Bio 3400 1nd Edition Lecture 28 Outline of Last Lecture I Interspecific competition II Lotka Volterra models III In class activity Outline of Current Lecture I Competition II Niche differentiation III Character displacement IV Exploitative Interactions V Diet width VI Optimal foraging theory Current Lecture I Competition a Competitive exclusion or coexistence Lotka Volterra models b What values should you compare to figure out if intraspecific competition is stronger than interspecific competition i Both species have a larger effect on themselves than on the other species c What form of competition intra within species or inter between species would you generally expect to be stronger i Competitive exclusion principle 1 If two competing species coexist in a stable environment they cannot have identical niches 2 Niche divergence intraspecific within one species competition stronger than interspecific competition coexistence ii Bed straw example 1 Both species can thrive alone but together they exclude the other iii Another example Balanus acorn cannot live in upper zone due to dessication drying out 1 Chthamalus settles in the middle but does not persist 2 Experiment exclude balanus chthamalus thrives control chthamalus excluded d How does niche differentiation evolve i Imagine two species of birds that are using similar seed resources Consider species 1 If there is variation in beak size and individuals with These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II III IV V VI larger beaks can eat seeds outside the typical range eaten by the two species how would you expect this to influence fitness What would you expect to happen over time 1 Character displacement changes in the physical characteristics of a population as a result of natural selection for reduced interspecific competition 2 Greater trait differences in sympatry same location than in allopatry different location 3 Mean phenotypes of species in an assemblage tend to be evenly spaced character displacement a character displacement is difficult to demonstrate definitively b show difference observe today is from competition that occurred in the past c there are several alternative hypotheses to test i patterns are pure chance ii differences in sympatric and allopatric populations are not genetic environmental iii patterns are outcome of species sorting biased extinction of species similar to resident species iv traits are not related to resource use v patterns stem from interactions other than competition Exploitative Interactions a True predators i Kill prey immediately ii Consume most or all of prey iii Affect many different individuals b Grazers i Rarely lethal effect ii Remove part of prey iii Affect many different individuals c Parasites i Rarely lethal effect definitely not immediate ii Consume part of prey iii Affect one or very few individuals How do predators and prey influence each other s population dynamics a Cycles lynx and hare example b Food comes first Is predation the only factor affect showshoe hare populations a Food and fertilizer also are proved to have an effect Diet width a Specialists i Feed on a single or few prey types ii Most parasites iii Some herbivores VII b Generalists i Feed on many prey types ii Many true predators iii Some herbivores iv Often have strong food preferences Optimal Foraging Theory a Assumptions i Foraging behavior has evolved via natural selection ii Fitness is maximized by maximizing energy intake b Expenses time and energy of foraging i Searching ii Handling c Gain in foraging i Prey types that vary in energy content d Predictions i If handling times are short compared to search times long search predators should be generalists ii If handling times are long compared to search times predators should be specialists iii In environments where prey is less abundant predators should be more generalist