Ecology

Ecology is the scientific study of interactions among living organisms and between organisms and their physical environment.

Levels of Ecological Organization

• Organism: An individual living thing (e.g., a single plant or animal).

• Population: A group of individuals of the same species living in the same area at the same time.

• Community: All the different populations of species that live and interact together in an area.

• Ecosystem: A community of living organisms interacting with the non-living physical parts of their environment.

• Biome: A large geographic area defined by its climate and typical plant and animal life (e.g., desert, tundra, rainforest).

• Biosphere: All regions of Earth that support life.

Components of an Ecosystem

• Biotic Factors: The living or once-living parts of an environment (e.g., plants, animals, fungi, bacteria).

• Abiotic Factors: The non-living physical and chemical parts of an environment (e.g., sunlight, temperature, water, soil, air).

Energy Flow in Ecosystems

• Producers (Autotrophs): Organisms that make their own food through photosynthesis using sunlight (e.g., plants, algae).

• Consumers (Heterotrophs): Organisms that must feed on other living things for energy:

  • Herbivores: Eat only plants.

  • Carnivores: Eat only other animals.

  • Omnivores: Eat both plants and animals.

• Decomposers: Organisms that break down dead organisms and recycle nutrients back into the soil (e.g., mushrooms, bacteria).

• Food Chain: A single pathway showing the direct flow of energy from one organism to another:

  • Irish Grassland Example: $\text{Sunlight} \rightarrow \text{Grass (Producer)} \rightarrow \text{Caterpillar (Primary Consumer)} \rightarrow \text{Song Thrush (Secondary Consumer)} \rightarrow \text{Sparrowhawk (Apex Predator)}$

  • Irish Aquatic Example: $\text{Sunlight} \rightarrow \text{Algae (Producer)} \rightarrow \text{Water Flea (Primary Consumer)} \rightarrow \text{Brown Trout (Secondary Consumer)} \rightarrow \text{Otter (Apex Predator)}$

• Food Web: A network of interconnected food chains showing all feeding relationships in an ecosystem.

• The 10% Rule: Only about $10\%$ of the energy stored in one trophic level is passed to the next level (the remaining $90\%$ is lost as body heat and waste).

Ecological Relationships

• Predation: An interaction where one animal (predator) hunts, kills, and eats another animal (prey).

• Competition: The struggle between organisms for limited resources like food, water, or territory.

• Symbiosis: A close, long-term relationship between two different species:

  • Mutualism: Both organisms benefit (e.g., bees pollinating flowers).

  • Commensalism: One organism benefits and the other is neither helped nor harmed (e.g., barnacles on a whale).

  • Parasitism: One organism benefits while harming the host (e.g., a tick on a dog).

Ecosystem Dynamics & Basic Graphs

• Habitat: The physical environment where an organism lives.

• Niche: The role an organism plays within its habitat (what it eats, what eats it, how it behaves).

• Limiting Factors: Biotic or abiotic resources that restrict population growth (e.g., water, shelter, food supply).

• Carrying Capacity: The maximum population size that an environment can sustainably support with its available resources.

• Predator-Prey Graph: A cyclical graph showing how predator and prey population sizes change over time:

  • When prey numbers increase, predators have more food, causing predator numbers to rise.

  • More predators cause prey numbers to drop, which soon causes predator numbers to fall.