Transcript Interactions in Ecosystems

INTERACTIONS IN ECOSYSTEMS
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.
BIOTIC INTERACTIONS
1) 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
2) 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
3) Symbiosis: close interaction between 2 different species,
one species live in, on, or near members of another.
A) Mutualism: both species
benefit (leaf-cutter ant &
fungus)
B) Commensalism: one species
benefits, other unaffected
(bird building a nest in a tree)
C) 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)
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.
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
PREDATION LIMITING FACTOR:
LYNX VS. SNOWSHOE HARE
HOMEWORK
1. How does the idea of niches explain how similar species
can coexist with a minimum of competition?
2. Cockroaches reproduce very rapidly. Why is the world not
covered in cockroaches?
3. 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.