Disturbance, Interactions & Ecosystem Change — Print · Grade 10 Science
Chapter: Ecosystems & Conservation DecisionsDisturbance, Interactions & Ecosystem Change
Learning goals
- I can explain how changing one population can affect several others.
- I can distinguish resistance, recovery, and a changing ecosystem baseline.
Readings for this unit
Before this unit
Trace direct and indirect effects through a food web.
Use three flexible study sessions: core explanation and Parts 1–2; Parts 3–4 with their reasoning checks and models; then the whole-unit application, worked examples, independent practice, and exit check. Allow about 50–60 minutes per session, including diagrams, data work, and notebook explanations. Attempt each check before opening its guidance. Schedule chapter investigations, review, and exams separately; add time where prerequisites are uncertain. Trace the explained visual parts and write a first model, then attempt the illustrated and changed independent cases. In the third session explain a correction and revise the opening account using evidence.
Start with something to explain
Can a system recover its biomass without recovering its earlier community?
Illustrative evidence case. A selected output can return while species composition and interactions remain altered.
Notice and wonder
Record two observations using the stated quantities or relationships. Keep observations separate from possible causes. Write one question that a new measurement could help answer.
Can a system recover its biomass without recovering its earlier community?
Your first model
Label disturbance, resistance, recovery interval and the indicator being measured.
Build the language from the idea
- disturbance
- An event that changes ecosystem conditions or structure.
- resistance
- The degree to which a system remains similar during a disturbance.
- succession
- Changes in community composition over time.
An ecosystem includes interactions among organisms and the physical environment. Competition, predation, mutualism, and other relationships can influence populations. A food web predicts possible pathways, but an arrow alone does not give the size or timing of every response. Alternative foods and other limiting factors matter.
A disturbance can change resources, populations, and conditions. Resistance describes how little a system changes; recovery describes its return after a disturbance. Resilience is used in different ways, so define the measured outcome. A population returning to its earlier count does not necessarily mean every part of the ecosystem has recovered.
Succession describes changes in communities over time. Soil, seed sources, dispersal, climate, and repeated disturbances influence the path. Ecosystems need not progress toward one fixed endpoint. Use time series, comparison sites, and evidence about mechanisms to judge a claim about recovery.
A disturbance can change resources, populations and interactions, producing effects that spread through a system. Removing a predator can alter herbivores and vegetation, but the outcome depends on the full network. Name the mechanism rather than assuming one universal cascade.
Resistance describes limited change during disturbance; recovery describes return afterward. Resilience is used in different ways, so state your operational measure. Recovery of one species count does not necessarily restore the original community or ecosystem functions.
Compare repeated measurements before and after with a reference when possible. Historical variability and repeated disturbances complicate claims of recovery. A useful model identifies thresholds and uncertainties without asserting that every ecosystem has one fixed stable balance.
Build your understanding
Use three flexible study sessions: core explanation and Parts 1–2; Parts 3–4 with their reasoning checks and models; then the whole-unit application, worked examples, independent practice, and exit check. Allow about 50–60 minutes per session, including diagrams, data work, and notebook explanations. Attempt each check before opening its guidance. Schedule chapter investigations, review, and exams separately; add time where prerequisites are uncertain.
Part 1 · Disturbance is normal
A disturbance changes conditions, resources or populations over a specified interval and area. Fire, storms, flooding and human actions can have different roles depending on intensity, frequency and ecosystem history. Some organisms depend on recurring disturbances, while extreme or altered patterns can reduce recovery. A decline in one selected biomass indicator is not the complete measure of all ecological functions. Define the affected system and compare expected historical variability before equating every disturbance with the same kind of damage.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Why is “all disturbances are ecologically identical damage” inaccurate?
Visual reasoning — after your attempt
Effects vary with organism adaptations, history, intensity and recurrence; some recurring disturbances support particular ecological processes.
Ecosystems are not static, and disturbance — fire, storm, flood, disease, grazing — is a regular feature rather than an exception. Many communities depend on it: some seeds germinate only after fire, and gaps opened by fallen trees allow light-demanding species to establish. Treating any change as damage misses that the community's composition reflects a history of disturbance.
What distinguishes a damaging disturbance is its scale, frequency, or novelty relative to that history. A fire regime a community is adapted to differs from one several times more frequent, and a disturbance with no precedent — a new pathogen, a novel chemical — is more likely to produce lasting change than a familiar one of similar magnitude.
Pause and explain
Why is it inaccurate to treat all disturbance as damage to an ecosystem?
Check your reasoning after answering
Many communities have developed under recurring disturbance and depend on it, with species whose reproduction or establishment requires fire or gaps. What matters is whether a disturbance's scale, frequency, or type departs from the regime the community developed under.
