Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
大學部 生態學與保育生物學學程 (必選) 2010 年 秋冬 天擇 (Natural selection) ─ 動物行為學(Ethology) 鄭先祐(Ayo) 國立 臺南大學 環境與生態學院 生態科學與技術學系 教授 Ayo NUTN Web: http://myweb.nutn.edu.tw/~hycheng/ Part 1. 動物行為的研究途徑 (個體行為) 歷史背景 (History of the Study of Animal Behavior ). 基因分析 (Genetic Analysis of Behavior ). 天擇 (Natural Selection and Behavior ). 學習與認知 (Learning and Cognition.) 生理分析 (Physiological Analysis) (一) 神經細胞 (Nerve Cells and Behavior ). (二) 內分泌系統 (The Endocrine System). 發育(The Development of Behavior ). Ayo 教材 (動物行為學 2010) 2 04 天擇 (Natural Selection) Natural selection Common misunderstandings Genetic variation Response to Natural selection The maintenance of variation Test hypotheses about natural selection and adaptation Ayo 教材 (動物行為學 2010) 3 Natural selection and behavior Species behaviors are well suited to their environments Kittiwake gulls treat strange chicks as offspring They nest on steep cliffs, where the chances of the wrong chick ending up in the nest are minimal The deeper nests are less likely to allow eggs to roll off cliffs Predators can’t reach the nests Ayo 教材 (動物行為學 2010) 4 Natural selection and behavior Herring gulls recognize their chicks They won’t care for neighboring chicks that wander into their nests Predators move freely through a herring gull colony Nests must be less obvious Parents remove eggshells and droppings Ayo 教材 (動物行為學 2010) 5 Closely related species are very different “Nothing in biology makes sense except in the light of evolution” Evolution: a change in the frequencies of different alleles in a population of organisms over generations Population: an interbreeding group of organisms of the same species Natural selection is the most important type of evolutionary force It is the reason why species are well suited for their environments Ayo 教材 (動物行為學 2010) 6 Natural selection Darwin contemplated many esoteric topics, including pigeons Over generations, extraordinarily bizarre pigeons could be bred through artificial selection Darwin noticed a parallel between the process that was happening in pigeon lofts and what might be going on in nature He published On the Origin of Species by Natural Selection or The Preservation of Favored Races in the Struggle for Life Ayo 教材 (動物行為學 2010) 7 Core concepts of natural selection Observation 1: Individuals in a population vary They differ in appearance, behavior, physiology, etc. Observation 2: Some variable traits are genetically based Traits inherited from parents can be passed to offspring Observation 3: Some inherited traits improve an individual’s chances of leaving more offspring Conclusion: Because offspring are likely to inherit their parents’ beneficial traits, these traits become more common in the population relative This is evolution by natural selection Ayo 教材 (動物行為學 2010) 8 Natural selection selects traits In natural selection, nature “selects’’ those traits that enhance reproductive success i.e. male bighorn sheep that win head butting contests leave more offspring Ayo 教材 (動物行為學 2010) 9 Evolution must occur Because of natural selection, the population’s genetic composition changes in future generations More individuals have alleles that code for “winning” traits Adaptations: traits that evolved because they allow individuals to survive and reproduce better Have a genetic basis Excludes learned behaviors, but the capacity to learn may be an adaptation Ayo 教材 (動物行為學 2010) 10 Nonscientists misunderstand natural selection Reinforced by poorly written articles in the popular press The terminology of evolution uses words that have other meanings In artificial selection, the selective force is imposed by humans that have particular goals in mind (有目 的) Natural selection is not capable of long-range or even short-range planning (沒有目的) It works only generation by generation Ayo 教材 (動物行為學 2010) 11 A troublesome phrase: “survival of the fittest” “Survival” is only one of many traits acted on by natural selection An animal must survive, compete, find a home and mates, and produce offspring These abilities are improved through natural selection “The fittest” suggests that the most physically fit, strongest, and aggressive individuals dominate all others In an evolutionary sense, fitness describes the reproductive success of a gene or an individual Other traits can be more important to evolutionary success than being the biggest or strongest Ayo 教材 (動物行為學 2010) 12 Different measures of fitness Direct fitness: the number of surviving offspring an individual produces Relative fitness: the average fitness of a gene or individual compared with the rest of its population Dictates how a population will change over generations Indirect fitness: fitness gained by helping relatives Inclusive fitness: direct