Food Chain, Food Web and Pyramid of Numbers

Food Chain

---

• A food chain is a sequence of organisms where each organism is eaten by the next one in the chain. Energy is lost at each stage.
• Each feeding stage in a food chain is called a trophic level.
• Food chains are usually short as lots of energy is lost at each level. About 90% of energy is lost at each feeding level.

---

Food Web

---

---

Pyramid of Numbers

---

• The length of each bar represents the relative number of organisms.
• The size of organisms usually increases as you move up the pyramid.

Standard Pyramid of Numbers:

Inverted Pyramid of Numbers:

Limitations of the Pyramid of Numbers

• Individual organism size is not taken into account.
• The pyramid may not be to scale because the numbers can be very large (e.g., millions of bacteria on one ash tree).

---

Niche

• Each organism is adapted to occupy a unique niche.
• No two organisms can occupy the same niche without competing.
• Example: Swallows and bats both eat insects. Swallows feed by day and bats feed by night. Therefore, they occupy different food niches.

---