Bio 28600 Exam 1 Study Guide
Bio 28600 Exam 1 Study Guide Biol 28600
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This 22 page Study Guide was uploaded by Fayette Adelaja on Friday February 12, 2016. The Study Guide belongs to Biol 28600 at Purdue University taught by Joshua Springer in Spring 2016. Since its upload, it has received 211 views. For similar materials see Introduction to Ecology and Evolution in Biology at Purdue University.
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BIO 286 Study Guide Exam I *Math from Population Lecture on Feb. 9th will not be included on exam. However must know terms and definitions from then. Ecology: Relationship of organisms to one another AND to their biotic (living) and abiotic (nonliving) surroundings (environment) The study of the structure and function of nature Ecological Systems: May be organism, population, multiple populations, ecosystem, or entire biosphere Fundamental unit of ecology is organism The organism approach = why some organisms are limited in their distribution and why related species living in different environments have different appearances. An ecosystem is composed of many different species, each of which is essential for a healthy ecosystem As biologists, we tend to focus on the “macroorganisms” plants, animals and fungi, but there are many species of microorganism that are key components to many ecosystems Evolution: cumulative change of heritable characteristics of population • cumulative change: small changes upon small changes over many generations • heritable characteristics: genecontrolled factors • population: not an individual ‘evidence of’ Descent with modification over many generations Not simply change over time but change in allele frequencies (form of a gene) over time Organisms share a common ancestor in the ancient historical past (millions of years) factors affecting pace of evolution: • rate of environmental change • amount of generic variation in species • size of population involved • how fast species reproduces (generation time) Large or Small population evolves faster? • Small populations evolve faster (genetic drift • BUT a chance for a NEW mutation to appear is higher in a larger population (mutation rate) • Small populations would show the effects of a mutation faster…can lead to faster evolution Examples of evolution: • a fungal population has a new ability to use and break down toxins in the environment • E. coli gains resistance to a new antibiotic Is NOT: • Perfect (we, as humans sometimes think things are perfect) • A cause to ‘believe in’ irreducible complexity (the idea that something is so complex it couldn’t have evolved) Vertebrate eye Flagella or cilia ‘motors’ • Untestable We test it all the time It took 70 years to become an accepted theory! Natural Selection The close correspondence of organisms to their environment derives from a process called natural selection. Only individuals that are well adapted to their environment will survive and produce offspring Favorable traits are passed on, unfavorable ones are removed Include physiological/biochemical adaptations and behavioral adaptations Chooses best adapted traits for current generation only Not necessarily the best adapted for the next or subsequent generations • Evolution by natural selection is NOT forwardlooking • It is not a ‘thinking process’ Sorts through allelic combinations that ‘work’ or don’t work for the present • (alleles= versions of a gene) Darwin’s Four Postulates for evolution by natural selection: • Individuals within populations are variable • This variation is at least partly heritable (passed from parent to offspring) • In every generation, some individuals survive and reproduce better than others • Differential reproductive success is tied to the variation among individuals (not random) The trait composition of the population then changes TESTABLE ideas (not just storytelling) “Darwinian fitness”: the ability of an individual to survive and reproduce in its environment Examples of natural selection • Galapagos Finches beak sizes changed over time with drought and food available Wet years: smallbeak birds do better Dry years: bigbeak birds do better • Cryptic peppered moths (Kettlewell): Industrial soot favored melanistic form, cleaner air favored return to light form 3 Ways Selection acts on trait: Ecology and Evolution: Considering the evolutionary history of organisms and their interactions with the environment • Can help explain characteristics of organisms and the origins of characteristics and species interrelatedness • Competitors, mutualisms, predators, prey and pathogens are commonly studied in this field helps to understand the origins of emerging diseases and the origins and evolutions of different species of animals HIV One main reason why HIV infection can change over time in person because errors in transcription accumulate Cuthunter hypothesis was proposed to explain the spillover event of HIV to humans Drug holiday: short break from HIV drugs Adaptation: heritable trait that confers a fitness advantage to its carrier (by improving the reproductive success of the carrier, and thereby the transmission of that trait) Can be sharper teeth, stronger wings, winning smile … We also speak of individuals “adapting” to changes, but this is “acclimatization” (winter fur) or “phenotypic variation” (faster growth in south) Transplant