Interspecific InteractionsThe NicheTypes of Interspecific InteractionsNeutralismCompetitionTypes of CompetitionExample of Interference CompetitionOutcomes of CompetitionThe Competitive Exclusion PrincipleEvidence for Competitive Exclusion.Slide 11Other experiments...Resource PartitioningSlide 14Example of Resource PartitioningCharacter DisplacementExample of Character DisplacementCompetition and the NicheTwo organisms cannot occupy exactly the same niche.AmensalismSlide 21Example: Allelopathy in the California ChaparralCommensalismSlide 24MutualismExamples of MutualismMutualistic SymbiosisFacultative vs. Obligate MutualismsOther Examples of MutualismsShort DiscussionPredation, Parasitism, HerbivorySlide 32Slide 33Slide 34Slide 35Slide 36Slide 37Predator-Prey and Parasite-Host CoevolutionSlide 39Example of Parasite-Host CoevolutionPredator-Prey Population DynamicsSlide 42Example of Regulation of Host Population by a HerbivoreSlide 44Slide 45The time-lag effect may lead to predator-prey oscillations.Cycles in the population dynamics of the snowshoe hare and its predator the Canadian lynx (redrawn from MacLulich 1937). Note that percent mortality is an elusive measure, it may, or may not, be useful since mortality varies with environment and time.Slide 48Slide 49Interspecific InteractionsReading: Freeman, Chapter 49The NicheThe niche is one of the most important concepts in ecology. Paradoxically, it is also one of the hardest to define (Ecology is still a young science). In essence, an organism’s niche is how it makes a living: the environmental conditions it tolerates, the important resources it needs to survive, and its ways of obtaining those resources.In obtaining energy, nutrients, etc.. a populations of one species frequently interact with populations of other species.Types of Interspecific Interactions Effect on Effect on  Species 1 Species 2Neutralism 0 0Competition - -Commensalism + 0Amensalism - 0Mutualism + +Predation, - +Parasitism, HerbivoryNeutralismNeutralism the most common type of interspecific interaction. Neither population affects the other. Any interactions that do occur are indirect or incidental.  Example: the tarantulas living in a desert and the cacti living in a desertCompetitionCompetition occurs when organisms in the same community seek the same limiting resource. This resource may be prey, water, light, nutrients, nest sites, etc.Competition among members of the same species is intraspecific.Competition among individuals of different species is interspecific.Individuals experience both types of competition, but the relative importance of the two types of competition varies from population to population and species to speciesTypes of CompetitionExploitation competition occurs when individuals use the same limiting resource or resources, thus depleting the amount available to others.Interference competition occurs when individuals interfere with the foraging, survival, or reproduction of others, or directly prevent their physical establishment in a portion of a habitat.Example of Interference CompetitionThe confused flour beetle, Triboleum confusum, and the red flour beetle, Triboleum castaneum cannibalize the eggs of their own species as well as the other, thus interfering with the survival of potential competitors.In mixed species cultures, one species always excludes the other. Which species prevails depends upon environmental conditions, chance, and the relative numbers of each species at the start of the experiment.Outcomes of CompetitionExploitation competition may cause the exclusion of one species. For this to occur, one organism must require less of the limiting resource to survive. The dominant species must also reduce the quantity of the resource below some critical level where the other species is unable to replace its numbers by reproduction.Exploitation does not always cause the exclusion of one species. They may coexist, with a decrease in their potential for growth. For this to occur, they must partition the resource.Interference competition generally results in the exclusion of one of the two competitors.The Competitive Exclusion PrincipleEarly in the twentieth century, two mathematical biologists, A.J. Lotka and V. Volterra developed a model of population growth to predict the outcome of competition. Their models suggest that two species cannot compete for the same limiting resource for long. Even a minute reproductive advantage leads to the replacement of one species by the other.This is called the competitive exclusion principal.Evidence for Competitive Exclusion.A famous experiment by the Russian ecologist, G.F. Gausse demonstrated that Paramecium aurellia outcompetes and displaces Paramecium caudatum in mixed laboratory cultures, apparently confirming the principle. (Interestingly, this is not always the case. Later studies suggest that the particular strains involved affect the outcome of this interaction).Other experiments...Subsequent laboratory studies on other organisms, have generally resulted in competitive exclusion, provided that the environment was simple enough.Example: Thomas Park showed that, via interference competition, the confused flour beetle and the red flower beetle would not coexist. One species always excluded the other.Resource PartitioningSpecies that share the same habitat and have similar needs frequently use resources in somewhat different ways - so that they do not come into direct competition for at least part of the limiting resource. This is called resource partitioning.Resource partitioning obviates competitive exclusion, allowing the coexistence of several species using the same limiting resource.Resource partitioning could be an evolutionary response to interspecific competition, or it could simply be that competitive exclusion eliminates all situations where resource partitioning does not occur.Example of Resource PartitioningOne of the best known cases of resource partitioning occurs among Caribbean anoles.As many as five different species of anoles may exist in the same forest, but each stays restricted to a particular space: some occupy tree canopies, some occupy trunks, some forage close