Interactions in Ecosystems
Chapter 14
KEY CONCEPT
Every organism has a habitat and a niche.
A habitat differs from a niche.
• A habitat is all aspects of the area in which an
organism lives.
– biotic factors
– abiotic factors
•
An ecological niche
includes all of the factors
that a species needs to
survive, stay healthy, and
reproduce.
– food
– abiotic conditions
– behavior
Resource availability gives structure to a
community.
• Species can share habitats and resources.
• Competition occurs when two species use
resources in the same way—competitive
exclusion
• Competitive exclusion keeps two species from
occupying the same niche—one species will be
better suited to the niche.
• Competitive exclusion has different outcomes.
– One species is better suited to the niche and the other will either be pushed
out or become extinct.
– The niche will be divided.
– The two species will further diverge.
• Ecological equivalents are species that occupy similar
niches but live in different geographical regions.
Madagascar
South America
•
Competition and predation are two
important ways in
Competition
occursorganisms
when two organisms
fight for the
which
interact.
same limited resource.
– Intraspecific
competition
– Interspecific
competition
• There are three major types of symbiotic relationships.
– Mutualism: both organisms benefit
•
There are three major types of symbiotic relationships.
– 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.
•
There are three major types of symbiotic relationships.
– 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
KEY CONCEPT
Each population has a density, a dispersion, and a reproductive strategy.
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.
Geographic dispersion of a population
shows how individuals in a population are
• Population dispersionspaced.
refers to
how a population is spread in
an area.
Clumped
dispersion
Uniform
dispersion
Random
dispersion
• There are three types of dispersion.
– clumped
• There are three types of dispersion.
– uniform
• There are three types of dispersion.
– random
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.
• 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
Changes in a population’s size are
determined by immigration, births,
emigration, and deaths.
• The size of a population is
always changing.
• Four factors affect the size of a
population.
–
–
–
–
immigration
births
emigration
deaths
Immigration vs Emigration
• Immigration—movement of individuals into a
population from another population
• Example: two fruit flies entering your
backpack to sit on a banana
• Emigration—movement of individuals out of a
population and into another population
• Examples—two fruit flies exited your backpack
to find other fruit
Population growth is based on available
• Exponential growthresources.
is a rapid population increase due to
an abundance of resources.
• Logistic growth is due to a population facing limited
resources.
• Carrying capacity is the maximum number of individuals
in a population that the environment can support.
•
A population crash is a dramatic decline in the size of a population over a short
period of time.
Ecological factors limit population growth.
• A limiting factor is something that keeps the size of a
population down.
•
Density-dependent limiting factors are affected by the number of individuals in a
given area.
• Density-dependent limiting factors are affected by the
number of individuals in a given area.
– predation
– competition
– parasitism and
disease
• Density-independent limiting factors limit a population’s
growth regardless of the density.
– unusual weather
– natural disasters
– human activities
KEY CONCEPT
Ecological succession is a process of change in the species that make
up a community.
Succession occurs following a disturbance
in an ecosystem.
• Succession regenerates or creates a community
after a disturbance.
– a sequence of biotic changes
– damaged communities are regenerated
– new communities arise in previously uninhabited areas
• There are two types of succession.
– primary succession — started by pioneer species
• There are two types of succession.
– secondary succession — started by remaining species