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Chapter 20
Community and Ecosystem Ecology
Community EcologySpecies living in same vicinityPotential interactions will occurInterspecific interactions
Interactions between speciesClassified according to effect on populations
Helpful (+)Harmful (-)
Community InteractionsOccurs in a few ways:
CompetitionMutualismPredationHerbivoryParasites 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
CompetitionCompetition can
lead to resource partitioning decreases
competition between the two speciesCharacter
displacement is often viewed as evidence that competition and resource partitioning have taken place
2. Mutualism (+/+)
Both members of the association benefit
3. Predation (+/-)PredatorPrey2 ways this regulates population growth:
A. Predator-Prey Population DynamicsB. Antipredator Defenses
3. PredationA. Predator-Prey Population Dynamics
Cycling of predator and prey populations
Occurs when either predators overkill
prey, or when prey overuse resources and
their numbers crashIn either case, predator numbers also decrease
from a decrease in food source
Predatory-Prey Cycling of a Lynx and a Snowshoe Hare
CoevolutionEvolutionary change in one species results
in an evolutionary change in the otherOrganisms in symbiotic associations are
especially prone to the process of coevolutionAlso 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. PredationB. Antipredator
DefensesCryptic coloration
Camouflage Warning
coloration Association with
undesirable consequences
3. PredationB. Antipredator Defenses
MimicryOne species resembles another species Can help capture food or avoid being preyed uponBatesian Mimicry
A prey that is not harmful mimics another species that has a successful antipredator defense
Warning colorations
Mullerian mimicrySpecies that resemble each other all have successful
defenses
Mimicry Among Insects
MullerianBatesian
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 regenerateEvolved defenses
5. Parasites & Pathogens (+/-)
ParasiteLives on or in a hostEndoparasiteEctoparasite
PathogensDisease-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 chainUnbranched
Trophic StructureAutotrophs (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 StructureHeterotrophs
(consumers)Need a preformed source
of organic nutrientsHerbivores
Graze directly on plants or algae
CarnivoresFeed on other animals
OmnivoresFeed on both plants
and animals
Trophic StructureHeterotrophs
DecomposersHeterotrophic bacteria
and fungiBreak down nonliving
organic matterThey release
inorganic matter to be used by producers
ScavengersFeed on dead remains
Ecosystem
Ecosystem Ecology Possesses both abiotic and biotic components
Biotic The various populations of organisms that form a
communityAbiotic
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 ecosystemChemical cycling
use and reuse of chemical elements within the ecosystem
Energy flow
Lightenergy
Bacteria,protists,and fungi
Chemicalelements
Chemicalenergy
Heatenergy
Chemical cycling
Energy FlowBiomass
Mass of living organic material in ecosystem
Ecological Pyramidsonly 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 CyclingBiogeochemical cycles
Biotic and abiotic components of the chemical cycles in an ecosystem
3 main cycles:Carbon cyclePhosphorus cycleNitrogen cycle
CO2 in atmosphere
Burning
Cellular respiration
Woodand fossil
fuels
Decomposition
Wastes; death
Decomposers(soil microbes) Detritus
Plant litter;death
Primaryconsumers
Higher-levelconsumers
Plants, algae,cyanobacteria
Photosynthesis
Figure 20.32
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