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Define the term population.
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Define the term population.
A population is a group of organisms of the same species living in the same place at the same time.
Define the term community.
A community includes all of the populations living in the same area at the same time.
Define the term ecosystem.
An ecosystem is all of the organisms that live in an area, and their interactions with the living (biotic) and non-living (abiotic) factors in their environment.
True or False?
Individual organisms only interact with the living components of their environment.
False.
Living organisms interact with both the living components (each other) and the non-living components (e.g. the temperature and rainfall) of their environment.
Define the term abiotic factor.
Abiotic factors are the non-living factors that influence ecosystems, e.g. temperature, sunlight, pH, salinity, precipitation.
What are some examples of abiotic factors?
Examples of abiotic factors include:
light intensity
temperature
water availability
polluting chemicals
soil pH / moisture / mineral content
wind speed
carbon dioxide concentration
water pH
oxygen concentration
How might a decrease in water availability affect a population of living organisms?
A decrease in water availability might affect a population of living organisms as follows:
the population size might decrease
the population might change its distribution by leaving one area for another in search of more water
Define the term biotic factor.
Biotic factors are the living factors that affect organisms in an ecosystem, such as competition, predation and disease.
Give examples of biotic factors that could affect populations.
Biotic factors that could affect populations include:
predation
competition
availability of food organisms
pathogens /disease
True or False?
An increase in the size of a prey population is likely to cause a decrease in the size of a predator population.
False.
A decrease in the size of a prey population will most likely result in a decrease in the size of a predator population. This is because there will not be enough food so predators will die, or leave.
Define the term competition in the context of biotic factors.
Competition occurs when organisms fight for the same resources, e.g. food or mates
True or False?
Populations that compete for the same resources are likely to be smaller than equivalent populations that are not experiencing competition.
True.
Competition is likely to reduce the size of a competing population. In extreme cases a less well-adapted population may die out.
In the context of ecosystems, what is interdependence?
Interdependence refers to the fact that organisms living in the same habitat depend on each other. A change in one species will affect other species.
What is parasitism?
Parasitism is a relationship between living organisms in which a parasite benefits from living in or on the body of a host species, while causing the host harm.
What is mutualism?
Mutualism is a relationship between living organisms in which both members of the relationship benefit in some way.
Define the term biodiversity.
Biodiversity is the variety of living organisms found in a habitat. This includes, e.g. the number of different species, the size of each population and the differences between individuals of a species.
Why is sampling used when determining the number of organisms in an area?
Sampling is used when determining the number of organisms in an area because it is easier than attempting to count all individuals. Sampling provides a representative sample from which a population size estimate can be calculated.
What is a quadrat?
A quadrat is a square frame that is placed on the ground to study the organisms within.
How can the abundance of a species be measured within a quadrat?
The abundance of a species can be measured within a quadrat as follows:
recording whether or not a species is present
counting the number of individuals of a species
estimating percentage cover
Why is it important to place quadrats randomly when studying population size?
Placing quadrats randomly avoids bias in an investigation, e.g. a student might choose to place all of their quadrats on bare ground because it would make counting easier, resulting in a biased sample.
True or False?
Increasing the number of quadrats will increase the likelihood that any results accurately represent the habitat sampled.
True.
Carrying out more quadrats will increase the sample size, meaning that the results are more likely to be a good representation of the area sampled.
How can an estimated population size be calculated from quadrat data?
An estimated population size can be calculated from quadrat data using the formula:
population size = (total area ÷ area sampled) x total no. individuals counted
What is a belt transect?
A belt transect is a line placed across a habitat, along which quadrat samples are taken, either continuously or at regular intervals.
What is investigated using a belt transect?
A belt transect is used to investigate how the distribution of species in a habitat is affected by a particular abiotic factor, e.g. distance from a path or water source.