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 StructureDecomposers

Heterotrophic bacteria and fungi

Break down nonliving organic matterThey release inorganic

matter to be used by producers

ScavengersFeed on dead remains

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