and indirect fitness together Ayo 教材 (動物行為學 2010) 13 Avoid the phrase “for the good of the species” Traits do not evolve to help a species survive Natural selection does not act with the species’ future in mind Traits that increase an animal’s fitness increase in the population Even if it means trouble for the species in the long term i.e. through natural selection, the frequency of a gene increases that allows a female to have more offspring The population can outstrip its available food resources and crash Ayo 教材 (動物行為學 2010) 14 Macroevolution vs. microevolution Macroevolution: large-scale changes over geological time Such as birds evolving from reptilian ancestors The concept of evolution also encompasses microevolution: small changes that happen over only a few generations An evolutionary change within species For example, some Colorado potato beetles have alleles that allow them to survive pesticides Finally, populations, not individuals, evolve Evolutionary change only happens to populations from one generation to the next Ayo 教材 (動物行為學 2010) 15 Variation in individuals is the rule Variation is the rule, rather than the exception Not even the offspring of the same parents are identical Ayo 教材 (動物行為學 2010) 16 Some differences are obvious Some differences between individuals are obvious (i.e. size or color pattern) Others are harder to detect (i.e. metabolic rate) Variants can be distinct or continuous, changing gradually from one extreme to the other Most individuals fall midway between the extremes Ayo 教材 (動物行為學 2010) 常態分布 17 Phenotypic variation has two sources Genetic variation: the key component of evolution If all individuals are genetically identical for a particular trait, that trait cannot evolve by natural selection The environment Evolution does not act directly on the genotype (the genetic makeup), but upon the phenotype (the observable traits) Selection cannot act on genetic differences if they have no effect on the phenotype Ayo 教材 (動物行為學 2010) 18 Mutations: raw material of genetic variation Mutation: a change in the DNA sequence of an organism They can be passed on to offspring Some mutations affect only a small part of the genotype Dramatically affect the function of structural and regulatory genes Other mutations are larger: genes may be duplicated or deleted Entire pieces of chromosomes can move or be reversed Variation produced by mutation is likely to be disadvantageous A random change is unlikely to be an improvement Ayo 教材 (動物行為學 2010) 19 Recombination: raw material of genetic variation Occurs during meiosis: cell division that results in the formation of gametes (eggs or sperm) Crossing over: pieces of chromosomes containing alleles for the same gene are swapped The combination of alleles is scrambled during gamete production Ayo 教材 (動物行為學 2010) 20 Stabilizing selection Genetic variation provided by mutation and recombination provides raw material on which natural selection can work Populations change when they undergo natural selection Stabilizing selection: under stable environmental conditions, animals with traits at the center of the distribution do best Are most successful in the current environment Those at the extreme ends of the distribution are less well-suited to current conditions Ayo 教材 (動物行為學 2010) 21 Directional selection Directional selection: the environment changes and the optimum phenotype shifts over time Those at one extreme become favored The curve that represents the population’s phenotype shifts in that direction The degree of change can be weak or strong Ayo 教材 (動物行為學 2010) 22 The existence of nonadaptive traits Why haven’t individuals with alternate traits been eliminated? Natural selection is not the only force that changes allele frequencies Gene flow: genes from populations mix It makes populations more similar It can slow or halt the effects of local adaptation Ayo 教材 (動物行為學 2010) 23 案例:Gene flow in the funnelweb-building spider This species occupies a wide variety of habitats from northern Wyoming to southern Mexico Some spiders live in lush riparian vegetation along rivers and lakes of Arizona Abundant insect prey Common predators of spiders Other spiders live in desert grassland Insect prey are few It’s too hot to forage through the day There are fewer good places to build a web Ayo 教材 (動物行為學 2010) 24 Funnel web spiders Funnel web spiders (Agelenidae) fit into the web building spider group. Their webs function as their primary hunting tool. The above picture shows its unique web design. It looks like a mass of silk with a hole, or funnel in the middle. Normally the spider sits at the end of the funnel waiting to pounce on a visiting insect. Ayo 教材 (動物行為學 2010) 25 Spiders have very different behaviors Grassland spiders are much more