HUMAN IMPACTS ON ECOSYSTEMS AND ORGANISMS POPULATIONS.
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GOALSWe will investigate a few specific examples of how humans have directly impacted organisms. – Students will be able to explain these direct human influences on organisms.We will investigate some potential unintended outcomes or indirect results.-Students will be able to explain these unintended outcomes and indirect results on other populations in the food web. Some of these indirect results may cause populations to decrease OR increase depending on their trophic (food chain) relationships with the directly effected organisms. -Students will be able to explain populations that will increase or decrease as a result of the initial human influence.
CAUSES OF LOW POPULATIONSIn the late 1800’s and early 1900’s wood duck populations were so low that scientists thought their extinction was eminent. The decrease in wood duck populations was due to couple of factors.
1a and 1bSEASON AND OVERHUNTING
First, the hunting season was open from Sept. to April. This hunting season was considered to be too long and too many wood ducks were shot. In addition, the type of hunting during the early 1900’s was not like the hunting of today. People could hunt wood ducks, and other ducks and sell them to restaurants. This type of hunting is referred to as market hunting and resulted in far too many birds being harvested.
Much of the dead timber in forests and swamps were cut for lumber leaving less places for wood ducks to nest and raise their young. With less young surviving wood duck populations decreased further.
In 1918 conservationists and sport hunters helped to pass the Federal Migratory Act. This limited hunting of wood ducks until 1941 when wood duck populations were high enough to allow limited hunting. This act also outlawed market hunting to further protect wood ducks and other ducks.
Hunters and conservationists also began to build wood duck houses. These wood duck houses were designed to replace the missing dead trees with holes. Around the country sportsmen, place thousands of these houses so that wood ducks would have more opportunity to nest safely. This helped increase the number of chicks that hatched and survived.
POSSIBLE PROBLEMS FROM TOO ANY WOOD DUCKSOther ducks also nest in holes of dead trees. One duck is the Bufflehead. Some conservationists and scientists were actually concerned that Buffleheads might be outcompeted for nesting sites. If wood ducks are taking up nesting sites, then there will be less sites for the bufflehead, less chicks will hatch and their populations might decrease.
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WHAT IS URBAN SPRAWL?Urban sprawl is the continued growth of housing, roads, and other human influences that take over natural habitats. This can reduce food sources and hiding areas for mule deer.
EFFECTS OF URBAN SPRAWL ON MULE DEERUrban sprawl affects mule deer in a couple ways. One way is during winter the deer have less food because homes are built in the deer's typical wintering areas. Food is especially important during winter months when it is cold and most food sources are not available. With less food many more deer die.
EFFECTS OF URBAN SPRAWL ON MULE DEERAnother way urban sprawl affects deer populations is related to concentrating many deer in smaller areas. With less land available to deer the deer are concentrated in smaller areas. This will actually make it easier for predators to kill more deer.
URBAL SPRAWL GOOD FOR SOME ORGANISMS?With more deer concentrated in smaller areas predators may actually experience an increase in population. With more deer in an area it is easier for predators to catch more deer. This will allow more predators to survive into the next year and reproduce potentially causing an increase in predator populations.
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WHAT IS ACID RAIN?Acid gases from cars, factories and other fuel burning sorurces get into the atmosphere, mix with rain, and fall to Earth as Acid Rain.
Gas phase chemistry
In the gas phase sulfur dioxide is oxidized by reaction with the hydroxyl radical via an intermolecular reaction:
SO2 + OH· → HOSO2·
which is followed by:
HOSO2· + O2 → HO2· + SO3
In the presence of water, sulfur trioxide (SO3) is converted rapidly to sulfuric acid:
SO3 (g) + H2O (l) → H2SO4 (l)
Nitrogen dioxide reacts with OH to form nitric acid:
NO2 + OH· → HNO3
WHAT IS ACID RAIN?Combustion of fuels (factories, electric generating plants that burn coal, and automobiles) creates sulfur dioxide and nitric oxides. They are converted into sulfuric acid and nitric acid and then it falls to the Earth with rain droplet's and flows into rivers, ponds, and lakes where frogs live.
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HOW DOES IT HURT FROGS?Some acid is not a big problem, however when acidity levels are near 5.5 to 6.5 some species of adult frogs cannot live in this water. The eggs of frogs become fragile and many will not not hatch at this level of acidity. Finally, some tadpoles will have lower body weight and be smaller as adult frogs. These frogs have a much less likely chance of surviving. As adult frogs die and less tadpoles hatch, the population of certain frog species will begin to decline.
IMPACT ON OTHER ORGANISMSMany organisms feed on frogs. One organism is the Great Blue Heron. With less frogs the Great Blue Heron population may also decrease due to the lack of food. With Great Blue Heron populations decreased, other organisms, such as fish and salamanders, may increase in population. The reason is because there are less Herons eating these organisms.
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