Populations In Ecosystems Flashcards
Population
Group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed
Community
Populations of different species that occupy the same space at a particular time
Ecosystem
A community and the non living components in its environment
Why do we need to conserve ecosystems?
For biodiversity
To conserve habitats and niches within the habitat
Habitat
Place where an organism lives
Niche
The role of an organism in the habitat, governed by biotic and abiotic factors
Carrying capacity
Long term maximum population size for a species
Graph to show carrying capacity
S shaped that starts slow, exponential growth, plateaus at the carrying capacity
Time on x axis
Number of individuals of the same species on y axis
Why does population growth of a species start slow?
Organisms need time to establish territory/food source/nests
When does exponential population growth occur?
When reproduction rate exceeds death rate
When does population size plateau
At the carrying capacity which is the maximum population size
What is occurring at carrying capacity?
Reproduction rate + immigration rate = death rate + emigration rate
What causes the carrying capacity being reached?
Abiotic factors: light intensity, temperature, water availability
Biotic factors: Competition, predation
Prevents the reproductive rate exceeding the death rate
Competition
Interactions individuals have as a result of competing for resources in a limited supply (food, nesting sites)
Intraspecific competition
Between organisms of the SAME SPECIES
Interspecific competition
Between organisms of DIFFERENT SPECIES
What reduces interspecific competition?
Different species occupying different niches in the habitat
Because each species has their own role: to feed on specific bug in specific area, so resources aren’t limited so less competition
Predation
if more Predators catching prey, it directly prevents reproductive rate of prey exceeding their birth rate
3 methods of estimating population size
Randomly placed quadrats
Quadrats along a belt transect
Mark-release-recapture
What organisms are quadrats (belt transect or random) used?
For slow moving ones eg snails
Or non motile ones eg plants
Method for randomly placed quadrats
Place 2 tape measures perpendicular to each other to create coordinate grid of habitat
Random number generator to get more than 20 coords
Place quadrat at every coord and count number of organisms
Why do we use the randomly placed quadrats method?
Want to estimate population size for slow moving/on motile organisms by taking a sample in quadrats of this area
There is no environmental gradient which means organisms
could be distributed non randomly to reflect this:
SO ORGANISMS ARE RANDOMLY DISTRIBUTED
Why use random sampling by generating coords to place quadrats and thus, sample?
Avoids bias
So the number of organisms in sample taken in quadrat is proportional to number in total area (aka sample is representative)
Can we throw quadrats?
No, will be biased based on how far you can throw or subconsciously may not throw randomly
What do you count inside a quadrat?
Number of different species you see (species richness)
Number of individuals of each species/ specific species (species abundance)
Percentage cover of species in quadrat
How to calculate number of individuals of a species in the total area from quadrats?
Mean number of individuals in a quadrat
Find quadrat area and how many quadrats make up 1m2
Multiply this by mean number of individuals = mean individuals per m2
Multiply by total area of target
When do we calculate percentage cover of individuals in a quadrat?
If its too hard to count every individual in a quadrat
What quadrat is used to calculate percentage cover of organisms
A gridded quadrat so each grid equals a certain percentage
Calculate percentage cover of species
Standardised counting method to find percentage cover
If a square in the quadrat is less than half full, dont count it
If its more than half full of species, count it
Assume errors cancel out
Why do we use the belt transect quadrat method?
Used when there is an environmental gradient: a gradual change in environmental conditions along a distance
(For slow moving/ non motile organisms)
NOT a random sampling method. Is systematic (involves sampling at regular intervals) because organisms are distributed along gradient not random
How to complete the belt transect quadrat method?
Lay tape measure along the environmental gradient
Place a quadrat at regular intervals + take reading at this quadrat of environmental change (light intensity etc)
Record what you need from each quadrat
Repeat using several parallel transects to ensure data is representative
Can you use random sampling to compare effect of environmental change on number of species?
Yes sampling in 2 different environments with a difference in environment (but not gradual to be belt transect) Eg use of weedkiller or not
Compare means in both samples
What organisms is the mark release recapture used for?
Motile organisms that can move themselves around
