io 171 Lecture 8: Endosymbiosis, food webs, indirect effects, and trophic cascades

Alpha-Proteobacteria

A group of bacteria that includes species important for nitrogen fixation and the ancestors of mitochondria.

Example: Rhizobium, which forms symbiotic relationships with legumes.

Assimilation Efficiency

The percentage of consumed food that an organism absorbs and uses for growth and energy.

Example: If a rabbit consumes 100 grams of food and assimilates 30 grams, its assimilation efficiency is 30%.

Autotroph

An organism that makes its own food, usually using sunlight or chemical energy.

Example: Plants, which use photosynthesis to create energy from sunlight.

Chloroplast

The part of plant cells that carries out photosynthesis.

Example: Chloroplasts contain chlorophyll, the pigment that captures sunlight.

Consumption Efficiency

The percentage of available food that is actually eaten by an organism.

Example: If a fish is offered 200 grams of food and eats 50 grams, the consumption efficiency is 25%.

Cyanobacteria

Photosynthetic bacteria that produce oxygen and help in nitrogen fixation.

Example: Nostoc species, which can live in symbiosis with mosses.

Decomposer

Organisms that break down dead matter and recycle nutrients into the ecosystem.

Example: Fungi and bacteria that decompose organic material.

Direct Effect

A direct interaction between two species, such as predation or competition.

Example: A lion chasing and killing a zebra.

Dominant Species

A species that has the highest biomass or greatest influence in an ecosystem.

Example: Oak trees in a deciduous forest.

Ecosystem

A community of living organisms interacting with their environment.

Example: A coral reef, with various marine species and their physical environment.

Ecosystem Engineer

An organism that shapes its environment, affecting other species.

Example: Beavers, which build dams that create wetlands.

Endosymbiont

An organism that lives inside another in a mutualistic relationship.

Example: Zooxanthellae, algae that live inside coral polyps.

Food Chain

A simple pathway showing how energy moves through organisms in an ecosystem.

Example: Grass → Grasshopper → Frog → Snake.

Food Web

A complex network of interconnected food chains in an ecosystem.

Example: A web that shows multiple paths of energy flow among species in a forest.

Heterotroph

An organism that cannot make its own food and must eat other organisms. Example: Humans, which eat plants and animals.

Indirect Effect

When one species affects another through a third species.

Example: A decrease in predator populations leading to an increase in herbivore populations, which then deplete plant resources.

Keystone Species

A species that has a crucial role in maintaining ecosystem balance.

Example: Sea otters, which help control sea urchin populations.

(Trophic) Omnivory

When an organism eats at multiple trophic levels.

Example: Bears that eat both fish and berries.

Mitochondria

The powerhouse of the cell, producing energy from food.

Example: Found in almost all eukaryotic cells, mitochondria convert nutrients into ATP.

Primary Consumer

An organism that eats plants (herbivore).

Example: Cows that graze on grass.

Primary Producer

An organism that makes its own food and provides energy for the food chain.

Example: Phytoplankton in the ocean.

Production Efficiency

The percentage of energy stored in food that gets converted into new biomass.

Example: A fish converts 10% of the energy from its food into growth.

Secondary Consumer

An organism that eats primary consumers (carnivore or omnivore).

Example: A fox that eats rabbits.

Secondary Production

The energy stored in the bodies of consumers after eating.

Example: Energy stored in the tissues of fish after consuming smaller prey.

Tertiary Consumer

A predator that eats secondary consumers.

Example: An eagle that feeds on snakes.

Theory of Endosymbiosis

The idea that mitochondria and chloroplasts evolved from bacteria that were absorbed by larger cells.

Example: This theory explains the origin of complex eukaryotic cells.

Trophic Cascade

A chain reaction where changes at one trophic level affect multiple levels.

Example: Removing wolves from an ecosystem leading to an overpopulation of deer, which then overgraze vegetation.

Trophic Efficiency

The percentage of energy passed from one trophic level to the next.

Example: Typically, trophic efficiency is around 10%.

Trophic Level

A position in the food chain based on energy flow.

Example: Primary producers (plants) are at the first trophic level.

Trophic Pyramid

A diagram showing energy loss at each trophic level.

Example: A diagram illustrating how energy decreases from producers to top predators.