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Department
Biology
Course
BIO120H1
Professor
James Thomson
Semester
Fall

Description
1 BIO120H1F Introductioth September 10 , 2012 Intro to the principles and concepts of evolution and ecology, related to the origins of adaptation and biodiversity. General Information Email: [email protected] Required Materials  Laboratory Manual, uoft bookstore on Wednesday  Why Evolution is True, by Jerry Coyne  Knowledge Project articles Labs th  01 Labs start week of Sept 17  Check “My Grades” on Portal on Friday Sept 14 to find lab room Quizzes  5% Course grste  12 in total, 1 quiz on syllabus Lecture Tutorials  Monday 5:00-6:00 PM and Wed 8:00-9:00 PM  ES 1050 Professor Introductions Thompson  Interaction between flowering plants and pollinating animals  How do plant-animal interactions drive evolution  The Economy of Nature by Robert Ricklefs (recommended reading)  Nature Education Knowledge (required reading) Barrett  Evolution = Ecology and genetics Lecture 1: Distributional Aspects of Biodiversity September 12 , 2012  Where we find organisms is not random – organisms are adapted for specific environment Abiotic (physical and chemical factors): resources and conditions  Organisms need resources – are exhaustible - Nutrients, space, etc.  Depend on conditions – not exhaustible - Temp, ph, salinity, etc.  Conditions vary across space and time (more or less in some places), we envision gradients of conditions - Organisms have ranges of conditions where it functions optimally  Species have ranges of tolerance along environmental gradients - Tails are called lethal zones - E.g. Mount Everest dead zone: variable of interest is t2e O concentration 2 BIO120H1F What factors are most important?  For terrestrial plants - Temp, soil moisture (most important) - Nutrients – dissolved elements (N most important, P, K – macronutrients)  Also lots of micronutrients needed - Disturbance (e.g. fire), herbivory, disease, pollinators, seed dispersers, mycorrhizal fungi  For aquatic plants: - Add salinity, remove moisture and fire, P key  For terrestrial animals (heterotrophs) - Food and water - Temp (cover, nesting sites) - Habitat quality (birds need nesting sites, woodpeckers need dead trees, etc.) - Predation, disease  For aquatic animals - Salinity/osmotic pressure – body functions differently in salt vs fresh water  Animals tend to follow plants Gradients at the global level: temperature, rainfall, seasonality  Seasonality is the timing of temperature and rainfall  Temperature is mostly a function of latitude: warmest at equator, coldest at poles  High latitude colder: seasonality a function of temperature  Lower latitudes warmer: seasonality a function of rainfall - Rainfall depends on atmospheric circulation, offshore ocean currents, rain shadows  These factors (temp, rainfall, seasonality) determine biomes, determined by temp, rainfall, and seasonality  At higher latitudes, light hits earth at lower anger and is spread out  At equator, sun is closer and shines directly down on earth‟s surface  Summer and spring equinox? Atmospheric circulation: Hadley cells make equatorial regions rainy  Solar rays heat not so much atmosphere, but land surface, which emits infrared and heats air  Heated (less dense) air rises (at equatorial region), cools as it rises, governed by adiabatic lapse rate (the cooling rate): 5-10C/km - Warm air can have a lot of vapour in the air  As air cools, water vapour condenses and falls as rain near equator - Warmer the air, the more water vapour it can carry  Air (wrung dry of moisture) keeps pushing up until it has nowhere to go and starts to move laterally - At +/- 30 north and south, the air starts to descend - No precipitation – air is very dry - High pressure areas (because air is coming down) because air is descending, creates desert areas  Blue skies, sunny day, no cloud  1 km of rise = air cools by 5-10C (Depends on water vapour content) 3 BIO120H1F  Air rises at 0 and 60 degrees, falls at 30 degrees  3 (or 6) cell model of atmospheric circulation  Intertropical convergence zones: line of thunder storms across Pacific where air is sucked in from north and south and is rising up - Shifts seasonally, not always at the equator exactly - Producing rainy and dry seasons for certain areas, and continuous rain for other  Little seasonality = tropics, evergreen forests Convergence Zones shift because earth is spinning Wind  Wind direction involves 2 things: Hadley (gives north and south direction) and the spinning of the earth (east and west direction  Winds will rise at a certain longitude and descend at different latitudes