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Lecture 1

AN100 Lecture 1: Test 3 study guide

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Department
Anthropology
Course
AN100
Professor
Amalia Philips
Semester
Winter

Description
BIO 111 TEST 3 STUDY GUIDE: ECOLOGY ❖ THE BIOSPHERE • studying the biosphere contributes to the study of ecology. The distribution of living organisms on Earth is not uniform. WHY? • Why are organisms distributed in patches? Think of Canada vs Rain Forrest. o ABIOTIC factors (for uneven distribution) to consider: 1. The distribution of dry land is not uniform. There is more land in Northern Hemisphere vs Southern Hemisphere, so we can assume there are more organisms in the Northern Hemisphere. 2. Seasons are caused by uneven solar radiation, which is caused by the tilt of Earth’s axis as it rotates around the sun. This means that the intensity of sunlight is lower at higher latitudes. This accounts for temperature differences between the equatorial habitats and your more northern or more southern areas. Radiation from the sun is spread over more surface area at higher latitudes, so its intensity is lower. The light rays also have to pass through more atmospheric gases, which lowers the amount of radiation that reaches Earth’s surface. 3. Because of the uneven heating of the atmosphere, we have wind currents, prevailing winds. There are areas where air rises as it warms up, then sinks as it cools. This causes movements of air and in addition to the rotation of the earth, these factors cause prevailing wind currents. 4. Wind currents and ocean currents can have profound effects on climate, especially movements of water (because water has a high heat capacity). Water can store and move thermal energy around the world. EX: The Gulf Stream ocean current. London and North Equatorial are on the same latitude, but the climate is milder in London because of the ocean currents that surround it. These movements of water can really affect climate. EX: California current is cold. 5. Interactions of currents and geography influence climate. A prevailing wind blowing over a mountain range can cause a rain shadow; which is when warm, wet air coming off the ocean rises up a mountain range and produces lots of cloud buildup and rain and you get a side with a wet forest, while on the other side, the air will be dry and you will get a desert. o Terrestrial Ecosystems’ assemblages of plants and animals: we find that similar latitudes always have similar biomes (assemblage of plants and animals). (EX: Canada’s pine forests are on same latitude as Siberia’s pine forests) Species may not be exactly the same, but the look of the places will be very similar. (EX: Russia’s “step” vs. US “short grass prairie”) • There are many biomes in our Hemisphere. 1. Starting from the North Pole  South, we have the Tundra. Tundra is a part of the habitat that has permafrost-the soil never thaws, so there is a permanent layer of frozen soil. Since water doesn’t drain in the soil, when snow melts, it just puddles and the ground stays wet, boggy. Therefore, not many trees grow in the Tundra because their trees can’t dig down. There are mainly sedges, small willows and marshy plants. There are lots of insects and few animals. 2. Moving South, you encounter - Coniferous Forest. 3. Moving further (east of the Mississippi River), you encounter-Temperate Deciduous Forest. In the North there are Sugar Maples in these forests while in the South there are Hickory and Oak trees. 4. (west of the Mississippi River), you encounter-Tall Grass Prairie (Temperate Grassland) 5. (further west), you encounter-Short Grass Prairie (Temperate Grassland) • The assemblages of plants in these terrestrial ecosystems determine what types of animals live there. Furthermore, the assemblage of plants is determined by a combination of temperature and rainfall. 1. The two plants have very similar morphology because they recently evolved from a common ancestor. 2. They have become adapted to similar habitats by natural selection. D (F,T) o A combination of amount of rainfall and average temperature is what determines these biomes and makes them different from each other. (EX: low temp all year- Tundra. lil warmer, low rainfall-Coniferous Forest. high temp, high rainfall-Tropical Rain Forest. warm, low rainfall-Warm Desert) (**stopped this lecture to do Biomes Video**) ❖ NORTH AMERICAN BIOMES o The largest, easily recognizable subdivisions of the biosphere are called biomes. Each biome is characterized by a particular general type of plant and animal community. These communities look much the same wherever the biome occurs, but the particular species making up the biome vary from place to place. This suggests the plants and animals have adapted in similar ways to the environment. A biome is a collection of similar and related ecosystems. o 3 ways to look at a biome: 1. A biome is the largest subdivision of the biosphere. 