Transcript File - Down the Rabbit Hole

Ecology
Biological Communities
NO species exists independently of other species
The Community
• A group of populations of different species living
close enough to interact
Interspecific
interactions between populations of different
species within a community
Community structure
• Community~ an assemblage of
populations living close enough together for
potential interaction
• Richness abundance and distribution of
numbers of different species
• Species diversity number of different
species
• Hypotheses:
– Individualistic chance assemblage
with similar abiotic requirement
– Interactive~ assemblage locked into
association by mandatory biotic
interactions
Interaction in Communities
• Community
interactions are
classified by whether
they help, harm, or
have no effect on the
species involved.
Co-evolution is a result of this history of interaction
How Competition Shapes Communities
When two species use the same resource,
they participate in a biological interaction
called competition
How Competition Shapes Communities
Intraspecific – between individuals
of the SAME species
Interspecific – between individuals
of DIFFERENT species
Interspecific Competition
• Competition occurs
when resources are
in short supply
• Competition is -/interaction between
the species involved
Competition evidence
• Resource partitioning~
sympatric species consume slightly
different foods or use other resources
in slightly different ways
Ex: Anolis lizard sp. perching sites in the
Dominican Republic
• Character displacement~
sympatric species tend to diverge in
those characteristics that overlap
Ex: Darwin’s finch beak size on the Galapagos
Islands
Central to Competition and
Community
• Law of Competitive
Exclusion
• No two species will occupy the
same niche and compete for
exactly the same resources for
an extended period of time.
• One will either migrate, become
extinct, or partition the resource
and utilize a sub-set of the same
resource.
• Given resource can only be
partitioned a finite number of
times.
• The Ecological Niche
Interaction By Predation
• The act of one organism killing another for food
• +/- interaction
• Often involves keystone species
Types of predators
• Carnivores – kill the prey
during attack
• Herbivores – remove
parts of many prey, rarely
lethal.
• Parasites – consume
parts of one or few prey,
rarely lethal.
• Parasitoids – kill one prey
during prolonged attack.
Cryptic Coloration
Striking adaptations often characterize
predators and their prey
Predators may evolve
cryptic morphology
(camouflage)
Cryptic Coloration
Prey may evolve to blend in
too!
Camouflage
Aposematism
Prey may evolve warning morphology
Aposematic colors = warning
Mimicry
Organisms may evolve to look like other organisms
Batesian mimicry
•
•
harmless mimic evolves to look like harmful model
looks like something that is dangerous or tastes bad
Viceroy
Monarch
Milk Snake
Coral Snake
Mimicry
Two bad tasting organisms resemble each other,
ostensibly so that predators will learn to avoid them
equally.
Mullarian mimicry
Bracoria Millipedess
Nudibranchs
Predation defense review
• Cryptic (camouflage) coloration
• Aposematic (warning) coloration
• Mimicry~ superficial resemblance to another
species
√
Batesian~ palatable/ harmless species mimics
an unpalatable/ harmful model
√
Mullerian~ 2 or more unpalatable,
aposematically colored species resemble each other
Interaction By Symbiosis
• Where two organisms live
together in close association.
• Can be mutually beneficial or
benefit one organism and
leave the other unharmed
Herbivory
• +/- interaction in which an
herbivore eats part of a plant.
• It is advantageous for an
animal to be able to
distinguish toxic from
nontoxic plants.
• A plant’s main protective
devices are chemical toxins,
spines, and thorns.
Commensalism
One member benefits while other is neither benefited nor harmed
mites hitching a ride on a beetle
Mutualism
A symbiotic relationship in which both species benefit
+/+
Parasitism
• Parasites derive nourishment from their
hosts +/- interaction
• endoparasites
Tapeworm
• ectoparasites
Tick
Ecological Niche
Often described in terms of how the organism affects energy
flow within the ecosystem, it is a pattern of living
To understand how competition influences the makeup of
communities, you must look at the functional role of the species:
• Niche
• Habitat & microhabitat (Space utilization)
• Food “spectrum,” essential nutrients
• Reproductive requirements
– Nutrition, nest/den sites
• Seasonality: When are resources required, used.
NOT TO BE CONFUSED WITH:
• Habitat - location where a particular organism lives
What is the niche?
set of conditions
within which an organism
can maintain a viable
light intensity ecological
population
niche
multi-dimensional
salinity
with as many
dimensions as their
are limiting conditions
okay
temperature
Size of the Niche
• Fundamental niche
– The entire range of opportunity
– The organism’s potential (the role it could play) in the
absence of biotic enemies
– depends on physical (abiotic) conditions.
• Realized niche
– The actual range of the organism (the role it does
play in the community) – in the presence of biotic
enemies
– depends on biotic as well as abiotic conditions
Competition and Limitation of Resources
Barnacles compete for space on rocky intertidal shores
What is the realized niche of each barnacle?
What is the fundamental niche of each?
Competition and Limitation of Resources
How can we determine the fundamental niche of each barnacle?
Removal experiments –
remove each species and see
where the other grows
Balanus alone
Balanus
fundamental
niche
growth
rate
low
Chthamalus alone
Chthamalus fundamental
niche
middle
high
Location in intertidal zone
Competition and Limitation of Resources
How can we determine the realized niche of each barnacle?
