Behavioural ecology Flashcards
1
Q
what are Niko Tinbergen’s four “why?”s questions?
A
- Causation - What are the Mechanisms causing the behaviour to happen - neurobiology, gene expression - the ST mechanisms that cause the bhv. 2. Development - Ontogeny (in invididual’s life) - is bhv learnt / instinctive? The degree to which the bhv is controlled by genes or environmental. 3. Evolutionary history or Phylogeny of the bhv - do we see similar bhv in close relatives? What point in evo time did this bhv first evolve?when was the transition + what was the selective force? 4. Function - Adaptive value - what use is it to the animal in its life? How does NS favour that bhv + how does NS act on it.
2
Q
How is an animal’s behaviour adapted to its ecological circumstances?
A
o Behaviour o Ecology o Evolution Understanding the function of behaviour requires an understanding of the ecology of the animal in question. Only by understanding the role of the behaviour in the animal’s life can one understand why the behaviour evolved and why natural selection favours it today.
3
Q
why is natural selection is an optimising agent?
A
works as if nature was optimising fitness: only the best survive + reproduce successfully. - The optimum behaviour will depend on the costs and benefits of alternative courses of action.
4
Q
what are the two types of economic model used by behavioural ecologists?
A
Optimisation - heavy use of economic models to understand behaviour and generate hypotheses that can be tested.: simple optimisation models, which quantify the costs and benefits associated with a behaviour and calculate the optimum trade-off between these costs and benefits, Game Theory - game theory is essential when the best thing to do depends on what other individuals are doing; (aggressive interactions etc) game theory becomes useful when analysing social behaviour.
5
Q
Why do black headed gulls remove the eggs of their newly hatched chicks some 15 to 20 minutes after the chicks are born? What is the adaptive value? how did Tinbergen solve this?
A
- There are many possible functional explanations. For example the chicks could injure themselves on the sharp shell, or bacteria could grow on the inside of the shell and be a source of infection Experiment: hen’s eggs in artificial nests: put painted hens eggs in artificial nests, as food for predators, and placed broken shell near these artificial nests or not. Result: enough, nests with white eggshell in them had a higher predation rate. Parents remove shells only after chick dried out and fluffy
6
Q
Why do male dungflies copulate as long (or as short) as they do?
A
There is a trade-off between the benefits of extra time increasing his paternity with this female (eggs fertilised) and time being wasted that could be better spent looking for a new female. The currency, the long-term rate of fertilising eggs, = the percentage of females egg is fertilised divided by the total time taken. The time is not simply the time is spent with the female copulating, it should also include the time searching for females.
7
Q
what are the three ingredients of the Marginal value theorem?
A
1) Choices a. possible copulation durations 2) Constraints a. gain curve (time)) b. search time 3) Currency a. long-term rate of fertilising eggs. - not just about success with this F, success over a long period of time (mating season of dungflie) a series of choices to pick between, a set of constraints within which the animal must operate, and a currency by which success is measured.
8
Q
what is the trade-off Foraging in patches?
A
between the gain rate within a patch (energy gain from food) at a high rate early on but slowing down with time in the patch, and the cost of travelling between patches.
9
Q
what did Alex Kacelnik (1984) do?
A
Trained wild starlings, feeding their young in nests, to come to feeder for mealworms, where they received mealworms at a controlled rate. o This ensured that all birds experienced a specific gain curve with diminishing returns o Varied distance between feeder and nest (greater distance, greater travel time) o experimental manipulation was to move the feeder different distances from the birds nests, and record how the time spent in the patch (and the number of mealworms) changed. This kept everything under tight environmental control.
10
Q
how did Krebs study Prey choice in great tits - Great tit, Parus major
A
Krebs varied the encounter rate of the birds with large chunks of mealworm (good prey) interspersed with small chunks (poor prey). He found that the birds were specialists when encounter rates with good prey were high (short search time) but became generalists when encounter rates were low. His experiment gave qualitative support for the optimal prey choice model, but unlike the model, the birds showed partial preferences. The model predicts you should either be a complete specialist or a complete generalist either side of the critical search time, but the birds did not show an all-or-nothing switch.
11
Q
Give a summary of Prey choice?
A
- If find type 1, always take it 2. If find type 2 take it if: energy content of poor prey / handing time for poor prey is > than good prey. 3. Otherwise reject it; specialise on type 1
12
Q
Possible reasons for a model to fail?
A
o Choices could be mis-specified (or wrong model) –> Animal might not be capable of behavioural choices o Missed constraints o Wrong currency –> Predicting behaviour (energy intake that is not most critical to the animal)
13
Q
What do we understand under The forager’s perspective?
A
Animal’s view of the world isn’t the same as ours e.g. we know the lab is safe, the animal doesn’t.
14
Q
What is animal’s behaviour Animal’s behaviour influenced by? (models)
A
Animal’s behaviour influenced by: o learning o risk sensitivity o predation (different currency)
15
Q
Steve Lima Woodpecker experiment: o Empty v 24 seeds (all holes in log filled/empty) o Empty v 12 seed o Empty v 6 seeds What did he find?
A
24 seeds: optimum number of holes checked –> 1 12 seeds –> 3 6 seeds –> 6 o Model assumes that woodpeckers can learn the number of seeds in non-empty logs o But once they find a seed, they tend to check every hole not predicted by model the birds have some sort of rule which gets them close to the optimal solution, but they are clearly not solving the problem the way Lima did with his model. It seems reasonable that animals use ‘rules of thumb’ which approximate good solutions to problems and don’t come equipped with specific probability distributions (or learn them).
16
Q
Explain risk sensitivity and give 2 risk levels?
A
uncertainty (variance) in reward rather than risk of death o Risk-averse: prefer less variability/uncertainty o Risk-prone: prefer more variability/uncertainty
17
Q
Risk sensitivity in small bird in winter, what was found?
A
During the day, as it feeds and accumulates fat, if it’s doing well (in the yellow zone) it should be RISK-AVERSE: there is no point gambling because you are on-track for the right reserves by dusk and so you should play safe. However, if you’re not on track and look like having a shortfall by dusk (in the red zone), you should be RISK-PRONE. There’s no point playing safe because a steady supply of food won’t get you above the threshold by dusk - you need to gamble.
18
Q
Caraco and colleagues (1990) on Yellow-eyed junco birds, Junco phaeonotus, what was found at different temperatures (low vs high) considering risk sensitivity?
A
Given two feeding options differing in variance, at low temperatures when the birds’ energy balance was negative, they were risk prone. When in a positive energy balance at higher temperatures, they were risk averse. Just as predicted. Switch according to their energy budget and fat reserves.
19
Q
Decisions on where to feed/when to feed influenced by what?
A
o Value of food o Reduces risk of dying from starvation and reserves for mate attracting and territory defense o Value of life o Effected by the value of predation o Probability of predation
20
Q
What if: can only get high rate of energetic gain by accepting high level of predation? What are the 2 contexts?
A
Trade-off: o energy vs. predation 2 contexts: o Vigilance o Habitat choice
21
Q
Metcalfe & Furness (1984) - Turnstone (small wading bird), Arenaria interpres?
A
o Adults but not juveniles migrate o vigilance ▼ with larger flock size o individual risk is lower and more eyes looking out for danger o adult vigilance ▼ before migration o with migration, lots of fat reserves needed (50% bodyweight gained) at the expense of higher predation risk o juvenile vigilance does not change.
22
Q
How does habitat choice influence the feeding behaviour in Bluegill sunfish, Lepomis macrochirus researched by Earl Werner and colleagues (1983)?
