Comprehensive summarized notes for the Environmental Studies section on Population and Community Ecology in the IEB syllabus. These notes include detailed graphs, essential terminology, and in-depth explanations, providing a robust resource for mastering key concepts. Ideal for students seeking to ...
COMMUNITY ECOLOGY
→ Individual: a single organism that forms part of a species.
→ Ecology: study of interactions of organisms with their physical and biological environments.
→ Population: an interbreeding group of individuals of a single species that occupy the same general
area and produce fertile offspring.
→ Community: the assemblage of interacting populations that inhabit the same area.
→ Ecosystem: comprised of 1 or more communities and the abiotic environment within an area.
→ Environment: the external factors, living (biotic) and non-living (abiotic) surrounding and organisms
and influencing its development and survival.
→ Habitat: the specific environment (home) in which a plant or animal species usually occurs.
→ Population size: total number of individuals in a population.
→ Population density: number of individuals per unit area.
FACTORS THAT AFFECT FUTURE POPULATION GROWTH:
Immigration (into) (movement of
organisms into an area)
+
+ -
Natality (birth rate) population Mortality (death rate)
-
Emigration (exit) (movement of
organisms out of an area)
Determining Population Size:
DIRECT TECHNIQUES: INDIRECT TECHNIQUES:
→ Counting all the individuals in a → Only part of the population is counted.
population. Also known as a census. → This tally /count is used as a sample to
→ Direct contact counting of smaller- determine the total estimated population
sized organisms or humans. size by means of statistical calculations.
→ Direct counting from → Choosing a method:
vehicle/helicopter/plane of larger 1. mobile organisms → mark and
organisms. recapture method
→ Counting from aerial photographs 2. sessile organisms → quadrat method
taken of larger moving organisms. 3. group organisms → sampling
→ Challenge: counting all the individuals
before they have time to re-distribute.
, POPULATION AND
ENVIRONMENTAL STUDIES
COMMUNITY ECOLOGY
Mark and recapture method:
𝒎 𝒙 𝒔
P= PRECAUTIONS TO TAKE WITH
𝒕 MARK & RECAPTURE METHOD:
→ The technique is only valid under the following
→ P = estimated population size. conditions:
→ m = total number of animals captured and The marking methods should not injures or damage
marked in 1st sample. the organism.
→ s = total number of animals captured in the The marks should be clearly visible for the duration
2nd sample. of the investigation.
→ t = number of marked individuals in the 2nd The marking methods should not affect the
sample. movement or behaviour of the organisms (chances
to be captured again should remain the same).
→ The estimate obtained from the mark & Marked organisms should be allowed enough time
recapture methods can be made more to mix with the rest of the population before the
accurate by repeating the sampling a few next sample is taken.
times and calculating an The population must be closed, so no immigration
average population size. or emigration takes
place.
The period between the two samplings should be
sufficiently brief, so that not births or deaths occur.
Quadrants:
total surface area
Population size = ave. no. of individuals /quadrat x
area of the quadrant
THE RELIABILITY OF THE TECHNIQUE DEPENDS ON THE FOLLOWING:
→ The exact number of organisms in each quadrat must be known.
→ The surface area and shape of the quadrat must be constant and must be known.
→ The surface area of the demarcated area must be known.
→ The quadrat must be placed randomly in the demarcated area.
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