PRINCIPLES OF ECOLOGY

Ecological Levels of Organization

Individual/Organism: A single, individual living thing.

Example: One elk.

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

Example: All the elk living in a specific forest.

Community: All the different populations of different species that live and interact in the same area.

Example: The populations of elk, moose, birds, and various plants in that same forest.

Biome: A large-scale area on Earth with a similar climate, plants, and animals.

Example: The tropical rainforest biome, or the grassland biome.

Biosphere: The sum of all ecosystems on Earth, representing all life and where it exists.

Energy Flow in Ecosystems

Trophic Levels:

Producers (Autotrophs): Organisms that create their own food, usually through photosynthesis (e.g., grass, tomato plants, phytoplankton, marine plants).

Consumers (Heterotrophs): Organisms that get energy by eating other organisms.

Primary Consumers (Herbivores): Eat producers.

Secondary Consumers (Carnivores/Omnivores): Eat primary consumers.

Tertiary Consumers: Eat secondary consumers.

Decomposers: Break down dead organic material, returning nutrients to the soil (e.g., fungi, bacteria, earthworms, mushrooms, mold, yeast, dung beetles, nematodes).

Food Chain vs. Food Web:

Food Chain: A simple, linear path of energy flow (e.g., grass \rightarrow rabbit \rightarrow fox).

Food Web: A complex network of interconnected food chains. Most ecosystems are represented by food webs.

The 10% Rule (Lindeman's Law of Ten Percent):

Only about 10% of the energy from one trophic level is transferred to the next; the rest is lost as heat.

Ecological Interactions

Mutualism (+/+): An interaction where both species benefit.

Example 1: A bee collects nectar from a flower; the bee gets food, and the flower is pollinated.

Example 2: A clownfish lives in a sea anemone; the clownfish gets protection, while the anemone is cleaned and lured prey.

Competition (-/-): An interaction where both species are negatively affected as they compete for the same limited resources (food, water, territory).

Interspecific Competition: Occurs between members of different species (e.g., lions and cheetahs competing for prey).

Intraspecific Competition: Occurs between members of the same species (e.g., two male deer fighting over a mate).

Resource Partitioning: Species evolve to utilize different resources/habitats to minimize conflict and coexist.

Population Regulation: Intraspecific competition acts as a density-dependent factor, naturally limiting population growth.

Competitive Exclusion: When two species compete for the exact same limiting resource, the more efficient competitor eventually eliminates the other.

Commensalism (+/0): An interaction where one species benefits and the other is neither helped nor harmed.

Example 1: Barnacles attach to a whale's skin to get rides to nutrient-rich waters.

Example 2: Cattle egrets follow grazing livestock to catch insects stirred up by their movement.

Parasitism (+/-): An interaction where one species (parasite) benefits by living on/in another species (host), causing harm.

Example 1: Fleas feeding on a dog's blood.

Example 2: A tapeworm living in a human's intestines.

Amensalism (-/0): An interaction where one species is harmed, and the other is neither helped nor harmed.

Example: Walking across a lawn and trampling the grass.

Predation (+/-): An interaction where one species (predator) kills and eats another species (prey).

Examples: A lion hunting a zebra; a wolf hunting a rabbit.

Population Oscillations: Fluctuations in prey numbers directly influence predator density.

Evolutionary Arms Race: Continuous adaptation of hunting strategies in predators and defense mechanisms in prey.

Trophic Cascades: Top-down effects where predator presence regulates multiple lower levels of the food web.

Biogeochemical Cycles

Pathways by which chemical substances cycle between biotic (living) and abiotic (non-living) components of Earth.

Carbon Cycle: Movement of carbon through the atmosphere, oceans, soil, and living things.

Photosynthesis: Plants take \text{CO}_2 from the atmosphere to make food.

Respiration: Organisms release \text{CO}_2 back when breathing.

Decomposition: Decomposers break down dead organisms, releasing carbon.

Combustion: Burning fossil fuels and wood releases \text{CO}_2.

Nitrogen Cycle: Movement of nitrogen (\text{N}_2) through the environment and organisms.

Nitrogen Fixation: Bacteria convert atmospheric \text{N}_2 into usable forms like ammonia (\text{NH}_3).

Nitrification: Bacteria convert ammonia into nitrates (\text{NO}_3^-)which plants absorb.

Denitrification: Bacteria convert nitrates back into atmospheric \text{N}_2.

Phosphorus Cycle: Movement of phosphorus (\text{P}) through rock, soil, water, and living organisms.

Weathering: Rocks break down and release phosphorus.

Uptake: Plants absorb phosphorus from soil.

Consumption: Animals get phosphorus by eating plants or other animals.

Decomposition: Decomposers return phosphorus to the soil.

Sulfur Cycle: Movement of sulfur (\text{S}) through the geosphere, hydrosphere, and atmosphere.

Weathering: Sulfur is released from rocks and minerals.

Volcanic Eruptions Volcanoes release sulfur dioxide (\text{SO}_2).

Decomposition: Decomposers release sulfur from decaying matter.

Combustion: Burning fossil fuels releases sulfur into the atmosphere, leading to acid rain.

Water Cycle: Continuous movement of water on, above, and below Earth's surface.

Evaporation: Liquid water turns to gas and rises.

Condensation: Water vapor cools into liquid droplets, forming clouds.

Precipitation: Water falls back as rain, snow, or hail.

Transpiration: Water evaporates from plant leaves.

Runoff: Water flows over land into rivers and oceans.

Ecological Succession

The gradual and predictable process of change in the species composition of an ecological community over time.

Primary Succession: Occurs on newly formed or exposed land without soil (e.g., bare rock).

Pioneer Species: Lichens and mosses.

Intermediate Species: Small annual plants, perennials, grasses, shrubs, shade-intolerant trees (pines).

Climax Community: Shade-tolerant trees (oak, hickory).

Takes hundreds of years.

Secondary Succession: Occurs after a disturbance destroys a community but leaves soil intact (e.g., after a forest fire).

Timeline: 0 Years (Fire)\rightarrow1–2 Years (Grasses and perennials) \rightarrow3–4 Years (Grasses, shrubs, pines) \rightarrow 5–150 Years (Young oak and hickory) \rightarrow 150+ Years (Mature oak and hickory forest).