A
o Added predator (bass) to one half of pond o Compared feeding behaviour of small and large fish Size o Predation risk goes down as fish gets bigger o The behaviour of the sunfish depended on their body size because predation risk goes down as they get larger. With predator o Small fish feed in vegetation around edge o One third less food, 27% less growth o Predator imposes cost even if it doesn’t kill The smaller fish accept a lower feeding rate in order to lower their predation risk. Note that this is a ‘hidden cost’ of predation risk - not death, but a lower growth rate.
23
Q
Experimental evidence (Locusts) by Raubenheimer & Simpson on trade-ff between nutrients
A
fed locusts on combinations of 5 different protein & 5 different carbohydrate levels o Locusts on low protein diet ate more to meet protein target… but got fat (because too many carbohydrates)
24
Q
What are the two types of competition face by species?
A
- Exploitation - resource used up by others: (eating / using them: not physical interaction but an affect on success) 2. Interference - interactions with others reduce intake rate (interfer another’s ability to forage successfully) o ‘getting in the way’ o resource defence o prey disturbed
25
what is ideal free theory and what does it assume?
aims to Predict the distribution of animals. Assume: animals know the value of the resources and they can move freely between them Important thing about the model: Distribution is stable if no one gains by moving (no one indiv can do better my moving = stable distribution)
26
what is the difference between ideal free theory when animals are equal and when they are un equal
equal: n1/n2 = r1/r2. - Ratio of numbers should = rate of energy supply of two sides UNEQUAL: cw1/cw2 = r1/r2 - Now the prediction is not n1/n2 = r1/r2 as before, but that the ratio of COMPETTIVE WEIGHTS should match the ratio of rates.
27
what happens when animals aren't equal?
give each competitive weights: if split up in certain ways, average rates at each side is same --\> data APPEAR to fit the prediction of input matching (the ratio of fish match the ratio of rates) even though all fish aren't equal, as Ideal Free Theory assumes.
28
what happens at IFD with animals with unequal abilities?
there may be several IFDs at IFD, o all animals of same type get same rate o BUT average intake rate may differ between the patches o Can have equal average rates (i.e. input matching) even though animals aren't equal, so need to check assumptions
29
what is a key concept in understanding why some animals defend territories, and only do so sometimes?
ECONOMIC DEFENDIBILITY, introduced by Jerram Brown. Defending a resource has costs (Time, energy, injury), so payoff from having unique access to the resources must outweigh the cost. Brown: Be territorial if costs \< benefits
30
how may be resources be distributed?
Space í Easier to defend if clumped: less cost. If all your resources are close together in one place, they may be easier to defend o Time í Harder to defend if clumped. Having a sudden floor of resources at one time may actually be hard to defend
31
When were sunbirds most territorial? (at which activity level) and why?
Sunbirds were most territorial at intermediate levels of nectar availability: . If low, not enough profit to make costs of defence worthwhile. If bountiful, no benefits to exclusive access to flowers, so not worth paying costs of territory defence.
32
what types of intruders into territories are there?
Sneaks: just take resources (don't hold territories, don't pay cost of defending) - steal food. /mates satellites: beneficial as well as costly:
33
what are some benefits of sharing a territory?
o Reduces feeding rate o Help with defence if there is enough food for two birds, it pays to defend a territory together because the costs of defence are shared and more than compensated for by the cost of sharing the food. With exclusive access to food - insects being washed up on the riverbank - the birds can allow depleted stretches of bank to replenish (like the sunbirds being able to allow nectar to replenish). Without exclusive use of a stretch of riverbank, you couldn't harvest your resources prudently.
34
What are secondary sexual characters?
Secondary sex characteristics are features that appear during puberty in humans, and at sexual maturity in other animals. These are particularly evident in the sexually dimorphic phenotypic traits that distinguish the sexes of a species, but unlike the sex organs, are not directly part of the reproductive system. - Body size - Weaponry - Coloration - Oramentation - Display - Aggresiveness - Sexual responsiveness - Growth rates + demands on parent - Mortality rate
35
Give example for weaponry Secondary sexual characteristics
o Bighorn sheep (larger horns) o Gelada baboon (enlarged canines) o Stag beetle (enlarged mandibles) o Pheasant (spurs on their legs used for fighting)
36
Give example for coloration Secondary sexual characteristics
(mainly in the primates because of superior colorvision) o Mandrill (male bright blue&red face and bottom) o Blue bird of paradise (male bright)
37
Give example for sexual responsiveness Secondary sexual characteristics
o Dungfly (Males aggregate on dung patches, will leap on every female) o Turkey (only stimulus male turkey needs to try and mount the female is a head sized ball at the hight the head of a female would be at)
38
Give example for ormantation Secondary sexual characteristics
o Peacock (train) o Bower bird (something the animal builds, e.g. bower: ornamental structure built by male that he decorates, purely as a display arena)
39
Give example for Growth rates + demands on parent Secondary sexual characteristics
o In many mammals (incl. humans), male embryos grow faster than female and so place a greater demand on the mother. Milk demand by male offspring is also higher (correlates with bodysize when they grow up).
40
Give example for Mortality rate Secondary sexual characteristics
o Kruger & Nesse (2004) Evolutionary Psychology 2: 66-85 o Plotted is the ration of male: female mortality (1 = equal, \>1 = higher in males) as a function of age, for a range of countries. Except in old age, male mortality higher, especially during peak reproductive years. o For most of our lives, males are dying at a faster rate, particularly in the peak reproductive rate. o Source of mortality is varied: often risk driving behaviour, but also sexdifference in many diseases.
41
Why these sex differences?
o Different selection pressures on the two sexes o Sexual selection (Darwin 1871); Darwin's answer: such features help reproductive competition. Called this sexual selection.
42
What is sexual selection
Sexual selection (Darwin 1871) o Features that promote success in reproductive competition o May be deleterious to survival o Natural (viability) selection and sexual selection may act in opposition
43
Give 2 examples for natural and sexual selection in opposition and what does it show?
Example 1. Tungara frog males (live in Costa Rica) croak to attract females. Mike Ryan et al. o Trade-off between croaking for mates and avoiding predation (attracting bats) Example 2. Guppies (Common aquarium fish; in wild live in streams in Trinidad) - males brighter than females. John Endler noted that males in streams where predators were absent were BRIGHTER. John Endler (1980) did an experiment in artificial pools and tracked evolution of colours over several generations. Within 2 years (8generations), males significantly more conspicuous in ponds with no or non-dangerous visual predators, but less conspicuous in ponds with dangerous visual predators. Shows (i) trade-off between colours being good for attracting females but bad 'cos they attract predators, and (ii) sexual selection can be a powerful evolutionary force leading to rapid change (when removing the restraining effects of predationa and natural selection).
44
What are Darwin's 2 mechanisms in which sexual selection acts?
1. Intra-sexual selection - Competition between members of one sex for access to the other sex a. Usually male:male competition 2. Inter-sexual selection: Choice of individuals of one sex by members of the opposite sex a. Usually female choice over mates rather than males
45
Why is inter-sexual selection this way around (female choice)?
Bob Trivers: due to differences in parental investment in offspring; the bottom line is a difference in investment in gametes (and so contribution to egg). o Males produce lots of cheap gametes o Females produce few expensive gametes o Therefore: o Males can increase fitness rapidly by mating many times. But for every successful male, there are many losers. o The cost of a 'bad' mating is higher for females o This explains why (usually) male competition over mating is more intense, and why females are more choosy.