experiments can separate genetically encoded adaptation from environmentally induced phenotypic variation Fitness: Proximate: ability of an organism to survive and reproduce Ultimate: relative representation of alleles in subsequent generations Measures of fitness • Absolute fitness: survival and reproduction of each genotype • Relative fitness: ability of one genotype to survive and reproduce relative to another Genetic Variance: Stabilizing selection on quantitative traits reduces genetic variance • extreme individuals are selected out of the population Balancing selection in Mendelian traits maintains genetic variation • Both alleles are maintained with heterozygote advantage Frequency Dependent Selection: Fitness of a phenotype affected by commonness of phenotypes; declines if too common Disruptive selection results when rare phenotypes have higher reproductive success than common phenotypes Selection can favor whichever phenotype is less common in a population Phenotype vs Genotype: Phenotype is the result of the genotype (in part)—the outward appearance or characteristic Genotype is the specific allele or alleles that code for a physical characteristic or trait (or physiological functioning) Cline: change or variation in a phenotype over the range of a species. One phenotype but it varies slightly Phenotypic plasticity: the ability for one genotype to produce more than one phenotype in the same local area Five Evolutionary Forces: Selection : • Important throughout the growing season or disease cycle (if talking about a pathogen) Differences in phenotype lead to variable survival and reproduction Some individuals have higher fitness • Evolution occurs if the trait under selection is variable, heritable, and differential in survival. • If a trait does not have variation (reached fixation), selection cannot generally act on it Random Genetic Drif t: • Not a selective force Doesn’t lead to adaptation Does (Can) lead to changes in allele frequencies by random chance • Alleles randomly reach fixation by chance Decline in heterozygotes, increase in homozygotes • Most important when population sizes are small By chance (sampling effect) alleles are represented in next generation As population size increases, effects of drift decrease When population size is small random genetic drift can overwhelm selection Migration (Gene flow) : • Mechanism of evolution if alleles inherited Establish and become part of breeding population • Has largest effect when populations are small New alleles make a larger proportion of the population If migrants differ in allele frequency…then inhibit or promote adaptation • Maladaptive or highly fit individuals • Homogenization among populations If selection is not acting Counteracts drift by preventing divergence of populations • High levels of migration in a species can prevent speciation if no barriers to migration exist (or are very inconsequential) • Population divergence (F ) ST Measures proportional reduction in heterozygosity • So = increase in homozygosity! • Subpopulation divergence Mutation : • Ultimate source of all genetic variation Almost never changes allele frequencies Most are quickly selected against (deleterious) • Chance of seeing mutation increases as population size increases Constant mutation rate = more seen in larger populations because higher proportion Recombination : • Important whenever it occurs because it creates new genotypic combinations and therefore produces new, variable phenotypes on which selection can act Note**: Changes in population size can GREATLY Influence relative importance of each genetic force and Population genetics can influence commonness or rareness of particular alleles and presence or absence of alleles that cause disease or resistance to a disease. Plant adaptations and resources: Plants use potassum, nitrogen, water in soil, carbon dioxide as resources plants obtain the carbon they need from the atmosphere Photosynthesis and respiration Environmental controls on photosynthesis Plant adaptations to: • High and low light • Water limitation • Nutrient availability Conditions are physical / chemical features of the environment • e.g. Temperature, humidity, pH, etc. Not consumed by living organisms (but may still be important to them) Resources are consumed • Once used, they are unavailable to other organisms (in that original form) • Plants: sunlight, water, mineral nutrients, … • Animals: prey organisms, nesting sites, … Plants are autotrophs make their own organic carbon form inorganic nutrients • Need light, ions, inorganic molecules Plants are sessile (do not move once established—but seeds…) • Grow towards nutrients Or in environments with the most appropriate nutrients Photosynthesis: Conversion of carbon dioxide into simple sugars • 6CO + 12H O C H O + 6O + 6H O 2 2 6 12 6 2 2 respiration: • C H O + 6O 6CO + 6H O + ATP 6 12 6 2 2 2 involves gas exchange controls of photosynthesis are light, water, nutrients, and temperature Tradeoff • Shade plants grow better in the sun than in the shade, • but sun plants grow faster than shade plants in direct sun • Shade plants survive well in either sun or shade • Sun plants cannot tolerate shade • Sun leaf: thicker, more cell layers, more chloroplasts Leaves at many angles High saturation point High compensation point High respiration Less chlorophyll Enzymes limit photosynthesis (limit to how much can be produced) • Shade