because earth is a sphere and it spins  Twisting of winds: corriolus effect  30 degrees north of south: horse latitudes – areas of weak and unpredictable wind  Between equator and horse latitude: air moves towards the equator - Corriolus effect turns these winds into easterlies  At equator: also unpredictable wind, areas called doldrums  North of horse latitudes – beyond 30 degrees: Westerlies winds - Stronger in southern 40s than northern 40s (because there‟s no continents there) - Called the roaring forties Wandering Albatross 4 BIO120H1F  Largest wingspan of 3.5 meter  Uses the surfaces of roaring forties for dynamic soaring – wings don‟t flap - Shoulder joint can actually lock into place, no muscles needed  Can fly for a long, long time  When albatrosses are taken and placed east/west of its home, it always flies in the direction of the wind General trends of terrestrial vegetation with climatic variables  Vegetation growth (and primary productivity) increases with moisture and temperature  Vegetation stature (height) also increases, so regions with certain combos of moisture and temp develop predictable, characteristic types of vegetation (biomes) - Ecological convergence : same biomes under same environmental conditions despite difference in plant species  Seasonality is secondarily important  Biomes have a latitude component (e.g. deserts at around 30 degrees) Additional climate patchiness overlaid on basic latitudinal belts  Maritime vs continental climate: how extreme are the seasons (i.e. how much hotter are the seasons?)  Water is resistant to change – has thermal inertia, unlike land, which heat up quickly - In the middle of continents, there are hot summers and cold winters - Near the coasts, the climates are more moderate  Temperature: land changes temps more readily than water: maritime climates are moderate, continental climates are extreme, oceans provide thermal inertia - Moderation effect of water is important to agriculture (cherries, grapes)  The driest deserts are found beside cold water upwellings - Cold water  air above has little moisture  as continental warm air rises, the air above the cold water replaces it  dry air blown on shore and exaggerates the desert effect  Precipitation: where does atmosphere get laden with moisture; where does it condense?  Rain shadows: prevailing winds contain air with certain amount of water vapour - Winds are pushed up and precipitates, rains on the „windward‟ side - Dry air heats up as it falls again due to friction - West side is wet, then turns into a dry grassland on the east side Biomes across elevational gradient: Arizona Mountains  Ranges drastically (very different systems) as elevation changes: Canada to Mexico (boreal to desert)  Exposure to sun is also important – vegetation will tend to grow on the north (hidden from sun) side Lecture 2: Species ranges and the physical challenges of the environment: heat balance Core Ideas in physiological ecology  Ranges of tolerance ultimately limit distribution 5 BIO120H1F - Organisms depend on chemical reactions in the body – and all reactions take place in a certain range  Reactions occur best at optimum temps and osmotic conditions  Many mechanisms for homeostasis have evolved to challenge hostile environments - Maintenance of homeostasis requires energy and is often limited Limited by habitat  Pronghorn: wide geographical range, narrow habitat range (hot continental grasslands)  Sometimes geographical distribution differ between similar species due to behavioural choices - E.g. yellow rumped warbler cover all of north America – very large range (extreme habitat generalist)  Kirtland‟s warbler however nests only in pine forests and have a narrow habitat range (extreme habitat specialist)  Tigers have broad temperature tolerance and broad habitat range (tropical forests to northern forests)  Coyote were once found only in grasslands 100 years ago, but have been expanding their range since North America has become densely settled by people - Wolves have been hunted, have disappeared, and Coyotes have expanded One selected limiting factor: heat budgets  For homeotherms: heat balance is especially important – environment will either give us or take away our heat  Radiation – heat transfer by electromagnetic radiation  Conduction – direct contact with substrate (e.g. Feet loses heat to ground)  Convection – heat transfer mediated by moving fluid (usually air or water, e.g. A fan)  Evaporation – efficient cooling from wet surfaces  Redistribution – circulatory system redistributes heat among body parts, esp. Core to appendages Size matters to heat balance (and other balances of