An ecosystem is all the organisms in a given area and their physical and chemical environment. Autotrophs such as plants, algae, and photosynthetic bacteria capture sunlight and fix it into organic compounds (primary production). Energy is also derived through chemosynthesis: the oxidation of inorganic nutrients by archaea and bacteria. Energy captured through primary production is in turn available for organisms at higher trophic levels in food webs (secondary production). Nutrients continually cycle between living organisms and the abiotic environment.
learning outcomes
You should be able to:
Compare different ways of defining an ecosystem, and contrast ecosystems with communities.
List sources of energy in ecosystems, and associate each source with the processes that produce them.
An ecologist measures the number of species in an ecosystem. Is she conducting ecosystem science? Explain.
Not necessarily. Ecosystem science is the study of how energy flows and nutrients cycle through the biotic and abiotic environment. The number of species is a descriptor of the biotic environment but does not give any information about the energy flow or nutrient cycling of the ecosystem.
Describe the two ways that energy and carbon are converted into primary production.
Energy and carbon can be converted into primary production through photosynthesis and chemosynthesis. Photosynthesis involves the capture of radiant energy by plants, algae, and photosynthetic bacteria to be used to fix CO2 into organic compounds. Chemosynthesis involves the capture of energy from inorganic compounds by archaea and bacteria to be used to fix CO2 into organic compounds. Chemosynthesis typically occurs in ecosystems such as hydrothermal vents, hot springs, and soils that lack sunlight and have high concentrations of particular inorganic compounds.
For the remainder of this chapter we will consider in more detail how energy flows and nutrients cycle through ecosystems as depicted in Figure 57.1. We will start with primary production, where energy and nutrients are first captured in ecosystems.