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SJSU ENGR 100W - Sea Otter Diets & Population Status

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Sea otter diets & population status: Causes and consequences of individual foraging specializationsConsumer-prey interactions represent one of the central themes of ecologyToday’s Presentation Niche breadth and the economics of consumer diet choiceOptimal Diet Choice Expected Diet ( Population-level)Alternative Explanation….How to distinguish between these two scenarios?Foraging Studies of Sea otters along Central Coast of CaliforniaA Fortuitous ExperimentSan Nicolas IslandHypotheses:Study Methods Study Methods Study Methods Checking our assumptionsChecking our assumptionsComparison ResultsWhy would animals specialize at low food availability?Predictions for behaviorally-mediated foraging polymorphismBehavioral Variables Cluster Analysis of Behavior VariablesPerformance Advantage?PART 1 ConclusionsPart 2: Conservation implications of dietary specialization:Toxoplasma gondii in sea ottersToxoplasma gondii life cycleSea otter Health Data Merging Ecology and Health DataFactors Increasing Risk of Toxoplasma gondii ExposureFactors that Reduce Risk of Toxoplasma gondii ExposureHigh Risk Exposure AreaResults of similar risk analysis for Sarcocystus neurona exposureIncreasing Risk of Sarcocystis neurona ExposureSeafood Guide for Sea OttersPART 2 ConclusionsFinal ConclusionThank-youHow to measure Rate of Energy Intake by a feeding sea otter?Sea otter diets Sea otter diets &&population status:population status:Causes and consequences of individual Causes and consequences of individual foraging specializationsforaging specializationsM. Tim TinkerM. Tim TinkerUSGS USGS --BRDBRDWestern Ecological Western Ecological Research CenterResearch CenterandandEE Biology,EE Biology,UC Santa CruzUC Santa CruzConsumerConsumer--prey interactions represent prey interactions represent one of the central themes of ecologyone of the central themes of ecologyTodayToday’’s Presentation s Presentation PART 1. Individual specialization as a behavioral PART 1. Individual specialization as a behavioral response to reduced food availabilityresponse to reduced food availability(Primary Collaborators: J. Estes and G. Bentall)(Primary Collaborators: J. Estes and G. Bentall)PART 2. Conservation implications of PART 2. Conservation implications of individual foraging specializations: a case study individual foraging specializations: a case study (Primary Collaborator: C. Kreuder(Primary Collaborator: C. Kreuder--Johnson)Johnson)Niche breadth and Niche breadth and the economics of the economics of consumer diet choiceconsumer diet choiceIn general, predators are In general, predators are expected to select prey in such a way as to expected to select prey in such a way as to maximize their lifetime fitnessmaximize their lifetime fitnessTheoretical and Empirical studies suggest that Theoretical and Empirical studies suggest that dietary diversity (predator niche breadth) dietary diversity (predator niche breadth) increases as food availability decreasesincreases as food availability decreasesOptimal Diet Choice Optimal Diet Choice Rank potential prey according to rate of energy Rank potential prey according to rate of energy gain:gain:Add prey types to diet until:Add prey types to diet until:Prediction:Prediction:when profitable prey types are abundant, when profitable prey types are abundant, predator diet breadth should be narrow predator diet breadth should be narrow 332211hehehe>>11111++==>+∑∑jjjiiijiiiheeeλλExpected Diet ( PopulationExpected Diet ( Population--level)level)Empirical support from crossEmpirical support from cross--sectional dietary data sectional dietary data (fecal composition and stomach(fecal composition and stomach--content analysis, etc.)content analysis, etc.)AssumptionAssumption: diets of con: diets of con--specifics are similarspecifics are similarLow Predator DensityHigh Predator DensityAlternative ExplanationAlternative Explanation……..In this scenario, same population pattern In this scenario, same population pattern produced by specialization and diversification produced by specialization and diversification of individual dietsof individual dietsLow Predator DensityHigh Predator DensityHow to distinguish between these How to distinguish between these two scenarios?two scenarios?Fairly Stringent Requirements: Fairly Stringent Requirements: experimental manipulation of food abundanceexperimental manipulation of food abundancecontrol for environmental effects, age/sex effects, control for environmental effects, age/sex effects, genetic differences genetic differences longitudinal dietary data from individualslongitudinal dietary data from individualsFew opportunities to test, particularly for Few opportunities to test, particularly for large vertebrates large vertebratesForaging Studies of Sea otters Foraging Studies of Sea otters along Central Coast of Californiaalong Central Coast of CaliforniaResource-limited pop’n?o High mortality rateso Poor body conditiono High % time feedingo Very diverse dietEasy to observe feedingo Near-shore distributiono Bring all prey to surfaceA Fortuitous ExperimentA Fortuitous Experiment1982 Recovery Plan 1982 Recovery Plan recommended recommended establishment of a establishment of a secondary colonysecondary colonySan Nicolas Island was San Nicolas Island was selected as preferred siteselected as preferred siteBetween 1987Between 1987--1990, 1990, sea otters were sea otters were translocatedtranslocatedfrom central from central CA to San Nicolas Island CA to San Nicolas Island 200 0 200 400 KilometerNEWS200 0 200 400 KilometerNEWSSan Nicolas IslandSan Nicolas IslandCentral Central CA rangeCA rangeSan Nicolas IslandSan Nicolas Island Remote population, distinct from the mainland range Population still small (N ~ 35 animals),food abundant  Current sea otters only 1-2 generations removed from founders  Perfect candidate for comparative studies: low population density at San Nicolas (SN) vs. high population density in range center (RC) Sea Otter Density/km20.00.51.01.52.02.53.0RCSNHypotheses:Hypotheses:At low population density, when food At low population density, when food is abundant, individuals converge on is abundant, individuals converge on single single ““bestbest””dietdiet……small niche small niche breadthbreadthAt high population densities, when At high population densities, when


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