leaf: flat, thin, larger surface area / unit weight Horizontal leaves, single layer Low saturation point Low compensation point Low respiration More chlorophyll Light availability limits photosynthesis rate Nutrient and Resource Poor Environments: Drought • Avoiders Short lifespan Wet season Seeds survive drought Drought deciduous species • Leaves shed in dry season • Tolerators Leaves transpire slowly Change orientation of leaves Sunken stomata (gas exchange organs) • E.g. pines More efficient photosynthesis • E.g. C4 > reduces photorespiration • E.g. CAM > stomata open at night (Details in Text) Root hairs in plants increase area for better water absorption Nutrients: • Macronutrients – needed in large amounts (e.g. C, H, O, … N, P, K, Ca, Mg, S) • Micronutrients – trace elements (e.g. Fe, Mn, B) • Micro/macro refer to the quantity needed Plants adapted to poor nutrient conditions tend to have evergreen leaves Temperature: Increase temperature > increase biochemical reaction rate At high temperature, enzymes denature > death Leaf temperature: • > 95% of sunlight absorbed by a leaf becomes heat • Cooling of leaves: Transpiration Convection (movement of cool air around a leaf) Keep a microclimate around leaves Response to cold: • chilling injury: near, >0C; cell membranes rupture • freezing: <0C; ice inside cells = death; ice outside cells = dehydration (may survive); may kill juveniles only Extreme Temperature: • Cold the effects of freezing: physical damage to structures caused by the formation of ice; the membrane bound structures are destroyed or damaged. • Heat: inadequate O2 supply for metabolic demands (especially in areas where O2 is low, such as water) • Heat and Cold: reduced activity or denaturation of proteins the inactivation of certain proteins with the result that metabolic pathways are distorted. • Not a resource used by plants Thermoregulation: Definition: maintenance of internal temperature within a range that allows cells to function efficiently Two main types: • ectothermy An animal that relies on external environment for temperature control instead of generating its own body heat “coldblooded” e.g., invertebrates, reptiles, amphibians, and most fish the majority of animals are ectotherms ectotherms cannot move very much unless the ambient temperature allows roughly, for each 10 degree increase in temperature, there is a 2.5 increase in metabolic activity ex: fish, frogs, lizards, insects, crustaceans • endothermy a warmblooded animal that controls its body temperature by producing its own heat through metabolism evolved approximately 140 mya E.g., birds, mammals, marsupial, some active fish like the great white shark and swordfish advantages: • external temperature does not affect their performance • allows them to live in colder habitats • muscles can provide more sustained power e.g., a horse can move for much longer periods than a crocodile can disadvantages: • energy expensive: an endotherm will have to eat much more than an ectotherm of equivalent size Where do endotherms thrive? • Higher latitudes and deserts • Terrestrial environments have more variation in daily and seasonal temperature which contributes to more endotherms in terrestrial environments • endotherms (mammals and birds) generally outcompete ectotherms if they are after the same food source Endothermy and evolution of sleep • evolutionary remnant of torpor of our ancestors • the body needs sleep in order to offset the high energy costs of endothermy: When animals fall asleep their metabolic rates decrease by approximately ten percent Law of Tolerance: for most requirements of life, there is an optimal quantity, above and below which the organism performs poorly There is much variation in the range of temperatures that a species can tolerate Behavioral adaptations: • Animals bathe in water to cool off or bask in the sun to heat up • shivering, sweating, panting • honeybees survive harsh winters by clustering together and shivering, which generates metabolic heat • Inefficient – 75% of energy is lost in mechanical movement • Torpor: metabolism decreases heart and respiratory system slow down body temperature decreases conserves energy when food supplies are low and environmental temps are extreme E.g., hummingbirds • Hibernation: Longterm torpor adaptation for winter cold and food scarcity E.g., ground squirrels • Aestivation: summer torpor adaptation for high temperatures and scarce water supplies E.g., mud turtles, snails Color: Change coloration (darker colors absorb more heat) • E.g., lizards, butterflies, crabs Posture: Change shape (flatten out to heat up quickly); Orientation changes Chemical adaptations: • Many Canadian butterflies overwinter further south and hibernate • they produce sugarlike substances as antifreeze • E.g., Mourning Cloak butterfly Size: • Small mammals (such as mice and shrews) have a greater dependence on internally generated heat than big mammals (such as elephants and hippos) • leads to: presence of insulation (fur large mammals generally have less hair) voracious appetites of small mammals (a shrew eats more per unit body weight than an elephant does) Populations: A population is a group of individuals of the same species that inhabit a given area Populations have structure, including density, spacing and age distribution Populations are dynamic, changing over time Why is it important that the individuals