D4.2: Stability and Change

Stability of Ecosystems

Ecosystem's ability to maintain its structure and function over time

-ecosystems are fragile, therefore minor disturbances can cause change

Long-Lasting Ecosystems (3)

1. Daintree Rainforest (Northern Australia) - 180M yrs old, contains species from ancient plants that evolved b4 flowering plants

2. Borneo Lowland Rainforest - 140M yrs old

3. Namib Desert (Southern Africa) - 44M-80M yrs old, thick, coastal fog provides moisture for unique animal species to thrive

Requirements for Ecosystem Stability (4)

1. steady supply of energy

2. nutrient cycling w/out leakages (leaving the system)

3. high genetic diversity of species to withstand selection pressures

4. climate range within tolerance levels

Disruption of Ecosystems (4)

Typically influence nutrients**

1. harvesting/removal of materials

2. erosion

3. eutrophication

4. selective removal of species by epidemics of poaching, especially keystone species

Tipping Point

The ecological threshold at which disturbances are difficult to reverse, once met, ecosystem faces abrupt changes that speed up degradation

Amazon Rainforest Tipping Point (3)

1. decreased forest cover from logging, decreases transpiration, which decreases cloud formation, decreasing rainfall, which further decreases forest size

2. droughts lead to fires, decrease forest size, which leads to further drought and forest decline

These changes could shift a forest ecosystem to a grassland ecosystem in large parts of the Amazon

*bc higher rainfalls foster forest development but moderate fosters grassland development*

Mesocosm

small area that stimulates the natural environment for ecological experiments

either terrestrial or aquatic

Terrestrial Mesocosm

Fenced-off enclosures in grasslands or forests

Aquatic Mesocosm

Tanks set up in labs

Purpose of Mesocosms

investigate effects of varied conditions, ex fish in aquatic environments or sustainability of ecosystems

Factors to Consider in Mesocosms (3)

1. Usage of glass jars or plastic containers

2. Groups that must be included for sustainability, eg autotrophs, consumers, saprotrophs, or detritivores

3. ensuring sufficient oxygen supply once mesocosm is sealed

Keystone Species

Species whose activity has a disproportionately large effect on the community structure

-species diversity is more likely to decrease and ecosystems are more likely to collapse if keystone species is removed

Ochre Sea Star

study done by Paine to study keystone species at Mukkaw Bay in Washington State

they were removed from a 8x2 meter area of seashore and adjacent area left as control

Experimental Area

-Acorn barnacles initially covered 70% of area

-then crowded out by goose-necked barnacles and bivalve mollusks

-bivalve mollusks became dominant species and caused seaweed to disappear

-other species were either crowded out or lost their food source, which caused them to migrate or die

Control Area

Showed no changes, high diversity of species remained, including seaweed

Paine's Conclusion

ochre sea stars were key predators of bivalve mollusks who prevented its dominance and maintained species diversity

Requirements for Sustainability (3)

nutrient availability, detoxification of waste products, energy availability

Nutrient Availability

nutrients can only be recycled indefinitely through decomposers, ensures availability of essential elements like carbon

Detoxification of Waste Products

Waste of one species can be used as a resource for another species, decomposers produce ammonium which is used by bacteria in the soil as source of energy

Energy Availability

Continuous supply of energy is necessary (sunlight)

eg. dust created by eruption of Mount Tamborn (1815) blocked sunlight that led to global crop failures and starvation

Sustainability

Occurs when rate of harvesting < rate of replacement

unsustainable human activities include burning of fossil fuels (finite and nonrenewable)

Brazil Nuts

Grow from amazon trees to be 50 meters and life for 1000 yrs

-but logging and intense harvesting do not leave enough nuts to germinate, preventing new trees from growing (sustainability issue)

Cod Sustainable Harvesting

Overfishing led to their population collapse in the 1990s bc they were open-access and there were limited incentives for conservation

as long as fish are not harvested at faster rate than their population growth, stocks shouldn't decline

International measures were put in place to reverse declining fish populations and since 2005, biomass of cod has tripled and is now considered sustainable

International Measures (4)

-exclusion zones to allow undisturbed breeding

increase in hole sizes of nets to allow the escape of smaller fish

-reduce size of fishing fleet by decommissioning some boats

-monitor fish populations and set catch quotas

Factors that Affect Agriculture Sustainability (5)

Overuse of Finite Resources

-tillage

-nutrient depletion

-monoculture

-mechanical tillage

Tillage

Preparation of soil for farming by loosening it with plowing and harrowing, destroys soil structure, leading to faster erosion

ex. cleared tropical forests have poorer soil, unsuitable for long-term, high-yield agriculture

Nutrient Depletion

Crop is removed and leeching occurs

-as water drains through depleted soil, nitrogen fertilizers initiate eutrophication

-further necessitates repeated application of fertilizer

Leeching

Loss of water-soluble plant nutrients from soil

Fertilizer Production

Production of nitrogen fertilizer requires energy from fossil fuels, phosphates are mined from non-renewable rock deposits

Monoculture

Growth of a single crop repeatedly in large areas, increases pests and weeds

-requires heavy pesticide and herbicide usage, leads to pollution, especially from DDT (banned)

-pests and weeds evolve agrochemical resistance in response to repeated pesticide/herbicide usage

-production of agrochemicals also requires energy from fossil fuels

Mechanical Tillage

usage of diesel-powered machinery like tractors

-agriculture has a high carbon footprint and contributes significantly to climate change

