Interactions of Organisms in
Ecosystems (Unit 3 – LT)
KEY CONCEPT
Every organism has a habitat and a niche.
A habitat differs from a niche.
Habitat
• The area or environment where an organism or
ecological community normally lives or occurs:
Marine habitat
Niche
>Rhymes with itch!
The functional role of a species in its environment‚
includes:
Food- how it fits in a food
web
Behavior-interaction with
other organisms and
environment
Abiotic conditions it can
tolerate.
Clown fish living among the
tentacles of a sea anemone.
KEY CONCEPT
Organisms interact as individuals and as populations.
Competition and predation are two important ways in
which organisms interact.
Competition
• Competition occurs when two organisms compete for the
same resource.
Intraspecific Competition
involving the same species
Interspecific Competition
involving different species
Predation
occurs when one organism captures and eat another.
Symbiotic Relationships
or Symbiosis
Symbiosis is a close ecological relationship
between the individuals of two (or more) different
species.
There are three major types of symbiotic relationships.
Mutualism:
Bat eats
nectar.
Cactus is
pollinated.
Organism benefits
+
+
+
.
both organisms benefit
+
+
+
Organism benefits
Commensalism:
-
Ø
one organism benefits, the other is
unharmed
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.
Parasitism:
–one organism benefits, the other is
harmed
+
Parasitism
+
_
Hornworm
caterpillar
The host hornworm
will eventually die as
its organs are
consumed
by wasp larvae.
_
Organism is affected negatively
+
Braconid
wasp
Braconid larvae
feed on their
host and
release
themselves
shortly before
reaching
the pupae
stage of
development.
Organism benefits
– Parasites meet their needs as either
Ectoparasites-outside
the body of host
Endoparasites- inside
the body of host
Hookworm
Leech
KEY CONCEPT
Each population has a density, a dispersion, and a reproductive strategy.
Population Density
Population density is the number of
individuals that live in a defined area.
• Scientists can calculate population density.
Geographic dispersion of a population shows
how individuals in a population are spaced.
• Population dispersion refers to how a population is
spread out in an area.
Clumped
dispersion
Uniform
dispersion
Random
dispersion
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
– One to two offspring
– An older population
– Slow to reach
reproductive age
– Common to large
mammals and
humans
Baboon
What ‘ll it be
berries or worms?
Type II
– survivorship rate is
equal at all stages of
life
– Multiple offspring
– Reproductive age
usually reached in
one or two years
– Common to birds
and reptiles
Feed us
now!
Type III
Cicada
– Very high birth
rate
– Very high infant
mortality
– Usually reach
sexual maturity
in one season
– Common to
invertebrates
and plants
KEY CONCEPT
Populations grow in predictable
patterns.
The size of a population is always changing.
. Four factors affect
the size of a
population.
–Immigration (in)
–Emigration (out)
–Births
–Deaths
Population Growth
• Population are directly effected by the amount
of resources available.
• There are two distinct types of population
growth
Exponential Growth
• Exponential growth is a rapid population increase
due to an abundance of resources.
Australian farmer introduced 24 rabbits (European) in 1859 today there are ~ 300 million rabbits.
Logistic Growth
• Logistic growth is due to a population facing limited
resources.
Starts slowly then becomes
exponential growth but
levels off as resources
become scarce.
Carrying Capacity
• Carrying capacity is the maximum number of individuals
in a population that the environment can support.
Population Crash
• A population crash is a rapid decline in the size
of a population over a short period of time.
Carrying capacity
Ecological factors
limit population growth.
• A limiting factor is “something” that keeps
the size of a population down.
Density Dependent
Density
Independent
Density-dependent
• Density-dependent limiting factors are affected by the
number of individuals in a given area.
– competition
– predation
– parasitism
– disease
Density-Independent
• Density-independent limiting factors limit a population’s
growth regardless of the density.
–unusual
weather
–natural
disasters
–human
activities