are members of the same species? Why is it important for a population to have a spatial boundary? • Human construct sometimes (we determine boundaries based on our studies) Organisms may be unitary or modular • Suckers – new stems that sprout from surface roots and may appear to be individuals • Genet – plant produced by sexual reproduction, a genetically unique individual • Ramet – module produced asexually by a genet (these are essentially clones) • New stems are formed from the root of an individual. These genets are genetically distinguished by the parent plant in that they are simply unique ramets. Separate stems connected by the same roots are still the same genets. Distribution of population defines spatial location • Ubiquitous species have a geographically widespread distribution • Endemic species have a geographically restricted distribution many endemic species have specialized habitat requirements • E. g., the shalebarren evening primrose is found only on hot, shalebarren environments, on south or southwest facing slopes in the Allegheny Mountains • There are many types of geographic barriers that reduce or prevent individuals from moving and colonizing new areas bodies of water, including rivers mountains large areas of unsuitable habitat such as deserts • Interactions with other species can also serve as barriers competition predation • The environment is heterogeneous; thus most populations are divided into subpopulations that live in suitable habitat patches surrounded by unsuitable habitat • A metapopulation is the collection of these local subpopulations • These subpopulations are spatially separated but connected by the movement of individuals between them (migration!) • can’t assume that all act in the same way; each has different dynamics Population density: • Abundance is a function of population density and the area over which the population is distributed • Crude density the number of individuals per unit area square meter (m )2 square kilometer (km ) 2 • Or the number of individuals per unit volume kiloliter 3m ) or liter (.003 m ) • Place a grid over a population distribution and calculate the density for a given grid cell • WE NEVER REALLY WANT TO USE THE U.S. SYSTEM OF MEASUREMENT; IT’S TERRIBLE! • three types of spatial distribution: random uniform clumped: This is the most common spatial distribution and results from a number of factors • suitable habitat or resources are found in patches • species form social groups (herds, flocks, schools) • ramets formed by asexual reproduction • Spatial distributions of individuals may be described at multiple spatial scales • In the savanna ecosystems of Southern Africa the shrub Euclea divinorum has a clumped distribution the clumps occur because Euclea grows under the canopy cover provided by Acacia tortilis trees the clumps are uniformly spaced because Acacia trees have a uniform distribution due to competition between individual trees for water • To account for the patch distributions of some species, ecologists may use • Ecological density – the number of individuals per unit of available living space bobwhite quail prefer hedgerow habitat density can be expressed as number of birds per mile of hedgerow rather than birds per hectare • However, it can be difficult to determine what part of a habitat is living space for a particular species • Population size (abundance) population density the area occupied • How is density determined? • Do some techniques work better then others for organisms with certain characteristics, for example, mobile versus sessile? • Sampling • How accurate is this method? • Depends largely on the spatial distribution of individuals in the population works well if individuals have a uniform distribution works less well with a random or clumped distribution • important to report a confidence interval or some estimate of variation = statistics! • Can also be influenced by the choice of boundaries or sample units • Markrecapture is the most commonly used technique to measure animal population size • This method is based on: capturing a number of individuals in a population marking them with a mark that will not be lost during the course of the study releasing a known number of marked individuals (M) back into the population (N the value being estimated) after an appropriate period of time, recapture a number of individuals in the population Of the individuals captured the second time (n), some will have been marked, or recaptured (R) To estimate the population density: Assume that the ratio of n/R represents the ratio for the entire population (N/M) N/M n/R Since N is the only unknown, rearrange the equation to solve for it: N nM/R Example: You are estimating the population density of the Northern Cardinals (Cardinalis cardinalis) in Tippecanoe County, Indiana. Your research team initially captures and bands 285 birds. Three months later, you return and capture 335 birds. Of those, 4 were banded on your previous trip. What is the estimated size of this N. C. population? M 285, n 335, R 4 N nM/R [(335 285)/4] 25,294 • Signs of the presence of animals include: counts of vocalization, such as bird song counts of animal scat seen along a certain length of trail counts of animal tracks, such as footprints in the snow Population Measures • Measures of Population Structure Include Age, Developmental Stage, and Size • Abundance does not provide any