aggressive Don’t allow other spiders near their webs Intense territorial disputes Fighting results in injury or death Very aggressive toward prey Riparian spiders have other problems Abundant web sites Abundant prey However, birds and other predators make riparian spiders very cautious Ayo 教材 (動物行為學 2010) 26 Behavioral differences in spiders are genetic Genetic differences exist between desert and riparian populations of funnel-web-building spiders Laboratory-raised spiders behaved like those that lived in the wild The behaviors responsible for territory size are genetically, rather than environmentally, determined Even under lush conditions, grassland spiders still maintain a large web Spiders collected from one habitat died when they were transferred to the other habitat Ayo 教材 (動物行為學 2010) 27 One spider population does not fit the behavioral pattern One riparian population shows more variability in behavior Including the highly aggressive territorial behavior of desert populations This population is not isolated from desert populations, but has a constant influx of immigrants When individuals were prevented from moving from one population to another The population evolved to become less aggressive and more cautious And more adapted to its local environment Ayo 教材 (動物行為學 2010) 28 Genetic drift: an evolutionary process Genetic drift: the change in allele frequencies in a population due purely to chance events Allele frequencies in populations drift over generations An allele might even drift to fixation - it is carried by every member of the population Genetic drift is more important as population size gets smaller Populations go through bottlenecks – a sharp reduction in population size Because of natural events Especially likely in rarer animals of conservation concern Ayo 教材 (動物行為學 2010) 29 Correlated traits Traits may be correlated with one another for several reasons Pleiotropy: one gene, such as a regulatory gene, may affect several traits Genes can be tightly linked when they are physically close together on the same chromosome Until recombination and selection break the link Ayo 教材 (動物行為學 2010) 30 Tightly correlated traits can be negative Two traits may share an underlying morphological and physiological basis that It is difficult to uncouple them When traits are tightly correlated, even negative traits might be maintained in the population if the net effect on the genotype is positive Behaving optimally in every situation is impossible Ayo 教材 (動物行為學 2010) 31 案例:A correlated trait: finch beaks Many finch species in the Galapagos Islands look similar But have very different beaks Darwin suggested that the species shared a common ancestor, but over time diverged and specialized on different food resources i.e. beaks for seeds vs. beaks for poking into flowers But finches use their beaks for more than just feeding: beak shape influences how males sing Females choose mates on based on their song Selective forces act on feeding, singing and mating behavior Ayo 教材 (動物行為學 2010) 32 Darwin Finches Galapagos Finches Ayo 教材 (動物行為學 2010) 33 Changing environmental conditions A population may seem to be poorly adapted to current conditions Today’s traits reflect past evolutionary pressures Humans change the environment An opossum’s naked tail and ears make it vulnerable to cold Opossums survive winter by living near humans Over time, there is selection for less fearful opossums Ayo 教材 (動物行為學 2010) 34 Opossums (負鼠) North American opossums can benefit from proximity to human habitation. Ayo 教材 (動物行為學 2010) 35 Human-caused changes pressure species Environmental changes are occurring so rapidly Many populations cannot evolve fast enough to keep up In Britain, newts(蝾螈) have responded to warming temperatures by entering ponds earlier than they used to But frogs still reproduce at the same time Frog eggs and tadpoles are exposed to more newt predators Habitat is lost to development Pollutants and fertilizers change water chemistry Traditional migratory stopovers disappear Light pollution interferes with animal navigation Ayo 教材 (動物行為學 2010) 36 The environment includes biotic factors Birds on New Zealand had no mammalian predators in their evolutionary past So they do not have antipredator skills Birds will land near dangerous animals Some, such as the kakapo (a parrot)(鸚鵡) , have lost the ability to fly Cats, rats and other predators became established Many bird populations are in dramatic decline Ayo 教材 (動物行為學 2010) 37 New Zealand parrot (鸚鵡) New Zealand robin (知更鳥) Ayo 教材 (動物行為學 2010) 38 Aversive conditioning can save species Some researchers have tried to instill fear of predators into naive birds by using aversive conditioning techniques For example, New Zealand robin chicks were presented with dead