IB Biology - Unit D4.2: Stability and Change

Sustainability

Sustainability

Maintenance or restoration of the composition, structure, and processes of ecosystems, including the diversity of plant and animal communities and the productive capacity of ecological systems

Driving Factor of Sustainability

Rate of harvesting being lower than the rate of replacement.

3 Requirements for Sustainability in Ecosystem

1. Nutrient Availability

2. Detoxification of Waste Products

3. Energy Availability

Nutrient Availability

As long as nutrients are cycled efficiently, they should be available indefinitely (with saprotrophs playing a key role).

Detoxification of Waste Products

Waste products of one species are usually exploited by other species (ammonium [can be toxic] released by decomposers is absorbed and used as an energy source by chemotrophic bacteria in the soil).

Energy Availability

As energy cannot be recycled, a continuous energy supply is necessary (most ecosystems rely on the sun; others rely on chemotrophs).

Example of Sustainable Harvesting of a Terrestrial Plant

Brazil Nut Tree

Benefits of Brazil Nuts

1. Supports local economies

2. Rich in essential nutrients, providing a source of fats and protein

Sustainable Harvesting of the Brazil Nut

1. Wild Harvesting

2. Selective Collection

3. Awareness

Wild Harvesting

Nuts are collected from wild trees rather than from plantations to maintain biodiversity and ecosystem health.

Selective Collection

Harvesting is limited to nuts already fallen to the ground during fruiting season

Awareness

Harvesters are frequently trained and depend upon FTC to ensure sustainable practices are maintained

Example of sustainable harvesting of a marine fish

Cod Fish

Benefits of cod fish

1. Nutritional benefits (high in protein, low in saturated fats, high in Omega 3-s)

2. Supports economies of those that harvest cod

Sustainable harvesting of a marine fish

1. Quotas and Limits

2. Seasonal/Area Closures

3. Gear Modifications

4. Monitoring

5. Marine Stewardship Council Certification

6. Innovation

Quotas and Limits

ICES (International Council for the Exploration of the Sea) establishes quotas to limit the amount of cod that can be caught each season to prevent overfishing

Seasonal/Area Closures

Fishing is restricted during spawning seasons to allow juveniles to reach maturity, increasing population recovery; some areas are designated as MPAs (marine protected areas) where fishing is prohibited; temporary closures can be implemented if needed

Gear Modifications

Nets are modified to prevent bycatch (unintentional capture of non-target species, including juvenile cod); trawls (which drag on the seafloor) are modified or limited in use to minimize damage to the seafloor

Monitoring

Onboard observers and/or electronic monitoring systems are used to improve data accuracy and to ensure sustainable practices are being implemented

Marine Stewardship Council Certification

MSC is a globally-recognized organization that certifies fisheries meeting sustainable standards (catch levels, protection of marine biodiversity, effective management practices); MSC-certified products often bear an eco-label to help consumers choose sustainably harvested cod products

Innovation

Satellite tracking, sonar, genetic tagging, and other programs help fisheries collect real-time data as well as identify key areas for conservation

Maximum Sustainable Yield (MSY)

Largest yield/harvest/catch that can be taken from a specific resource population over an indefinite period without depleting the population.

Calculation of Maximum Sustainable Yield

K (carrying capacity) / 2

Methods of Collecting Data to Calculate MSY

1. Capture-Mark-Release-Recapture

2. Echo Sounders

3. Analysis of Fish Catch Data

Capture-Mark-Release-Recapture

Method to estimate population size with application to Lincoln Index, can capture through electro-shocking fish

Echo Sounders

Transmission of sound waves to identify sizes of fish shoals/schools

Analysis of Fish Catch Data

Method that collects data from fisherman to measure fish catch numbers

Limitations of MSY

1. Requires accurate estimates of population size (that fluctuate)

2. Does not account for environmental variability

3. Does not account for species interactions

4. Does not account for long-term changes

Factors Impacting Sustainability of Agriculture

1. Soil

2. Harvesting

3. Biodiversity

4. Carbon Footprint

Soil Impacting Agriculture

• Tilling prepares soil for a crop, which degrades the soil, making it erode at a faster rate than new soil can be generated

