Transcript Community Ecology Notes

COMMUNITY
ECOLOGY
Community Structure
• Depends on 4 factors:
–Physical appearance
–Species diversity
–Species abundance
–Niche structure
Factor 1: Physical
Appearance
• A) biomes
–Aquatic ecosystems
B) Differences within
communities ex. (edge
effect)
Edge Effects
• Transitions between ecosystems
(ecotones) such as forest and
field: differences in sunlight,
temp., wind, etc.
• Some animals like “edges”
(deer, quail)
Edge Effects
• Due to habitat fragmentation,
“edges” are on the rise
• Negative impacts:
–Increasing predation, fires, disease,
parasitism, road mortality
–Creates barriers preventing species
from finding food, mates
Edge Effects – Habitat
Fragmentation
Edge Effects
• Nest parasitism
Edge Effects
• Road Mortality
Edge Effects
• Preventing mortality by creating “habitat
corridors”
Factor 2: Species Diversity
• Number of different species
• 3 factors determine diversity:
–Latitude: diversity decreases as you
increase latitude (move away from
the equator)
–Depth: increasing diversity as
increasing depth to approx. 2,000
meters, then decreases with depth,
until you get to the bottom
Factor 2: Species Diversity
(con.)
3 factors affecting diversity
(con.):
pollution: increasing pollution
causes a decrease in diversity
Factor 2: Species Diversity
• Other factors: (in general these
cause an increase in species
diversity)
–Increased sunlight
–Increased precipitation
–Pronounced seasons
Factor 2: Species Diversity
• Theory of Island Biogeography
(MacArthur & Wilson)
• Species number on an island is
determined by a balance between 2
factors:
–Rate of immigration (new species
arriving)
–Rate of extinction
• Island Biogeography
Factor 2: Species Diversity
(island)
• Rate of immigration and
extinction depends on 2 factors:
–Size of the island
–Proximity to the mainland
Factor 2: Species Diversity
(island)
• The bigger the island, the more
diversity
–Small islands are a smaller target for
immigrators & fewer resources
• The closer it is to the mainland, the
more diversity
–Close island has a higher
immigration rate
Factor 3: Species
Abundance
The number of individuals in each
species:
although tropical rainforests and
coral reefs have high diversity,
these areas tend to have low
species abundance
Factor 4: Niche Structure
• Number of niches (roles) in
ecosystem, similarities and
differences between these niches,
and species interaction determines
niche structure
Factor 4: Niche Structure
• Different niches in an ecosystem
(a niche is defined as the role and
organism plays in the ecosystem):
–Native
–Nonnative (exotic, alien, invasive)
–Indicator
–keystone
Niches
• Native: species that normally live
and thrive in a particular
ecosystem
Niches
• Nonnative: species that migrate or
are accidentally or deliberately
introduced into an ecosystem by
humans
• Can out-compete native species and
crowd them out (invasive species)
–Exs.: zebra mussels, kudzu
Niches -- Invasives
• Zebra mussel
Niches -- Invasives
• kudzu
Niches – Indicator Species
• Indicators: species that serve as
early warnings to damage to an
ecosystem
• Exs. Migratory
• songbirds, frogs
Niches – Indicator Species
• Migratory songbirds respond
quickly to environmental change
–Habitat fragmentation in both
winter and summer habitat (can’t
find suitable nesting sites, increased
predation)
–Forest interior loving species
Niches – Indicator Species
• Frogs (25% of all known
amphibian sp. are extinct,
endangered, or vulnerable)
• Eggs have no protective shells to
block out UV rays
• Adults take in water and air
through skin, also absorbing
pollutants
Niches – Indicator Species
• frogs
Niches: Keystone Species
• Role in ecosystem is more
important than abundance or
biomass would suggest
• Strong interactions with other
species
• Loss could lead to population
crashes or extinctions of other sp.
