Chap 51 cont. and 52

• capturing, and eating food items 

Evolution of Foraging Behavior 

• In Drosophila, variation in a single gene (for^R & for^S) dictates foraging behavior in the larvae 

  • Larvae with for^R allele travel farther while foraging than larvae with the for^S allele 

  • Larvae in high-density populations benefit from foraging farther for food, while larvae in low-density populations benefit from short-distance foraging 

• Natural selection favor different alleles (for^R and for^S) depending on the density of the population 

• Under laboratory conditions, evolutionary changes in the frequency of these two alleles were observed over several generations 

Optimal Foraging Model 

• Optimal foraging model view foraging behavior as a compromise between benefits of nutrition and costs of obtaining food (a cost-benefit analysis) 

  • It’s an economic approach to look at ultimate causation 

• The costs of obtaining food include energy expenditure and the risk of being eaten while foraging 

• Natural selection should favor foraging behavior that minimizes the costs and maximizes the benefits 

Evolution and Human Culture 

• Human culture is related to evolutionary theory in the distinct discipline of sociobiology 

  • Human behavior, like that of other species, results from interaction between genes and environment 

  • However, our social and cultural institutions may provide the only feature in which there is no continuum between humans and other animals 

• Another example of mate choice by females occurs in zebra finches 

  • Female chicks who imprint on ornamented fathers are more likely to select ornamented mates 

  • Experiments suggest that mate choice by female zebra finches has played a key role in the evolution of ornamentation in male zebra finches  

Balancing Risk and Reward 

• Risk of predation affects foraging behavior 

  • E.g., mule deer are more likely to feed in open forested areas where they are less likely to be killed by mountain lions 

  • E.g., Northwestern crows choose a drop height which takes the fewest times to crack a whelk 

Mating Behavior and Mate Choice

• Mating behavior and mate choice play a major role in determining reproductive success 

• Mating behavior includes seeking or attracting mates, choosing among potential mates, competing for mates, and caring for offspring.

  • Who is the choosiest sex? 

  • Which sex has the most to gain or lose by being choosy?

Mating Systems and Sexual Dimorphism

• Mating relationships define a number of distinct mating systems 

  • In some species, mating is promiscuous, with no strong pair-bonds or lasting relationships 

  • Other species form monogamous relationships where one male mates with one female 

  • Males and females with monogamous mating systems tend to have similar external morphologies 

• In polygamous relationships, an individual of one sex mates with several individuals of the other sex 

  • Species with polygamous mating systems are usually sexually dimorphic: males and females have different external morphologies 

  • Polygamous relationships can be either polygynous or polyandrous 

• In polygyny, one male mates with many females 

• The males are usually more showy and larger than the females 

• Polygyny is the most common mating system in animals - why?

• In polyandry, one female mates with many males 

• The females are often more showy than the males 

• This is a very rare mating system in animals. 

Mating Systems and Parental Care 

• Needs of the young are an important factor constraining evolution of mating systems 

• The amount of parental care needed (and who gives it) factors in mating systems. 

• Consider bird species where chicks need a continuous supply of food 

  • A male maximizes his reproductive success by staying with his mate and helping care for his chicks (monogamy) 

• Consider bird species where chicks are soon able to feed and care for themselves 

  • A male maximizes his reproductive success by seeking additional mates (polygyny) 

• Certainty of paternity influences parental care and mating behavior 

  • Females can be certain that eggs laid or young born contain her genes; however, paternal certainty depends on mating behavior 

  • Paternal certainty is relatively low in species with internal fertilization because mating and birth are separated over time 

    • Male-only parental care is relatively rare in mammals & birds 

• Certainty of paternity is much higher when egg laying and mating occur together, as in external fertilization 

• In species with external fertilization, parental care is at least as likely to be by males as females 

  • <10% of fishes & amphibians with internal fertilization have parental care. 

  • >50% of those with external fertilization have parental care. 

• Certainty or paternity isn’t necessarily a conscious thing. 

