Biology Unit 4.2 Stability in Ecosystems

• Stable ecosystems have the following features.

  • Efficient nutrient cycling which allows the system to be self-supporting
  • High biodiversity and stability
• Examples of tropical rainforests include the Amazon rainforest in South America and the Congo rainforest in Africa
• These rainforests have high levels of light and moisture mean that photosynthesis rates are high
• In these rainforests organic matter is cycled by detritivores such as termites, slugs and worms, and by decomposers such as fungi; the nutrients are then taken up again by the trees
• In these rainforests water is cycled within the ecosystem as it is lost from trees by transpiration before condensing and falling again as rain
• Requirements for ecosystem stability:

  • A reliable source of energy must be present
  • For most ecosystems this energy source is sunlight
  • Light energy is converted into chemical energy by photosynthesis
  • Many photosynthetic organisms must be present
  • Stored chemical energy is then passed up food chains through consumption
• In order for an ecosystem to support itself, the cycling of nutrients is essential. If nutrients are not recycled then the supply of nutrients will run out
• Nutrients are cycled when decomposers such as bacteria and fungi break down the carbon compounds, e.g. proteins and nucleic acids
• Minerals such as nitrates and phosphates are released into the soil
• The nutrients released by decomposers can then be taken up again by producers and re-enter the food chain
• If nutrients are removed from an ecosystem then cycling will be interrupted and productivity will be reduced
• Genetic diversity the number of different alleles of genes present in a population
• High levels of genetic diversity mean that natural selection can act on favourable alleles, providing a population with the potential to adapt to changes in the environment
• Genetic diversity allows populations to resist the effects of change in their environment
• Human activities are causing climate change at such a rapid rate that climatic variables are changing beyond tolerance levels in some ecosystems
• The stability of an ecosystem can be investigated using a model ecosystem known as a mesocosm
• A mesocosm is an experimental container in which a naturally occurring ecosystem is simulated
• Mesocosms can be used to study the response of an ecosystem to changes in specific factors such as nutrient and light levels
• Unlike a real ecosystem, it is possible in a mesocosm to control all of the factors other than the variable being studied
• The two types of mesocosms are terrestrial and aquatic
• The Amazon rainforest is an example of an ecosystem where human activities are endangering ecosystem sustainability
• Temperature and rainfall are factors in the rates of photosynthesis and nutrient cycling
• Deforestation could have a knock-on effect on other important ecosystem stability factors
• Keystone species are species that have a disproportionate effect on the structure and function of their ecosystem
• The removal of keystone species can cause significant changes in the ecosystem, including the loss of other species and possible ecosystem collapse
• In order for a resource to be sustainable, its use needs to be carefully regulated and monitored to ensure that it is not over-harvested
• Eutrophication is the process in which a water body becomes overly enriched with nutrients, leading to the plentiful growth of simple plant life
• Biomagnification is the increase in concentration of persistent or non-biodegradable pollutants with ascending trophic level through a food chain
• As pollutants are passed up the food chain from one trophic level to the next, they can become more concentrated due to the decrease in total biomass of organisms at higher trophic levels
• Toxins such as DDT  are persistent pollutants that can enter food chains
• DDT would then enter food chains via plankton and accumulate in the bodies of fish 
• These fish would then be eaten by birds, which would accumulate higher concentrations of DDT
• Mercury is another example of a pollutant that can accumulate through food chains
• Plastics have a large negative impact on both land and water habitats due to their non biodegradable nature
• Macroplastics include plastic bags, bottles, food packaging, and fishing nets
• Microplastics come from macroplastics that have been broken into smaller pieces by, e.g. wave action or UV rays
• Human activities such as deforestation and overharvesting of resources can destabilise ecosystems