d4.2 stability and change

evidence for ecosystem stability

Some forests/deserts have shown continuity for long periods, for millions of years

 requirements for stability in ecosystems

• Supply of energy

  • Rely on a continuous supply of energy from the sun, to drive photosynthesis, converting light to chemical energy that support food webs

• Nutrient recycling

  • Ecosystem has finite amount of nutrients, so decomposers are needed to break down organic matter and return nutrients to soil (eg carbon, nitrogen, phosphorus for fertility of soil/essential for plants)

• Genetic diversity

  • Higher genetic diversity within species enhances resilience to diseases, environmental changes, and other stressors, maintaining stability

• Response to climate change

  • Shifts in species composition, migration, and other mechanisms, keep climatic changes within tolerance range

possible tipping point in ecosystem stability

• Currently, a large area of the Amazon rainforest produces water vapour by transpiration producing a cooling effect when vapour evaporates. this influences air flow and rainfall of the entire region. 

• However deforestation causes increased temp and lower rainfall volume

• Uncertain how much more land can be lost until tipping point is reached and processes cannot be maintained

mesocosms, how are they set up

• mesocosm sealed vs open?

  • Mesocosms can be set up in open tanks. But sealed glass vessels are preferred to prevent the entry and exit of matter while allowing energy transfer (light)

• what kind of mesocosm will be successful

  • Aquatic/microbial ecosystems probably more successful than terrestrial bcs of ease of manipulation in water vs soil, and aquatic is usually simpler in structure

role of keystone species

• Keystone species are organisms of any type that play an important role in the biodiversity of their ecosystem

• If they are removed, this will cause disproportionate impact on the community structure with the risk of ecosystem collapse if they are removed

• Loss of stability

 Explain how sustainability of resource harvesting from natural ecosystems is assessed, with 2 examples.

• For resource harvesting to be counted as sustainable, the rate of harvesting should be lower than the rate of replacement

• Chilean sea bass

  • Population collapsing due to overwhelming demand for it that led to overfishing, so regulations put in place: must have documents to verify that fish were caught legally, limit on number of fish caught. population now monitored to ensure sufficient repopulation is taking place

• Black cherry tree

  • Wood wanted for furniture, obtained through clear cutting (removed all trees) which had env impacts (eg soil erosion). changed to selective logging to select trees based on age/size, only at pace that does not surpass growth rate of remaining trees to allow natural replacement

 Outline the factors affecting the sustainability of agriculture.

• oil erosion → loss of fertile topsoil so need more fertilisers. shld use plant to cover crops to reduce impact of rain

• leaching of nutrients → rain dissolves nutrients and carries them away, increasing fertiliser dependency, shld use sprinkler to regulate water

• supply of fertilisers → overuse causes nutrient imbalances, high cost so farmers use less env friendly alternatives. shld use organic ones

• agrochemical pollution → excessive use of fertilisers/pesticides/herbicides contaminate water bodies and harm biodiversity, shld also use organic fertilisers

• carbon footprint → high carbon emissions from machinery, shld use renewable energy sources

Explain the eutrophication of aquatic and marine ecosystems due to leaching of nitrogen and phosphate fertilisers

• Phosphates and nitrates from excess fertilisers are washed into river due to leaching

• High level of phosphates allows algae to grow faster, algal blooms block out light

• The aquatic plants beneath the algae mat will not be able to photosynthesise to make food and die/algae below also die due to insufficient sunlight reaching them

• All algae eventually dies when nutrient depletes or due to toxins released from algae bloom

• Aerobic bacteria decomposes the dead organisms and uses up a lot of oxygen which cannot be replenished bcs producers all die. BOD increases!! 

• Hypoxic condition in the water kills off many more aquatic organisms

• Eventually, all life is gone and a dead zone is created

Outline the biomagnification of pollutants in natural ecosystems, using the examples of DDT and mercury.

• DDT (CTs answer key)

  • Some DDT are persistent/degrade slowly once released into the environment (from insecticide)

  • They enter the food chain through producers/lower trophic levels (specifically for DDT, phytoplankton)

  • Some DDT are passed on to higher trophic levels in the food chain and are not excreted (bird which prey on fish as their primary food source

  • Some DDT accumulates in fatty tissues of animals

  • Highest trophic levels/top consumers have the highest concentration of DDT in their bodies

  • Hence, DDT bioaccumulates/biomagnifies

  • (While DDT did not immediately kill the birds, it affected their eggs which contained less calcium and thus were more fragile. The number of offspring in these populations decreased greatly.)
    

• mercury→mercury from factory released as wastewater, bacteria in the water transformed it into organic form, methyl mercury, which was incorporated into the local food chains. Methyl mercury became concentrated by biomagnification in shellfish and fish which were eaten by local people as a major part of their diet, causing central nervous system disease

Outline the effects of plastic (microplastic and macroplastic) pollution on marine life.

• Note: macro vs microplastic

  • macro plastic debris >5mm, micro plastic granules in face wash, <5mm

• Effects of plastic pollution on marine life

  • IT IS NON BIODEGRADABLE

    • Ingestion which leads to starvation as stomachs fill w indigestible plastic

    • Entanglement leading to injury, suffocation or drowning

    • Toxic contamination by harmful chemicals which are absorbed by organisms and accumulate, affecting humans

    • Habitat disruption, plastic smothers coral reefs

methods of restoration of natural processes in ecosystems (rewilding), giving an example

• Rewilding is conservation efforts aimed at restoring and protecting natural processes and wilderness areas

• Methods of rewilding include the reintroduction of apex predators and other keystone species, reestablishment of connectivity of habitats and minimisation of human impact

• Hinewai reserve → A New Zealand ecological reserve showcasing the success of rewilding efforts.

Define ecological succession and outline its causes.

Ecological succession is defined as the change in the species living in an area over time, caused by changes in abiotic and biotic factors in an ecosystem

Outline the process of changes occurring during primary succession

• Primary succession is when an area where no previous ecosystem existed (such as bare rock) forms a mature ecosystem after thousands of years. 

• soil is built up with growth and death of pioneer species, facilitated by bacteria that helps with decomposition

• soil can now retain water and support growth of simple plants, increase in primary production

• bacteria are involved in nutrient cycling as they release nutrients from the breakdown of organic matter, and some can fix nitrogen from the atmosphere to make it available to the plants

• with establishment of producers, there are food and habitats which attract the invertebrates to start colonizing the area and begin simple food chains

• more soil that are enriched with nutrients, larger shrubs and trees start to grow with seeds brought in by birds and wind.

• more animals will join the growing community, attracted by the abundance of food and lack of competition

• climax community is achieved

Give an example of cyclical succession in ecosystems

• Cyclical succession is a cycle of communities rather than single unchanging climax community

• For example, wood pasture

  • Thorned, unpalatable thickets grow, then trees grow using thicket as protection from herbivores, but shade of trees restrict growth of thicket; trees eventually die and area is open pasture again

climate communities and their arrested succession

A climax community is ecologically stable, and will not usually change unless environmental conditions change (temperature, rainfall)

Arrested succession can occur by humans removing forest for livestock grazing or draining wetlands for development