What keeps an ecosystem stable, and how does it recover from disturbance?
Analyze and interpret data on how biodiversity, species interactions, and disturbance affect ecosystem stability and resilience, including succession (Tennessee Academic Standards for Science, Biology I, BIO1.LS2).
A standard-level answer on ecosystem dynamics for the Tennessee Biology I EOC: how biodiversity and species interactions support stability, the symbiotic relationships, how disturbance affects an ecosystem, and ecological succession (primary and secondary).
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this topic is asking
The Tennessee LS2 standards ask you to analyze how biodiversity, species interactions, and disturbance affect ecosystem stability and resilience, including succession. For the Biology I EOC that means understanding why more diverse ecosystems are generally more stable, knowing the symbiotic relationships (mutualism, commensalism, parasitism) and other interactions (competition, predation), and being able to describe ecological succession (primary and secondary). Items often give a scenario of a disturbance or a relationship and ask you to name or predict the outcome.
Stability and resilience
The standard expects you to connect stability and resilience to biodiversity. A diverse ecosystem, with many species and a complex food web, has a kind of redundancy: if one species is lost or declines, others can fill similar roles, so the ecosystem absorbs the change. A simple ecosystem with few species is more fragile, because the loss of one species can have large knock-on effects. This links directly to biodiversity and its importance.
Species interactions: symbiosis and more
Organisms in an ecosystem interact in ways that shape its dynamics. Symbiosis is a close, long-term relationship between two species:
- Mutualism. Both species benefit (clownfish and sea anemone; bees and flowering plants; nitrogen-fixing bacteria and legumes).
- Commensalism. One species benefits and the other is unaffected (a bird nesting in a tree; barnacles on a whale).
- Parasitism. One species (the parasite) benefits at the expense of the other (the host), which is harmed (a tapeworm in an intestine; a tick on a mammal).
Two other key interactions are competition (organisms vie for the same limited resource) and predation (one organism eats another). These interactions help regulate population sizes and contribute to the balance of the ecosystem. The EOC commonly gives a scenario and asks which relationship it is, so track who benefits and who is harmed.
Disturbance and ecological succession
The contrast to remember: primary succession starts with no soil (slow, begins with pioneers building soil); secondary succession starts with soil present (faster, after a disturbance). A scenario describing regrowth after a fire is secondary succession; a scenario describing life colonizing fresh lava rock is primary succession.
Try this
Q1. State the difference between mutualism, commensalism, and parasitism. [3]
- Cue. Mutualism, both species benefit; commensalism, one benefits and the other is unaffected; parasitism, one (the parasite) benefits and the other (the host) is harmed.
Q2. State the key difference between primary and secondary succession. [2]
- Cue. Primary succession starts on bare rock with no soil (pioneers build the first soil, so it is slow); secondary succession starts where soil already remains after a disturbance (so it is faster).
Exam-style practice questions
Practice questions written in the style of TDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
TN Biology I EOC (2023 released style)1 marksAfter a forest fire clears an area down to bare soil, small plants and grasses grow first, then shrubs, then trees over many years. This gradual change in the community is called: (A) natural selection. (B) ecological succession. (C) carrying capacity. (D) the nitrogen cycle.Show worked answer →
A 1-point multiple-choice item on succession.
The correct answer is B. Ecological succession is the gradual, predictable change in the community of an area over time; here it is secondary succession (because soil already remained after the fire). Natural selection (A) acts on populations, carrying capacity (C) is a population limit, and the nitrogen cycle (D) is a nutrient cycle.
TN Biology I EOC (2024 released style)2 marksTwo communities of clownfish and sea anemones live together: the clownfish is protected among the anemone's stinging tentacles, and the anemone is cleaned and defended by the clownfish, with both benefiting. (a) Name this type of symbiotic relationship. (b) Explain how high biodiversity helps an ecosystem recover from a disturbance.Show worked answer →
A 2-point item on symbiosis and resilience.
(a) 1 point: mutualism (both species benefit).
(b) 1 point: with many species and feeding relationships, the loss or decline of one species can be compensated for by others filling similar roles, so a diverse ecosystem is more resilient and recovers more readily after a disturbance.
Markers reward identifying mutualism and the redundancy or compensation idea for resilience.
Related dot points
- Use a model to illustrate how energy flows through an ecosystem from producers to consumers and decomposers, and why it decreases at each trophic level (Tennessee Academic Standards for Science, Biology I, BIO1.LS2).
A standard-level answer on energy flow for the Tennessee Biology I EOC: producers, consumers, and decomposers, food chains and food webs, trophic levels, energy pyramids, and the 10 percent rule for energy transfer.
- Construct an explanation for how matter cycles through ecosystems, including the carbon, nitrogen, and water cycles, and the role of photosynthesis, respiration, and decomposers (Tennessee Academic Standards for Science, Biology I, BIO1.LS2).
A standard-level answer on biogeochemical cycles for the Tennessee Biology I EOC: how the carbon, nitrogen, and water cycles move matter through ecosystems, the role of photosynthesis and respiration in the carbon cycle, and the role of decomposers and bacteria.
- Use mathematical or graphical representations to explain how carrying capacity and limiting factors control population size (Tennessee Academic Standards for Science, Biology I, BIO1.LS2).
A standard-level answer on populations for the Tennessee Biology I EOC: exponential versus logistic growth, carrying capacity, density-dependent and density-independent limiting factors, and how to read a population-growth graph.
- Communicate information about biodiversity, how it arises through evolution, and how it supports ecosystem stability and benefits humans (Tennessee Academic Standards for Science, Biology I, BIO1.LS4).
A standard-level answer on biodiversity for the Tennessee Biology I EOC: the levels of biodiversity, how it arises through evolution and speciation, why genetic variation supports a population's survival, and how biodiversity supports ecosystem stability and benefits humans.
- Evaluate evidence about how human activities (habitat loss, pollution, climate change, and overuse) affect ecosystems and biodiversity, and how conservation can reduce the impact (Tennessee Academic Standards for Science, Biology I, BIO1.LS2).
A standard-level answer on human impact for the Tennessee Biology I EOC: habitat destruction, pollution, climate change, invasive species, and overharvesting, their effects on biodiversity and ecosystems, and the conservation strategies that reduce the impact.
Sources & how we know this
- Tennessee Academic Standards for Science — Tennessee Department of Education (2022)
- TNReady EOC Science Item Release (Biology and Chemistry) — Tennessee Department of Education (2018)