• Fertility and nutrient composition of the soil can alter over time

Harvesting Impacting Agriculture

• When crops are harvesting, soil is depleted of nutrients

• Fertilizers leach into nearby water sources, causing eutrophication

• Nutrient depletion leads to increased used of fertilizers, mining non-renewable resources

Biodiversity Impacting Agriculture

• Long term cultivation of crops increases likelihood of weeds and pests, increasing use of herbicides and pesticides

• Use of agrochemicals leads to pollutants entering the environment

• Organisms develop resistance to these chemicals, requiring use of new/different chemicals

• Manufacturing of these chemicals requires energy/power

Carbon Footprint

Amount of carbon dioxide/methane released into the atmosphere as a result of a particular activity

Impact of Agriculture on the Environment

• Agricultural practices require power, supplied through fossil fuels

• Farm machinery is operated from diesel oil

• Transportation of crops require energy

Eutrophication

Process in which minerals from fertilizers leach into water ways causing an excess of algal growth

Leaching

When not all nutrients are taken in by plants, and the remaining minerals are picked up by groundwater

Algal Blooms

High reproductive rate of algae, resulting in a layer of algae across the surface of the water

Impact of Algal Blooms

• No light penetrates the surface

• Life below the surface begin to die and decompose

• Decomposition occurs at a higher rate

Biological Oxygen Demand

Oxygen requirement for the decomposition process in aquatic habitats

Way to stop Eutrophication

Prevent nutrients from entering the waterways

Biomagnification

When harmful substances in the environment accumulate in the organisms at the top of the food chains/webs

Reason for Biomagnification

There is a reduction in biomass that occurs at each trophic level, and higher trophic levels must consume more organisms of the preceding trophic level

Impact of Biomagnification

Levels of the toxin increase in concentration as the trophic levels increase

2 Main Pollutants that Contribute to Biomagnification

Mercury and DDT

Characteristics of Mercury

• Naturally occurring element

• Released by combustion of coal and production of cement

• Mercury enters atmosphere and is diffused into oceans

• Microorganisms convert elemental mercury into methylmercury

• Results in human exposure to mercury when consuming long-lived fish (tuna)

Characteristics of DDT

• Synthetic insecticide

• Highly effective, long-lasting, and cheap to manufacture

• Used against disease-carrying insects (mosquitoes and mites)

• DDT was delivered via plane, leaching into waterways

• Mosquitoes developed resistance to DDT and hurt other insects

• DDT was absorbed by marine producers

Non-Biodegradable

Once it enters an environment, they will persist forever

Microplastics

• Smaller than 5 mm

• Parts of a macroplastic

Macroplastics

• Larger than 5 mm

• End up in the environment as a result of careless disposal

• Large plastics get caught in gyres

Examples of Plastic Pollution

• Sea turtles mistaking plastic bags for jellyfish

• Plastic rings from canned beverages entrapping wildlife

• Seabirds picking up plastics and feeding them to their chicks

• Fishing nets trapping marine wildlife

• Microplastics are ingested by marine animals and fill their stomac

Rewilding

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

Methods of Rewilding

• Reintroduction of apex predators and other keystone species

• Distributing seeds of plants that do not have a natural seed source

• Establish wildlife corridors/bridges to connect habitats

• Minimizing human influences

• Stopping agriculture and resource harvesting

Example of Rewilding

Hinewai Reserve, NZ

Stability

Ecosystem can persist indefinitely because of the mechanisms operating within it

3 Examples of Stable Ecosystems

1. Borneo Lowland Rainforest

2. Daintree Rainforest

3. Namib Desert

Requirements for Stability

• Steady supply of energy

• Efficient nutrient cycling

• High genetic diversity (to survive environmental pressures)

