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Ecology and Evolution Exam 4 and Assignment 4 – December 7th Biomes • Major landscape associations of organisms (plants, animals) • Have a characteristic ‘appearance’ • Defined by regional variations in climate Tropical Forest – equatorial, rainfall 150 - 450 cm/yr Figure 19.34a Savanna – equatorial / mid latitude, rain 75 – 125 cm/year Figure 19.34b Desert – mid latitudes, < 25 cm/year rainfall Figure 19.34c Chaparral – mid latitudes, coastal, Figure 19.34d Grassland – mid latitudes Figure 19.34e Temperate Deciduous Forest – mid to high latitudes Figure 19.31f Coniferous (Evergreen) Forest – high latitudes Figure 19.34g Tundra – arctic (very high) latitudes Figure 19.34h What factors are responsible for creating these different biomes? How Climate Affects Biome Distribution • Because of its curvature, Earth receives an uneven distribution of solar energy Low angle of incoming sunlight Sunlight directly overhead Low angle of incoming sunlight Atmosphere Figure 19.30 Where are certain types of Biomes found? While the relationship varies slightly, in general: 1000 feet of altitude = 100 miles of latitude = 3.5°F temperature drop What factors directly affect the population size of Phoenix? • • • • • Births Deaths Immigration Emigration Change in population size = B – D + I – E. A farmer has a pond on his property in which a fast growing water weed has just appeared. He calculates that area the weed covers on his pond doubles each day, so that after 30 days the pond will be fully covered. On which day will the weed cover half of the pond? Exponential Growth Growth of Plant on Pond % of pond covered 100 80 60 40 20 0 0 5 10 15 days 20 25 30 Exponential Growth • When a population is growing at its maximum rate. • Often occurs when a population first invades an area. • There is plenty of food and space. • All species are capable of growing exponentially, but species differ in their growth rates. • In exponential growth, births >> deaths. Exponential growth High r Population size (N) 500 400 300 ‘r’ is how fast the population is growing, its growth rate 200 Moderate r Low r 100 Very low r 0 time Logistic Growth • Sometimes populations increase in size to certain level and then stabilize. • This type of growth (logistic) yields an S-shaped curve. • The population size at which the growth stabilizes is called the carrying capacity. • Carrying capacity: maximum population size the environment can support indefinitely. • At carrying capacity, births = deaths. Population size Carrying capacity Time Comparison of Exponential and Logistic Growth What factors maintain a population near its carrying capacity? • Density-dependent factors: mortality rate (% of population that dies) depends on population size. • disease • lack of food • lack of space • build up of wastes • predation What would happen if a densitydependent factor were removed? • If the population was already at its carrying capacity, it would increase, overshooting its carrying capacity. • Population overshoot • Deer lower carrying capacity by overgrazing. Population Overshoot in Reindeer What factors affect populations regardless of their size? • Density-independent factors: mortality rate (% of population that dies) independent of population size. • They are usually natural disasters. What factors affect populations regardless of their size? • Density-independent factors: mortality rate (% of population that dies) independent of population size. • They are usually natural disasters. • Ex. frost, flood, hurricane, hot spell, drought, volcano. Factors that affect human population growth • Culture and Attitude • Poorest nations have the highest growth rates. • Why? Poorly educated women. • Rich people have fewer children than poorer people. • This trend extends between countries, or within the US despite ethnic differences. • Certain religions advocate large families. Human Population Growth Ecology: Explaining the distribution and abundance of organisms • Interactions between populations – Predation – Competition – Symbioses KEY PROPERTIES OF COMMUNITIES • A community – Is an assemblage of populations of different species living close enough together for potential interaction Predation: when one organism consumes another. Competition • When two organisms are competing for the same resource. • Interspecific competition: between members of different species. • Intraspecific competition: between members of the same species • Why type of competition is most intense? • Intraspecific, because they share the same niche. They even share the same interest in mates! How to demonstrate competition is occurring in nature (what kind is this?). • Remove one species and record effects on other species. Symbiosis • Two