14.2 Community Interactions
Definitions
• Competition: ecological relationship in which two organisms attempt
to obtain the same resource.
• Predation: process by which one organism hunts and kills another
organism for food.
• Symbiosis: ecological relationship between members of at least two
different species that live in direct contact with one another.
• Mutualism: ecological relationship between two species in which
each species gets a benefit from the interaction.
• Commensalism: ecological relationship in which one species
receives a benefit but the other species is not affected one way or
another.
• Parasitism: ecological relationship in which one organism benefits by
harming another organism.
14.2 Community Interactions
KEY CONCEPT
Organisms interact as individuals and as populations.
14.2 Community Interactions
Opener: Habitat or Niche
•
•
•
•
•
•
•
•
Sister
House
Tree
Teacher
Bully
Mommy
Grandma
Cave
14.2 Community Interactions
Competition and predation are two important ways in
which organisms interact.
• Competition occurs when two organisms fight for the
same limited resource.
1. Intraspecific
competition
2. Interspecific
competition:
14.2 Community Interactions
• Intraspecific competition: occurs when individuals of a
particular species struggle against one another for limited
resources. (ex. Bird species breeding: a typical male will
share a particular territory with males of different bird
species,but will not tolerate another male of its own
species in the same area)
• Interspecific competition: occurs when two different
species compete for a limited resource, such as space.
(ex. In your lawn: grass, dandelions, and other plants
compete for nutrients and water)
14.2 Community Interactions
• Predation occurs when one organism captures and eats
another.
14.2 Community Interactions
• There are three major types of symbiotic relationships.
1. Mutualism: both organisms benefit
14.2 Community Interactions
• There are three major types of symbiotic relationships.
2. Commensalism: one organism benefits, the other is
unharmed
Ø
Human Our eyelashes
are home to tiny mites
that feast on oil
secretions and dead
skin. Without harming
us, up to 20 mites may
be living in one eyelash
follicle.
Commensalism
Ø Organism is not affected
+
+
Organism benefits
Demodicids Eyelash
mites find all they need to
survive in the tiny follicles
of eyelashes. Magnified
here 225 times, these
creatures measure 0.4
mm in length and can be
seen only with a
microscope.
14.2 Community Interactions
• There are three major types of symbiotic relationships.
3. Parasitism: one organism benefits, the other is harmed
0
Parasitism
+
_
Hornworm
caterpillar
The host hornworm
will eventually die as
its organs are
consumed
by wasp larvae.
_
Organism is not affected
0
Braconid
wasp
Braconid larvae
feed on their
host and
release
themselves
shortly before
reaching
the pupae
stage of
development.
Organism benefits
14.2 Community Interactions
• There are three major types of symbiotic relationships.
– Parasitism meet their needs as ectoparasites (such
as leeches) and endopaasites (such as hookworms)
14.2 Community Interactions
Mutualism
• The termite and its intestinal flagellate symbionts
exemplify Obligate Mutualism: Neither organism can
survive without the other.
14.2 Community Interactions
Mutualism
• The Clown Fish and its Sea Anemone partner both
benefit from the relationship: Nemo gets a safe home that
protects him from predators, and he fiercely protects his
sea anemone from predators. He also feeds the
anemone. How cute is that?
14.2 Community Interactions
Competition
• The Green Anole (Anolis carolinensis) is native to the southern
United States. In the 1960's, The Brown Anole (Anolis sagrei) was
introduced from Cuba. The two species vie for habitat and food
resources, and it appears that the exotic Brown Anole has displaced
the native Green Anole in some physical spaces, such as lower
shrubbery and grass. The Green Anole generally lives higher up in
the trees and foliage than the Brown Anole does. This result of
competition is known as resource partitioning.
14.2 Community Interactions
predation
• This is possibly the most familiar type of symbiosis. The predator species (in
the illustration below, the Lion (Panthera leo)) kills and consumes the prey
species (in this case, a Cape Buffalo (Syncerus caffer). You can no doubt
think of dozens of other examples of predation. Predation has driven the
evolution of some truly amazing phenomena, such as crypsis (camouflaging
coloration), aposematism (warning coloration), mimicry, and other ways
animals avoid being eaten.
14.2 Community Interactions
Parasitism
• A parasite is an organism that takes up residence in or on a host
organism and feeds on the host's body without killing it outright.
Tape Worm.
14.2 Community Interactions
Commensalism
•
In this case, one species benefits from the presence of another, which is not
affected by the presence of the first species. An example is the Cattle Egret.
As large grazers move through the grass, they stir up insects. Cattle Egrets
follow them and get a banquet. The large grazers are neither helped nor
harmed by the presence of the birds.
14.2 Community Interactions
Homework
• Book: Read Section 14.3
• Study Guide: 149-150
14.2 Community Interactions
14.3 Definitions
• Population density: measure of individuals living in a
defined area.
• Population dispersion: way in which individuals of a
population are spread out over an area or volume.
• Survivorship curve: graph showing the surviving
members of each age group of a population over time.
14.2 Community Interactions
KEY CONCEPT
Each population has a density, a dispersion, and a
reproductive strategy.
14.2 Community Interactions
Population density is the number of individuals that live
in a defined area.
• Population density is a measurement of the number of
individuals living in a defined space.
• Scientists can calculate population density.
14.2 Community Interactions
Geographic dispersion of a population shows how
individuals in a population are spaced.
• Population dispersion refers to
how a population is spread in
Clumped
an area.
dispersion
Uniform
dispersion
Random
dispersion
14.2 Community Interactions
• There are three types of dispersion.
1. clumped
14.2 Community Interactions
• There are three types of dispersion.
2. uniform
14.2 Community Interactions
• There are three types of dispersion.
3. random
14.2 Community Interactions
Survivorship curves help to describe the reproductive
strategy of a species.
• A survivorship curve is a diagram showing the number of
surviving members over time from a measured set of births.
14.2 Community Interactions
• Survivorship curves can be type I, II or III.
– Type I—low level of infant mortality and an older
population
– common to large mammals and humans
– Type II—survivorship rate is equal at all stages of life
– common to birds
and reptiles
– Type III—very
high birth rate,
very high infant
mortality
– common to
invertebrates
and plants
14.2 Community Interactions
Homework
• Book: Read 14.4
• Study Guide: pg 151-152