AP Environmental Science: Ecosystems, Biomes, Cycles, and Population Dynamics

What is an ecosystem?

An ecosystem is a community of living things (biotic) interacting with nonliving factors (abiotic) in a specific area.

What are biotic factors? Give examples.

Biotic factors are living components of an ecosystem, such as plants, animals, fungi, bacteria, and algae.

What are abiotic factors? Give examples.

Abiotic factors are nonliving components of an ecosystem, such as sunlight, temperature, water, salinity, pH, soil, oxygen, and nutrients.

What is the difference between habitat and niche?

A habitat is where an organism lives (address), while a niche is the role, resource use, and conditions needed by the organism (job).

What is a limiting factor?

A limiting factor is a resource or condition that restricts population growth, even if other conditions are favorable.

What is carrying capacity?

Carrying capacity is the maximum population size that an ecosystem can sustain due to resource limitations.

What is the role of producers in an ecosystem?

Producers capture energy from sunlight and convert it into food through photosynthesis.

What is the role of consumers in an ecosystem?

Consumers move energy through the food web by eating producers and other consumers.

What is the role of decomposers in an ecosystem?

Decomposers recycle nutrients back into the soil and water by breaking down dead organic matter.

What defines a biome?

A biome is a large region defined mainly by climate (temperature and precipitation) and dominant vegetation.

What are the characteristics of tundra biomes?

Tundra biomes have very cold climates, low precipitation, permafrost soil, and are characterized by low shrubs, mosses, and lichens.

What threats do boreal forests face?

Boreal forests face threats from logging, insect outbreaks, and increased wildfire risk due to warming.

What defines a temperate deciduous forest?

Temperate deciduous forests have moderate precipitation, four seasons, and are characterized by broadleaf trees that drop leaves.

What are the main threats to tropical rainforests?

Tropical rainforests are threatened by deforestation for agriculture, logging, and palm oil production, leading to biodiversity collapse.

What is the significance of wetlands?

Wetlands provide water filtration, flood control, and high productivity, supporting diverse food webs.

What are estuaries and their importance?

Estuaries are where rivers meet oceans, characterized by brackish water and are nutrient-rich nursery habitats for many fish and shellfish.

What adaptations do desert plants have?

Desert plants have adaptations such as water storage, deep roots, and some exhibit nocturnal activity to conserve water.

How does human activity impact biomes?

Human activity can change land cover, affecting climate patterns, water cycles, erosion, and biodiversity.

What is the carbon cycle?

The carbon cycle describes how carbon moves through the atmosphere, biosphere, oceans, and geosphere, influencing climate.

What is the role of algae in aquatic systems?

Algae, found in the limnetic zone of lakes and ponds, produce energy through photosynthesis and support aquatic food webs.

What are the four zones of a lake?

The four zones are littoral (near shore), limnetic (open surface), profundal (deep water), and benthic (bottom sediments).

What is a key concept regarding dissolved oxygen in water?

Dissolved oxygen tends to be higher in colder, faster-moving water.

What is the significance of coral reefs?

Coral reefs are warm, shallow, and clear water ecosystems that support high productivity through symbiosis with algae.

What are the threats to coral reefs?

Coral reefs face threats from warming (causing bleaching), acidification, and pollution.

What is the impact of nutrient input in aquatic systems?

Increased nutrient input can lead to algae blooms, which affect dissolved oxygen levels and aquatic life.

What are the major reservoirs where carbon is stored?

Atmosphere, biosphere, oceans, geosphere.

What process do plants use to convert CO2 into sugars?

Photosynthesis.

What is released back into the atmosphere during cellular respiration?

CO2.

What do microbes release during decomposition?

CO2 and, in low oxygen environments, methane.

What is the effect of combustion on carbon storage?

It rapidly releases stored carbon as CO2.

How does ocean uptake affect CO2 levels?

Colder water absorbs more CO2 than warmer water.

What human activity moves carbon from geosphere to atmosphere quickly?

Fossil fuel combustion.

What are the consequences of increased atmospheric CO2?

Stronger greenhouse effect and ocean acidification.

What is nitrogen fixation?

The process of converting N2 gas into NH3/NH4+.

Which organisms are primarily responsible for nitrogen fixation?

Bacteria in soil and root nodules of legumes.

What is the process of converting NH4+ to NO3- called?

Nitrification.

How do plants assimilate nitrogen?

By taking up NH4+ or NO3- to build proteins.

What human activity leads to groundwater nitrate contamination?

Fertilizer production and use.

What is the main reservoir of phosphorus?

Rocks and sediments.

What process releases phosphate from rocks into soil and water?

Weathering.

What is the consequence of excess phosphorus in water bodies?

Eutrophication.

What are the key processes in the hydrologic cycle?

Evaporation, condensation, precipitation, infiltration, runoff.

What effect does urbanization have on the water cycle?

It reduces infiltration and increases runoff.

What is primary productivity?

The rate at which producers convert sunlight into chemical energy.

What is the formula for net primary productivity (NPP)?

NPP = GPP - R.

Where is net primary productivity typically high?

Estuaries, wetlands, tropical rainforests.

What are the main trophic levels in a food chain?

Producers, primary consumers, secondary consumers, tertiary consumers, detritivores, decomposers.

