4.3 Populations, Ecosystems and Succession Flashcards
What is a community?
All the populations of different species in a habitat at the same time
What is a population?
The number of all the organisms of one species in a habitat
What is a niche?
An organisms niche is governed by its abiotic requirements and position in the food web; how the organism fits into an ecosystem
No two species occupy the same ecological niche
Why take a large number of samples?
Ensures the samples are representative of the population
Why take random samples?
To prevent bias
How do we use quadrats?
Used to sample plants or slow moving animals. Placed on ground and count species abundance.
How do we measure abundance of an organism?
The frequency can be calculated and working out the mean density. (total number of individuals//no of quadrats x area)
The percentage cover can be estimated by eye, useful for plants that form clumps.
How do we make sure sampling of quadrats is random?
Divide the study area into a grid. Calculate random numbers/co-ordinates to generate where we will put the quadrats. Place them at the intersection of each pair of co-ordinates and the number is recorded.
How do we use a transect?
Used in changing areas eg; sand dunes.
A tape is run along the ground in a straight line. Quadrats are placed at regular intervals and the species are counted.
What is mark-release-recapture?
We capture a representative sample of organisms, record the number and mark them accordingly.
Release them into the general population.
Collect a second sample at a later stage.
How do we estimate total population size from mark-release-recapture?
(Number captured and marked in first sample x Number captured in second sample)
_______________
Number captured in second sample that are marked
What assumptions must we make about the mark-release-recapture calculations?
Organisms mix randomly
Time must elapse to allow random mixing
Organisms disperse evenly
Changes of population size are not important
Marking doesn’t hinder movement/predation
