4/24/08. Behavioral Ecology / Evolutionary Ecology

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1 Behavioral Ecology / Evolutionary Ecology What is it? How to study it? Optimal Foraging Optimal Clutch Size Optimal vs. Stable Flock Size Behavior in a changing environment Niko Tinbergen ( ) Two ways to ask why? Proximate Questions how... genetic, development, sensory or hormonal mechanisms. Ultimate Questions function, evolutionary history Ecological cues Studying ultimate causes: is it adaptive? Behavioral Response experience Several ways to study: Study process of natural selection Variation, heritability, fitness effects, then study change across time Ideal approach but often not feasible evolution Optimality approach Fitness effects Evolutionary Stable Strategy (ESS) approach

2 Optimality Theory Look at phenotypic selection within generations ASSUMPTION: individuals are selected to MAXIMIZE FITNESS GOALS: Make a simple model can we explain what we see? If not, identify the constraints that limit adaptation Process: (a) make model Identify costs and benefits of behavioral trait Identify currency that is under selection Build simple model (b) test model with empirical data Optimal Foraging Set up: parent with offspring in nest. Need to bring back food. Q: How long should you stay in an area to forage? Benefit more time in patch = more food Cost more time in patch = slower rate of finding food What is the currency under selection here? Test of the optimal foraging model Prediction: For a given patch, birds should take more worms from farther patches Study done on European starlings (Kacelnick) Treehole nesters (can use bird boxes) Will readily consume worms put out in experimental feeders Experimental design: Distance A Distance C Can control the rate of food coming out conveyor belt design Test of the optimal foraging model Results: Starlings did optimize the rate at which they brought worms back to their nestboxes Nest Distance B

3 4/24/08 Lessons Learned Optimal Foraging Optimality model can help identify the currency of selection In this case, it is the RATE of bringing food to nest We can predict how foraging strategy might change with different ecological conditions. If you re further away, spend more time and bring back more food Optimality approach 2: Optimal clutch size in birds Tree swallows : - Forage in nearby marshes - Feed chicks every 3~5 minutes - Load size: small mouthfull (~10 mayflies) Optimal Foraging by Dai Distance 2 blocks 3x / week, ~1 bag 15 minutes 1~2x / week, ~2 bags 45 minutes 1x / 10 days, 4~5 bags Emperor Penguins: - Forage ~70 miles away - Foraging trip = 3 months! - Load size: big belly full of fish Clutch size of Parus major in England (Perrins and Moss 1975) Experiment: Add more eggs and see how many they raise -They could raise 10~12 chicks -But average clutch size was 8.5 eggs Question: How many eggs should you lay? More eggs = more potential offspring More eggs = less resource per offspring -General pattern is right, but exact number is not correct -Should we throw out the model?

4 Lessons Learned Optimal Clutch Size Sometimes empirical data does not fit model EXACTLY. Leads to further understanding of what is important under selection Important currency is NOT survival of a clutch, but LIFETIME REPRODUCTIVE SUCCESS Large clutch has costs in future survival of parents, clutch size the next year, Also, environmental variation across years = optimal clutch size is different every year. Living in groups optimality vs. stability Northern Bobwhite Q: How large should the flock be? Benefits reduced predation Costs more competition for food What is the optimal size of the flock? Testing optimal flock size (Williams et al. 2003) Bobwhites and other quails form coveys Tested how covey size affects flock stability and individual survival There was indeed an optimal flock size Lessons Learned Flock size There is a flock size that is optimal from the flock member s perspective Flock size was stable (no birds left) even past optimal flock size But what is optimal is not always what you see influenced by what is STABLE Ecology includes what other individuals are doing, and how that influences you That is the essence of Evolutionary Stable Strategy approach in behavioral ecology Williams et al. 2003

5 Behavior in a changing environment Behavior is a response to external cues But the environment keeps changing. How does behavior change when ecology changes? Oak budding date Moth egg hatching date Insects hatch earlier as climate gets warmer Q: How will climate change affect bird migration? Proximate factors in bird migration: Timing of migration tied to photoperiod Timing of breeding tied to amount of food van Asch et al and birds breed earlier in response to earlier bug season So no effect of climate change on birds?? Laying date (Jan.1 = 1) Dunn and Wi But timing of migration hasn t changed! (Both and Visser 2001) Summary: Climate change and birds? Pied flycatcher Temperature increase in Netherlands Birds start laying early but they haven t been arriving earlier The time between arrival and breeding has decreased! This has led to population decrease Mismatch in the external cues used in migration vs. breeding leads to population decline Understanding PROXIMATE mechanism helps us predict how behavior will be affected with climate change The ULTIMATE effects of behavior helps us predict how populations will be affected QUESTION: How quickly will behavior evolve?