Disturbances to Stability

• Harvesting of materials disrupting nutrient cycling

• Erosion causes the loss of nutrients

• Eutrophication can cause population imbalances

• Selective removal of a species

• Drop in genetic diversity

• Climate Change

Tipping Points

A threshold for an ecological system that results in instability that is difficult to reverse

Transpiration

Water Evaporation from Plants

Outline of Amazon Rainforest Reaching a Tipping Point

• Deforestation and Logging reduces transpiration and photosynthesis

• Decrease in cloud formation (condensation)

• Decrease in precipitation

• Loss of plant species and increases periods of drought

• Increases wildfires

• More trees loss

Percent Change Calculation

new value - old value / old value

Mesocosm

Small Experimental area set up as ecological experiments

Keystone Species

Organisms whose activity has a disproportionate effect on the structure of a community

Example of Keystone Species

Ochre Sea Star

Outline of Ochre Sea Star Experiment

• A barnacle species spread to occupy over 70% of the area

• This barnacle species was soon overcrowded by the gooseneck barnacle and a mussel

• The mussel dominated the area which eliminated the majority of the seaweeds

• Other animal species died or migrated due to the loss of their food source

Ecological Succession

The sequence of changes that progressively transform ecosystems, including species composition and abiotic factors

Causes of Ecological Succession

• Disturbances (natural or anthropogenic) which could be abiotic or biotic

• Abiotic changes (climate, soil composition, water pH, etc.)

• Biotic interactions (competition, predation, migration, disease, etc.)

• Resource availability (variation in nutrient, light, or space availability)

• Reciprocal interactions

Effects of Ecological Succession

• Changes in biodiversity (increase in species diversity and complexity over time)

• Formation of stable communities (end result is a climax community = a relatively stable and mature ecosystem)

• Altered abiotic conditions (organisms cause modifications to soil, water, and atmosphere)

• Ecosystem services (enhanced nutrient cycling, energy flow, and habitat creation for various species)

Reciprocal Interactions

Exchanges in which organisms exhibit similar behaviors either simultaneously or in a back-and-forth manner.

Examples of Reciprocal Interactions

1. Lichens and Bare Rock

2. Plants and Soil Nutrient Enrichment

3. Mangroves and Coastal Sediments

Lichens and Bare Rock

1. Lichens secrete acids that chemically weather bare rock, breaking it down into particles that form the initial stages of soil

2. Newly formed soil allows simple plants (i.e., mosses) to establish, further enriching the substrate/soil with organic matter due to decomposition

Plant + Soil Nutrient Enrichment

1. Some early plant colonizers (legumes) have mutualistic relationships with nitrogen-fixing bacteria in their root nodules, adding nitrogen to the soil

2. This improves soil fertility which in turn supports the growth of larger, nutrient-demanding plant species, increasing the rate of succession

Mangroves + Coastal Sediments

1. Mangroves trap sediments within their complex root systems, stabilizing the coastline and altering tidal flow

2. The accumulation of sediment creates a stable substrate for salt-tolerant grasses and eventually other coastal plants, increasing biodiversity

Pioneer Species

First species to inhabit an environment

Example of a Pioneer Species

Lichens + moss

Primary Succession

Where living organisms are largely or ccompletely absent, only pioneer species can colonize these inorganic substrates (no soil)

Example of Primary Succession

Glacier Bay, AK

Outline of Primary Succession in Glacier Bay, AK

1. Pioneer Stage (20 yrs)

2. Early Succession Stage (30 years)

3. Intermediate Successional Stage (100 years)

4. Climax Community (300 years)

Pioneer Stage in Glacier Bay, AK

1. After the glacier retreats, the land is barren rock, gravel, and silt with NO soil. Harsh conditions prevail, including high winds and limited nutrients.