Sexual Selection and Mate Choice 

• Sexual dimorphism results from sexual selection, a special form of natural selection that deals with reproductive success 

  • In intersexual selection, members of one sex choose mates on the basis of certain traits 

  • Intrasexual selection involves competition between members of the same sex for mates 

Mate Choice by Females 

• Female choice is a type of intersexual selection 

• Females can drive sexual selection by choosing males with specific behaviors or features of anatomy 

  • For example, female stalk-eyed flies choose males with relatively long eyestalks 

• Ornaments, such as long eyestalks, often correlate with health and vitality. 

• Mate-choice copying is a behavior in which individuals copy the mate choice of others 

  • For example, in an experiment with guppies, the choice of female models influenced the choice of other females 

  • If a female guppy observed a model female courting a drab male, she often copied the preference of the model female

  • However, it didn’t occur when differences between males was more marked 

Male Competition for Mates

• Male competition for mates is a source of intrasexual selection that can reduce variation among males 

• Such competition may involve agonistic behavior, an often ritualized contest that determines which competitor gains access to a resource

Applying Game Theory 

• In some species, sexual selection has driven the evolution of alternative mating behavior and morphology in males. 

• The fitness of a particular phenotype (behavior or morphology) depends on the phenotypes of other individuals in the population 

• Game theory (John Nash, Beautiful Mind) evaluates alternative strategies where the outcome depends on each individual’s strategy and the strategy of other individuals 

• For example, each side-blotched lizard has a blue, orange, or yellow throat 

• Each color is associated with a specific strategy for obtaining mates 

  • Orange-throat males are the most aggressive and defend large territories 

  • Blue-throats defend small territories 

  • Yellow-throats are nonterritorial, mimic females, and use “sneaky” strategies to mate

• When blue are abundant, they can defend a few females in their territories from sneaky yellow throats, but orange throats can overwhelm them. 

• When orange are abundant, they have more females in their territories; the yellow throats can gain greater success by sneaking 

• When yellow are more abundant, blue have an advantage by being able to defend their territories and females 

• Like rock-paper-scissors, each strategy will outcompete one strategy but be outcompeted by the other strategy 

• The success of each strategy depends on the frequency of all of the strategies; this drives frequency-dependent selection

Concept 51.4: Genetic analyses and the concept of inclusive fitness provide a basis for studying the evolution of behavior 

• Animal behavior is governed by complex interactions between genetic and environmental factors

• Selfless behavior can be explained by inclusive fitness (personal fitness plus that of close relatives) 

Genetic Basis of Behavior 

• A master regulatory gene can control many behaviors 

  • For example, a single gene (fru) controls many behaviors of the male fruit fly courtship ritual 

    • If fru is mutated to an inactive form, males don’t court or mate with females. 

    • If females express the male fru, they court other females

    • Hence, fru oversees a lot of male specific wiring of the nervous system

• Variation in the activity or amount of a gene product can have a large effect on behavior 

  • For example, male prairie voles pair-bond with their mates, while male meadow voles do not (and provide little care for pups) 

    • The level of a specific receptor for a neurotransmitter (vaspressin) determines which behavioral pattern develops 

    •   Vasopressin is released during mating and binds to receptors in the male brain. More receptors, more pair-bonding 

Genetic Variation and the Evolution of Behavior 

• When behavioral variation within a species corresponds to environmental variation (within populations), it may be evidence of past evolution and natural selection.

Case Study: Variation in Prey Selection 

• The natural diet of western garter snakes varies by population 

  • Coast populations feed mostly on abundant banana slugs, while inaldn populations do not eat banana slugs, which are rare in their habitat

  • The differences in diet are genetic 

• The two populations differ in their ability to detect and respond to specific odor molecules produced by the banana slugs 

Case Study: Variation in Migratory Patterns

• Most blackcaps (birds) that breed in Germanyy winter in Africa, but some winter in Britain 

• Under laboratory conditions, each migratory population exhibits different migratory behaviors 

• The migratory behaviors reflect genetic differences between populations

Altruism 

• Natural selection favors behavior that maximizes an individual’s survival and reproduction 

• These behaviors are often selfish 

• On occasion, some animals behave in ways that reduce their individual fitness but increase the fitness of others 

• This kind of behavior is called altruism 

• E.g., under threat from a predator, an individual Belding’s ground squirrel will make an alarm call to warn others, even though calling increases the chances that the caller is killed 