gains and losses)  Bigger things equilibrates more slowly with the environment  Homeostasis and surface area: volume ratio  Surface area determines equilibration rate - Sphere has least surface area, small sphere equilibrates quicker  Volume provides the inertia  Bergmann‟s rule: homeotherms tend to be larger at higher latitudes (colder) and smaller at lower latitudes - Exception: africa‟s elephant? There used to be wooly mammoth up north where it was cold Shape Matter  Allen‟s rule: appendages reduced in cold climates - Must lose heat in hot environments by increasing surface area - Sphere shaped organisms will be in cold environments, and flat shaped organisms will be in hot environments  Sphere has least SA:V  Maximum SA:V ratio: Gliding snake, restricted to warm tropics  Minimum SA:V ratio: Pika, the alpine tundra rabbit, restricted to cold habitats for its spherical shape, reduced ears - Variation in shapes of arctic and desert hares: sphere and small ears vs long legs and big ears  Big ears allow the jackrabbit to dumb heat to the atmosphere Insulation  Northern animals tend to have lots of insulation - Musk oxs are very shaggy, can huddle together in a group - Feathered dinosaurs - Aquatic animals like seals? Insulation in the form of fat (blubbler)  Insulation on the inside, with a smooth outside  58% of cross section area is blubber  Birds can change their shape depending on whether or not they‟re taking flight - Being in flight requires a streamline body – otherwise they can afford to not be streamline Convection cooling enhanced by vascularization  Ears of a rabbit: pumps hot blood to vessels in ears where it loses heat (vs heat damaging core)  African elephants have giant ears (vs mammoths had small ears) Countercurrent circulation to limbs conserves heat 6 BIO120H1F  Arteries and veins should be appressed in appendages to conserve heat; and separated in appendages designed to shed heat - Appressed: heat is lost as blood flows out, then regained as blood flows back to the body  Countercurrent flow maintains gradient, so heat is always flowing from outgoing blood to incoming blood Convection enhanced by evaporation  Sweating in humans  Dogs panting  Elephants spraying water on themselves – particularly on their ears to dump heat  Kangaroos lick forearms to encourage evaporative cooling Lecture 3: Physical challenges of the environment for animals, emphasis on tradeoffs and alternatives  Autumnal equinox: solar equator is the same as the geographical equator  Homeotherms must expend energy to keep body temperature in a certain range  Do not expect evolution to produce perfection, tradeoffs being one of the reasons Weasels  Weasels have a high surface area to volume ratio  Weasels are long and thin: metabolisms of weasels (newspaper article) compared woodrats and weasels in cold temperatures - Woodrats rolled into a spherical ball shape, weasel cured into a flat disk, which had a higher SA:V ratio than woodrats  Weasel live in cold climates, but bodies are suited for warm climates, paradox?  Must look at benefits of being long and thin? - Gives them access to underground holes dug by prey (much like snakes)  Pocket gophers, with adaptations underground: big claws, small eyes, tiny ears - Short fur as well leads to problem thermoregulating, but aids in capturing prey  Example of a tradeoff: being long and thin makes weasels subject to thermal stresses, but allows them to be better predators (cost and benefit) - Because they are long and thin, the fitness gains of being a good hunter offsets the fitness costs of an expensive metabolism  Phenotypes of all organisms are riddles with compromises dictated by tradeoffs - Natural selection can‟t compromise some two things at the same time Two reasons why natural selection produces deeply imperfect organisms  Natural selection is descent with modification (Darwin)  Tradeoffs: being good at x may imply being bad at y  Constrainsts: selection builds on what is already there - Tinkering, not fundamental fresh redesign Dealing with extreme water stress  Kangaroo rat, in the Sonoran desert, never require free water in their diet  Kangaroo rat: - Anatomy: bipedal, less heat gain from the ground - Physiology: really efficient kidneys, urine is 8 times more concentrated than humans, metabolic water (breaking down fat molecules and producing water biochemically) is sufficient - Behaviour: nocturnal (spends hot days underground), stash seeds underground which recapture water vapour from exhalation Evasions: options when physiological stress becomes overwhelming When environmental conditions become much too stressful  Enter dormant stages (seeds-plants, cysts, eggs, pupae-insects, torpor), with minimal metabolism - Hibernate or estivate (get through hot weather) as adult, store fat - Plants may just have adults die and get through the season as seeds - Torpor – low energy state gone through by organisms daily  Nest or den (protected microhabitat)  Store food 7 BIO120H1F  Migrate to milder climate  Hibernation and migration is usually driven more by food supply than abiotic stress Masters of evasion  Garter snakes: hibernaculum (an underground cavern where snakes come together and ball up)  Chipmunks: hibernators, have brown fat in mitochondria that lets them go through hibernation  Muskrats: builds a shelter on water to stay warm above an aquatic environment  Migration: bluebirds and hummingbirds must migrate because they live a warm weather lifestyle (feed on nectar) - Other birds, like crossbill, are built to feed on conifer seeds - Gray jay are very opportunistic, flexible, are willing to try anything - Clark‟s nutcracker stashes foods, can remember 1000s of places  Pika dries summer plants for winter consumption (making hay, literally) Basic conclusions for “physiological ecology” of animals  Its more than physiology, it‟s also:  Gross anatomy (size, shape, insulation, vascularisation) plus microanatomy and molecular variation  Behaviour (including parental care) is usually an essential component - Most vulnerable to environmental stresses at a young age - In higher vertebrates, parents make up for environmental stress  Natural selection creates multiple adaptations that work together – behavioural an physiological adaptations that work side by side towards the same goal  Diverse solutions for common problems (e.g., cold seasons) in different organisms - E.g. a hummingbird and musk ox will have different responses to the cold Lecture 4: Physical Challenges for Terrestrial Plants September 24 , 2012 Main themes in plant physiological ecology  Stresses on plants are especially challenging because plants can‟t evade stress by moving  Plants solve problems by growth & development, not behaviour, so carbon balance is central  Tradeoffs on photosynthesis: compromises involving 3 necessities: light, temperature, water  Adaptations to an extreme habitat: deserts  Adaptations to an extreme lifestyle: epiphytes  Sclerophylly: resolving a multi-part paradox, live in nitrogen poor soils Plant ecophysiology of carbon balance: tradeoffs and constraints abound  Autotrophs: depend on net photosynthesis (= gross Ps minus respiration); conversion of CO2 to fixed carbon  CO +2H O 2 Carbohydrates + O 2  Must bring together light, gases, and water in functioning photosynthetic tissue - Requires also OK temp, osmotic balance, enzymes, dissolved nutrients from soil (N,K,P), etc.  Any of these components can limit fitness  Anatomy and physiology reflect constraints Photosynthetic structures embody adaptations to environmental stresses  Photosynthetic structures (green) are usually leaves, but can be stems  Leaf size and shape (SA:V ratio) is important, because - Benefits of large leaf surface: good for harvesting light, CO2 - Costs: bad for overheating, to prevent high temp, there is water loss by evapotranspiration through stomata (little mouths that can open and close) opening  Leaf can only absorb certain wavelength of light from sun, others go to heat up the heat  Closing stomata shuts off all gas exchange, including CO2 input, so photosynthesis shuts down, plants stop growing  Tradeoff: water conservation and rapid growth  Consequences seen in desert plants  Also avoid overheating by growing in shady habitats  Desert plants: can conserve water and prevent overheating? - Palo verde (green stick): photosynthesis occurs in weak, thin bark  Has microphylly leaf - Desert plants generally have very tiny leaf – has to do with SA to V ratio 8 BIO120H1F - Microphylly taken to extremes: cacti – modified stems make up most of the plant, no leaves  Prickly pear all oriented in the north-south plane, so broad side never directly faces the sun - Cacti underground: very extensive but shallow roots, why?  Spring time, rainfall and snow melts, fills up river banks - Saguaro cactus, adapted to episodic rains – first off, they grow very big  Extensive shallow roots can absorb up to 800L of water from one storm, and stores it for gradual growth  Roots have succulent tissues - Cacti have pleated cross section – have ribs  This allows them to grow according to how much water there is (no water = ribs sticking out)  Can pump water up and gradually use the water  Ecological convergence: desert plants have a very narrow phenotype, all are similar despite coming from different families How do plants avoid stress without moving?  