Why are decomposers important in ecosystems?

They recycle nutrients so producers can keep growing.

What is the role of ammonification in the nitrogen cycle?

Decomposers convert organic nitrogen in dead matter into NH3/NH4+.

What happens during denitrification?

NO3- is converted back to N2 gas, returning nitrogen to the atmosphere.

What is the impact of deforestation on carbon storage?

It removes carbon sinks and releases CO2 when trees burn or decay.

What is the significance of the water table in groundwater?

It is the top of the saturated zone where groundwater is stored.

What is a trophic level?

A feeding position in a food chain.

What are producers in an ecosystem?

Autotrophs such as plants, algae, and phytoplankton.

Who are primary consumers?

Herbivores that eat producers.

What do secondary consumers eat?

They eat primary consumers (herbivores).

What is the role of tertiary consumers?

They eat secondary consumers.

What are detritivores?

Organisms that eat dead organic matter, such as worms and some insects.

What is the function of decomposers?

Bacteria and fungi that chemically break down matter and recycle nutrients.

Why is decomposition essential in ecosystems?

It recycles nutrients so producers can keep growing; without it, nutrients get locked in dead matter.

What is the 10% rule in energy transfer?

Only about 10% of energy is transferred to the next trophic level; most is lost as heat.

What happens to energy at each trophic step?

Most energy is lost as heat due to metabolism.

Why are food chains typically short?

They often have only 4 to 5 levels due to energy loss at each step.

What is biomagnification?

The process where contaminants concentrate in top predators due to consuming many contaminated prey.

What is a food chain?

One linear path of energy flow in an ecosystem.

Define a food web.

A network of many interconnected food chains.

What is a trophic cascade?

A change at one trophic level that causes changes across multiple levels.

What is a keystone species?

A species with a large ecosystem effect relative to its abundance; its removal dramatically changes the system.

What is biodiversity?

The variety of life at multiple levels, including genetic, species, and ecosystem diversity.

Why is biodiversity important?

It contributes to ecosystem stability, resilience, and provides ecosystem services.

What are the four categories of ecosystem services?

Provisioning, regulating, supporting, and cultural services.

What factors affect species richness on an island?

Island size (area) and distance from the mainland (isolation).

What is ecological tolerance?

The range of conditions in which a species can survive and reproduce.

What are natural disturbances?

Events that change ecosystem structure without human influence, such as hurricanes and floods.

What is primary succession?

The process of ecological change starting from bare rock, with pioneer species like lichens and mosses.

What is secondary succession?

The recovery process after a disturbance where soil remains, allowing faster recovery.

What are structural adaptations?

Traits that improve survival and reproduction, such as cactus spines reducing water loss.

How can climate change affect species adaptations?

Species may not adapt quickly enough and could migrate, decline, or go extinct.

What is the difference between generalist and specialist species?

Generalist species have a broad niche and can use many food sources and habitats, while specialist species have a narrow niche with specific habitat needs or diets.

Give an example of a generalist species.

Rats, raccoons, and cockroaches.

Give an example of a specialist species.

Koalas, many coral reef fish, and pandas.

What are r-selected species traits?

Many offspring, early maturity, little parental care, short lifespan, and populations that fluctuate a lot.

What are K-selected species traits?

Few offspring, late maturity, high parental care, long lifespan, and populations that stay near carrying capacity.

What happens to r-selected and K-selected species after a major disturbance?

R-selected species colonize quickly, while K-selected species become more common as the ecosystem stabilizes.

What does a survivorship curve represent?

A graph of survival rate across lifespan.

Describe Type I survivorship curve.

High survival in early and middle life, a drop in old age, few offspring, and lots of care (e.g., humans, elephants).

Describe Type II survivorship curve.

Constant death rate throughout life (e.g., many birds, rodents).

Describe Type III survivorship curve.

High death rate early in life, survivors live long, many offspring, and little care (e.g., many fish, plants).

What is carrying capacity (K)?

The largest population an environment can sustain long term given food, water, space, disease, waste removal, and predation pressure.

What occurs if a population exceeds its carrying capacity?

Overshoot happens, followed by dieback due to resource depletion, increased competition, and rising death rates.

What factors can change carrying capacity?

Drought (lowers K), habitat restoration (raises K), pollution (lowers K), and invasive species (changes K).

What are the two major population growth models?

Exponential growth (J-shaped curve) and logistic growth (S-shaped curve).

What is the formula for growth rate?

Growth rate = (birth rate − death rate) plus net migration.

How do you calculate doubling time?

Doubling time ≈ 70 / growth rate (%).

What does an age structure diagram show?

Population pyramid indicating the number of males and females in each age group.

What does a wide base in an age structure diagram indicate?

Many young people, indicating rapid growth and high demand for schools and jobs in the future.

What does a narrow base in an age structure diagram indicate?

Fewer young people, indicating a shrinking population and more healthcare costs for an aging population.

What is Total Fertility Rate (TFR)?

The average number of children a woman has in her lifetime.

What is replacement-level fertility?

Roughly 2.1 in many developed countries, accounting for child mortality and those who do not reproduce.

What factors decrease Total Fertility Rate?

Education for girls, access to contraception, urbanization, higher costs of raising children, later marriage age, and increased female workforce participation.