3.7.4 Populations in ecosystems Flashcards
Define populations
group of organisms of the same species living in the same area at the same time that can interbreed to make fertile offspring
Define habitat
Part of ecosystem where an organism lives
Define community
All populations of different species living in the same area at the same time
Define ecosystem
A community and the biotic and abiotic factors
Define niche
Organisms role in an ecosystem, e.g. position in the food web, habitat. Each species occupies its own niche governed by adaptations to biotic and abiotic factors
Define carrying capacity
Maximum population size an ecosystem can hold
Define abiotic factors
non - living conditions
Define biotic factors
living conditions
Name 5 abiotic factors
1) oxygen and carbon dioxide concentration
2) temperature
3) light intensity
4) pH
5) soil conditions
How do abiotic factors affect population size?
The less harsh the abiotic factors the larger the range of species and the larger the population size
How does temperature affect population?
- Extreme temperatures affect enzymes. Too cold - enzyme does not have enough kinetic energy to catalyse reaction. Too hot - enzyme will denature. Reducing overall metabolic
activity. Reduces survival - Too hot causes excess water loss and dehydration
- The more extreme the temperature, fewer species survive. Those who do survive have a smaller population size
How does light intensity affect population?
- Light is needed for photosynthesis. Higher light intensity, greater rate of photosynthesis so more energy for seed/spore production and the population will increase faster
- More plants grow the more respiratory substrates available for animal populations (glucose and amino acids)
How does water availability affect population?
Water needed as solvent and in metabolic reactions. Lower the humidity means more water loss. Different species water toleration varies.
How does pH affect population?
pH affects enzymes and proteins. More extreme pH, more organism is affected, lower population size and range of species present.
What is interspecific competition?
Members of different species compete for the same limited resource. Individual better adapted to environment is more likely to succeed.
What is intraspecific competition?
Members of the same species are competition for resources. Tends to be fiercer as same species have the same requirements.
What three patterns do predator and prey patterns always follow
1) Size of predator and prey population both fluctuate
2) Prey population will peak at a higher point
3) Size of population will change in prey and then predators (lag time)
How does predator and pray relationships affect population?
- as prey population increases, more food for predators, inftaspecific competition reduces. Population of predator increases
- as more prey is consumed, prey population falls. Intra-specific competition increases and there’s less food. Predator population decreases
When would you use mark-release-recapture?
Mobile/moving organisms
Describe mark-release-recapture method
1) Initial species ethically captures
2) Individuals marked
3) Individual released and left for a period of time to randomly redistribute through habitat
4) Catch a second sample. Record total of sample and number who were recaptured (had marking)
5) Estimate population size
How to estimate population size mark-release-recapture?
N1 x N2 / Nm
N1 - sample one
N2 - sample two
Nm - Number of second sample which were marked
How to get more accurate results in mark - release - recapture?
Repeat and calculate mean to make it more reliable
Ethics to consider in mark - release - recapture
- How species are captures and marked must cause no permanent harm
- Mark not toxic
- Mark mustn’t increase predation
- Marks must not reduces chances of reproduction
Why might mark - release - recapture may not be accurate (2)
- we assume population is constant (no births/death/migration)
- we assume animals redistribute evenly
What is succession?
Change in ecological community over time
What is the pioneer species?
Organisms that first colonise an area
What is a climax community?
Is stable and changes very little. Last stage in succession
Describe and explain how succession occurs?
1) Colonisation by names pioneer species
2) Changes in environment caused y organisms
3) Enables other named species to colonise and survive
4) Changes in biodiversity
5) Stability increases and makes a less hostile environment
6) Climax community represented by named species
When do you use percentage cover when investigating populations? (4)
- Too many individuals to count
- Organism is too small
- Hard to identify
- Overlap with other species
When would you use quadrats?
Non-mobile or slow moving organisms with uniform distribution
When would you use transects?
Slow moving/ non-mobile organisms with uneven distribution
Random sampling method
1) Lie two tap measures at a right angle to create a gridded area
2) Use a random number generator to generate coordinates
3) Place the quadratic and collect the data
4) Repeat at least 30 times to collect a mean
What is a belt transect
Place quadratic at every position along tape measure
What is an interrupted belt measure?
Quadra placed at uniform intervals along the tape
Describe line transect method
1) Place the tape measure at a right angle to shore line
2) Place the quadrat every 4 meters
3) Collect the data
4) Repeat by placing another 30 transects along the beach at right angle to the shore lone
What is and how to measure frequency?
- The proportion of quadrats that contain a particular species
What is and how to measure density?
- The number of one species in a given area
- density = (area of whole area/area of quadrat) X number of species in quadrat
What is and how to measure percentage cover?
- proportion of ground occupied by species
- (total area covered by species/ total area of all quadrants) x 100
Advantages of frequency (2)
- quick to sample large area
- useful if its difficult to identify or too many to count
Disadvantages of frequency (1)
Poor accuracy as it doesn’t consider overlapping or size of plant
Advantages of density (2)
- More accurate if organism is easy to distinguish
- Used to estimate species richness (count the number of different species present)
Disadvantages of density (1)
Time consuming
Advantages of percentage cover (2)
-Quicker
- Useful for organisms that are hard to identify or too many to count
