Ch16 Competition.docx

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Spencer Barrett

BIO120H © Lis| Page 1011 chapter 16: COMPETITION  closely related plant species living in the same region often grow in diff. habitats or on diff. types of soil  ecological segregation resulted from competition for resources, A.G. Tansley leading to the exclusion of one species (ecological  saxatile lives on acidic, peaty soils segregation  sylvestre lives on alkaline soils of limestone hills and pastures resulted from  planted them singly and together w/ the 2 diff. soils competition)  results:  planted alone  grew and maintained itself on both soils (but bedstraws (genus most vigorous on natural soil type) research study G.  together on calcareous (limestone) soils  sylvestre overgrew saxatile, G. and shaded saxatile sylvestre  together on acidic, peaty soils  saxatile overgrew  thus, species are restricted to the most favourable soil when competing species are present, but can broadly be distributed over other soils in the absence of competition  the presence or absence of a species could be determined by compet. w/ other species  the conditions of the envmt affected the outcome of the compet.  the present ecological segregation of species might have resulted from competition in the past  ccompetition any use or defence of a resource by one indiv. that reduces the availability of that resource to other indiv.  iintraspecific competition competition b/w indiv. of the same species  iinterspecific competition competition b/w indiv. of diff. species  more crowded = stronger effects of compet.  compet. can depress the pop. of both species  superior competitors can persist at lower resource levels, thus curtailing the other pop. and replace it (it will outcompete) CONSUMERS COMPETE FOR RESOURCES  DDavid Tilman  resource: any substance or factor that is both consumed by an org. and supports increase pop. GR as its availability in the envmt increases  a resource is consumed and its amount or availability is reduced  a consumer uses a resource or its own maintenance and growth  when resource availability is reduced, biological processes are affected in such a way as to reduce consumer pop. growth  resources for sessile animals: (not only food)  space (open, available sites)  crowding increases adult mortality and reduces fecundity (limit growth of adults, and recruitment o larvae)  they “consume” open space  ex. barnacles attached to rocks  refuges and other safe sites (are also resources)  each habitat has limited # of holes, crevices, or patches  temp. is not a resource  org. don’t consume it, but can still limit the growth of pop. BIO120H © Li| Page 22011 Competition Between Closely and Distantly Related Species  Charles Darwin  compet. should be most intense b/w closely related species  “As species of the same genus have usu., though by no means invariably, some similarity in habits and constitution, and always in structure, the struggle will generally be more severe b/w species of the same genus, when they come into compet. w/ each other, than b/w species of distinct genera”  similar structure = similar function  distantly related org. also use same resources Renewable and Nonrenewable Resources  nonrenewable resources: resources that are not regenerated  ex. space (only “replenished” when consumer leaves)  renewable resources: constantly regenerated/renewed  ex. birth of prey provides continual supply of food for predators  types of renewable resources:  some renewable resources originate beyond the influence of consumers ex. sunlight  thus, consumers reduce its immediate availability but not their supply  the resource doesn’t respond to consumption  generated w/in the ecological sys.  predator-prey, herbivore-plant, parasite-host  supply of prey, plants, and hosts is constantly regenerated  by reducing pop. of resources, they reduce rate of renewal  regenerated w/in ecosystem linking indirectly to their consumers  through food chain links or abiotic processes  ex. nitrogen cycle: plants assimilate nitrate from soil  herbivores eat plants  return nitrogen to soil  broken down by microorganisms  release nitrogen as nitrate  plants use o uptake of nitrate by plants indirectly effects on its renewal by detritivores o consumption of detritus doesn’t immediately affect plant production (do affect indirectly through the rate they release N into soil) Limiting Resources  Justus von Liebeg  Justus von Liebeg  Liebig’s law of the minimum: the principle that the growth of a pop. is limited by the resource whose supply is most scarce relative to demand (the limitilimiting resource  each pop. increases until the supply of the limiting resource no longer satisfies the pop.’s need for it  law applies only to reaources having an independent influence on the consumer pop.  sometimes, more than 2 or more resources interact to determing the pop.’s GR  when two resources together enhance the growth of a consumer pop. more than the sum of both indic., the resources are synergistic  seeds in fertilized and unfertilized (control) soil W. J. H. Peace P.J. Grubb  exposed seedlings to diff. levels of light  results:  added light enhanced growth of ferti. more than controls Impatiens  thus, ability to use light depends on the availability of other parviflora (herbaceous resources research study  plant growth needs C from photosynthesis and CHO, N, P plant)  N and P were shown to interact synergistically to enhance growth BIO120H © Lis| Page 3011 FAILURE OF SPECIES TO COEXIST IN LABORATORY CULTURES LED TO THE COMPETITIVE EXCLUSION PRINCIPLE  typical experiments to determine effect of one species on pop. growth on another:  2 species grown separately  carrying capacity determined  species were then grown together (interspecific competition)  intensity of competition was the measure of the difference b/w the pop. growth of one species in the presence and absence of the other  competitive exclusion principle: the principle that 2 or more species cannot coexist competitive exclusion principle indefinitely on the same limiting resource  so how much diff. in resource requirement allow for coexistence? THE THEORY OF COMPETITION AND COEXISTENCE IS AN EXTENSION OF LOGISTIC GROWTH MODELS  (p. 334) Coexistence on Multiple Resources  when 2 species compete for 2 limiting resources needed in diff. amounts by each species, certain combinations of resource abundance allow the species to coexist  both require silicon and phosphorus (in diff. relative amounts)  PG of Cyclotella was equally limited by Si and P when ratio Si/P=6  Asterionella (need more Si) Si/P=90 David Tilman  at nutrient ratios below these levels, each of the species is Si- limited; above, P-limited (coexistence)  Cyclotella uses Si more efficiently (able to increase on lower Si 2 diatom species supplies) – same w/ Asterionella and P  predicted that they should coexist in culture b/w Si/P ratios of 6 Cyclotella and and 90 research studyella  C limited by P  A limited by Si  thus, the
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