Ecosystems and Species Interactions

Ecosystem Basics

Individual: One organism (e.g., elk).
Population: Group of individuals of the same species (e.g., elk herd).
Community: All living organisms in an area.
Ecosystem: All living and nonliving things in an area (e.g., plants, animals, rocks, soil, water, air).
Biome: Large area with similar climate conditions that determine plant and animal species there (e.g., tropical rainforest).

Competition: Organisms fighting over a resource like food or shelter, which limits population size.
Predation (+/-): One organism using another for energy source. Includes hunters, parasites and even herbivores.
- Herbivores: Eat plants for energy (e.g., giraffe).
- True Predators: Kill and eat prey for energy (e.g., leopard).
- Parasites: Use a host organism for energy, often without killing the host and often living inside the host (e.g., mosquitoes, tapeworms, sea lamprey).
- Parasitoids: Lay eggs inside a host organism; eggs hatch, and larvae eat the host for energy (e.g., parasitic wasps, bot fly).
Mutualism (+/+): Relationship that benefits both organisms (e.g., coral reef).
- Coral (animals) provide reef structure & CO$_2$ for algae; algae provide sugars for coral to use as energy.
- Lichen = composite organism of fungi living with algae; algae provide sugars (energy) & fungi provides nutrients
Commensalism (+/0): Relationship that benefits one organism and doesn't impact the other (e.g., birds nest in trees).

sym = together | bio = living | osis = condition
Any close and long-term interaction between two organisms of different species.
Mutualism (+/+), commensalism (+/0), and parasitism (+/-) are all symbiotic relationships.