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Course: Class 12 Biology (India) > Unit 12
Lesson 3: Population Ecology- Age pyramids
- Population Density
- Population attributes
- Population growth rate based on birth and death rates
- Per capita population growth and exponential growth
- Logistic growth versus exponential growth
- Exponential & logistic growth
- Population growth and carrying capacity
- Population growth and decline
- Life history strategies and fecundity
- Population ecology review
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Population growth and carrying capacity
Review your understanding of population growth and carrying capacity in this free article aligned to NGSS standards.
Key terms
| Term | Meaning |
|---|---|
| Population | A group of organisms of the same species living together in a particular area |
| Ecosystem | All of the organisms in a particular area, along with the nonliving parts of the environment with which they interact |
| Population size | The total number of individuals in a population |
| Population density | The number of individuals in a population, per unit area |
| Exponential growth | Population growth that is unlimited by resource availability, which allows the population growth rate to increase continuously over time |
| Logistic growth | Population growth that is limited by resource availability, causing the population growth rate to slow as population size increases |
| Limiting factor | A feature of an ecosystem that restricts a population’s size |
| Carrying capacity | The maximum number of organisms or populations an ecosystem can support |
Exponential growth
Exponential growth describes a hypothetical model for population growth in which space and resources are available in unlimited supply. As a result, the population growth rate increases with each new generation. Under this model, a population rapidly grows quite large, and continues to grow indefinitely:
Logistic growth and carrying capacity
In reality, there is simply not enough space or resources for natural populations to continue to grow unchecked. Limiting factors within every ecosystem, such as the availability of food or the effects of predation and disease, prevent a population from becoming too large. These limiting factors determine an ecosystem’s carrying capacity, or maximum population size the environment can support given all available resources.
Logistic growth describes a model for population growth that takes into account carrying capacity, and is therefore a more realistic model for population growth. According to the logistic growth model, a population first grows exponentially because there are few individuals and plentiful resources. As the population gets larger and approaches the environment’s carrying capacity, resources become more scarce and the growth rate slows. This leads to the logistic growth model’s characteristic S-shaped curve:
The logistic growth model reflects the natural tension between reproduction, which increases a population’s size, and resource availability, which limits a population’s size. The result of this tension is the maintenance of a sustainable population size within an ecosystem, once that population has reached carrying capacity.
What else should I know about population growth and carrying capacity?
- Real population growth often deviates from the ideal logistic model. The ideal logistic growth curve shows population size leveling off as a flat line just below carrying capacity. However, a real population’s size typically oscillates around its carrying capacity. This means it’s common even for a stable population to briefly exceed or dip below its carrying capacity, even though the average growth rate of the population is zero.
- Carrying capacities can change. An ecosystem’s carrying capacity may fluctuate based on seasonal changes, or it may change as a result of human activity or a natural disaster. For example, if a fire destroys many trees in a forest ecosystem, the forest's carrying capacity for tree-nesting birds will decrease.
Want to join the conversation?
Is anyone else doing this in 9th grade?(12 votes)
I could possibly be doing this in a grade equal to my age minus 5.(1 vote)
- human activity or natural disaster For example if a fire destorys many trees in a forest ecosystem the forest's carryng capacity for tree -nesting birds will decrease(8 votes)
Either. It's not important for this example whether the fire was the result of human activity or natural disaster. All that matters is the end result of the fire destroying many trees.(2 votes)
- How far underwater does coral have to be to grow?(5 votes)
- Healthy tropical coral reefs grow horizontally from 1 to 3 cm (0.39 to 1.18 in) per year, and grow vertically anywhere from 1 to 25 cm (0.39 to 9.84 in) per year; however, they grow only at depths shallower than 150 m (490 ft) because of their need for sunlight, and cannot grow above sea level.(2 votes)
- how long does it take on average to build a decent population?. Also How much food intake does every animal need in that population. Another question I have is why is there a limiting factor on how many animals their could be?. Does seasonal change always happen with this?(5 votes)
- Corals prefer clear and shallow water, where lots of sunlight filters through to their symbiotic algae. It is possible to find corals at depths of up to 300 feet (91 meters), but reef-building corals grow poorly below 60–90 feet (18–27 meters).(5 votes)
How long does it take to build a population up altogether(4 votes)
I still don't understand how this works(4 votes)
Buenoo y esto q se cree(3 votes)- the capacity in the population is higher .(3 votes)
- is this this for real for real(2 votes)
- no its not its a joke(3 votes)