Community EcologyChapter 54

Interspecific Interactions• Competition --/--• Competitive exclusion• Ecological Niches (Habitat-address;

niche-profession)• Resource partitioning-allows similar

species to coexist in a community• Fundamental niche-potential• Realized niche-actual-may be result

of interspecific competition

Character Displacement• Tendency for characteristics to

diverge more in sympatric pop of 2 species than in allopatric pop

Predation +/--• Can be animal eating plant tissues• Defensive adaptations

– Cryptic coloration

Aposematic coloration-warning

Batesian mimicry-harmless or palative looks bad

Mullerian mimicry• 2 unpalatable species look alike

Herbivory +/--

Plants have chemical toxins, spines, thorns

ex strychnine, nicotine, selenium toxinsHerbivores-special adaptations

– Insect-chemical sensors– Sense of smell– Specialized teeth– Length of digestive systems

Symbiosis• Parasitism +/--• Mutualism +/+ obligate; facultative• Commensalism +/0

Facilitation• Species can have positive effects on

the survival and reproduction of another species without living in direct or intimate contact.

• Ex. Juncus grows in salt marshes and prevents salt buildup-benefits other species

Species Diversity• Species richness• Relative abundance

Shannon diversity (H)• Index based on species richness and

relative abundance

Trophic structure• Food Chain

Food Webs (Elton 1920s)

Limits on length of foodchain

• Energetic hypothesis-inefficiency of energy transfer -10% rule

• Dynamic stability hypothesis-long food chains are less stable than short ones-population fluctuations at lower trophic levels are magnified at higher levels

• Also-carnivores tend to be larger at successive trophic levels-can’t get enough food to meet needs

Dominant species• Most abundant-have the highest

biomass• Exert a powerful control• Are they are competitively superior in

exploiting limited resources?• Are they are most successful at

avoiding predation?-would explain effect of invasive species…

Invasive pressure• American Chestnut• Before 1910-40% of US trees-fungal disease-Chestnut blight-killed all the trees-oak, hickoryreplaced; mammals, birdsok, but 7 species of moths and butterfliesbecame extinct

Keystone species• Sea otters: Sea otters are a keystone species in the kelp

forests. They eat many invertebrates, but especially sea urchins. If there are too many sea urchins, they will eat too much of the kelp and destroy it.

• Elephants: By eating small trees, elephants preserve the grasslands, because the grasses need plenty of sun to survive. If they were not there, the savanna would convert to a forest or scrublands.

• Grizzly bears: As predators, bears keep down the numbers of several species, like moose and elk. They also carry and deposit seeds throughout the ecosystem. Bears that eat salmon will leave their dropping and the partially eaten remains that provide nutrients such as sulfur, nitrogen and carbon to the soil.

Foundation species• Ecosystem “engineers”• Affect by causing physical changes in

the environment• Ex beavers• Facilitators-may help other species

Models of organization• Bottom up VH increase of veg-more

H• NVHP• Top down VH increase in H- less V• NVHP Trophic Cascade (ex.

Remove top carnivoresprimary carnivores so upherbivores decreasephytoplankton goes upnutrients go down) (Manipulate +/- effect

Biomanipulation-prevent algal blooms by adding consumers rather than chemicals

Disturbance• Influences species diversity and

composition• Storms, waves, fires, freezing,

drought, • Moderate disturbance can foster

greater diversity than low or high levels

Ecological succession• Species are replaced by other species• Primary• Secondary• Climax community

Island Biogeography• http://www.youtube.com/watch?v=2R

avt4AqdZI

Island Equilibrium Model

Latitudinal gradients• Species richness increases as

approach tropics• Tropics-older; others have repeatedly

started over (glaciers retreating, etc)• Growing season longer• Sunlight and precipitation higher• Evapotranspiration-evap of water for

soil and plants together

• Zoonotic pathogens: transferred to humans from other animals (vector)

Detritivores• Return nutrients to the soil• Law of conservation of mass

Aquatic Ecosystem• Light limitation• Nutrient limitation• Eutrophication

Biomass-dry mass• *

• *In inverted pyramid, phytoplankton grow, reproduce, and are consumed so quickly by the zooplankton that they never develop a large population size, or standing crop

• Phytoplankton continually replace their biomass at such a rapid rate, they can support a biomass of zooplankton bigger than their own biomass.

The Green World Hypothesis

• Terrestrial herbivores are held in check by a variety of factors.– Mechanical defenses– Chemicals

– Low nutrient concentrations so must consume large quantities

– Abiotic factors-temp & moisture extremes

– Competition

Productivity• GPP-gross primary production• NPP-net primary production• NPP=GPP – R(autotrophic respiration)• Primary production

– in aquatic is mostly affected by light and nutrients-N and P

– Eutrophic-nutrient rich; oligotrophic-nutrient poor

– On land-temp and water– evotranspiration

Biogeochemical cycles

Nitrogen cycle

Additional Terms• Bioremediation-use of organisms to

detoxify polluted areas• Bioaugmentation-add desirable

species such as nitrogen fixers• Biodiversity (3 Levels)-genetic

diversity, species diversity and ecosystem diversity

• Threats: habitat loss, introduced species, over-harvesting, global change

Population conservation• Focuses on:

– Population size– Genetic diversity– Critical habitat

MVP• Minimum Viable Population• Extinction Vortex

Landscape and regional conservation

• Habitat fragmentation• Movement corridors• Biodiversity hot spot-small area with

an exceptional concentration of endemic species

Human Actions• Agriculture-nutrient cycling-take it

out of soil or too much in water• Acid precipitation• Biological magnification• Greenhouse effect• Global warming• Ozone layer

• BIDE birth immigration death emigration

• Additive growth• Multiplicative growth

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