University of Louisiana at Lafayette
Popular in Evolutionary Biology
Popular in Science
Joseph Merritt Ramsey
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This 11 page Class Notes was uploaded by Lauren Notetaker on Saturday April 16, 2016. The Class Notes belongs to EBIO 1010 - 02 at Tulane University taught by Bruce Fleury in Spring 2016. Since its upload, it has received 23 views. For similar materials see Evolutionary Biology in Science at Tulane University.
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Date Created: 04/16/16
Lindeman’s paper transformed ecology, as Elton’s book had done earlier The flow of energy and materials through ecosystems is the basic organizing principle in modern ecology Lindeman’s paper was rejected by Ecology for being too theoretical!! Finally accepted and published, thanks to G.E. Hutchinson, influential ecologist Autotroph = self-feeder, autotrophic organisms produce their own energy(photosynthesis) 6CO 2 12H O 2 light => C H 6 126H6O + 62 2 Autotrophs are the producers, herbivores and carnivores are the consumers Plants, cyanobacteria, some protists transform light into chemical energy, stored in the chemical bonds of glucose How efficient is photosynthesis? Efficiency of photosynthesis is actually less than 2% !!! Less than 2% of the light that strikes green leaves gets captured as chemical energy About 25% of this captured energy goes into growth, maintenance, and reproduction of the plant The remaining 75% is available to the next trophic level (herbivores) Plants are primary producers The solar energy assimilated by plants is called their gross primary production (GPP) Subtract from this GPP the fraction that the plant uses for itself (~25%), what’s left is called net primary production (NPP) Net primary production is relatively easy to estimate, = total dry weight of new biomass added over the course of one year (g/m / 2 yr) NPP gives us a rough yardstick to compare the productivity of different types of ecosystems Highest NPP - wetlands, tropical forests, estuaries, coral reefs Lowest NPP - desert, open ocean Open ocean is a biological desert!! - most of the ocean’s productivity is in the plankton, the upper few inches Conversion of solar energy to plant tissues is very inefficient Conversion of plant tissue to herbivore tissues is very inefficient Conversion of herbivore tissue to carnivore tissues also very inefficient Heterotrophs = fed by others, heterotrophic organisms eat other organisms to survive Heterotrophs burn (oxidize) glucose (and other compounds) to recover the energy stored in the chemical bonds (respiration) C 6 12+ 6O + 62 O =>26CO + 12H 2 + ener2y 90% of the energy at any trophic level is lost going to the next trophic level Only ~ 0.03% of the original solar input remains by the time you reach the end of the food chain Most ecosystems have 4 trophic levels, some have 5 - 6 (secondary, tertiary carnivores) One hill cannot shelter two tigers Because of the inevitable loss of most of the solar energy that enters the ecosystem, only a tiny portion remains when you reach the peak of the pyramid of energy But - could one hill have sheltered two Tyrannosaurs?? That depends - on whether or not T. rex was warm-blooded or cold-blooded Warm-blooded animals (endothermic) need more energy to sustain themselves that cold-blooded animals (ectothermic) The laws of thermodynamics have not changed since the Cretaceous The pyramid of numbers must have applied to extinct communities as well How can we estimate the way energy moved through a vanished ecosystem? Many lines of circumstantial evidence that at least some dinosaurs were warm blooded Many lines of circumstantial evidence that at least some dinosaurs were warm blooded Erect stance Rapid gait (run, gallop) - trackways Feathered dinosaurs - insulation Predator/prey ratios Calculate the number and relative mass of predators and prey in the ecosystem Total biomass predator / total biomass prey Ectothermic communities have high PPR Calculate the number and relative mass of predators and prey in the ecosystem Total biomass predator / total biomass prey Ectothermic communities have high PPR Endothermic communities have low PPR How can we calculate this ratio for dinosaurs?? Pick one formation, all dinosaur fossils from that formation are about the same age Estimate mass per species, calculate PPR Dinosaurs are at the upper end of the range for modern mammalian communities Estimates have a built in bias - what is it?? Probably overestimating the number of large carnivores Collection bias in favor of big carnivores One hill cannot shelter two tyrannosaurs Competition The natural theologians were fascinated by the balance of nature What cosmic forces kept the delicate balance between organisms and their environment? Darwin also worried about this - why aren’t we up to our neck in house flies?? Populations of most organisms have an incredible potential for growth Consider the lowly house fly House flies have seven generations per year, 120 flies per generation - what would happen if they all lived? Forget nasty little flies, what about cute little robins? Afemale robin lays four eggs per clutch She can lay two clutches in one year What if all 8 baby robins survived? End of one year = 64 robins End of ten years = 