AP Biology Unit 8: Ecology

How do organisms change their behavior or body functions in response to changes inside or outside their body?

Stimulus response: organisms detect stimuli using receptors, process the information, and activate effectors such as muscles or glands to produce a response that helps maintain homeostasis.

Example: a person touches a hot surface → receptors detect heat → the nervous system sends signals → muscles pull the hand away.

How do organisms communicate with each other when they experience internal or environmental changes?

Sending and receiving signals: cells detect a change and release chemical or electrical signals that travel to other cells, causing a specific response.

Example: A plant attacked by insects releases chemical signals than warn nearby plants.

What are different ways animals communicate?

Sounds: calls, songs, or noises to attract mates or warn others of danger.

Visuals: colors, body movements, or displays to attract mates or show aggression.

Chemicals: Pheromones or scents to attract mates, mark territory, or signal danger.

Touch: Physical contact to bond, groom, or comfort.

How does behavior affect an organism’s fitness and helps populations survive over time?

Behaviors that help an organism survive and reproduce increase its fitness. If these behaviors are heritable, they can become more common in a population over generations through natural selection.

Example: birds that migrate to warmer areas during winter are more likely to survive and reproduce; migration behavior can be passed to offspring; the behavior becomes more common in the population.

Example 1 of how communication and cooperation between organisms help improve survival and reproduction:

Wolves hunt in packs: Wolves communicate using howls, body language, and other signals and cooperate to surround and capture prey. This helps them get more food, increasing their chances of survival and successful reproduction.

Example 2 of how communication and cooperation between organisms help improve survival and reproduction:

Meerkats warn each other of predators: One meerkat watches for danger and makes a warning call when a predator approaches. The others respond by hiding or escaping, helping the group survive and protect offspring.

How do organisms get and use energy to stay alive, grow, and reproduce?

Plants capture energy from sunlight through photosynthesis and store it as glucose. Animals get energy by consuming those plants or other animals.

Ectotherms vs. endotherms: How do they regulate body temperature and metabolism?

Ectotherms: Body temperature depends on the environment. They use behaviors like basking in the sun to warm up. They generally have a lower metabolic rate and use less energy.

Endotherms: Maintain body temperature by producing heat internally through metabolism. They have a higher metabolic rate and require more energy.

How does energy availability affect population size and the balance of ecosystems?

Energy enters ecosystems through producers and is transferred to consumers through food chains. Because less energy is available at each trophic level, ecosystems can support fewer organisms at higher trophic levels.

How do autotrophs and heterotrophs contribute to energy flow in ecosystems?

Autotrophs (producers) capture energy from sunlight and convert it into chemical energy (food). Heterotrophs (consumers) get energy by eating other organisms and transfer that energy through the food web.

How do organisms break down food molecules to get usable energy?

Organisms use cellular respiration to break down food molecules, and convert their stored chemical energy into ATP, the cell’s usable form of energy.

What factors influence how populations grow or shrink over time?

Births and immigration → population increases

Deaths and emigration → population decreases

How does resource availability affect population density and growth?

When resources are abundant, populations grow and reach higher densities. When resources become limited, competition increases, causing lower population density.

How do populations interact, and how does this affect ecosystems over time?

Competition, predation, mutualism, commensalism, and parasitism. These interactions affect population sizes, resource availability, and the flow of energy.

N

Population size

r

Per capita growth rate

dN/dt

Rate of population growth (how quickly the population changes)

t

Time

K

Carrying capacity

(1−N/K)

Environmental limits on population growth

D

diversity

n

number of Individuals of a particular species

How does energy flow affect how communities are built and how they function?

Energy flows through ecosystems from producers → consumers → decomposers. Because energy is lost as heat at each trophic level, there is less energy available to support organisms at higher levels. This limits the number and size of populations that ecosystems can support.

How does ecosystem diversity make communities more resilient to environmental changes?

If one species is harmed by a disturbance, other species may fill similar roles, helping the ecosystem continue functioning.

What happens when a keystone species is removed or added to an ecosystem?

A keystone species has a large effect on an ecosystem relative to its abundance. Removing one can cause major changes in population sizes, food webs, and biodiversity. Adding one can change the ecosystem by altering predator-prey relationships and resource availability.

How do variations in traits help organisms survive and reproduce in different environments?

If a trait gives an organism an advantage in its environment, it is more likely to survive and reproduce, passing the trait to its offspring. Over time, natural selection can make advantageous traits more common.

How do mutations lead to adaptations over time?

Mutations create genetic variation in a population. If a mutation gives an organism an advantage in its environment, natural selection can favor that trait. Over many generations, the beneficial trait becomes more common in the population, becoming an adaptation.

How do invasive species disrupt ecosystems by outcompeting native species or changing resource availability?

Invasive species can outcompete native species for resources, causing native populations to decline and disrupting food webs.

How do human activities change ecosystems? including habitat destruction and the spread of disease

Destroying or changing habitats, introducing invasive species, polluting, over hunting/fishing, and spreading diseases. These changes can reduce biodiversity, disrupt food webs, and cause population sizes to decrease.

How do natural events like earthquakes or storms changes ecosystems and influences where species live?

They rapidly change habitats and cause populations to decrease, move to new areas, or adapt.