Chapter 54 Community Ecology PDF

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Chapter 54 Community Ecology- Doebel...

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54.1 Community interactions are classified by whether they help, harm, or have no effect - Interspecific interactions: competition, predation, herbivory, parasitism, mutualism, and commensalism Competition (-/-) - Individuals of different species compete for a resource that limits the survival and reproduction Competitive exclusion - When even a slight reproductive advantage will lead to elimination of the inferior - Leads to extinction of one species, shift to a different ecological niche (behavioral shift like resource partitioning, evolutionary shift such as character displacement) - Behavioral shift is a precursor to evolutionary shift - Complete competitors do not exist!!!! Ecological Niches and Natural Selection - Ecological nicheL specific set of biotic and abiotic resources that an organism uses in its environment - Can use this to say: 2 species can’t coexist permanently if niches are identical - But can coexist if 1+ significant differences in their niches arise through time - Resource partitioning: differentiation of niches that enables similar species to coexist in a community - Fundamental niche: potentially occupied by that species which is often different from the realized niche, the portion of its fundamental that it actually occupies - ID the FN by testing the range of conditions in which it reproduces in the absence of competitors - Niches can be partitioned in time too Character Displacement - Closely related species who are geographically separate provide more evidence of competition in communities - In some, allopatric may show similar morphologically while sympatric will show difference - Character displacement: the tendency for characteristics to diverge more in sympatric than in allopatric populations Exploitation (+/-) - All non photosynthetic organisms must eat and all are at risk of being eaten - Includes predation, herbivory, and parasitism Predation - Aposematic coloration: chemical defenses (bright coloration) - Adaptive - Cryptic coloration: camouflage - Batesian mimicry: harmless species mimics harmful species - mulleria n mimicry: two harmful species resemble each other

Herbivory - Organism eats part of a plant - Some plants feature chemical toxins or have spines and thorns Parasitism - One organism, the parasite, derives its nourishment from another organism, its host - Endoparasites: parasites that live within the body of their host - Ectoparasites: live on external surface - Parasitoid: lay living eggs inside the host where larvae then eat the body Positive Interactions (+/+) or (+/0) - Mutualism: both benefit - Commensalism: one benefits and one is neutral - Both can become each other 54.2 Diversity and trophic structure characterize biological communities Species Diversity - The variety of different kinds of organisms that make up a community - 2 components: species richness (# different species) and relative abundance (proportion each species represents of all individuals in community) - Shannon diversity: calculates diversity Diversity and community stability - Biomass: most diverse plots consistently produced more (total mass of all organisms in a habitat) - Invasive species: higher diversity communities are more resistant (organisms that become est. outside of their range) Trophic Structure - The feeding relationships between organisms of a community - Trophein (greek)= food, nutrient Food Webs - Food chains are linked together to form a web Limits on Food Chain length - Energetic hypothesis: the length of a food chain is limited by the inefficiency of energy transfer along the chain - On 10% of energy stored is converted at the next level - Carnivores at the end of a chain tend to be larger and that puts an upper limit of the size of food it can take into its mouth Species with a large impact - Dominant species: species that are the most abundant or have highest biomass - Keystone species: not usually abundance, but provide pivotal ecological roles, usually top predators - Rocky intertidal pool: kid threw away starfish and the number of species present decreased drastically

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Ecosystem engineers: species that dramatically alter their environment - Ex: beaver by creating ponds, and building dams Bottom up and top down controls - Bottom up: postulates a unidirectional influence from lower to higher trophic levels - Ex: more vegetation means herbivores can increase N→ V → H → P - Top down: predation controls community organization because predators limit herbivores…. - AKA trophic cascade model - Biomanipulation: attempts to prevent algal blooms by altering the number of higher level consumers 54.3: Disturbance influences species diversity and composition - FE Clements: argued in early 1900s that the community of plants at a site had only one stable equilibrium, a climax community controlled solely by climate - Biotic interactions caused species to work together - AG Tansley: challenged climax community and said differences in soils, topography and other factors created many potential communities that were stable within a region - HA Gleason: saw communities as chance assemblages of species found together because have similar abiotic requirements - Disturbance: even such as a storm, flood, grought, that changes a community by removing organisms from it or altering resource availability - Nonequilibrium model: describes most communities as constantly changing after disturbance Characterizing Disturbance - Intermediate disturbance hypothesis: states that moderate levels of disturbance foster greater species diversity than do high or low levels of disturbance - High and low levels reduce diversity - In some cases small and large disturbances can have important effects on community structure Ecological Succession - When an area is disturbed and replaced by other species - Primary succession: process begins in a virtually lifeless area where soil hasn’t formed yet - Only present are prokaryotes and protists - Facilitate: when early arrivals influence the appearance of later species by making the environment more favorable - Inhibit: opposite - Glacier Bay, AK 1: pioneer (liverworts, mosses scattered dryas), 2: (30 years.. Dryas dominate), 3: (decades later area is invaded by alder), 4: 20o years (alder overgrown by Sitka spruce and later by hemlock) - Secondary succession: occurs when an existing community has been cleared, but soil is still intact Human Disturbance - Strongest disturbances (agriculture, lumber harvesting, grazing)

54.4 Biogeographic factors affect community diversity Latitudinal Gradients - Two key factors that affect: evolutionary history and climate - Tropical communities are generally older than temperate or polar communities which started over after glaciations - Thus diversity may be highest in tropics - Climate is another factor: sunlight and precipitation (occur at high levels in tropics) - Evapotranspiration: evaporation of water from soil and plants - Potential evapotranspiration: a measure of potential water loss that assumes that water is readily available (determined by amount of solar radiation and temp) Area Effects - Alexander von Humbdoldt described the first pattern of species richness: species area curve which is the larger the geographic area of a community the more species it has - S=cA^z (where S=# species in habitat, c=constant, A=area of habitat, z=how many more species should be found in a habitat as its area increases) Island Equilibrium Model - The number of species on an island reps a balance between immigration of new species to the island and the extinction of species already there - Immigration rate decreases as # of species on island increases which extinction rate increases - 2 physical features affecting immigration and extinction are size and distance from mainland 54.5 Pathogens alter community structure locally and globally - Pathogens: disease causing microorganisms, viruses, viroids, or prions - Produce especially clear effects when introduced into new habitats Pathogens and Community Structure - Highlighted in coral reef communities - Also seen in terrestrial ecosystems such as sudden oak death Community ecology and zoonotic diseases - Zoonotic: transferred from animals to humans - Vector: means of intermediate species 55.3 energy transfer between trophic levels is typically only 10% efficient - Secondary production: the amount of chemical energy in consumers food that is converted to their own new biomass during a given period Production efficiency

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Production efficiency= (net secondary production *100%)/assimilation of primary - Percentage of energy stored in assimilated food that is used for GROWTH and REPRODUCTION not respiration Trophic Efficiency and Ecological pyramids - Trophic efficiency: percentage of production transferred from one trophic level to the next - 5%-20% Diversity- measure that captures the # of different taxa (S) and or their relative abundances Structure- the way in which various species present in a community are connected...