Niches: Keystone Species
• Critical Roles:
– Pollination
– Seed dispersal
– Habitat modification
– Predation by top predators
– Improve ability for nutrient uptake
by plants
– Efficiently recycle animal wastes
Niches: Keystone Species
• Pollination and seed dispersal
Niches: Keystone Species
• Habitat modification
Niches: Keystone Species
• Predation by top predators
Niches: Keystone Species
• Recycling of animal wastes
Niche Structure: Species
Interactions
• Species Interactions:
– Intraspecific competition
– Interspecific competition
– Predation
– Symbiotic relationships
• Parasitism
• Mutualism
• commensalism
Niche Structure: Species
Interactions
• INTRAspecific competition:
competition for resources
between members of the same
species
Niche Structure: Species
Interactions (intraspecific)
• Allelopathy: one species releases a
chemical substance to inhibit
growth near it. Ex. Black walnut
Niche Structure: Species
Interactions (intraspecific)
• Black walnut
Niche Structure: Species
Interactions (intraspecific)
• Territoriality:organisms mark and
defend an area around home, nest
site
Niche Structure: Species
Interactions (intraspecific)
• territoriality
Niche Structure: Interspecific
• INTERspecific competition:
competition between two or more
different species for food, space, or
any other limited resource
–Fundamental niche: the niche a
species would occupy if there was
no competition
Niche Structure: Species
Interactions (interspecific)
• The more two species’ niches
overlap, the more competition
–Competitive exclusion principle:
one species eliminates another in a
particular area because they outcompete for limited resources
Niche Structure: Species
Interactions (interspecific)
• Competitive
exclusion principle:
Niche Structure: Species
Interactions (interspecific)
• How do species reduce competition?
– Over time, species that compete for the
same resources evolve adaptations that
reduce competition or overlaps of their
fundamental niches
– Resource partitioning
Niche Structure: Species
Interactions (interspecific)
• Resource partitioning: dividing up
of scarce resources so that species
can use them at different times,
different ways, or different places
–Exs. Hawks hunt by day, owls by
night
lions take larger prey,
while cheetah take smaller
Niche Structure: Species
Interactions (interspecific)
• Resource partitioning and niche
specialization
Interference Competition
• A species may limit another’s access to
some resource
• Ex. Hummingbird’s defending patches of
wildflowers by chasing away other
humming bird species
Exploitation Competition
• Competing species have equal access to a
specific resource, but differ in how fast or
efficiently they exploit it
• Ex. humans
Niche Structure: Species
Interactions (Predator-Prey)
• Predator-Prey Relationship: as
prey pops. Increase, after an initial
delay, the predator pops. Increase,
eventually causing a decrease in
prey, thereby after an initial delay,
causing a decrease in predator
pops… and so on (cycle)
Niche Structure: Species
Interactions (Predator-Prey)
• Predator-prey relationship
Niche Structure: Species
Interactions (Predator-Prey)
Predator-prey – didinium & paramecia
Niche Structure: Species
Interactions (Predator-Prey)
• Seems to harm prey population,
but in reality it often reduce sick,
aged, weak members
• Increase food supply for prey and
genetic stock (increasing
reproductive success and longterm survival
Niche Structure: Species
Interactions (Predator-Prey)
• How do predators increase their
chance for success of prey
acquisition?
