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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.
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.
True or False?
A habitat is the place that an organism lives.
True.
The place where an organism lives is its habitat, e.g. a meadow or a woodland.
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?
Living 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.
What is a quadrat?
A quadrat is a square frame that is placed on the ground to study the organisms within it.
Define the term abundance in the context of a quadrat investigation.
The term abundance is how common a species is within a quadrat. Abundance across a series of quadrats can be used to estimate the size of a population.
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
When might percentage cover be used as a measure of abundance within a quadrat?
Percentage cover is often used to measure the abundance of a species where individual organisms are difficult to tell apart, e.g. grass or barnacles
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.
When using quadrats to compare population sizes in two areas, what variables should be kept the same? (CORMMS)
Variables that should be kept the same when using quadrats to compare the populations of a species in two areas include:
Size of quadrat
Number of quadrats sampled
Time of day / time of year
Knowledge of species identification
This is part of the CORMMS criteria for planning an investigation.
What are some of the challenges of studying populations using quadrats?
Challenges of using quadrats to investigate populations include:
It can be easy to miss organisms when counting, e.g. if they are underneath another organism or if two individuals are counted as one
Some species might be difficult to identify
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.
Define the term biodiversity.
Biodiversity is the variety of different species 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.
What are the benefits to an ecosystem of having high biodiversity?
The benefits of high biodiversity include:
Increased availability of food and shelter
Increased resilience to change
True or False?
Low biodiversity increases ecosystem stability.
False.
Low biodiversity decreases ecosystem stability. This is because when fewer species are present a change in one species is more likely to have a significant impact on other species.
Define the term distribution in the context of a quadrat investigation.
Distribution refers to where a species occurs within its habitat.
When using quadrats to investigate biodiversity, what variable could be measured? (CORMMS)
When using quadrats to investigate biodiversity, the following variables could be measured:
The number of species in each quadrat
The abundance of each species in each quadrat
This is part of the CORMMS criteria for planning an investigation.
True or False?
A series of quadrats in field A contain more species than the same number of quadrats in field B. Field A is likely to have higher biodiversity than field B.
True.
A quadrat that contains more species is likely to have higher biodiversity. There are exceptions to this, but this is likely to be the case.
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
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
True or False?
An increase in temperature from 20 °C to 30 °C would result in an increased population size for a plant species.
True.
An increase in temperature from 20-30 °C will increase the rate of photosynthesis in plants, so it is likely that the plants will grow faster and the population size will increase.
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:
Predators
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.