1. 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. Biotic and Abiotic Factors in Ecosystems 2.1 VOCABULARY ecology organism habitat population community ecosystem biosphere biotic factor abiotic factor dynamic equilibrium limiting factor

2. Ecological Roles and Relationships 2.2 VOCABULARY nutrients producer autotroph phytoplankton consumer heterotroph herbivores primary consumer zooplankton carnivore omnivore detrivore decomposer biodegradation predation predator prey predator–prey cycle 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.

3. Symbiosis 2.3 VOCABULARY symbiosis mutualism commensalism parasitism host parasite Symbiosis refers to any close relationship between two different species. There are three types of symbiotic relationships: 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).

4. Nutrients are cycled back into the ecosystem, but energy only moves in one direction through the community from producers to herbivores to carnivores. Trophic level describes the position of the organism in relation to the order of nutrient and energy transfers in an ecosystem. Organisms that eat the same type of food belong to the same trophic level. Food chains show a single pathway taken by nutrients and energy through the trophic levels. In reality, ecosystems have more complex food webs, showing the different cross-linked food chains. Trophic Levels and Energy Flow 2.4 VOCABULARY trophic level food chain food web

5. Ecologists use three different types of ecological pyramids to illustrate ecosystems: 1.Pyramid of energy: represents how much energy is available in each trophic level 2.Pyramid of numbers: represents the actual number of organisms present in each trophic level 3.Pyramid of biomass: represents the total mass of living things in each trophic level Ecological Pyramids 2.5 VOCABULARY ecological pyramid food pyramid pyramid of energy pyramid of numbers pyramid of biomass

6. Interactions in Ecosystems 2 CHAPTER 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

7. 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. 2 CHAPTER

8. Interactions in Ecosystems 2 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. CHAPTER