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Information about Lec9_Slideshow_2007

Published on December 18, 2008

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Slide 1: APS 209 Animal Behaviour Lecture 9 The Evolution of Feeding Behaviour Search Images Social Foraging: Insects, Birds, Mammals Selecting What to Eat: Costs and Benefits Slide 2: Aims & Objectives Aims 1. To describe how animals may help each other in foraging, particularly by sharing information. 2. To present a special reading that builds on the discussion in the chapter. 3. To introduce cost-benefit analysis and optimality. Objectives 1. To understand why some animals living in social groups may not be selected to transfer information deliberately. 2. To understand the logical basis of cost-benefit analysis and optimality, and learn some examples. Slide 3: Search Image Slide 4: Finding Food: Search Image How do predators find their food? Predators and prey are often locked into a co-evolutionary struggle. Prey may evolve to be harder to find and predators better at detecting prey. Tinbergen observed the following. When a certain type of caterpillar started to appear in Dutch woodlands, breeding songbirds rarely brought it back to their nests. But once a few had been brought back, the birds started to collect them at a far greater rate. It was as if the birds had come to recognise the subtle visual characteristics and had formed a search image. Slide 5: Search Images in Humans Slide 6: Testing the Search Image Hypothesis Pietrewicz and Kamil used operant conditioning using blue jays and moths to investigate whether search images occur. Captive blue jays were shown 16 slides, 8 of which had a cryptic moth positioned on an appropriate background. In 1 series, the 8 moths were same species. In the other, 2 species of moth with different colour patterns and resting positions appeared in random order. Slide 7: Testing the Search Image Hypothesis The birds’ performance improved when presented with one species or the other, but not when given both species. Slide 8: Olfactory Search Image Humans are primarily visual creature. This can cause us to be vision-centric when we consider animal behaviour. This is something you must train yourself not to be. Think about the sensory world of any animal that you are studying. Some animals use their sense of smell to find food and may also form the equivalent of a search image but for smells. Or at the least they may learn to associate a particular smell with food. Slide 9: Finding Food By Smell in Skunks Striped skunk is nocturnal and forages at night. It locates food by odour. Young hand reared skunks were allowed to forage for dry dog food in an outdoor enclosure. Food was located at greater and greater distances as they gained experience. Orientation behaviour was shown by its distinctive posture, with nose held high and direct march to food. Slide 10: Maximum distance over which is detected also increases. Finding Food By Smell in Skunks Slide 11: Lizard Foraging: Evolutionary History Slide 12: Social Foraging Slide 13: Getting Help from Companions Animal Groups as Information Centres Social Insects Groups (colonies) composed of related individuals Cooperation is strongly favoured by natural selection (kin selection/inclusive fitness). Deliberate communication with nestmates. Methods include: waggle dancing, direct leading, pheromone trails. Other group living animals Groups normally composed of mostly unrelated individuals. Cooperation less strongly favoured by natural selection (kin selection/inclusive fitness). Incidental communication with conspecifics. Methods: observing foraging orientation of successful foragers Other foraging advantages of being in a group Take prey much larger than themselves wolves taking moose; or army ants large arthropods or other insect colonies. Slide 14: Social Foraging: Waggle Dance and Communication Information Slide 15: Getting Help From Companions Social Insects Groups (colonies) composed of related individuals. Cooperation is strongly favoured by natural selection (kin selection, inclusive fitness). If worker A helps worker B gather more food this is as good to worker A as collecting more food herself, as the food comes back to the same nest. Workers may help each other in capturing prey (e.g., army ants), or defending a food patch (ants, some stingless bees). The most common means of helping each other is by communicating the location of food to nestmates. There are many methods including: waggle dances in honey bees and direct leading and pheromone trails in ants. Slide 16: Honeybee Foraging Honeybees forage for pollen, nectar, water and propolis Workers that have found a good source of pollen or nectar communicate the location to nestmates by a dance If food is close (<50m), the bees perform a ‘round dance’ Slide 17: The Waggle Dance If food is more distant, then foragers perform a waggle dance Slide 18: The Waggle Dance In the nest, the dances are performed on vertical combs in darkness Slide 20: Dancer (forager) Dance Followers (unemployed foragers) The Waggle Dance Slide 21: Waggle Dance: Communicating Direction In a ‘fan test’ Karl von Frisch trained scout bees to a feeder at F. He then put out feeders of equal attractiveness at all 7 feeding stations and counted the recruits. More arrived at the advertized location, F, than other equidistant locations. Slide 22: Train bees to a feeder 750m from hive. These bees dance in the hive. Capture recruits at feeders at different distances in the same direction. The training distance gives most recruits. Waggle Dance: Communicating Distance Slide 23: Removing Directional Information Honey bee foragers will dance on horizontal combs. They will orient the dance to light instead of to gravity if there is a strong directional light source. But if there is no directional light source they will dance in random directions. By making the combs horizontal (which they are not in nature) and having no directional light source it is possible to remove the directional information provided in the dances. In this way, it is possible to compare the recruitment to a food source of bees from normal hives, with informative dances, to bees from horizontal hives where dances are non-informative. Slide 24: Removing Directional Information A larger proportion of the recruits come to the advertized site when combs are vertical. Slide 25: Recruits are more tightly bunched around advertized site when combs are vertical than horizontal. Removing Directional Information Slide 26: Benefits of Waggle Dance By following waggle dances, honeybee foragers do not find flowers faster. But they do find better quality flowers. This is because only bees who are working a high quality patch of flowers make dances. Slide 27: Social Foraging: How Waggle Dance Improves Colony Foraging Special Reading: Honeybee colonies achieve fitness through dancing : Special Reading: Honeybee colonies achieve fitness through dancing Slide 29: Does Dancing Improve Foraging? Test by comparing the weight gain in hives with waggle dances without waggle dances Problem: It is not possible to prevent dancing. Solution: It is possible to cause disoriented dancing (no direction information). Method: Compare the weight gain in hives with correctly oriented waggle dances with disoriented waggle dances Prediction: hives with oriented waggle dances collect nectar more efficiently, leading to greater weight gain. Sherman, G., Visscher, P. K. 2002. Honeybee colonies achieve fitness through dancing. Nature 419: 920-922. Slide 30: Observation Hives Used V. Vertical O. Oriented Light (Horizontal) D. Diffuse Light (Horizontal) Foragers in horizontal observation hives with diffuse light make disoriented dances. Those in vertical hives or horizontal hives with oriented light correctly oriented dances. Slide 31: Does Random Dancing Affect Recruitment? Syrup feeder Syrup feeder 250m 250m north south south north 2. Repeat (1) but to opposite feeder 1. Train foragers from each hive to a feeder, allow to dance, and count recruits to feeder 3. Repeat (1, 2) for 400m and 460m feeders 250m 250m Slide 32: Recruitment to Syrup Feeders N hive S Trial 1 250m N hive S Trial 2 400m N hive S Trial 3 460m No. of recruits 151 19 15 8 18 2 recruits to feeder 100% 50% 0% Oriented light Diffuse light On average, one third as many recruits came to the feeders visited by foragers from the diffuse light hives as the oriented light hives. This indicates that waggle dances in diffuse light hives were not working. Slide 33: Results: Hive Weight Changes +300g In all three seasons the hives with oriented light do better than those with diffuse light. But this difference is only significant in winter. Over all three seasons the difference is significant. -300g Summer P = 0.22 Autumn P = 0.85 Winter P = 0.0005 Oriented light Diffuse light Change in hive weight over 11-day period Slide 34: Analysis of Variance of Change in Hive Weight Source of Variation d.f. Probability Season (summer, autumn, winter) 2 0.0001 highly significant 11-day period within season 16 0.0001 highly significant Colony pair 1 0.0693 not significant Colony within pair 2 0.268 not significant Light treatment (diffuse, oriented) 1 0.0038 highly significant Season x light treatment 2 0.0319 significant Residual 51 Anova shows that season and period both have an effect. This is not surprising. Some seasons are better than others and some 11 day periods are better than others. Light treatment also had a significant effect, with colonies subjected to oriented light gaining more weight. There