Biology · Ecosystems, Energy Flow & Biogeochemical Cycles

Ecosystem feedback, disturbance and resilience

Two imagined systems both have a baseline process rate of ten. After a disturbance, one falls to six and later returns to ten; the other falls only to nine but remains at nine through the last supplied observation. One resists the initial change more; the other returns to the selected baseline sooner.

Begin with Organisms, Environments & Ecological Niches for ecological boundaries and scales, and Energy, Enzymes & Metabolism for chemical energy and respiration. Communities, Species Interactions & Food Webs explains why feeding relations form a web. That chapter is a reading preparation path once available, rather than a claim of an already published lesson. The budgets here introduce every symbol and require ordinary addition, subtraction and ratios. Advanced carbon-cycle measurement methods and chemical reaction mechanisms are not required.

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By the end, you can

Define the variable and comparison for resistance or recovery, and distinguish unchanged aggregate function from unchanged ecosystem composition.

Resistance and recovery require a stated measure

A disturbance changes conditions or system components over a specified time and space. Its effects can concern abundance, composition, productivity, nutrient retention or another variable. The word ecosystem alone does not identify the response measure. The original comparison follows one assigned process index at four matched observation times.

Resistance here means remaining close to the chosen pre-disturbance value at the first matched observation after the event. With baseline ten, system A at six differs by four; B at nine differs by one. On this supplied absolute-change metric, B shows greater initial resistance. A later value cannot replace that explicitly defined initial comparison.

Recovery here means returning to the selected baseline value within the supplied observation window. A follows ten, six, eight, ten; B follows ten, nine, nine, nine. A returns by the final observation; B has not returned in this record. These meanings are specified for this example. Other resilience concepts concern recovery rates, thresholds or the capacity to maintain identity under changing conditions.

Initial resistance and later return give different comparisons

The first observed response and later return answer different questions. A return not observed within this window is not a claim that it can never occur.

Read the diagram in words

Both begin at ten. A records six, eight and ten, so its initial deviation is four and its final value returns to baseline. B records nine three times, with initial deviation one and no observed return in the supplied window.

Assigned process index
Matched supplied observation time	System A	System B
0	10	10
1	6	9
2	8	9
3	10	9

First observed deviation from baseline
System A / System B	\|Δ\| · First observed deviation from baseline	\|Δ\| / 10	Selected baseline · Matched supplied observation time
System A	4	0.4	3
System B	1	0.1	? The first observed response and later return answer different questions. A return not observed within this window is not a claim that it can never occur.

Selected baseline: 10

Disturbance occurs after the first observation

Line connections order the records; intermediate values are not observed

Original four-observation process-index records, common baseline and matched times, with a disturbance after time zero. No actual effect estimate, causal treatment design, interpolated continuous trajectory or guaranteed future equilibrium.

The same process total can hide different contributors

Two original complete contributor inventories each produce a total process index of ten. In state one, group X contributes eight and Y two; in state two, X contributes three and Y seven. The aggregate function is unchanged, while the contributions differ. The model does not specify whether species abundances or biomass composition changed. A stable total therefore cannot prove that every group remained unchanged.

Functional redundancy concerns the extent to which different components can contribute similar functions under stated conditions. Similarity for one measured process does not establish similarity for all processes, environments or future responses. Interactions and component-specific responses can matter even when a current aggregate measurement matches.

The model has only two assigned groups and additive contributions to one index. It does not prove replacement caused the stable total, identify species traits or establish that either community will recover after a later disturbance. Composition, function and response need their own evidence and measurements.

An equal total can hide changed contributions

The total remains ten while contributions to this one process change. These contributions do not establish species abundance or every ecosystem function.

Read the diagram in words

The first state has X eight and Y two; the second X three and Y seven. Both totals are ten. X shares are 0.8 and 0.3; Y shares are 0.2 and 0.7.

First supplied state
Group X contribution	Group Y contribution	Aggregate process index
8	2	10

First supplied state · Share of this specified total
Group X contribution · Share of this specified total	Group Y contribution · Share of this specified total
0.8	0.2

Second supplied state
Group X contribution	Group Y contribution	Aggregate process index
3	7	10

Second supplied state · Share of this specified total
Group X contribution · Share of this specified total	Group Y contribution · Share of this specified total
0.3	0.7

Contributor shares change while total remains ten

Equal aggregate function does not establish identical composition or all other functions

Original two-group additive contributions to one aggregate process index. No claim of species abundance, biomass proportions, full functional redundancy or cause of compensation.

A feedback has a variable, sign and conditions

A feedback occurs when a change in a variable affects processes that influence that variable again. A reinforcing loop tends to amplify a specified initial change under its stated relations. An opposing loop tends to counter it. The sign concerns the response relationship, not whether the ecological outcome is desirable.

For example, suppose an increase in an assigned available resource increases uptake and the greater uptake reduces that same resource pool. Under those two specified influences, the loop opposes the initial resource increase. If an increase instead raises a release process that supplies more of the same resource, the stated loop reinforces it. These conditional sign examples do not establish actual effect strength.

Delay, saturation, boundary inputs and changing organismal responses can alter the outcome. An opposing loop does not alone guarantee return to one equilibrium; a reinforcing loop does not alone prove collapse. Time records and a defined model are needed to connect feedback signs to dynamics. Preserve the chosen variable and time window when comparing ecosystem responses.

Worked example

Compare the response stages separately

The initial deviations from ten are |6 - 10| = 4 for A and |9 - 10| = 1 for B. Relative deviations are 0.4 and 0.1. Those values support the stated initial-resistance comparison.

At later observations A is eight and then ten; B remains nine and nine. A reaches the baseline by the final supplied observation. B remains one unit away. The record does not say when B might return later or what happened between readings.

For function, eight plus two and three plus seven both equal ten. X changes from eighty to thirty percent of the total, and Y from twenty to seventy percent. Stable aggregate index and changed contributions are simultaneously true.

Check your understanding

Which system shows greater initial resistance under the supplied metric?
Show reasoning
B. Its first post-disturbance value nine differs from baseline ten by one, while A differs by four. This comparison concerns the matched initial observation.
Which system has returned to the selected baseline within the record?
Show reasoning
A, whose final supplied value is ten. B remains nine. The comparison does not establish its later outcome or a universal definition of ecosystem resilience.
Does an unchanged process total ten prove contributor composition is unchanged?
Show reasoning
No. The supplied contributions change from eight plus two to three plus seven. One aggregate function can remain equal while its component contributions change.

What to carry forward

Name the variable, baseline, response stage and observation window; aggregate stability does not establish unchanged composition or future recovery.

References

Resources supporting this lesson’s explanations and examples.