2. It is a type of ecosystem or community shaped by a particular combination of climate and topography. 3. A biome is a collection of smaller, similar, and related ecosystems. 1. TUNDRA – adjoins the artic regions and North America and Eurasia. • beautiful, dotted with lakes and streams, mosses, sedges, willows. • cold and frost shape the landscape. under 3 feet, its only permafrost. the layer of permafrost prevents the penetration of liquid water into plant root, so the vegetation is sparse. • as a result, the Tundra appears waterlogged, in spite of relatively light precipitation. • Caribu is the dominant herbivore in the Tundra of North America while the Reindeer fills this role in Eurasia. other animals are the muskox, wolverine, artic fox, lemming. their activity is geared for short summers and long winters. many of the animals posses extra fax and fur levels. some change color in season. • the food chains of the Tundra are simple and limited because of the low amount of plants and animals involved. Because animals man rely on one particular plant or species, population of animals in the Tundra show extreme oscillation in numbers. Owl (predator) will oscillate with lemming (prey). 2. ALPINE TUNDRA – occurs on high mountains in the temperate zone. • alpine forget-me-nots grow 11,000 ft in Rocky Mountain National Park. • the marmot is an inhabitant of the Alpine Tundra. 3. NORTHERN CONIFEROUS FOREST – stretches across North America and Eurasia and is just south of the Tundra. • occur in mountainous areas like cascades, rockies. • summers are cruel and winters and cold, and rainfall is moderate. • dominant plants are evergreen trees, pine, fern. because the forest floor is shaded year round, the forest floor is usually very bare. • animals are adapted for life in the cool forest; squirrels, beaver, porcupine depend directly on trees for food and shelter. black-tail deer, black bear, bobcat, wolf and moose, dwell in the ecosystem that make up the forest, • a biome is not just a single homogenous community. it consists of smaller, related ecosystems. the Northern Coniferous Forest consists of many types of forest that are often very near to one another. along with many different types of forests, creeks and rivers may also be a part of this biome. Ecological succession could turn these lakes into land then into trees over time. • even though redwood trees are coniferous, they are not a part of the Northern Coniferous Forest biome. 4. MOIST CONIFEROUS FOREST – stretches from Alaska to Northern California. • the Pacific Ocean moderates temperatures, cooling in the summer and warming in the winter. masses of air moving in from ocean deposit moisture in the form of rain or fog. these forests can get 200 in rain a year. • unlike the drier, colder Northern Coniferous Forest, the understory vegetation in this forest is good because light can filter through to the bottom. • animals of the Moist Coniferous Forest are similar to animals in Northern Coniferous Forest, but these animals’ adaptations to cold are not as important. 5. TEMPERATE/ EASTERN DECIDUOUS FOREST – forests of eastern north America are very different than the forests in the north and west. • these have trees that lose their leaves every fall. • Deciduous Forest occurs in areas of abundant, year-round, precipitation. temperatures are moderate and there are distinct seasons. • one covered a lot of area, but now half of the original 1% remains. • like other biomes, it is not uniform in species composition. • animals are gray squirrel, wild turkey, black bear, raccoon, and white tailed dear, insects in spring. • the most striking characteristic of the Deciduous Forest is the brilliant display of color in Autumn when the chlorophyll breaks down. 6. GRASSLANDS – are found on every continent except Antarctica. • Grasslands usually occupy the interior of continents where rainfall is relatively light. Grasslands occur in areas too dry to support forest but too wet to be desert. • Tall Grass Prairie was one dominant in the EAST. Short Grass Prairie in WEST are called the plains. • Trees are limited. Since rainfall is light, so nutrients are not leached from the soil, thus grassland soils are the most fertile in the world. a lost of grassland is devoted to agriculture. • animals are usually runners like the antelope, bison, prairie dog. 7. TROPICAL SAVANNA BIOME – (does not occur in North America) grassland with scattered trees. • occurs in warm regions with abundant rainfall, but also a prolonged dry season in which fires occur. • not many plant species dwell in the Savanna. a few species of grass and trees are dominant in wide areas. • although, its animal diversity is unrivaled: wildebeests, zebra, giraffe, lion, cheetah. 