Lecture 3 - feeding behaviour Flashcards
why was the evolution of feeding behaviour so important?
- a greater foraging efficiency results in more offspring
- feeding is necessary for both survival and reproduction
how did tinbergen come up with the search image hypothesis?
Tinbergen observed that when a new type of caterpillar appeared in woodlands, songbirds rarely brought it to their nests. But once a few had been located, the birds collected them at a greater rate.The birds had come to recognise the caterpillars and had formed a search image.
- thought that birds nervous system is constrained in some way - it cannot get better at detecting one type of cryptic caterpiller without getting worse at recognising another
how did Pietrewicz and Kamil test the search image hypothesis and what were the results?
- they used operant conditioning to investigate search images in captive blue jays
- Blue jays were shown slides of cryptic moths of either the same or 2 different species
- the birds improved when presented with 1 species but not when given both
describe an experiment that demonstrates finding food by a search image in skunks?
Striped skunk is a nocturnal forager and finds food by odour. Young skunks were allowed to forage in an outdoor enclosure. Food was found at greater and greater distances as they gained experience - the maximum distance over which food is detected also increases
when are birds less likely to develop search images and what implications does this have?
- less likely to develop search images for rare species so they may be predated less
- in cost benefit terms, natural selection should favour a bird becoming better at detecting a common prey species at the expense of becoming worse at detecting a rare species - this favours rare types of species
describe social foraging in insects
groups composed of related individuals - cooperation favoured by kin selection
what are the majority of groups of living animals composed of?
opposite to social insects - they are normally composed of mostly unrelated individuals with cooperation not favoured by kin selection
describe a foraging advantages for groups
can take prey much larger than themselves e.g. wolves take moose - this has evolved several times independently in carnivores
describe the difference in how social insects and other group living animals can communicate about food?
social insects - Deliberate communication with nestmates.
e.g. waggle dancing, direct leading, pheromone trails.
other group living animals - Incidental communication with conspecifics.
e.g. observing location of successful foragers
what are 2 jobs of the worked insects in social insect colonies?
Workers help by capturing prey (e.g. army ants), or defending a food patch (ants, some stingless bees).
Or, most commonly, by communicating the location of food to nestmates (e.g. waggle dances in honey bees and direct leading and pheromone trails in ants.
who cam up with the waggle dance and what is it?
Karl von Frisch - honeys bees cooperate by dancing to tell each other where the flowers are
what does the round dance and figure of 8 dance indicate to other bees?
Round Dance (food <50m) Figure of Eight Dance (food >50m)
where are waggle dances performed?
Dances are performed in nest on vertical combs in darkness.
what are the 3 hypotheses to explain the waggle dance?
1) finding flower patches quicker
2) finding better quality patches
3) being able to monopolise a food patch
what information suggests the hypothesis about better quality patches and monopolisation of patches is correct?
- it is discovered that bees which read dances take longer to find the flowers than bees which scout out a patch for themselves
- this is because the recruit only finds the patch advertised by the dance about 1/4 of the time as the dance is imprecise
- however recruits that do find a patch advertised by a dance are more likely to keep foraging on it than a scout who has located a patch by herself
- a forager only dances when she is working a highly rewarding patch
- suggested that the dance allows a colony to monopolise a patch of flowers because it can recruit foragers quickly
describe karl von frish fan test
- trained scout bees to a feeder at point F.
- He then put out feeders of equal attractiveness at 6 other stations and counted the recruits.
- More arrived at the advertised location, F, than other locations
- this experiment proved the bees could communicate direction
describe karls experiment to prove the bees can communicate distance
Scout bees trained to a feeder 750m from hive. After waggle dance recruits went most often to feeders close to 750m (all feeders in same direction).
how does the positioning of the combs affect the waggle dance?
- natural honey bee combs are vertical
- Honey bee foragers will dance on horizontal combs, orienting to a directional light source instead of gravity.
what affect does removing light from the horizontal combs have and how can this be used?
be removing directional light you are removing the directional information in the dances - this makes it possible to compare the success of bees with informative dances, to bees with non-informative dances
what were the results from the experiment removing directional information?
- A larger proportion of recruits come to the advertised site when combs are vertical
- Recruits locate advertised site more easily when combs are vertical
- because the angle from sun and food source is the same as vertical distance angle for direction
- the distance is indicated by how long it takes to perform the waggle dance
describe the experiment used to work out how honey bees measure distance?
- used a tunnel down which bees fly ( top covered with netting)
- tunnel is covered by 1x1cm random pattern or 1cm parallel striped running lengthwise
what was the image motion hypothesis for the distance measuring experiment and the results if the experiment?
honeybees use the speed at which images pass their eyes during flight to estimate the distance theyve flown - the bees in random pattern tunnels were less successful at identifying distance
the experiments all give proximate explanations for the honey bee foraging strategy but what is the ultimate hypothesis?
- by following dances, foragers dont find flowers faster but they find better quality ones, as only scouts finding high quality flowers dance
what is the fitness benefit of the waggle dance?
- honeybee colonies achieve fitness in winter not summer, through dancing
describe how ospreys forage?
in coastal areas ospreys form loose gregarious nesting colonies - they are not closely related so we would not expect these animals to deliberately communicate to each other
- shoaling fish are a particularly good prey item
what did experiments show about informed and naive ospreys?
Informed birds find fish faster than naïve birds - If they didn’t, there would be no benefit in receiving information
how is the information transmitted between the bird colonies?
incidentally - an osprey can learn the direction of shoal fish by observing the direction of a returning osprey carrying a fish - use information centres to passively gain information from their conspecifics
what animals dont benefit from being in a group when finding food?
- colonial nesting animals e.g. barn swallows
- barn swallows feed on insect prey that is ephemeral in time and space (lasts for a short time) - by the time information was passed on it is likely that they prey would have moved away so information centres would not be adaptive
- unsuccessful foragers dont follow successful ones
describe group hunting in female lions
Female African lions live in groups and hunt together. Group hunting carnivores take larger prey than solitary hunters - however when prey is scarce, small groups of 2-4 females have lower food intake per day than females that hunt alone however they continue to hunt alone and do not disband even in times of scarcity
describe creel and creels (1995) experiment on African wild dogs
- when studying group hunting in wild dogs they found that they are maxamising the difference between energy gained and energy expended during the hunt
- the net energy gained INCREASED in larger groups
- this is because as well as benefits in terms of meat gained there are also costs in terms of energy expended chasing prey etc
