Sustainability and change

ecosystem stability

• systems are stable if they can continue for an unlimited period of time

• e.g the daintree forest in australia has remained for over 100 million years, since the conditions remained warm and wet

• mechanisms that sustain ecosystems are fragile and can be easily disrupted, so ecosystems are not always stable

maintaining stability in ecosystems

• must be a steady supply of energy as it cannot be recycled

• nutrient cycles should replenish abiotic reserves of all chemical element needed by organisms

• climatic variables, especially temp and rainfall, must remain within ranges of tolerance of organisms in ecosystem

• supplies of water for rainfall

• oxygen for aerobic respiration released by autotrophs

• carbon dioxide released from respiration required photosynthesis

• individual species, must have high genetic diversity so there is variation for natural selection to work on

tipping points in ecosystem sustainability: amazon rainforest

• amazon rainforest is so vast it has major effects on climate

  • evaporation of water from leaves (transpiration) has a cooling effect

  • water vapour transpired from leaves condenses in the atmosphere above forest, lowering air pressure and causing wind

  • condensed water falls again as rainfall, so can be absorbed by trees

• ecosystems show resilience, but above a certain level of disturbance, a tipping point is reached, beyond which positive feedback mechanisms cause rapid irreversible changes

  • amazon rainforest has disturbance due to deforestation

  • if a tipping point is reached, positive feedback cycle will cause unstoppable changes

  • it is uncertain what area of amazon rainforest is needed to prevent the tipping point being reached

modelling ecosystem sustainability

• ecosystem sustainability can be investigated using mesocosms

  • a small experimental enclosure, in which a naturally occurring ecosystem is simulated

  • used to study response of an ecosystem to changes in specific factors

• fenced-off enclosures or forest model terrestrial ecosystems

• open tanks or sealed glass vessels model aquatic ecosystems

  • sealed vessels allow entry and exit of matter to be controlled with energy transfer happening freely

• aquatic ecosystems are likely to be more successful than terrestrial

keystone species

• has a disproportionate effect on the structure of an ecological community

• species diversity decreases if the keystone species is lost, may result in collapse of entire ecosystem

sustainability in resource harvesting

• harvesting is sustainable if the rate of harvesting is lower than the rate of replacement

• e.g brazil nuts

  • 40’000 tonnes of nuts are harvested each year from trees in the amazon rainforest

  • sustainable harvesting depends on leaving some nuts to germinate and grow into new trees

  • in areas of intense harvesting there are few/no young trees, so harvesting is unsustainable

• e.g atlantic cod fishing

  • over a million tonnes of cod is harvested per year from north atlantic

  • there was once a very large population, but overfishing led to a total collapse in 1990s

  • international agreements have been put in place to reverse this, in 2005 biomass of adult cod in north sea tripled, so cod fishing in North sea is sustainable

the sustainability of agriculture

• human population depends on foods produced by agriculture, sustainability in agriculture is influenced by many factors:

• soil erosion

  • land needs to be cleared to make space for crops

  • removal of trees means the roots that hold soil together are lost, resulting in less stable soil that can be easily washed away

  • this leads to soil erosion, and a reduction in the availability of soil needed for crops

• leaching and nutrient-run off

  • use of synthetic fertilisers in agriculture leads to nutrient runoff due to leaching

    • when rainfall washes fertilisers out of soil into nearby bodies of water

• fertiliser supply

  • chemical fertilisers are important but expensive and not easy to supply

• pollution

  • some farming relies on the use of chemicals e.g pesticides, needed to improve yield which would be damaged by pests

  • these chemicals can enter natural environment and cause problems

• carbon footprint

  • reliance on fossil fuels for transport, machinery, has significant implications for sustainability of agriculture

eutrophication as a result of leaching

• when rainwater falls on ecosystems, soluble nutrients from fertilisers such as phosphates and nitrates dissolve and are washed out of the soil into nearby water sources like rivers, lakes, this is leaching

• this causes nutrient enrichment in these water bodies - eutrophication

  • causes excessive growth of algae and bacteria

  • algae and bacteria rise to seek light (algal bloom), but some are shaded out and die

  • decomposition of dead organisms cause high biochemical oxygen demand (BOD)

  • water becomes anaerobic due to high BOD from decomposer respiration, so fish die

biomagnification/bioaccumulation

• natural ecosystems are polluted with human made chemicals, in some organisms the concentrations of these can be lethal

  • e.g DDT caused catastrophic falls in populations of falcons, otters in 20th century

• bioaccumulation is an increase in the conc of a toxin in adipose tissues

  • e.g methyl mercury accumulating in adipose tissue

• biomagnification is an increase in conc of a chemical substance at each successive trophic level in a food chain

  • enter food chain through lower trophic levels and are passed to higher trophic levels

effects of plastic pollution of the oceans

• oceans contain huge quantities of plastic because it is non-biodegradable

• macroplastics

  • large, visible items

  • marine wildlife can become entangled in nets and ropes and ingest plastic bags

• microplastics

  • fragments of plastic that are not visible

  • are ingested by many types of marine wildlife, some of which are toxic

NOS scientific influence on citizens

• scientists can influence actions of citizens if they provide clear information about their findings

• media coverage of the effects of plastic pollution on marine life changed public perception globally, driving measures to address this problem.

rewilding

• efforts are being made to encourage natural ecosystems to return after being damaged by human action

• essential principle of rewilding is there should be very minimal human interaction

  • reduction of human activities e.g agriculture, logging

• or there is a need for intervention to reverse past human actions:

  • reintroduction of apex predators and other keystone species

  • reestablishment of connectivity where natural ecosystems have been fragmented

  • control of invasive species

• e.g: Hinewai reserve in New zealand

  • successful ecological restoration

  • invasive mammals e.g goats are rigorously controlled but other than that there is minimal human interferance

ecological succession and its causes

• ecological succession: sequences of changes that progressively transform ecosystems

• changes in the ecosystem often trigger other changes, so one ecosystem replaces another

  • a stable and persistent ecosystem may then develop that does not undergo any further significant change - this is the climax communtiy

• can be triggered by changes in both biotic

  • e.g beavers colonising a river causing flooding leading to open water becoming a swamp

• and abiotic environment

  • e.g an avalanche sweeping forest away

principles of primary succession

• primary succession: begins in environments where living organisms are largely or completely absent. colonisation of previously uninhabited areas

  • early colonisers generate small amounts of soil, allowing herbs with roots to start to colonise

  • as deeper soil develops, successively larger plants colonise

• general principles of primary succession:

  • species diversity increases as more species join the community than are eliminated

  • primary production increases as larger plants colonise and theres more photosynthesis

  • food webs become more complex

  • sizes of organisms increase

  • nutrient cycling increases as animals and plants generate more dead organic matter

cyclical succession

• some ecosystems are characterised by cycles of change rather than a stable climax

• in cyclical succession, species replace each other over time repeatedly

• e.g Wood pasture in northwest europe

human influences blocking formation of climax communities

• as succession proceeds, stable climax community may develop which is not superseded

  • type of climax community developed depends on climate and other environmental changes

• human influences can cause a deflected or a arrested succession so a plagioclimax develops (an alternative stable community)

• grazing

  • grasses and many herbs may tolerate grazing but tree and shrub seedlings are killed, so grassland persists as plagioclimax where it would naturally be replaced by a forest

• drainage of wetlands

  • removes water from swamps and increases soil aeration

  • organisms adapted to wetlands and die, allowing saprotrophic fungi to decompose any peat developed in the swamp