra and giraffe in a National Park. • Ecosystem – Interaction between the biotic factors  and abiotic factors in a particular area  • Ecology – Study of mutual interaction among living organisms and environment in which they live J Gerber and J Goliath

  8. Terminology • Ecological niche – Each species has a specific role in a community. Each species needs a particular set  of environmental conditions and resources to survive and reproduce in its habitat  J Gerber and J Goliath

  9. Size of a population & population density • Size of a population – the number of individuals  in a population  • Population density – the number of individuals  of the population per unit of area  J Gerber and J Goliath

  10. Population parameters • Natality – birth rate  of a population expressed as the number of live births per thousand individuals  per year. • Mortality – death rate of a population expressed as the number of deaths per thousand individuals  per year. • Immigration – one-way movement of organisms into an area  • Emigration – one-way movement of organisms out of an area  • Migration – moves from one place to another and returns to the original place  J Gerber and J Goliath

  11. Impact of population parameters • Natality and immigration cause an increase in population size. • Mortality and emigration cause a decrease in a population size. • No immigration or emigration in a closed population e.g animals on an island. • Natality and mortality can affect the population size in a closed population. J Gerber and J Goliath

  12. Impact of population parameters J Gerber and J Goliath

  13. Population fluctuation and regulation • Carrying capacity – maximum number of individuals of a species that an ecosystem can continually supply resources to. • Certain factors prevent a population from unlimited growth and exceeding its maximum growth rate – limiting factors and together are called environmental resistance. • Seasonal fluctuations – Swallows fly from the cold European winter to Southern Africa where the summer temperature is more favourable. • Annual fluctuation – Migration of millions of wildebeest in East Africa. This phenomen is determined by the availability of grazing which is also dependant on rainfall. J Gerber and J Goliath

  14. Growth patterns/forms – Geometric or J – shaped curve • Population size increases unrestricted and rapidly with time. • A population can reach its full reproductive potential because of enough food, water and no predators. • Environmental resistance increases when numbers of population increase. • Number of population can decrease rapidly due to limiting factors. J Gerber and J Goliath

  15. Graph of repeated growth pattern J Gerber and J Goliath

  16. Logistic growth form (S - shaped) Lag phase: • Population acclimates, individuals become sexually mature and seek partners for mating. Accelerating growth phase • Population grows rapidly and reaches its maximum growth rate. Deceleration growth phase • Growth rate decreases due to an increase in environmental resistance. Equilibrium phase • Population numbers reach the carrying capacity. J Gerber and J Goliath

  17. Geometric and logistic growth phase J Gerber and J Goliath

  18. Methods to determine population size - direct technique (census) • Count of all individuals in a population and includes human population census. • Aerial photography may be used in the counting of larger animals in nature reserves. J Gerber and J Goliath

  19. Indirect technique – simple sampling (quadrated method) • A square frame (quadrat) is used • Place it on the ground and count the individuals inside the quadrat • It gives the number of individuals (density) per unit area • Repeat in different places at random and calculate the average density • Method is used for plants and slow moving animals J Gerber and J Goliath

  20. Mark-recapture technique (Peterson) • Demarcate a specific area. • Capture a number of individuals, count and mark them (first sample). • Set the marked individuals free in the area. • Allow the marked individuals enough time to mix with unmarked individuals in the area. • Capture a second number of individuals and count them (second sample). • Count the number of previously marked individuals in the second sample. J Gerber and J Goliath

  21. Mark-recapture technique • Use this information to calculate the total size of the population by means of the following formula: P = m x s t • P = estimated population size. • m = total number of animals captured and marked in first sample. • s = total number of animals captured in second sample. • t = number of marked individuals in second sample. J Gerber and J Goliath

  22. Mark-recapture technique - validity • Marking methods should not injured the organism. • Marks should be clear for the duration of the investigation. • Marking methods should not affect the movement of the animals. • Marked organisms should be allowed enough time to mix. • Population must be closed. • Period between two samplings should be sufficiently brief – no births or deaths. J Gerber and J Goliath

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