Page 652 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

616 part IV Soils, ecosystems, and Biomes
Producers
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NUTRIENTS
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Primary consumers
(b) A bearded seal on a bergy bit in the Arctic Ocean.
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Detritivores (detritus feeders) and decomposers
Higher-level consumers
Nutrients Energy/heat
(a) The flow of energy, cycling of nutrients, and trophic (feeding) relationships portrayed for a generalized ecosystem. The operation is fuelled by radiant energy supplied by sunlight and first captured by the plants.
▲Figure 19.7 Energy, nutrient, and food pathways in the environment. [Photos by Bobbé Christopherson.]
webs that range from simple to complex. As discussed earlier, autotrophs are the producers. Organisms that depend on producers as their carbon source are hetero- trophs, or consumers, and are generally animals.
Trophic Relationships The producers in an ecosystem capture sunlight and convert it to chemical energy, in- corporating carbon, forming new plant tissue and bio- mass, and freeing oxygen. From the producers, which manufacture their own food, energy flows through the system along an idealized unidirectional pathway called a food chain. Solar energy enters each food chain through the producers, either plants or phytoplankton, and subsequently flows to higher and higher levels of consumers. Organisms that share the same feeding level in a food chain are said to be at the same trophic level. Food chains usually have between three and six levels, beginning with primary producers and ending with detritivores, which break down organic matter and are the final link in the theoretical chain (Figure 19.7).
(c) A solitary male polar bear drags its prey, a seal, across pack ice.
(d) A mother polar bear and cubs eat a seal on an iceberg. Glaucous Gulls and Ivory Gulls consume part of the leftovers.
The actual trophic relationships between species in an ecosystem are usually more complex than the sim- ple food chain model might suggest. The more common arrangement of feeding relationships is a food web, a complex network of interconnected food chains with multidirectional branches. In a food web, consumers often participate in several different food chains.
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