8. CHAPARRAL – occur in temperature areas with winter rains, but hot, dry summers. • vegetation consists of evergreen shrubs. • all Chaparral areas look very much alike, even though the animals are different. • unrelated species of plants and animals have adapted to the similar environment. this convergence happens in all biomes. • characteristics like long roots, tree knees, reflective leaf surfaces help any species in the Chaparrals conserve water. • fire affects the Chaparral. some plants in the Chaparral germinate with fire. In a way, fire maintains the Chaparral. • animals are coyote, gray fox, mule deer. most others are small and inconspicuous. 9. DESERT – light rainfall, dry. • form in rain shadows sometimes (EX: Cascades in Washington) • climate and topography can shape biomes • plants and animals have crazy adaptations to store water. catfish store water in cells, reptiles have dry feces, some never need to drink. 10. TROPICAL RAIN FOREST – seasonal variation in temperature is very very low. • climate is warm and rainy with one dry season. • plant growth is dense, dark, and stratified in layers. • there is little growth on the floor because light cannot penetrate that far. • its diversity is its biggest characteristic. • animals are mostly herbivores and some spend their whole life in trees. SUMMARY: • the species making up a biome differ from place to place. • each biome has a characteristic structure wherever it occurs. • in each biome, plants and animals have been shaped by a particular type of environment. this illustrates how organisms adapt to their environments. (**continuing biosphere lecture**) o Aquatic Habitats (many types like: rivers and streams, slower moving water, estuaries where fresh water and sea water mix, oceans, large freshwater lakes, and large saltwater lakes) • Salinity & Species Diversity: o there is a correlation between salinity levels and organisms that can tolerate it. o Ocean salinity is around 35; many species live in that salinity level. o Marine salinity; a rapid drop off of species number that can tolerate this level of salinity. (EX: Great Lakes and Dead Sea) o Brackish Water (estuary where fresh water and oceanic water meet; less salty than ocean); big dip in number of species. the diversity is very low. this phenomenon is called the Brackish Water Paradox. some say diversity is so low here because the amount of variability that can happen to the species (like estuaries having tidal fluctuation in dry years & floods, oxygen levels, temperature, tidal fluctuations) makes it a harsh environment to live in. BUT, the Caspian Sea has brackish water and much lower species diversity than the ocean. BUT it doesn’t have tides, fluctuations. Its like one big freshwater lake without the species diversity it should have. No one can explain this. o Fresh Water; lots of species o take home: most important environmental factor that determines species diversity in aquatic habitat is how much salt is dissolved in the water. aquatic habitat types: • Freshwater Lakes ➢ Life Zones: light limit of penetrating into water is about 300 ft, so most animals live in the upper water column. Animals can’t live at the bottom where there is no light. plants can emerge from the shore with roots in the water. ➢ Seasonal Changes (in lakes in temperate areas) Seasonal Turnover in water occurs. Winter: ice covers a thin layer of water that is just below 4°. 4° water sits right below that layer because water at 4° is denser. There is little circulation because no winds affect water under the ice. Spring: when the ice from winter melts, warms, and sinks down, winds create currents that produce a turnover of the water temperatures. this creates a whole mix and brings nutrients up to the top of the lake. Summer: a barrier between the cold & warm water called a thermocline that does not allow cold and warm water to mix. Warm is at top and cold is at bottom. Fall: another Spring-like turnover of water occurs. • Streams & Rivers ➢ (fast-flowing) - water moves fast, so there is lots of aeration, a lot of oxygen content. although, the water moving fast washes away nutrients. ➢ (slower-flowing) – water moves slow, so there is lower oxygen. but there is more nutrients for plant growth. • Estuaries (EX: Chesapeake Bay) ➢ fresh water rivers mix with seawater ➢ In Louisiana, we have 2 types of estuaries because our state is at latitude where a transition between salt march estuaries and mangrove estuaries occurs. • Coral Reefs ➢ (EX: The Great Barrier Reef) ➢ Corals under great stress undergo a phenomenon called bleaching. Healthy corals are brown because of symbiotic algae that are harbored to tissues of the coral. When the corals are stressed due to pollution, etc; they expel the symbiotic algae and it leaves the corals a white color. Coral reefs usually do not recover from this. • The Open Ocean = Aquatic “Desert” ➢ this is the aquatic desert because of the lack of food in this habitat makes is very hard to live there. the open ocean is clear because there is no food and nutrients. when there are no plankton, other fish have nothing to eat. ➢ this can be compared to Louisiana’s brown, nutritious water that makes us the #1 in fishery. ➢ Life Zones: (same as in freshwater) light penetrates about 300 ft and then photosynthetic activity is low below that. animals on bottom are benthic and animals that swim around are pelagic. 