D4.2 Stability and Change

Requirements for sustainable ecosystems

• Sufficient energy supply

  • Light, harnessed through photosynthesis by producers—> move up food web to all trophic levels

• Nutrient recycling

  • Carbon, phosphorus, nitrogen cycling → Nutrients are finite so must be recycled

• Genetic diversity

  • Protects against events that can decimate entire populations —> disease, climatic events, increase in predators

• Response to climate change

  • Genetic diversity can help is variables of climate change are within species tolerance levels

Mesocosm

A self-contained system that provides a living environment for organisms

Keystone species

Species that have a disproportionate effect on the structure and function of their ecosystem

Trophic cascade

When changes at one trophic level have indirect effects on other trophic levels

Eutrophication

The process by which bodies of water becomes unnaturally enriched with nutrients, leading to excessive plant and algae growth and subsequent oxygen depletion

Explain the process of eutrophication

• Excessive nutrients from fertilizer run-off on land enters body of water

• Minerals promote aquatic plants and algae to grow rapidly

• Algae bloom blocks sunlight from penetrating below surface of water and therefore aquatic plants

  • Water oxygen levels fall

• Aerobic bacteria decomposes excess algae growth and organic matter at an increased rate

  • Increased biochemical oxygen demand (BOD), depleting levels of dissolved oxygen in water

  • Aerobic organisms die due to insufficient oxygen in water

Biochemical oxygen demand

The oxygen needed by bacteria in a body of water

Biomagnification

When harmful substances in the environment build up in the organisms towards the top of the food chain

• Substance becomes more concentrated in tissue of the consumer organism

• e.g. Mercury, DDT

Explain the biomagnification of Mercury

• Industrial sources emit mercury into aquatic environments

• Microorganisms at bottom of aquatic food chain convert elemental mercury into methyl mercury

• Methyl mercury becomes more concentrated in animal tissues as it moves up ocean food chain

  • Humans who eat large fish (e.g tuna) are at risk to high levels of mercury exposure

Explain the biomagnification of DDT

• DDT is a synthetic insecticide that was discovered to be harmful to birds

• DDT sprayed on crops would leech into waterways, eventually entering marine and freshwater ecosystems

• DDT enters food chain through plankton and accumulates in bodies of fish

• Birds eat the fish, accumulating higher concentration of DDT

  • Lead to thin eggshells that couldn’t survive incubation, fewer young birds in population

Microplastic

Plastic debris smaller than 5mm

Macroplastic

Plastic debris larger than 5mm

Describe ways animals are impacted by plastic

• Turtles may eat plastic bags that resemble jellyfish

• Albatrosses accidently consume plastic when fishing, and may feed it to their chicks when they regurgitate food —> chicks starve due to stomach being filled with plastic

• Animals get caught in plastic

• Breakdown of plastic releases toxins and biomagnification in food chain

• Microplastics ingested by animals enters food chain

Rewilding

Conservation activities aimed at restoring and protecting natural processes and wilderness areas

• Form of ecological restoration that leaves an area to nature, as opposed to active resource management

List the methods of rewilding

• Reintroduction of apex predators and keystone species

• Establishing wildlife corridors to connect habitats over larger areas

• Limiting human influences

  • Stopping agriculture and resource harvesting (e.g logging, hunting)

  • Ecological management techniques (Controlled grazing or burning to restore habitat)

Ecological succession

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

Primary succession

When newly formed or newly exposed land is inhabited by an increasing number of species

• Magma from erupting volcanos cooling and forming new rock surfaces

• Landslide that exposes bare rock

Colonization

The arrival of organisms on bare land

Secondary succession

When an existing ecosystem is drastically altered, and the remains of the previous ecosystem are used as a starting point for further changes

• Soil is already present

Compare primary and secondary succession

• Primary succession begins with no life while secondary succession follows a disturbance of primary succession

• Primary succession starts with no soil while secondary succession has soil

• Primarily succession begins in a new area while secondary succession occurs in an old area

• Primarily succession has low biomass while secondary succession had higher biomass

• Primary succession has low production while secondary succession had higher production

Primary production takes much longer to occur than secondary succession due to the process of creating soil

Production

The increase in biomass

Pioneer species

The first species to colonize new land

Climax community

The relatively stable, mature community that has reached the end of ecological succession

Characteristics of primary succession progression over time

• Increasing species diversity

• Increasing size of plants in the community

• Increasing primary production

• More complex food webs

• Increasing nutrient cycling

Cyclical succession

A repeating pattern in which communities in an ecosystem replace each other in a cycle

Arrested succession

When a community is held or deflected at a stage before the natural climax is reached

Explain how loss of the Amazon rainforest can reach a tipping point

• A tipping point is a threshold beyond in which a small additional change can cause a large and irreversible ecosystem shift

• Deforestation of the Amazon affects the climate and weather patterns by reducing transpiration and water vapour

• This decreases rainfall, causing soil and vegetation to dry

• Increased drought and forest fires, causing tree growth and survival to decline

• Forest cover declines, decreasing transpiration

• Positive feedback loop

Factors affecting sustainable harvesting

• Soil erosion —> Erosion of topsoil from heavy rainfall can wash away nutrients and organic matter

• Leaching of nutrients —> Rain and irrigation water dissolves nutrients and carries them away from the root zone of a crop. Typically ends up contaminating nearby water supply

• Fertilizer supply —> Farmers demand for fertilizer exceeds supply, Fertilizer production is energy intensive so costs are affected by global energy prices

• Pollution —> Water runoff + leaching pollutes water —> kill non-target species

• Carbon footprint —> Reliance on fossil fuels for transportation, machinery, and synthetic fertilizers increases carbon footprint

Tipping point

A critical threshold within an ecosystem where a small change can lead to significant, often irreversible shift’s in the systems state

Carbon footprint

The total amount of greenhouse gases that is generated by an activity

Outline the process of cyclical succession in wood pastures

• Grazers graze on pockets of land, consuming tree seedlings (prevents tree growth)

• Thorny species (e.g thickets, brambles) grow within the open pasture

• Tree species survive using thorny vegetation as protection, deterring grazers

• Later, shade from the tree restricts the thicket from growing and eventually dies

• Once the tree dies, the cycle restarts

Distinguish between primary and secondary succession

Autogenic succession

Succession driven by interactions among species in an ecosystem

Allogenic succession

Succession influenced by external environmental factors (e.g climate change, soil development)