Transcript File - Down the Rabbit Hole

Ecosystems
Structure and Dynamics
Community Ecology
The scientific study of interactions among organisms and
between organisms and their environments.
Ecosystems: Everything Is Connected
Everything in an
ecosystem is
connected.
What affects one
part of an
ecosystem often
affects many other
parts of the
ecosystem as well.
Organisms and Species
• An organism is a single
living thing.
• A species is a group of
organisms that can
produce fertile
offspring with the
same characteristics.
Populations
• A population is a group of organisms from
the same species living in the same place.
• There may be thousands of populations
for any particular species.
The Community
• A group of populations of different
species living close enough to interact
Interspecific interactions = all the species in a
given area.
Any place within the
ecosystem
where a population or
community lives
Some habitats
Forest
• Tree
Lake or pond
City park
Cave
Fen or swamp or
marshland
Reef
Habitat
Species
Population
Levels of Organization
Community
Ecosystem
Biome
Biosphere
Biome
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
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
How Species Interact With Each Other
• Ecosystems work best
•
when every niche in it
is filled.
Species interact with
each other in many
ways. The most
common
relationships are:
1. Predation
2. Competition
3. Parasitism
4. Mutualism
5. Commensalism
Central to Competition
and Community
The 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
• Habitat & microhabitat
•
•
•
•
(Space utilization)
Food “spectrum,” essential
nutrients
Reproductive requirements
Nutrition, nest/den sites
Seasonality: When are
resources required, used
Predation
• In predation, one organism
•
•
•
•
•
eats another.
The animal that kills and eats
is the predator.
The animal that is eaten is the
prey.
Predators typically kill the
young and weak/sick
members of their prey.
Consequently they help limit
the size of the prey
population.
As the prey die off, the
predators either switch their
prey or die off also.
This creates a specific cyclical
relationship between
predators and prey.
Predation
Hare cycles may be caused
by increasing food shortages
during winter caused by
overgrazing
Or they may be due to
predator-prey interactions
Cycles could be affected by a
combination of food
resource limitation and
excessive predation
Predators reproduce more
slowly than their prey so
they always lag behind prey
in population growth.
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.
Interaction By Symbiosis
• Two organisms living
together in close
association.
Mutualism
A symbiotic relationship in which both species benefit
+/+
• Parasitism is a relationship
•
•
•
between two organisms in
which one feeds off another.
The organism that feeds off
the other is the parasite.
The organism that contains
the parasite is the host.
The main difference
between parasitism and
predation is that in
parasitism, the parasite does
not usually kill the host
quickly.
Parasitism
Tapeworm
Tick
Commensalism
One member benefits while other is neither benefited nor
harmed
mites hitching a ride on a beetle
Population 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
realized
niche
low
Chthamalus
Chthamalus
realized
niche
middle
high
Location in intertidal zone
Law of Competitive Exclusion
Two species cannot coexist if they occupy the same niche)
• No two species can occupy
the same niche and compete
for exactly the same
resources for an extended
period of time.
• One will either migrate,
become extinct, or the two
species will partition the
resource and utilize a sub-set
of the same resource.
• Given resource can only be
partitioned a finite number of
times.
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
Biodiversity
• 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?
Barnacles
Balanus
competito
rs
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
starfish
removed
%
of
intertidal
zone
time
mussels