different species living in close association with each other. • At least one species always benefits. • Mutualism • Commensalism • Parasitism Mutualism: both benefit Commensalism: one benefits, one unaffected Cattle egrets, again Parasitism: one benefits, one hurt What relationship is this? What relationship is this? What relationship is this? What relationship is this? Explaining the Abundance of Organisms: Data from the Hudson Bay Trading Company • Bought animal furs from traders. • Distributed them to Eastern seaboard and Europe. • Kept records of pelts bought each year. • One fur they bought was the snowshoe hare. • Let’s see how the number of furs varied… Why the fluctuation in abundance? • Hypothesis 1: Hare populations fluctuate with their food supply. • Prediction 1: Their food supply should increase and decrease along with hare densities. • We cannot test prediction 1, because we have no index of past food supplies. • Hypothesis 2: Hare populations are kept down by their predators. • Prediction 2: Their predator, the lynx, should increase as the hare increases, and decrease following the decline of the hare. • Lynx populations rise and fall in a way that suggests that hare may be controlled lynx predation Conclusion? • Lynx may indeed control hare populations. • But, what if the hare population is controlling the lynx population? What would this graph look like if hare were not controlled by lynx, but instead were controlled only by food availability? How do materials travel in ecosystems? • If a Sacred Datura takes in 7 units of phosphorus during the summer, but loses 3 units, how much does it have left? • How did figure that out? • You used the First Law of Thermodynamics, which states: Energy and Matter cannot be created or destroyed. Energy flow in ecosystems • Consider a cheetah that ingests 10,000 Calories of antelope in a week, and loses 3,000 from activities (hunting, mating, etc.) as well as the energy left in its urine, feces, hair, nails, etc. • If the cheetah gets larger by 500 Calories, where did the rest go? • It’s lost as heat! Second Law of Thermodynamics • No energy transformation is 100% efficient, as energy is always lost as heat. • Remember your car. Why does it get warm? • The energy that’s making it warm could be used to propel it. It’s not 100% efficient in coverting gas combustion into motion. • The same thing happens with the cheetah. It loses energy as heat. Implications of Second Law of Thermodynamics • Consider a simple ecosystem. • 100 units of energy produced by grass/month. • How much turns up as Thomson’s gazelle? • Only 10 units! • How much of the gazelle turns up as cheetah biomass? • Only 1 unit! Why are big fierce animals, which are predators at top of the food chain, rare? • Very little energy from primary producers (plants) makes it all the way to the top of the food chain. • Called the 10% rule, as only about 10% makes it to the next trophic (i.e., feeding) level. Other reasons? Efficiency of Energy Transfer in a Food Chain Tertiary consumers 10 kcal Secondary consumers 100 kcal Primary consumers Producers 1,000 kcal 10,000 kcal Figure 19.26 A few terms to know • Food chain (ex. Grass antelope lion) • Food web (more realistic/complex than food chain; many chains make up the web) • Producers (mostly plants: convert sunlight energy to chemical bond energy (sugars) by photosynthesis) • Consumers (can’t photosynthesize, must eat other organisms). These include 2 categories: - Herbivores (plant eaters) - Carnivores (animal eaters) • Decomposers (break down dead organisms, return elements (C, N, P, etc.) to the soil, where they are recycled. Quaternary consumers Carnivore Carnivore Tertiary consumers Carnivore Carnivore Secondary consumers Carnivore Carnivore Primary consumers Zooplankton Herbivore Producers Plant Phytoplankton A terrestrial food chain A marine food chain Quaternary, An ecosystem Food Web (more realistic) Is made up of many food chains tertiary, and secondary consumers Tertiary and secondary consumers Secondary and primary consumers Primary consumers Producers (plants) What do food chains/webs and the Second Law of Thermodynamics imply about world hunger? • Which diet is most energy efficient? – A beef diet, because it has similar elements to our own body? – A milk diet, because then we don’t kill the cow but still get a high protein meal? – A vegetarian diet, because the smallest amount of energy is lost as heat. • Energetically, a vegetarian diet could feed how many more people than a totally meat diet? Efficiency of Energy Transfer in a Food Chain for which WE are the top consumer • Eating producers (plants) instead of consumers (animals) requires less photosynthetic productivity and reduces the impact on the environment Human meat-eaters Secondary