Transcript Community Ecology - Anderson School District One

Community Ecology
Campbell & Reece
Chapter 54
Community

a group of populations of different species
living close enough to interact
Interspecific Interactions
interactions with individuals of other
species
 includes:
 Competition
 Predation
 Herbivory
 Symbiosis
 Facilitation

Competition

interspecific
competition is a +/interaction that
occurs when
individuals of
different species
compete for a
resource that limits
their growth &
survival
Competitive Exclusion


grown separately, both
show logistic growth
when compete
Paramecium caudatum

became extinct in the
culture
2 species competing for
same limiting resource:
1 will have advantage in
either using resources or
in reproduction
Ecological Niche


is the sum of a species’ use of the biotic &
abiotic resources in its environment
Eugene Odem: “If an organism’s habitat is
its “address”, then niche is the organism’s
“profession,”
Niche

not just where an organism lives but also
what it eats, when it eats, who eats it, how
many resources it uses, how much & what
type of wastes it produces, what its
parasites are, etc
Niches: Resource Partitioning

3 birds live in spruce
tree: each lives in
different level so
there is no
competition even
though all live in
same trees
Character Displacement

closely related species may have
populations that are sometimes allopatric
(geographically separate) & sometimes
sympatric (geographically overlapping)
Character Displacement
allopatric populations will be
morphologically more similar & use
similar resources
 sympatric populations more likely to show
differences in body structures & in the
resources they use

Predation

refers to the +/- interaction between species
in which 1 species, the predator, kills &
eats the other, the prey
Feeding Adaptations of Predators
acute senses
 claws, teeth, fangs, stingers, or poison
 those that have to chase their prey have
adaptations that make them fast & agile
 those that lie in ambush have adaptations
that disguise their position

Adaptations of Prey
hiding, fleeing, forming herds or schools
 active self-defense less common except for
mothers protecting young (especially in
larger, grazing mammals)
 alarm calls  mob the predator

Defensive Coloration in Animals
Cryptic Coloration


Camouflage
makes prey difficult to
see
Defensive Coloration in Animals


warning coloration
often used by animals
that have effective
chemical defenses

Aposematic Coloration
Defensive Coloration in Animals

Batesian mimicry: a palatable or harmless
species mimics an unpalatable or harmful
one
Defensive Coloration in Animals

Mullerian mimicry: 2 or more unpalatable
species resemble each other; the more
unpalatable prey there are the more
quickly predators learn to avoid anything
that resembles them
Herbivory
refers to a +/- interaction in which an
organism eats parts of a plant or alga
 most herbivores are invertebrates
 specialized adaptations:


some insect have sensors on feet to detect
toxins, or to detect nutritious & less nutritious
plants
Plant Adaptations


feature toxins, spines, thorns
some toxins:
 Strychnine: produced by tropical vine
 Nicotine: tobacco
 Tanins: variety of plants
 Selenium: found in “locoweeds” because sheep
& cattle that eat them found wandering
aimlessly, some die
Plant Adaptations

produce chemicals their predators find
distasteful:
Cinnamon
 Cloves
 Peppermint

Symbiosis
when 2 or more species live in direct &
intimate contact w/each other
 some: helpful, harmful, or neutral

Parasites
Ecologists estimate that 1/3 of all species
are parasites
 many have complex life cycles requiring
multiple hosts
 some change behavior of their host to
increase probability of it being transferred

Parasitic accanthcephalan

leads their crustacean host to leave shelter
increasing chances it will be eaten by a
bird, its next host
Parasitism
a +/- symbiotic interaction in which 1
organism, the parasite, derives its
nourishment from another organism, its
host, which is harmed in the process
 Endoparasites: live w/in body of their host



ex: tapeworm
Ectoparasites: feed on external surface of
their host

ex: ticks, lice
Parasitoid Insects

small wasps that lay their eggs in living
hosts that feed on the body, killing it
Mutualism
an interspecific interaction that benefits
both species, +/+
 Acacia trees & stinging ants:

ants feed on nectar & protein-rich swellings on
tree
 tree protected by thorns (ants live inside) &
stinging ants that attack any herbivores & ants
clip vegetation that grows near the tree

Mutualism
Commensalism
an interaction between species that
benefits one of the species but neither
harms nor helps the other +/0
 in reality may have some slight + or affect

Facilitation
species can have +/+ or +/0 effects on the
survival or reproduction of other species
w/out living in direct, intimate contact
with each other
 this type of interaction = facilitation


common in plant ecology
Black rush increases # of plant
species that can live in upper
middle zone of salt marshes
Species Diversity
variety of different kinds of organisms that
make up a community
 Species richness: # of different species in
community
 Relative abundance: proportion each
species represents of all individuals in
community

Which is Which?
Shannon Diversity
Ecologists use different tools to compare
the diversity of different communities over
time & space.
 Shannon diversity is an index of diversity
based on species richness & abundance

Shannon Diversity




Shannon diversity = H
ni = # of 1 species
n = # of all species
In = natural logarithm
Which Forest is More Diverse?
Diversity & Community Stability

higher diversity communities generally
are more productive & better able to
withstand & recover from environmental
stresses
Invasive Species

higher diversity communities more
resistant to effects of invasive species
Trophic Structure

layers in food chains/ pyramids
Food Webs


summary of
trophic
relationships
of a
community
tells whom
eats whom
Limits of Food Chain Length

