1.2: Understanding characteristics of populations Flashcards
(32 cards)
Why did the number of monarchs declined?
due to the logging in Mexico
use of pesticide
loss of breeding habitat in eastern North America
Define population
Is a group of individual organisms of the same species that live together in the same geographic area.
Biologists describe populations in two ways:
Population density
Population dispersion
What does a population density describe?
It describes how many individuals are there in a given area
What does a population dispersion describe?
It describes how the individuals are distributed over the area
Define a population density
number of individuals per unit area
Formula for population density
D= N/S (N= number of individuals; S= space occupied)
What is a crude density? How is it helpful?
Its a simple measure of density and is helpful if the entire habitat included in the calculation is useable habitat for population.
Define ecological space (Se)
The size of the area that is actually usable by a species
Function for ecological density
De = N/Se
Why does clumped dispersion occur in animals?
- protection
- exploitation of a resource
Why does clumped dispersion occur in plants?
because of asexual reproduction
When does uniform dispersion occur in animals?
- defending a small territory
When does uniform dispersion occur in plants?
when a plant is using all of its resources around it
When does random dispersion occur?
When individuals are not affected by each other
Where does random dispersion occur in plants
rainforest trees and microscopic marine organisms for example algae
Several sampling methods can be used depending on:
how large the population is
the way that it is dispersed
how difficult it is to see
What is Quadrat sampling used for?
is used for counting abundant organisms, like plants, or organisms living beneath the soil, like earthworms, that do not move much and can easily be seen.
Quadrat sampling steps
- An area in which a population is being studied is mapped out.
- A grid is drawn over the map.
- Grid squares within the mapped area are chosen at random to be sampled.
- The actual sampling area on the ground is defined using a square made of wooden sticks or plastic pipes, called a quadrat. In surveys of small plants, or soil-inhabiting organisms like worms, the quadrat is usually 1m2 in size.
Calculating the average value per quadrat
- First, all of the individuals found within a quadrat are counted.
- This process is repeated several times over the grid.
- The counts within each quadrat are summed up and the average value per quadrat is calculated.
- Because the locations of the quadrats are chosen at random, the average count per quadrat should give a good estimate of the average count per square meter for the entire area.
Average count per quadrat
Average count per quadrat= Total of milkweed Individuals in all quadrants/Number of quadrats
Describe the limitations of Quadrat Sampling method
- the quadrats sampled are representative of the area; if not, then the estimate may be either too high or too low.
- the organism has a heavily clumped dispersion; if so, the quadrats may have missed the clumps just by chance, making the population estimate too low. Or, too many clumps may have been sampled just by chance, and so the estimate will be too high. Taking more samples will help limit the chances that clumps are either overlooked or overrepresented in the study.
Mark and recapture sampling procedure
- To estimate population size, a sample of individuals is taken from the population and marked in some way.
- Marked individuals are then returned to the population.
- After a short time, a second sample is taken.
- The ratio of the number of marked individuals in the second sample (called recaptures) to the unmarked ones gives an estimate of population size.
Thus the mark and recapture formula to estimate the population size is:
Total Population (N)= Total # marked (M) x Size of second sample (n)/ # of recaptures (m)