1. Both coral reefs and tropical rain forests have very high species diversity. 2. In both ecosystems, abiotic conditions have been very stable for a long time. A (T, T, related) *Species diversity is related to stability of a habitat. • Hydrothermal Vents are unique aquatic ecosystems. (cool video bout them) ➢ people used to think all ecosystems on earth were sustained by photosynthetic activity, but then hydrothermal vents were discovered. Hydrothermal vents have a lot of variability in organisms even though they occur at the bottom of the ocean with no sunlight. the ecosystem is supported by primary producers called chemoautotrophic bacteria that obtain energy from oxidation of hydrogen sulfide. organisms eat these bacteria or harbor energy from these bacteria. ➢ In Gulf of Mexico, we have hydrocarbon seeps where methane gas leaks out of cracks in the seabed and there are communities like above ^ except bacteria use methane instead of hydrogen sulfide. o Ocean-Air Interactions o interactions between prevailing winds and ocean currents can also cause changes in local climate. o El Nino year: wind direction south of the equator changes, which prevents a mixing of water off the west coast of South America. this means the productivity of the area goes down. fish die in el nino years. changes in winds affect the amount of moisture carried west  east, which means, this affects rainfall on land masses like the US. o take home: occasional changes in wind direction can have an effect on global climate. ❖ OCEAN DESSERT VIDEO • Sargasso Sea is a paradox. It is calm, and open sea. The open sea is usually marine desert, because of lack of plankton for nutrients. Although, the Sargasso Sea has plankton and productivity is very low. Why do so many animals live in such an unproductive place? Its stability allows for slow development and no extinction. • The Sargasso Angler fish has a history of adapting to living life among Sargasso weed. Natural selection has molded the Sargasso Angler fish. It has camouflage and other protective and hunting mechanisms. • The Sargasso Sea offers a place to hide. Sargasso weed is a refuge for poor swimmers. One disadvantage of living on Sargasso Weed is: as the weed grows larger, they produce less air bubbles to keep them afloat. Sooner or later they sink. • The open ocean has many fast-swimming organisms. • The Flying Fish finds ways to make nests in the Sargasso Sea out of Sargasso Weeds. After hatching, the tiny fish quickly swim free, on their own against ocean predators. • Sargasso Weed is a refuge for swimming organisms too. They also provide a place for things to grow on. Barnacles and goose barnacles and worms live side-by-side and share food on the Sargasso Weed. • Sargasso colonies are also home to tentacle animals. The animals hide in exoskeletons. When the Sargasso weed dies, the skeletons of the animals end up on shore. These tentacles animals may live next to an anemone; its stinging cells catch copepods, which are food for Sargasso dwellers. Slugs eat anemones. • “Sinkermyknee” is a Sargasso weed neighbor that stings copepods with tentacles. • SO Sargasso weed has provided living space for animals at sea. It has created a community filled with contradictions. It is nutrient poor, but species rich. A desert full of life. ❖ VOLCANOES OF THE DEEP SEA • The oldest living fossil in the world - Paleodictyon nodosum • Bound for the Galapagos Drift, Alvin (sea camera) • A volcanic process underground was building elaborate structures. Water descending into fishers in the seafloor was apparently interacting with hot rocks beneath, to reemerge as a black cocktail of poisonous chemicals. It was difficult for scientists to understand the geological processes at work, but the animals were impossible to comprehend. They were living in water hot enough to melt lead. Life shouldn’t have been present at all. • The worm alvinella was among these organisms. They danced in and out of the poison water. • Humans didn’t think to look in the dark, boiling water for life. The discovery of these hypothermal vents was the first step in making a