46
What is the 1st prediction for proving Trivers theory on why inter-sexual selection this way around (female choice)? +2 case studies
Prediction 1. Where males invest a lot in offspring, one expects sex-role reversal o Gwynne (1981) - Mormon cricket o Males produce a nutrient rich spermatophore o Males are choosy about whom they mate with o After courtship, males deposit a nutrient rich package of sperm and protein for the female to pick up (she eats the nutrient sac and MAY use the sperm). Males pay a high price if they let a female take the spermatophore but DON'T use the sperm. So they're choosy over whom they try and court. o Direct benefit to the female (direct correlation to how many eggs they can fertilize) and high cost to male for producing the spermatophore o Example 2. Pipefish are relatives of seahorses. The males accept eggs from females, fertilise them and brood them in a pouch. o Berglund + Rosenqvist o Males pipefish brood young in a pouch o Females are ornamented and compete for males o Males are choosy o As with mormon crickets, the males are investing a lot in reproduction and a good father is worth a lot to females. So females are ornamented and compete for the best males. Males, in turn, are choosey about which females they respond to.
47
What is the 2nd prediction for proving Trivers theory on why inter-sexual selection this way around (female choice)? +2 case studies
Prediction 2. Sexual selection should be more intense in polygynous species with low male investment Another prediction from Trivers theory: where the prize from being the top male is larger for males, sexual selection should be more intense. Harem size in primates Positive correlation: difference in body size between the sexes (sexual dimorphism) depends on the harem size. Gorillas: large harems for top silverback and males are much larger than females. Gibbons: monogamous and both sexes similar in size.
48
Is there sexual selection in monogamous species?
1. First, there's still variation in QUALITY. - so yes, here is still competition for the best mates 2. Second, social monogamy doesn't mean sexual monogamy (i.e. fidelity).
49
In which animal can we see that social monogamy doesn't mean sexual monogamy ?
Great tit: thought to be strictly monogamous (male and female pair and care for young, equally, together) until advent of DNA fingerprinting in the 80's. Actually 10-15% of young NOT fathered by the social father í Extra-pair copulations. a. Often neighbour that is of higher genetic quality (mating cannot be forced in tits).
50
What traits were evolved for male-male competition (intra-sexual selection)?
o Body size o Weapons like teeth, antlers, horn o Aggression (INTRA-sexual selection was rapidly accepted because it's easy to see how a trait such as large body size helps males compete/fight with each other.) o Penis morphology (damselfly's penis is shaped like a loo-brush, with spines and bristles. This allows the male to scoop any previous male's sperm from the female's genital tract before injecting his own sperm) o Chastisty belts - (In acanthocephalan worms (hermaphrodite internal parasites), after mating the female's genital opening is sealed up by the male)
51
Which two questions have been the focus of attention in regards to sexual selection?
1. Are females really choosing between males? or are the males sorting it out via competition and the females get the winner); + 2. What benefits do they get from being choosy? (why are they choosing)
52
What did Malte anderson in 1982 do? What did he find?
maped out territories of male widowbirds, and randomly allocated them to four treatments (shortened taill / elongated tail / cut +reglued for control / capture + release control): results: males with elongated tails attracted more females
53
Why are female pied flycatches interested in males who sing more?
• Females interested in territory quality and are simply using male song as a cue – not really interested in male at all. (F listening to songs knows that where the song is coming from has good food: good for her + easy to feed the young). It is a M trait F selct on but females only use this as a cue to the quality of food.
54
What are cases where only indirect benefits seem to be likely?
Leks - F only get sperm: must be something genetic
55
What are the two things that genetic benefits mmight be releated to and why are they benefits?
Attractiveness: Attractive mate = attractive sons --\> mating advantage. 2. viability: "Good genes" - male ornament is a handicap + costly to produce / detrimental to suvival so only igh quality males can afford the cost of producing / maintaining the handicap --\> cost ensures ornament is a cheat proof signal of quality.
56
What is fisher's run away process?
The more females there are that prefer long tails, the bigger the gain, Females who mate with long-tailed males gain, because their sons have long tails (and so are preferred), BUT, because choosy females mate with long-tailed males, their sons not only spread the tail genes, but also spread their mother’s preference genes
57
How does preference reach a threshold?
genetic drift, sensory bias, Fisher's own idea (initially a lsight eaggeration signalled viability, F gained from prefering this --\> mating advantage to M with it)
58
What are some problems with the handicap principle?
1.: males passs on handicap too, but: dissapears if handicap is strategic + if cost to low quality males is higher than for high quality 2. if good genes are good, they will spread rapidly to fixation, BUT: disappears if there are other forces maintaining genetic diversity
59
What can maintain the genetic variation between males (that makes female choice worthwhile)?
1. ongoing recurrent deleterious mutation, host parasite coevolution.
60
Define 'communication', 'signals' and 'cues'
Communication = Process in which signallers use particular traits to transfer information and modify the actions of receivers Signals = Traits that have evolved to influence the behaviour of other individuals Cues = Traits that provide others with information unintentionally (by-product)
61
Difference between signal and cues
Critical distinction is between signals and cues: the former have been selected over time specifically to convey information. o Footprint convey information but are not a signal (=cue) o Mouse rusting through the grass: Another example of an inadvertent cue of presence … Draws attraction of predator, but not strictly communication: If anything, selection should have acted to minimise the sounds of movement in mice, because of the predation threat (=cue). o Example of a signal: Dewlaps are used by males to help in the defence of their territories. o Anolis lizards: dewlap has evolved to convey information and is a signal o Behavioural ecologists are interested in the evolution of signals
62
What do animals communicate about?
1. Identity: Information from what species you are, through signals about sex, dominance status, kin, group membership, etc, all the way to your individual identity. - Identity: species (Narrow-mouthed toads) - Identity: sex (Longtail knifefish) - Identity: Individual (Bottlenose dolphins) 2. Environment: Animals also convey all sorts of information about the surrounding environment. - Environment: Food (Honey bees) - Environmen: Danger (Vervet monkeys) 3. State - A third major category of information concerns the current state of an individual. - State: Hunger (Canaries) - State: Intention(Dogs) = Information about potential future actions and motivation are also available, as shown classically by domestic dogs. - State: Quality (Peafowl)
63
Identity: species (Narrow-mouthed toads), How do they communicate species identity?
Communicate to vocal signals: - When these two particular species are found in allopatry (that is, when each is the only species in a given area), the calls of the males have a similar pitch; frogs and toads rely heavily on vocal communication. - When the two species are found in sympatry (that is, when both are in the same area), selection has led to divergence in call pitch; if males of both species sound the same, mating errors are more likely and so individuals sounding distinct and ensuring successful matings with females of their own species would have had a selective advantage.
64
Identity: sex (Longtail knifefish), how do they communicate sex?
South American longtail knifefish (Sternopygus macrurus). o Many species of fish use electrical discharges to stun prey and/or to help 'see' their environment. Longtail knifefish also use them for communication, with males and females producing different frequencies, thus making them readily identifiable. o Males and females differ in steady-state electrical discharges (=are sexually dimorphic)
65
Identity: Individual (Bottlenose dolphins), how do they communicate?
Each dolphin has its own unique signature whistle; that whistle encodes individual identity independently of voice features (=almost how human name. Group members use this whistle to get attention from called individual) --\> huge debate about what constitutes true individual recognition
66
Environment: Food (Honey bees), how do they communicate the location of the food?
One major environmental feature about which important information is conveyed is the availability and whereabouts of food. A classic example comes from the dancing of honey bees when workers return to the hive. o Returning workers dance to convey information o Marking bees to study recruiting behaviour o Waggle dance: signal gives information about direction, distance and quality of food resource o There are two types of dance given by worker honey bees. When food is nearby, they give what is called the 'round' dance; workers about to leave obtain information simply from the odours on the returning individual, and when leaving the nest they search for these odours and thus the food source. For food sources further afield, workers use the 'waggle' dance. This conveys information about the direction the food can be found (the angle of the bee dance relative to vertical indicates the direction leaving workers should follow relative to the sun) and its distance and quality (information that is conveyed by the duration that the dance lasts). Also, acoustic signal. Experiments manipulating these characteristics have neatly demonstrated that workers do indeed gather all of this information from their hive-mates.