information on the characteristics of individuals within a population • Why do populations with overlapping generations have an age structure? • What can the population’s age structure tell you about the growth of the population? • A population with nonoverlapping generations does not have an age structure individuals reproduce and die within a single season • annual plants and some insects • A population with overlapping generations has an age structure there are individuals in different age classes • reproduction is restricted to certain age classes • mortality is more common in certain age classes • Populations can be divided into three ecologically important age classes prereproductive reproductive post reproductive • How long an individual is in each age class depends on the organism’s life history some organisms, such as mice, have a very short span of time between generations other organisms, such as elephants, have a very long span of time between generations • The most accurate method is to mark young individuals in a population and follow their survival through time • This is also the most difficult many individuals must be marked and subsequently checked at regular intervals, often over many years • Less accurate methods include • Examining a sample of bodies of individuals that have died and determine their ages at death • Look for characteristics that indicate age wear and replacement of teeth growth rings in the teeth or horns plumage changes and wear in birds annual growth rings on scales and ear bones in fish • It can be more challenging to estimate age structure in plants • Trees with seasonal growth produce annual growth rings • Dendrochronology – counting annual growth rings to determine the age of a tree • Size of the tree based on diameter at breast height (dbh) can also be used however, growth conditions can strongly affect this measurement • An age pyramid is a graphical representation of the age structure of a population Sex: sex ratios in populations may shift with age In most mammalian populations, the sex ratio at birth (secondary sex ratio) is slightly weighted towards males (estimated at 107 males/100 females, or 1.07:1 for humans) • the sex ratio shifts towards females in older age classes • males generally have a shorter life span than females many species are characterized by rivalries among males for resources or mates • In birds, the number of males tends to be higher than females nesting females are more susceptible to attack and predation Movement within populations: Dispersal is the movement of individuals in space Generally implies the movement of individuals away from one another • emigration – when individuals leave a subpopulation • immigration – when individuals enter a subpopulation Movement of individuals between subpopulations is an important part of metapopulation dynamics • maintains gene flow between the subpopulations Migration is movement of organisms that is roundtrip. These trips may be daily or seasonal: • zooplankton move in the water column; lower depths during the day and the surface at night • bats leave caves at dusk, move to feeding areas, then return at dawn • earthworms move deep into the soil for winter to avoid freezing, then move back up in the spring • gray whales feed in the Arctic during the summer, winter off the California coast where calves are born Population density and distribution change in both time and space Dispersal can affect the spatial distribution of individuals within a population. • emigration leads to a decline in density • immigration leads to an increase in density, or can establish a new subpopulation in a previously unoccupied habitat Species introduced into an area where they did not previously live can expand into new areas These introductions may be intentional or unintentional Humans aid in dispersal of many species: Dispersal by humans has led to the redistribution of species on a global scale Invasive species – organisms successfully introduced to places they have never occurred • freed from the constraints presented by their predators, parasites, and competitors in their native range, many species have become established and spread Sometimes the introduced species are harmless, but more often they have negative effects on native species and ecosystems Unintentional introductions often happen through the importation of agricultural and forest products • weed seeds may be included in a shipment of crop seeds or carried in the fur or feathers of domestic animals • soil carrying seeds is used as ballast in a ship, then dumped in another country when cargo is picked up • major forest insect pests have come in through wooden shipping containers and pallets Humans have intentionally introduced nonnative plants for ornamental and agricultural purposes There are many examples of this in North America • purple loosestrife – introduced from Europe, it has spread into wetlands, eliminating native plants • Australian paperbark tree – introduced as an ornamental plant in Florida, it has displaced many native species • kudzu – an ornamental vine that has spread throughout the southern United States, outcompeting other plants Aquatic environments have also been affected More than 139 nonnative aquatic species have invaded the Great Lakes through shipping • the zebra mussel is native to the lakes of southern Russia and was introduced in ballast water • it