Deciduous habit: dropping leaves during dry or cold seasons can reduce water stress and tissue damage - Ground is frozen, no water, too cold = no photosynthesis - Keeping leaves makes them subject to damage by wind or ice - Note: deciduous areas in tropics is due to droughts  Term clarification, “evergreen” - Leaves are kept on the plant throughout the year - Evergreen =/= conifers, depending on where you are  Mesophyll leave: thin papery leave, large SA, negligible volume  Sclerophyll leave: small SA:V, tend to be tough, leathery and waxy, almost always evergreen  Leaf shape also influences gas exchange through laminar vs turbulent flow of fluids over surfaces - Laminar flow is smooth (with no bumps or changes in its shape)  Creates a boundary layer near the surface where velocity is much slower (sometimes zero), resulting in overheating, not enough gas exchange - Turbulent flow results in eddies, resistance of movement  Turbulence = no boundary layer, would do better in hot environments  E.g. Zig zag edges - Sun leaves vs shade leaves differ: those in sun have more turbulence for better cooling - Arctic hare vs desert hare, good example of laminar vs turbulent flow (recursive digression)  E.g. Saguaro cactus grows in the shade of palo verde in its youth (nurse tree effect) Life form digression: the unrooted life of epiphytes  Epiphytes grow on trees not the ground, and are unable to put roots in the soil  Leads to water stress and nutrient shortages, because soil act as water and nutrient bank - Must have a method of storing large quantities of water  Have a sponge type structure made out of its tissues that absorbs water  Tend to grow in environments with a lot of rain (tropical forests)  Home to ants – which bring in nutrients  Have tanks (bowl formed by leaves?) That stores water Plants with sclerohyll leaves in 4 environments 1. Boreal spruce-fir forests: high latitude/altitude, cool summers, sever winters, moist soils 2. Pine barrens, sandy soils: hot summers, mild winters, dry, sandy, nutrient-poor, acidic soils 3. Maine bogs: cool summers, very wet soil (grow in water), acidic 4. Mediterranean heaths, semidesert: dry, very hot summers  Small leaves (i.e. Low SA:V) favoured in dry habitats for resisting heat and drought - Mediterranean semidesert, pine barrens  Spruce-fir growth form sheds snow and catches sun (and allows photosynthesis) in high latitudes - Boreal  Evergreen habit conserves nutrients in poor soils (building leaves costs a lot in terms of nutrients, eg nitrogen) - Boreal, acid bogs, Mediterranean semidesert, pineland Lecture 5: Population Ecology: Models without age structure 9 BIO120H1F September 26 , 2012  Defining populations and individuals, with a focus on some unusual cases  Taxonomy of simplest possible mathematical models - Exponential and geometric population growth models without density dependence - Incorporating density dependence, effects of crowding, etc. - More complex density dependence: time delays, allee effects  Population: collection of individuals (in a certain area) – populations are spatially limited - Population size N = number of individuals - Population density = N/area  Population ecology: what influences N?  Population genetics: what genetic variation resides in N? Population ecology developed by zoologists (more ambiguity about plant individuals)  Less ambiguity for „higher‟ individuals, e.g. If a human dies, all of the human dies  Aspen: clones, not really genetically different – one seed produces many identical, connected stems  Larkspur: many unique seeds produce many unique plants  Dandelion: no sex, are triploids many identical seeds produce many identical, unconnected plants Relationships among models in BIO120 Discrete time steps (difference Infinitesimal steps (differential equations, equations, arithmetic) calculus) Density independent Geometric growth model Exponential growth model Density dependent None - Logistic growth model  Extensions: - Geometric growth model  add age structure - Logistic growth model  add time lag and allee effect The goal of most population models  Predict the trajectory of a population growth through time (i.e. N as a function of t)  How many individuals are in the population now? One step later? (N ts N t+1  General model: N t + 1 f ( t ) Choice: what are the time steps?  