Part 2 · Succession
Succession is change in community composition through time. Primary succession begins in settings with little developed soil; secondary succession can follow disturbance where soil and biological legacies remain. Soil, seed sources, dispersal, climate and further disturbances affect rates and routes. Secondary recovery can be faster in a relevant comparison, but it is not guaranteed under every condition. Communities need not converge to one fixed universal climax, and species order alone does not establish all underlying interactions.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Why can surviving soil and seed sources alter recovery compared with a bare-substrate setting?
Visual reasoning — after your attempt
They preserve material, organisms and establishment opportunities that would otherwise need to develop or arrive.
Succession is the sequence of change in community composition after a disturbance. Primary succession begins where there is no soil — bare rock, a new lava surface — so the first organisms must establish without it, and soil accumulates slowly. Secondary succession begins where soil and often seeds remain, as after a fire or on abandoned farmland, and therefore proceeds much faster.
The sequence is directional but not fixed. Early colonists are typically fast-growing and tolerant of exposure; later species are often slower-growing and more shade-tolerant, and they may exclude the earlier ones. The endpoint is not a single predetermined community, since the outcome depends on which species arrive, on soil and climate, and on further disturbance along the way.
Pause and explain
Why does secondary succession proceed faster than primary succession?
Check your reasoning after answering
Soil is already present, along with seeds, roots, and soil organisms. Primary succession must first build soil from bare rock, which takes a very long time, whereas secondary succession starts with the substrate and often a seed bank already in place.
Part 3 · Resistance and resilience are different properties
Resistance describes how little a system changes during a specified disturbance. Recovery describes return of selected properties afterward. Resilience is used in several related ways, so define the sense and measured variable before comparing systems. A system can change strongly yet recover rapidly, while another changes little but recovers slowly. Returning one output to baseline does not guarantee identical species composition or restored every function. Compare reference variability and the time interval rather than rank ecosystems by one undefined resilience label.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Which supplied model has lower resistance but faster recovery?
Visual reasoning — after your attempt
A changes from 100 to 20, then returns to 100 by year four; B changes less but has not returned in that interval.
Two distinct questions can be asked about a community facing disturbance. Resistance asks how little it changes when the disturbance hits — the size of the immediate drop. Resilience asks how quickly and completely it returns afterwards — the time to recover to a stated fraction of its former state.
The two are independent, which is why they must be reported separately. A grassland may lose most of its standing biomass to fire and recover within two seasons: low resistance, high resilience. A mature forest may lose little to a storm but take decades to replace a large tree: higher resistance, lower resilience. A single statement that a community is "stable" conceals which property is meant.
Pause and explain
A community loses 80 percent of its biomass to fire and returns to its former level in three years. Describe it in terms of both properties.
Check your reasoning after answering
It has low resistance, since the initial loss was large, and high resilience, since recovery was rapid and complete. Reporting only one property would describe it as either fragile or robust, both of which would be misleading.
Part 4 · Diversity, redundancy, and limits
Functional redundancy can buffer loss when other organisms supply a relevant function, but effects depend on traits, interactions and conditions rather than species count alone. Thresholds describe changes in response behavior under a specified model; altered soil, resources or feedbacks can make return difficult even after a pressure is removed. Lost source populations, dispersal limits and repeated disturbance also matter. A causal explanation identifies the continuing constraints and tests a restoration pathway rather than assumes biodiversity guarantees rapid return everywhere.
Read the visual model
Identify the labeled structures and units, then trace the arrows or compare values under the caption’s stated conditions. Separate the displayed evidence from a further inference. Write your reasoning before opening the guidance.
Why might removing the original pressure still leave a changed community?
Visual reasoning — after your attempt
Missing source species, altered resources or reinforcing interactions can prevent the earlier state from re-establishing without further changes.
Communities with more species often absorb disturbance better, and the usual explanation is redundancy: where several species perform a similar role, the loss of one can be compensated by the others. Diversity also raises the chance that some species present will tolerate the particular conditions a disturbance creates.
The relationship has limits worth stating. Diversity is not a guarantee, a disturbance can remove many species at once, and some ecosystems shift to a persistently different state rather than returning — a lake that turns turbid and stays turbid, a reef replaced by algae. Such shifts matter because the new state can resist return even after the original pressure is reduced, so recovery is not simply a matter of waiting.
Pause and explain
Why can an ecosystem fail to recover even after the pressure that changed it is removed?
Check your reasoning after answering
It may have shifted to a different state that is self-sustaining, where new conditions or species keep it from returning — turbid water preventing the plants that would clear it, for example. Removing the original pressure is then not sufficient, because the new state maintains itself.