• E.g., in naked mole rat populations, nonreproductive indivudals may sacrifice their lives protecting their reproductive queen and kinds from predators

Inclusive Fitness

• The evolution of altruistic behavior can be explained by inclusive fitness

• Inclusive fitness is the total effect of an individual has on proliferating its genes by producing offspring and helping close relatives produce offspring

Hamitlon’s Rule and Kin Selection

• William Hamiton proposed a quantitative measure for predicting when natural selection would favor altruistic acts among related individuals 

• Three key variables in an altruistic act 

  • Benefit to the recipient (B) 

  • Cost ot the altruistic ©

  • Coefficeint of relatedness (the fraction of genes that, on average, are shared, r)

• Natural selection favors altruism when 

  • rB>C

• This inequality is called Hamilton’s rule 

• Hamilton’s rule is illustrated with the following example of a girl who risks her life to save her brother 

• Assume the average individual has two children; as a result of the sister’s action 

  • The brother can now father two children so B=2

  • The sister has a 25% chance of dying and not being able to have two children, so C=0.25 x 2 = 0.5 

  • The brother and sister share half their genes on average, so r = 0.5

  • If the sister saves her brother rB(=1) > C(=0.5)

• Kin selection is the natural selection that favors this kind of altruistic behavior by enhancing reproductive success of relatives 

  • An example of the relationship between kin selection and altruism is the warning behavior in Belding’s ground squirrels

    • In a group, most of the females are closely related to each other 

    • Most alarm calls are given by females who are likely aiding close relatives 

• Another example of kin selection comes from naked mole rats - they live colonies and are closely related to each other. 

  • One queen, 1-3 “kings who mate with her. 

  • Non-reproductive individuals increase their inclusive fitness by helping the reproductive queen and kings (their close relatives) to pass their genes to the next generation

Reciprocal Altruism 

• Altruistic behavior toward unrelated individuals can be adaptive if the aided individual returns the favor in the future

• This type of altruism is called reciprocal altruism

  • Reciprocal altruism is limited to species with stable social groups where individuals meet repeatedly, and cheaters (who don’t reciprocate) are punished

  • Reciprocal altruism has been used to explain altruism between unrelated inidividuals in humans 

• In game theory, a tit-for-tat strategy has the following rules

  • Individuals always cooperate on first encounter 

  • An individual treats another the same way it was treated the last time they met

    • That is, inidivudals will always cooperate, unless their opponent cheated them the last time they met

• Tit-for-tat strategy explains how reciprocal altruism could have evolved 

• Individuals who engage in a tit-for-tat strategy hav a higher fitness than indiivduals who are always selfish

Evolution and Human Culture 

• No other species comes close to matching the social learning and cultural transmission that occur among humans 

• We are better at acquiring new skills than any animal

• Not all of our activities seem to have a survival or reproduction role 

• Play behavior may improve our ability to use objects and develop social skill, or prepare us to handle unexpected events 

• Human culture is related to evolutionary theory in the distinct discipline of sociobiology 

  • Human behavior, like that of other species, results from interaction between genes and environment 

  • However, our social and cultural institutions may provide the only feature in which there is no continuum between humans and other animals

Discovering Ecology

• Ecology is the scientific study of the interactions between organisms and the environment 

• These interactions determine the distribution of organisms and their abundance 

• Modern ecology includes observation and experimentation 

• E.g., the discovery of two new grog species in papua New Guinea raises many ecological questions

  • What environmental factors limit their geographic distribution? 

  • What factors (food, pathogens) affect population size?

The Scope of Ecological Research 

• Ecologists work at levels ranging from individual organisms to the planet 

Global Ecology 

• The biosphere is the global ecosystem, the sum of all the planet’s ecosystems 

• Global ecology examines the influence of energy and materials on organisms across the biosphere

Lanscape Ecology 

• A landscape (or seascape) is a mosaic of connected ecosystems 

• Landscape ecology focuses on the exchanges of energy, materials, and organisms across multiple ecosystems

Ecosystem Ecology 

• An ecosystem is the community of organisms in an area and the physical factors with which they interact 

• Ecocystem ecology emphasizes energy flow and chemical cycling among the various biotic and abiotic components 

Community Ecology (no abiotic conditions, just interactions with living stuff) 

