Ecosystems
All the wildebeest living in the same area make up this ecological group.
A population.
The seasonal movement of animals between areas is called this.
Migration
A resource or condition that restricts population growth is called this.
A limiting factor.
This term describes the population size an environment can support over time under its current conditions.
Carrying capacity.
The “30 by 30” proposal introduced in the unit calls for protecting what percentage of U.S. lands and waters by 2030?
30 percent.
An ecosystem includes living organisms and these other components.
Nonliving components, such as water, sunlight, soil, and temperature.
What food resource do wildebeest depend on?
Grass
Name two resources that can limit an animal population.
Accept food, water, space, or suitable shelter.
Can carrying capacity change? Give one reason.
Yes. Changes in resources or environmental conditions can change how many organisms the environment supports.
Which ecosystem serves as the unit’s main case study?
The Serengeti.
Identify one biotic and one abiotic component of a grassland ecosystem.
Biotic: grass, wildebeest, or predators.
Abiotic: rainfall, soil, sunlight, or temperature.
Explain how rainfall can influence where wildebeest move.
Rainfall affects grass growth and water availability. Wildebeest move to areas where they can obtain needed resources.
How can competition for food change as a population grows?
More individuals share the available food, so competition can increase and less food may be available per individual.
What may happen when a population exceeds the resources its environment can provide?
Resource shortages can reduce reproduction or increase deaths, causing the population to decline.
In a classroom model, each animal needs two food tokens to survive. If 40 tokens are available, how many animals can survive that round?
20 animals, assuming all tokens are accessible and distributed so each survivor gets two.
Explain how a change in a nonliving component can affect a population.
Example: Less rainfall can reduce grass growth, leaving less food for herbivores and reducing their survival or reproduction.
A fence blocks access to an area animals normally use during the dry season. Explain one possible effect on the population.
Animals may lose access to food or water, increasing competition and potentially reducing survival or reproduction.
A disease reduces a population even though food is plentiful. Can disease still be a limiting factor? Explain.
Yes. Disease can reduce survival or reproduction independently of food availability.
A population grows quickly, then fluctuates around a similar size for several years. What could explain this pattern?
Limiting factors may be keeping the population near carrying capacity. Births and deaths vary, so the population can fluctuate.
A conservation team wants to reintroduce African wild dogs into a protected area. Identify two kinds of evidence it should collect to estimate how many dogs the area could support.
Accept prey abundance, available habitat, water availability, disease risk, or competition with other predators. Students should connect each to survival or reproduction.
A student’s ecosystem model shows animals and plants but no connections between them. What should the student add, and why?
Labeled connections showing interactions, such as feeding or competition. These explain how one component affects another.
Two areas receive similar rainfall, but only one has many wildebeest. Give two additional factors you would investigate.
Accept food quantity or quality, access to water, barriers to movement, predators, disease, or competition. Students should explain how their choices could affect occupancy.
A population receives more food, but its size does not increase. Explain why that might happen.
Another factor may still limit growth, such as water, habitat, disease, or predation. More food alone does not guarantee population growth.
A drought reduces grass growth for several years. Predict what could happen to carrying capacity for herbivores and explain why.
It could decrease because less food is available to support the population. Movement to other areas could affect the actual outcome.
A student says, “Rainfall and animal numbers increased together, so rainfall directly caused the population to grow.” What additional evidence would strengthen that explanation?
Evidence of the mechanism: rainfall increased food availability, which improved survival or reproduction. Investigating other possible influences would also strengthen the explanation.