Chapter 13. Ecology and the Environment

Ecology studies interactions among organisms and their environment. Levels of organization: organism, population, community, ecosystem, biome, biosphere [16].

Energy flow. Producers (plants, algae, some bacteria) capture energy from sunlight; consumers (herbivores, carnivores, omnivores) obtain it by feeding; decomposers recycle nutrients. Only about 10% of energy is typically passed to the next trophic level.

Matter cycles: the water, carbon, nitrogen and phosphorus cycles move essential elements through living and non-living parts of ecosystems.

Interactions: competition, predation, parasitism, mutualism and commensalism.

Populations. Growth is limited by carrying capacity, the maximum population an environment can support.

Human impact. Habitat loss, pollution, overharvesting, invasive species and climate change reduce biodiversity. Conservation, sustainable resource use and restoration help protect ecosystems [13][16].

Climate change. The atmosphere is about 78% nitrogen and 21% oxygen, with carbon dioxide at a small fraction of a percent. Burning fossil fuels has raised carbon dioxide levels, strengthening the greenhouse effect and warming the planet [13].

Review: In the food chain grass → grasshopper → frog → snake, which organism is the secondary consumer? (Answer: the frog.)