stuffed cats and ferrets while hearing robin alarm and distress calls Robins learned to associate cats and ferrets with danger And reduced their tendency to approach them Techniques such as these are time-intensive But may be useful as a last-ditch measure to save severely threatened populations Ayo 教材 (動物行為學 2010) 39 Adaptations in a species affect others Adaptations that evolve in one species may change the selection pressures on other species Which may change the selection pressures on the first For example, insectivorous bats locate flying moths by sonar In response, some moth species have evolved the ability to detect the ultrasonic signals emitted by the bat And undertake evasive action with a fast erratic flight Bats are under even greater pressure to detect and follow moths This coevolution is known as an evolutionary arms race Ayo 教材 (動物行為學 2010) 40 Frequency-dependent selection Variation can be maintained in a population because different genotypes are favored at different times Frequency-dependent selection: an allele has a greater selective advantage when it is rare than when it is common As a result, the frequency of any given allele fluctuates It increases until it is common and then decreases once the alternative allele is favored Two examples of frequency-dependent selection are Frequency-dependent predation Frequency-dependent reproduction Ayo 教材 (動物行為學 2010) 41 Frequency-dependent predation maintains variation Although predators have a varied diet, they often attack one prey type more often than expected by chance A predator might concentrate on the most common prey The more common individuals are attacked until their numbers, and their alleles, decline in frequency The rarer form survives and reproduces and its relative frequency increases Then the predator switches to the new most common prey Which eventually decreases in number, and the cycle begins again Ayo 教材 (動物行為學 2010) 42 Predators choose the most common prey Frequency-dependent predation can maintain variation in prey appearance Especially if the prey density is low For example, blue jays “preyed on” virtual moths presented on computer screens by pecking on the screen The blue jays preyed on the most common form of moth And switched to alternative forms when that form became less common In nature, the maintenance of prey polymorphism (“many forms”) would also maintain the genetic variation underlying it Ayo 教材 (動物行為學 2010) 43 Frequency-dependent reproduction Frequency-dependent reproduction (the “rare male” effect) can maintain a variety of male phenotypes in the population A male with a rare phenotype mates more expected The alleles of the rare phenotype increase in the population until they become common and are no longer favored The allele frequencies of different phenotypes seesaws Male guppies have extremely variable coloration Females choose males with novel color patterns—rare males—over males with a familiar color pattern Ayo 教材 (動物行為學 2010) 44 Both types of frequency dependence in crickets Male Texas field crickets rub their wings to attract females Males vary in the time they devote to calling every night Some rarely or never call, and others call for hours Why would there be this much variation? Calling also attracts parasitoid flies, which lay their eggs on the crickets, eventually killing them When flies are common, the calling males are soon parasitized, and the males that call less end up with more mates over their (longer) lives When flies are rare, the calling males have the advantage Ayo 教材 (動物行為學 2010) 45 Male Texas field crickets Ayo 教材 (動物行為學 2010) 46 Evolutionarily stable strategies A individual’s success may depend on what others are doing A “strategy:” the set of behaviors available to an animal “Winning:” the individual’s fitness increases more than its competitor’s does (i.e., it leaves more offspring) Evolutionarily stable strategy (ESS): the optimal strategy for an individual to follow when the rewards (payoffs) depend on what others are doing When adopted by most members of a population, this strategy cannot be beaten by a different strategy: no other strategy confers more fitness benefits Ayo 教材 (動物行為學 2010) 47 An ESS: herring gulls (銀鷗) A herring gull (銀鷗) will not care for a neighboring chick that wanders into its nest This is an ESS: there is no alternative behavior that will yield greater reproductive success The alternative strategy: caring for other birds’ chicks But herring gull parents would waste time and energy caring for offspring that are not their own An ESS is unbeatable and uncheatable in the long run A pure ESS: a single strategy A mixed ESS: several strategies in a stable equilibrium Ayo 教材 (動物行為學 2010) 48 The favored strategy maximizes benefit A hypothetical population of