2.5 Investigating Ecosystems

Significant Ideas

• The description and investigation of ecosystems allows for comparisons to be made between different ecosystems and for them to be monitored, modeled and evaluated over time, measuring both natural change and human impacts.

• Ecosystems can be better understood through the investigation and quantification of their components.

Knowledge and Understanding

1. The study of an ecosystem requires that it be named and located; for example, Deinikerwald in Baar, Switzerland—a mixed deciduous–coniferous managed woodland.

2. Organisms in an ecosystem can be identified using a variety of tools including keys, comparison to herbarium or specimen collections, technologies and scientific expertise.

3. Sampling strategies may be used to measure biotic and abiotic factors and their change in space, along an environmental gradient, over time, through succession, or before and after a human impact (e.g., as part of an EIA).

4. Measurements should be repeated to increase reliability of data. The number of repetitions required depends on the factor being measured.

5. Methods for estimating the biomass and energy of trophic levels in a community include measurement of dry mass, controlled combustion and extrapolation from samples. Data from these can be used to construct ecological pyramids.

6. Methods for estimating the abundance of non-motile organisms include the use of quadrats for making actual counts, measuring population density, percentage cover and percentage frequency.

7. Direct and indirect methods for estimating the abundance of motile organisms can be described and evaluated. Direct methods include actual counts and sampling. Indirect methods include the use of capture–mark–recapture with the application of the Lincoln index.

Textbook Reading and/or Activities

• Pages 125-141

  • Topic 2 Review (p.142-143)

Notes

i-Biology Notes (Not available)

A detailed set of notes, created by Stephen Taylor, examining UX - UY and AX - AY.

i-Biology Study Questions (Not available)

A series of questions, created by Stephen Taylor, to help check your understanding of the IB learning expectations. This is VERY GOOD practice.

Bioknowledgy Notes (Not available)

A detailed set of notes, created by Chris Paine, examining all of the IB learning expectations.

Bioknowledgy Study Questions (Not available)

A series of questions, created by Chris Paine, to help check your understanding of the IB learning expectations. This is VERY GOOD practice.

Learning Activities

Constructing a Dichotomous Key

This worksheet provides an opportunity to use and create a biological key, which can help identify an unknown (but previously discovered) species in the environment.

Sampling a Population

This worksheet outlines the process by which quadrats and transects can be used to estimate the population of a NON-MOBILE (not moving or moving incredibly slowly) species within a given area.

Virtual Lab - Estimating Population Size

Click on the "Estimating Population Size" icon and carry out this virtual investigation, prepared by Class Zone, to better understand how scientists estimate the population of a mobile organism within an area.

Virtual Lab - Tracking Grizzlies

This virtual lab, prepared by McGraw-Hill, provides a real-world simulation of how grizzly bear populations are monitored using DNA fingerprinting techniques (gel electrophoresis).

Lincoln's Index

This activity outlines the process by which Lincoln's Index can be used to estimate the population of a MOBILE (moving) species within a given area.

Supplemental Reading

Offwell Woodland & Wildlife Trust

This website has a variety of resources to help clarify the different types of sampling techniques (quadrats, transects, Lincoln's Index, etc.). It is clearly organized and easy to understand.

• • • n₁ is the number caught in the first sample.

    • n₂ is the number caught in the second sample.

    • n_m is the number caught in the second sample that were marked.

1. Species richness is the number of species in a community and is a useful comparative measure.

2. Species diversity is a function of the number of species and their relative abundance and can be compared using an index. There are many versions of diversity indices, but students are only expected to be able to apply and evaluate the result of the Simpson diversity index as shown below. Using this formula, the higher the result (D), the greater the species diversity. This indication of diversity is only useful when comparing two similar habitats, or the same habitat over time.

• • • D is the Simpson diversity index.

    • N is the total number of organisms of all species found.

    • n is the number of individuals of a particular species.

Applications and Skills

1. Design and carry out ecological investigations.

2. Construct simple identification keys for up to eight species.

3. Evaluate sampling strategies.

4. Evaluate methods to measure at least three abiotic factors in an ecosystem.

5. Evaluate methods to investigate the change along an environmental gradient and the effect of a human impact in an ecosystem.

6. Evaluate methods for estimating biomass at different trophic levels in an ecosystem.

7. Evaluate methods for measuring or estimating populations of motile and non-motile organisms.

8. Calculate and interpret data for species richness and diversity.

9. Draw graphs to illustrate species diversity in a community over time, or between communities.

Guidance

1. When constructing identification keys, students should be reminded that generic terms such as “big” or “small” are not useful. Comparative, quantitative descriptors and simple identification of the presence or absence of external features are most useful in keys.

2. The design of sampling strategies needs to be appropriate for its purpose and provide a valid representation of the system being investigated. Suitable sampling techniques include random or systematic in a uniform environment, or transects over an environmental gradient.

3. Students should be familiar with the measurement of at least three abiotic factors. These could come from different ecosystems, such as:

   • marine—salinity, pH, temperature, dissolved oxygen, wave action

   • freshwater—turbidity, flow velocity, pH, temperature, dissolved oxygen

   • terrestrial—temperature, light intensity, wind speed, particle size, slope, soil moisture, drainage, mineral content.

4. Suitable human impacts might include toxins from mining activity, landfills, eutrophication, effluent, oil spills, overexploitation and change of land use (for example, deforestation, development or use for tourism activities).

5. Interesting studies can be made using historic maps or geographic information system (GIS) data to track land use change.

6. Formulae do not need to be memorized but should be applied to given data.

7. Percentage cover is an estimate of the area in a given frame size (quadrat) covered by the plant in question. Percentage frequency is the number of occurrences divided by the number of possible occurrences; for example, if a plant occurs in 5 out of 100 squares in a grid quadrat, then the percentage frequency is 5%.

8. Similar habitats can be compared using D; a lower value in one habitat may indicate human impact. However, low values of D in the Arctic tundra may represent stable & ancient sites.

Key Vocabulary

• Here

This video, although not exciting, provides a description for how to measure stream flow in a freshwater ecosystem.