An ecosystem's carrying capacity is the maximum population size its resources (food, water, space) can sustainably support. When a population exceeds carrying capacity, resource shortages typically cause the population to decline back toward a sustainable level, often following an S-shaped (logistic) growth curve rather than growing exponentially forever. Biodiversity — the variety of species within an ecosystem — generally makes an ecosystem more resilient to disturbances like disease or environmental change.
Example
A deer population introduced to an island with no natural predators might grow rapidly at first, but once it exceeds the island's carrying capacity for food, starvation and competition cause the population to crash back down, illustrating the logistic growth pattern rather than unlimited exponential increase.
Key terms
Carrying capacity:
The maximum population an ecosystem can sustainably support.
Logistic growth:
An S-shaped growth pattern where population growth slows as it approaches carrying capacity.
Biodiversity:
The variety of species within an ecosystem.
Questions
1. Carrying capacity is:
The maximum population an ecosystem can sustainably support
The minimum population needed for survival
A fixed number that never changes for any ecosystem
Unrelated to resources like food and water
2. Logistic growth follows a:
S-shaped curve
Perfectly straight line
Random, unpredictable pattern
Curve with no defined shape at all
3. Biodiversity refers to:
The variety of species within an ecosystem
The total weight of all organisms combined
Only the number of predators present
A single dominant species only
4. When a population exceeds carrying capacity, it typically:
Declines back toward a sustainable level
Continues growing forever with no limit
Stays exactly the same forever
Immediately reaches zero
5. Greater biodiversity generally makes an ecosystem:
More resilient to disturbances
Less resilient to disturbances
Completely unaffected by any change
Impossible to study
6. Resources limiting carrying capacity include:
Food, water and space
Only sunlight, with nothing else
Nothing measurable at all
Only temperature, with nothing else
7. A population introduced with no natural predators may initially:
Grow rapidly
Immediately go extinct
Stay exactly the same size forever
Never reproduce at all
8. Why does population growth typically slow down as it approaches carrying capacity, rather than continuing at a constant rate?
Increasing competition for limited resources reduces survival and reproduction rates
Resources become more abundant as population size increases
Carrying capacity has no effect on population growth rate
Populations always grow at an identical rate regardless of resource availability
9. Why might a population "crash" after exceeding carrying capacity, rather than simply levelling off?
Severe resource shortages can cause starvation and competition that reduce the population sharply
Populations can never exceed their carrying capacity under any circumstances
Exceeding carrying capacity always has no negative consequences
A population crash has no connection to resource availability
10. Why might an ecosystem with only one dominant species be more vulnerable to a disease outbreak than a highly biodiverse one?
A disease targeting that one species could devastate the whole ecosystem, with fewer other species to maintain balance
Biodiversity has no connection to how an ecosystem responds to disease
A single dominant species is always more resistant to disease than diverse ecosystems
Disease outbreaks never affect ecosystems with low biodiversity
11. Introducing a new predator to an ecosystem with an overpopulated prey species could help by:
Helping bring the prey population back toward a sustainable level
Always causing the ecosystem to collapse entirely
Having no effect on population dynamics whatsoever
Immediately eliminating all species in the ecosystem
12. Why might carrying capacity change over time for the same ecosystem, rather than remaining fixed?
Changes in resource availability, climate or habitat can raise or lower how many individuals the ecosystem can support
Carrying capacity is a permanently fixed number that never changes for any reason
Environmental change never has any impact on carrying capacity
Carrying capacity is entirely unrelated to environmental conditions
13. Why is understanding logistic growth (rather than assuming unlimited exponential growth) important for wildlife management?
It reflects the real-world limits resources place on population growth, allowing more accurate predictions and planning
Exponential growth always accurately predicts real wildlife population changes
Wildlife populations are never limited by any environmental factor
Logistic growth models have no practical use in wildlife management
14. Why might removing a keystone species (one with a disproportionately large effect on its ecosystem) cause effects far beyond just that species' population?
