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Bio 120 Lecture slide notes.docx

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Paul Thompson

Bio 120 Lecture slides #1: - Higher latitudes colder; seasonality a function of temperature (summer-winter) - Lower latitudes warmer; seasonality a function of rainfall (dry season-wet season) - so regions with certain combinations of moisture and temperature develop predictable, characteristic types of vegetation = biomes - Orogenic precipitation: air forced up mountainsides undergoes adiabatic cooling, precipitates on upper windward slopes - Rain shadows created on leeward slopes of mountain ranges #2 - Maintenance of homeostasis requires energy and is often limited by constraints & tradeoffs - Sphere has least SA:V, so why shouldn’t homeotherms be spheres in cold climates? - Sometimes SA is needed for function; Sometimes particular shapes are needed for function - Example: pikas curl into a ball and have reduced ear sizes in their restrictive cold climates - Countercurrent flow maintains gradient, so heat is always flowing from outgoing blood to incoming blood #3 - Weasels : paradoxal distribution from northern Canada to northern America - Typical prey for weasels are pocket gophers… tradeoff; weasels are subject to thermal stresses but this allows them to be better predators - Fitness gains offset the fitness costs #4 - Autotrophs depend on net photosynthesis - Plants battle overheating and water loss by closing stomata …but that shuts off all gas exchange, including CO2 input, so photosynthesis shuts down. Plant stops growing… - …and risks overheating & tissue damage. - Fundamental tradeoff between water conservation and rapid growth - Example: palo verde; “green stick” – photosynthetic bark on trunks and branche, grows without incurring water loss or heat load - Saguaro cactus – adapted to episodic rains, has shallow but extensive roots. Has an accordion- pleated trunk, can absorb up to 800 L of water from one storm and uses it gradually for growth - Deciduous habit: dropping leaves during dry or cold seasons can reduce water stress and tissue damage - Angiosperms and conifers are not the same as evergreen … - Smooth, streamlined surfaces produce laminar flow; rough edges & irregularities produce turbulent flow (drag) - For cooling leaves, turbulence is better -> better cooling - Epiphytes grow in trees and are unrooted, leads to water stress and nutrient shortages - Convergent evolution : unrelated lineages that look and act similarly #5 - Geometric growth : assume no immigration/emigration, births and deaths as constants, lambda is a factor by which population changes over one time unit (net reproductive rate) - Exponential growth - Instantaneous, per-capita rates of birth and death fixed (b and d), where the difference is r, a constant, and results in the equation dN/dt = r N - Some factors must tend to keep populations from exploding or going extinct - Two kinds of factors may be acting, o Density-dependent (growth depends on N), o Density-independent #6 - Life tables, growth formulas … etc - Semelparity selects for synchrony - Predator satiation also selects for synchrony #7 - Lotka-volterra equations for two competing species - Coexistence requires both species to inhibit their own growth more than they inhibit each other’s - LV outcomes are widely interpreted as basically unstable, “complete competitors cannot coexist” - In a mathematical model, this is true, but not in nature - Experiments by Gause (1930’s) o Good description of competition by protozoa in artificial culture vessels; saw both stable coexistence and competitive exclusion: can often be unstable o Predator-prey strongly tended to be unstable (predators eat up all the prey, then starve) unless habitat complexity added - Competitive exclusion is less likely to go to completion… - …but abundances can be drastically affected and distributions in space altered. - Example: barnacles in intertidal zone - Predator-prey echo effect, mites on oranges - Snowshoe hare, lynx predator/prey -> not an example of LV predator/prey cycles - - Niche differentiation theory o Limiting similarity – niches had to be sufficiently different to allow coexistence o Resource partitioning – expect to see similar organisms dividing up resources o Assembly rules – some species pairs are incompatible, if a species is in an area first, the second species cannot establish o Character displacement – coexisting similar species should evolve differences - Niche studies faded in the 1970s - Most species do not occur in isolated populations but rather in metapopulations connected by dispersal #8 - Fender’s Blue Butterfly goes through annual pulses of reproduction followed by heavy larval mortality - Undergo annual cycles of reproduction, then disperse across habitat - They must discover prairie or they will die without reproducing - Deterministic models have fixed parameters and single outcomes, stochastic models include chance; parameters vary, multiple outcomes - Organismal or holistic hypothesis – certain species found together because they are biologically integrated and depend on each other’s presence - Individualistic hypothesis, species are distributed independently