Describe the levels of ecological organization and the biotic and abiotic factors that make up an ecosystem (Ohio's Learning Standards for Science, Biology, B.DI.2).

What this topic is asking

Ohio standard B.DI.2 (Ecosystems) is the foundation of the ecology module: before tracing energy or matter, you need to know how life is organized and what an ecosystem is made of. The Ohio Biology EOC turns this into items where you name the level of organization in a scenario or sort factors into biotic and abiotic. The crosscutting idea is systems and system models: an ecosystem is a system of interacting living and non-living parts. This sets up the rest of the module, especially energy flow and food webs.

The levels of ecological organization

Ecology arranges life into nested levels, each larger and more inclusive than the last:

• Organism. A single living individual (one deer, one oak tree).
• Population. All the individuals of one species living in the same area at the same time (all the deer in a forest).
• Community. All the different populations (all the living things of every species) interacting in an area (the deer, wolves, oaks, fungi, and bacteria together).
• Ecosystem. The community plus the non-living environment: all the living things together with the abiotic factors (soil, water, temperature) they interact with.
• Biome. A large geographic region with a characteristic climate and community of organisms (desert, tropical rainforest, tundra, grassland).
• Biosphere. The sum of all ecosystems, all life on Earth and the environments it occupies.

Two boundaries are tested most. A population is one species; a community is all species in the area. A community is only the living things; an ecosystem adds the non-living environment.

Biotic and abiotic factors

Everything in an ecosystem is either a biotic or an abiotic factor.

• Biotic factors are the living (or once-living) components: plants, animals, fungi, protists, and bacteria, plus things like dead organisms and waste that come from living things. Predators, prey, competitors, and decomposers are all biotic factors.
• Abiotic factors are the non-living physical and chemical components: sunlight, temperature, water, air (oxygen and carbon dioxide), soil, minerals, pH, and salinity.

Both shape where and how well organisms live. A cactus is suited to the abiotic conditions of a desert (intense sun, little water); a fish depends on the abiotic factor of dissolved oxygen in its water. Biotic and abiotic factors constantly interact, which is what makes the ecosystem a system.

Why the system view matters

Because an ecosystem is a system of interacting parts, a change in one component can affect many others. A drop in an abiotic factor (less rainfall) can reduce plant growth, which reduces food for herbivores, which affects predators. Keeping the levels and the biotic/abiotic distinction clear is what lets you reason about these knock-on effects in the rest of the module, from food webs to population dynamics.

Try this

Q1. State the difference between a population and a community. [2]

• Cue. A population is all the individuals of one species in an area; a community is all the different populations (all species) living and interacting in that area.

Q2. Classify sunlight, a frog, water temperature, and a water lily as biotic or abiotic factors in a pond. [2]

• Cue. Biotic: the frog and the water lily (living). Abiotic: sunlight and water temperature (non-living).