Ultimate Guide: AP Environmental Science
Chapter 1: The Living World (Ecosystem)
1.1: Introduction to Ecosystems
● Ecosystem: A community of living (biotic) organisms interacting with the non-living
(abiotic) components of their environment as a system through various nutrients and
energy cycles.
Biological Populations and Communities
● Organism: A living thing that can function on its own.
● Species: Organisms that resemble each other; are similar in genetic makeup, chemistry,
and behavior; and are able to interbreed and produce fertile offspring.
○ Interspecific: Means between different species.
● Population: Organisms of the same species that interact with each other and occupy a
specific area.
● Community: Population of different species.
Ecological Niches
● Ecological Niche: A particular area within a habitat occupied by an organism, as well as
the function of that organism within its ecological community.
● Physical environment: It influences how organisms affect and is affected by resources
and competitors.
● Niche: It reflects the specific adaptations that a species has acquired through evolution.
● Characteristics of a niche include:
○ Habitat.
○ Interactions with living and nonliving factors.
○ place/role in the food web.
○ Types and amounts of resources available.
,Interactions Among Species
● Symbiosis: A term used to describe any type of close and long-term biological interaction
between two different biological organisms of the same or different species.
Symbiotic Interactions
● Amensalism: The interaction between two species whereby one species suffers and the
other species is not affected.
○ Example: The black walnut tree releases a chemical that kills neighboring plants.
● Commensalism: The interaction between two species whereby one organism benefits and
the other species is not affected.
○ Forms of commensalism include:
○ using another organism for transportation
○ using another organism for housing, and
○ using something that another organism created.
● Competition: It can be either intraspecific and interspecific.
○ It is the driving force of evolution whether it is for food, mating partners, or
territory.
○ Intraspecific: Competition between members of the same species.
○ Interspecific: competition between members of different species.
○ Competition is prominent in predator–prey relationships, with the predator
seeking food and the prey seeking survival.
● Mutualism: The interaction between two species whereby both species benefit.
● Parasitism: The interaction between two species whereby one species is benefited, and
the other species is harmed.
● Predation: Predators hunt and kill their prey.
○ Opportunistic predators kill and eat almost anything.
○ Specialist predators only prey upon certain organisms.
● Saprottrophism: Saprotrophs obtain their nutrients from dead or decaying plants or
animals through the absorption of soluble organic compounds.
Law of Tolerance
, ● Law of Tolerance: It states that the existence, abundance, and distribution of species
depend on the tolerance level of each species to both physical and chemical factors.
○ Some factors can control an organism's abundance or distribution if they exceed
its tolerance limits.
Limiting Factors
● Limiting Factor: Any abiotic factor that limits or prevents the growth of a population.
● Limiting factors in terrestrial ecosystems may include:
○ the level of soil nutrients,
○ the available amount of water and light, and
○ the temperature
● In aquatic ecosystems, major limiting factors may include:
○ the pH of the water,
○ the amount of dissolved oxygen, light, or
○ the degree of salinity.
Predator-Prey Relationship
● Predator-prey cycles are based on a feeding relationship between two species:
○ If the prey species rapidly multiply, the number of predators increases until the
predators eventually eat so many of the prey that the prey population dwindles
again.
Resource Partitioning
● Morphological partitioning: It occurs when two species share the same resource but have
evolved slightly different structures to utilize the same resource
● Spatial partitioning: It occurs when competing species use the same resource by
occupying different areas or habitats within the range of occurrence of the resource
● Temporal partitioning: It occurs when two species eliminate direct competition by
utilizing the same resource at different times
, 1.2: Terrestrial Biomes
● Biomes: These are major regional or global biotic communities characterized by dominant
forms of plant life and the prevailing climates
○ Temperature and precipitation are the most important determinants of biomes.
● The geographical distribution of the various terrestrial biomes is controlled primarily by
the average air temperature and the amount of rainfall the biome receives.
Deserts
● Deserts: Defined in terms of the amount of rainfall they receive, not temperature.
○ They cover about 20% of Earth’s surface and occur where rainfall is less than 20
inches (50 cm) per year.
○ Daily extremes in temperature result from exceptionally low humidity as water
vapor tends to block solar radiation.
○ Most deserts are located between 15° and 35° north and south latitudes.
○ Arctic tundra is a cold desert due to the low amount of rainfall it receives yearly.
● Succulents
○ Plants that have fleshy leaves or stems that store water.
○ They have:
○ deep roots to tap groundwater;
○ open stomata at night;
○ shallow roots to collect and store water after short rainfalls;
○ small surface areas exposed to sunlight;
○ vertical orientation to minimize exposure to the sun; and
○ waxy leaves to minimize transpiration.
● Cactus
○ They have sharp spines that create shade, reduce drying airflow, discourage
herbivores, and reflect sunlight.
○ They also secrete toxins into the soil to prevent interspecific completion.
● Wildflowers
○ They are dependent on water for germination;
○ They have short life spans;
○ They perform their entire life cycle from seed to flower to seed within a single
growing season; and
○ They store biomass in seeds.