fish-catching birds has two strategies for getting dinner Catch your own fish or steal one from another bird Thievery is favored first: it minimizes its costs and gets full benefits from the efforts of others As the number of bandits increases, so does the chance of encountering another robber or a bird that had its fish stolen Then, honesty becomes the best policy When hard-working birds become common, thievery once again becomes profitable Ayo 教材 (動物行為學 2010) 49 Nesting strategies of digger wasps The nesting behavior of female digger wasps is a mixed ESS, with two strategies digger wasps (掘鑿蜂) Ayo 教材 (動物行為學 2010) 50 Female digger wasps must make a choice A female can dig her own nest Digging is expensive in time and energy Another female may take the nest Ants or centipedes could invade the nest She can enter an existing burrow, reaping benefits without costs This is the favored strategy if the burrow is abandoned Ayo 教材 (動物行為學 2010) 51 A female digger wasp’s alternative nesting strategies and their outcomes But there is no way to determine whether the nest is abandoned or whether the resident is just out hunting Eventually the two females will meet and fight sometimes to the death, and winner takes all The two available strategies: to “dig” and to “enter” Three possible outcomes of a decision to dig Two possible outcomes of a decision to enter an existing burrow Ayo 教材 (動物行為學 2010) 52 A female digger wasp’s alternative nesting strategies and their outcomes Ayo 教材 (動物行為學 2010) 53 Female digger wasps: to dig or not to dig Depends on what other members of the population are doing Entering an existing burrow is the successful strategy when it’s rare As entering becomes more common, there are fewer diggers Which increases the chance of entering an occupied nest, along with costly fights Eventually digging becomes a better strategy Ayo 教材 (動物行為學 2010) 54 The digger wasp’s strategies to “dig” and to “enter” are a mixed ESS. Ayo 教材 (動物行為學 2010) 55 Mixed ESS strategies cycle Mixed ESS strategies cycle between generations For example, fitness changes among male side-blotched lizards with alternative reproductive strategies Male lizards come in three genetically determined throat colors: Orange, Yellow, Blue Each color morph displays a different reproductive strategy A population of only one morph is not evolutionarily stable Ayo 教材 (動物行為學 2010) 56 Uta stansburiana Side-blotched lizards are some of the most abundant and commonly observed lizards in the deserts of western North America. Males often have bright throat colors. Orange-throated males establish large territories and accommodate multiple females. Yellow stripe throated males (sneakers) stay on the fringe of orange-throated lizard territories and mate with their females while the orange-throat is absent as the territory to defend is large. Blue-throated males defend a small territory large enough for one female. They can fend off the yellow stripe throated males but they can't withstand attacks by orange-throated males. Ayo 教材 (動物行為學 2010) 57 Different reproductive strategies of lizards Orange throats: very aggressive, defend large territories with several females Can’t defend every female all the time Yellow throats: don’t defend territories “Sneak” matings from females in orange territories Blue-throated males: defend territories holding a single female Successfully defends her against yellow-throated males Ayo 教材 (動物行為學 2010) 58 Side-blotched lizards: a mixed ESS A population of only orange-throated males is not evolutionarily stable; yellow males can win over orange males Only yellow-throated males is not evolutionarily stable, because they can be invaded by males with blue throats Orange-throated males can invade a population of bluethroated males and have higher reproductive success When yellow-throated sneaker males are rare, it pays to defend large territories with several females In this mixed ESS, yellow beats orange, blue beats yellow, and orange beats blue But, different color morphs predominate in different years Ayo 教材 (動物行為學 2010) 59 Negative-assortative mating: opposites attract Negative-assortative mating also preserves genetic variation in a population, but is uncommon Females choose mates with a different phenotype from theirs It is not rare-male advantage (where females of all phenotypes prefer unusual males) Females of different phenotypes have different preferences If the difference has a genetic basis, variability is enhanced Can prevent inbreeding Mice can determine whether others share certain alleles by the smell of urine Ayo 教材 (動物行為學 2010) 60 案例:Negative-assortative mating of sparrows It maintains the tan-striped and white-striped morphs of white-throated sparrows in equal numbers in a population Both female morphs