2. Cyanobacteria, lichens, mosses, and some nitrogen-fixing organisms (legume root nodules) act as the pioneer species. These organisms weather the rock and add organic matter to the substrate, and enriching the soil with nitrogen and other nutrients.

Early Successional Stage in Glacier Bay, AK

1. Herbaceous plants like fireweed, willows, and alders began to grow in the area

2. The decomposition of these organisms allows organic matter to accumulate, improving soil quality and increasing water retention

3. More species establish themselves in the area due to these better conditions, including small animals like insects and birds

Intermediate Successional Stage in Glacier Bay, AK

1. Alder plants dominate, forming dense thickets that stabilize the soil and provide shade. Their roots fix nitrogen, enhancing soil fertility, benefitting the establishment of conifers like spruce trees.

2. These larger plants create habitats for a wider range of animals, fungi, and microbes, increasing the biodiversity and food web complexity.

Climax Community in Glacier Bay, AK

1. Spruce and hemlock trees dominate, forming a stable and diverse forest ecosystem

2. High biodiversity exists with multiple trophic levels within food webs

3. Efficient nutrient cycling occurs as organic matter from the forest floor supports soil fertility 

4. The ecosystem becomes more resistant to disturbances and achieves dynamic equilibrium

Cyclical Succession

A recurring series of changes in an ecosystem caused by natural or periodic disturbances that reset certain stages of the ecological community

Characteristics of Cyclical Succession

• Recurring disturbances (events like fire, grazing, or storms)

• Predictable patterns (the ecosystem’s resilience and adaptability to disturbances allows cycling through a sequence of stages)

• Dependence on disturbance (disturbance is integral to maintaining the ecological community and diversity)

Example of Cyclical Succession

Scottish Heathlands

Outline of Cyclical Succession in Scottish Heathlands

1. Building Phase (10 years)

2. Mature Phase (20 years)

3. Degenerate Phase (10 years)

4. Disturbance Phase

Building Phase in Scottish Heathlands

Following a disturbance (fire or grazing), heather seeds can begin to germinate 

Mature Phase in Scottish Heathlands

1. Young, fast-growing heather plants dominate but a low level of biomass is maintained

2. As heather plants reach their full size, the dense shrubbery supports diverse wildlife, such as red grouse and insects like moths and butterflies

   1. Livestock or wild herbivores prevent tree encroachment and maintain the heathland

Degenerate Phase in Scottish Heathlands

1. As heather ages, it becomes woody and less productive, allowing for the invasion of mosses, lichens, and grasses

2. This lowers the nutritional value of these plants, affecting herbivores that feed upon them

Disturbance Phase in Scottish Heathlands

1. Natural or human-induced disturbances (fire, grazing, cutting) reset the cycle

   • Controlled/prescribed burns are used to clear old heather to promote regeneration

Climax Community

The final, stable stage of ecological succession, where the ecosystem reaches equilibrium with its environment.

Plagioclimax

A stable community resulting from human interference, where succession is deliberately or unintentionally halted before reaching the natural climax community

Examples of Arrested Succession

1. Grazing

2. Draining Wetlands

Outline of Grazing causing a Phagioclimax

• Livestock grazing prevents the establishment and growth of woody plants through the consumption of saplings and grasses, maintaining an open, low-growing vegetative structure

• Grazing also compacts the soil, limiting seed germination and water infiltration

• Selective grazing can favor certain plant species, reducing diversity in the long term

• The ecosystem is maintained as a plagioclimax, such as a grassland or heathland, rather than transitioning into a forest or shrubland

Draining of Wetlands Causing a Phagioclimax

• Draining wetlands removes standing water, lowering the water table and altering soil moisture levels

• This prevents the establishment of water-tolerant vegetation, disrupting wetland succession toward swamps or marshes

• Aerated soils in drained areas favor upland plant species over wetland species, effectively halting aquatic succession