Topic 7- estimating the size of a population Flashcards
What is sampling used to investigate?
the abundance and distribution of species and populations
What are the 2 types of sampling?
Random
Systematic
Give a benefit of random sampling
there will be no bias as it is completely random/ due to chance
What is systematic sampling?
the sampling points are chosen by the person carrying out the sampling
Give some disadvantages for systematic sampling/
- unrepresentative of the whole area
- may deliberately place the quadrats in areas with the least species as these will be easier and quicker to count
-a possibility that the person choosing could show bias towards or against certain areas
What are the 3 sampling methods?
Quadrats (for non-motile or slow-moving species)
Transects (for non-motile or slow-moving species)
Mark-release-recapture (for motile species)
Define distribution
how a species is spread throughout the ecosystem
Define abundance
the number of individuals of that species
How do you calculate the population size in mark release recapture
N = (n1 × n2) ÷ m2
Where:
N = population estimate
n1 = number of marked individuals released
n2 = number of individuals in the second sample (marked and unmarked)
m2 = number of marked individuals in the second sample
What are the assumptions of mark release recapture
The marked individuals are given sufficient time to disperse and mix back in fully with the main population
The marking doesn’t affect the survival rates of the marked individuals (e.g. doesn’t make them more visible and therefore more likely to be predated)
The marking remains visible throughout the sampling and doesn’t rub off
The population stays the same size during the study period (i.e. there are no significant changes in population size due to births, deaths or migrations into or out of the main population