• A community is a group fo populations of different species in an area 

• Community ecology  examines the effect of interspecific interactions on community structure and organizations 

Population Ecology 

• A population is a group of indiivduals of the same species living in an area

• Population ecology focuses on factors affecting population size over time

Organismal Ecology 

• Organismal ecology studies how an organism’s structure, physiology, and (for animals) behavior meet environmental challenges 

• Organismal ecology includes physiological, evolutionary, and behavioral ecology 

Concept 52.1 Earth’s climate varies by latitude and season and is changing rapidly

• The long-term prevailing weather conditions in an area constitute its climate 

  • Four major abiotic components of climate are temperature, precipitation, SUNLIGHT (determines the rest!), and wind

  • Macroclimate consists of patterns on the global, regional, and landscape level 

  • Microclimate consists of very fine patterns, such as those encountered by the community of organisms underneath a fallen log 

Global Climate Patterns 

• Global climate patterns are determined largely by solar energy and Earth’s movement in space 

• The warming effect of the sun causes temperature variations, which drive evaporation and the circulation of air and water 

• This causes latitudinal variations in climate 

Latitudinal Variation in Sunlight Intensity 

• The angle wat which sunlight hits earth affects its intensity, the amount of heat and light per unit of surface area 

• The intensity of sunlight is strongest in the tropics (between 23.5 degree north latitude and 23.5 south latitude) where sunlight strikes Earth most directly

Global Air Circulation and Precipitation Patterns 

• Global air circulation and precipitation patterns play major roles in determining climate patterns

• Water evaporates in the tropics, and warm, wet air masses flow from the tropics toward the poles

Global Climate Patterns

• Rising air masses release water and cause high precipitation, especially in the tropics 

• Dry, descending air masses create arid climates, especially near 30 north and south 

• Air flowing close to Earth’s surface creates predictable global wind patterns 

• Cooling trade winds blow from eat to west in the tropics; prevailing westerlies blow from west to east in the temperature zones 

Regional and Local Effects on Climate

• Climate is affected by 

  • Seasonality 

  • Large bodies of water 

  • Mountains 

Seasonality 

• Seasonal variations of light and temperature increase steadily towrad the poles 

• Seasonality at high latitudes is caused by the tilt of Earth’s axis of rotation and its annual passage around the sun 

• Belts of wet and dry air straddling the equator shift throughout the year with the changing angle of the sun 

• Changing wind patterns affect ocean currents 

Bodies of Water

• Oceans, their currents, and large lakes moderate the climate of nearby terrestrial environment 

• Currents flowing toward the equator carry cold water from the poles; currents flowing away from the equator carry warm water toward the poles 

  • These large gyres have a significant impact on the climate of terrestrial regions 

• Land and sea breezes 

  • During the day, air rises over warm land and draws a cool breeze from the water across the land 

  • As the land cools at night, air rises over the warmer water and draws cooler air from land back over the water, which is replaced by warm air from offshore 

Mountains 

• Rising air releases moisture on the windward side of a peak and creates a “rain shadow” as it absorbs moisture on the leeward side 

• Mountains affect the amount of sunlight reaching an area 

• In the Northern Hemisphere, south-facing slopes receive more sunlight than north-facing slopes 

• Every 1,000 m increase in elevation produces a temperature drop of approximately 6 degrees C 

Microclimate 

• Microclimate is determined by fine-scale differences in the environment that affect light and wind patterns 

• Every environment is characterized by differences in 

  • Abiotic factors, including nonliving attributes, such as temperature, light, water, and nutrients 

  • Biotic factors, including other organisms that are part of an individual’s environment 

Global Climate Change

• Changes in Earth’s climate can profoundly affect the biosphere 

• One way to predict the effects of future global climate change is to study previous changes 

• As glaciers retreated 16,000 years ago, tree distribution patterns changed

• As climate changes, species that have difficulty dispersing may have smaller ranges or could become extinct 

• Burning of fossil fuels and deforestation are increasing CO2 concentrations in the atmosphere and other greenhouse gases 

• The Earth has warmed about 0.8C (1.4F) since 1900 and is projected to warm 1-6C more by the year 2100 

• We can look at ice age changes to predict how this affects the distribution of living things