Unit Four: I Depend on You

What is Symbiosis? Any close relationship among species. Not all relationships among organisms involve food; many organisms can live together and share resources in other ways. In order for a relationship to be symbiotic, there must be two organisms that can be identified. There are various forms of symbiosis, including: mutualism, commensalism, and parasitism.

What is mutualism? A symbiotic relationship in which both species benefit. Example: Fungi & Algal (found in lichens)

What is commensalism? A symbiotic relationship in which one organism benefits and the other is not affected. Example: Remoras & Sharks

What is parasitism? A symbiotic relationship in which one organism benefits but the other is harmed. Example: Dogs & Roundworms

Now, it’s time to….

Burdocks and Passing Vertebrates Burdocks are common weeds found along roadsides and fields. The seed heads (burs) of burdocks are long spines with hooked tips. The hooked tips catch onto the hair of passing vertebrates (cows, deer, dogs, humans) and are carried elsewhere until they finally fall off or are pulled off by the carriers.

Burdocks and Passing Vertebrates

Monarch Butterfly and Milkweed Plants The Monarch butterfly feeds on species of milkweeds. The milkweeds contain a group of chemicals called cardiac glycosides. Cardiac glycosides are poisonous to vertebrates (although not to invertebrates). The butterflies store these cardiac glycosides. If a bird (or other vertebrate such as a mouse or frog) eats a Monarch it finds them distasteful and is later sick. Experimentally vertebrate learn to avoid Monarchs butterflies.

Monarch Butterfly and Milkweed Plant

Cattle Egret and Cattle The Cattle Egret resides in pastures and fields among livestock such as cattle and horses, feeding on the insects stirred up by the movement of the grazing animals. The egrets benefit from the arrangement, but the livestock, generally, do not.

Cattle Egret and Cattle

Mistletoe and Surrounding Trees The mistletoe develops high up on the branches of other trees. It develops root-like structures from its stem which penetrate the surrounding trees and take water from the water-carrying vessels. A mistletoe plant can be easily identified in winter because it remains green when the leaves of its host have fallen to the ground.

Mistletoe and Surrounding Trees

Mushroom and Tree A mushroom is made up of fungus. The fungus aids the tree in absorbing water from the soil, increases the stability of the root system, and protects the roots from drying out. In return, the tree provides sugars and starches to the fungus that the fungus uses in its metabolism.

Mushroom and Tree

Pseudo-Scorpions and Beetles Pseudo-scorpions are scorpion-like animals. They have pinchers like scorpions, but lack a sting. A few species of pseudo-scorpions hide by concealing themselves under the wings of large beetles. The pseudo-scorpion gains the advantage of being hidden over wide areas while simultaneously being protected from predators. The beetle is, presumably, unaffected by the presence of the hitchhikers.

Psuedo-Scorpions and Beetles

Now that we have the basics about symbiosis, it’s time to put our knowledge to work!