The Intricate Web of Feeding
Food Chains and Food Webs
A food chain is a simple, linear sequence of organisms where nutrients and energy are transferred from one organism to another. It shows a single pathway of energy flow.
Example: Grass → Grasshopper → Frog → Snake → Hawk
A food web is a more realistic model that consists of many interconnected food chains. It shows the complex feeding relationships within an entire ecosystem.
Keystone Species
A keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance. The removal of a keystone species can cause dramatic changes in the ecosystem's structure.
They are not necessarily the most abundant species.
Example: Sea otters are a keystone species in kelp forest ecosystems. They prey on sea urchins. If otters are removed, the sea urchin population explodes and consumes all the kelp, destroying the entire kelp forest ecosystem.
Trophic Cascades
A trophic cascade is a powerful indirect interaction that can control an entire ecosystem. Trophic cascades occur when a top predator (an apex predator or keystone species) is removed from or added to an ecosystem, causing a series of cascading effects down through the lower trophic levels.
Top-Down Control: The abundance of lower trophic levels is controlled by the effects of predators at high trophic levels.
Classic Example: Wolves in Yellowstone National Park
1.Removal of Wolves (Top Predator): The elk population (primary consumer) increased dramatically.
2.Effect on Producers: The large elk population overgrazed willow and aspen trees, especially along rivers.
3.Cascading Effects: The loss of these trees led to increased riverbank erosion and the loss of habitat for beavers and songbirds.
4.Reintroduction of Wolves: The elk population was reduced and their behavior changed (they avoided open river areas). This allowed the willow and aspen to recover, which in turn stabilized the riverbanks and brought back beavers and other species.