67
Environmen: Danger (Vervet monkeys), alarm calls and why different calls?
Vervet monkeys (Chlorocebus pygerythrus), an Old-World monkey of the family Cercopithecidae native to Africa. o Alarm calls - 3 different alarm calls depending on type of predator Different escape responses to 3 different types of predator o As well as simply announcing the presence of danger, many species convey additional information in their alarm calls. In the case of vervets, that is referential information about the type of predator that is approaching. Different calls are valuable to receivers because the best response varies depending on the type of predator: for example, if a leopard approaches, climbing quickly high in a tree is a good option, but putting yourself at the top of a tree is a bad plan if an eagle is flying past. o Signal urgency of the threat (how imminent the threat is)
68
State: Hunger (Canaries), how do chicks communicate?
o Gape colour- Blood diverted from gut, uncheatable (red=full; yellow=hungry) o Begging - Calls and posture, Honesty maintained by cost Hunger level in chicks is conveyed through various means. One physiological method is through the colour of the gape: this is dependent on the amount of blood flow to this part of the body, which is lowered when the animal has lots of food to digest; blood is diverted to the stomach and the gape appears a paler colour, making this an uncheatable, honest signal to parents. Information on hunger is also available from the begging calls and posture of chicks - the more they beg and the further they reach up, the hungrier they are; the honesty of these signals is maintained because they are costly (both in terms of energy and attracting predators) and so it only pays to do so when chicks are truly hungry.
69
State: Intention (Dogs), how do they show submission/aggression and why?
o Signals conveying different messages tend to exhibit maximal contrast o This was one of Darwin's own examples, and the pictures are taken from On The Origin of Species. Maximal contrast evolves to minimise ambiguity; the last thing a retreating individual wants is to continue to be attacked.
70
State: Quality (Peafowl), relationship between trail and quality?
A classic example of this comes from the beautiful tails of peafowl (Pavo cristatus); males are called peacocks, females are known as peahens. o Females prefer to mate with males with more eyespots in tail display o Experimental work has demonstrated that females prefer males with more eyespots in their tail displays, and that the reason for this is because their offspring grow better and also survive better. Females are selecting for male quality (good genes) and eyespot number is an honest indicator of that.
71
Why are many signals so exaggerated?
1. To increase efficacy: Increase likelihood signal is detectable and recognisable, and reduce ambiguity 2. To overcome receiver reluctance: Conflicts of interest between signaller and receiver 3. To provide inherently honest information
72
How can efficacy be increased? (exaggerated signals)
Efficacy can be increased in a number of ways: o Conspicuousness means making a signal stand out, either from the background or from other signals. o Stereotypy involves repeating the same signal several times, such that the message is conveyed even if only one rendition is picked up by a receiver. o Redundancy involves using several different means to convey the same message (e.g. a visual display, a vocalisation, etc).
73
What kinds of conflicts can there be between signaller and receiver?
o Sexual conflict: Males want many mates, females want better mate o Parent-offspring conflict: Offspring want more care than parents want to/are selected to give (trading off investment from this offspring for future offspring). Desires of the two parties do not perfectly align. As a consequence, receivers might be reluctant to do exactly what senders want.
74
How can Senders and receivers can therefore be viewed as being in a coevolutionary arms race? (Receiver reluctance)
o Senders and receivers can therefore be viewed as being in a coevolutionary arms race, whereby the actions of one party create a selection pressure on the other, which in turn lead (Manipulators) are trying to manipulate receivers to do something they don't necessarily want to do; receivers (Mind readers) are trying to act as mind readers and prevent this happening. o Exaggerated signals more likely to persuade receiver: Exaggerated signals are more likely to overcome receiver reluctance (e.g. they are less likely to be able to resist) and so this is the second major reason for the evolution of such extravagant signals.
75
How is signalling is costly:?
o Intrinsic costs: Long tail streamers in males signal quality to females, but reduced maneuverability of longer tail (=sexual selection vs natural selection trade-off) o Social costs: throat patch signals dominance, but increased aggression because of dominance hierarchies (the bigger the patch the more dominant): get challenged, honesty of signal maintained by social cost
76
How does the Handicap principle affect communication?
High cost for low quality individuals, low cost for high quality individuals í only pays superior individuals to employ signal (Amotz Zahavi) o Differential costs to having a particular signal depending on your quality. o Exaggerated (costly) signals less open to exploitation o The more exaggerated the signal, the harder it is for low quality individuals to cheat, and thus honesty is more likely. o Only pays for superior individuals to employ signal o Exaggerated (costly) signals less open to exploitation
77
Do animals ever give dishonest signals + examples?
Dishonest signals: brood parasites o Parasite young raised by another species o Brood parasitism (cuckoo) Dishonest signals: Batesian mimicry o Palatable species mimics distasteful or dangerous one o Coral snake (deadly model) vs Kingsnake (non-venomous mimic) o Predators learn not to eat prey that look like this, so harmless (non-venomous) kingsnakes benefit from mimicry of deadly coral snakes without paying the cost for what the defense is Dishonest signals: false alarm calls o Used to kleptoparasitise other species o Scares forager away when it finds a juicy prey item o Drongo perches above foraging meerkat group, waiting for an individual to dig up a good prey item. Then gives false alarm call (alarm call even though no predator is nearby), hoping to scare meerkat to cover and thus collecting any dropped food.
78
How do dishonest signals work?
Average signal must be honest across the population. Dishonest signals can persist at a low frequency relative to the honest form = Relative frequency dependence. Key principles for stability of dishonest signals. If there were more kingsnakes than coral snakes, predators would learn that on average that particular coloration pattern signalled something tasty and harmless. So, dishonesty is frequency dependent and mimic must be at lower frequency than model.
79
Combined signalling: what advantage?
Individuals produce a signal together rather than individually. Combining in this way may: o Enhance the effectiveness of the signal o Result from permanent associations between individuals with shared resources
80
Examples of organisms that use combined signalling?
Red-headed manakins: Males dance in teams to impress females. Males signalling as a pair or a trio are much more likely to gain matings from a female than males dancing alone. Australian magpie-larks: Pairs duet to defend territory. Duetting is common among pair-living species. Kookaburras: Group members (8-10) combine in laughing choruses to deter rival groups. In many group-living species, individuals combine together in displays. Youngsters get laughing lessons!
81
what is an overview of "normal" and alternaive mating strategies?
• Some males adopt expensive forms of competition (e.g. calling, fighting, aggressive defence of territory) o Often considered ‘normal’ (larger / older males) • Other males adopt less expensive tactics (often cryptic, steal matings) o Sneakers o Satellites (hover around male) o Cuckolders (A male of certain kinds of fish that interrupts a mating pair to release sperm in an attempt to fertilize the female.) o Pseudo-females - mimicking females Note that it may be misleading to think of one behaviour as ‘normal’ and others as ‘aberrant’. Game Theory can lead us to think that, sometimes (though not always), the variation represents multiple solutions to a behavioural problem: there is no single best (or normal) solution.
82
Why is an expanation for alternative mating strategies needed? What are the 3 possible mating strategies?
Natural selection should favour the strategy with the highest fitness So why do we find alternative behaviours within the same species? 1. Different behaviours suit different environments 2. Same environment but there is an equilibrium at which alternatives have equal fitness 3.S ame environment but behaviour depends on state
83
What is ESS? Who created it?
ESS is a strategy that when common cannot be invaded by an alternative (there is no mutant that can do better) • John Maynard Smith imported this idea (game theory) from Economics into evolutionary biology in the 1970’s (although we’ve already seen that Fisher had used similar logic some 40 years earlier): Maynard smith applied game theory to genetically controlled strategies evolving over time. • He coined the term ‘Evolutionarily Stable Strategy’ (often misspelled as an adjective, without the ‘il’), or ESS for short.
