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Week 8 Bio Notes

by: Nikki Hovland

Week 8 Bio Notes Biol 180

Nikki Hovland
GPA 3.82
Introductory Biology
Scott Freeman

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About this Document

This week's notes cover population growth, life histories and behavioral ecology, particularly sexual selection.
Introductory Biology
Scott Freeman
Class Notes
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This 7 page Class Notes was uploaded by Nikki Hovland on Wednesday November 18, 2015. The Class Notes belongs to Biol 180 at University of Washington taught by Scott Freeman in Summer 2015. Since its upload, it has received 124 views. For similar materials see Introductory Biology in Biology at University of Washington.


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Date Created: 11/18/15
INTRODUCTORY BIOLOGY 180 Thursday November 19 2015 Week 8 Notes Lecture 27 Behavioral Ecology Sexual Selection selection based on success of courting a mate is also a mechanism of evolutionary change sexual selection natural selection that favors individuals with traits that increase their ability to obtain mates acts stronger on males intersexual selection selecting an individual of one gender to mate by individual of the other gender intrasexual selection selection within a gender competition between individuals of one gender for mates Fundamental Asvmmetrv of Sex Theorv pattern sexual selection acts on males much more strongly than on females traits that attract the opposite gender are more elaborate in males process energy cost of creating large egg is very high while sperm requires little energy eggs are expensive but sperm are cheap Theory females put much more energy and resources into offspring than males in most species 2 main consequences females produce few young since eggs are large and require a lot of energy female s fitness limited by ability to find resources to produce healthy young male can have almost unlimited offspring because sperm require little energy male s fitness limited by number of females he can mate with not producing enough sperm predictions males compete with each other to gain female mates females should be more choosy about picking male mate sexual selection should act more strongly on males male fitness limited by finding mates so alleles that increase attractiveness or success in competition should quickly increase in frequency INTRODUCTORY BIOLOGY 180 Thursday November 19 2015 females often choose to mate with males that care for the young or provide the most resources to produce eggs ANDOR have physical characteristics that suggest males have good genes like coloration maletomale competition usually decides territorieshow many females he can mate with Ex elephant seals dominant males usually win gt mate with more females gt alleles for larger dominant body size increase in more offspring bc better fitness gt evolution of large male size via directional selection sexual selection acts stronger in males because they have more traits that function solely for courting mates or competition sexual dimorphism any trait that differs between male and female BECAUSE sexual selection tends to more intense in males sexual dimorphism RESULTS from sexual selection they are not the same thing ecological or environmental selection all other types of selection that favor traits that help individual survive in physical and biological environments not obtain mates remember natural selection is only selection that results in adaptation altruism self sacrificing behavior with fitness cost to individual doing the behavior but a fitness benefit to whom the behavior is being done for decreases individual s offspring but increases others offspring Hamilton s Rule formulation of Br gt C stating that altruistic behavior is most likely when three conditions are met 1 fitness benefits are high for recipient 2 altruist and recipient are close relatives 39 3 fitness costs to altruists are low B fitness benefit to recipient C fitness cost to actor of behavior r coefficient of relatedness probability that the alleles in two individuals are identical by descent measure of how closely the actor and recipient are related and varies between Onot relatedand 1 probability two offspring each receive same allele from mom 12 r between half siblings 14 12 12 two independent events INTRODUCTORY BIOLOGY 180 Thursday November 19 2015 probability of two offspring getting same allele from dad 14 probability of two offspring getting same allele from mom 14 r between full siblings 12 14 14 same event to occur diff ways if Hamilton s rule holds natural selection favors the altruistic alleles because close relatives are likely to have copies of the alleles IMPORTANCE of Rule individuals can pass on alleles to next generation by helping close relatives AND producing own offspring inclusive fitness combination of direct and indirect fitness direct fitness derived from individuals own offspring parental care parents increase own fitness by helping offspring with resources indirect fitness derived from helping relatives produce more offspring than they could on their own kin selection natural selection that acts through the benefits relatives receive at expense of acting individual kin selection decreases direct fitness of individual but increases indirect fitness gt overall increase in inclusive fitness most cases of selfsacrificing behavior that have been analyzed follow Hamilton s rule and hypothesized to be result of kin selection sometimes altruistic behavior is involuntary reciprocal altruism exchange of fitness benefits that are separated in time individuals help others who have helped them in the past or likely to in the future widely thought of explanation for why humans help others not related to them some behaviors may seem altruistic but are actually selfish because they may increase fitness of individual doing the behavior assisting others benefits gt costs Lecture 28 Population Growth population s overall growth rate is function of birth rates death rates immigration rates and emigration rates growth rate change in individuals in population delta N per unit