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Ch.37 NOTES COMMUNITIES AND ECOSYSTEMS
COMMUNITY STRUCTURE AND DYNAMICS 37.2 Define the following and give examples. INTERSPECIFIC DEFINITION COMPETITION -­‐/-­‐ popul. of 2 different species com-­‐ Competition petes for the same limited resource. Mutualism Predation Herbivory Parasitism +/+ Both popul. benefit +/-­‐ One species kills and eats the other +/-­‐ Consumption of plant parts or algae by an animal. +/-­‐ parasite/host or pathogen/host Predation resulted in prey adapting to avoid being seen or eaten. • Camou
flage: Color and/or texture cause animal to blend with their environment. Example: Gray tree frog on bark (fig. 37.5a) • Mechanical defenses: protective quills, hard shell of clams, oysters, turtles. • Chemical defenses: include noxious taste or painful sting. Predators learn to associate bright colors with these animals. Examples: monarch butterflies, poison-­‐arrow dart frog. (37.5b) EXAMPLES Desert plants compete for water while tropical plants compete for light. Plants and mycorrhizae, flowers and pollinators. Predator/prey: lynx and hare; crocodile and fish Hippo, Cattle, deer eating grass Heartworm/dog; Salmonella/humans 37.6 Explain why many plants have chemicals, spines, or thorns. Define coevolution and describe an example Hervibory resulted in plants adapting to avoid having to regrow eaten parts. • Spines and thorns: roses, hawthorn trees, cactus • Chemical toxins: distasteful so herbivores learn to avoid them o strychnine: tropical vine o morphine: opium poppy o nicotine: tobacco plants o mescalin: peyote cactus o tannins: variety of plants o sulfur: Brussels sprouts, cabbage toxic to insects and cattle. Coevolution: a series of reciprocal evolutionary adaptations in two species. Occurs when a change in one species acts as a new selective force on another species, and counter adaptation of the second species in turn affects the selection of individuals in the first species. fig. 37.6 and lab manual cover. 37.8 Identify and compare the trophic levels of terrestrial and aquatic food chains. Both begin with producers (autotrophs) which are eaten by primary consumers (herbivores) which are eaten by secondary consumers (carnivores and insectivores) which are eaten by tertiary consumers which are eaten by Quaternary consumers. Detritivores and decomposers eat detritus, the dead material produced at all levels. Examples: earthworms rodents, insects, crows, and vultures. Catfish and crayfish. Decomposers secrete enzymes that digest molecules. Examples: Fungi and bacteria 37.9 Explain how food chains interconnect to form food webs. fig. 37.9 • A consumer may eat more than one type of producer and • Several species of primary consumers may feed on the same species of producer. • Some animals weave into the web at more than one trophic level. •
•
Examples: o the lizard and mantid are strictly secondary consumers, eating insects. o The woodpecker is a primary consumer when it eats cactus seeds and a secondary consumer when it eats ants or grasshoppers. o The hawk is a secondary, tertiary, or quaternary consumer, depending on its prey. For humans to get the most calories per gram of biomass eaten, they should eat…?... Meat? Eggs? Grain? 37.10 Describe the two components of species diversity. Explain why large fields of a single crop are vulnerable to devastating disease. Species diversity: species richness: number of different species in a community + relative abundance, the proportional representation of a species in a community. Example: fig.37.10a,b richness = 4 species abundance = % of each species Pathogens (viruses, bacteria, fungus) infect a limited range of host species (maybe just one). The more closely spaced the hosts, the more likely the pathogen will spread. (Irish potato famine 1845 due to potato blight a fungus). 37.11 Define a keystone species. Explain why the long-­
spined sea urchin is considered a keystone species. A keystone species is a species whose impact on its community is much larger than its biomass or abundance indicate. It occupies a niche that holds the rest of its community in place. Researchers compare the species diversity with and without the potential keystone species. The long-­‐spined sea urchin, Diadema, naturally grazes on seaweed and scrape patches of substrate clear of algae, providing platforms for coral larvae to settle. In 1983, a disease killed massive numbers of urchins.  Seaweed grew replacing the low turf of encrusted red algae that is vital to reef building.  This prevented light from reaching symbiotic dinoflagellates that corals depend upon for food.  In the following decade, the area of reef covered by living coral animals plummeted, along with overall species diversity. 37.12 Explain how disturbances can benefit communities. Distinguish between primary and secondary succession. Communities are constantly changing due to disturbances. Disturbances are events such as: • storms • fire • floods • droughts • overgrazing • human activities can: o damage biological communities o remove organisms from them o alter the availability of resources. Disturbances can have a positive impact on a community: • tree falls in a storm creates new habitats • More light can reach floor allowing new plants to grow • depression made by roots may fill with water and used as egg-­‐laying site for amphibians or insects. • Small disturbances increase patchiness which increases diversity. Ecological Succession: Primary and Secondary Primary succession begins in a lifeless area with no soil o volcanic islands o volcanic ash o rubble from receding glacier PRIMARY SUCCESSION bare rock  autotrophic bacteria  lichens and mosses grow from windblown spores  soil develops from weathered rock and detritus  grasses and shrubs move in windblown seeds or carried by animals  plants SECONDARY SUCCESSION soil remains after a disturbance wipes out an existing community. Example: clear-­‐cutting woods for a field then abandoning it as nutrients are depleted. SECONDARY SUCCESSION Abandoned farm field becomes a hardwood forest (fig. 37.12) Abandoned farm field  favorable to r-­‐selected species (early reprod. age, many offspring, no parental care, competition not a major factor)  weedy annuals like crabgrass and ragweed  perennial grasses, small broadleaf plants  softwood species like pine after 5 years  pine forest in 10-­‐15 years  hardwoods like oak and hickory take over deciduous seedlings are shade tolerant, pine is not. Favorable to K-­‐selected species.  final mixture of species depends on abiotic factors such as soil and topography. animal community undergoes succession along with plants 37.13 Explai
