Species and communities 4.1

Ecology is the study of the interconnections between living organisms and their environment. There is such a complex network of links in any location that ecologists have to break down and classify these relationships whether they be feeding, competition or reproduction. This topic is an introduction to these divisions.


Key words

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Revision summary list for topic 4.1 Species and communities

  • Species are "groups of organisms that can potentially interbreed to produce fertile offspring".
  • Members of a species may be reproductively isolated in separate populations.
  • Species can be autotrophic or heterotrophic in nutrition (a few species are both).
  • Consumers are heterotrophs that feed on living organisms by ingestion.
  • Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.
  • Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.
  • A community is "populations of different species living together and interacting with each other."
  • An ecosystem is "a community and its interactions with the abiotic environment."
  • Autotrophs obtain inorganic nutrients from the abiotic environment.
  • The supply of inorganic nutrients is maintained by nutrient cycling.
  • Ecosystems have the potential to be sustainable over long periods of time

Skills (can you ....)

  • Classify species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition.
  • Set up sealed mesocosms to try to establish sustainability. (Practical 5)
    Mesocosms in sealed glass vessels are preferable because entry and exit of matter can be prevented but light can enter and heat can leave. Aquatic systems are likely to be more successful than terrestrial ones.
  • Test for association between two species using the chi-squared test with data obtained by quadrat sampling.
    For example An ecosystem chosen where varying factors affect the distribution of the chosen species. Random quadrat sampling should be used to measure the presence or absence of the chosen species.

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Review questions

This is a self marking quiz containing questions covering the topic outlined above.
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1

Which classification grouping includes all organisms which have the potential to interbreed and produce fertile offspring?

Species are "groups of organisms that can potentially interbreed to produce fertile offspring".

2

When members of a species are separated by a physical barrier this can lead to populations which are prevented from reproducing, because individuals from each population never meet.

What is the name given to this situation?

Members of a species may be reproductively isolated in separate populations.

3

Which is the best definition of the term, "Heterotrophic"

Heterotrophs need to obtain organic material from other organisms. They cannot produce organic material from inorganic molecules.

4

Energy in an ecosystem is passed from organism to organism in food, but it is eventually lost to the environment as heat. Inorganic nutrients are not usually lost from the ecosystem?

What is the name given to the process which keeps the inorganic nutrients in the ecosystem?

Autotrophs obtain inorganic nutrients from the abiotic environment. Heterotrophs get nutrients by eating other organisms, but this is not the reason why the community is sustainable.

The supply of inorganic nutrients is maintained by nutrient cycling.

Ecosystems have the potential to be sustainable over long periods of time

5

The organisms in the photo below are classified in ecology according to their mode of nutrition.

Which of the following correctly describes their mode of nutrition?

Classifying species using their mode of nutrition begins with the division into Heterotrophs, who get organic molecules (nutrients) from other organisms and autotrophs, who can make organic molecules from inorganic molecules, using photosynthesis.

6

Mesocosms can be used by ecologists to investigate natural systems.


Which variables could be easily controlled in experiments using these aquatic mesocosms?

Mesocosms can allow the control of variables much more than the natural environment.
These tanks are all the same size, so naturally volume, and surface area can be easily controlled.
In setting up the tanks the concentration of salts can be accurately measured, as there is no movement of water through the tanks, this can also be controlled.

7

In an experiment in a small garden, quadrat frames were used to sample the flowers.

Why is it important to use random sampling in the placement of the quadrats?

Random quadrat sampling is a standard method used to avoid bias and selection.

8

What is the term given to a community and it's abiotic environment?

A community is "populations of different species living together and interacting with each other."
An ecosystem is "a community and its interactions with the abiotic environment."
A habitat usually relates to one species, and a biome is more than one ecosystem.

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