What controls how big a population can grow in an ecosystem?
Analyze data on population growth, including exponential and logistic growth, carrying capacity, and limiting factors (density-dependent and density-independent) (GSE SB5.a).
A Georgia Milestones Biology EOC answer on population growth: exponential versus logistic growth, carrying capacity, density-dependent and density-independent limiting factors, and how to read a population growth curve.
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What this topic is asking
Standard SB5.a asks you to analyze data on populations, including growth patterns, carrying capacity, and limiting factors. For the Georgia Milestones Biology EOC you must distinguish exponential from logistic growth, define carrying capacity, and classify limiting factors as density-dependent or density-independent. Items often show a population growth curve and ask you to read or explain it.
Exponential versus logistic growth
In the real world, no population grows exponentially for long, because resources are finite. As a population grows, food, water, and space become scarce, so growth slows and the curve flattens, giving the logistic (S-shaped) pattern.
Carrying capacity
A population may fluctuate slightly above and below its carrying capacity, but over time it tends to stay near .
Limiting factors
A limiting factor is anything that restricts the size of a population. They come in two types the EOC asks you to classify:
- Density-dependent factors have a greater effect as the population becomes denser (more crowded). Examples: competition for food and space, predation, and the spread of disease, which all intensify in a crowded population.
- Density-independent factors affect a population regardless of its size. Examples: drought, wildfires, extreme temperatures, floods, and other natural disasters, which harm a population whether it is large or small.
The test is simple: does the factor's impact depend on how crowded the population is (dependent) or not (independent)?
Try this
Q1. Define carrying capacity. [1 point]
- Cue. The maximum population size an environment can support over time, given its resources (the level-off on a logistic curve).
Q2. Classify each as density-dependent or density-independent: a flood, competition for food. [2 points]
- Cue. A flood is density-independent (affects the population regardless of size); competition for food is density-dependent (worse when crowded).
Exam-style practice questions
Practice questions written in the style of GaDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Milestones (style)1 marksA population grows quickly, then levels off and stays roughly constant at the maximum the environment can support. This maximum is called the: (A) limiting factor (B) carrying capacity (C) biotic potential (D) trophic levelShow worked answer →
A 1-point selected-response item on carrying capacity.
The correct answer is B. The carrying capacity is the maximum population size that an environment can support over time, given its resources. When a population reaches it, growth levels off (the logistic curve flattens), because resources such as food, water, and space limit further increase. A limiting factor (A) is what restricts growth, biotic potential (C) is the maximum possible growth rate under ideal conditions, and a trophic level (D) is a feeding position. The level-off value is the carrying capacity.
Milestones (style)2 marksClassify each limiting factor as density-dependent or density-independent: competition for food, a drought, disease spread, a wildfire. Explain the difference.Show worked answer →
A 2-point classification item.
Density-dependent factors depend on how crowded the population is: competition for food and the spread of disease both intensify as the population grows denser, so these are density-dependent. Density-independent factors affect a population regardless of its size: a drought and a wildfire harm a population whether it is large or small, so these are density-independent. The difference is whether the factor's effect changes with population density (dependent) or not (independent). Full points need the correct classification of all four and the explanation of the difference.
Related dot points
- Analyze the flow of energy through ecosystems using food chains, food webs, and energy pyramids, including the roles of producers, consumers, and decomposers and the ten percent rule (GSE SB5.b).
A Georgia Milestones Biology EOC answer on energy flow: producers, consumers, and decomposers, trophic levels, food chains and food webs, the ten percent rule, and why energy pyramids narrow toward the top.
- Evaluate the factors that affect biodiversity and the stability of ecosystems, including keystone species, the effects of removing species, and symbiotic relationships (GSE SB5.c).
A Georgia Milestones Biology EOC answer on biodiversity and stability: why diverse ecosystems are more stable, the role of keystone species, the effects of removing a species, and the three types of symbiosis (mutualism, commensalism, parasitism).
- Predict the impact of environmental change on the stability of an ecosystem, including ecological succession (primary and secondary) and the effects of natural and human-induced disturbances (GSE SB5.d).
A Georgia Milestones Biology EOC answer on environmental change: ecological succession (primary versus secondary), pioneer and climax communities, and how natural and human-induced disturbances affect the stability of an ecosystem.
- Analyze the cycling of matter through ecosystems, including the carbon, nitrogen, and water cycles, and the roles of photosynthesis, respiration, and decomposers (GSE SB5.b).
A Georgia Milestones Biology EOC answer on the cycling of matter: the carbon cycle (photosynthesis and respiration), the nitrogen cycle (fixation by bacteria), and the water cycle, and how decomposers recycle nutrients, contrasted with the one-way flow of energy.
- Evaluate the impact of human activities on ecosystems (habitat destruction, pollution, invasive species, climate change) and design solutions to reduce that impact (GSE SB5.c, SB5.e).
A Georgia Milestones Biology EOC answer on human impact: habitat destruction, pollution, invasive species, and climate change, their effects on biodiversity and ecosystem stability, and conservation solutions to reduce the impact.
Sources & how we know this
- Biology Georgia Standards of Excellence (GSE) — Georgia Department of Education (2024)
- Georgia Milestones Biology EOC Assessment Guide — Georgia Department of Education (2024)