–Speed, stealth, keen senses,
cooperation, camouflage
Niche Structure: Species
Interactions (Predator-Prey)
• Camouflage – preying mantis (in memory
of Darwin)
Niche Structure: Species
Interactions (Predator-Prey)
• How do prey protect themselves? Prey
Avoidance
• Protective shell
Niche Structure: Species
Interactions (Prey Adaptations)
• Spines or thorns
Niche Structure: Species
Interactions (Prey Adaptations)
• mimicry
Niche Structure: Species
Interactions (Prey Adaptations)
mimicry
• mimicry
Niche Structure: Species
Interactions (Prey Adaptations)
• Poison and warning colors
Niche Structure: Species
Interactions (Prey Adaptations)
• camouflage
Niche Structure: Species
Interactions (Prey Adaptations)
• Changing color camouflage
Niche Structure: Species
Interactions (Prey Adaptations)
• Behavioral strategies
Niche Structure: Species
Interactions (Prey Adaptations)
• Schooling, flocking (safety in numbers)
Niche Structure: Species
Interactions (parasitism)
• Parasitism: one species feeds on
part of another; parasite
benefits, host is harmed (rarely
killed)
Niche Structure: Species
Interactions (ectoparasite)
Niche Structure: Species
Interactions (endoparasite)
Niche Structure: Species
Interactions (mutualism)
• Mutualism: the two species involved
benefit from the relationship
(nutritional, protection,
reproductive)
–Ex. Lichen:fungi collect and hold
moisture, photosynthetic algae
provide food
–Birds remove parasites from rhinos
–Clownfish gain protection from
Niche Structure: Species
Interactions (mutualism)
Niche Structure: Species
Interactions (mutualism)
Niche Structure: Species
Interactions (commensalism)
• Commensalism: one species
benefits and the other one is
neither harmed nor benefited
Niche Structure: Species
Interactions (commensalism)
Epiphytes: use other plants
for support, to reach
elevations for increased
sunlight
Ecosystems Respond to Change
• Ecological succession: gradual
change in species composition
of a given area
–Primary succession
–Secondary succession
Primary Succession
Ecological succession
• Primary succession
–Soil formation begins when
pioneer species attach themselves
to bare rock, over time adding
organic material and breaking the
rock down further
Ecological succession
• Pioneer species example:
Ecological succession
• After patches of soil are built up,
small grasses and herbs can grow
• Characteristics:
– Large pops. Under harsh conditions
– Short lives
Ecological succession
• Next, more grasses, herbs and
shrubs, and small trees begin to
grow
• Characteristics
–Need lots of sunlight (shade
intolerant)
Ecological succession
• Finally a mature forest is in
place (oak, hickory) – climax
community
• Characteristics
–Shade tolerant
Ecological succession
Early Successional
Species
Midsuccessional
Species
Late Successional
Species
Wilderness
Species
Rabbit
Quail
Ringneck pheasant
Dove
Bobolink
Pocket gopher
Elk
Moose
Deer
Ruffled grouse
Snowshoe hare
Bluebird
Turkey
Martin
Hammond’s
Flycatcher
Gray squirrel
Grizzly bear
Wolf
Caribou
Bighorn sheep
California condor
Great horned owl
Ecological succession
Fig. 8.17, p. 190
Ecological succession
• Secondary succession: begins
when a natural area has been
disturbed or removed
• Examples: abandoned farmland,
burned or cut forests, land that has
been dammed or flooded, heavily
polluted streams
Ecological succession
• 3 factors that affect rate of
succession
–Facilitation
–Inhibition
–tolerance
Ecological succession
• Facilitation: one set of species
makes an area suitable for species
with different niche requirements
• Ex. Legumes add nitrogen to soil
Ecological succession
• Inhibition: early species prevent
the growth of other species
(allelopathy)
Ecological succession
• Tolerance: late successional
species are unaffected by earlier
species
Ecological Stability
• Stability is maintained only by
constant dynamic change in
response to changing
environmental conditions
• 3 factors affect stability: inertia,
constancy, resilience
Ecological Stability
• Inertia or persistence: the ability
of a living system to resist
disturbance
Ecological Stability
• Constancy: ability of a living
system to keep its numbers
within limits imposed by
available resources
Ecological Stability
• Resilience: ability of a living
system to bounce back after an
external disturbance
Ecological Stability
• Intermediate Disturbance
Hypothesis: moderate disturbance
in communities promote greatest
species diversity
Ecological Stability
• Intermediate Disturbance Hypothesis
Precautionary Principle
• When evidence indicates that an activity
can harm human health, we should take
measures to prevent harm even if causeand-effect relationships have not been fully
established scientifically