Lecture 10
Community Ecology
Today’s topics
•
•
•
•
What is community ecology?
Interspecific relationships
Community Structure and Function
Exam 1 review
Community Ecology
• Community – assemblage of multiple species
populations that live in the same place at the
same time.
• The interaction among species and the effect
those interactions have on both living and
nonliving features of their environment.
Interspecific relationships
• All the interactions that exist between
organisms of different species in an ecosystem
fall in the category of symbiosis meaning “to
live together”.
– Competition (-/-)
– Predation (parasitism) (+/-)
– Commensalism (+/0)
– Mutualism (+/+)
Mechanisms of Competition
• Species can compete directly by fighting to
gain access to resources (interference
competition) http://www.youtube.com/watch?v=EOB5S5IXCFg&feature=related
Mechanisms of Competition
Or compete indirectly by consuming the same
resource (exploitative competition)
Competitive Exclusion Principle
Two species competing for the exact same
limited resource cannot stably coexist.
If two competing species coexist in a stable
environment, they do so as a result of
differentiation of their niche.
The Ecological Niche
• Distributional component - A habitat a species occupies as a
function of its physiological and behavioral attributes.
• Functional component – A species role in the community in
terms of its trophic level
• Most ecologists include both in the definition
an consider a niche to be all adaptations of a
species to a particular environment
Two types of niche
• 1. Fundamental niche – all the potential
resources that a species can use in its
environment.
– Requires the absence of competition
Two types of niche
• 2. Realized niche – some habitats and
resources are not available because
competitors occupy them.
– This is what the species actually uses
Pretend this is
a mountain
Tamias alpinus
Tamias speciosus
Tamias amoenus
Tamias minimus
Fundamental niches
Realized niches
Character Displacement
• 2 sympatric species differ more than 2
allopatric
– Sympatric = ranges overlap
– Allopatric = ranges do not overlap
Predation
• Parasitism is a similar form of this symbiotic relationship, but
the host may only be weakened.
• As we discussed in the previous lecture, predation has negative
immediate consequences, but can have positive long-term.
• For instance, thinning out the weak or sick.
Predators may play a significant role in
structuring communities
• Important concepts:
• Trophic cascade –predators depress
populations of herbivores to the point that
plant biomass increases (Dr. Murphy will talk more
about this later)
• Keystone Predators
• Guilds
Keystone predators – exert a
controlling force over community
structure and function
Guilds – more than one species occupying the same
trophic level and exploited a common resource
• Keystone Guilds – more than one species plays
a keystone role in the same community
Mutualism
• Both species benefit
•
http://www.youtube.com/watch?v=Qqa0OPbdvjw&feature=related
Commensalism
• One species benefits while the other neither
benefits nor is harmed
Community Function
• Evaluating energy flow and food webs are
comment ways to understand how a
community functions.
Energy flow through trophic levels
Mammals typically do not account for a large proportion of total energy flow
in communities, but total effect on energy flow can be significant
Food webs