Populations in ecosystems Flashcards
What is an ecosystem?
Made up of a community and all of the non-living components of the environment. They are very dynamic systems
What are the three phases in the usual pattern of growth for a natural population?
- period of slow growth - as organisms adjust to their environment
- period of rapid growth - ever-increasing number of individuals continue to reproduce
- period where population growth declines until stable - always fluctuations because food supply changes, disease, resource exhaustion and migration in/outward
What can cause the size of a population to vary?
- abiotic factors
- interactions between organisms (inter/intraspecific competition)
What is ecological niche?
How an organism fits into its environment, involving its adaptation to both biotic and abiotic factors which allow it to survive, reproduce and maintain a viable population
How should you plot a growth curve when growth occurs rapidly?
Using log number of individuals
Why does bacteria population eventually level off?
Initially there are no limiting factors so growth is rapid
- mineral ions are consumed as population grows larger
- bacteria at surface prevent light from reaching those beneath
- other species may be introduced which use the bacteria for food, or compete for light and mineral ions
- winter brings lower temperatures and lower light intensity
What are some abiotic factors?
- temperature
- pH
- light/shade
- water and humidity
What are some biotic factors?
- food supply
- predation
- inter/intraspecific competition
- disease
How does light affect the organism?
- photosynthesis rate increases as light intensity increases
- opening of stomata
- kinesis
How does wind/water current affect the organism?
- transpiration rates
- evaporation of water from animals
- seed dispersal - effects competition
How does water/humidity affect the organism?
- transpiration rates
- evaporation from animals
How does pH affect the organism?
- tertiary structure of enzymes
How does temperature affect the organism?
- enzymes
- kinetic energy
- lower temp = more dissolved O2
What techniques can be used to investigate populations?
- transect sampling - tape is stretched along a habitat and measurements taken at regular intervals (where conditions and organisms change over distance)
- gridded frame quadrat sampling - gridded quadrat placed at random coordinates ( collects frequency data)
- open frame quadrant sampling - quadrat without subdivisions placed at random coordinates (estimates percentage cover)
- point quadrat sampling - horizontal bar with 10 holes at set intervals, a pin is dropped into the holes and each species touching the pin can be counted (estimates percentage occurrence of individuals)
How can you measure abundance of species?
- frequency eg. if the species occurs in 15/30 quadrats, frequency is 50%
- percentage cover