time delta t INTRODUCTORY BIOLOGY 180 Thursday November 19 2015 difference between birth rate and death rate per individual per capita rate of increase symbolized by r per capita per each individual intrinsic rate of increase rmax when r reaches its maximum value birth rates as high as possible and death rates as low as possible r max deltaN delta N delta t Exponential Growth exponential population growth when r does not change over time KEY it is density independent growth rate does not depend on number of individuals in the population RATE of increase is the same but number of individuals added is not Exponential growth common in two situations 1 few individuals in a new pop in a new habitat 2 population devastated by catastrophe and begins to recover starting with few survivors exponential growth cannot continue indefinitely Logistic Growth growth is density dependent pop density gets high then per capita birth rate decreases per capita death rate increases gt r decreases carrying capacity K maximum number of individuals in a population that can be supported by habitat depends on food water space soil quality restingnesting places can change year to year depending on conditions logistic growth equation deltaN deta t r maxNKN K as N gets bigger gt KN K close to 1 growth rate high vise versa as population approaches carrying capacity growth rate slows logistic population growth changes in growth rate that occur as function of population size Limitations on growth ratespopulation sizes INTRODUCTORY BIOLOGY 180 Thursday November 19 2015 density independent factors change birth and death rates no matter how many individuals in population abiotic factors like volcanoes hurricanes etc density dependent factors change as function of pop size and are biotic trees crowding gt less water nutrients etc competition for resources carrying capacity is not fixed K varies with space and time conditions are better in some years and not in others KEY population grow exponentially unless slowed by density dependence Population Dynamics population dynamics changes in populations through time and space metapopulation a larger populations made up of small isolated populations connected by migrations balance between extinction and recolonization occurs in metapopulation gt stable number of individuals over time populations cycle either because of interspecific interactions between species predation parasitism competition among species or intraspecific interactions within species competition among individuals for food populations are effectedlimited by both food and predation in most cases often species in a predatorprey relationship may cycle closely together Lecture 29 Human Population Growth Life Histories trade off inescapable compromise between traits tradeoffs like energetic investment in reproduction and immune system are very common KEY the ability to acclimatize is an adaptation in itself genetically variable trait that can respond to natural selection ie ability to tan population group of individuals of same species that live in same area at same time population ecology study of how and why number of individuals in a population changes over time and space INTRODUCTORY BIOLOGY 180 Thursday November 19 2015 range geographic distribution dynamic always in flux as abiotic and biotic factors change throughout time population density number of individuals per unit area distribution patterns within populations random clumped or uniform more and more species are becoming metapopulations as humans reduce forest and grassland areas demography study of factors that determine size and structure of populations across time number of individuals present in population depends on birth death immigration and emigration immigration individuals enter a pop moving from another pop emigration individuals leave a population to join another life table summarizes probability an individual will survive and reproduce throughout its life time usually focus on females in life table data because number of males rarely affects population growth cohort group of the same age that is followed through time survivorship proportion of offspring produced that survive on average to a certain age types of curves Type 1 survivorship through life is high most live to max life span humans Type 2 individuals have same probability of dying as living steady curve blackbirds 39 Type 3 extremely high death rates but then high survival rates later in life PLANTS lots of seeds don t survive fecundity number of female offspring produced by each female in population net reproductive rate determines whether population is increasing or decreasing KEY fitness trade offs occur because every individual has restricted amount of time and energy resources are limited INTRODUCTORY BIOLOGY 180 Thursday November 19 2015 life history describes how an individual allocates resources to growth reproduction and activitiesstructures related to survival KEY often shaped by natural selection so that fitness of individual is maximized in their environment General trends species with high fecundity grow quickly quickly reach sexual maturity produce many small eggs or seeds species with high survivorship grow slowly invest resources in traits to reduce damage from enemiesincrease ability to compete for resources food water Human Population Growth age pyramids give a lot of information about population s history and can help predict population future human population has DRAMATICALLY INCREASED recently worry that we will overshoot the carrying capacity of the planet consequences of overpopulation primary cause of habitat loss and species extinction decline in living standards politcal instability mass movements of people shortages of water fuel and other resources fertility rates average number of children surviving that each woman has in her life replacement rate average fertility required for each woman to produce exactly enough offspring to replace herself and the father of the child when this occurs for one generation zero population growth future of human population relies on fertility rates how many kids each woman decides to have


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