connection to the fossils of the Paleodictyon found in Spain to the mysterious life forms on the sea floor. • Alvin traveled to the bottom of the sea floor, and glimpsed creatures never seen by human eyes. These soft-body animals will never leave a fossil trace, but they have probably been around for hundreds of millions of years – like phantoms of the sea. • Alvin landed on a fantastic landscape – it was a recent volcanic eruption. (Alvin was between the American and Atlantic Sea plates: the Mid-Ocean Ridge. It is the largest geological feature on the face of the earth. The large outer shell of the earth floats on a hot underlying layer. Where the plates move apart, magna rises to form the Mid-Ocean Ridge. The volcanic system is the oven of plant earth. It bakes the earth’s crust, boils sea water, and serves up nutrients to the animals of the abyss, and occasionally roasts them alive, like what happened at this eruption.) • It was like the ruins of an ancient civilization of life burned away. Although, scientists were puzzled at what Alvin was seeing: Spaghetti worms covered the rocks, and there were large anemones growing. Crabs, octopus, even fish, giant tubeworms, and golden mussels. There were billons of tiny white feather duster that were filtering nutrients from the hot water emerging from the rocks. Live hadn’t just returned, but it had come back with larger scale and vigor than was believable. It was a place of darkness and no seasons and no time, but it was driven by the inner earth. At the center of the life was a 40ft high volcanic monument, decorated with 6ft long tubeworms. The tubeworms prospered in the hottest water upward and at the bottom, there worms tubes, but no worms. They were unable to move and had starved to death. With no mouth or stomach and planted permanently in the rock, the tubeworms seemed like plants instead of animals. But scientist found specialized bacteria in the tubeworms’ tissues that were using chemical energy in hot water to make nutrients. They were, in effect, turning poison into food and sharing it with their host, the tubeworm. The red filaments on the top of the worms draw in hydrogen sulfide from the water to feed the bacteria inside. This is called chemosynthesis. The tubeworms red color comes from blood containing hemoglobin. So who are these animals that share our blood? • 5 billion years ago, a giant star blew itself into a supernova. Debris from that created our sun. It’s believed that the planets that formed, orbiting around the sun, growing larger and larger, acquiring debris from space. The Earth cooled and built a solid crust, the oceans formed, life flourished by harnessing energy from the sun using photosynthesis. It was once believed that the sun’s radiation was the only source of energy for all life on earth, but deep in the earth’s crust, radiation from the old supernova still exists. This energy gives life to deep-sea animals. • Alvin found so many products of this radiation, including “The Lost City.” Enormous limestone structures stand and bacteria lives here. Ancient methane chemistry allows life. How was life on earth building complex structures? Paleodictyon is a living fossil. Over hundreds of millions of years, the creatures have learned how to build hexagonal patterns. They’ve survived mass extinction. What’s it secret? • Scientists began finding hydrothermal structures everywhere along the Mid-Ocean Ridge. Life was rich. The structures were so perfect for the animals living in them that the geology seemed alive. At the center of the relationship between the animals and the flow of energy from the crust are hundreds of species of specialized bacteria growing on the rocks. They use chemical energy from the hot water to produce nutrients. The shrimp on the rocks use these bacteria as food. Most shrimp burn off their extremities while trying to eat these bacteria. • Mid-Atlantic Ridge held a fantastic vent, the size and shape of a football stadium. Chemosynthetic bacteria weren’t just on the rocks, but on the shrimps themselves. They scrape this layer off and eat it. Scientists probed deeper into the crust itself and made the most important discovery. In total darkness, in 3000lb of pressure and in 230 F water, the microscopic parasite hyperthermophile. This is the harshest environment on earth. Yet its molecules of DNA share our 4 base chemicals, the language of DNA. We are related to them in this sense. This is where life began on earth. We evolved from this. • With the discovery of microbes living in the vents, scientists considered that most of the biomass on earth lives beneath the volcanoes of the deep sea. No one knows why vents shut off and leave mounds of minerals behind. This is where the scientists searched for their mysterious hexagonal fossils. In the “Valley