1.
Why are they short?
Energetic Hypothesis

2.
length limited by inefficiency of nrg transfer
Dynamic Stability Hypothesis


longer food chains less stable
population fluctuations @ lower trophic
levels magnified @ higher levels
Dominant Species
the more abundant species in a
community
 are highly competitive

Dominant Species
1 way to measure effect is to study what
happens when a dominant species is
removed:
 ex: tree, American Chestnut was dominant
tree in deciduous forests before 1910
 fungal disease chestnut blight introduced:
killed almost all of them  didn’t bother
maples, beeches, oak, or hickories, or birds,
or mammals, but 7 species of moths &
butterflies became extinct

Keystone Species
not usually abundant in community
 exert strong control by their pivotal
ecological role or niche

Ecosystem Engineers
species that dramatically alter their
physical environment
 aka: foundation species
 effect on other species can be + or –
depending on needs of other species

Bottom-Up Model

proposes a unidirectional influence from
lower to higher trophic levels
presence or absence of mineral nutrients (N)
controls plant (V) #s which in turn controls
herbivore (H) #s which in turn controls
predator (P) #s
 N  V  H  P
 adding or removing #s of P will not effect
lower trophic levels but adding or removing N
will affect biomass of all higher trophic levels

Top-Down Model

postulates #s of predators mainly controls
community organization because
predators limit herbivores, herbivores
limit etc:
NVHP
 aka: trophic cascade model
 used to improve water quality in polluted
lakes (approach called biomanipulation)

Disturbance

an event (storm, flood, fire, drought,
overgrazing, or human activity) that
changes a community by removing
organisms from it or altering resource
availability
Nonequilibrium Model

evidence suggests that disturbance & lack
of equilibrium not stability & equilibrium,
are the norm for most communities
Characterizing Disturbance
type of disturbance, their frequency &
severity vary among communities’
 high level of disturbance is generally the
result of a high intensity & high frequency
disturbance

Intermediate Disturbance
Hypothesis

says moderate levels of disturbance can
foster higher species diversity than can low
or high levels of disturbance
Ecological Succession
the sequence of community & ecosystem
changes after a disturbance
 Primary Succession: type of ecological
succession that occurs in an area where
there were originally no organisms present
& where soil has not yet formed

Primary Succession
Secondary Succession

type of succession that occurs where an
existing community has been cleared by
some disturbance that leaves the soil or
substrate intact
Succession
early arrival species may facilitate the arrival
of late arriving species by making
environment more hospitible
 sometimes the early species inhibit
establishment of later species so the later
species succeeds in spite of the presence of
early species
 early species may be completely independent
of later species which tolerate conditions
created by early species

Human Disturbance
humans are the most widespread agents
of disturbance
 man‘s effects usually reduce species
diversity
 humans also interfere with natural
disturbances like fires which can be
important disturbances to some
communities

Biogeographic Factors

large-scale factors that influence the
diversity of communities
Latitudinal Gradients
species richness generally declines along a
latitudinal gradient from the tropics  the
poles
 tropics are much older which may
contribute to species richness but it is also
affected by climate (amt heat, sunlight,
water)

Species-Area Curve

the biodiversity pattern that shows that the
larger the geographic area of a community
is, the more species it has
Energy, Water, & Species Richness

Species richness of North
American trees increases
most predictably with
actual evapotranspiration
(evaporation of water from
soil + transpiration of
water from plants) which is
a function of solar
radiation, temp, & water
availability
Species-Area Curve

explanation for this phenomena: the larger
areas offer greater diversity if habitats &
microhabitats
Island Equilibrium Model
are generally isolated, limited size so ideal
for studying biogeographic factors that
affect biodiversity
 “islands” = oceanic islands + habitat islands

ex:
 mountain tops
 Lakes
 woodland fragments

Island Equilibrium Model

Immigration & Extinction Rates:

equilibrium # of species on an island
represents a balance between the immigration
of new species & extinction of established
species
Island Equilibrium Model

Effect of Island Size:

larger islands may ultimately have a larger
equilibrium # of species than smaller islands
because immigration rates tend to be higher &
extinction rates lower on larger islands
Island Equilibrium Model

Near islands tend to have larger
equilibrium #s of species than far islands
because immigration rates to near islands
are higher & extinction rates are lower
Pathogens

are disease causing microorganisms
Viruses
 infectious RNA molecules: viroids
 infectious RNA proteins: prions

Pathogens

can quickly & extensively alter community
structure
especially when introduced into new habitats
 new hosts have not had chance to become
resistant thru natural selection

Zoonotic Pathogens
pathogens transferred from other animals
 humans
 cause of largest class of emerging human
disease
 community ecology provides framework
for identification of key species
interactions ass’c with such pathogens &
for helping us track & control their spread

Zoonotic Pathogens

can be transferred by
direct contact
 thru intermediate species called a vector

Vectors

often parasites
Ticks
 Lice
 Mosquitoes
