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CHAPTER 2 Interactions in Ecosystems • Ecosystems are made up of living things (biotic factors) and non-living things (abiotic factors), which are connected to each other in complex interrelationships. • Nutrients are cycled within an ecosystem. producers consumers decomposers producers CHAPTER 2 Interactions in Ecosystems • Energy flows through ecosystems. • This energy comes from an outside source: the Sun. • Ecologists represent food and energy flows in food chain, food web, and pyramid diagrams. CHAPTER 2 Interactions in Ecosystems Activity Using the food web on the right, predict what might happen if a disease killed all the krill in the ecosystem. Which species would be affected, and how? Try drawing a new food web. You can find more information on food chains and webs on pages 34–36 in the student book. CHAPTER 2 Interactions in Ecosystems Key Ideas • Living things are connected to each other in complex interrelationships. • Biotic and abiotic factors are responsible for shaping a community of living things. • Nutrients cycle within ecosystems. • Energy flows through ecosystems. 2.1 Biotic and Abiotic Factors in Ecosystems • An ecosystem is made up of a community of organisms and the non-living environment. • The living components of the ecosystem are called biotic factors, which include plants, fish, invertebrates, and single-celled organisms. • The non-living components, or abiotic factors, include the physical and chemical components in the environment—temperature, wind, water, sunlight, and oxygen. • Biotic and abiotic factors influence each other in an always changing balance called dynamic equilibrium. VOCABULARY ecology organism habitat population community ecosystem biosphere biotic factor abiotic factor dynamic equilibrium limiting factor 2.2 Ecological Roles and Relationships • An ecosystem is a complex network of interactions. • All organisms must take in water, food, and nutrients. Nutrients are elements and compounds that organisms need to live and grow. • Organisms can be producers, consumers, herbivores, carnivores, or decomposers in ecosystems. • Eventually nutrients cycle back into the ecosystem for the producers. VOCABULARY nutrients producer autotroph phytoplankton consumer heterotroph herbivores primary consumer zooplankton carnivore omnivore detrivore decomposer biodegradation predation predator prey predator–prey cycle 2.3 Symbiosis • Symbiosis refers to any close relationship between two different species. There are three types of symbiotic relationships: VOCABULARY symbiosis mutualism commensalism parasitism 1. Mutualism is a relationship in which both species obtain some benefit from the interaction. 2. Commensalism is an interaction in which one organism benefits while the other is unaffected. 3. Parasitism occurs when one organism (the parasite) lives and feeds on, or in, the body of another organism (the host). host parasite