Fix the mistake: Ecosystems and Their Conservation

Ecosystems, Food Chains, and Food Webs

A system including organisms and the abiotic environment is called an ecosystem. Within an ecosystem, organisms are connected through relationships of eating and being eaten.

Basic Knowledge

An ecosystem consists of a biotic environment (plants, animals, and microorganisms) and an abiotic environment (light, water, temperature, soil, and so on), forming a system through which matter and energy flow. This concept was proposed in 1935 by ecologist Tansley, and is considered at scales such as forests, lakes, and oceans.
Organisms are divided into the following trophic levels.
① Producers: autotrophs that make organic matter through photosynthesis, including plants, algae, phytoplankton, and photosynthetic bacteria.
② Consumers: heterotrophs that eat other organisms. Primary consumers (herbivores) are followed by secondary consumers (small carnivores) and tertiary consumers (large carnivores).
③ Decomposers: organisms that decompose remains and waste products and return them to inorganic substances. They include fungi, bacteria, earthworms, and pill bugs. Decomposers are also a type of consumer.
A straight-line eating relationship is a food chain, while a complex, interwoven relationship is a food web. Actual ecosystems are represented by food webs.

Key Terms
Ecosystem (a system consisting of biotic and abiotic environments)
Producer (an organism that makes organic matter through photosynthesis, such as plants and algae)
Consumer (an organism that eats other organisms, such as animals)
Decomposer (an organism that returns remains and waste products to inorganic substances, such as fungi and bacteria)
Food chain (a sequence of eating and being eaten)
Food web (a network of several interconnected food chains)
Trophic level (a nutritional level beginning with producers and continuing through primary, secondary, and tertiary consumers)

Further Exploration

If the biomass of each trophic level is stacked vertically, it forms an ecological pyramid with a wide base and a narrow top. Producers are usually overwhelmingly abundant, while higher-level predators have fewer individuals and less biomass. The reason is the low energy efficiency studied in the next lesson.
Food webs create ecosystem stability. In a straight food chain, the chain collapses if one species becomes extinct, but in a network, matter and energy can flow through another pathway. However, a species with especially great influence on other species in a food web is called a keystone species. If it is lost, the entire community may collapse (for example, if sea otters disappear, sea urchins increase and kelp forests disappear).

Key Points
  • Ecosystem = biotic environment + abiotic environment
  • Producers, consumers, and decomposers
  • Food chain = linear relationship; food web = network relationship
  • Actual ecosystems are described by food webs
  • Trophic levels: producers → primary → secondary → tertiary consumers
  • Ecological pyramid = broad base and narrow top
  • Keystone species support the community

Points to Note

① Distinguish an ecosystem (biotic and abiotic components) from a community (living organisms only). ② Decomposers are a type of consumer, but they are treated separately because their role is to decompose matter into inorganic substances. ③ Distinguish a food chain (linear) from a food web (network). In tests, the correct answer is that actual ecosystems are networks. ④ A keystone species is not necessarily numerous; it is a species with great influence.

Practice

  1. Which ecologist proposed the concept of the ecosystem in 1935?
  2. What are organisms such as fungi and bacteria that decompose remains and waste products into inorganic substances called?
  3. What is a species with a major influence on the stability of an entire community in a food web called?

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