Biology unit 4 notes
- Created by: jaymini
- Created on: 09-06-13 15:04
Populations and ecosystems
Ecology- study of the inter relationships between organisms and their environment (living and non-living)
Biosphere- life supporting layer of land, air and water that surround the Earth
Ecosystem
Self-contained functional units
Two main processes to consider: the flow of energy through the system and the cycling of elements within the system
Within each ecosystem there are a number of species which are made up of many groups that make up a population
Population
Group of interbreeding organisms of one species in a habitat
Populations of different species form a community
Community
All the populations of different organisms living and interacting in a particular place at the same time
Habitat
Place where a community of organisms lives
Many habitats within an ecosystem
Within each habitat there are smaller units each with their own microclimate= microhabitats
Ecological niche
How an organism fits into the environment- where it lives and what it does there
No two species occupy the same ecological niche
Investigating populations
Number of individuals in a given space= abundance
It would damage the habitat to sample a whole population so we use a sample representative of the whole
Quadrats
Need to consider:
Size of the quadrat to use- depends on size of plant or animals being counted and how they are distributed within the area
Number of sample quadrats to record within the study area- larger number of sample quadrats the more reliable the results but can be time consuming. Greater number of species the greater number of sample quadrats needed to give valid results
Position of each quadrat within the study area- to produce statistically significant results random sampling must be used
Random sampling
Used to avoid bias data
To get truly random sampling we must lay out 2 long tape measures at 90° angle along two sides of study area, obtain coordinates by using a random number generator and place quadrat at intersection of each pair of coordinates and record data
Systematic sampling along transect
More informative to measure abundance and distribution of a species in a systematic way
Line transect- a piece of string or tape is used and anything that passes the line is recorded
Belt transect- ***** usually a metre wide which is marked using a second line parallel to the first and anything between the two is recorded
Measuring abundance
Random sampling is used to obtain measures of abundance
Measured using:
Frequency- likelihood of a particular species occurring in a quadrat used when counting in grass where it is difficult to accurately measure
Percentage cover- estimate the area within a quadrat that a plant covers
Mark-release-recapture technique
Used to measure the abundance of animals in a population
Known number are caught, marked in some way, and then released back into the community and sometime later a given number are recaptured randomly and the number marked is recorded.
Population size = Number of animals marked X total caught second time
Number of marked animals caught second time
Relies on…
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