84
Why is equal sex ratio an ESS?
• So, when one sex is common, selection favours sex ratios biased towards the opposite sex. The only sex ratio which is stable is 50:50 – where there IS no rarer sex and so the best thing for any one female to do is ALSO have equal numbers of sons and daughters
85
What are some outcomes of negative frequency dependence?
negative frequency dependence (better when rare than common) • Possible that no one strategy is an ESS • the stable result is a mixture of 2 or more pure strategies: ESS may be a mix of 2 (or more) pure strategies • At equilibrium, average fitness of the strategies is the same • Each indiv only does one thing but average fitness of strategies is the same.
86
What are the outcomes at evolutionary stability?
• Population is polymorphic (1+ morph present) - Key points for this sort of explanation of the coexistence of more than one mating strategy in the population • Mean fitness of all strategies is equal • At equilibrium, no new strategy can do better than existing ones (it’s stable) • Novel mutant can’t invade - the general condition for an ESS. (at equilibrium, no mutant strategy can do better than existing strategies and so invade)
87
What are two possibilites for different strategies? (in game theory and ESS?)
• Example just considered: mixture of pure strategies: Each individual is either a Fighter or a Sneak (for life) and the frequency of each is determined by selection • Another possibility: everyone follows a mixed strategy (each indiv capable of both strategies): Fight with probability p AND Sneak with probability 1-p Key message from both is that stable outcome involves TWO (or more) behaviours . It could, of course, involve more than two behaviours; the important point is that it is more than ONE.
88
What are some of the conditional strategies in the third explanation of diff mating strategies: Same environment but behaviour depends on state?
g. “if large, fight; if small, sneak” o if animal is growing, sneaking is “just a phase” (if doing diff things dep. on age + size), when it is big + strong enough to fight it will switch. o “making the best of a bad job” • Still involves frequency dependence – even though strategy is conditional • No need to expect fitness of two (or more) behaviours to be equal; it’s the fitness of the whole strategy that counts (you wouldn’t expect young deer to have same sex as stags; fitness across lifetime that matters)
89
in the third explanation of diff mating strategies: Same environment but behaviour depends on state, what does NS act on?
Here NS acts on the threshold for switching behaviour (i.e. the value of condition below which you do one thing and above which you do the other). The ESS will be an ESS switching threshold.
90
how are Side-blotched lizards an example of behaviour depending on state?
• Strategies have frequency dependent pay-offs: each strategy beats one other and loses to one other Equal success for each strategy, but frequencies vary over time • Each strategy has a strength which allows it to outcompete neighbours of one other morph, but also has a weakness that makes it vulnerable to the remaining morph. It’s a Rock-Paper-Scissors game. Orange beats Blue, Blue beats Yellow, Yellow beats Orange (can sneak onto large territory of Orange males, but not smaller territory of Blue males).
91
What is the conditional strategy in natterjack toads?
Conditional strategy: Male tactic (calling i.e. CROAK vs. acting as satellite) dependent on own size (need to be big to have deep + loud croak) and depends on environmental factors: female abundance (if loads of F, easier to be sneak: bump into F more), weather (if pouring with rain, croak won’t be heard) and level of competition on a given evening (large males are removed from the chorus in an experiment, small males are more likely to call) • ESS is for (size-dependent) threshold for responding to environmental conditions that favour croaking
92
What is an explanation for the sex change in the blue headed wrasse
• Higher fitness as female when small (bigger you are the more eggs you can produce, linear RS) • Higher fitness as male when large – non linear change :not much chance at success as small M, but when big it rapidly accelerates; if you’re a big male with good territory may have several F’s on territory: v. high success. • Thus, change sex where the two lines cross (when you get big enough to be successful as a male)
93
What is parental care?
Any behaviour shown by parent that is likely to increase fitness of offspring o Egg size (amounts of resources put into the egg) o Food (amount of food provided) o Heat (amount of heat provided) o Defence (amount of protection offered)
94
What is parental investment and who defined this?
Any character or behaviour of parent that: ▲ offspring fitness (benefit) ▼ parent's subsequent reproduction (cost) --\> survival, growth, matings, fecundity Bob Trivers provided a clear definition of parental investment. Makes clear the potential for trade-offs between what's good for the young and good for the parent: by giving to current young, parent may be paying a cost, either through reduced survival chances or reproduction in the future.
95
What is parental effort?
total given by parent to young
96
What are semelparous species and what are iteroparous species?
o Semelparous species: Semelparous organisms reproduce only once in their lives and then die. The most well known ones are Pacific salmon that perish after spawning. Other examples are squid, mayflies and plants which die after setting seed (annuals). o Iteroparous species: Iteroparous if it is characterized by multiple reproductive cycles over the course of its lifetime.
97
What is the max. lifetime production of offspring Life-history trade-off?
Current reproduction vs future reproduction; current vs future reproductive success Trade-off between current and future investment.
98
How do you manipulate the parental effort in birds?
by changing clutch or brood size. In blue tits, was an obvious effect on % adult survival during the following winter. Sometimes, the consequences take a little longer to become apparent (see later slide on collared flycatchers for a delayed effect of working harder).
99
What is the Life-history theory?
Life-history theory concerns such trade-offs and how they affect decisions over reproductive effort, care, etc. o When to breed o How many young to produce o What resources to supply
100
What is the optimum clutch size called and named by whom?
Lack's idea: lay a clutch size that matches the number of young you can feed and rear to fledging (=optimises success) --\> Average clutch size is 8 eggs David Lack, the Oxford ornithologist famous for setting up long term studies of great and blue tits --\>Lack clutch size maximises number of offspring raised
101
Why is optimum clutch size important?
Too many eggs means each offspring gets less food, so lower survival. Too few eggs, could have raised more. So, an OPTIMUM. N.B. Again, can't rely on natural variation because of confounding effect of variation in individual quality (of territory and food supply as well as parents) - need to manipulate clutch size.
102
Brood size in flycatchers study by Lars Gustafsson, what was found about the lack vs actual clutch size?
o Lars Gustafsson et al moved young between nests to manipulate brood size o Birds do best with number they laid: natural clutch gives highest lifetime success o Lay less than 'Lack clutch size' o Long term effect on female fecundity Are the clutches smaller than the Lack clutch size because of future costs that raising more young would bring? Yes, because of a long term effect on future female fecundity: increasing the number of young reduced subsequent fecundity, although not survival through following winter (cf. blue tit example earlier) --\> trade-off between current and future. Still don't know exactly WHY future fecundity is reduced.
103
Who cares for young? Optimality vs game theory?
Optimality theory: fitness does not depend on behaviour of others e.g. o Prey choice o Marginal value theorem o --\> Life-history decisions Game theory: fitness depends on behaviour of others e.g. o Alternative mating strategies o Co-operation o --\> Parental care Decision of a parent about care often not in isolation. If two parents: effort of one will affect payoff (offspring survival) of other. So, need Game Theory, as with alternative mating strategies (last lecture) or cooperation (as we'll see in later lectures and a practical).
104
What are the 2 strategies and its 4 outcomes of parental care according to John Maynared Smith and his game theory?
Two strategies: care or desert ESS: neither sex can do better by changing behavior. Four outcomes: o Both desert (as soon as offspring is produced) o Female cares, male deserts o Female deserts, male cares o Both care
105
What are the 3 types of parental care and who do they apply to?
o No care: many invertebrates o Biparental care: many birds o Exclusive female care: many mammals
106
Why is male care so common in fish?
