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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?- IndividualPopulationCommunityEcosystem- 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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UMD PSYC 355 - EXAM 4 Study Guide

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