of Paleodictyon,” they looked where there was no life and that ended up being the animal’s secret. They found thousands of paleodictyons. They dissected the sections of the sample gathered, and the hexagonal tunnels were present, but no paleodictyons were present. Although, scientists now believe that the paleodictyon is forming bacteria in its tunnels, which enables it to live in the sparse chemical remnants of the volcanoes in the deep sea. They have outlived all forms of life on earth. ❖ POPULATION ECOLOGY • A population is all of the individuals of one species in the same place at the same time. • People that study population ecology are interested in: ➢ Demographics: 1. size: how many individuals are in it 2. density: “” 3. distribution: how they’re distributed among the available habitat 4. age structure: how many young organisms vs. how many old organisms, etc • Distribution o the special distribution of the individuals in a population varies from species to species and from habitat to habitat. o there are 3 general ways to distribute 1. clumped – clumped together in separate sections 2. uniform – uniform distribution 3. random – completely random distribution **effects on population growth under ideal conditions with no limitation on growth rate** • Population Size & Exponential Growth o a population just beginning to growl shows exponential growth. (J shape curve) growth rate = birth rate – death rate • Influence of death rate on population growth o with no deaths, population grows very fast o with deaths, the rate of a population reaching a certain number of individuals is slowed. o both are still J-shaped growth curves • Life history affects population growth o (EX: populations that reproduce at 4 years old will grow faster than population that reproduce at 6 years old. ) o this creates a lag in achieving the same size as the faster population ** effects on population growth under non-ideal conditions** • Limits on growth o if not enough nesting sites are available, there will be competition o other competitive factors include: food, space, places to hide. The combination of all these factors leads to limits on population growth. o the environmental carrying capacity is where the J-shape curve of exponential growth levels off. when a population reaches this point, limiting factors have been reached. the actual size of population that can be supported by the environment’s available resources is called the carrying capacity. this causes the growth curve to change from a J shape to an S shape. • Limits can be density-dependent or density-independent 1. density dependent factors depend on the number of individuals in the population o EX: in bees, the number of eggs laid each day decreases as population density increases & as the population density increases, the lifespan of the bees decreases. (both of these seem to happen because they don’t want the population to overgrow) 2. density independent factors do not depend on the number of individuals in a population o EX: drought where animals die. (it doesn’t matter how many individuals there are; without water, everything will die) • boom and bust population pattern o when favorable growth conditions are occurring, there will be an increase in population growth (boom) (this will be a J-shape curve because there are no limits to population growth here) but then you can reach limit of the resources and exceed the carrying capacity and when the resources are used up the population falls (bust) o EX: *lemming population in biome video fluctuating from year to year depending on plant availability* warm springs with lots of plants- lemmings boom. harsh winter-lemmings bust • Survivorship Patterns o If the data of the US people were plotted as the number of survivors at each age, the result is a survivorship curve. o the death rate increases as age increases in humans. the death curve is steeper for men. o different species have different survivorship curves (3 types) 1. Type I curve: EX: goats. mortality is highest very late in life (like humans) 2. Type II curve: EX: lizard. mortality does not vary with age (ends up showing a linear relationship between survivorship and age) 3. Type III curve: EX: shrub. mortality is highest early in life (very few survive to be old.) o Type I & Type III are extremes, while Type II is a middle ground. The two extremes represent r-selected & K-selected species. These are Life History Strategies o r-selected species: ▪ shorter development ▪ reproduce when very young ▪ few breeding episodes with many young per episode ▪ parental investment is small ▪ high mortality rate, shorter life span ▪ EX: lemmings ▪ *better for an unpredictable environment* o K-selected species: ▪ longer development ▪ reproduce later in life ▪ more breeding episodes with few young