1) Paternity certainty (Trivers) a. External fertilisation occurs at oviposition (female produces eggs and male produces sperm immediately afterward and fertilizes the eggs) b. Paternity more certain than when fertilisation internal c. Problem: 'sneaks' lower paternity in external fertilisers (sneak by and fertilise the eggs) 2) Order of gamete release (Dawkins & Carlisle) a. Male can desert first when internal fertilization (female has to wait until after she's laid the egg/after gestation in mammals) b. Female can desert first when external (leaving the male to do the care) c. Problem: often simultaneous release and sex depositing gametes first may care (females) 3) Costs and benefits (Gross & Sargent) --\> most plausible a. Benefits: similar for males and females b. Costs: differ between the sexes c. Generally cost in fish quite low, especially for males: i. Doesn't have to feed eggs or keep them warm ii. Is territorial anyway (having eggs doesn't change his behaviour) d. Benefits of care similar for males and females, but costs may differ. In fish, these costs (of care) may be quite low.
107
Why is the cost of parental care lower in male fish than in female fish + study?
St Peter's fish: an African freshwater species. Studies of St. Peter's fish, in which sometimes male care and sometimes female (but more often male), suggest costs of care greater for female than male. Care reduces male's chances of mating again (soon), while care reduces female fertility (future egg production). St Peter's fish: cost of care o Mouth-brooding cichlid o Take eggs into mouth and only release them once the offspring hatch - Cost: can't feed and brood, so lose weight - Time till next spawning increases in both males & females, but more in females - Female fecundity reduced (because lose weight, would produce fewer eggs in the next clutch) o Mating cost for males (delay until net spawning attempt) o Mating cost (longer than in males) and fertility costs for females
108
Is there an added benefit to male parental care for the male + study?
The fathead minnow (Pimephales promelas), is a species of temperate freshwater fish found in North America. Fathead minnow: Additional benefit? o Males compete for nest sites o If a male gains a site with eggs, he may keep them (even though no paternity) o Eggs may attract further matings (signal to females that he is of good quality) o So caring boosts mating success, without high cost o Male care as a mating tactic? Caring for eggs can, in some species, BOOST mating success - attracts more females
109
What conflicts exist in the family (related to parental care/survival of the offspring)
Parent-offspring conflict: Parents are selected to stop giving care before offspring are selected to give up care. Lat Tactic to manipulate parents into giving care: o Convulsions in pelican chicks o Temper tantrums in chimp babies Sibling conflict: But there are also other conflicts in the family. Conflict between siblings can occur through begging - trying to obtain more than your fair share. But, most extreme case is killing of siblings (=siblicide in bee-eaters, black eagles, herons&egrets, ect.) Sexual conflict o Penduline tit sexual conflict o Only 1 parent needed to incubate/feed o Males can desert first o BUT, female conceals information from male o Buries eggs and prevents male entering nest o Conflict over who stays and cares for young
110
What are the different types of mating systems?
Monogamy: each individual has only one mate Polygamy an individual may have several mates Polygyny - 1 male, several females Polyandry - 1 female, several males promiscuity Polygynandry - males and females have multiple mating partners during a breeding season.
111
According to Elmen + orneg, When is it economically viable to monopolise potential mates
• Economics of defending mates depends on distribution in space & time • Conditions for a species may change: within season / between years/ across evo time – doesn’t hav to be fixed scenario, we’re examining a given scenario across time
112
What are the things that matter in being monogomous or polygamous?
defendability in time - varition in space + time Parental care
113
How does variation in space influence being monogamous or polygamous?
Spatial distribution matters. If females are dispersed then it will be hard for a male to monopolise more than one female. (may lose his F to a sneaky male) Monogamy favoured. If females are clumped then some males may be able to monopolise several females. (clumped to minimise risk of predation / help with raising young): so some M can defend a little area + get exclusive access to multiple females Polygyny favoured.
114
How does variation in time influence being monogamous or polygamous\?
Temporal distribution matters. If females ‘clumped’ in time (e.g. common toad), HARDER for any male to monopolise \>1 (Few M get 2nd mate) female. Monogamy favoured. A pop in which F arrive from a diff area + arrival times are spaced out If asynchronous breeding (e.g. bullfrog), the ‘best’ males can mate several times. Polygyny favoured. Can get a mate in the early season, wit until she lays eggs to ensure paternity, then can ensure another one from other F arriving now: potential at least for polygyny.
115
How are parental care + mating systems are tightly linked?
Most commonly, in birds we find bi-parental care + monogamy (if both parents tied up for several weeks to raise young, little chance to find other mates). Mammals: F dominated parental care(they can lactate + gestate): POLYGYNY (SEX, then M leaves); FISH: M care + polyandry / promiscuity because the M is left to tend for the eggs and this means F are freed to look for multiple mats.
116
What are the two results of clumped ditrsibution of females in systems with no male care in terms of defence by males?
1. resource defence polygyny: males defend the clumped resources that females need or come to - and so get access to the F 2. female defence polygyny: defend females directly if clumped in space, follow them around and protect them.
117
what are the different tactics M may use to defend females (Female-defence polygyny)? depending on if they're solitary / gregarious?
• If females solitary, male tries to defend territory containing several female territories e.g. many rodents ( this is the only way they could get a polygynous system) • If females gregarious (Living in flocks or loosely organized communities) , male tries to monopolise a group (harem) e.g. seals
118
What are reasons for why male care may be in song birds?
In songbirds, it is less clear-cut, as females can raise some (although not as many) offspring alone. But in songbirds, it’s different: reasons why: • Remove male: female can raise young. Male help only important in bad years? So biparental • Limited opportunities for polygyny? – best thing for M to do is help raise offspring because the output is greater (more offspring like that in if she raises alone); so if no opp to have another family the best thing to do is stay and help.
119
why doesn't Social monogamy (pair bond) ≠ sexual monogamy (fidelity)? give an example in birds
• Superb fairy wren: 80+% chicks sired by a male other than social partner • Before dawn, M were singing in their territories + F were sneaking out, going to find M, mating with him + getting home for breakfast with partner (sneaky pre-dawn mating of F) o There are super studs in the population that are v. popular with the F: sired 100 chicks (loads of F fly to them in the mornings + mate with them) o During the day, M fly around into other territories + dance to F (announcing presence), and it seems to be that this dance is telling F where to find them at dawn the next money (which direction etc)
120
Why is there a conflict of interest in polygyny with male care of young?
Conflict of interest between sexes: Benefit to male: more offspring than if single mate Cost to females: share resources and/or male's care fewer offspring than if single mate (exclusive help of that male) Choice for a female: do you become polygynous with a male who has a good territory and lots of resources, or be monogamous with a male that has a poor territory and few resources?
121
what are some reasons a second female will mate with a male that has mated? (they don't get his help)?
1. Alatalo and colleagues Male deception? – fly to a diff area: there is no obvious info that he already has a F somewhere else. 2. 2. Slagsvold & Dale - Too costly to continue searching? – better to raise some offspring alone than raise none at all by not mating with anyone.
122
What are the variable mating systems in Dunnock?
1 male, 2 F: F share help from male; Dominant female tries to drive away other female Female seeks copulations from other males (will get more care) Male tries to entice second female to sire more offspring. 2 M, 1 F: Both males may feed young. Dominant male tries to drive away other male
123
what is the problem with cooperation?
how does it evolve?any selfish indiv should be selected to gain a benefit from the cooperative behaviours of others, while avoiding paying the costs of cooperating themselves; cheating or defecting should arise
124
What is the prisoner's dilema?
