D4.2 Stability and change

Features of stable ecosystems

Energy supply (usually sunlight), nutrient recycling (decomposers break down carbon compounds, carbon dioxide is released, nitrates and phosphates are released into the soil), genetic diversity (natural selection can act), climatic variables must remain within tolerance levels

Genetic diversity

The number of different alleles of genes present in a population

Mesocosm

An experimental container in which a naturally occurring ecosystem is simulated. They are used to study the response of an ecosystem to changes in specific factors

Building a mesocosm

The container must be transparent for sunlight to reach autotrophs. Small primary consumers can be included, but not secondary consumers as there will not be enough energy to sustain them. Can be open or closed systems, but closed systems are more controlled

Stability

The ability of an ecosystem to maintain structure and function over time, even when faced with changes

Example of a stable ecosystem

The Amazon rainforest, it is highly diverse, containing millions of different species. High levels of light and moisture mean photosynthesis rates are high, and organic matter is cycled by detritivores and decomposers. Water is cycled as it is lost from trees by transpiration before condensing and then rain

Deforestation of Amazon rainforest

Transpiration releases water vapour into the air above the rainforest, having a cooling effect which affects air movement and rainfall. Changes in the number of trees transpiring influences local temperatures and rainfall. Temperature and rainfall are factors in the rates of photosynthesis and nutrient cycling

Tipping point

A critical threshold in an ecosystem where a small change can lead to a large, often irreversible shift in the system's structure and function

Keystone species

A species that has a disproportionately large impact on the environment relative to its abundance. Their removal can cause significant changes in the ecosystem, thus by protecting keystone species, stability can be maintained

Example of keystone species

Sea otters help to control the population of sea urchins in kelp forests. Without them, sea urchins can overgraze vegetation, leaving no food for other species

Requirements for sustainability in ecosystems

Resources must be replaced as rapidly as they are harvested. Their use needs to be carefully regulated and monitored to ensure that they are not over harvested

Resource harvesting

The process of gathering natural resources, such as timber and crops, from an environment

Sustainable harvesting of black cherries

Black cherry is a species of hardwood tree that is popular for furniture production. It grows slowly, so it is important that sustainable harvesting methods are used. The sustainable harvesting of black cherry timber involves selective feeling (choosing specific trees to harvest), leaving enough trees behind to flower and produce seeds, and regular monitoring to ensure new growth

Sustainable harvesting of alaskan pollock

Pollock are a species of fish found across the North Pacific. The fishery is considered to be sustainable because pollock are a fast growing species, the nets have minimal contact with the sea bed (do not damage habitat), and close monitoring is carried out

Factors affecting sustainability of agriculture - soil erosion

Land needs to be cleared to make space for crops or grass. The removal of larger trees and shrubs means that the roots that hold the soil together are lost, resulting in less stable soil, leading to soil erosion

Factors affecting sustainability of agriculture - leaching and nutrient run-off

The use of synthetic fertilisers in agriculture leads to nutrient runoff due to leaching. When rainfall washes fertilisers out of soil, it can enter nearby bodies of water

Factors affecting sustainability of agriculture - fertiliser supply

Chemical fertilisers are important for many farmers, but they are expensive and not easy to supply. The process of fertiliser production is energy intensive, so the cost is affected by energy prices

Factors affecting sustainability of agriculture - pollution

Chemicals used in agriculture can enter the natural environment and kill non-target species

Factors affecting sustainability of agriculture - carbon footprint

The combustion of fossil fuels for transportation and machinery releases carbon dioxide, contributing to climate change

Eutrophication

When a body of water becomes overly enriched with nutrients (nitrates and phosphates), this results in excess growth of plants and algae. The algal bloom can block out sunlight and prevent it from penetrating below the water surface. Aquatic plants can no longer photosynthesise and die. Decomposing bacteria feed on dead organic matter (plants and algae) and increase in number. They use up the dissolved oxygen in the water, creating dead zones where there is not enough oxygen to support aquatic life

Biomagnification

A process in which chemical substances become more concentrated at each higher trophic level

