Measuring Populations Flashcards
What is a population?
A group of individuals of the same species living in a particular area at the same time.
What are three ways we can measure populations?
Using quadrants, transects and capture-recapture.
What types of organisms do each population measuring techniques measure?
- Quadrats and transects are used for sessile or slow-moving organisms.
- Capture-recapture are used for fast-moving organisms.
How are quadrats used?
A quadrat is a frame that is placed onto the ground at random throughout the study area, the number of species in the qudrat is recorded.
How are quadrants used to estimate population size and density?
- Population size (no. of individuals) = no. of individuals in selected quads/no. of selected quads x total no. of quads.
- Population density (no. of individuals per square meter) = population size/area x total no. of quads.
What are the advantages and disadvantages of using quadrants to measure populations?
Advantages:
- Inexpensive
- Easiest method and uses the least amount of time and energy.
- Minimal disturbance to the environment (ethical).
Disadvantages:
- Not accurate (depends on chance)
- Only used for sessile/slow moving organisms.
How are transects used?
- Plan and profile sketches.
- A line or rope you move along and record which species are located at each point.
What are the advantages and disadvantages of using transects to measure populations?
Advantages:
- Minimal disturbance to the environment (ethical).
- Broad view of community land use.
- Can be used on any area
- Can be used to illustrate a particular gradient or linear pattern along which species of plants and animals are living.
Disadvantages:
- Not accurate (only short distances)
- Line can be interfered with
- Cannot be used for a large abundance of plants.
- Only used for sessile/slow moving organisms.
What are the 3 types of distribution?
Random, uniform and clumped.
What is random distribution?
Spaced irregularly, the location of one organism does not effect the location of another (more common for plants than animals).
What is uniform distribution?
Evenly spaced, the presence of one organism determines how close or distant another will be. Common in high density populations of organisms that set up breeding grounds.
What is clumped distribution?
A number of individuals grouped together and the groups make up the population. Can result from social behaviour e.g. schools of fish or mini habitats were the abiotic and biotic factors are favourable.
What are population pyramids used for?
They show the age distribution and sex ratios of populations.
What is important for future growth of populations?
Populations maintain a high level of reproduction aged individuals of both sexes and individuals below reproducing age.
Why is it important for populations to maintain a high level of reproduction aged individuals of both sexes and individuals below reproducing age?
For future growth, without individuals of reproducing age no more individuals can be born, which will decrease the chances of the population survival rate.
If there are no individuals of below reproducing age in a population, when the individuals who can reproduce now get older and can’t reproduce anymore, there will be no individuals to reproduce in the future and ensure growth of the population.
What is the formula for population growth rate (word and letters)?
Growth rate = (birth rate + immigration rate) - (death rate + emigration rate)
r = (b+i) - (d+e)
How is capture-recapture used?
- Select a population
- Do the first capture and mark individuals captured
- Release captured individuals
- Do the second capture after organisms have had time to recover
- Find the number of marked individuals in the second capture
- Release captured individuals.
What is capture-recapture used for?
Used to estimate the size of a mobile species.
How is population size estimated in capture-recapture?
No. of individuals in the first capture x no. of individuals in the second capture/no. of marked individual in the second capture.
What are the advantages and disadvantages of using capture-recapture to measure populations?
Advantages:
- Easy and simple
- Good for determining populations of animals
Disadvantages:
- Inconsistent (most inaccurate)
- Requires a large sample
- Only works for fast moving animals
- Cannot calculate diversity
- Disturbance to the environment
- Time consuming