Chapter 19 - Populations in ecosystems Flashcards
What is ecology
Ecology – the study of the inter-relationships between organisms (living) and their environment (non-living).
What is the definition of a population
Population = number of individuals of the same species in the same habitat at the same time. That can breed to create a fertile offspring
Populations are dynamic as they change in size and composition
labelled image of population graph
Why is there a lag phase in a population graph
Lag phase – small number of bacteria, getting used to conditions but not dividing
Why is there a log phase in a population graph
Exponential or log phase - exponential growth with bacteria dividing by binary fission, doubling in number for every generation. No limiting factors
Why is there a stationary phase in a population graph
Stationary phase - growth reaches a plateau as the number of dying cells equals the number of dividing cells. Resources (e.g. respiratory substrate, oxygen) become limiting.
Why is there a death phase in a population graph
Death phase - exponential decrease in the number of living cells. Resources run out and waste products reach toxic levels.
What are the two types of population growth that are shown on population graphs
logistic growth - will reach a carrying capacity
exponential growth - no limiting factors
graph of logistic growth
graph of exponential growth
What are some examples of abiotic factors
- Temperature
- Light
- pH
- Water availability
- Humidity
- Oxygen levels
What are some examples of biotic factors
- Competition
- Predation
- Disease
What is intraspecific competition
- Competition between individuals of the same species
- The more resource present, the less competition so the population gets larger
- The less resource present, the more competition so the population gets smaller
What is interspecific competition
- competition between individuals of the different species
Examples of interspecific competition
- Food
- Light
- Water
What is the competitive exclusion principle
- Where two species are competing for limited resources, the one that uses these resources most effectively will ultimately eliminate the other.
- No two species occupy the same niche indefinitely.
What is the definition of a niche
- the role an organism plays in the ecosystem
- e.g. what resources do they use, what do they eat, what eats them, what do they provide shelter for.
What is predation
- When one organism (the predator) consumes another (the prey)
- Demonstrated in predator – prey cycles in natural environments
- Example: snowshoe hare and Canadian lynx
example of a predator prey cycle
What happens at each stage of the predator prey cycle
What can cause an ununiform predator prey cycle graph
- Predators normally have other sources of food (more than one type of prey)
- Disease and climatic factors
What is the definition of abundance
the number of individuals of a species in a given area (measured as frequency (number of) or percentage cover)
What is the definition of distribution
where a species occurs within a given area
With both of these you can investigate both the species and the factors influencing abundance or distribution – abiotic and biotic factors
Distribution and abundance will both give you quantitative data
What is sampling
- Used to provide an estimate of quantitative data
- Less time consuming
- Large number of samples needed to be representative of whole population
What are the two types of quadrats
- Frame quadrats
- Point quadrat
what are the features of frame quadrats
- Open or gridded
- Give a 2D (top down) image of area
- Used with low level vegetation
- Vary in size depending on size of organism sampled, and area
what are the features of point quadrats
- Used with taller, layered vegetation
- Give a 3D (side on) image of area
- Count the number of times plants touch the pins
what are the features of random sampling
- Random – reduces bias
- Used to compare abundance in different areas
- Non-motile organisms
- Example: lichen on north and south side of a wall
What is the method for random sampling
- Use a tape measure to divide area into squares/sections
- Obtain random coordinates using a calculator
- Place quadrat at random coordinates
- Count number of X in a quadrat and record
- Use a large sampleandcalculate mean number per quadrat
- Calculate total number of X in area e.g. mean number of plants per quadrat multiplied by number of quadratsin area
(If question asks about comparing two areas – include: - Repeat for other area and compare)
What are the features of systematic sampling
- Systematic – at regular intervals along a transect
- Non-motile organisms
- Used to investigate distribution along an environmental gradient
- Can form a continuous belt transect
- Example – light intensity as you move out from under a tree
What is the method for systematic sampling sampling
- Lay a tape measure along the length of the environmental gradient
- At regular intervals along the transect, place a quadrat
- Count the number of X in a quadrat and record
- Continue for the length of the transect
- Repeat for several parallel transects and calculate mean number in quadrat at each distance
If the question asks about an abiotic factor, take readings for this in each quadrat
What is the method for mark release recapture
Capture/collect sample, mark and release (ensure marking is not harmful)
Allow time for organism to randomly distribute before collecting a second sample
population = (number in first sample x number in second sample) / number recaptured
What are the assumptions required for mark release recapture
- The marked sample must have time to mix back in with population
- Marking must not affect survival of the organism – not toxic or increase risk of predation
- No changes in population during period of the investigation
What is succession
succession is a change in species in an area over time.
It is caused by a change in abiotic factors brought about by species living in an area
What are the stages in succession
- Colonisation bypioneer species e.g. lichen
- Species change the environmental conditions e.g. soil forms and organic matter and nutrient levels increase
- Environment becomes lesshostile
- Leads to new species able to colonise
- Previousspeciesout-competed.
- Increase inbiodiversity as more food sources and habitats arise
- Stable climax community is reached
What is secondary succession
- Occurs on land that has previously been colonised
- Land is altered due to fire, disease, grazing or agriculture
- Soil remains with seeds and spores
- Succession starts again and reaches the climax community much faster
diagram for primary succession
overall diagram for succession
What are the similarities between primary and secondary succession
- Species change the abiotic factors to make them less hostile so new species can colonise and outcompete current species
- Both increase in biodiversity and stability with time
- Both end in a climax community
What are the differences between primary and secondary succession
- Primary succession begins with barren land and secondary succession starts with land altered by e.g. fire, grazing, agricultural land clearance
- Secondary succession already has soil containing seeds and spores but primary succession is barren with no soil
What is the conservation of habitats
- Conservation is the protection and management of ecosystems
- It often involves preventing succession reaching the climax community
- It involves human intervention either directly or indirectly