Apply the whole unit · Compare two recovery records
Illustrative recovery data after comparable fires, biomass as a percentage of the pre-fire level, with species richness in brackets. Community A (grassland, 14 species before fire): year 0 after fire 18 percent (5); year 1 62 percent (10); year 3 96 percent (13); year 6 99 percent (14). Community B (woodland, 15 species before fire): year 0 after fire 54 percent (11); year 1 61 percent (12); year 3 70 percent (13); year 6 78 percent (14); year 20 94 percent (15).
Your task
Describe each community in terms of resistance and resilience with figures, calculate how many times longer B takes to reach 94 percent or more than A takes to reach 96 percent, explain why describing either community simply as more stable would be misleading, and state what the species-richness figures add that biomass alone does not. Then name one factor the data cannot distinguish.
What your response should show
- Choose the appropriate biological model or relationship and state the conditions it assumes.
- Show the counts, rates, ratios, or intermediate reasoning the question requires.
- Use the supplied evidence to justify the conclusion and separate observation from inference.
- Identify a meaningful limitation, uncertainty, or next measurement.
Response guidance — after your attempt
Community A resistance: biomass fell to 18 percent immediately, so resistance is low; richness fell from 14 to 5 species.
Community A resilience: 96 percent of pre-fire biomass by year 3 and 13 of 14 species, so resilience is high.
Community B resistance: biomass fell only to 54 percent, so resistance is substantially higher; richness fell from 15 to 11.
Community B resilience: 94 percent reached at year 20, so resilience is much lower.
Ratio: 20 years against 3 years is a factor of about 6.7 for comparable recovery.
Explain the trap: A is less resistant but more resilient and B the reverse, so one label cannot rank them; which matters depends on whether disturbances are frequent or rare.
Interpret richness: biomass can recover while species are still missing, so richness shows whether composition as well as quantity has returned — B regains full richness only at year 20, A by year 6.
Name what is indistinguishable: the data cannot separate intrinsic recovery rate from differences in fire intensity, soil, climate, or seed availability between the two sites.
Community A has low resistance and high resilience: biomass fell to 18 percent and richness from 14 species to 5, but it reached 96 percent of pre-fire biomass with 13 species by year 3. Community B is the opposite — biomass fell only to 54 percent, showing much higher resistance, but it needed 20 years to reach 94 percent, about 6.7 times as long as A took to reach a comparable level. Calling either community more stable would therefore be misleading, because the two properties point in opposite directions, and which matters depends on how often disturbance occurs: A suits a frequently burned landscape, while B's slow recovery makes repeated fires far more consequential. The richness figures add what biomass conceals — B's biomass was at 78 percent by year 6 while one species was still absent, so quantity recovers before composition does. What the data cannot separate is intrinsic recovery capacity from site differences: fire intensity, soil depth, rainfall, and nearby seed sources could each account for part of the contrast, and comparable fires on paired sites would be needed to isolate the communities' own properties.
Scientific references and adapted source figures
Parent / teacher teaching notes
Resistance and resilience are the whole unit, and the two-community comparison makes them impossible to conflate: the community that drops furthest recovers fastest. Insist on figures for both rather than the word "stable." The richness-against-biomass point is the second idea worth securing, because recovery of quantity is routinely reported as recovery of the ecosystem, and the data here show those are not the same thing. Ask for an explanation of each label, arrow and axis before calculation. Keep first and revised models; attempt the changed case before consulting guidance. Distinguish invented instructional records from named historical sources. Source chromosome symbols are allele-category models, not DNA sequences. These independently authored high-school supplements are not the full OpenSciEd teacher editions or an endorsement.
The key idea
Ecosystem change depends on interacting populations, conditions, and history; define what recovery would mean.
Worked examples
Example 1
- Cover has increased from the immediate post-disturbance value.
- It remains below the initial cover.
- Species composition and other functions need separate evidence.
Example 2 · Worked application
- Species richness and soil function measure different properties.
- One has recovered while the other has not.
- A complete claim requires multiple relevant indicators.
Define recovery operationally instead of assuming one universal measure.
Example 3
- Richness is one structural indicator.
- Nutrient retention measures a different function and remains altered.
Example 4 · Find and fix the mistake
- Test the claim against the stated conditions: Define recovery operationally instead of assuming one universal measure.
- Composition, abundance and functions can still differ.
Define recovery operationally instead of assuming one universal measure.
Example 5 · Reason from the visual evidence
- Resistance describes how little a system changes during a specified disturbance. Recovery describes return of selected properties afterward. Resilience is used in several related ways, so define the sense and measured variable before comparing systems. A system can change strongly yet recover rapidly, while another changes little but recovers slowly. Returning one output to baseline does not guarantee identical species composition or restored every function. Compare reference variability and the time interval rather than rank ecosystems by one undefined resilience label.
- A changes from 100 to 20, then returns to 100 by year four; B changes less but has not returned in that interval.
Original resistance/recovery comparison with arbitrary output indices, not complete ecosystem restoration evidence.
