What affects population size and competition.

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What are the 3 stages a population goes through over time?
1. Lag phase, 2. Log phase, 3. Stationary phase
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Describe the lag phase
Initially only a few individuals still acclimatising to their habitats. Rate of reproduction is slow as is growth in population size.
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Describe the log phase
Resources are plentiful and conditions are good. Rate of reproduction is fast and exceeds mortality. Population size increases rapidly.
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Describe the stationary phase
Population growth levels out at carrying capacity. The habitat cannot support a larger population. Rates of reproduction and mortality are equal. Population size fluctuates slightly.
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Define carrying capacity
The maximum population size of the species that the habitat can sustain for a period of time. Death and birth rate must be equal for this.
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What factors can affect population size?
Competition, seasons, disease, variation in birth rate to death rate ratio, predation, availability of food.
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Define a limiting factor
The affecting factor in shortest supply. Limits the rate of the process and determines the carrying capacity.
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What are some examples of BIOTIC (living) factors?
Disease, predation, competition, parasites.
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What are some examples of ABIOTIC (non-living) factors?
Windspeed, temperature, sunlight, pH, CO2 concentration, oxygen, space, food, water, shelter.
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What are density INDEPENDENT factors?
Same effect whether population is large or small. Typically ABIOTIC factors.
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What are density DEPENDENT factors?
Greater effect at HIGHER population densities, usually BIOTIC factors, more competition at higher density.
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Describe the trend of predator-prey relationships.
1. Predators reduce prey numbers through predation. 2. Fewer prey means greater competition amongst predators. 3. Predator numbers decrease as there is not enough prey. 4. Fewer predators means less predation so prey numbers increase. 5. Cycle begins
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What are 2 other key reasons for cyclic fluctuations?
Climate change and disease. These are key for evolution as they create selection pressures.
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What are K-strategists?
Species whose population size is determined by the carrying capacity. Limiting factors have a more significant effect
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What are r-strategists?
Species with population size that increases so quickly it exceeds carrying capacity before limiting factors start to have an effect.
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What is the death phase?
Where the carrying capacity has been exceeded and there is a shortage of nutrients. Build-up of waste products causes them to begin to die.
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What are the 2 types of competition?
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What causes competition?
Inadequate amounts of resources such as food and water to satisfy the needs of a;ll the individuals that depend on these resources.
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Who does INTRAspecific competition occur between?
Individuals of the SAME species.
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What does this type of competition result in?
Slight fluctuations in population size as it enters the stationary phase. The best adapted will survive and reproduce, whilst others will die or fail to reproduce.
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Who does INTERspecific competition occur between?
Individuals of DIFFERENT species.
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What can interspecific competition affect?
The population size of a species and the distribution of species in an ecosystem.
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Card 2


Describe the lag phase


Initially only a few individuals still acclimatising to their habitats. Rate of reproduction is slow as is growth in population size.

Card 3


Describe the log phase


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Card 4


Describe the stationary phase


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Card 5


Define carrying capacity


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