D4.2 - Stability & Change

Resistance

Ability to withstand change or maintain stability in a system, often in the face of external pressures or stresses.

Resilience

The capacity of a system to recover quickly/bounce back from difficulties or adapt to change.

Requirements for stability in ecosystems

• complex food webs

• genetic + species diversity

• a steady supply of energy (sun)

• recycling of nutrients within ecosystem (saprotrophs/decomposers)

• climatic variables remaining within tolerance limits

Disruptions can include

• removal of species - poaching

• Removal of materials - deforestation

• Eutrophication - algae blooms changing oxygen availability

• Climate change

Stability as a property of natural ecosystems

To maintain its structure + function overtime - able to resist change if disturbances in it

• Stable ecosystems can persist for very long period of time without turning into another ecosystem

• E.g. Amazon rainforest - high biodiversity, complex food webs

• E.g. Sonoran desert - bi-annual rainfall allow more diverse plant life (more than other deserts), high biodiversity

Role of Keystone species in the stability of ecosystems

One whose activity has a disproportionate effect on structure of ecological community + is very fundamental

• if taken out - the ecosystem is at risk of collapse

  • E.g. Wolves in yellowstone park

  • coral

  • bees - need for pollination

  • sea otters

  • ochre sea star - removal of them caused complete collapse in a model

  • beavers - make dams + wetland environment

deforestation of amazon rainforest as an example of a possible tipping point in ecosystem stability

Tipping point: reaching a level of disturbance that causes quick change that is difficult to reverse

Threshold crossed by stable ecosystems + cannot be reversed

• E.g. Amazon rainforest

  • So many trees causes evapotranspiration - which makes clouds - which makes rainfall - in which trees take up h2o - which causes evapotranspiration

  • Certain amount of land is needed for cloud forest so tipping point isn’t reached

  • Positive feedback: humid, evaporation cools temperature, makes more clouds,…

  • After tipping point is reached - no rain anymore resulting in ecosystem collapse.

  • Deforestation = fewer trees = less transpiration = drought = fires =…

  • Tipping point is uncertain

Use of a model to investigate the effect of variables on ecosystem stability

Mesocosms

Experimental system to simulate the natural environments under controlled conditions - used to model + evaluate how communities might react to environmental change in larger settings

• advantages: replicates, easy, control factors

• Disadvantages: impossible to replicate all natural factors

• E.g. Biosphere 2

  • large closed ecological system in Arizona created to study self-sustaining environments

  • in 1991, 8 people lived in it for two years to test how humans could survive in space or in other planets

  • Contains various biomes (rainforest, desert) + aims to simulate earth’s ecosystems

  • Despite challenges like oxygen shortages - it provided valuable insights into ecological balance + resource management

  • Now = research facility

Sustainability

Using natural resources for today’s needs without compromising the needs of future generations

What we need to know to assess if harvesting is sustainable

• harvest - number and age of individuals harvesting

• population size and factors affecting natural fluctuations

• reproductive rates and strategies

• food web iterations

Sustainability EXAMPLE 1

• Cod - Gadus morhua

• North atlantic cod experiences overexploitation due to new harvesting techniques

• in the 1990s the population collapsed + still not fully recovered

• harvesting reached unsustainable levels

• methods put in place to allow recovery of the cod population + maintain sustainable yields:

  • specific areas of fishing

  • increase mesh size for all little ones to leave to reproduce

  • setting quotas on yields

  • monitoring population

Sustainability EXAMPLE 2

• Black cherry trees - Prunus serotine

• used for furniture - attractive wood colour

• Slow growing hardwood

• With increased demand = deforestation —> unsustainable harvesting

• FSC formed to regulate sustainable logging

• Methods put in place to allow recovery of the black cherry population + maintain sustainable yields:

  • selective logging practices - certain age + area selected to harvest

  • Limits set to ensure enough trees remain to produce fruit and seeds for next generation

  • Data collected to compare harvesting + growth

Agriculture vs sustainable agriculture/harvesting

The practice of cultivating plants + livestock for food

• many processes in agriculture produce Greenhouse Gases - carbon footprint is high in agriculture

Sustainable harvesting: replacement must be greater or equal to harvesting rate

Factors affecting sustainable agriculture

• Soil erosion - e.g. after harvesting

• Loss/leaching of nutrients - plants harvested = soil is depleted of nutrients and nutrients are replaced by fertiliser

• Agrochemicals - fertilisers/pesticides = change balance of soil

  • pesticides kill microbes in soil important for decomposition and recycling of nutrients

• Carbon footprint - energy and fuels

Impacts of humans on the environment - Eutrophication

1. Nitrates and phosphates (usually from fertilisers) dissolve in water + drain through the soil when it rains or through irritation

2. These find their way into bodies of water such as lakes and rivers or even the ocean - run off

3. Algae and plants in these bodies of water grow well due to the rich supply of nutrients, sometimes causing algal blooms

4. These usually cause carpets of algae on top of the water and prevent light from penetrating below the surface

5. The algae (and many of the plants below the surface) die and are decomposed by saprotrophic bacteria. As these are aerobic they increase the BOD (biochemical oxygen demand) and use up much of the oxygen in the water.

