D4.2 Stability and Change

Stability of an ecosystem

ecosystem can endure over time because of the processes functioning within it. (has gradual changes)

Stable ecosystem example

Daintree rainforest - oldest continuously forested rainforest on earth

What does the structural and functioning stability of an ecosystem depends on

Sufficient supply of energy

Recycling of nutrients

Genetic diversity

Climatic variables remaining within tolerance levels

Sufficient supply of energy

Energy enters an ecosystem as light, so it's important that there are producers and they are efficient for the ecosystem to be stable

Recycling of nutrients

There is a finite supply of nutrients in an ecosystem, so they must be recycled by organisms for it to thrive

Genetic diversity

large gene pools mean protection if there is significant changes, because some alleles will allow the species to adapt, keeping the ecosystem stable

Climatic variables remaining within tolerance levels

species in an ecosystem can tolerate some abiotic changes, but not significant. so variables must stay in tolerance levels for ecosystem to be stable

Possible tipping point of ecosystem stability - Amazon Rainforest

- so large that it influences its own weather + climate, if disrupted:

- normally water vapour is produced by vegetation transpiration (has cooling effect)

- condensation of water vapour turns into clouds/rainfall (influences wind patterns)

Amazon forest deforestation cycle

deforestation = less transpiration = less water vapour = less natural cooling event = higher temperature = easier to burn = reduced forest

Tipping point

point where an ecosystem can no longer cope with environmental change, shifting from one state to another

Amazon tipping point

17% cleared over 60 years

tipping point unknown

Mesocosm

portion of a natural ecosystem to be used for ecological experiments

Sealed mesocosm

allows energy transfer but prevents matter exiting/enterin

How mesocosm allow for ecperiments

once set up, a specific condition can be changed, then the changes in mesocosm are monitored and analysed

When to address ethical considerations - mesocosms

when animals are involeved

Keystone species

species whose activity has a disproportionate effect on the structure of an ecological community (risk of ecosystem collapse if they're lost)

What keystone species impact

prevalence and population levels of other species in community

Keystone species examples

cassowaries, ochre sea star

Keystone species ochre sea star

- found in intertidal zones in western North America, predator of mussels

- removal of sea stars = increase mussel population = less invertebrates/algae ∴ decrease biodiversity

Keystone species cassowaries

- large, flightless birds found in topical rainforests, swamps, mangrove forests, woodlands, beaches in Queensland

- eat fruit, then disperse and germinate seeds

- animals rely on these plant species

sustainable harvesting: brazil nuts

- harvested from Bertholletia excelsa trees in the Amazon

- area is threatened by logging

sustainable harvesting = selective logging + leaving some nuts to germinate

Issues with agriculture

- soil erosion

- leaching of nutrients

- supply of fertilisers + other inputs

- agrochemical pollution

- carbon footprint

soil erosion

wearing away of surface soil by water and wind

leaching of nutrients

rainfall/irrigation water dissolving nutrients in soil and carrying them away from crop roots

supply of fertilisers + other inputs

chemical fertilisers increase levels of nutrients in soil (production + transport = expensive + energy extensive)

agrochemical pollution

chemical pesticides contaminate soils

- carried away to waterways

runoff

water that moves across the land surface and into streams and rivers

leaching

removal of dissolved materials from soil by water moving downwards

eutrophication

nutrient enrichment of aquatic environments from runoff and leaching

eutrophication effect on ecosystem

chain reaction that reduces level of dissolved oxygen

how does eutrophication reduce oxygen levels

BOD increase (caused by extra decomposition by excessive algal growth) = oxygen levels depleting

- deprives aquatic animals of oxygen

biochemical oxygen demand (BOD)

the amount of oxygen needed by bacteria in a body of water

1. excess nitrates + phosphates = rapid algae/plant growth

2. sunlight blocked by algae on water surface so plants deep under water die

3. excess algae/plants = increase organic material available to bacteria (increasing their pop.)

4. increase bacteria = more oxygen needed for respiration (increase BOD), decreasing level of dissolved oxygen in water

5. aquatic animals cannot obtain enough oxygen to survive

biomagnification

increase in toxin concentration in trophic levels

biomagnification process

- small amount enters at producer/primary consumer levels

- toxin from prey accumulates in body tissue of predators

- repeated along food chain until level of toxin is high enough to cause illness/death

biomagnification: mercury

-mercury biomagnifies as it goes up the food chain

-mercury-contaminated fish are the primary pathway of mercury into humans

biomagnification: DDT (dichloro-diphenyl-trichloroethane)

Persistence: Banned in many developed nations but remains in water sediments due to its chemical stability.

Bioaccumulation & Biomagnification: Absorbed by bottom feeders/zooplankton, then concentrated up the food chain, reaching highest levels in top predators (e.g., eagles, ospreys).

Ecological Effects: Causes eggshell thinning in birds, leading to population declines (e.g., bald eagles). This prompted the 1973 Endangered Species Act in the U.S.

Recovery: After DDT was banned, environmental and animal concentrations declined, aiding species recovery.

effect of microplastics

- not biodegradable

- can be ingested by marine animals

- accumulate in body tissues

- passes to predators

- some plastics slowly release chemicals that have been associated with certain types of cancer

macroplastics

pieces of plastic bigger than 5 mm

microplastics

pieces of plastic smaller than 5 mm (found in every marine ecosystem studied so far)

north pacific subtropical gyre

- plastics get caught in gyres (large ocean currents)

- great pacific garbage patch created in north pacific subtropical gyre

- high level of microplastics

macro/microplastic impact on marine life

- sea turtles eat plastic bags (think they're jellyfish)

- plastic rings from six-packs of canned drinks stuck on wildlife necks

- fishing nets trap fish, turtles, marine mammals

- microplastics take up space in digestive tract of marine animals (less nutrient intake)

rewilding methods

- reintroducing apex predators/keystone species

- re-establishing connectivity of habitats over large areas

- minimisation of human impact

rewilding

approach to restoring natural ecosystems (minimal human intervention)