prefer tan-striped males They are better parents because they spend more time feeding chicks White-striped females outcompete tan-striped females for access to the tan-striped males So, tan-striped females pair with the white-striped males As a result, 93% to 98% of the population mates with an individual of the opposite morph Ayo 教材 (動物行為學 2010) 61 Tan-striped form white-striped form white-throated sparrows house sparrows (麻雀) Ayo 教材 (動物行為學 2010) 62 A trait does not need to be optimal to exist Natural selection acts on the total phenotype of the individual Which consists of good and bad traits, so perfection is elusive Natural selection can act only on the available alternatives Which depend on the population’s evolutionary history and Each individual’s present conditions—ecological, anatomical, and physiological Natural selection works in a given environment Conditions vary from place to place or change over time Ayo 教材 (動物行為學 2010) 63 A nonadaptive behavior is actually adaptive A seemingly nonadaptive behavior of black-headed gulls is that Parents do not immediately remove broken eggshells Eggshells in the nest can attract predators This trait is adaptive Newly hatched, wet chicks are eaten by neighboring gulls They are easier to swallow than dry chicks Delaying egg shell removal until the chicks were dry decreased the likelihood of the chicks’ being cannibalized While the parents were away removing the shells Ayo 教材 (動物行為學 2010) 64 black-headed gulls Kittiwakes Ayo 教材 (動物行為學 2010) 65 The experimental approach tests multiple hypotheses Kittiwakes, with low predation rates, leave eggshell pieces in the nest Ground-nesting gulls, with high predation rates, remove eggshells The survival value of shell removal: to reduce predation on the young White eggshells attract predators Other hypotheses to egg removal Sharp shells may hurt chicks The shell might suffocate a chick It might attract parasites Ayo 教材 (動物行為學 2010) 66 Testing multiple competing hypotheses California ground squirrels and rock squirrels chew shed skins of rattlesnakes, a major predators, and lick their fur It depends on who applies the scent (氣味) Hypothesis 1: it defends against parasites (e.g., fleas, ticks) Juveniles: they have more parasites\ Hypothesis 2: it distracts conspecifics during aggressive interactions Males: they fight each other Hypothesis 3: it deters(嚇住) predators Juveniles and adult females are most vulnerable The experimental approach supports hypothesis 3 Ayo 教材 (動物行為學 2010) 67 The comparative approach Related species inherited common genes because they have a common ancestor If related species live in different situations, they experience different selection pressures Unrelated species in the same environment and experiencing the same selection pressures may display similar behaviors The comparative approach is seen in the herring and kittiwake gull example They descended from a recent, common groundnesting ancestor but now live in very different ecological situations Ayo 教材 (動物行為學 2010) 68 Correlation may be coincidental A correlation between behavior and the environmental might be just a coincidence A large sample size is needed to rule out random chance This method works best when a taxonomic group has been well studied The phylogeny (historical relationships) among a group of organisms is known The phylogeny show the order in which behavioral and morphological traits evolved Ayo 教材 (動物行為學 2010) 69 The comparative method: swordtail fish (劍尾魚) Males of some species in the swordtail fish have long tailfin extensions called swords Males in other species do not Females prefer males with swords Even females in species where the males have no swords A phylogenetic reconstruction suggests that the female’s preference for swords evolved before the sword itself Females were predisposed to be attracted to swords even before males evolved them Ayo 教材 (動物行為學 2010) 70 swordtail fish (劍尾魚) Ayo 教材 (動物行為學 2010) 71 Another use of phylogenetic information It can examine the relationship between behavior and various ecological variables (i.e. predation risk) It’s best to have multiple species from different environments i.e. the Galápagos swallow-tailed gull chooses nest sites with characteristics between kittiwakes and herring gulls It also shows intermediate behavioral patterns Ayo 教材 (動物行為學 2010) 72 swallow-tailed gull kittiwakes herring gulls Ayo 教材 (動物行為學 2010) 73 Phylogenetic trees A hypothetical example illustrating the effect of wise choice of species on our ability to test hypotheses about the influence of the environment on traits. (有20個物種) Ayo 教材 (動物行為學 2010) 74 (b) Sleeping in groups evolved eight times. Ayo 教材 (動物行為學 2010) 75 Limitations of the comparative approach The comparative method must be applied carefully