of each other, important limitations o Dispersal o Filtering o Both by the physical environment #9 - Vegetation changes spontaneously as the vegetation itself modifies the environment - Primary succession – new substrate created, no pre-existing vegetation - Secondary succession – pre-existing vegetation undergoes a disturbance - Disturbance – discrete event that causes abrupt change in ecosystem, community, population; sets back succession. Ex- fire, windstorm, agriculture etc - Soil development, especially accumulation of organic matter, nitrogenic content, pH buffering, water retaining capacity is especially important in primary succession - Shading where soil is already developed, is especially important in secondary succession. Shade tolerant species replace shade-intolerant ones - Succession may reach a stable climax configuration, but often does not - Examples where no climax-type equilibrium is attained are fire-prone ecosystems, systems driven by seasonality and boreal forest - Ecobeaker demo – add fire which spreads and empties cells, starting secondary succession in patches #10 - - - Lizards do benefit - - Direct and indirect effects can be opposed - Indirect and direct effects can be equally as strong - Keystone consumers can shift communities between alternative states - Outcomes depend on interaction strengths - Experiments are needed - Plant tissues are harder to convert into animal tissues, this makes it more difficult to be a herbivore - Pikas manipulate toxin levels and preserve winter food o Toxins break down over months in storage - The physical environment isn’t complex enough to prodce extraordinary species diversity #11 - Flowering plants seem to be most numerous where the soil surface is very rocky - Seed germination experiment -> buried organic soil is the best - - Desiccation- should find more plants away from thin soil around rock outcrops shown by experiments - Weak dispersal – should find most seedlings near flowering plants - Most seeds are produces in rocky areas and fall there, but most desiccate and die - The few seeds that reach moist, deep-soil areas are more likely to survive and produce seedlings, however, seedlings that get established in deep-soil areas are likely to be killed by gophers before they reach flowering age – “rock-refuge hypothesis” - Pocket gophers are keystone species in the aspen-meadow mosaic - Indirect effects – gophers hurt lilies directly, but help them by maintaining meadows #12 - Evolutionary biology o Evolutionary mechanisms (microevolution) - experimental o Evolutionaru history (macroevolution) – pattern based and non-experimental - Founder event - introduction of a small number of individuals that possess a small sample of the genetic diversity of the source population - Water hyacinth – world’s most serious invasive aquatic plant, reproduces by both clonal and sexual reproduction, most reproduction in introduced range by cloning, massive founder event associated with human introduction to alien range - Rat’s tail – perch removal results in significant reductions in fertility and outcrossing, increases self-fertilization - Birds are major plant pollinators and either hover (new world) or perch (old world) during nectar feeding - The perch is an adaptation promoting plant reproductive success #13 - Theory of evolution involves two controversial ideas o Concept of a changing universe  Replaced view of a static world o A phenomenon with no purpose  Replaced view that the causes of all phenomena had to have a purpose - Jean-baptiste de Lamarck was the first to use the term evolution o Linear rather than braching view of evolution o First to provide a causal mechanism – the inheritance of acquired characters - Lamarck’s example for the inheritance of acquired characters was the giraffe’s neck, which he said increased within a lifetime of an individual and then is passed on to offspring - Charles Darwin and Alfred Russell Wallace co-discovered the chief mechanism of evolution – Natural selection - The origin of species by means of natural selection or the preservation of favoured raced in the struggle for life is published in 1859 - The Origin of species has two key components o All organisms have descended with modification from common ancestors o The Major agent of modification is natural selection operating on variation among individuals - Darwin travels the world on the H.M.S. Beagle - Creationism is not science because it is not supported by any empirical observations, does not infer its principles from observation, as does all science, and its assumptions lead to no testable or falsifiable hypotheses #14 - Most time spent in south America on the voyage on H.M.S. beagle - Tropical forests have high species diversity and individuals of the same species are widely separated, unlike temperate forests - Dense canopies and long-distances between trees make wind a poor agent of pollen dispersal - Janzen’s pest pressure hypothesis – predicts that tropical tree seedlings are less likely to establish close to the maternal parent, a result confirmed through field experiments - Epiphytic life form has evolved independently in many unrelated families
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