Populations in Ecosystems

Define Population

All the individuals of the same species in a habitat at the same time that can interbreed

Define community

All the populations of different species in a habitat

Define niche

The role of a species in its ecosystem and how it interacts with all the biotic and abiotic factors

Define biotic factors and give 2 examples

Living factors that can impact the size of a population

Examples:

• Food

• Predators

• Prey

• Diseases(bacteria)

Define abiotic factors and give 2 examples

Non-living factors that can affect the size of a population

Examples:

• Weather

• Humidity

• Soil pH

• Water

• Light intensity

• Disease (viruses)

Define carrying capacity

Th maximum population size of species an ecosystem can support

Define ecosystem

Formed from a community and the non-living components of its environment. E.g. rainforest

Define interspecific competition

Competition between different species

Define intraspecific competition

Competition between individuals of the same species

Define predation

How the population of predators and prey can affect each other

Explain how intraspecific competition affects the number of organisms. Explain the graph that shows this

• Members of same species compete for the same resources eg. Food

• If the population gets too big, intraspecific competition increases, so the population falls again

• If the population gets too small, intraspecific competition decreases, so the population increases again

Explain how interspecific competition affects the number of organisms. Explain the graph that shows this

One species will out-compete the other one if they occupy the same niche

Explain how predation affects the number of organisms. Explain the graph that shows this

• Prey population increases so more food for predator so predator population increases shortly after

• More predators than prey so more prey get eaten so prey population decreases

• Less prey to eat so predator population decreases because they die of starvation

• Less prey eaten so prey population increases and the cycle starts again

Explain the advantage of two different species occupying different niches and give example

• Reduces interspecific competition between species

• Example: Animals may compete for food

  Always include an example

Explain why sampling should be carried out at random

To prevent bias

Explain why a large sample should be used when sampling

• So that the sample is more representative

• To calculate a more reliable mean

• To allow the use of statistical test

Describe how you would achieve representative data when sampling

By using a large sample size

What is the use of a quadrat

Quadrants are used to estimate the size of a population of a particular species in a certain area

Describe the steps of how you would estimate the numbers of daises in a woodland by random quadrant sampling

• Split area into a grid and assign coordinates randomly using a random number table

• Place quadrat at coordinate and count number of individuals or % cover

• Repeat a large number of times and calculate a mean

• Multiply this mean by the number of times the quadrat fits in the area

How can you find the correct number of quadrants to use to get representative data

Calculate a running mean until the mean remains constant/ shows little change

What is the use of a transect

Transects are used to show changes dawn a n environmental gradient

How would you make sure that you have a representative sample of data using transects

• Select the position of the transect at random

• Use a large number of parallel transects and calculate the mean at each distance

Describe the steps if how you would carry out a transects to measure the change in % cover of barnacles own a rocky seashore (using belt transects)

• Several belt transects are placed at parallel across an area and numbered

• A transect is chosen at random using a random number generator button on a calculator

• A quadrat is placed along the straight line at regular intervals

• The % cover or number of each species are counted in each quadrat

• This is repeated across a large number of parallel transects and a mean at each interval is calculated

What method can be used to estimate the sizes off population of motel organisms (organisms that can move)

Mark, release and recapture

What is the equation for estimating the population

Number of organisms in the first sample X Number of organisms in the second sample

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Number of marked organisms in the second sample

Describe the steps of how you could estimate the numbers of turtles on a coral reef (mark, release and recapture)

1. Capture a sample of a species and count individuals. Mark them all and release.

2. The mark should not affect the organism’s survival (should be non-toxic / not make the animal more vulnerable to predation)

3. After release, the organisms are left for long enough time to randomly and evenly distribute back into the population

4. A second sample is captured and number is counted, as well as how many are marked

5. State the formula for estimating the population size

Name the assumptions that are made when the mark, release and recapture method is used

• Birth rate = Death rate

• The marking does not influence the survival such as increasing the chances of predation and is non-toxic

• There is no immigration or emigration

• Large population

• Long enough time for the marked individuals to randomly and evenly distribute into the population between release and recapture

What is succession

Succession is where communities nd abiotic factors change over time

What does succession start and end with

Succession starts with hostile conditions and develops into a climax community

What is primary succession and what does it usually start with

• Occurs in an area that has not been inhabited before.

• Starts with bare rock or sand.

• Takes longer

What is secondary succession and what does it usually start with

• Occurs in an area that has been previously inhabited but has experienced a disturbance eg. Forest fire or flooding.

• Starts with soil or some vegetation

• Faster than primary succession

Stages of succession (Using data)

• Starts with pioneer species in hostile conditions (name the pioneer species)

• Pioneer species changes the abiotic conditions (give example: for animal they provide food for others) form soil/ humus

• The environment becomes less hostile and more suitable for new species to colonise (name the new species)

• The new species outcompete the pioneer species, so the pioneer numbers reduce (name the species)

• From stage to stage the species diversity increases (give example from the data)

• Eventually a climax community is reached

Explain what the ecosystem is like in a climax community

• Population is stable

• Abiotic conditions remain constant

• Same species present

What is conservation

The protection and management of species and habitats in a sustainable way.

It is not leaving the environment untouched but managing the existing environments

Reasons for conservation, using rainforests as an example

• Conserve species

• Conserve habitats

• Sources of medicines / wood

• Reduces climate change / takes up carbon dioxide

• Reduces erosion

• Tourism