Bioaccumulation

The build-up of pollutants within an organism, or within a single trophic level

Process of biomagnification

As pollutants are passed up the food chain from one trophic level to the next, they become more concentrated due to the decrease in total biomass of organisms at higher trophic levels

Biomagnification of DDT

DDT was a widely used insecticide that was found to have harmful effects on top predators. When DDT was sprayed on crops, it would leach into waterways and enter water ecosystems. It would enter food chains via plankton and accumulate in fish bodies. These fish would be eaten by birds, which would accumulate higher concentrations of DDT. It leads to the thinning of eggshells and reduced reproductive success

Biomagnification of mercury

Mercury is released through coal-fired power plants and gold mining. Mercury can be converted by microorganisms into a highly toxic form called methyl mercury, which accumulates in fish bodies. As larger fish eat smaller fish, the concentration of methyl mercury within their tissues increases, leading to harm for humans who eat large predatory fish

Macroplastics

Plastic items that are more than 5mm in length

Microplastics

Pieces of plastic that are less than 5mm in length. They come from macroplastics that have been broken into smaller pieces

Biodegradable

Capable of being broken down

Effect of macroplastics in an ocean ecosystem

Animals often try to eat plastic (turtles or albatrosses), they can become caught in plastic (leading to injuries and death)

Effect of microplastics in an ocean ecosystem

As plastic breaks down it can release toxins that lead to biomagnification. Once broken down into very small particles, it is commonly ingested by animals and enters the food chain

Rewilding

The use of conservation strategies to restore ecosystems to their natural conditions

Restoration strategies - species reintroductions

The reintroduction of apex predators will control populations of herbivores and allow the restoration of habitat vegetation. The reintroduction of keystone species can improve the structure of the ecosystem

Restoration strategies - limiting human influence

Preventing the harvesting of resources and ecological management techniques can help to restore the habitat

Rewilding of the Hinewai Reserve in New Zealand

Involved the removal of non-native species. The area is now managed with minimal human intervention to allow native communities to be restored

Succession

Progressive change in the species that make up an ecological community over time

What causes succession?

Abiotic (volcanic activity that creates new land for an ecosystem to develop, or a fire that destroys part of an ecosystem, leaving unfilled niches for a new community) and biotic (death of an organism and its decomposition) factors

Primary succession

Succession that occurs when newly formed or newly exposed land is inhabited by an increasing number of species. It can occur on any type of bare land

Changes during primary succession

1. Seeds that are carried by the wind land on exposed rock and begin to grow (they are the first species to colonise the new land, known as pioneer species)

2. As new organisms die and decompose, the dead organic matter forms soil

3. Seeds of small plants and grasses land on this soil and grow

4. The roots of these plants form a network that helps to hold the soil in place

5. As these small plants die and decompose, the soil becomes deeper and more nutrient rich

6. Larger plants can grow

7. The final species to colonise the new land become the dominant species

8. The final community formed is known as the climax community

Observations of succession

Larger plant species can be supported, an increase in the primary production of a community, species diversity increases, the complexity of food webs increases, increased nutrient cycling

Secondary succession

Takes place in areas where a disturbance has occurred but soil and some organisms remain intact

Cyclic succession

A changing cycle of communities rather than a single, unchanging climax community

Example of cyclic succession

In a grazed wood pasture, grazers (cattle) graze on open grassland, where they consume tree seedlings and prevent the growth of trees. Fast growing species such as brambles may grow in some areas and create a thorny scrub. Tree seedlings can survive within the thorny vegetation, they will grow up, but eventually fail to get enough light and die off. The tree dies and falls which creates an open area where grass can grow, restarting the cycle

Plagioclimax

A stable ecosystem that has been prevented from reaching its natural climax community due to human influence

The impact of grazing my farm livestock on arresting succession

Sheep and cattle prevent tree seedlings from establishing, meaning that a forest community may not develop

The impact of drainage of wetlands on arresting succession

Drainage of wetlands will prevent the formation of peat bogs