IB Biology Topic D4.2.4: Use of a Model to Investigate the Effect of Variables on Ecosystem Stability Notes

Mesocosms Are Miniature Ecosystems Built to Test What Affects Stability

1. How would you build a tiny ecosystem in a jar that keeps itself alive for months?
2. A mesocosm is a controlled, small-scale model of a natural ecosystem used to test how variables affect its stability.
3. Because everything inside is set up and measured by the researcher, a mesocosm lets you change one factor and watch how the whole system responds.

A Working Mesocosm Needs the Same Four Components as a Real Ecosystem

1. A mesocosm only stays self-sustaining if it contains every part that cycles energy and matter in a real ecosystem.
2. Autotrophs (producers)
   1. Plants or algae capture light and produce oxygen and organic matter.
3. Consumers
   1. Herbivores and carnivores feed through the food web.
4. Decomposers
   1. Bacteria and fungi break down waste and recycle nutrients.
5. Abiotic factors
   1. Soil, water, light, and temperature set the physical conditions organisms live in.

Sealed and Open Mesocosms Suit Different Kinds of Study

1. Whether a mesocosm is sealed or open depends on what the experiment needs to control.
2. Sealed mesocosms
   1. They let energy such as light pass in but stop matter from entering or leaving, which suits long-term closed-system studies.
3. Open mesocosms
   1. They exchange matter with their surroundings, which suits testing a specific variable such as added pollution.

Mesocosms Are Powerful Because They Control and Repeat Conditions

1. Controlled variables
   1. Researchers can change one environmental factor at a time to test a specific hypothesis.
2. Replicability
   1. The same setup can be repeated many times to check that results are reliable.
3. Scalability
   1. Mesocosms range from small jars to large outdoor tanks, so they fit many research goals.

Mesocosms Are Limited Because They Simplify the Real World

1. Oversimplification
   1. A mesocosm cannot capture the full diversity and complexity of a natural ecosystem.
2. Small size
   1. A small model misses large-scale processes such as migration or wide nutrient flows.
3. Edge effects
   1. The container walls create boundaries that can change how organisms behave and skew the results.