3.7.4 Populations in ecosystems Flashcards
(41 cards)
Why is sampling used on populations?
investigates the abundance and distribution of species and populations
What are the benefits of random sampling?
-no bias
What are the negatives of systematic sampling?
-potential bias towards certain areas
-unrepresentative data of whole area
What are the 3 main sampling methods used when estimating size of population?
-quadrats (non-motile/ slow-moving)
-transects (non-motile/ slow-moving)
-mark-release-recapture (motile)
Method of measuring population size using quadrats
- Lay 2 tape measures at right angles to create a gridded area
- Use a random number generator to generate 2 random coordinates
- Place quadrat in location and collect data (% cover/ no. organisms/ frequency)
- Repeat at least 30 times
- Calculate mean/ multiply up for area size
What is species frequency?
probability that the species will be found within any quadrat in the sample area
What are the benefits of calculating % cover using a quadrat?
-fast
-no problem of identifying where organism starts/ finishes or if there is any overlapping of organisms
What are the benefits of calculating density (number of individuals of a particular species) using a quadrat?
-estimates species richness
-accurately represents population size
-able to identify individual species
When is systematic sampling more appropriate?
where abiotic factors change throughout an area (uneven distribution)
What is a belt transect?
placing quadrat at every position along tape measure
What is an interrupted belt transect?
place quadrat at uniform intervals along tape measure (e.g. every 5 metres)
How do you sample motile organisms?
mark-release-recapture
What is the method of mark-release-recapture?
- Capture first sample + mark
- Release + leave (for 24 hours) to allow distribution within habitat
- Reset traps and capture second sample
- Count number marked vs total number captured
- Use calculation to estimate size of population
- Multiple repeats (to increase accuracy and reliability)
Equation for estimated population size using mark-release-recapture
no. organisms initially caught * no. organisms in second sample / no. organisms marked that were recaptured
What are the 2 main assumptions made when calculating population size using mark-release-recapture?
- Population size is constant (no new births/ deaths/ migration - in reality this will not happen)
- Evenly distribute when released (reality they will distribute to one location - rich in food, shelter, water, lack of predators)
What is succession?
sequential changes within an ecosystem over time
What is each stage of succession called?
seral
Seral 1: What species colonise the bare habitat?
pioneer species
What are key features of pioneer species?
-tolerant to extreme conditions
-grow quickly
-are not able to compete for resources
-are not influences by or dependent on animal species
Example of species colonising bare rock
Lichen
-algae (photosynthesis - glucose)
-fungi (release extracellular enzymes and break down rock to access minerals)
Seral 2: What forms as pioneer species die and decay?
thin layer of hummus - retains water and some minerals (allows growth of small and simple plants)
Seral 3: What species grow and why?
larger species - soil depth has increased, so more nutrients and water are retained in soil so larger species can dig in roots and survive
Seral 4: Why are pioneer species and smaller species not present?
taller/ larger species create shading (outcompeted for resources/ sunlight)
Seral 5: What are the species called that are found here?
climax species (trees e.g. oak)