consumers Primary consumers Human vegetarians Corn Producers (a) Cattle Corn (b) Figure 19.27 Why should we care about food webs and trophic relationships in ecosystems? - Energy efficiency and ecosystem impacts of herbivorous vs. carnivorous diets: - human carnivory (meat-eating) adds another link to the food chain in food production, compared to vegetarianism - this additional link (cows, pigs, chickens, etc.) places greatlyincreased demands on habitat for “feed” production for these animals. Animals also produce extra wastes. - Biological magnification of fat-soluble toxins (like mercury, pesticides, PCB’s) in food webs. • Biological magnification – A process in which fatsoluble toxins become more concentrated in successive trophic levels of a food web. (Fat-soluble means that the toxins dissolve, and are stored, in lipids.) DDT concentration increase of 10 million times DDT in fish-eating birds 25 ppm DDT in large fish 2 ppm DDT in small fish 0.5 ppm DDT in zooplankton 0.04 ppm DDT in water 0.000003 ppm Figure 20.7 Producer, herbivore, carnivore, or decomposer? Producer, herbivore, carnivore, or decomposer? Producer, herbivore, carnivore, or decomposer? The role of decomposers • Most people don’t like to think of scavengers and decomposers, but they serve a vital role. • What would the world be like without these organisms? • Dead stuff would not decompose. • Nutrients would not be recycled. Sphagnum moss • Releases acid as part of its physiology. • Acid prevents decomposing bacteria from thriving in bogs • Thus, nutrients aren’t recycled, because the dead matter doesn’t decompose. • Peat moss is harvested, revealing all kinds of dead preserved organisms in bogs. An example of what was found in a Danish bog • The nitrogen cycle Nitrogen (N2) in atmosphere Detritus Amino acids and proteins in plants and animals Denitrifying bacteria Detritivores Assimilation by plants Decomposition Nitrates (NO3– ) Nitrogenfixing bacteria in root nodules of legumes Nitrogen fixation Nitrifying bacteria (b) The nitrogen cycle Ammonium (NH4+ ) Nitrogenfixing bacteria in soil Figure 19.29b • The phosphorous cycle Uplifting of rock Phosphates in rock Weathering of rock Phosphates in organic compounds Consumers Producers Phosphates in soil (inorganic) Rock Precipitated (solid) phosphates (c) The phosphorus cycle Phosphates in solution Detritus Detritivores in soil Figure 19.29c • The carbon cycle CO2 in atmosphere Photosynthesis Burning Producers Wood and fossil fuels Cellular respiration Higher-level consumers Primary consumers Decomposition Detritivores Detritus (a) The carbon cycle Figure 19.29a How can we explain the diversity of life on this planet? Charles Darwin • Started medical school. • Traveled on H.M.S. Beagle for 5 years, collecting specimens from 1831 to 1836. • Didn't formulate the idea of evolution until 1837, due to mounting evidence. Darwin’s Voyage on the Beagle Evidence Darwin found Geographic variation of species • Galapagos Islands: The resemblance of the different finches (a variety of bird) on the individual islands caused him to question the “fixed” nature of species. • On Continents: Observed differences between “fixed” species when they were separated by long distances on the mainland Adaptive radiation • Occurs whenever there are open niches. • Some individuals of a species expand into unfilled niches (roles) in the environment. • Thus, over LONG time periods through selective reproduction and genetic variation, the population may evolve slightly and better fit that role. Adaptive radiation Darwin to pigeon and plant breeders about artificial selection • By selective breeding, you can change appearance of birds, dogs, cattle Theory of Evolution by Natural Selection • 1) There are inheritable differences within a population. • 2) Reproduction exceeds carrying capacity. • 3) Competition for resources. • 4) Survival of the fittest: most fit survive and pass down genes to next generation. Natural Selection affects the reproductive success of individuals, and so through time populations evolve. • Individuals cannot evolve. • Individuals either live or die, depending in part on their adaptations (luck also matters somewhat). • Populations evolve through changes in the proportion of certain alleles (genes) in the population. We call the features that organisms have that enable them to survive well in their environment adaptations. • These adaptations do not happen because animals and plants "want" them to happen (it's not goaloriented). • Natural selection can only work with the available material (the genetic variation) already present in the population. • Because of this, many adaptations aren't designed the 'best' or most logical way. Mechanisms of Speciation • A key event in the potential origin