Investigating populations and succession Flashcards
Describe the process of succession
- (Colonisation by) pioneer species;
- Pioneers cause change in environmental abiotic / biotic factors(give an example);
- Pioneers make the environment less hostile for new species;
- New species change/make conditions less suitable for previous species;
- Change/increase in diversity/biodiversity;
- Stability increases [population/richness/abiotic factors];
- Climax community;
Describe random sampling
[estimation of population density]
- Use a grid / split area into squares/sections;
- Method of obtaining random coordinates / numbers, e.g. calculator/computer/random numbers table/random number generator;
- Count number/frequency of plants in a quadrat;
- Large sample (20+ quadrats) AND Calculate mean/average number (per quadrat/section);
- Valid method of calculating total number of ……… e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in wood;
Describe systematic sampling
- Transect/lay line/tape measure (from one side of the dune to the other);
- Place quadrats at regular intervals along the line;
- Count plants/percentage cover/abundance scale (in quadrats) OR Count plants and record where they touch line/transect;
Describe how you would determine the mean percentage cover for beach grass on a sand dune.
- Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
- Large number/sample of quadrats; (min 20)
- Divide total percentage by number of quadrats/samples/readings;
Describe the mark, release, recapture technique
- Capture sample, mark and release;
- Appropriate method of marking suggested / method of marking does not harm fish;
- Take second sample and count marked organisms;
- No in No in Population =
No in sample1 × No in sample2
Number marked in sample2;
Describe how you would determine how many quadrats to use when investigating a habitat.
- Calculate running mean/description of running mean;
- When enough quadrats, this shows little change/levels out (if plotted as a graph);
- Enough to carry out a statistical test;
- A large number to make sure results are reliable;
- Need to make sure work can be carried out in the time available;
What is carrying capacity?
Carrying capacity is the maximum, equilibrium number of organisms of a particular species that can be supported indefinitely in each stable environment. birth rates and death rates are in equilibrium
what is a population?
A population is all the individuals of a given species living together in the same area at the same time
why do organisms have different niches?
so that it reduces competition between them
what is the difference between interspecific competition and intraspecific competition?
Interspecific - between different species
Intraspecific - between the same species
Two species do not occupy the same niche because…
- Different niches reduces competition between species (food, shelter, space)
- so, ensures both species survive (otherwise the better adapted type displaces the other)
- called “competitive exclusion principle”
Abiotic factors is…
a non-living factor which affects the distribution of an organism.
e.g soil, water, pH, forest fire, humidity, temperature, pesticides, salinity of water
Biotic factors is…
a living factor which affects the distribution of an organism
e.g interspecific and intraspecific competition, parasites, predator disease
What is a running mean?
A new mean value is calculated after each sample is taken. Enough samples have been taken when the running mean shows little to no change.
To ensure data collected is reliable and representative….
…. a large enough number of samples must be taken. more than 20.