Two suspects are arrested by the police. The police have insufficient evidence for a conviction, and, having separated the prisoners, visit each of them to offer the same deal. If one testifies for the prosecution against the other (defects) and the other remains silent (cooperates), the defector goes free and the silent accomplice receives the full 10-year sentence. [NB defect and cooperate refer to the two prisoners’ behaviour relative to one another; they are the participants in this ‘game’, not the prisoner and the police.] If both remain silent, both prisoners are sentenced to only six months in jail for a minor charge. If each betrays the other, each receives a five-year sentence. Each prisoner must choose to betray the other or to remain silent. Each one is assured that the other would not know about the betrayal before the end of the investigation. How should the prisoners act?
125
What is the best outcome for A in the prisoner's dilema?
is silent, and A is silent, Good for A as only gets 6 years. But if B silent then A goes free. (best thing). – this is temptation to defect (if B cooperates best thing for A is to defect). • If B defects: if A cooperates, A gets ‘suckers play off’ = 10 years in jail; if A defects, term split so 5 years: if B defects, best thing A can do is also defects.
126
how can cooperation be at ESS?
• Many repeated interactions between the same individuals + if the individuals can recog one another (not a one off game, so there is a chance to change how thing pan out over many interactions ) • Remember what partner did – otherwise you’d be back at 1 gen game: need some memory. o Initially cooperative = starting point even if they are going to repeatedly react – the starting point is initialy good Quick to punish – need to pay them back by deflecting in next round: can’t let them get around it Quick to forgive – as soon aas they cooperate, at the v. next opp you also cooperation.
127
Why is it thought vampire bats partake in blood sharing?
The volume of blood ingested has a diminishing return in terms of enhancing survival; the first parts of the meal are disproportionately important. Hence, the donation of a set amount (V) of blood by a well-fed individual results in a much lower cost ) compared to the benefit (B) gained by the recipient (who has obtained little or no blood of its own on that particular night).
128
What are the wways in which you can escape the prisoners' dilema?
reciprocal altruism PD payoff matrix doesn’t apply - policing / punishing of cheats or biparental care
129
why is biparental care likely to lead to cooperation?
because here, the payoff matrix doesn't apply if the remaining player doesn't fully compensate - INCOMPLETE COMPENSATION e.g. starlings
130
Who demonstrated that strlings do incomplete compensation? how so?
• Wright & Cuthill (1989) • Handicap one parent with small weights: o Male only / Female only / neither parent (control) o Neither parent (control) • Measured feeding rates & chick growth addition of weights reduced the workrate, and the other increased workrarte a little but not to the same extent as the reduction. -\>• The reduced total food delivery resulted in reduced chick weight at fledging, which is likely to lead to reduced over-winter survival. • - cost to both: deflecting parent doesn’t get qual amount of offspring rasied
131
What did Bill hamilton propose in 1971?
• BUT if behaviour affects relatives… (if behavioural interactions are between relatives), because at this point, Spread of the gene depends on costs & benefits to both actor and recipient (you share copies of same gene with relative) • Need to consider both partners in the game if they are relatives.
132
What is hamilton's rule?
• Gene for altruism can spread if this is met: r.B \> C • B = benefit to recipient • C = cost to altruist • r = ‘coefficient of relatedness’ – the Probability the recipient shares an identical copy of the gene, by descent (level of relatedness between the parties) = prob of you sharing a gene with another individual
133
What is inclusive fitness?
• I.F = own offspring + extra number of offspring relatives’ produce due to your help \*r. • Crucially, it is the EXTRA offspring arising from your HELP that is included, not the simply number of offspring that your relatives produce in total --\> You can obtain fitness directly from having your own offspring and indirectly from helping to raise the offspring of relatives.
134
Definition of group by wilson (1975)
A group is “any set of organisms that remain together for a period of time spent interacting with each other” Can range from From temporary aggregation of individuals (millions of locusts or 10 of thousands of birds), to stable/more constant smaller groups.
135
Why do some animals live in groups?
Trade-off between costs and benefits with respect to group living.
136
What are the benefits of living in a group?
1. Anti-predator benefits 1a. Vigilance 1b. Dilution 1c. Confusion 1d. Defence 2. Foraging benefits 2a. Better prey capture 2b. Better food finding (Parasitism of knowledge) 3. Other benefits 3a. Energy saving 3b. Social learning - Learning from the behaviour of others
137
1a. Vigilance: Give case study of vigilance benefit and why cheating isn't a problem
Ostriches • More chance of spotting predator • Individuals can spend more time foraging --\> even though each individual spends less time being vigilant, the total vigilance of the group still increases Why no cheating? --\> Thomson’s gazelles/ Cheetahs One possibility, is that there are repeated chances to gain (spot a predator) or lose (get eaten) and so reciprocal altruism may play a part. Another factor (not mutually exclusive) is that the individual spotting the predator may have the edge in escape (because it knows EXACTLY where the threat is coming from).
138
Other animal groups that have vigilance sentinels?
• Pied babblers • Dwarf mongooses
139
What is meant by the 'dilution' effect of living in a group + animal example?
“Dilution” is simply the reduced per capita chance of being the one eaten is a predator attacks --\> seen in monarch butterflies • Less likely to be you that is attacked • Swamp predators in space • Swamp predators in time
140
What is meant by the 'confusion' effect of living in a group + case study?
Classic experiments done by Manfred Milinski on sticklebacks attacking dophnias More targets can lead to what has become known as the “confusion effect” – a difficulty for the predator in targeting one particular prey. • Harder for predator to focus on target • Predator appears to target edges of group --\> Sticklebacks tried to attack the edges more often – lower density made it easier to target one prey item.
141
2 Case studies of how living in a group is a benefit for defence
Guillemots harder for predatory skuas to take chicks in denser parts of guillemot colonies --\> by-product of everyone selfishly defending their own nest --\> Many defending own nest in colony – benefit to neighbours Musk Oxen Form defensive circle around most vulnerable individuals (young in the centre), and effectively make it much harder for the predator (wolf) to attack
142
How does living in a group help with 2a. Better prey capture +3 example animals
• Combine forces to catch larger prey • Some prey CAN’T be tackled by an individual or small group (4 lions needed for one buffalo) Lions: Catch larger prey with help from group-mates Killerwhale: group to catch more elusive prey --\> group to chase down dolphin because v agile and hard to catch Wild dogs: as a team, they constantly who’s going flat out at the front to chase down the prey
143
How does living in a group help with 2b. Better food finding + 2 animal examples + Quote by Ward & Zahavi
Info from knowledgeable individuals (that have found a food source) e.g. Cliff swallows --\>Parasitism of knowledge • Colonies of several hundred • Feed on insect swarms • Shared knowledge This is NOT a case of signalling. Rather, there are cues to recent success (a larger throat bolus indicates good recent feeding) which other colony members can tap into and utilise. Individuals who had an unsuccessful foraging trip last time often follow someone the next time. If you already know where the food source is, you rarely follow someone out. Cooperative exchange of information E.g. honey bees - You all know about honeybee dances (L6) = cooperative exchange of information. Colonies act as information centres (Ward & Zahavi).
144
Animal example for how living in a group helps with 3a. Energy saving
• Huddling for warmth • Emperor penguins - Produce young when weather conditions relatively less harsh, come together to survive bitter winters (-60°C) • Seems like whole colony is moving across the ice = By-product of everyone trying to get into the middle of the group or shuffling around to the other side.
145
Benefit of group living 3b. Social learning, animal example
Chimpanzees • In some populations, individuals modify sticks to extract termites • Youngsters improve by copying adult group members
146
What are the costs of living in a group?
