Ecosystem
Structures
Ecosystem Structure
Different Species Playing Different Roles
• Biological communities differ in the types and numbers of
species they contain and the ecological roles those species
play.
• Species diversity: the number of different species it contains
(species richness) combined with the abundance of individuals
within each of those species (species evenness).
• Types of species–
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–
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Indicator
Keystone
Foundation
Umbrella
Native vs. Non-indigenous/Invasive
Indicator Species
 Indicator Species
 Biological Smoke Alarm
 Have a very small limit of tolerance
 Serve as early warnings of damage to a community
or an ecosystem.
 Trout species- indicator of water quality
 sensitive to temperature and oxygen levels of water
 Lichen – indicator of air quality
 Sensitive to toxic gases like sulfer and ozone
 Frogs- indicator of water pollution
Case Study:
Why are Amphibians Vanishing?
 Frogs serve as indicator
species because different
parts of their life cycles can
be easily disturbed.
 Amphibians breathe partially
through their skin, which is
constantly exposed to the
environment so their bodies
are much more vulnerable
and sensitive to factors such
as disease, pollution, toxic
chemicals, radiation, and
habitat destruction
Figure 7-3
Case Study:
Why are Amphibians Vanishing?
 Habitat loss and fragmentation.
 Prolonged drought.
 Pollution.
 Increases in ultraviolet radiation.
 Parasites.
 Viral and Fungal diseases.
 Overhunting.
 Natural immigration or deliberate introduction of
nonnative predators and competitors.
Why are Amphibians
Vanishing?
• Farm fertilizers often contain large
amounts of phosphorous and nitrogen.
• Boosts algae production which in turn
boost the population of certain
flatworm parasites.
• These parasite attack frogs at their
larval stage tadpoles causing them to
develop deformities in adulthood.
• Deformities include missing or extra
limbs.
Keystone Species
 Keystone Species a species whose role is
essential for the survival of
many other species in an
ecosystem
 help determine the types and
numbers of other species in a
community thereby helping to
sustain it.
Keystone Species
– Sea Stars
• Keeps mussels from dominating
the shore line thus helping less
competitive species to persist
– Sea Otters• Eat sea urchin that destroy kelp
beds
– Grizzly Bear• Transfers nutrients from oceanic
ecosystems to forest ecosystems
by catching salmon rich in
nitrogen, carbon, phosphorous
and sulfur.
Sea Otters and West Coast of North America.
European and Russian trappers hunt sea otters to near extinction
in the 18th and 19th centuries.
• The decline of the sea otters, which are essential to keeping sea
urchins in check, allows sea urchin populations to explode.
• The burgeoning sea urchins feast on and decimate the kelp
beds, which are critical habitat for spawning fish.
• Fish begin to decline for lack of spawning habitat; this affects
fishermen's catches.
• In areas where the otters recovered, urchin populations are
once again kept down, the kelp beds recover, fish nurseries
recover, and fish catches rise again.
Foundation Species– Dominant primary producer in an
ecosystem in both abundance and
influence
• Kelp/Kelp Forest
• Coral/ Coral Reef
• Trees within a forest
Removal disrupts fundamental
ecosystem processes, including
rates of decomposition, nutrient
fluxes, carbon sequestration, and
energy flow
Umbrella Species
 Umbrella Species species that, through
its protection, protects
other species that live
within its habitat.
Native and Invasive Species
 Native species those that normally live and thrive in a particular
community.
 Invasive species those that migrate, deliberately or accidentally
introduced into a community.
Introduced Species:
Rabbits in Australia
 Introduced into Australia from England in 1859
 No natural enemies – rabbit population exploded
 Overabundant herbivore population devastated
natural vegetation.
 Used disease-causing viruses to control rabbit pop.
 Using disease as control measure – why will this
procedure fail in the long-term?
 Would this particular virus be considered a parasite
or a predator?
Rabbits Overgrazing in Australia
Phillip Island 1978
Largely devoid of vegetation
Phillip Island 1988 After Rabbit Removal
Interactions Among Species
• Species can interact through competition,
predation, or symbiosis (mutualism,
commensalism, parasitism)
• Some species evolve adaptations that allow them to
reduce or avoid competition for resources with
other species (resource partitioning).
• Competition for–
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Food
Space
Water
Mates (among species)
Interactions Among
Species
Resource Partitioning
• Each species minimizes
competition with the others for
food by spending at least half its
feeding time in a distinct
portion of the spruce tree and
by consuming somewhat
different insect species.
Figure 7-
Interactions Among Species
 Predation
 Predator (organisms that captures & feeds on parts
or all of another animal) vs. Prey (organisms that is
captured & serves as a source of food for another
animal).
Interactions Among Species
 Predator/Prey populations are often cyclical
Interactions Among Species
Mutualism:
 Win-Win
Relationship
 Two species can
interact in ways
that benefit both
of them.
Figure 7-9
Interactions Among Species
Commensalism:
• Using without
Harming
• Some species
interact in a way
that helps one
species but has
little or no effect on
the other.
Figure 7-10
Interactions Among Species
Parasites:
• Sponging Off of Others
• Parasites harm their hosts
– Some parasites live in host
(micororganisms, tapeworms).
– Some parasites live outside
host (fleas, ticks, mistletoe
plants, sea lampreys).
– Some have little contact with
host (dump-nesting birds like
cowbirds, some duck species)
Population Dynamics
Carrying CapacityThe maximum population of a
particular species that a
given habitat can support
over time.
The barrel represents the
habitat, the water pouring
out represents population
loss due to various elements
and the water in represents
new species within the
population being born into
that particular habitat
Population Dynamics
• A population can grow until
competition for limited
resources increases & the
carrying capacity (C.C.) is
reached.
• Populations grow rapidly with
ample resources, but as
resources become limited, its
growth rate slows and levels
off.
• As a population levels
off, it often fluctuates
slightly above and below
the carrying capacity.
• Members of populations
which exceed their
resources will die unless
they adapt or move to an
area with more
resources.
Figure 8-
Population Dynamics
A: Represents the biotic
potential of the species
B: Shows how the population
overshoots the carrying
capacity
C: Represents the logistic
growth
D: Represents linear growth
E: Carrying capacity- the
maximum number of
individuals that can be
supported by a particular
ecosystem.
Reproductive Patterns
The populations of different species
vary in how long individual
members typically live.
Survivorship Curve-
• The way to represent the age
structure of a population is with
a survivorship curve.
– Late loss population live to an
old age.
– Constant loss population die at
all ages.
– Most members of early loss
population, die at young ages.
Reproductive Patterns
Reproductive Patterns
 r-selected species tend to be opportunists
 K-selected species tend to be competitors.
Reproductive Patterns
Reproductive Patterns:
Opportunists and
Competitors
• Large number of smaller
offspring with little parental
care (r-selected species).
• Fewer, larger offspring with
higher invested parental
care (K-selected species).