How do organisms interact in a community, and how do ecosystems change over time?
Describe the relationships between organisms (competition, predation, and symbiosis) and explain how ecological succession changes a community over time toward a stable state (NYSSLS LS2, stability and change; cause and effect).
A NYSSLS-level answer on ecological interactions for the New York Life Science: Biology Regents: competition, predation and symbiosis (mutualism, commensalism, parasitism), and how succession changes a community toward a stable climax community.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this topic is asking
NYSSLS LS2 wants you to describe how organisms interact in a community and how communities change over time through succession. On the Life Science: Biology Regents this comes as a cluster describing several relationships to classify, or a sequence of changes after a disturbance. The crosscutting concepts are cause and effect and stability and change.
Competition
Competition can be between members of the same species (often intense, because they need exactly the same resources) or between different species. It is a key force in ecosystems and links to natural selection: individuals better at obtaining resources tend to survive and reproduce more.
Predation
Predation is the relationship in which one organism (the predator) kills and eats another (the prey). Predation controls prey populations and is a strong selection pressure: it favors prey that can avoid being eaten (camouflage, speed) and predators that can catch prey. Predator and prey numbers are often linked: a rise in prey allows predators to increase, which then reduces the prey, and so on.
Symbiosis
Examples: a bee and a flower (mutualism, the bee gets nectar and the flower is pollinated); a bird nesting in a tree (commensalism, the bird benefits, the tree is unaffected); a tick on a deer (parasitism, the tick benefits, the deer is harmed). To classify, ask what each partner gains or loses.
Ecological succession
A typical sequence after a clearing is: small, fast-growing plants colonize first, then shrubs, then trees, gradually changing the conditions and the mix of species. Succession tends toward a relatively stable, mature climax community, in which the species composition changes little as long as conditions stay stable. This is a clear example of stability and change: the community changes through succession but settles toward stability. A disturbance (fire, storm, human activity) can restart succession.
Try this
Q1. Name the three types of symbiosis and state who benefits in each. [2]
- Cue. Mutualism (both benefit), commensalism (one benefits, the other unaffected), parasitism (one benefits, the other harmed).
Q2. Explain what is meant by ecological succession. [2]
- Cue. The gradual, predictable change in the species of a community over time, often from pioneer species toward a stable climax community.
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (Life Science sample, 2024)3 marksIn a meadow, bees feed on nectar from flowers and carry pollen between them, ticks feed on the blood of deer and harm them, and two species of plant compete for the same sunlight. (a) Identify the relationship between the bees and the flowers. (b) Identify the relationship between the ticks and the deer. (c) Explain why the two plant species compete.Show worked answer →
A 3-point constructed-response item assessing cause and effect.
(a) 1 point: mutualism (both benefit: the bee gets food, the flower is pollinated).
(b) 1 point: parasitism (the tick benefits, the deer is harmed).
(c) 1 point: the two plant species need the same limited resource (sunlight), so they compete; if one obtains more, the other gets less, reducing its growth or survival.
Markers reward mutualism, parasitism, and competition for a shared limited resource.
Regents (Life Science CR, 2025)2 marksAfter a fire clears an area of forest, the area gradually changes: first small plants grow, then shrubs, then trees, until a stable forest returns. (a) State the term for this gradual change in a community over time. (b) Explain what is meant by a stable (climax) community.Show worked answer →
A 2-point item on ecological succession.
(a) 1 point: ecological succession.
(b) 1 point: a stable (climax) community is the relatively stable, mature community that succession leads to, in which the mix of species changes little over time as long as conditions remain stable.
Markers reward "succession" and the idea of a stable, mature end community.
Related dot points
- Describe the levels of ecological organization (organism, population, community, ecosystem) and the roles of biotic and abiotic factors and the producers, consumers and decomposers within an ecosystem (NYSSLS LS2, systems and system models; structure and function).
A NYSSLS-level answer on ecosystem structure for the New York Life Science: Biology Regents: the levels of ecological organization, biotic and abiotic factors, and the roles of producers, consumers and decomposers.
- Explain how populations grow and how limiting factors and carrying capacity control population size, interpreting population-growth graphs (NYSSLS LS2, stability and change; analyzing data).
A NYSSLS-level answer on population dynamics for the New York Life Science: Biology Regents: how populations grow, the limiting factors that control them, carrying capacity, and how to interpret population-growth graphs.
- Explain how energy flows one way through food chains and webs and is lost at each trophic level, and how matter (carbon and nitrogen) cycles through an ecosystem (NYSSLS LS2, energy and matter; using mathematics).
A NYSSLS-level answer on energy flow for the New York Life Science: Biology Regents: food chains and webs, trophic levels and the energy pyramid, why energy is lost at each level, and how carbon and nitrogen cycle through an ecosystem.
- Explain what biodiversity is, why genetic and species diversity matter for the resilience of populations and ecosystems, and how human activity threatens it (NYSSLS LS4, stability and change; cause and effect).
A NYSSLS-level answer on biodiversity for the New York Life Science: Biology Regents: what biodiversity is, why genetic and species diversity make populations and ecosystems more resilient, and how human activity threatens it.
- Explain how human activities (pollution, habitat destruction, resource use and the enhanced greenhouse effect) disrupt ecosystems and reduce biodiversity, and evaluate ways to reduce these impacts (NYSSLS LS2 and LS4, cause and effect; stability and change).
A NYSSLS-level answer on human impact for the New York Life Science: Biology Regents: how pollution, habitat destruction, resource use and the enhanced greenhouse effect disrupt ecosystems and reduce biodiversity, and how these impacts can be reduced.
Sources & how we know this
- New York State P-12 Science Learning Standards (Life Science) — New York State Education Department (2016)
- Educator Guide to the Regents Examination in Life Science: Biology — New York State Education Department (2025)