Populations and Ecosystems

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Ecosystem and factors affecting populations

—Ecosystem  - self supporting system of organisms interacting with each other and their environment —Interactions include:

- Competition for resources (e.g. food, space, water)

—Every species occupies a different niche (how the species functions in it's habitat)

—If a species tries to occupy the same niche then they will compete, one will outcompete the other. —the availability of resources affects Population size is dependent on 

—Main biotic (living) factors = competition & predation: -Interspecific -> competition between different species -Intraspecific -> competition between same species

—Main abiotic (non living) factors: -CO₂ concentration, Mineral ion availability, Light intensity ( all plant populations only)

-Water availability and Temperature -> both animal and plant populations

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Biotic: Predator prey relationships

—biotic factors that influence population size:

-predation -> reduces the prey population

-disease causing organisms -> slows population growth


—The predator prey relationship -the populations size of the predators and prey are interdependent - Prey pop. increases, so Predator increases (more food)

-prey population decreases as Predators kill more prey -Less food for predator, so predator population decreases

-Less predators to kill prey, so prey population increases

-Predator population always lags behind prey population, because the predator is dependent on prey for food.

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Investigating populations

—Quadrats - Static population -Use a quadrat divided into 100 squares -Random coordinates (avoid bias using a random no. generator) -Record abundance of species in quadrat (species frequency) & percentage cover. —

Transects- plant populations -Lay tape across area -at regular intervals take measurements —

Mark-release-recapture - mobile species -capture,  mark and release into wild -second sample, count number that are marked and total sample -Total population size = No. Caught in 1st sample x No. caught in 2nd sample / No. marked in 2nd sample

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Assumptions when using mark-release recapture

1)The marked sample has enough time and opportunity to mix back into population 2)Marking doesn’t effect behaviour

3)No migration

4)No reproduction

5)No deaths

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Human Populations

—Population growth rate = birth rate – death rate —

Most populations are restricted by limiting factors, but humans can modify their environment to allow rapid population growth —

Human population has been increasing because:

1.Increased quality and quantity of food

2.Improved sanitation

3.Improved medical care

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