-energy is also necessary for heating/maintaining greenhouses and animal housing

Eutrophication

Nutrient enrichment of water

-water-soluble nutrients like nitrates and phosphates from agriculture dissolve in rainwater, reaching lakes, rivers, and seas (nutrients from manure, livestock urine, and untreated sewage)

Such nutrient enrichment causes algal blooms

Algal Blooms

Algae and photosynthetic bacteria grow rapidly, blocking light

-they, along w/ plants underneath, eventually die

-leads to their decomposition by aerobic bacteria

But this decomposition increases biochemical oxygen demands (BOD) which leads to oxygen depletion, creating an anoxic environment that kills fish and other organisms

Bioaccumulation

increase in toxic [] in an organism's body over its lifetime, especially of fat-soluble toxins (not easily excreted)

-ex. DDT and mercury

Biomagnification

Increase in toxin [] at each trophic level of food chain

-predators accumulate higher toxin levels than their prey

-biomagnification varies across organisms and trophic levels, some toxins can be taken up directly from abiotic environment (ex mercury)

Plastic

Range of polymers widely used in manufacturing, often as single-use items

-they are non-biodegradable or slow to degrade and accumulate over time

*350 million tons discarded annually*

Degradation of plastic waste releases toxic carbon compounds into ocean, which can bioaccumulate and biomagnify

Macroplastic

large visible debris (nets, bottles, etc)

-wildlife like seabirds and turtles ingest it or become entangled in it

-physical and chemical degradation of macrolastic products microplastic

Microplastic

smaller than 5mm, less visible but far more numerous (over 50 trillion particles estimated in oceans)

-found in all investigated marine ecosystems and animal tissues in these ecosystems

-full impact is still unknown

Consequences of Ecosystem Degradation (3)

1. loss of biodiversity

2. rapid rate of species extinction

3. loss of ecosystem services

Ecosystem Services (5)

carbon sequestration, climate regulation, flood protection, prevention of soil erosion, and water purification

Rewilding

Attempts to return ecosystems to their natural states with as little human intervention as possible

-first key step is to stop human activities

Stop Human Activities (2)

-stop agriculture and logging to allow recovery

-re-establish fishing exclusion zones

Other Rewilding Interventions (4)

-Distribute native plant seeds where no seed source exists

-reintroduce apex predators (top-down regulation) and keystone species

-re-establish connectivity in fragmented ecosystems

-control invasive species

Example of Rewilding

Hinewai reserve, New Zealand

-allowed 1,250 hectares of farmland to return to native forest

-controlled alien species like goats and possums, w/ minimal human interference in other aspects

-tolerated some alien species like gorse (plant) bc they provided canopies for saplings, then died out from shading caused by trees once grown

regeneration of forest has occurred somewhat rapidly, but climate change poses ongoing threats

Ecological Succession

sequences of changes that progressively impact ecosystems, including species composition and abiotic environment

-species composition and abiotic environment influence each other towards succession

Example of Succession

Shrubs and trees colonize grasslands

-light intensity at ground level decreases, which leads to lower temperatures and higher humidity

-leaf litter increases nutrient [] and water retention in soil

-plant species suitable for forest conditions replace grassland species, further changes animal species due to interdependency

Succession leads to...

Climax community (stable, persistent ecosystem) or recurring cycles of ecosystems w/out a specific one persisting indefinitely

ecosystem changes during succession

often trigger other changes, leading to succession

-ex triggers can be abiotic (avalanche) or biotic (beaver colonization causing flooding)

Primary Succession

Occurs in environment with little or no existing soil, such as bare rock, sand, or silt

-colonization usually begins w/ bacteria, lichens, and mosses

-they generate small amounts of soil, which allow herbaceous plants w/ roots to colonize

once deeper soil develops, larger plants like shrubs and trees colonize, animal and decomposer population changes as well

Principles of Primary Succession (4)

1. species diversity increases

2. primary production increases as larger plants colonize and greater photosynthesis occurs per unit area

3. food webs become more complex

4. nutrient cycling improves as animal and plants produce more dead organic matter

Cyclical Succession

Ecosystems characterized by cycles rather than stable climax, species replace each other repeatedly, even without large-scale disturbance

Cyclical Succession Example

North Island, New Zealand

-honeycomb barnacles settle on bare rock

-crustose algae and black muscles colonize, forming a dense carpet

-mussels smother barnacles and algae underneath

-eventually all three detach, restarting cycle on newly exposed rock

Climax Community

Stable community that persists until disturbance

may be the result of deflected (some human interference) or arrested (lots of human interference) succession, produces stable but alternative community (plagioclimax)

Plagioclimax

Stable but alternate community resulting from human action that alters natural processes

Human Intervention Examples (2)

Grazing and drainage of wetlands

Grazing

livestock are protected from predation which allows existence in higher densities

-prevents forest development by killing shrubs and tree saplings (encourages grasslands)

ex. bison in north america

Wetlands

swamp ecosystems developed on waterlogged sites, with organisms adapted to anaerobic conditions

-absence of O2 inhibits saprotrophic fungi which produces peat

Peat Bogs

wetlands that store large amounts of carbon, reducing atmospheric CO2

Drainage of Wetlands

Draining water from wetlands aerates soil for crop growth

-plants adapted to drier conditions colonize

-in unmaintained, waterlogged conditions return, reestablishing peat bogs, causing tree death