Page 100 - Environment: The Science Behind the Stories

Aquatic examples Terrestrial examples

Tertiary consumers

Cormorant Hawk

Secondary consumers

Fish Rodent

Detritivores and decomposers Primary consumers Detritivores and decomposers

Crayfish Zooplankton Grasshopper Earthworm

Producers
Water mold Aquatic Shelf fungus Soil
bacteria bacteria

Phytoplankton Grass

Figure 4.9 Ecologists organize species hierarchically by trophic level. The diagram shows aquatic (left)
and terrestrial (right) examples at each level. Arrows indicate the direction of energy flow. Producers generate
food by photosynthesis, primary consumers (herbivores) feed on producers, secondary consumers eat primary
consumers, and tertiary consumers eat secondary consumers. Detritivores and decomposers feed on nonliving
organic matter and “close the loop” by returning nutrients to the soil or the water column for use by producers.

secondary consumers, as are rodents and birds that prey on decomposers, such as fungi and bacteria, break down leaf CHAPTER 4 • S PEC i ES i n TERA CT i on S A nd Co mmuni T y E C ology
grasshoppers. Predators that feed at still higher trophic lev- litter and other nonliving matter into simpler constituents
els are known as tertiary consumers. Examples of tertiary that can be taken up and used by plants. These organisms
consumers include hawks and owls that eat rodents that have enhance the topmost soil layers (p. 236) and play essential
eaten grasshoppers. Note that most primary consumers are roles as the community’s recyclers, making nutrients from
herbivores because they consume plants, whereas second- organic matter available for reuse by living members of the
ary and tertiary consumers are carnivores because they eat community.
animals. Animals that eat both plant and animal food are In Great Lakes communities, phytoplankton are the
referred to as omnivores. main producers, floating freely and conducting photosyn-
thesis using sunlight that penetrates the upper layer of the
Detritivores and decomposers Detritivores and water. Zooplankton are primary consumers, feeding on
decomposers consume nonliving organic matter. detritivores, the phytoplankton. Phytoplankton-eating fish are primary
such as millipedes and soil insects, scavenge the waste consumers, and zooplankton-eating fish are secondary con-
products or dead bodies of other community members. sumers. Tertiary consumers include larger fish and birds 99

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