Community Ecology Interactions among species living in the same place Reading AssignmentInteractions in communitiesSpecies InteractionsDescribing InteractionsRelations of humans and cattleBiological CompetitionAlone versus TogetherInteractions among Algal speciesResources that might limit algaePopulation Size Outcomes when two species are grown togetherOther ways to look at competitionNiche OverlapCompetitive Exclusion PrincipleExperimental CompetitionNiche DifferentiationMutualismMutualism Examples Distantly RelatedRhizobium-Legume MutualismMutualism Examples Closely RelatedMutualisms involving AntsSlide Number 22Ants & TreehoppersProblem/SolutionVocabularyx3 lecture #6 UIC BioS 101 Nyberg 1Community Ecology Interactions among species living in the same placeIndividuals may utilize the same resource, but they may also cooperate to gain a resource. Populations interact with one another as well. Today we consider competition and mutualism as interactions between species.x3 #6 UIC BioS 101 Nyberg 2Reading Assignment• Today’s reading is Chapter 53, pages 1058 - 1062, 1068-1070 plus pages 509-512 on How microbes affect global change.x3 #6 UIC BioS 101 Nyberg 3Interactions in communities• There are normally many species living together in the same area. What are the possible interactions among individuals in a community?• Abundance and habits of individuals are an important part of interactions.• Individuals in common species have many intraspecific interactions.• Individuals in rare species mostly interact with common species, interspecific interactions.Species Interactions• A simple categorization of effects of interactions is to consider species in pairs• focusing effects on abundance when grown together (mixed) versus alone.• In this lecture we consider competition, a -,- effect where both species have reduced population sizes, when mixed compared to alone and mutualism, a +,+ effect where each species benefits from the presence of the other species.x3 #6 UIC BioS 101 Nyberg 5Describing Interactions• Interaction between species as seen in population sizes can be pretty complex as subpopulations (eg juveniles vs adults) may interact differently.• The roles of short-term behavioral interactions may not translate to populations.• The relations of populations may be conditional on abiotic variables of the environment.Relations of humans and cattle• People eat cattle, so one usually thinks of humans as predators and cattle as prey, a +, - interaction but...• The size of the human population has been increased by cattle and the abundance of cattle has definitely been increased by people, so• Human, cattle relationship is mutualism, +,+.x3 #6 UIC BioS 101 Nyberg 6x3 lecture #6 UIC BioS 101 Nyberg 7Biological Competition• The operational definition of biological competition is to compare population size when grown together (mixed) versus alone (on the same resource).• Two species are said to be competitors if both species have smaller populations (-, -) when grown together compared to when grown alone.x3 #7 UIC BioS 101 Nyberg 8Alone versus TogetherAbundance Alone & Mixed020040060080010001200alone mixedNumber per mlP. tetraureliaP. caudatumLower together = -,-x3 #6 UIC BioS 101 Nyberg 9Interactions among Algal species• Some algae can be cultured in the lab and you used such species in your lab.• When a single resource is limiting growth of both species, the species are expected to compete, i.e., be less abundant together than alone. • What are the resources algae need?Resources that might limit algae• If one species could grow on the wall of the tube, it could limit access to light.• Algae could compete for nutrients in water.• What else do you think algae might compete for?• Maybe all resources are present in excess.x3 #6 UIC BioS 101 Nyberg 10x3 #7 UIC BioS 101 Nyberg 11Population Size Outcomes when two species are grown togetherPossible Outcomes of Mixing Species0200400600800100012001400AloneCompetitionMutualismIndifferenceN per mlP. tetraureliaP. caudatumx3 #6 UIC BioS 101 Nyberg 12Other ways to look at competition• Niche overlap• Niche is range of resources a species can use.• Overlap of resource use and access to same resources leads to expectation that species will interfere with each others growth.• The greater the overlap the more the interference.x3 #6 UIC BioS 101 Nyberg 13Niche Overlapx3 #6 UIC BioS 101 Nyberg 14Competitive Exclusion Principle• Formulated by G. F. Gause based on experiments with Paramecium and yeast, it states “It is not possible for species with the same niche to coexist”.• Exclusion principle has primarily motivated studies looking for differences between two species. There are always differences between different species.Experimental Competition• Two Barnacles living on rocks along shore.– Chthamalus only above water line– If Semibalanus removed from below water line the Chthamalus could grow below water line. • Semibalanus can not survive above the water line, but below line that species can detach (out-compete) the smaller species.Niche Differentiation• When two species each can utilize a variable resource, competition for the resource can be reduced if each species utilizes different parts of the resource.• Natural selection does not avoid competition, rather poor competitors can persist utilizing parts of the resource that are not utilized effectively by better competitors.x3 lecture #6 UIC BioS 101 Nyberg 17Mutualism• Interactions between two species in which both species have larger populations when together than when alone (+, +).• Some pairs of species are so dependent on one another that one or both species can not survive alone much less be grown alone.x3 #6 UIC BioS 101 Nyberg 18Mutualism Examples Distantly Related• The species involved in a mutualism may be far apart taxonomically– Ants & Fungi– Bees & Plants– Shrimp & Fish– Fungi & protists Lichens, so distinct that they are given ‘species’ namesx3 #6 UIC BioS 101 Nyberg 19Rhizobium-Legume Mutualism• Nitrogen used to be a limiting nutrient for plants in many terrestrial environments.• Lightening is a major source of nitrogen compounds.• Nitrogen fixation by bacteria is another major source of nitrogen compounds.• The symbiosis between legumes and Rhizobium is a source of nitrogen for plants.x3 #6 UIC BioS 101 Nyberg 20Mutualism Examples Closely