1. Increased conspicuousness 2. Competition for food 3. Interference while foraging 4. Parasite/disease transmission
147
Animal example: cost of living in a group for 1. Increase conspicuousness
Sparrowhawks and finches (Lindström) • More likely to be spotted by predator • Attack rate higher for bigger flocks • Group members hinder one another’s escape
148
Animal example: cost of living in a group for 2. Competition for food
Fork-tailed drongos use false alarm calls to get others to leave the food --\> kleptoparasitism • Kleptoparasitism just means one animal pinching food from another (steal food)
149
Animal example: cost of living in a group for 3. Interference while foraging
• Mobile prey moves off • Godwits – touch feeders, little interference between neighbours – Dense flocks • Plovers – sight feeders, more interference between neighbours – Solitary feeding, because more efficient • Redshank – feed by both methods o When probing for food – dense flock, because interference not an issue o When feeding on surface food – loose flock
150
Animal example: cost of living in a group for 4. Parasite/disease transmission
• Higher likelihood in groups • Prairie dogs • Live in colonies of several thousand individuals • Highest number of fleas in largest colonies
151
What is the Optimal group size and is the optimal group size STABLE??
Equilibrium between cost and benefits. The trouble is that even if the optimal group size has formed, a solo animal will benefit from joining it – so the group is now larger than the optimum. And so on for other individuals – one expects to see groups that are larger than the optimum for this reason (unless a group can easily drive ‘extras’ away).
152
Food not only consideration, when living in a group. give example
Lions • Optimum size = 2 • But, often larger prides • Other factors at prey o Defence of territory against other prides (if there’s only 2, then less likely to be successful) o Defence of young (Infanticide, male try and kill young cups so that female come into oestrus quicker: Bad news for females and more successful in preventing this in larger group size
153
Are there individual differences when living in a group and name them
1. Spatial position 2. Dominance status
154
Animal example: 1. Spatial position
Jack: Food intake • More food caught by larger groups • But, not shared equally – those at front benefit most • If positioned in the front, more prey/individual • Unlikely to be the case that all individuals get a turn at the front.
155
Does Spatial position influence the predation risk? +2 animal examples
Is there any evidence that animals prefer the middle of a group, as Hamilton would predict? • Geometry of the selfish herd • Safer in middle of group than on edge • Another of Hamilton’s insights. The closer you are to other individuals, the more of reduced zone of danger you are in as the predator is more easily distracted by another prey item Minnows Predation risk • Wounded individuals produce alarm chemical • Experiment: habituate shoal to chemical • Add naïve fish • When chemical added, naïve fish to middle of the shoal (evolved to go to the middle when a predator is around) • Centre viewed as safest position --\> Yes, experimental test indicates that increased predation risk results in individuals trying to move to the centre of a group. Ducks • Peripheral birds keep the eye that faces out of the group open while sleeping! • Birds in the middle sleep with both eyes shut
156
Animal example: 1. Spatial position
Jack: Food intake • More food caught by larger groups • But, not shared equally – those at front benefit most • If positioned in the front, more prey/individual • Unlikely to be the case that all individuals get a turn at the front.
157
Does Spatial position influence the predation risk? +2 animal examples
Is there any evidence that animals prefer the middle of a group, as Hamilton would predict? • Geometry of the selfish herd • Safer in middle of group than on edge • Another of Hamilton’s insights. The closer you are to other individuals, the more of reduced zone of danger you are in as the predator is more easily distracted by another prey item Minnows Predation risk • Wounded individuals produce alarm chemical • Experiment: habituate shoal to chemical • Add naïve fish • When chemical added, naïve fish to middle of the shoal (evolved to go to the middle when a predator is around) • Centre viewed as safest position --\> Yes, experimental test indicates that increased predation risk results in individuals trying to move to the centre of a group. Ducks • Peripheral birds keep the eye that faces out of the group open while sleeping! • Birds in the middle sleep with both eyes shut
158
Animal example for how dominance status is an individual difference when living in a group
Willow tits • Dominants can monopolise best positions • Prefer central positions because: o Safer from predation o Good for monitoring scrounging opportunities from others (as a dominant would be able to get subordinate to leave food source) • If most dominant removed, then second most dominant moves to the centre
159
What are the different type of cooperative breeders?
faculative, obligate + eusocial
160
Why may individuals stay at home?
1. ecological constraints. - shortage of territories (acorn woodpecker); 2. gain valuable breeding experience (Seychelles warbler)
161
Why do helpers help?
1. coercion (superb fairy wren) 2. indirect benefits - fitness benefits by helping relatives (: rB – C\>0) 3. direct benefits - group augmentation (meerkats)
162
who do they help?
closest relatives / kin: White fronted bee eater / long tailed tit
163
what are advantages that can arise from being in a larger group?
o Better provisioning ofyoung: Reduced work loads o Better predator detection and defence large splinter groups.
164
What are brood parasitic bees? how do they operate?
• Host: Bombus bumble bees • Parasite: Psythirus bumble bees (never have own nest / workers) - queen invades Bombus nest and kills host queen. Initially attacked by Bombus workers, but once she is covered in the nest pheremones, those workers start helping her raise Psythirus offspring • Obligate parasites: Take over nests & utilise workforce • Timing of take-over is therefore crucial: too early in season and there are insufficient Bombus workers already present to mean Psythirus queen has sufficient help to raise young successfully (Psythirus queen produces no workers of her own); too late and there are sufficient Bombus workers to kill her
165
What is the evidence for coevolution for the brood parasitism cuckoo and its hosts?
• Why does cuckoo have mimetic eggs → Hosts reject poor mimics: better at recog problem if doesn’t look like their own • Why does cuckoo waist until host in laying period: hosts reject early eggs ( they can’t count but know if they’ve laid or not) • Why have cuckoos evolved to lay so quickly? Put in model stuffed cuckoos → if host alerted, more rejection • Why removes host egg? → improves incubation of the cuckoo egg. • Why does cuckoo lay such small eggs? (smaller eggs than we would expect) → large eggs rejected • Why does the cuckoo CHICK eject other eggs? (why doesn’t mother throw everything out when she lays?) bc hosts desert nests with only single egg: mum has to leave them + so chick needs to eject them.
166
in which females of cuckoos has egg mimicry evolved? why?
the hosts have different looking eggs: Cuckoos lay eggs that match eggs of host, except those parasitising dunnocks (no host discrimination: no selection pressure on F cuckoos to evolve egg mimicry). This might be because Dunnocks are a relatively new host of cuckoos: early on in the evolutionary arms race. Egg mimicry has only evolved in female races that specialise on hosts that show egg discrimination. When the selection pressure from host defences is apparent, evolution has led to a response from the cuckoos.
167
How do host females know what their own eggs look like?
on great reed warblers teased these possibilities apart. If experienced females and those breeding for the first time were allowed to lay a whole clutch, and then the final egg was replaced with a non-mimetic model, virtually all females of both types rejected the model egg (inc 1st time breeders). However, if natural eggs were replaced as soon as possible after laying with non-mimetic models: experienced females still rejected the non-mimetic eggs, but now far fewer first-time breeders rejected them. The argument is that experienced females already know (from previous attempts) what their eggs look like, but first-time breeders are learning and so can make mistakes. F LEARN WHAT OWN EGGS LOOK LIK
168
qhat is Signal detection theory, how is it involved in hosts rejecting cuckoos?
. Two extreme options: 1. Very fussy – reject every cuckoo egg but many mistakes( might throw out some of your own) (reject everything to right of line 1) 2. Very relaxed – never reject own egg but
169
What are the pay offs for warbler birds in rejecting eggs?
170
171
Why are chicks not rejected? Given that there is often incredible discrimination of eggs, why are chicks that look completely different fed so readily?
strongest argument for this is from analysis of costs + benefits: MISTAKES IN LEARNING ARE TOO COSTLY(if F parasitised in 1stbreeding season, you would learn to identify cuckoo as your egg: because the cuckoo ejects all the host eggs/young, the only chick left is a cuckoo; with none of their own to compare it against, the host would learn that this is what their own young looks like. In subsequent seasons, they would either reject their own young or raise those of another species (if parasitised again).
