Ecology Essentials: Interactions, Energy Flow & Cycles

Fundamentals of Ecology

Ecology is the scientific discipline in which the relationships among living organisms and the interactions they have with their environments are studied.

Key Concepts

The biosphere consists of all life on Earth and all parts of the Earth in which life exists, including land, water, and the atmosphere. A habitat is an area where an organism lives.

Ecosystem Components

Abiotic factors are nonliving factors in an organism’s environment, while biotic factors are living factors in an organism’s environment.

Levels of Ecological Organization

Ecological studies focus on several levels:

• Organism
• Population
• Community
• Ecosystem
• Biome
• Biosphere

Energy Flow in Ecosystems

Producers and Consumers

Autotrophs (producers) make their own food, while heterotrophs (consumers) depend on other organisms for food. Heterotrophs obtain energy by consuming other organisms, eating different types of food in various ways.

Food Chains and Food Webs

Each step in a food chain or food web is called a trophic level. A food chain is a single series of steps showing energy transfer, while a food web consists of multiple interconnected food chains. An example of energy transfer in a food chain is a snake eating a rat.

Ecological Pyramids

An ecological pyramid is a diagram that can show the relative amounts of energy or biomass at each trophic level. The base of the pyramid, the first trophic level (producers), contains the most energy and biomass. Only about 10 percent of the energy from one trophic level is transferred to the next.

Relationships Between Organisms

Symbiotic Relationships

Symbiosis describes close and long-term interactions between different biological species. There are several types:

Mutualism

The relationship between two or more organisms that live closely together and benefit from each other.

Example: Lichens are formed by algae and fungi living together. A tree merely provides a habitat for lichens. The algae provide food for the fungi, and the fungi provide a habitat for the algae.

Commensalism

A relationship in which one organism benefits and the other organism is neither helped nor harmed.

Example: The relationship between clownfish and sea anemones. Clownfish swim among the stinging tentacles of sea anemones without harm. The sea anemones protect the fish from predators, while the clownfish eat bits of food missed by the sea anemones.

Parasitism

A symbiotic relationship in which one organism (the parasite) benefits at the expense of another organism (the host).

Example: Parasites such as ticks and fleas. Fleas on a dog (the host) will live on the dog until treated (e.g., with a flea collar or bath).

Biogeochemical Cycles

The pathways through which essential elements like water, carbon, and nitrogen are cycled through the biotic and abiotic components of an ecosystem are called biogeochemical cycles.

The Water Cycle

Earth's water consists of approximately 97% saltwater and 3% freshwater.

Key processes in the water cycle include evaporation, condensation, and precipitation. Water in oceans and lakes evaporates and rises into the atmosphere where it condenses to form clouds. When clouds become saturated, water falls back to Earth as precipitation (rain, snow, etc.). This water may collect in bodies of water, become groundwater, or run off across the land surface. Water is also taken up by plants and returned to the air through the process of transpiration.

The Carbon Cycle

Animals obtain carbon primarily by eating plants or other animals that eat plants.

The Nitrogen Cycle

Nitrogen is returned to the environment when organisms urinate or decompose.

Human Impact: Eutrophication

Runoff containing excess fertilizer (nitrogen) can enter lakes, streams, and ponds. This added nitrogen can cause algal blooms (eutrophication), turning the water green and depleting oxygen, which harms aquatic life.