n how invasive species can affect commu
nities. An invasive species is a non-­‐native species that has been moved by humans either intentionally and unintentionally. They can spread far beyond original point of introd. and cause environmental or economic damage by colonizing and dominating wherever they find a suitable habitat. Example fig. 3713b: • 1859, 12 pairs of rabbits released on a ranch in S. Australia by a European who wanted to hunt familiar game. • In 1865, 20,000 rabbits were killed on the ranch • By 1900, several hundred million rabbits were all over the continent. Catastrophic because: • farm and grazing land became rabbit food • loss of plant cover caused erosion • Burrows made grazing treacherous for cattle and sheep • Competed with native herbivorous marsupials Biological Control: the intentional release of a natural enemy to attack a pest population. A virus lethal to rabbits was introduced Several coevolutionary cycles followed New viral strains introduced as rabbits became resistant 1995, different pathogen used to maintain control. Article on eradication of European rabbit from Australia. http://www.sciencedirect.com/science ECOSYSTEM STRUCTURE AND DYNAMICS An ecosystem consists of all the organisms in a community as well as the abiotic environment with which the organisms interact. 37.14 Compar
e the movemen
t of energy and chemicals through ecosyste
ms. fig. 37.14 “Matter
cycles,
energy flows.” 37.15 Compare the primary production of tropical rain forests, coral reefs, and open ocean. Explain why the differences between them exist. Most of the energy of the sun is scattered, absorbed, or reflected by the atmosphere or surface of Earth. Of the visible light that reaches plants, algae, and cyanobacteria (autotrophs), only about 1% is converted to chemical energy (glucose sugar) by photosynthesis. Biomass is the amount, or mass, of living organic material in an ecosystem. The amount of solar energy converted to chemical energy by an ecosystem’s producers for a given area and during a given time period is called primary production. (unit = g/m2/yr) Net primary productivity = biomass produced – amt used by producers as fuel for themselves Highest: algal beds and coral reefs tropical rain forests estuary temperate deciduous forest savanna boreal forest (taiga) cultivated land temperate grassland tundra open ocean Lowest: desert and semidesert scrub % of globe x productivity contributes to overall production so open ocean contributes the most overall because it is so vast. 37.16-­17 Describe the movement of energy through a food chain. Explain why there are more producers than consumers and why eating meat counts as a great luxury.  Energy supply limits the length of food chains. fig. 37.16 Illustrates the cumulative loss of energy with each transfer in a food chain. Only 10% of the energy available at each trophic level becomes incorporated into the next higher level. Only a tiny fraction of the energy stored by photosynthesis flows through a food chain all the way to a tertiary consumer. Top-­‐level consumers require a large geographic territory. It takes a lot of vegetation to support trophic levels so many steps removed from photosynthetic production. Food chains are limited to 3-­‐5 levels; there is simply not enough energy at the very top of an ecological pyramid to support another trophic level. Meat is a luxury for humans. fig. 37.17. Many more people are supported by eating a vegetarian diet. Feeding the vegetation to cattle leaves much less to support humans. Explain how carbon, nitrogen, and phosphorus cycle within ecosystems. Chemical cycles in an ecosystem include both biotic and abiotic (geological and atmospheric) components; they are called biogeochemical cycles. Chemicals Biotic Reservoir Plants draw CO2 out of air into sugar Passed along food chain by consumers Carbon Cellular Resp. returns CO2 to atmosp. (Depends of Photosyn. & Decomposers break down carbon compounds Cell Resp.) in detritus and releases it as CO2 fig.37.19 Burning wood and fossil fuels releases large amts of CO2 back into the air. Weathering of rock adds phosphate (PO4-­‐3) to the soil -­‐3
Plants t
ake u
p P
O
4 and make compounds Phosphorus Consumers eat plants to get phosphorus (Depends on weathering of (PO4-­‐3) returned to soil by decomposers rock) Runoff takes PO4-­‐3 to the sea where it will fig. 37.20 become incorporated into rock but not used until geologic processes uplift rocks and expose to weathering. Nitrogen Fixation: (N2) + bacteria  nitrogen compounds (NH4+) which can be used by plants. Mutualism between legumes and bacteria Free-­‐living bacteria both fix nitrogen. Nitrogen (Depends on (NH4+) in soil can convert to nitrate, (NO3-­‐), bacteria) which is more readily absorbed by plants and fig. 37.21 converted to protein. Herbivores eat plants and also make protein. Protein metab. releases nitrogen as urea (in urine) Decomposition releases (NH4+) to soil. Phosphates in fertilizers (commercial and animal waste) can run-­‐off into ponds. Phosphates are scarce enough to be a limiting factor for algae. Adding phosphates can cause an “algal bloom.” Abiotic Reservoir Atmospheric Fossil fuels Dissolved carbon compounds in oceans Sedimentary rocks like CaCO3 Rocks Atmosphere: 80% N2 gas but is not usable by plants. Soil So much algae grows that it does not produce enough oxygen during the day to supply the demands of cellular respiration throughout the night. This can cause the pond, all the life in it, to die. Also called eutrophication. fig. 37.23b