Alternate hypotheses must be considered, tested, and ruled out Confirmation of predictions lends more weight to some hypotheses Correlations between traits and ecological variables do not prove there is a common cause For example, is diet a cause or an effect of sociality in weaver birds (織巢鳥) ? Ayo 教材 (動物行為學 2010) 76 weaver birds (織巢鳥) Ayo 教材 (動物行為學 2010) 77 案例:Diet and sociality in weaver birds 兩種類型: Species in the forest eat insects and forage alone Species in the savannah eat seeds and feed in flocks Does diet cause flocking? Groups are likely to find a patch of seeds that can feed them all Does flocking protect birds? Seeds may be the only food source that could supply enough food to a flock The correlation does not answer the question Ayo 教材 (動物行為學 2010) 78 The lack of a pattern can be important The lack of a pattern between traits and ecological variables can also answer questions One hypothesis for why birds roost in groups at night is because of thermoregulation Huddling together conserves body warmth Hypothesis: species that spend time in cold areas and species that have lower body masses need this thermoregulatory boost A phylogenetically-based study of distantly related groups of birds did not find this pattern Ayo 教材 (動物行為學 2010) 79 Be careful of confounding variables (困擾的變項) A confounding variable: any variable other than the factor of principal concern that may contribute to or cause the correlation i.e. age and body size These factors must be controlled to prevent incorrect conclusions For example, antler size is correlated with reproductive success among male red deer. Ayo 教材 (動物行為學 2010) 80 案例:紅鹿的 antler size antler size is correlated with reproductive success among red deer stags ? Antler size is also correlated with age and body size When one controls for age no association is found between antler length and reproductive success Antler size is not the primary factor in determining reproductive success Ayo 教材 (動物行為學 2010) 81 Monitoring selection in the field It’s very hard to measure evolution in the field 需要非常長時期的研究。 In an intensive 30-year-long field study, Rosemary and Peter Grant and their colleagues documented changes in beak size in medium ground finches (Geospiza fortis) in response to the environment. Ayo 教材 (動物行為學 2010) 82 案例: Ground finches and beak size beak size and shape in Darwin’s finches change in response to the environment During drought, medium ground finches with deeper beaks were able to eat hard seeds and produced more offspring The offspring also had deeper beaks During rainy years, more small seeds were available - birds with smaller bills had the advantage Ayo 教材 (動物行為學 2010) 83 Modeling the costs and benefits of traits The best choice: the strategy in which the advantages outweigh the disadvantages by the greatest amount The decision is difficult because it requires integration of concerns along different dimensions For example: animals must decide to stay in a safe place where there is not much to eat Or go out to forage in a place with abundant food but predators Ayo 教材 (動物行為學 2010) 84 Optimality modeling Optimality modeling weighs the pros and cons (the costs and benefits) of each available strategy A model: a mathematical expression of the costs and benefits of each strategy All costs and benefits are translated into common units that represent a measure of fitness Currency: the measure of fitness which allows different strategies to be compared The optimal strategy: the behavioral alternative that maximizes the difference between the costs and benefits In terms of evolution, this choice maximizes fitness Ayo 教材 (動物行為學 2010) 85 Models gives insight into behavioral rules The term “decision rules” does not imply that animals make conscious decisions to find the optimal course of action Natural selection has shaped behavior over generations The animal responds appropriately to a set of circumstances Complex behavior may occur by following a simple strategy Models provide insight into how simple behavioral rules can generate complex behavior Given just a few rules to follow, computer-generated animals exhibit behavior that resembles territoriality Ayo 教材 (動物行為學 2010) 86 Summary Animals match their environments through natural selection Natural selection occurs when there is phenotypic variation in a population Changing allele frequencies in a population causes evolution In small populations, genetic drift becomes very important Selection pressures change over time, and evolution lags behind Selection pressure on a genotype may depend on its frequency in the population An evolutionarily stable strategy cannot be beaten by another Ayo 教材 (動物行為學 2010) 87 問題與討論 [email protected] Ayo 台南 NUTN 站 http://myweb.nutn.edu.tw/~hycheng/ Ayo 教材 (動物行為學 2010) 88