When using differential equations, time steps are very very small: use limits and calculus; growth is smooth, best suited for species with continuous reproduction  When using difference equations, time steps are discrete units (days, years): use iterated recursion equations; growth is stepwise and bumpy, best suited for episodic reproduction  Also called continuous time and discrete time approaches  Different organisms fit different equations How can N change from N totN ? t+1  D = # who die during one time step  E = # who emigrate  B = # born during one time step  I = # who immigrate  So N t+1 N-t+B-E+I Simplify and convert changes to per capita rates  Treat birth and death as fixed constants: population changes by a certain factor each times step  N = λ N t + 1 t  Where λ is the factor by which the population changes over one time unit (the growth rate) - If λ =1, population is stable  Geometric growth – graph looks like step function Alternate version with continuous time  Instantaneous, per-capita rates of birth and death fixed (b and d)  Instantaneous per capita rate of change is b – d = r (constant)  Differential equation: dN/dt = r N  Exponential growth – graph is continuous Regardless of model used, consequence is the same 10 BIO120H1F  In both models, growth rate (lamba or r) is a constant that simply reflects biology  But a constant positive growth rate produces a population size that is not constant – rather it is exploding  All species have the potential for positive/negative population growth under good/bad conditions - But no species has ever sustained λ >1.0 for a long period, and no extant species has maintained λ <1.0 for long The implications  Simple exponential growth is a bad model of reality over long term  Some factors must be present to keep populations from exploding or going extinct - K = carrying capacity of the environment - If N is small, the braking term is close to 1.0; when B approaches K, the braking term approaches zero (population does not change)  Sigmoid growth curve (know shape of trajectory) - Logistic trajectories are truly sigmoid only when starting from low numbers (start below carrying capacity)  Overall rate of population increase is highest at K/2, the inflection point - However, based on individual peak time, it‟s at t=0 when there is no crowding - But because population size must also be taken into account, the overall population growth rate is the product of per capita rate of increase and population size Logistic model: good and bad features:  Good: mathematically tractable model of intraspecific competition for resources - Simple: only 1 extra parameter beyond exponential - Can be expanded to consider multispecies competition  Bad: too simple  specifies one particular kind of density dependence, perfect compensation - Always a gradual approach to carrying capacity when in reality, density dependence is likely to be non linear, or over shoot K Alternate forms of density dependence  Alternate forms of density dependence 1: allow braking function to have different shapes (add exponent z to the braking term)  Alternate forms 2: time delayed logistic, population is not immediately responsive to limitation of carrying capacity - Keeps growing (population overshoot) past the carrying capacity - At a certain threshold, population oscillates violently and never really has a limiting capacity - In these models, per-capita growth rate is fastest when population is near zero. (i.e. any crowding in population is bad) Realistic?  Allee effects are negative effects of low density, arising from social benefits such as mate finding, group living, group defense (e.g. One human being stuck on an island) - Populations may fluctuate between carrying capacity K (upper limit) and lower limit - Dropping below the lower limit goes to extinction - Concept of „undercrowding‟ 11 BIO120H1F Lecture 6: Age Structured Populations std Life Histories October 1 , 2012  Breaking a population into age classes  Life table parameters, survivorship and fecundity  Life histories: tradeoffs, cost of reproduction  Alternative life history strategies: iteroparity and semelparity  Summary statistics derivable from life tables Typical life history for higher plants and animals  Not all individuals have same capacity for birth and death, this must be included in population models  For most organisms, start life at small size (not bacteria)  Grow for a period without reproducing (for resource accumulation)  When there are enough resources, organisms become mature, start spending resources on reproduction - Organisms show various lifestyles after sexual maturity  Need to consider age structure of populations to: - Better predict population trajectories - Understand paradoxes of evolutionary ecology Age-structured population growth  Still considering a single population, but now, fecundity (reproduction rates) and survivorship (how many survive) vary with age  Variation summarized by life tables of age specific rates  Important implications for: - Evolution of life histories - Conservation of populations - Human affairs  Age-sex pyramid depicts how many there are in certain age groups  Populations will have age structures depending on how many old and young there are  No change in age specific death/birth rates, stable age distribution – no change, same pyramid shape  Without age structure, assuming that N=24 are made of equivalent individuals to reproduce - With age structure, break into different age classes, only some of which reproduce - Age classes are denoted by subscripts Time now measured in age-class intervals  Arbitrary unites of time chosen to give a reasonable number of age classes for the organism in question - Microbes: minutes to hours - Insects: weeks - Mammals and birds: years - Humans: typically 5 year intervals, about 20 age classes Life tables  Data that summarize the life events that are statistically expected for the average individual of a specified age in a population - E.g. Birthrate of 2.5 = 2.5 babies in a 5 year interval  Life tables will include age of death (probability of dying) – treated as a constant  Age and timing of reproduction  For modeling, these are treated as constants  Usually consider females only (sperm supply is not limited, therefore males are not considered) Survivorship Schedules (……..)  Age classes denoted by subscript x  L x probability of being alive at age x  L 0 1.0 by definition (probability of being alive at age 0) 12 BIO120H1F  “Survivorship curve” = a graph of x vs. X  Lxnecessarily declines with x  Shape of Lxcurve is characteristic of species  Simplest survivorship curve = radioactive decay (half life), if mortality is constant with age, constant probability of death - Type 1: death rates are higher later on in life - Type 2: constant death rates - Type 3: huge death rate early in life (e.g. Plants that give off lots of seeds)  Real survivorship curves are more complex Fecundity Schedules  (mx = bx in fecundity slide)  Age class denoted by subscript x  bx= the number of daughters born to female of age x during the interval of time x to x+!  Shape of the x curve is characteristic of species  Resource accumulation phase usually precedes reproductive period  Curve shows us quantitative version of qualitative version of how life depends on resources accumulation and when maturity starts  Fecundity-survivorship tradeoffs (cost of reproduction) = more reproduction is costly for females - Reproducing = mortality increase Population growth rates  Average (expected) number of daughters a female has in her lifetime = net reproductive rate0= R  R = ΣL b 0 x x  R0is like lamba, but time units of one generation rather that one time interval Generation time T (=average age at which a female gives birth)  T= σxl x x σlx x= σxl x x R 0 Approximate relationship between R(0) and lambda  Both indicate the factor by which a population changes – but the time intervals differ R = λ T o 1/T λ = R o  Generally, organisms with higher lamba‟s have higher fitness (i.e. reproduction early in life in large quantities)… So why aren‟t all plants annuals? Why aren‟t all mammals mice? Why aren‟t all lives short and fast? - Constrainsts and tradeoffs: reproduction is costly. Longer pre-reproductive periods allow time to accumulate more resources - Starting too early = bad output  Organismal digression: costs of reproduction in glacier lily - Short annual growth span, above ground with 2 ½ months, must accumulate resources effectively during these months - Costs of reproduction: does making fruits exact a cost in terms of corm growth?  More fruits = less corm growth (cost of making fruit)  Fecundity schedules vary widely among species, usually genetically determined - Iteroparous organisms = multiple age classes where one can reproduce 13 BIO120H1F - Semelparous (big bang) organisms = longer period accumulating resources, and reproduce once with huge number of offsprings, and die from this huge reproduction - Obligate semelparity: century plant agave – grow without flowering for decades (up to 100 years), at one point a flowering stalk is made in one year with thousands of flowers, and the whole plant dies - Salmon: long lived semelparous animals, when big enough swim back to stream and produce lots of eggs, then the adults die Factors that select for semelparity  Environmental factors – harsh seasonality prevents adult survival - More efficient to kill adults, and store life as seeds  When reproductive output is increased by accumulating resource for longer, for example if: - Massive flower/fruit displays attract more beneficial animals (pollinators or seed dispersers like bigger displays) - Massive seed crops satiate seed predators populations, allowing more seeds to go uneaten  Monument plant: semelparity plus local synchrony - Once big enough, a habitat/climate variation synchronizes them to bloom at the same time at the same season (unlike agave, where blooming is random)  If bloomed separately, there would be Allee effect (insufficient mates to trade pollen)  Local synchrony is beneficial for pollination - Scarlet gilia: flexible semelparity based on resources  Pollinator preference for larger displays, so best tactic is to delay reproducing  Bamboo: extremely synchronized semelparity - Synchronized despite different locations - Satiating seed predators: a floor of bamboo seeds  Blue oak: iteroparity plus local synchrony = “masting” - Do not wait long time, typically 4-5 years, then an acorn burst (satiating seed predators like squirrels) Recap: intertwined themes in life-history  There are fitness consequences of alternative life history strategies and tradeoffs between current reproduction and future reproduction  Selection generally selects for early reproduction: more gene copies into population  But the need to accumulate resources, and size dependent mating success (e.g. Larger display of flowers) can override that effect, and end up producing delayed reproduction and/or semelparity - Semelparity selects for synchrony - Predator satiation (e.g. With seeds) also selects for synchrony  Leads to an increase in rat populations. Once the seeds are gone, the rats ravage human crops More fun with life tables  Can calculate “life expectancy”,xe (expected years left to an individual of age x)  Can calculate “reproductive value”,xv (expected number of future daughters left to an individual of age x) - Vx is higher at age 19 than with a newborn What might vx affect?  Success of captive breeding/release programs for conservation: release animals with highest reproductive value  Dispersal of new habitats: roaming behaviour is highest at certxin v  Attractiveness to potential mates: age of high v should maximize x 14 BIO120H1F Implications for your life: “antagonistic pleiotropy” theory of senescence  Why does natural selection build short term organisms?  Pleiotropy: one gene may have multiple different functions throughout life - Products of genes do different thing in different parts of the body  Antagonistic pleiotropy: a gene may have opposite effects on survival at different ages - A gene with positive value in young animals but negative value in old animals will be favoured by natural selection because reproducing early increases fitness  Natural selection loves these genes and most of the genes are like this  Accumulation of such genes causes senescence - E.g. Gene tp53 makes a protein p53 that protects youths from cancer (tumour suppressor), but causes premature aging by later destroying stem cells A sample of Darwinian medicine (Adaptive medicine): Age structure and life-history theory matter for humans  Antagonistic pleiotropy (an ultimate explanation to aging) predicts that many such genes will accumulate - Standard medical approaches to treating aging won‟t work – natural selection encourages these effects if they have benefits early on in life  Current proximate explanations for aging include: telomere shortening, oxidative stress, glycation - Influencing these processes won‟t stop aging, natural selection encourages genomes that causes negative effects later on in life Lecture 7: Species interactions – from 2 species popurdtion models to community structure October 3 , 2012 Partial classification of species interactions  Must consider species population by considering other species they‟re interacting with  Types of interactions: - Consumer-resource (+/-)  Predator prey, herbivore plant, parasite host  One population drops, another rises - Competition (-/-) - Mutualism (+/+)  Focus of study: population dynamics (Ecological effects on N‟s, can species coexist?) - Evolutionary dynamics (adaptations, coevolution – changes in one species genome affects changes in another species‟ genome) Interspecific competition for resources  Lotka-Volterra equations for 2 species competing for resources  Simple outgrowth of logistic equation: add second braking term for interspecific competition between species (there is already a breaking term for intraspecific competition)  „Competition coefficient‟ is required because species may compete differently 15 BIO120H1F Possible outcomes of the L-V competition
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