of species occurs when a population is somehow separated from other populations of the parent species • The two modes of speciation are – Allopatric speciation – Sympatric speciation (a) Allopatric speciation (b)Sympatric speciation Figure 14.8 Allopatric Speciation • Geological processes – Can fragment a population into two or more isolated populations – Can contribute to allopatric speciation Figure 14.9 • Speciation occurs only with the evolution of reproductive barriers between the isolated population and its parent population Homologous and Analogous structures • Homologous: similarity in structure and/or position due to common ancestry A Homologous structure: Forelimb bones in mammals Homologous Structures • Must be derived from the same basic body parts. • Can be used for a similar purpose or for a different purpose. • Ex. Human forearm, chimp forearm, and bird wing. • They are all derived from the same parts but may have different uses. Homologous or Analogous structures • Homologous: similarity in structure and/or position due to common ancestry • Analogous: similarity in function but different evolutionary origin- no (recent) common ancestry Analogous Structures Homologous or Analogous? • Turtle shell and Clam shell. – Analogous: similar function (protection) but different origins. • A Dog’s fur and a Mouse’s fur. – Homologous: Both dogs and mice shared a common mammalian ancestor, which had fur. Homologous or Analogous? • A Bird wing and a Bat wing. – Both! Homologous as forelimbs (ancestral reptile had front limbs). Analogous as wings, each group developed wings independently (no common ancestor with wings). Molecular evidence • If species share a common ancestor, then their DNA, and the molecules constructed from that DNA, should be similar. • This has shown to be true for virtually every molecular example. • Example: All organisms require molecules that break down sugar to acquire energy. • Thus, we could compare very different creatures because they all share that type of molecule… Molecular evidence: Differences in Cytochrome C molecule Cytochrome C: a protein essential in the production of a cell’s energy Organism • • • • • • • • • Chimpanzee Rhesus monkey Rabbit Cow Pigeon Bullfrog Fruit fly Wheat germ Yeast Number of Amino Acid Differences from Humans 0 1 9 10 12 20 24 37 42 More Misunderstandings about Natural Selection Natural selection tries to help individuals become adapted. Natural selection has no goal. It is not teleological (goal-oriented). Natural selection depends upon random chance. Chance should lead to randomness, not adaptation. • Natural selection depends on mutations to provide variation, and it is true that these mutations are random. • But natural selection determines which variants (genes) get passed on. • Favorable traits are much more likely to be passed on than unfavorable traits, since the organisms possessing favorable traits have a much better chance of surviving and reproducing. Natural selection is the survival of the fittest and so leads to the evolution of traits that promote the survival of individuals. • Survival is important but what's really important is how many fertile offspring you produce. • (Ex. Old gorilla never mates, but young one mates and dies young. Young one has been genetically successful, but not the older one.) The Greenhouse Effect: a) in a greenhouse b) on the planet as a whole. a) b) Gases which trap the re-radiating heat: -CO2 (carbon dioxide) -CH4 (methane) -N2O (nitrous oxide) -Chlorofluorocarbons (A/C, spray cans) But, is the Greenhouse Effect from human activities really changing our biosphere? • The best way to answer this question is to study the earth’s historical climate Global Temperatures are increasing Robert A. Rohde Meehl, G.A., W.M. Washington, C.A. Ammann, J.M. Arblaster, T.M.L. Wigleym and C. Tebaldi (2004). "Combinations of Natural and Anthropogenic Forcings in Twentieth-Century Climate". Journal of Climate 17: 3721-3727. Robert A. Rohde Robert A. Rohde Is global warming caused by humans? • Fact: global temperatures are rising • Fact: global CO2 levels are rising • Fact: CO2 levels have risen with the industrial revolution • Strong correlation between greenhouse gasses and temperature. – this alone does not prove global warming as human caused Global Warming controversy • Use of proxy data vs. use of direct measurements • Possibility of taking a global temperature • Question of normal vs. human caused change • Extreme complexity • Exaggerated claims and politics Is global warming caused by humans? • Very likely human caused to a certain degree • Pollution in any amount is harmful • Even too much of a good thing is harmful • My opinion: Even if global warming is not caused by anthropogenic pollution, pollution is bad…