Its role in the food web and habitat can be so central that its loss disrupts many interconnected relationships
Every species in an ecosystem has an exactly equal impact on the whole system
Removing any single species always has no effect on the rest of the ecosystem
Keystone species have no special role compared to any other species
15. Why might human activity (like habitat destruction) lower an ecosystem's effective carrying capacity for native species?
Reducing available habitat and resources directly reduces how many individuals that environment can sustainably support
Human activity always increases carrying capacity for every species
Habitat destruction has no measurable effect on carrying capacity
Carrying capacity is entirely independent of available habitat
16. Why might conservationists prioritise protecting biodiversity hotspots (areas with unusually high species variety) in their efforts?
Protecting these areas can preserve a disproportionately large share of the world's overall biodiversity
Biodiversity hotspots have no greater conservation value than any other area
Protecting a single species is always more effective than protecting a diverse ecosystem
Species variety has no bearing on an area's conservation priority
17. Why might reintroducing a locally extinct species to an ecosystem sometimes trigger unexpected ripple effects on multiple other species?
Species interact through complex food webs, so changes to one population can cascade through predator-prey and competitive relationships
Reintroducing a species always has an effect limited to that single species alone
Ecosystems have no interconnected relationships between different species
Ripple effects from reintroduction are always predictable and never unexpected
18. Why might a sudden drought reduce an ecosystem's carrying capacity for many species at once?
Water scarcity limits a resource many different species depend on, lowering the population several species can sustainably reach
Drought only ever affects a single species within an ecosystem
Water availability has no connection to carrying capacity for any species
Carrying capacity always increases during periods of drought
19. Competition between two species for the same limited resource (like food) is an example of a factor that can:
Limit population growth as it approaches carrying capacity
Always increase carrying capacity without limit
Have no effect on either species' population
Only ever affect predator species, never prey
20. Why might monoculture farming (growing a single crop species over a large area) be considered ecologically risky compared to a more biodiverse approach?
A pest or disease affecting that one species could devastate the entire crop, with no varied species to limit the spread
Monoculture farming always increases an area's overall biodiversity
A single crop species is always more resistant to pests than a diverse mix
Crop diversity has no bearing on agricultural or ecological risk
21. Why might invasive species introduced to a new ecosystem sometimes grow far beyond the carrying capacity seen in their native habitat?
They may lack natural predators or competitors in the new environment that would normally help limit their population
Invasive species always face identical carrying capacity limits everywhere they are introduced
Introducing a species to a new ecosystem never has any effect on its population growth
Native and invasive populations are always limited by exactly the same factors
Answer key (parent copy)
1. The maximum population an ecosystem can sustainably support
2. S-shaped curve
3. The variety of species within an ecosystem
4. Declines back toward a sustainable level
5. More resilient to disturbances
6. Food, water and space
7. Grow rapidly
8. Increasing competition for limited resources reduces survival and reproduction rates
9. Severe resource shortages can cause starvation and competition that reduce the population sharply
10. A disease targeting that one species could devastate the whole ecosystem, with fewer other species to maintain balance
11. Helping bring the prey population back toward a sustainable level
12. Changes in resource availability, climate or habitat can raise or lower how many individuals the ecosystem can support
13. It reflects the real-world limits resources place on population growth, allowing more accurate predictions and planning
14. Its role in the food web and habitat can be so central that its loss disrupts many interconnected relationships
15. Reducing available habitat and resources directly reduces how many individuals that environment can sustainably support
16. Protecting these areas can preserve a disproportionately large share of the world's overall biodiversity
17. Species interact through complex food webs, so changes to one population can cascade through predator-prey and competitive relationships
18. Water scarcity limits a resource many different species depend on, lowering the population several species can sustainably reach
19. Limit population growth as it approaches carrying capacity
20. A pest or disease affecting that one species could devastate the entire crop, with no varied species to limit the spread
21. They may lack natural predators or competitors in the new environment that would normally help limit their population