EXAM 4 Study GuideCommunity EcologyBiodiversity- Soy expansion is hurting the amazon!- David Tilman- Director of the cedar creek ecosystem science reserve. o It is broken into different zones to examine plant competition and biodiversity.o Varies the number of species in each plot. o Species suffered a year of drought and change in biomass was looked at. o Looks at behavior plots with more species can recover faster than plots withlower species (more species=more land covered)o Higher diversity=more stabilityWhy conserve biodiversity? - Community Stability and Productivityo High Diversity= High Productivity (all resources are fully used)=greater resistance to disturbance (lower declines in biomass)=Greater Resilience (biomass recovered quicker)What is a community?- Physically defined- all of the organisms that inhabit a particular area- Interactively defined- different species living close enough for potential interaction- Physically and interactively defined- all of the species that interact with each otherin a certain areaHow could we characterize a community?- Species Diversity- o 1. Species richness- # species in communityo 2. Evenness- the relative abundance of species in a communityo High diversity is associated with High productivity b/c resources are more fully used1EXAM 4 Study Guide Greater resistance to disturbance; lower declines in biomass (biological material derived from living organisms like plants/plant-derived material) Greater resilience; biomass recovered more quickly- Species composition- types of species in a community- Trophic/feeding relationship -Trophic levels and food webso Very complexo **To find % efficiency, divide top by bottom- Community structure- top predators are highly competitive!Why is Community ecology important?- Health-o Your body is a community of/for many organisms Ex. Yeast infections, antibiotics ect.o Disease outbreaks are community ecology phenomena Ex. Lyme disease is increasing.. why? Ticks?- Basic Management of exploited and unexploited populationso What determines species richness? o Why does it decrease towards the poles? Mammals, snakes, copepods, marine invertebrateso A species can be very abundant and exert a control on the community- Regulation of Community Structure o Biotic factors Large number of species (abundant) vs. species that play a vital role (pivotal) Competition- decreases richness by competitive exclusion- Niche Differentiation and Character Displacement can increase species richness- Species packing (results from biotic competition) into one area Predation- increase species richness- Keystone species= effect not by abundance in the community but by their role o Ex. Pisaster starfish are needed for species to be present because muscles overtook the community Mutualism and/or facilitation- Ex. Nitrogen fixing bacteria in Aldero Abiotic factors 2EXAM 4 Study Guide Environment gradients: (i.e. H2O, Nutrients, Light, Temperature) Disturbance – - Can reduce dominance (like predation), - Favors different life history characteristics- Ex. Succession- Primary (new habitats) vs. Secondary (pre existing Habitats) Intermediate disturbance hypothesis- disturbance is a regular event in many communities; species diversity is at its peak when there is a mix between r and k- High disturbance= species diversity keeps having to regrow- Moderate disturbance= greatest species diversity- Low= high competitors dominate- What’s more important? (abiotic more supported)o Individualistic hypothesis- emphasizes abiotic factors Depicts a community as a chance assemblage of species found in the same area because they happen to have similar abiotic requrments Gleason- communities are composed of species that assemble along the same combinations of abiotic gradientso Interactive hypothesis- Emphasizes biotic factors Depicts a community of an assemblage of closely linked species locked in by mandatory biotic interactions Destruction of one species in a community could greatly affect other members of the community Clements- communities are tightly interacting groups of species; Proposed that community members were closely linked and functioned almost as a superorganismo More evidence for abiotic factors- Communities are often not stable, predictable, or highly interdependent. Disturbance is a regular thing Succession is not always predictable3EXAM 4 Study GuideWhy does species richness decrease towards the poles? - Latitude and species richnesso Species richness increases as you move from poles to the equator Ex. mammals, snakes, copepods, marine invertebrateso Older habitats have more time to generate species, character displacement and species packing result from competition Evidence: Glaciation at high latitudes makes them relatively young(strong abiotic effects), however old lakes have more specieso Heterogeneity - Tropical habitats are more diverse at higher altitudes (moreniches), more opportunity for specialization Evidence: tropics not more diverse topographically, plants more diverse = animal diversity, doesn’t explain marine life (not convincing)o Productivity - More sun= more energy; more opportunity to specialize and still get energy; reduce extinction; increase diversity longer food webs Evidence: Higher produce=higher diversity, but not always- *High species diversity=greater productivity= resistance to disturbance=resilienceafter disturbanceFood Webs and EnergyWhat is an Ecosystem?- IndividualPopulationCommunityEcosystem- The organisms that live in an area and their physical and chemical (abiotic) environment- Composed of multiple communities- 4 components of an Ecosystem- 1. Abiotic environment4EXAM 4 Study Guide- 2. Primary producerso Making biological tissues using inorganic molecules. o Photosynthesis by photoautotrophs: 6CO2 +12H2O +energy C6H12O6 +6O2+6H2Oo Chemosythesis by chemoautotrophs: 6CO2 +energy C6H12O6 +waste +6H2Oo Ex. Plants, Phytoplankton (cyanobacteria, Diatoms, Dinoflagellates, algae) Collectively capture 1% of lighto Primary producers (autotrophs) and detritus (decaying plant material), are at the lowest trophic level in a food webo Primary Production and energy uptake and flow GPP=Gross Primary Production (rate at which chemical energy isstored in biomass) NPP= Net primary production (amount of energy available to higher trophic levels)- NPP= GPP-Respiration- High species
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