Avoid these mistakes
- Ecosystems are dynamic, and returning to one indicator's old value need not mean complete recovery.
Check your understanding
After a flood, species richness returns but nutrient retention remains low. Has every function recovered?
Discuss the answer
No; different indicators reveal different aspects of recovery.
Why can a food-web change have indirect effects on organisms not directly involved?
Discuss the answer
Changes in one population can alter resource use or other partners, sending indirect effects through the network. Link evidence to mechanisms rather than infer only direct interactions.
Return to the phenomenon
Return to the initial case. Can a system recover its biomass without recovering its earlier community? Revise your drawing or explanation using two named ideas and one stated limitation.
Compare explanations after your attempt
Response and recovery are separate; multiple indicators, initial legacies and continuing feedbacks determine what restoration evidence means.
What should we investigate next?
Which comparison would test a remaining uncertainty? State what you would change, keep comparable and measure.
Investigate, explain and revise
Complete these tasks after the teaching parts. Preserve your first model and a supported revision; use guidance after a real attempt.
Activity 1 · Return to the opening case
Use the opening question, defined terms, Parts 1–4 and your notebook. The supplied-data route needs no equipment or external account.
Your task
Return to the initial case. Can a system recover its biomass without recovering its earlier community? Revise your drawing or explanation using two named ideas and one stated limitation.
Success criteria
- Use relevant stated observations.
- Explain the mechanism with a labeled model.
- Distinguish quantities and assumptions.
- Describe a revision and a useful next test.
Hint
Follow objects, materials and information separately. Check what each measured quantity means.
Response guidance — discuss after your attempt
Response and recovery are separate; multiple indicators, initial legacies and continuing feedbacks determine what restoration evidence means.
Activity 2 · Transfer to a changed case
Cover the worked guidance and use the unit explanations/figures to solve a changed problem.
Your task
A supplied system loses 80% of its output during disturbance and returns to its initial output after three years. Describe resistance and recovery and explain one limit of that evidence.
Success criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the biological mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.
Hint
Name the stated conditions, select the relevant mechanism and show intermediate reasoning.
Response guidance — discuss after your attempt
It has low resistance for this disturbance/output but relatively rapid recovery over the stated interval. Output recovery alone does not establish restored species composition or every ecological function.
Words to know
- disturbance
- An event that changes ecosystem conditions or structure.
- resistance
- The degree to which a system remains similar during a disturbance.
- succession
- Changes in community composition over time.
In the real world
Exit check
Why should a prediction after disturbance include uncertainty?
Check your explanation after answering
Resources, dispersal, interactions, climate, and later disturbances can change the response.
Explain your reasoning without notes. If a key idea is missing, revisit the lesson and try again.
Problem 1
Answer and explanation
30 percentage points
60 − 30 = 30; this differs from percent reduction.
Problem 2
- A time series and suitable comparison sites
- Only one decorative photo
- The species name alone
- A guaranteed endpoint
Answer and explanation
A time series and suitable comparison sites
Repeated and comparison evidence helps separate recovery from other changes.
Problem 3
Answer and explanation
Changes in herbivores can alter grazing, but other interactions may modify the response.
Problem 4
Answer and explanation
No; different indicators reveal different aspects of recovery.
Richness is one structural indicator.
Nutrient retention measures a different function and remains altered.
Response criteria
- Use the stated conditions.
- Show the evidence or calculation.
- Explain the conclusion and any stated limitation.
Problem 5
Hints
Define recovery operationally instead of assuming one universal measure.
Answer and explanation
Repeated abundance and feeding data, comparisons and mechanisms that rule out alternative resource or climate changes.
Problem 6
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
The second may arrive before populations, soils or resources recover, altering thresholds and trajectories.
Problem 7
Answer and explanation
A changes from 100 to 20, then returns to 100 by year four; B changes less but has not returned in that interval.
Resistance describes how little a system changes during a specified disturbance. Recovery describes return of selected properties afterward. Resilience is used in several related ways, so define the sense and measured variable before comparing systems. A system can change strongly yet recover rapidly, while another changes little but recovers slowly. Returning one output to baseline does not guarantee identical species composition or restored every function. Compare reference variability and the time interval rather than rank ecosystems by one undefined resilience label.
A changes from 100 to 20, then returns to 100 by year four; B changes less but has not returned in that interval.
Response criteria
- Read the structures, axes, directions and units correctly.
- Connect the evidence with the biological mechanism.
- Respect stated model assumptions and distinguish an observation from a further inference.
Problem 8
Answer and explanation
It has low resistance for this disturbance/output but relatively rapid recovery over the stated interval. Output recovery alone does not establish restored species composition or every ecological function.
It has low resistance for this disturbance/output but relatively rapid recovery over the stated interval. Output recovery alone does not establish restored species composition or every ecological function.
Response criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the biological mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.