6 - MZH - Populations & Sustainability Flashcards
Define:
Population
Population size
Population density
Population = All the organisms of one species in a habitat
Population size = No’ of individuals in a population
Population density = No’ of individuals per unit area
What is the shape of the population growth curve called?
Sigmoid growth curve
What is happening during the lag phase (2)
Lag phase = growth is slow because:
- Yeast cells are adjusting to the nutrient solution + the genes that synthesise the enzymes needed to make use of it are being switched on
- Only a few yeast cells present ∴ even doubling has little impact on population size
What’s happening during the log phase? (2)
Exponential (log) phase = when cell reproduction is at it’s max
- Nutrients are plentiful + waste products have not built up to harmful levels
- Population doubles during a givent ime interval ∴ gradient of curve is increasingly steep
What’s happening at the stationary phase? (2)
Stationary phase = period when rate of yeast cells being made = death rate of yeast cells
- Living population - reaches the carrying capacity (k) ∴ curve is horizontal
- In reality it’s not completely straigh, it fluctuates around k
- NOTE: only measuring the living members of the population. Total no’ of yeast cells (living + dead) will continue to increase
What’s happening in the decline phase? (2)
Death/ decline phase = Living population size decreases, growth curve falls steadily because:
- More yeast cells die than are produced
- Limiting factors - nutrients, build up of waste products, not enough space…
Why does the actual population fluctuate around k? (3)
Food supply
Predation
Extreme weather conditions
What would the population growth curve look like without any limiting factors vs what it actually looks like?
What are the limiting factors collectively grouped as?
Environmental resistance
What are the 2 types of limiting factors? Give 3 examples of each
Density dependant factors:
- Factors with effects that depend on the density of the pop
- E.g. large pop will use up the available food more quickly than a small pop
- Usually biotic
- Food availability, predation and disease
Density independant factors:
- Similar effects regardless of the pop size
- e.g. A sudden fall in temp may kill most of a pop whether it’s large or small
- Usually abiotic
- Light intensity, temp or salinity
How have predators and prey evolved to show specific adaptations?
3 for each
- Predators may be faster than prey
- Predators may be camouflaged
- Predators may work together to catch their prey
- Prey may be camouflaged
- Prey may ahve protective features e.g. spines
- Prey may cooperate to avoid being predated, by hearding, having lookouts or defensive behaviour
Describe the predator prey relationship with the use of this graph (5)
- Predators eat their prey ∴ pop of prey decreases
- Increases intraspecific competition (within the same species) for the prey that’s left
- Predator pop reduced as some individuals are unable to obtain enough prey for survival
- Fewer predator left to hunt prey ∴ prey pop can increase as fewer prey are eaten
- More prey available, predator pop can increase because more food available
What is interspecific competition and intraspecific competition
Interspecific competition = Competition between different species
Intraspecific competition = Competition between the same species
Intraspecific = Same species
Interspecific = Different species
Is predation good for a population? (5)
Yes for populations of prey/predators but no for individuals that are predated or die due to shortage of prey:
- Predators tend to taget the weakest members of the prey pop e.g. young, old or injured
- Predation puts a selection pressure on prey pop ∴ only the fittest survive
- When the prey pop is at it’s lowest only the most successful predators will survive to go onto breed
- Selection pressure on predator pop as only the fittest survive
