Section 2: Living Things and Their Environments
Interdependence of Living Things

This section focuses on analyzing the interdependence of living things with each other and with their environment (e.g., food webs, ecosystems, and pollution). The material presented is designed to help you meet the following objective.

  • Analyze the interdependence of living things with each other and with their environment (e.g., food webs, ecosystems, and pollution).

Mutual benefits and food webs

Every species is linked, directly or indirectly, with a multitude of others in an ecosystem. Plants provide food, shelter, and nesting sites for other organisms. For their part, many plants depend upon animals for help in reproduction (bees pollinate flowers, for instance) and for certain nutrients (such as minerals in animal waste products). All animals are part of food webs that include plants and animals of other species (and sometimes the same species). The predator/prey relationship is common, with its offensive tools for predators—teeth, beaks, claws, venom, etc.—and its defensive tools for prey—camouflage to hide, speed to escape, shields or spines to ward off attackers, irritating substances to repel. Some species come to depend very closely on others (for instance, pandas or koalas can eat only certain species of trees). Some species have become so adapted to each other that neither could survive without the other (for example, the wasps that nest only in figs and which are the only insect that can pollinate them).

There are also other relationships between organisms. Parasites get nourishment from their host organisms, sometimes with bad consequences for the hosts. Scavengers and decomposers feed only on dead animals and plants. And some organisms have mutually beneficial relationships—for example, the bees that sip nectar from flowers and carry pollen from one flower to the next, or the bacteria that live in our intestines and synthesize some vitamins and protect intestinal linings from germs.