24,414,060 robins At the end of 30 years, the entire planet Earth would be buried under a blanket of robins 4.5 miles thick !!! Needless to say, most organisms don’t live long enough to reproduce There are many limiting factors in nature that regulate the growth of populations Limiting factors can act from outside the population - extrinsic limiting factors - can be physical (abiotic) factors: Sunlight Water Nutrients Food Resources Limiting factors can act from outside the population - extrinsic limiting factors - can be biotic factors: Competition Predation Symbiosis Limiting factors can also act from inside the population - intrinsic limiting factors Changes in reproductive physiology Changes in behavior Limiting factors can act in proportion to how dense the population has become - density- dependent limiting factors Limiting factors can have the same effect regardless of how dense the population has become (forest fires, tidal waves) - density-independent limiting factors Most populations are regulated by a combination of limiting factors - they never reach their full reproductive potential Charles Elton proposed that equilibrium in nature resulted from a balance of interactive forces, especially competition and predation Modern ecologists are fascinated by non-equilibrium theory, which stresses the importance of disturbance Disturbances are forces that disrupt a natural ecosystem Abiotic - forest fires, floods Biotic - diseases, parasites Elton’s focus on predation and competition was ahead of his time Both predation and competition are important forces in regulating the growth of natural populations Competition occurs when two or more organisms use the same resource in a way that affects the birth rate or death rate of the competitors Which is true competition, limited tickets for a Peter Paul and Mary reunion, or a Black Sabbath reunion concert?? The intensity of the competition will depend to a large degree on the density of the population in the parking lot outside the arena Competition is an extrinsic, density-dependent limiting factor Competition can be intraspecific, between members of the same species Competition can be interspecific, between members of different species Which type of competition will be the most intense?? Intraspecific competition! Why?? Intraspecific competition is most intense, because your needs exactly match the needs of other members of your species Niche is the ecological role that a species plays in a biological community, the sum total of its needs and the parameters within which it can survive (niche = job, habitat = address) Individuals of different species will occupy a different niche The intensity of the competition between them depends on the extent to which their niches overlap Competition limits the ability of either species to realize its full potential, its fundamental niche Competition forces organisms into a much narrower niche - the realized niche Consider the flour beetle, Tribolium Larvae are found in grain storage areas - look like the closely related mealworms sold in pet stores Thomas Park raised flour beetles under several different sets of conditions Set up six types of environments in six tubes full of wheat flour Hot / temperate /cold Dry / moist Added Tribolium castaneum to one set of vials, Tribolium confusum to another Put equal numbers of both in another set When grown alone, each species could thrive under any set of conditions When grown together, one species proved a superior competitor, depending on conditions When grown alone, each species showed the same fundamental niche When grown together, competition forced them into a realized niche Consider two species of Paramecium, grown in a jar Either P. aurelia or P. caudatum can do equally well under the same conditions But P. aurelia is a superior competitor, and when raised together it always eliminates P. caudatum Two species cannot coexist if they share the same limiting resource Competitive exclusion occurs when one species is a better competitor than another, and forces it into local extinction Scotland - intertidal zone has two competing species of barnacles - Semibalanus and Cthamalus When the ecologist Connell removed Semibalanus from the rock, Cthamalus would fill the entire space Both have overlapping fundamental niche Semibalanus is the better competitor - overgrows Cthamalus and smothers it, or grows under it and pries it off the rock! But they coexist on the same rock Cthamalus can tolerate drier conditions that Semibalanus, so holds on in high tide zone We have always been fascinated by competition, the struggle for existence But most species manage to coexist peacefully in nature How do species avoid or minimize competition with one another? There are several ways in which species can coexist with one another Live in different geographic areas - don’t meet, don’t compete - NorthAmerican Bison andAustralian Kangaroo are both grazing herbivores on grassy plains, but never encounter one another in the wild There are several ways in which species can coexist with one another Live in same geographic area, but in a different habitat Like the deer mouse Peromyscus in the forest and Peromyscus in the meadows Like grazing mammals on a mountain peak Live in same geographic area, and same habitat, but use