Population and Community Ecology. Complexity POPULATION ECOLOGY.
Population and community ecology Population ecology J Gerber and J Goliath 1.
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Transcript of Population and community ecology Population ecology J Gerber and J Goliath 1.
Population and community ecology
Population ecology
J Gerber and J Goliath1
Terminology
Species Habitat Population Community Ecosystem Ecology Ecological niche
J Gerber and J Goliath2
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 Goliath3
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 Goliath4
Activity 1- Terminology
InstructionsExplanation of activity on terminology.In pairs/groups define the terms on the work
sheet given.After 10 minutes each pair/group give
feedback.
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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
speciesthat occur in a particular areain a
particular time so that interbreeding occurs
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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
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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
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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
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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
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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.
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Impact of population parameters
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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.
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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.
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Graph of repeated growth pattern
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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.
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Geometric and logistic growth phase
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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.
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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
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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.
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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.
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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.
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