Chapter 1: The Living World (Ecosystem)
1.1: Introduction to Ecosystems
● Ecosystem: A community of living (biotic) organisms interacting with the non-living
(abiotic) components of their environment as a system through various nutrients and
energy cycles.
Biological Populations and Communities
● Organism: A living thing that can function on its own.
● Species: Organisms that resemble each other; are similar in genetic makeup, chemistry,
and behavior; and are able to interbreed and produce fertile offspring.
○ Interspecific: Means between different species.
● Population: Organisms of the same species that interact with each other and occupy a
specific area.
● Community: Population of different species.
Ecological Niches
● Ecological Niche: A particular area within a habitat occupied by an organism, as well as
the function of that organism within its ecological community.
● Physical environment: It influences how organisms affect and is affected by resources
and competitors.
● Niche: It reflects the specific adaptations that a species has acquired through evolution.
● Characteristics of a niche include:
○ Habitat.
○ Interactions with living and nonliving factors.
○ place/role in the food web.
○ Types and amounts of resources available.
,Interactions Among Species
● Symbiosis: A term used to describe any type of close and long-term biological interaction
between two different biological organisms of the same or different species.
Symbiotic Interactions
● Amensalism: The interaction between two species whereby one species suffers and the
other species is not affected.
○ Example: The black walnut tree releases a chemical that kills neighboring plants.
● Commensalism: The interaction between two species whereby one organism benefits and
the other species is not affected.
○ Forms of commensalism include:
○ using another organism for transportation
○ using another organism for housing, and
○ using something that another organism created.
● Competition: It can be either intraspecific and interspecific.
○ It is the driving force of evolution whether it is for food, mating partners, or
territory.
○ Intraspecific: Competition between members of the same species.
○ Interspecific: competition between members of different species.
○ Competition is prominent in predator–prey relationships, with the predator
seeking food and the prey seeking survival.
● Mutualism: The interaction between two species whereby both species benefit.
● Parasitism: The interaction between two species whereby one species is benefited, and
the other species is harmed.
● Predation: Predators hunt and kill their prey.
○ Opportunistic predators kill and eat almost anything.
○ Specialist predators only prey upon certain organisms.
● Saprottrophism: Saprotrophs obtain their nutrients from dead or decaying plants or
animals through the absorption of soluble organic compounds.
Law of Tolerance
, ● Law of Tolerance: It states that the existence, abundance, and distribution of species
depend on the tolerance level of each species to both physical and chemical factors.
○ Some factors can control an organism's abundance or distribution if they exceed
its tolerance limits.
Limiting Factors
● Limiting Factor: Any abiotic factor that limits or prevents the growth of a population.
● Limiting factors in terrestrial ecosystems may include:
○ the level of soil nutrients,
○ the available amount of water and light, and
○ the temperature
● In aquatic ecosystems, major limiting factors may include:
○ the pH of the water,
○ the amount of dissolved oxygen, light, or
○ the degree of salinity.
Predator-Prey Relationship
● Predator-prey cycles are based on a feeding relationship between two species:
○ If the prey species rapidly multiply, the number of predators increases until the
predators eventually eat so many of the prey that the prey population dwindles
again.
Resource Partitioning
● Morphological partitioning: It occurs when two species share the same resource but have
evolved slightly different structures to utilize the same resource
● Spatial partitioning: It occurs when competing species use the same resource by
occupying different areas or habitats within the range of occurrence of the resource
● Temporal partitioning: It occurs when two species eliminate direct competition by
utilizing the same resource at different times
, 1.2: Terrestrial Biomes
● Biomes: These are major regional or global biotic communities characterized by dominant
forms of plant life and the prevailing climates
○ Temperature and precipitation are the most important determinants of biomes.
● The geographical distribution of the various terrestrial biomes is controlled primarily by
the average air temperature and the amount of rainfall the biome receives.
Deserts
● Deserts: Defined in terms of the amount of rainfall they receive, not temperature.
○ They cover about 20% of Earth’s surface and occur where rainfall is less than 20
inches (50 cm) per year.
○ Daily extremes in temperature result from exceptionally low humidity as water
vapor tends to block solar radiation.
○ Most deserts are located between 15° and 35° north and south latitudes.
○ Arctic tundra is a cold desert due to the low amount of rainfall it receives yearly.
● Succulents
○ Plants that have fleshy leaves or stems that store water.
○ They have:
○ deep roots to tap groundwater;
○ open stomata at night;
○ shallow roots to collect and store water after short rainfalls;
○ small surface areas exposed to sunlight;
○ vertical orientation to minimize exposure to the sun; and
○ waxy leaves to minimize transpiration.
● Cactus
○ They have sharp spines that create shade, reduce drying airflow, discourage
herbivores, and reflect sunlight.
○ They also secrete toxins into the soil to prevent interspecific completion.
● Wildflowers
○ They are dependent on water for germination;
○ They have short life spans;
○ They perform their entire life cycle from seed to flower to seed within a single
growing season; and
○ They store biomass in seeds.
