15. Behavioural ecology 2 Flashcards
What is optimal foraging? 2
- Optimal foraging proposes that in a given circumstance, and animal seeks to maximise the rate of energy gain since this would ultimately maximise reproductive success. 2. However other factors are also important so whilst maximising food intake animals also need to minimise risks eg. predation.
how is optimum prey size reached? Use crows and whelks as an example. 5
- Crows feeding on whelks appear to choose only large individuals and they break the shells by flying 5m into the air before dropping them (Zach 1979) 2. Counted how easily whelks broke at different heights 3.bigger whelks broke more easily at 5m 4. cost of flying outweighs benefits for small whelks 5. Seems optimal
Use leaf cutter ants as an example of risks vs gain in optimal foraging. 5
- Smaller ants go out in the day 2. bigger ones go out at night but are more efficient 3. there is a parastic fly that lays eggs in ant bodies but spermatophore can only enter larger ants 4. the fly is only active in the day 5. balances requirements vs risks
How do lions exhibit a preference for optimal prey? 5
- Hayward et al 2. studied distribution of prey animals 3. lion showerd strong preferences in how many turned to hunts and kills 4. try to avoid ostrich or elephants 5. studied hunting success - those that were successful more frequently were preferred eg. warthogs
How can territories be made optimal? 5
1 One way of improving your access to resources (food, mates, shelter) is to have a territory that you defend. 2 Lots of animals have territories but there are costs and benefits. 3. The territory requires time and energy to defend (patrols, marking, fights) and this increases with territory size. 4 The territory benefits probably also increase with size. 5 This suggests that there are probably optimal territory sizes for specific animals in specific ecological conditions.
How do territory sizes differ between species? 3
- sunbirds have consistent number of plants in territory rather than space 2. cheetahs have very large territories and frequently scent mark 3. gannets have pecking distance territories when nesting
What are the hawk and dove strategies of territory defense? 6
- Territory defence is interesting because often it is accomplished by display rather than actual fighting. 2. Maynard Smith (1976, 1982) investigated this using game theory similar to the Prisoners Dilemma. 3. He suggested that individuals defending territories could use one of two strategies: Hawks and Doves. This assumes that the individuals are fairly close in body size - if you are clearly going to win a fight then you should obviously go for it. 4. A population of all doves can be invaded by hawks, and a population of all hawks can be invaded by doves in terms of payoff per encounter. 5. However the population becomes stable (an evolutionary stable strategy) when the average reward is equal for hawks and doves. 6. In this theoretical example this occurs when the proportion of hawks is 7/12 and the proportion of doves is 5/12 but the exact numbers would depend on the actual costs and benefits of the interactions.
What is the dove, hawk and bourgeois model? 4
1• The hawk and dove model is very simplistic and does not encompass observed behaviours in many cases. 2• Davies (1978) observed that in equal-sized male speckled wood butterflies, territory fights were always won by the resident. 3• This is better explained by another of Maynard Smith’s models: Hawk, Bourgeois and Dove. 4• Bourgeois is an individual who acts like a hawk if they own the territory and a dove if they are the intruder. In this model, 5. Bourgeois only is the stable strategy because it cannot be invaded by the other strategies. 6• A Bourgeois individual would find itself in control of a territory half the time.
What territorial fighting strategies may be used? 5
1 Despite the simplicity of the models we can draw some conclusions.
2• Fighting strategy is frequency dependent. A hawk strategy is a good strategy in a population of doves but not in a population of hawks.
3• The ESS is in the model often a mixture of strategy types and this is often seen in nature.
4• The ESS is dependent on the value of the costs and benefits. However as long as the cost of injury is higher than the value of winning then all hawks or all doves will never be an ESS.
5• The frequency of hawk behaviour increases as the payoff increases. For males, often the biggest payoff is the opportunity to mate with females, because failure to do this is genetic death. Fights for females are therefore commonly sever and Hawk-like strategies dominate.
How do sex ratios balance themselves? 4
1• Generally you do not need as many males in a population as females.
2• Yet sex ratios are almost always very close to 1:1.
3• Fisher (1930) demonstrated that this ratio was an ESS because if the population had 20 females for each male, then it would be beneficial to produce male offspring and that this benefit would prevail until the ratio dropped back to 1:1.
4• However this is the average sex ratio. It does not mean that one female will always mate with one male.
What are promiscuous mating systems? 5
- Chimpanzees and bonobos are a good example.
2• It has been suggested that this may occur when the risk of not finding a mate is high but this does not seem all that likely for social primates.
- It may well be linked to social cohesion and complex interactions but promiscuity is actually very uncommon among primates
- Many to many mating
- as important as grooming in primate circles
What are monogamous mating systems? 7
1• Individuals mate exclusively over at least one breeding season.
2• This may be related to the practicality of mate guarding since it may be in the male’s interest to guarantee that the offspring are his.
3• The male-assistance hypothesis suggests that monogamy is preferred when male help at the nest has a large impact on offspring survivorship. This is the commonest explanation in birds.
4• The female-enforced monogamy hypothesis suggests that it in the female’s interest to ensure male assistance and that she will enforce it.
5• Molecular studies of actual paternity, and more detailed field studies have shown that true monogamy may be less common than previously thought
- More common in birds as mammals suckle
- eg. vultures - life long monogamy
What are polygynous mating systems? 7
1• Monogamous mating systems are common in birds because males often contribute to rearing the offspring.
2• This is very rare in mammals and polygynous mating systems (one male to more than one female) are much more common.
3• This reflects the fact that it is strongly in the male interest (in terms of fitness) to mate with as many females as possible and to defend this if he can.
4• Resource Based Polygyny occurs when there is a resource that a male can dominate. e.g. Lark bunting nests in grassland where a shady site is key to nestling survival.
5• Harem mating structures occur when a male defends a group of females without a specific territory. This is more common in social animals where females naturally group such as horses and zebras. Commonly linked with infanticide.
6• Communal courting (lek). Males perform elaborate courtship displays and females choose the best - gene shopping
- eg. ground dwelling birds and lions
What are polyandrous mating systems? 4
1• One to many mating systems are predominantly one male to many females but in rare cases the opposite occurs.
2• In a number of social mammals such as Kalahari meerkats and spotted hyena females compete by fighting to maintain their rank and their offspring are reared by other members of the group.
3• Polyandry is also sometimes seen in species where egg predation is common. Among jacanas (a tropical bird) males build nests and females compete with other females to lay their eggs in multiple nests where they are reared by males
- Extra males provied more man power to do things for female
How does sexual selection play a role in mate choice? 5
1• Sexual selection is selection that promotes traits that will increase an organism’s mating success.
2• Intersexual selection: one sex (usually females) chooses mates based on an attractive feature.
3• Intrasexual selection: members of one sex (usually males) compete over partners with the winner performing most of the matings.
- if males and females look the same, it is a sign of little/no competition ie. monogamy or promiscuity
- in polygyny, the male is larger, and in polyandry, the female is larger