is now found in most eastern rivers and the Great Lakes The San Francisco Bay Area has 96 nonnative invertebrate species Introduced exotic fish are responsible for 68 percent of recent fish extinctions in North America Population Growth: Individuals are added to a population through births and immigration Individuals leave the population through deaths and emigration An open population has immigration and emigration A closed population does not have or has a very low level of immigration and emigration that doesn’t influence population growth Growth reflects the difference between birth and death rates We can create simple mathematical models to describe how a population changes with time. • Example: Hydra in an aquarium Immigration Emigration Birth Death Population size Closed population (no aquarium escapes!) most reproduction is asexual by budding Assume all reproduce asexually and all have one offspring at a time How will the population size change over time? • Genetically diverse? N number of individuals in the population t time N(t) number of individuals in the population at a given time • We read this “N of t”, short for “N is a function of t” • This is “function notation”, not multiplication. Assume the initial population size is 100 at time zero (here day zero) • N(0) 100 • Assume this population size is much lower than the available food and resource supply in the aquarium This population is closed • No immigration or emigration are possible Budding will produce new Hydra – births Some Hydra will die • these processes are continuous, not synchronized B number of new Hydra produced each day D number of Hydra that die each day For this population B 40, D 10 How do you calculate the size of the population at the end of day one? To calculate the new population size, add the births and subtract the deaths N(0) B D N(1) 100 40 10 130 Now, how do you calculate the population size at the end of day two? Can you use the same values for births and deaths? • No. Obviously, the actual number of births and deaths depends on population size • An estimate that is independent of population size can be expressed as a rate, rather than an absolute number To determine the per capita birthrate, b b B/N(0) 40/100 0.4 Similarly, death rate d D/N(0) 10/100 0.1 If we assume that b and d are constant, they can be used to predict the growth of a population over time regardless of population size Therefore, the population on a given day can be represented by the equation: N(t 1) N(t) bN(t) dN(t) How would you determined the size of the Hydra population after one day? After two days? The size of the hydra population after one day N(1) 100 0.4(100) 0.1(100) 130 The size of the hydra population after two days N(2) 130 0.4(130) 0.1(130) 169 This represents a geometric population growth pattern Then plug'n'chug. N(t 1) N(t) (b d)N(t) For the first day N(1) N(0) (0.4 0.1)100 30 For the second day N(2) N(1) (0.4 0.1)130 39 In this equation, the term on the left side represents a change in population size over a period of time In 1911, the United States government introduced 25 reindeer (4 males and 21 females) onto the island of St. Paul in the Pribilof Islands, Alaska The purpose of the introduction was to provide fresh meat for the native residents Within 30 years, the population grew to more than 2000 individuals A life table is an agespecific account of mortality Ecologists use life tables to examine systematic patterns of mortality and survivorship within populations Life tables can follow a cohort, a group of individuals in a population born in the same period of time Insurance companies use these types on data on us also!! • How much to charge us for premiums. A cohort life table followed 530 gray squirrels until all individuals died within six years after the study began (none survived to age six) Column x age classes (in years, for this example) Column n x number of individuals from the cohort that are alive at age x Survivorship, lx, is the number of individuals surviving to a given age (x) as a proportion of the original cohort size (x /0 ) lx starts as 1.0 for the first timepoint x, because none of the organisms you're counting is dead. For age 0, l0 n0 0 530/530 1.0 For age 2, l n /n 80/530 0.15 2 2 0 Agespecific mortality, d , is the difference between the number of individuals alive for any x age class (n ) and the next older age class (n ) x x 1 Dying from age 0 to 1, d n n 530 159 371 0 0 1 Dying from age 3 to 4, d n n 48 21 27 3 3 4 Agespecific mortality rate, q , is determined by the number of individuals dying during a x given time interval (d ) divided by the number alive at the beginning of that interval (n ) x x All the animals die at the end of their lifespan, so the lasx q is 1.0 For age 0, q d /n 371/530 0.70 0 0 0 For age 4, q 4 d 4 4 16/21 0.75 A mortality curve plots mortality rates (qx) against age For the gray squirrel example, the graph shows that there are two distinct parts in the life history • a juvenile phase when mortality is high • a post juvenile phase when mortality rate decreases with age to a point, then increases again A cohort, or dynamic, life table shows the fate of a single group of individuals born at a given time (the cohort) from birth to death • a dynamic composite life table is constructed from individuals born over several time periods, not one A timespecific (static) life table is constructed by sampling