Carrying capacity
What is the term for the maximum number of individuals of a species that an environment can support over time?
Carrying capacity is the maximum number of individuals of a species that an environment can support over time
Define population density.
Population density is the number of individuals of a species per unit area or volume
Name two common limiting factors in terrestrial ecosystems.
Examples: water, food, shelter, space, predators, disease, sunlight (for plants).
Name the three main energy roles in an ecosystem
What are producers (autotrophs), consumers (heterotrophs: primary, secondary, tertiary), and decomposers.
What is one main difference between a food chain and a food web?
A food chain shows a single linear path of energy flow; a food web shows multiple interconnected food chains and feeding relationships.
Describe one way limiting resources can cause a population to stop growing as it nears carrying capacity.
As population grows, limited resources (food, space, water) become scarce; individuals compete more, reproduction may drop and mortality may rise, causing growth to slow and level off near carrying capacity.
How does high population density increase competition among organisms? Give a classroom-level example.
High density means more individuals share the same limited resources—more competition for food, mates, nesting sites.
Explain why water can be a limiting factor even in areas that get regular rainfall.
Even with regular rainfall, water may be limited seasonally, or stored water may be inaccessible (deep in soil), or evaporation may reduce availability; human diversion or poor soil retention can make water effectively limiting.
Explain why producers are essential for ecosystem energy flow.
What is producers convert sunlight (or chemical energy) into biomass via photosynthesis, forming the base of energy flow that supports consumers; without producers, energy would not enter the ecosystem’s food chains.
Why are food webs better than single food chains for showing ecosystem interactions?
Food webs more accurately represent ecosystem complexity because most species eat and are eaten by multiple others; webs show multiple pathways for energy and provide resilience information.
Give an example of how a sudden habitat change (like a drought) could temporarily reduce carrying capacity for a species.
Drought reduces water and plant growth, so food and habitat for animals decline; fewer resources cause lower survival and reproduction, reducing the lake’s or habitat’s carrying capacity temporarily.
Describe one method scientists use to estimate the density of a population (for animals that move).
Methods include mark-recapture for mobile animals, transect counts, quadrat sampling, or camera traps with statistical estimation.
Describe how a predator can act as a limiting factor for a prey population.
Predators reduce prey numbers by increasing mortality; when predator numbers are high, prey population growth slows or declines—predation limits prey population size.
Using a bear as an example of an organism that can be both a primary and secondary consumer depending on food available, and explain how.
What is a bear can be a primary consumer when eating berries (plant material) and a secondary or tertiary consumer when eating fish or small mammals—its role depends on diet available.
Show how removing a top predator might affect multiple species in a food web
Removing a top predator can cause direct effects (prey populations increase due to less predation) and indirect effects (vegetation decline if herbivores increase).
Explain how carrying capacity can change over time and name two factors that might cause it to increase.
Carrying capacity can increase if resources improve (e.g., more food, restored habitat, reduced predation, improved water supply) or decrease if resources worsen (habitat loss, pollution, drought, new predators). Two factors: availability of food and quality/area of habitat.
Explain how changes in population density can provide evidence about resource availability in an ecosystem.
Rising density may indicate abundant resources or immigration; falling density may indicate resource shortage, disease, emigration, or increased predation. Thus, changes in density can be interpreted as evidence about changes in resource availability.
Give an example of a human-caused limiting factor and explain its likely effect on local populations.
Example: Pollution, habitat destruction (deforestation), over-hunting /fishing. Effect: reduces available habitat or resources, causing population declines or forced migration; could reduce carrying capacity.
Describe how changes in producers’ abundance can affect consumers at different levels, using cause-and-effect language.
If producers decline, primary consumers have less energy and food, causing their populations to drop; secondary and tertiary consumers then lose food and may decline as well.
Explain why energy pyramids usually have a broad base and narrow top.
Because producers capture most of the energy from the environment; only a fraction (~10%) is passed to each higher trophic level, so there are more producers (broad base) and fewer top predators (narrow top).
A lake can support 1,200 fish when food is abundant. After an invasive plant takes over, food availability drops by 40%. Estimate qualitatively how carrying capacity for the fish might change and explain your reasoning
If food availability drops by 40%, carrying capacity would likely decrease substantially (not necessarily by exactly 40% but proportionally). Qualitative estimate: carrying capacity might fall from 1,200 fish to a lower value (e.g., on the order of several hundred fewer fish). Reasoning: less available food supports fewer individuals; resource-availability limits population siz
A field study recorded the number of rabbits per hectare over five years and found large yearly fluctuations. List three possible ecological explanations tied to resources and limiting factors.
Possible explanations: (a) Food availability fluctuates seasonally (e.g., plant growth variation) causing rabbit numbers to change; (b) Predator population changes (more predators reduce rabbits); (c) Disease or drought reduces reproduction or survival; (d) Human activities or habitat changes alter resources. Each ties fluctuations to limiting factors or resources.
Using data: If plant biomass in a meadow drops by 60% over two seasons while herbivore numbers stay similar, what limiting-factor explanations could account for this mismatch
Plausible interpretations: (a) Herbivore numbers stayed similar because mortality or reproduction hasn't yet responded—there may be a time lag between plant loss and herbivore decline; (b) Herbivores switched diet or migrated and are feeding elsewhere; (c) Measurement error—plant biomass might be measured in limited plots while herbivores use broader area; (d) An increase in supplemental food (human feeding) kept herbivore numbers stable despite plant loss.
A field graph shows plant biomass decreasing over time while decomposer activity increases. Interpret these data to explain how resource availability and energy flow are being affected.
What is plant biomass decreasing reduces energy input;
Describe how a major loss of producers would affect the shape of an energy pyramid and the populations at higher levels.
Major loss of producers narrows the base of the pyramid, reducing energy available to all higher trophic levels