Species InteractionsSlide 2Types of ConsumersResourcesSlide 5Renewable ResourcesLimiting ResourcesSlide 8Consumer-resource ExperimentKaren Porter’s DaphniaSlide 11Slide 12Slide 13CompetitionSlide 15What is competition?Slide 17Experimental CompetitionTansley’s Classic StudyThe Common GardenSlide 21Slide 22Tansley’s ConclusionsGeneric Experiment on CompetitionRoots vs. ShootsSlide 26Slide 27Competition in NatureField studies of competitionSlide 30Use of parasitoid wasps to control scale insectsSlide 32Competition Between Distantly Related SpeciesCompetitive ExclusionCompetitive exclusion among ParameciumSlide 36Slide 37Slide 38SummarySpecies Interactions1. Species Interactions2. Resources3. Consuming Resources4. Consumer-resource interactions5. CompetitionSpecies InteractionsCompetition may be interspecific or intraspecificTypes of ConsumersPredatorsParasitoidsParasitesHerbivoresDetritivores“-ivore” means “-eater.” Ecologists talk about insectivores, piscivores, planktivores, folivores, frugivores, granivores....ResourcesResources are “substances” required for maintenance, growth and reproduction.When used, the amount of a resource available to others is reducedResources•Non-renewable resources occur in fixed quantities–habitat space–“released” by a consumer •Renewable resources are continually regenerated–food, soil nutrients, sunlight, rainRenewable ResourcesRenewable resources are those resources that are continually regeneratedLimiting ResourcesA resource whose available quantity cannot meet a population’s requirement for itIf add more of a limiting resource, then population will increase in size since K has changed.However, a different and second resource may now be limiting the population’s size.Consumer-resource ExperimentKaren Porter’s Daphnia•System with a single consumer (Daphnia magna) and a single resource (C. reinhardi)•Treatments: different concentrations of algae•Things measured:–number of algal cells ingested –how often and how many eggs were producedKaren Porter’s DaphniaFiltering RateIngestion RateUnable to assimilate added food (type II functional response)less food needed with higher ingestion rateKaren Porter’s DaphniaKaren Porter’s DaphniaWhy isn’t maximum resources best?r decreases with fewer reproducingIncreased respiration rates from rejecting overcollected food may cause decline in energy for reproductionCompetitionWhat is competition?•Competition is any use or defense of a resource by one individual that reduces the availability of that resource to other individuals.•Competition among individuals may be:–intraspecific (within species)–interspecific (between species)•Competition models predict the winners and losersCompetition leads to decrease in carrying capacityExperimental CompetitionTansley’s Classic Study•First demonstration of competition between closely related species:•Galium saxatile is found on acid, peaty soils•Galium sylvestre is found on limestone hills and pasturesThe Common GardenWhat is our hypothesisWhat are our predictions?Alkaline soilThe Common GardenEach species performed better on its preferred soilEach could grow on the other soil type.The Common Gardeneach species overgrew and shaded the other on its preferred soil typeTansley’s Conclusions•Tansley’s conclusions have far-ranging implications for all competitive situations:–the presence or absence of species can be determined by competition with other species–conditions of environment affect outcome of competition–competition may be felt broadly throughout community–present segregation of species may have resulted from past competitionGeneric Experiment on Competition•Remove, add, swap, substitute species•Observe “performance” as a response variable–growth–reproduction–physiological function–long term: population demographyRoots vs. Shoots•Root competition: water & nutrients•Shoot competition: lightHow do you tell which one matters?Roots vs. Shoots•No competition•Roots together, shoots “apart”•Shoots together, roots, apart•All togetherRoots vs. ShootsCompetition in NatureField studies of competition•Sequential introductions of biological pest controls provide evidence for competitive exclusion among species utilizing a limiting resource:–various species of parasitoid wasps in the genus Aphytis have been introduced to control citrus scale in California citrus groves:•the earliest introduction, A. chrysomphali, was readily displaced by A. lingnanensis•A. melinus subsequently displaced A. lingnanensis in all but the coastal areasScale insects parasitize citrus fruitsecrete waxy cover for defenseUse of parasitoid wasps to control scale insectsCompetition Between Distantly Related Species•Darwin proposed that competition among closely related species (e.g., those belonging to the same genus) should be more intense than competition among distantly-related species:–although this is likely true, distantly-related species often utilize common resources:•krill, shrimplike crustaceans of subantarctic waters, are fed upon by fish, squid, diving birds, seals, and whales•recent reductions in whales (by commercial exploitation) have resulted in expansions of seal and penguin populationsCompetitive ExclusionCompetitive exclusion among ParameciumPredators can drive prey locally extinctMigration mattersHabitat structure mattersCompetitive exclusion amongParameciumG. Gause (Russian ecologist; 1930s) showed extinction among competing populations in lab experimentsCompetitive ExclusionTwo species cannot coexist on a single resource that is scarce relative to the demand for it.Easy to observe in the lab.How do we see it in nature?Opius – braconid waspCompetitive ExclusionTwo species cannot coexist on a single resource that is scarce relative to the demand for it.Summary•Competition is the use or defense of a resource by two or more consumers.•Competition is usually for one or a few limited resources whose supply relative to demand is least.•No two species of competitor can coexist on the same limiting