it at a different time of day Like the night herons and other wading birds Like birds (diurnal) and bats (nocturnal) Live in same geographic area, same habitat, use it at same time of day, but exploit the resource in a different way - resource partitioning Like mixed species foraging flocks Mixed species foraging flocks have higher rates of food capture than solitary birds Specialize in different feeding zones Some specialize in tops or bottoms of leaves Some glean insects from cracks in the trunk Some work along the main branches There are several ways in which species can coexist with one another Modify your physical shape through natural selection - character displacement Geospiza fortis alone, beak size ~8-12 mm, same as G. fulginosa G. fortis beak size is 11-15 mm on Santa Cruz, where it competes with G. fulginosa In 1982 a breeding population of G. magnisrostris arrived on Daphne, began competing with G. fortis for large size seeds Grant 2006 (Science) reports 2003/2004 droughts hit G. fortis with bigger beaks, population now has smaller average beak size Coexistence and competition are both important factors in the regulation of natural populations Competition is inevitable if two organisms need the same thing to survive or reproduce Competition can take many forms Scramble competition - exploit resources by using them up (exploitative) Contest competition - engage in a face to face contest over limited resources (interference) will appear in pairs on test Scramble competition - exploit resources by using them up (exploitative) Everyone gets at least some of the available resources - examples??\ Mardi Gras !! - Zulu parade Contest competition - engage in a face to face contest over limited resources (interference) Winner takes all - one organism gets all the resource, the other competitor gets none - Rex parade!! example of type of comp; fill ins Contest competition is typical of animals that defend a territory Territory = any area that an animal defends against other animals Usually defend territory against members of your own species - except mockingbirds!! Territories vary greatly in size - depends on the needs of the species Most often defend feeding territories, breeding territories, nesting territories Sometimes defend courtship territories (leks) Limited number of high quality territories Only territory holders will mate Bachelor males will become “floaters” High stakes competition, but injuries and deaths are relatively rare Advertise your ability to defend your territory with recognized signals - body postures, vocalizations, plumage displays Territory defense can be very costly - Why? Stereotyped, ritualized behaviors are used to defend territories - pushing, shoving, hollering, butting heads… Means of minimizing the physical effects of intraspecific competition Humans like to think they are above the fray, but we are one on the most territorial animals on Earth!! Phallus stones used to mark property in jolly old England - analogous to primate displays of erect penis! Predation Is peaceful coexistence the rule in nature? Most animals seek to avoid or minimize competition But some struggles are always to the death - the contest between predators and their prey Predator is any organism that eats another organism (plant or animal etc…) Organism that is injured or killed is the prey There are many ways to be a predator True predators - kill it and eat it Parasites - feed on it, but don’t kill it Parasitoids - insects lay their eggs in hosts (often paralyzed), young hatch, eat host alive Herbivores (!) - prey upon innocent plants We’ll focus on true predators Strong force in natural selection - must be big enough, smart enough, fast enough, or mean enough to avoid being eaten Predators prey mostly on old, weak, sick or injured animals - Why?? Predators are simply trying to avoid injury Stumble in a hole, get gored by a hoof or horn, no ambulance in the jungle - so predators prey mainly on the helpless… Predation ultimately improves the overall fitness of the survivors, prey benefit from being eaten in the long run Several different strategies for catching prey Active pursuit - chase it and kill it Solo pursuit Pack pursuit Ambush - hide, wait for prey to come to you Active pursuit - chase it and kill it Solo pursuit - lone predators - examples?? - cheetah Pack pursuit - group of predators - examples?? lion, wolves Packs can adjust their aggregate body size to match the size range of the available prey Ambush - hide, wait for prey to come to you Lizards - evolutionary constraint due to primitive stance - easily fatigued Ant lions - dig little pits in the sand for unwary travelers (called doodlebugs re: sand tracings) Sarlacc - native to Tatooine desert Many strategies for prey as well… Run away!! Hide (camouflage) Stand and fight Many strategies for prey as well… Bluff or startle Warning coloration Travel in herds Prey can defend themselves in many ways Chemical weapons Secondary compounds - phenols, alkaloids Chemical spray - skunks, bombardier beetle Taste bad - Monarch butterfly, caterpillar; monarch vs viceroy Venom Prey can defend themselves in many ways Mechanical weapons Spines and thorns - roses, hedgehogs Suit of armor - isopods Hooves, horns, teeth…
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