was also a significant interaction of season and light treatment meaning that the effect of the light treatment varied among seasons. Overall, this means that dances are useful, and are more useful in some seasons that others. Slide 35: Social Foraging in Birds Slide 36: Social Foraging in Birds: Ospreys In some coastal areas, ospreys (large fish-eating hawks) form loose gregarious nesting colonies. Shoaling fish are a particularly good prey item. Do ospreys watch colony mates to find fish? Slide 37: Getting Help from Companions: Ospreys Departing ospreys leave in all directions (A). But if an osprey returns with a fish, others may leave in that direction (B). Information is not deliberately communicated, and the forager probably receives little or no benefit (and maybe even a cost) for informing other birds where fish are. Slide 38: Getting Help from Companions: Ospreys Informed birds find fish more quickly than naïve birds. If this were not the case, then there would be no benefit in receiving information. Slide 39: Getting No Help from Companions: Swallows Barn swallows nest in colonial aggregations If they gain information on food location from successful colony mates then unsuccessful foragers should tend to follow a successful departing neighbour. But they do not (see slide). In addition, successful foragers were no more likely to be followed than unsuccessful ones Slide 40: Getting No Help from Companions: Swallows Slide 41: Group Hunting Slide 42: Army Ant Colony Small ants can capture larger prey by working together. Slide 43: Group Hunting in Female Lions African lion females live in groups and hunt together. Slide 44: Group Hunting Social carnivore mammals can capture prey weighing between 6-12 times as much as any one adult hunter. Solitary carnivores typically hunt much smaller prey species This is a common pattern across carnivores in unrelated taxa (hyenas, cats, dogs). Also, divergence in some groups between related species The ‘comparative method’ indicates that group hunting is a behavioural adaptation for hunting larger prey. Slide 45: Group Hunting Singletons often eat as much or more than group hunters. So why group? Small groups do not disband during times of prey scarcity Slide 46: Group Hunting Why continue to hunt in groups? Creel and Creel pointed out that benefit in terms of meat gained is only half the equation. There are also costs in terms of energy expended chasing prey etc. Are group hunters actually maximizing the difference between energy gained and energy expended?? They studied this in African wild dogs. Slide 47: African Wild Dogs Slide 48: African Wild Dogs The Creels measured weight of meat gained by wild dogs in packs of between 3 and 20. Measured costs in terms of distance run during hunting. They calculated:1) meat gained per dog per day; 2) meat gained per dog per day minus energetic cost of hunting. Slide 49: Selecting What to Eat: Costs & Benefits Slide 50: Selecting What to Eat: Costs & Benefits Optimality logic Selection will favour animals that forage more efficiently. Costs and benefits of different behaviours e.g., maximising food intake per unit time When a hypothesis based on cost benefit logic is found to be incorrect this can lead to further insights, such as an additional factor that affects foraging efficiency. In the study of oystercatchers feeding on mussels, it was found that some large mussels were impossible to open. Optimality modelling To determine the best course of action for an animal e.g., maximising food intake per unit time Frequently graphical models, simple underlying mathematics Slide 51: Oystercatchers: Choosing Mussels Predictions of two cost benefit models The oystercatchers do better by selecting larger mussels (Model A) as these yield more food. But when only mussels that can successfully be opened are considered, the optimum size of mussel is not as large as possible, but c. 50mm. This matches better with observations, which show that birds do not select both small mussels, and the very largest. Slide 52: Whelk Choice by Northwestern Crows Observations Northwestern (USA) crows drop whelks on rocks to break them open. Always select large whelks, drop them from c. 5m. Keep dropping a whelk until it breaks. Data. Dropping whelks from a tower. Slide 53: What Would You Predict if…... What differences from the observed behaviour would you predict if 1. Some whelks are impossible to break open 2. Robber birds are present which steal dropped whelks 3. Small whelks are much easier to break open than large whelks 4. Only small whelks are present Slide 54: Social Foraging: Pharaoh’s Ant Trails Slide 55: Trail Re-establishment Slide 56: Antennae Down Slide 57: Antennae Up Slide 58: Trail Re-establishment

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