per episode ▪ parental investment is large ▪ lower mortality rate, longer life span ▪ EX: humans • Life history traits are subject to evolutionary selection pressure o EX: Cichlids prefer large guppies & Killifish prefer small guppies o Data of this study shows that the phenotype of the guppies is affected by the presence of different predators. o Killifish (eat small fish) so the guppies tend to be larger. o Cichlids (eat large fish) so the guppies tend to be smaller. o The phenotype of the adult guppies is affected by the presence of different predators’ preferred traits. o Embryo weight is a measure of how much parental energy is put into each egg. In streams with Killifish (eat small fish), the females lay fewer eggs, but the eggs are larger. In streams with Cichlids (eat large fish), the females lay lots of eggs that are small. • Global Human Population Growth o human population grew very slowly until Industrial Evolution o our population doubles every 50 years o The Black Death caused a huge dent in population growth • Changes in US Survivorship Curve o There used to be a higher mortality rate early in life o Some factors that have contributed to our survivorship curve changes are prenatal care, immunizations, vaccines, things to stop diseases. Some very old diseases are reoccurring, like whooping cough. • Population Age Structure o If you divide the population into pre-reproductive age, reproductive age, and post-reproductive age, and make a pyramid model; that shows the population age structure. 1. a population age structure shaped like a triangle will grow over time 2. a population age structure shaped like a rectangle will stay the same (as people come into reproductive age, the same amount leaves it) (this is a concern in European countries) 3. a population age structure shaped like an inverted triangle will decrease over time. 4. In China, the government wanted to limit population growth and this changed the population age structure from a rectangle to an upside down triangle. o the point is that population studies are not only interesting to biologists but to government as well, in terms of health care, where to build schools, etc. ❖ COMMUNITY ECOLOGY • a community is all of the populations in the same place at the same time. • community ecology encompasses all of the biotic components of an ecosystem and how they interact. • many communities make up a biome (EX: Deciduous Forest community and river community and stream community make up the biome) • people that study community ecology are interested in: ➢ Species Richness - how many species there are in a particular area. o EX: species richness of birds is high near the equator and in the tropics and low in the artic and in high altitudes. What causes this? • Patterns in Community Structure • Species richness is high at the equator and falls off as you near the poles. Why is biodiversity higher in the tropics (near equator)? • Explanations: 1. Species Area Effect o area of habitat for species is high in tropic places because there’s more structure and space for animals. EX: as the area of trees increases, the number of insects increases. more area; more species. 2. Primary Productivity o the green plants photosynthesizing and producing biomass (growth of trees). the productivity levels are associated with species richness. EX: in warm areas with year-round tree growth, there are more species. 1. Salt marshes are highly productive. 2. Salt marshes have high species diversity. C (T,F) *This is an exception to the productivity hypothesis, which makes these ideas about community ecology fuzzy. 3. Intermediate Disturbance hypothesis o relates species richness as a function of disturbances. EX: in a rainforest, a tree falls and that opens up the sub-canopy level to more light and more shrubs and trees can grow, which increases diversity. o frequent disturbances results in low species richness o infrequent disturbances results in low species richness o Maximum richness occurs at intermediate levels of disturbance o high disturbance leads to r-selected species while low disturbance leads to K-selected species. o regular disturbances creates a mix of the two life history strategies. 4. Diversity-Stability Hypothesis (opposite of last idea) o relates stability to species richness. EX: an increase in stability results in an increase in species diversity **think of Tropics relation to all these hypothesizes. It’s an exception how?** • Ecological Succession (2 types) – changes in communities over time. 1. Primary Succession - colonization of an abiotic habitat. o EX: bare rock with no organisms, organic matter comes in from dead lichens, rock is broken down, soil forms, weed species form, shrubs form, trees form, then finally, a
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