6. This has a knock on effect on all life in the water, causing animals in the water to suffocate, further increasing the BOD due to decomposition.

7. Eventually this aquatic ecosystem becomes devoid of life and may take years to recover

Impacts of humans on the environment - Biomagnification

The process whereby toxins accumulate in organisms as they move up the food chain, leading to higher concentrations in predators than in their prey. This can result in harmful effects on wildlife and human health.

• Bioaccumulation: increase in toxin levels throughout an organisms life

• Bio magnification: increase in toxin levels through trophic levels

  • Due to loss of energy the next consumer has to eat a lot more of the previous one which means more exposed to a lot more of those chemicals/tocins

• chemicals or microplastics are not metabolised so the concentration builds up

• In lower trophic levels their concentrations are not usually sufficient to cause harm but in organisms higher in the food the relative concentrations in their tissues increase due to accumulation over their longer lifetimes

• Accumulate in adipose tissue if fat soluble

• E.g. DDT

  • Used as a revolutionary pesticide in the mid 20th century

  • Particularly effective against mosquitoes and the spread of malaria

  • in the 1950/60s scientists noticed drastic fall in populations of birds of prey

• E.g. Mercury

  • Heavy metal released into environment in some industrial processes + burning of fossil fuels

  • Cannot be metabolised or excreted - accumulates in bodies of organisms

  • Can pose a threat to humans if we consume large numbers of fish that has mercury

  • Minamata disease - caused by severe mercury poisoning - first recorded in Japan

Impacts of humans on the environment - Micro/macro plastics

• Microplastics: fragments of plastic smaller than 5mm - found everywhere + effect is yet to be fully determined

• Macroplastics: larger than micro and visible to human eye —> ingested by marine life + cause entanglement

• Major problem is that they are non biodegradable or degrade very slowly - persist in the environment or as microplastics that accumulate inside organisms

• Not plastic themselves causing issues - as they degrade they release toxic carbon compounds or toxic compounds can accumulate inside them or on their surfaces

Restoration of natural processes in ecosystems by Rewilding

Process involving restoring ecosystems that have been degraded due to human activity - aims to use as little intervention by humans as possible

Steps needed:

• Ecological management - e.g. stop human sources that were impacting + monitoring

• Species reintroduction - e.g. keystone species + control of invasive species

• Habitat restoration - e.g. reforestation/reconnecting habitats over large areas using wildlife

CASE STUDY

• Hinewai reserve in New Zealand

• From farmland —> native forest

• Alien animals controlled (goat)

• Human interference has been minimal

• Allow naturally occurring species to outcompete alien species by returning the habitat to natural state

Ecological succession

Process whereby ecosystems change over time due to biotic or abiotic changes

• Primary succession occurs in lifeless areas, such as after a volcanic eruption or glacier retreat, beginning with pioneer species like lichens and mosses, leading to a mature ecosystem.

  1. Bare rock

  2. Early colonisers such as bacteria, lichen and moss become established - called ‘pioneer species’

  3. They generate small amounts of soil through erosion and decomposition that allow herbs and grasseds with shallow roots to colonise

  4. These plants provide habitats for small animals such as insects, and food an refuge for birds. As these communities become established, dead and decaying matter builds more soil

  5. Larger plants such as shrubs and small trees are able to take root

  6. Eventually a climax community may become established. This is a stable and biodiverse ecosystem

     • Climax community doesn’t remain indefinitely - natural cycles which takes back to early stage (cyclical succession)

     • Forest forest = natural way move back to the beginning

     • E.g. California Coastal chaparral forest fires returns back close to bare rock every 10-15 yrs

What happens to following factors during primary succession = INCREASE

• Primary production

• Species diversity

• Complexity of food webs

• Nutrient cyclign

• Secondary succession occurs in areas where a disturbance has cleared an ecosystem but left the soil intact, such as after a fire or flood, leading to a faster recovery compared to primary succession.

Cyclical succession in ecosystems

Patterns of change and succession that occurs either naturally or due to periodic disturbances

• No stable climax community - that’s in linear succession

• E.g. evergreen forests regenerating after fires

Arrested succession

Human influences can prevent succession from reaching the climax community - due to persistent disturbances and is called arrested succession

• E.g.

  • Grazing

    • Protected areas, artificially high population of livestock

    • Grasses persist

    • No succession by shrubs or trees - no forest development

  • Wetland drainage

    • Swamps and bogs are natural carbon sinks - have peat which can sequester a lot of carbon

    • Water logged and anoxic environment - only some orgs have special adaptations for living there

    • Drainage of water causes other plants to thrive - no longer anoxic

    • Dead plant matter tends to accumulate forming peat