1. Interactions in Ecosystems

2. Learning Goals
Understand how biotic interactions in a community work, include predation, competition, and symbiosis.
Explain how abiotic and biotic factors prevent a population from increasing beyond its carrying capacity.

3. Biotic Interactions
Competition: interaction between two or more organisms (same or different species) competing for the same resource in a habitat (mates, food, homes, etc.)
For similar species to coexist, they must have slightly different niches - different species warblers feed on spruce budworms, but each species feeds in a different part of the spruce tree  reduces competition

4. Predation: one organism eats another to obtain food
Predation: one organism eats another to obtain food. Prey animals are well adapted to avoid being eaten.
Physical defences – speed, quills, etc.
Camouflage – stick insect
Foul Taste – monarch butterfly
Mimicry – viceroy butterfly

5. Symbiosis: close interaction between 2 different species, one species live in, on, or near members of another.
Mutualism: both species benefit (leaf-cutter ant & fungus)
Commensalism: one species benefits, other unaffected (bird building a nest in a tree)
Parasitism: one species benefits other is harmed. Parasites live on or inside the host species and obtain some or all of their nutrition from the host. (ticks feeding on host blood)

6. Populations
Equilibrium: number of individuals in a population stays the same (# of births = # of deaths)
Carrying capacity: maximum # of individuals an ecosystem can support without reducing its ability to support future generations. If a population exceeds its carrying capacity for a long time, it can harm its environment.

7. Factors affecting populations
Limiting factor: environmental factor preventing a population increase or movement into new habitats
Vital to keeping an ecosystem healthy (no overpopulation)
Abiotic – sun, H2O, soil, air; natural disturbances (storms, fires, droughts); human disturbances (logging)
Biotic – competition, predators, reliance on
other organisms, disease-causing organisms

8. Predation limiting factor: Lynx vs. snowshoe hare

9. Homework
How does the idea of niches explain how similar species can coexist with a minimum of competition?
Cockroaches reproduce very rapidly. Why is the world not covered in cockroaches?
Classify as mutualism, commensalism, or parasitism.
(a) A yucca moth caterpillar feeds on the yucca plant & pollinates the yucca plant.
(b) Lice feed harmlessly on the feathers of birds.
(c) A cowbird removes an egg from a robin’s nest and replaces it with one of its own.