Wildlife Encounters - 5th - 8th grade
Lesson 3: Humans & Wildlife
  • Key Words


An ecosystem includes all the living species in an area and all the non-living factors of the environment that affect them, like soil nutrients underwaterand sunlight. Ecosystems can vary in size and can be simple or complex. They can be as small as single tidal pool with just a few species of hardy invertebrate animals. The largest ecosystem is the biosphere, or the global ecosystem. It includes every portion of the Earth that is inhabited by life, from several kilometers above the Earth's surface to several kilometers below the surface and almost every space in between.

dominoesThe one factor that all ecosystems have in common is the interrelatedness of every component in the ecosystem. All the species and non-living parts of an ecosystem interact in a complex collection of relationships that depend on every part being present and functional. If one part is lost or unhealthy, the entire ecosystem can be impacted. To lose a component of an ecosystem is like knocking down one domino in a circle of dominoes. All the other dominoes fall too.

The interrelatedness of ecosystems is illustrated by the importance of the sea otter to its ecosystem. Sea otters are considered a keystone species, or one that plays a critical role in maintaining its ecosystem. Sea otters were almost hunted to extinction by fur traders. The loss of this species from the kelp forest ecosystem of the Pacific Northwest resulted in the population of one of their prey species, sea urchins, growing unchecked. The unnaturally large number of sea urchins consumed too much of these large seaweed forests, leading to the area becoming barren. Little life could be found in a space that was once home to a diverse and complex ecosystem. With a ban on hunting and many conservation programs in place, the sea otter population has begun to recover, resulting in kelp forest growing once again, and the reestablishment of the kelp forest ecosystem.


sea otter population