Where do they grow when allowed to compete?
Balanus
growth
rate
Balanus s
realized
niche
low
Chthamalu
Chthamalus
realized
niche
middle
high
Location in intertidal zone
Competitive Exclusion Principle
Two species cannot coexist if they occupy the same niche
(the barnacles did not coexist where their fundamental niches overlapped)
• Competition between two species with
identical niches results either in
competitive exclusion or the evolution of
resource partitioning
• Stable coexistence requires niche
differentiation,
– members of each species compete
more strongly among themselves
than with members of the other
species
– (intraspecific > interspecific)
Avoiding Competition
• Resource partitioning
sympatric species consume
slightly different foods or use
other resources in slightly
different ways
Ex: Anolis lizard sp. perching
sites in the Dominican Republic
• Character displacement
sympatric species tend to
diverge in those characteristics
that overlap
Ex: Darwin’s finch beak size on
the Galapagos Islands
Resource Partitioning
Competition: a closer look
• Interference~ actual fighting
•
•
over resources
Exploitative~ consumption
or use of similar resources
Competitive Exclusion
Principle
– (Lotka / Volterra)~ 2 species
with similar needs for the
same limiting resources
cannot coexist in the same
place
Gause Experiment
two species of Paramecium
predict the outcome of
interspecific competition
P. aurelia
P. caudata
•Competitive exclusion
–When forced to compete, one species eliminates other
Species Diversity
• Measures the number of different species in the community
•
(species richness) and the relative abundance of each species.
Community with even species abundance is more diverse than
one in which one or two species are abundant and the
remainder are rare.
Keystone Species
• Exerts strong control on the community structure
• The affect on its community or ecosystem is much larger
and more influential than would be expected from mere
abundance.
– Often large predators
– Critical food organisms (bamboo and pandas)
– Often, many species are intricately interconnected so that it is
difficult to tell which is the essential component.
– Picky predators can promote coexistence among competing prey
species.
– Competitive exclusion is prevented when the dominant
competitor is the preferred prey.
How Keystone Species Affect Community Structure
Starfish
Pisaster
preditor
How do starfish promote coexistence?
competitors
Barnacles
Balanus
Mussels
Mytilus
Starfish are picky – they prefer to eat mussels (dominant competitor),
allowing barnacles (weaker competitor) to coexist.
Removal experiment
- mussels are the dominant competitor
- competitive exclusion of barnacles
starfish
removed
%
of
intertidal
zone
mussels
barnacles
time
GENERALIST VS SPECIALIST
•Animals are generally
selective and efficient in their
food choices
–Some animals, such as
gulls, are feeding
“generalists”
–Other animals, such as
koalas, are feeding
“specialists”
GENERALIST VS SPECIALIST
narrow
diet
specialist consumes only one prey type
broad diet
generalist consumes many prey types
GENERALIST VS SPECIALIST
Generalists - Broad niche
Specialists - Narrow niche
When generalists and specialists
collide, generalists usually win
Invasive Species
• Invasive species
competitively exclude
native species
– Imported fire ant
– Kudzu
– Purple loosestrife
– Zebra mussel
– Squirrels
Ecosystem Change: Succession
•Succession - orderly, natural changes that take
place in communities of an ecosystem over time.
Pioneer species: first organisms to live in a new habitat.
Tend to be small, fast growing plants, lichens, fungus. Increase
soil and make the ground more hospitable for other species.
Ecosystem Change
• Constant state of change
– Disturbance influences species diversity
and composition
– Storm, fire, flood, human activity
changes a community by removing
organisms or changing resource
availability
– Not necessarily bad
Ecosystem Change
• Intermediate disturbance
hypothesis
– Moderate levels of disturbance
create conditions that foster
greater species diversity than
low or high levels of disturbance
Primary Succession
• Primary succession is
colonization by communities
of organisms where life has
not existed before.
Terrestrial Primary Succession
Secondary Succession
• Secondary succession is the sequence of community
changes that occur when a community is disrupted by
natural disasters or human actions.
Climax Community
• The final stable plant community is called a climax
community. This community may reach a point of
stability that can last for hundreds or thousands of years.
Ecosystem Stability
• The interrelationships and
interdependencies of
organisms affect the
development of stable
ecosystems – in other words
the homeostasis of
ecosystems.
Tolerance
• Tolerance is the ability to
withstand fluctuations in
biotic and abiotic
environmental factors.
• Biodiversity gives an
ecosystem more
tolerance.
• The greater the
biodiversity, the healthier
the ecosystem.
Island Biogeography
• Because of their isolation
•
and limited size, islands are
natural laboratories for
studying bio-geographical
factors
Also applies to islands of
land such as national parks
or preserves.
Island Biogeography
• Two factors
– Rates of immigration and
extinction are influenced
primarily by the size of the
island and the distance of the
island from the mainland.
• The greater the size of the
island, the higher the
immigration rates and lower the
rates of extinction.
• As the distance from the
mainland increases, the rate of
immigration falls, whereas
extinction rates increase