Community ecology (chapter 54)
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. What would you like to do?
the role an organism plays in its community
what kind of system do we use to characterize interactions?
+ and -
What is competition between species represented as?
During evolution some species have learned to partition resources, what is an example? how is this characterized?
- one being nocturnal and other diurnal
- 0/0, they do not compete
Fundamental vs. Realized niches
- (some species can occupy niches when not competed by another species)
- ex- brown barnacles can live in wetter elevations if blue barnacles are not around, thus brown has a fundamental much that is contracted into a realized niche.
- occurs in sympatric regions (ex- two finches have much different beak depth when found together, but each has an intermediate size when separated in allopatric regions
- occurs because they are so close in proximity
How are predator and prey species represented?
What are some senses that predators have evolved to help find prey?
vision, hearing, smell, heat sensing, echolocation
What are strategies that prey use to prevent predation?
- Cryptic coloration (blending into environment)
- Aposematic coloration (opposite of cryptic coloring, use striking colors to warn predators of harmful/lethal prey)
- Batesian Mimicry (mimick harmful species to fool predators
- Mullerian mimicry (two obnoxious species evolve to resemble each other, similar in color and warning signals)
How do plants protect themselves from herbivores?
grow spines, or bad tasting metabolites
- species in close proximity
- includes parasitism (+/- relationship, endoparasites-viruses, live inside you. ectoparasites-ticks live on you)
- apprx 1/3 of species are parasites
What are the symbiotic relationship examples?
Parasitism(+/-), mutualism(+/+), and commensalism (+/0)
What a great example of mutualism?
- both benefit from each other
- bacteria inside intestines, give us nutrients from bacteria who degrade compounds like starch into sugars that can be taken up by the cells lining your intestine. In turn, the bacteria doesn't have to seek out food sources, you feed them 3 times a day.
What is commensalism
- a symbiotic relationship we don't understand whether there is mutual benefit. (+/0)
- ex- buffalo get anything from egrets? probably not
When does facilitation occur?
- When one species conditions the environment for another. (+/+ or +/0 relationship)
- ex- juncos plant conditions the soil by preventing salt buildup and oxygen loss
- can occur over time
number of different species (diversity)
relative number in community
What does higher diversity promote?
more productive and more tolerant communities
what does the trophic structure define?
autotrophs, herbivores and carnivores in a community
How many steps can a food chain be?
- Organism can only derive 10% of the energy stood in an organism to eat. (10% up from food below/per level)
- ex- if the land (or sea) has only a finite amount of autotrophs (plants), then each step up gets less and less of the finite amount until there is too little too support a higher trophic level (a higher predator)
What is the dynamic stability hypothesis?
the longer the food chain, the more unstable is becomes because small fluctuations amplify as they go up (will be fewer and fewer organisms at top of chain)
- the most in number or highest in biomass
- Some so well adapted that they are the sole species in the environment
- ex- sugar maples in eastern north America (invasive species), fungal infection on american chestnut, english sparrows, dandelions, erosion milfoil, zebra clams, and asian carp may dominate because they don't have predators, parasites or pathogens to limit them.
- has a large influence on community structure
- ex- starfish allows other species to compete with the muscle species
- alter their environment for good or bad
- ex- beavers create wetlands that benefit many other species
Bottom up and top down control
- arrows designate change in biomass of a trophic species in relationship to a species in an adjacent level
- V(veggies)-> H(herbivores) means that the biomass of plants controls that of herbivores
- V<-H means herbivores control biomass of plants by grazing to limit their biomass
- bottom up relationship shows nutrients limit autotrophs limit herbivores, limit predators (N->V->H->P)
- This relationship is consistent wight he energetic hypothesis that limits how many steps can be in a food chain
- Top down relationship shows opposite )(N<-V<-H<-P)
- manipulation of predators at the top of some chains show that top-down control is operative in some communities.
What does the non equilibrium model hypothesize?
- that constant disturbances keep communities from equilibrium (most communities have disturbances often)
- Intermediate disturbances, like species diversity, appears to be god for many communities
- Primary- soil formation as a first step (ex- what happens afar a volcanic island in the hawaiin islands protrudes from the sea. soil created from lava)
- secondary- growth from established soil (the progression after a fire like that in yellowstone park
Some dominant species can alter the environment
like dryas and alder, rhizomes that have symbiotic bacteria in their roots that convert atmospheric N2 to ammonia NH3
How does geography influence communities?
Lower latitudes (equatorial tropics)= greater plant and animal species richness, more yearly sunlight hastening plant growth, greater water availability from soil evaporation and plant transpiration. (should evaporation and plant transpiration are the two sources of water and are lumped together as evapotranspiration)
Evapotranspiration correlates with what? what happens if moisture gets greater?
- animals and plants
- greater richness of trees and animals
The larger the area, the more species (results from what?)
from the fact that larger areas are likely to have more niches (this is a log-log plot of bird species in North America, very good comparison)
- a major disturbance
- all species have them
- New ones evolve quickly and decimate populations
- eventually species evolve to resist them, and cycle begins anew
- Pathogens geographically isolated can become worldwide problem because of shipping agriculture
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