CH BIO 38A Extended version!

Community

A community includes all the populations that live and interact in the same area.

Niche

A species’ niche includes all the resources required for survival, growth, and reproduction, plus interactions with other organisms and the abiotic environment.

Difference between niche and habitat

A habitat is where a species lives; a niche is the species’ role, interactions, and resource use within the environment.

Competition interaction

Species A: – , Species B: – ; Example: Blackbird and fieldfare fighting over food.

Mutualism interaction

Species A: + , Species B: + ; Example: Bees pollinating flowering plants.

Commensalism interaction

Species A: + , Species B: 0 ; Example: Barnacles attaching to whales.

Parasitism interaction

Species A: + , Species B: – ; Example: Tapeworms living in a mammal’s intestines.

Herbivory interaction

Species A: + , Species B: – ; Example: A cow eating grass.

Predation interaction

Species A: + , Species B: – ; Example: A hawk eating a mouse.

Competition definition

Occurs when two species require the same limited resource.

Competitive exclusion principle

Two species cannot coexist indefinitely in the same niche; the species that acquires more resources will eventually win.

Resource partitioning

Reduces competition through evolution of slightly different niches separated by location or time.

Predator–prey cycle

When predator density and prey density affect each other over time.

Prey avoidance strategies

Escape, fleeing, or camouflage.

Types of prey defenses

Camouflage; warning coloration; chemical defenses.

Mimicry definition

When one species resembles another; it reduces predation and increases survival.

Batesian mimicry

A harmless species mimics a harmful one.

Müllerian mimicry

Two harmful species resemble each other, reinforcing predator avoidance.

Coevolution

Adaptations in one species select for adaptations in another species.

Example of coevolution

Flowers and their pollinators evolving together.

Species richness

The number of species in a community.

Species evenness

The relative abundance of each species in a community.

Ecological succession

The gradual change in a community’s species composition.

Primary succession

Occurs on surfaces with no soil, such as bare rock.

Secondary succession

Occurs after a disturbance removes organisms but leaves soil intact.

Pioneer species

First species to colonize new areas and pave the way for later species.

Climax conditions

Stable, long-term community conditions that few communities reach due to disturbances.

Trophic level

An organism’s position in the food chain.

Producers

Autotrophs that use energy from inorganic sources to produce organic molecules.

Consumers

Heterotrophs that obtain energy by consuming other organisms.

Decomposers

Return inorganic nutrients to the environment.

Food web

A more realistic depiction than a food chain due to complex feeding structures.

Keystone species

A species with a disproportionately large effect on community structure.

Example of keystone species

Sea otters controlling sea urchin populations.

Invasive species

Non-native species that spread widely and cause ecological or economic harm.

Example of invasive species

Zebra mussels.

Effect of losing a keystone species

Decreases species richness and disrupts evenness due to imbalanced populations.

Type of succession after forest clearing

Secondary succession.

Example of mutualism

Bees get nectar for food; flowers get pollinated.

Why competitive exclusion might not occur

Resource partitioning reduces competition, allowing coexistence.

How mimicry and warning coloration protect species

Warning coloration deters predators by signaling danger; mimicry protects by resembling harmful species.