4.2: Interactions among Organisms

When two species use the same resource, they participate in a biological interaction called competition. Competition occurs for resources in short supply – food, nesting sites, living space, light, mineral nutrients, and water. To understand competition, you need to understand the “day-to-day” activities of organisms.

habitat is the place a plant or animal lives An earthworm’s habitat is SOIL! 3

niche is an organism’s total way of life can be thought of as its “job” for the ecosystem includes what it eats and what eats it! 4

competitive exclusion principle: no two species can occupy exactly the same niche in exactly the same habitat at exactly the same time direct competition between different species always produces a winner and a loser with the losing species dying out instead of competing for similar resources, species usually divide them

three species of warblers all live in the same trees and feed on insects one species feeds on high branches, another on low branches & the third feeds in the middle 6

Some relationships between organisms are not “healthy” for both. Predation is the act of one organism killing another for food.

herbivory: special type of predation where plants are preyed upon by herbivores

keystone species: one special species that directly or indirectly affects the survival of many other species loss of the keystone species can cause dramatic changes in the health of the whole ecosystem tends to be a top predator but can also be an important food source for many other organisms 9

Which is the keystone species? What would happen if the wolf population was removed? The deer population would explode, causing the plant population to crash. This will cause the insects to drop which will cause the rodent population to crash then the snake population to crash….

Symbiotic Species In symbiosis, two or more species live together in a close, long-term association. Symbiotic relationships can: ~ benefit one organism and harm the other ~ benefit both organisms ~ benefit one organism and leave the other unaffected

Parasitism symbiotic relationship where one organism feeds on & usually lives on/in another (usually larger) organism lamprey parasitizing a trout tapeworm from human intestine

Parasites do not usually kill their prey (known as the host) because they depend on the host for food and a place to live. flea bites on a human engorged deer tick attached to back of a toddler's head

Mutualism symbiotic relationship in which both species benefit Bird removes bugs from the alligator’s mouth for food while the alligator gets parasites removed from it’s teeth. Bee gets food (pollen) from flower while the flower gets it’s pollen spread to other plants to continue the species.

How is this an example of mutualism?

Commensalism symbiotic relationship in which one species benefits & the other is neither harmed nor helped A titan triggerfish creates feeding opportunities for smaller fish by moving large rocks too big for them to shift themselves. Smaller plants use larger trees as a way to climb up and reach the sun they need to survive.

So… How well do YOU know interactions among organisms?