D4.2 Stability and change

Ancient rainforests, deserts and long-lived communities show that ecosystems can persist over very long timescales when supporting conditions and ecological processes continue.

• Repeated recovery after disturbance supports resilience.
• Small fluctuations around a characteristic state support continuity.
• A long history does not guarantee survival after a new disturbance of greater magnitude or rate.

1. A disturbance weakens a stabilizing process.
2. The weakened process amplifies the original disturbance through positive feedback.
3. Recovery becomes progressively harder as the system approaches a threshold.
4. Beyond the threshold, the system may settle into a different equilibrium.

1. Deep-rooted trees take up soil water.
2. Transpiration transfers water vapour to the atmosphere.
3. Condensation and air movement support regional cloud formation and rainfall.
4. Rain replenishes soil water and sustains further forest growth and transpiration.

• Evapotranspiration cools the regional surface.
• Continuous canopy and moisture transport extend rainfall beyond local forest patches.
• Large connected forest areas sustain the loop more effectively than fragmented remnants.

(−709,165 ÷ 4,100,000) × 100 = −17.3%. The negative sign indicates loss; the chosen initial year determines what the percentage describes.

A sealed bottle can restrict matter exchange while still receiving light energy and losing heat. Producers, consumers and decomposers must together recycle matter within the model.

1. Agoutis open Brazil-nut pods that most animals cannot access.
2. They carry and bury seeds as food stores.
3. Some buried seeds are not recovered and germinate away from the parent tree.
4. Brazil-nut recruitment supports forest structure, nesting sites, food and human livelihoods.
5. Removing agoutis therefore affects more than one predator–prey pair.

The keystone role here is seed dispersal and recruitment. The prediction follows the controlled interaction: fewer agoutis → fewer successfully dispersed Brazil-nut seeds → long-term decline of trees and dependent species.

1. Estimate stock size and its uncertainty.
2. Measure recruitment, growth, age or size structure and natural mortality.
3. Record harvested biomass, by-catch and habitat damage.
4. Compare removal with replacement across many years.
5. Reduce harvest when recovery indicators weaken.

Maximum sustainable yield is an estimated long-term catch near the balance between stock growth and losses. It depends on uncertain, variable recruitment and should be updated with long time-series data.

Seedlings planted today are not immediate replacements for mature trees. Assessment must use the time needed to restore biomass, habitat and carbon, not just a count of stems planted.

1. Vegetation removal exposes soil to rain and wind.
2. Soil particles and organic matter are detached and transported.
3. Topsoil depth, structure, water retention and nutrient stores decline.
4. Crop growth becomes more dependent on irrigation and external fertilizer.
5. Further poor cover or tillage accelerates the loss.

• maintain soil depth, structure and nutrient balance
• protect water quality and biodiversity
• keep greenhouse-gas emissions and fossil-energy use within long-term limits
• judge yield together with external inputs and damage

1. Measure dissolved oxygen in a known water sample.
2. Incubate the sealed sample in darkness at 20 °C for five days.
3. Measure dissolved oxygen again.
4. Initial oxygen − final oxygen gives the five-day BOD.

Darkness prevents photosynthesis from replacing oxygen during incubation. High BOD indicates much respirable organic matter and/or strong decomposer activity, not high oxygen availability.

Early nutrient enrichment can produce high primary production; later death, decomposition and hypoxia create the ecological damage. Sampling at only one time point can miss this sequence.

1. A dilute persistent pollutant enters producers from water or soil.
2. Primary consumers eat many contaminated producers.
3. Predators retain pollutant faster than they eliminate it and consume many contaminated prey.
4. Concentration per gram of tissue increases at successive trophic levels.
5. Long-lived top predators receive the greatest dose and may suffer reproductive or neurological harm.

1. Wind, rivers and ships deliver plastic to surface water and coasts.
2. UV radiation and wave action fragment items but do not mineralize them rapidly.
3. Biofouling can make particles sink; resuspension can return them to water.
4. Plastic and associated chemicals enter organisms and food webs.

Sea turtles can mistake plastic bags for jellyfish. Albatrosses skim food from the ocean surface, where floating debris accumulates; mechanism and feeding behavior explain exposure better than a generic pollution claim.

• reconnect habitat fragments so organisms can disperse and breed
• remove or control invasive species that block native recovery
• reintroduce missing keystone species or apex predators where risks are understood
• reduce intensive harvesting and allow succession, predation and decomposition to operate

The goal is a more self-sustaining system whose interactions maintain diversity and function with less continuous human control.

1. Formerly cleared land is protected from renewed intensive use.
2. Alien trees and vines that suppress native regeneration are removed.
3. Native plants recolonize and succession rebuilds forest structure.
4. Habitat and food resources permit endemic fauna to re-establish.
5. Management monitors recovery while allowing natural processes to do most of the work.

Minimal intervention occurs after key pressures are removed. Hinewai therefore links restoration to succession: management creates conditions in which native community change can proceed.