INVESTIGATION Flashcards
We can measure the biotic factors in 5 ways
Abundance of population: counting the number of organisms in the sample
Richness of population: number of different species found in a sample
Diversity of population: Simpson Diversity index which takes into account the richness and abundance
Growth of population: comparison of growth with between species
Biomass of population: used when studying productivity of an organism
Abundance of the population
Frequency: the likelihood of the species occurring in a quadrat
Percentage Cover: Estimate of the area within a quadrat that a species covers
How Percentage Cover of an organism of an area may be measured
Use of quadrats that are randomly placed
Use a large number of quadrats so as to reduce sampling error
Estimate percentage of area covered by organism (by counting all the squares occupies by the species)
Why Percentage Cover is better to use than Frequency
Frequency is too large
Plants are too small
How you would decide the number of quadrats to use
Take enough to carry out a statistical test
Take into consideration the amount of time you have to carry out the investigation
Take a large enough number to make results reliable
Ensure unnecessary extra quadrats are not placed
What size the quadrat should be
Depends on size of animal
If a species occurs in a series of groups in an area, then use a large number of small quadrats to give representative data
Purpose of a Chi-Squared test
To compare different numbers collected from the two sites and show whether the differences are significant enough to confirm or reject the null hypothesis
RANDOM SAMPLING
Divide study area into grid of numbered line
Using random numbers, from a table or generated by computer, obtain a series of coordinates
Take samples at the intersection of each coordinates of number of individuals and number of species
Repeat many times and take a mean
How Mark-Release-Recapture can be used to estimate the number of a population that is MOBILE
Capture sample, mark and release
The harming must not harm the animal, (mention method of marking)
Take second sample and count marked organisms
Use the LINCOLN INDEX which is (Number in sample 1 x Number in sample 2) ÷ Number marked in sample 2
Things to ensure when using Mark-Release-Recapture
Animals are not harmed
Animals must not be made less mobile or more visible to predators due to the mark; one way to do this is to mark the animal using an ultra-violet marking pen which can only be seen under ultra-violet light
Leave enough time for the marked individuals to redistribute themselves and mix with the population
Ensure it is not breeding season of the animal, as breeding season increases the population size
The mark must not be rubbed of or lost during investigation
The population has a definite boundary so there is no migration
The proportion of marked to unmarked in second sample is the same as the proportion of this in whole population
Sampling method is the same
Why population size may change during a year
Breeding Availability of food source Predator presence Variation in disease Temperature variation Availability of water
Precautions and ethical considerations when doing field work
Only work in places where risk of falling in water is small
Only work in places where risk of pollution is small
Ensure cuts and broken skin are covered
Ensure all participants wash hands afterwards
Ensure not to disrupt the food chain of the environment
Predation can help other species
Predator eats a specific species
The other species has less competition and therefore can now increase percentage survival rate
Although predators reduce population size of prey, they actually increase mean mass of prey
Predators kill prey therefore reducing prey population size
Therefore less competition between prey population
More food available
Therefore more food eaten by a single prey than would be eaten before presence of predator
Therefore preys may be small in number but each one will be fatter than usual
Population Growth
Lag Phase; small number of individuals reproduce slowly
Rapid Growth Phase; increasing number of individuals reproducing
Stable Phase; population GROWTH declines and population size remains stable
Carrying Capacity is established
(Births + Immigration)-(deaths + emigration)
