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Community and Ecosystem Ecology
Chapter 20
Community Ecology
 Species living in same vicinity
 Potential interactions will occur
 Interspecific interactions
 Interactions between species
 Classified according to effect on populations
 Helpful (+)
 Harmful (-)
Community Interactions
 Occurs in a few ways:
 Competition
 Mutualism
 Predation
 Herbivory
 Parasites and pathogens
1. Competition (-/-)
 Occurs when members of two
different species try to utilize the
same resource
 Competitive Exclusion Principle:
 No two species can occupy the same
ecological niche at the same time
Competition Between Two Species
of Barnacles
Competition
 Competition can lead
to resource
partitioning
 decreases competition
between the two species
 Character displacement
is often viewed as evidence
that competition and
resource partitioning have
taken place
2. Mutualism (+/+)
 Both members of the
association benefit
3. Predation (+/-)
 Predator
 Prey
 2 ways this regulates population growth:
Predator-Prey Population Dynamics
 B. Antipredator Defenses
 A.
3. Predation
 A. Predator-Prey Population Dynamics
 Cycling of predator and prey populations
 Occurs when either predators overkill prey, or when prey
overuse resources and their numbers crash
 In either case, predator numbers also decrease from a decrease in
food source
Predatory-Prey Cycling of a Lynx
and a Snowshoe Hare
Coevolution
 Evolutionary change in one species results in an evolutionary
change in the other
 Organisms in symbiotic associations are especially prone to the
process of coevolution
 Also occurs between predators and prey
 Example: Cheetah sprints forward to catch prey, and this behavior might
be selective for those gazelles that jump high in the air
3. Predation
 B. Antipredator
Defenses
 Cryptic coloration
 Camouflage
 Warning coloration
 Association with
undesirable consequences
3. Predation
 B. Antipredator Defenses
 Mimicry
 One species resembles another species
 Can help capture food or avoid being preyed upon
 Batesian Mimicry
A prey that is not harmful mimics another species that has a successful
antipredator defense
 Warning colorations

 Mullerian mimicry

Species that resemble each other all have successful defenses
Mimicry Among Insects
Mullerian
Batesian
Coral snake vs. Milk snake
http://www.youtube.com/watch?v=LU8DDYz68kM
4. Herbivory (+/-)
 Consumption of plants by an
animal
 Plant must expend energy to
regenerate
 Evolved defenses
5. Parasites & Pathogens (+/-)
 Parasite
 Lives on or in a host
 Endoparasite
 Ectoparasite
 Pathogens
 Disease-causing
microorganisms
Trophic Structures
 Feeding relationships among species in a community
 Determines the passage of energy and nutrients
 Sequence of food transfer is a food chain
 Unbranched
Trophic Structure
 Autotrophs (producers)
 Require an energy
source and inorganic
nutrients to produce
organic food molecules
 Manufacture organic
nutrients for all
organisms
 Green plants and algae
carry on photosynthesis
Trophic Structure
 Heterotrophs
(consumers)
 Need a preformed source of
organic nutrients
 Herbivores
 Graze directly on plants
or algae
 Carnivores
 Feed on other animals
 Omnivores
 Feed on both plants and
animals
Trophic Structure
 Heterotrophs
 Decomposers
 Heterotrophic bacteria
and fungi
 Break down nonliving
organic matter
 They release inorganic
matter to be used by
producers
 Scavengers
 Feed on dead remains
Ecosystem
Ecosystem Ecology
 Possesses both abiotic and biotic components
 Biotic
 The various populations of organisms that form a community
 Abiotic
 Includes resources such as sunlight, inorganic nutrients, soil,
water, temperature and wind
 Two major processes sustain all ecosystems:
 Energy flow
 passage of energy through the components of the ecosystem
 Chemical cycling
 use and reuse of chemical elements within the ecosystem
al
Energy flow
Light
energy
Bacteria,
protists,
and fungi
Chemical
energy
Heat
energy
Chemical
elements
Energy Flow
 Biomass
 Mass of living organic material in
ecosystem
 Ecological Pyramids
 only about 10% of the energy of one
trophic level is available to the next
trophic level
 Producers at the base
 Most available energy
 Energy is given off in less usable forms as
producers are eaten by primary
consumers, etc.
Chemical Cycling
 Biogeochemical cycles
 Biotic and abiotic components of the chemical cycles in an
ecosystem
 3 main cycles:
 Carbon cycle
 Phosphorus cycle
 Nitrogen cycle
CO2 in atmosphere
Burning
Photosynthesis
Cellular respiration
Higher-level
consumers
Plants, algae,
cyanobacteria
Primary
consumers
Wood
and fossil
fuels
Decomposition
Wastes; death
Decomposers
(soil microbes)
Plant litter;
death
Detritus
Figure 20.32