a population in a way that obtains a distribution of age classes during a single period • this is easier to construct than a cohort life table • The assumptions for a timespecific life table: each age class sampled in proportion to its numbers in the population agespecific birthrates are constant over time agespecific mortality rates are constant over time Lifetables for longlived vertebrates almost always have overlapping generations Some animals, especially insects, live only one breeding season so generations do not overlap • all individuals belong to the same age class • to obtain the value of n for these species, observe a natural population over several x annual seasons, estimating population at each time • for many insects, n xcan be obtained by estimating the number surviving from egg to adult Three general types of curves • Type I (strongly convex) – survival rate is high throughout the life span, with most mortality at the end humans and other mammals, some plants • Type II (straight) – survival rates do not vary much with age adult birds, rodents, reptiles, many perennial plants • Type III (concave) – mortality is very high early in life oysters, fish, many invertebrates, many plants Agespecific mortality rates (q ) and agespecific birthrates (b ) can be combined to project x x future changes in the population How is a population projection table constructed? Why are only females followed in constructing the table? What assumptions does this approach require? A population projection table projects the growth of a population using information from a life table and fecundity table Uses a new term s is agespecific survival (the proportion of the population that survives to the next age class) x and is calculated using the agespecific mortality information s x 1 q x For a hypothetical population of gray squirrels introduced into an unoccupied oak forest Only females are followed – females form the reproductive units of the population Must assume that the q values in the life table are the same for both males and females x This population is established in year 0 N(0) 30 • the population consists of 20 juveniles (age 0) and 10 adults (age 1) To project the fate of the initial population of 30 squirrels For those in year 0, s 0.30 (surviving to year 1) 0 20 0.30 6 For those in year 1, s 0.50 (surviving to year 2) 1 10 0.50 5 Now calculate recruitment into age class 0 during year 1 For those in age class 1, b 1 2.0 (birthrate in year 1) 2.0 6 12 For those in age class 2, b 2 3.0 (birthrate in year 1) 3.0 5 15 Then add. 12 + 15 = 27 new squirrels Survivorship and fecundity are determined in the same way for each successive year This population is estimated to grow from 30 squirrels in year 0 to about 211 in year 10 An age distribution, the proportion of individuals in each age class for any one year, can be calculated from a population projection table • divide the number in each age class (x) by the total population size for that year, N(t) • In the gray squirrel population, from year 7 on, a stable age distribution, with the proportion of each age class the same in the population, is reached. The population projection table also provides an estimate of population growth The finite multiplication rate N(t 1)/N(t) Initially varies from one year to the next, but once a stable age distribution is reached, is constant What does it mean when 1.0? If 1.0, the population size is constant If 1.0, the population is growing If 1.0, the population is declining How can be used to project population size into the future? Stochastic processes and the environment: Environmental stochasticity is the random variation in the environment that can influence birthrates and death rates in a population. This variation can be the result of • annual variations in climate temperature precipitation • natural disasters fire flood drought Life histories: Life cycle: reproduction, development, individual, migration, maintenance, molt acquire energy through foraging and allocate energy through life cycle we measure energy allocated through life cycle by phenotypic traits Tradeoff occur when individuals allocate resources to one trait reducing the expression of other trait • detected by survival rates of adults with specific traits • sometimes tradeoff not detected due to third variable problem: cause of lack of expression due to another variable besides the environment constraints on life can be: • ecological: food availability and temperature interacting to make niche space for species • physiological: ex: hummingbirds and passerines pollinate different kinds of flowers based on amount of sucrose, fructose, and glucose in flowers • phylogenetic: linear relationship between body mass (x) and generation time (y); microorganisms < arthropods < mammals Optimization resource allocation principle: better resource allocation = greater fitness; optimal trait level and optimal fitness level for survival in environment fecundity: offspring number change in development from importance on fecundity to importance on offspring quality (increase parental care) • reduces time that offspring are exposed to predators Slowfast life histories (R vs. K) • Rstrategists maximize intrinsic growth rate • Kstrategists maximize carrying capacity of environment • For mammals rK explains 48% of the total diversity in life histories
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