Environmental Studies Summary Life Sciences with diagrams (Biology) Life Sciences, ISBN: 9781776113316
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Course
Life Sciences
Institution
12
Book
Life Sciences
extensive and understandable population ecology notes summarized from textbook with additional notes from IEB life science examiner. Graphs and diagrams included. Also aesthetically pleasing :)
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ENVIRONMENTAL STUDIES
1. Population Ecology
Ecology = study of interactions of organisms with their physical and biological environments
Population ecology = concerned with fluctuations in population size and factors that regulate populations
POPULATION SIZE
- Population size = total no. of individuals in a population.
- Population density = no. of individuals of a population per unit area
POPULATION PARAMETERS
→ 4 main factors, known as parameters, effect population size:
o Natality
Birth rate
o Mortality
Death rate
o Immigration
One-way movement into an area
o Emigration
One-way movement out of an area
→ A population where immigration/emigration don’t occur = closed population
DETERMINING POPULATION SIZE
- Can be determined by direct or indirect method.
- Method is determined by:
• The size
• The mobility
DIRECT TECHNIQUES
- Involve the total count of all individuals in the populations
- Direct counting (census)
- Census methods include:
• Direct contact counting of humans.
• Direct counting from vehicle/helicopter.
• Counting from aerial photographs.
INDIRECT TECHNIQUES
- Includes counting only part of the population
- This count is used as a sample to estimate population by statistical calculation.
- It includes:
• Mark-recapture technique
• Quadrat technique
Mark-recapture technique
- A specific area is demarcated
- A no. of individuals are caught, counted and marked , and they are known as the 1st sample.
- The marked individuals are released into the environment.
- Sufficient time must be allowed for the marked individuals to mix with the rest of the population.
- Another group of individuals is caught and counted and they are known as the 2nd sample.
- The number of marked individuals in the 2nd sample are counted.
- This data is used to determine the estimated size of the population:
, 𝑚×𝑠
P=
𝑡
p = estimated population size
m = total number of animals captured and marked in 1st sample
s = total number of animals captured in 2nd sample
t = number of marked individuals in 2nd sample
▪ Population must be closed
▪ Time must be short enough that no births/deaths occur
Quadrats
- Quadrat = a square frame
- An area where organisms must be counted is demarcated and the surface area determined.
- The quadrat is placed on the ground in the demarcated area and the organisms concerned are
counted inside the frame i
- This is the no. of individuals per unit area
- This process is repeated a few times in diff. areas of the demarcated area by placing the quadrat
randomly of the ground.
- The average no. of individuals per quadrat is calculated.
- The total number of individuals in the population is determined using the following formula.
POPULATION GROWTH FORMS
- Populations have distinctive growth patterns (population growth forms)
- Two growth forms are distinguished:
▪ Geometric J-shaped growth form
▪ Logistic or S-shaped (sigmoid) growth form
Geometric (J-shaped) growth form
- A population can result its full reproductive potential when it has unlimited resources such as food, water
and space and no predators.
- These ideal environmental conditions result in the maximum possible growth rate and population figures
increase rapidly.
- This type of growth is called geometric or exponential growth.
Example
→ If a population of bacteria in an environment has sufficient food and oxygen as well as the ideal
temperature, the bacteria will increase rapidly.
→ If the no. of bacteria in the population is recorded over a period of 14 days and the data represented
as a line graph, it will form a curve.
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