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 helps plants absorb nitrogen, belongs to this group.
Assimilation Efficiency – The percentage of consumed food that an organism absorbs and uses for growth and energy.
Example: A wolf eating meat has high assimilation efficiency compared to a cow eating grass.
Autotroph – An organism that makes its own food, usually using sunlight or chemical energy.
Example: Plants and algae are autotrophs because they perform photosynthesis.
Chloroplast – The part of plant cells that carries out photosynthesis.
Example: Leaves contain chloroplasts that turn sunlight into energy.
Consumption Efficiency – The percentage of available food that is actually eaten by an organism.
Example: A caterpillar may eat only 50% of a plant’s leaves, leaving the rest uneaten.
Cyanobacteria – Photosynthetic bacteria that produce oxygen and help in nitrogen fixation.
Example: Blue-green algae in ponds are cyanobacteria.
Decomposer – Organisms that break down dead matter and recycle nutrients into the ecosystem.
Example: Fungi and bacteria decompose fallen leaves in a forest.
Direct Effect – A direct interaction between two species, such as predation or competition.
Example: A hawk eating a mouse is a direct effect.
Dominant Species – A species that has the highest biomass or greatest influence in an ecosystem.
Example: Oak trees dominate temperate forests by providing shelter and food.
Ecosystem – A community of living organisms interacting with their environment.
Example: A coral reef ecosystem includes fish, coral, water, and sunlight.
Ecosystem Engineer – An organism that shapes its environment, affecting other species.
Example: Beavers build dams that create wetlands for many other species.
Endosymbiont – An organism that lives inside another in a mutualistic relationship.
Example: The bacteria inside human intestines help digest food.
Food Chain – A simple pathway showing how energy moves through organisms in an ecosystem.
Example: Grass → Rabbit → Fox.
Food Web – A complex network of interconnected food chains in an ecosystem.
Example: In an ocean food web, fish eat plankton, and sharks eat fish.
Heterotroph – An organism that cannot make its own food and must eat other organisms.
Example: Humans, lions, and mushrooms are heterotrophs.
Indirect Effect – When one species affects another through a third species.
Example: Wolves in Yellowstone control deer populations, which helps plants grow.
Keystone Species – A species that has a crucial role in maintaining ecosystem balance.
Example: Sea otters eat sea urchins, preventing them from overgrazing kelp forests.
(Trophic) Omnivory – When an organism eats at multiple trophic levels.
Example: Bears eat both plants (berries) and animals (fish).
Mitochondria – The powerhouse of the cell, producing energy from food.
Example: Your muscle cells have many mitochondria to provide energy for movement.
Primary Consumer – An organism that eats plants (herbivore).
Example: A cow eating grass is a primary consumer.
Primary Producer – An organism that makes its own food and provides energy for the food chain.
Example: Phytoplankton in the ocean are primary producers.
Production Efficiency – The percentage of energy stored in food that gets converted into new biomass.
Example: Insects have high production efficiency, turning most of their food into body mass.
Secondary Consumer – An organism that eats primary consumers (carnivore or omnivore).
Example: A frog eating insects is a secondary consumer.
Secondary Production – The energy stored in the bodies of consumers after eating.
Example: When a deer eats grass and gains weight, that weight is secondary production.
Tertiary Consumer – A predator that eats secondary consumers.
Example: A hawk eating a snake is a tertiary consumer.
Theory of Endosymbiosis – The idea that mitochondria and chloroplasts evolved from bacteria that were absorbed by larger cells.
Example: Mitochondria have their own DNA, supporting this theory.
Trophic Cascade – A chain reaction where changes at one trophic level affect multiple levels.
Example: Removing wolves led to deer overpopulation, which damaged plants and ecosystems.
Trophic Efficiency – The percentage of energy passed from one trophic level to the next.
Example: Only about 10% of the energy from plants is passed to herbivores.
Trophic Level – A position in the food chain based on energy flow.
Example: Grass is at the first trophic level (producer), while lions are at the fourth (top predator).
Trophic Pyramid – A diagram showing energy loss at each trophic level.
Example: A pyramid with plants at the base, herbivores in the middle, and carnivores at the top.