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Community Ecology By: Diana Capalbo, Jane Joseph, Nicole Rebusi Sunny Yoo “These sprays, dusts, and aerosols are now applied almost universally to farms, gardens, forests, and homes-nonselective chemicals that have the power to kill every insect, the 'good' and the 'bad,' to still the song of birds and the leaping of fish in the streams, to coat the leaves with a deadly film, and to linger on in soil-all this though the intended target may be only a few weeds or insects. Can anyone believe it is possible to lay down such a barrage of poisons on the surface of the earth without making it unfit for all life? They should not be called 'insecticides,' but 'biocides.” ---Rachel Carson, Silent Spring Biodiversity in an Ecological Community Biodiversity is the range of organisms present in a particular ecological community or system. Chapter 53 discusses the biogeographic features that affect community biodiversity. These factors include: Geographic size on the community: Species richness is directly related to geographic size, and this is shown in the “Species-Area Curve” Equatorial Polar Gradients: Species richness generally declines along an equatorial polar gradient. Silent Spring describe many human activities that affect biodiversity. These include: - Environment Destruction: Destruction of habitats all over the world is happening so that agriculture, and urban development can take place. -Introduced Species: Humans move species to new places, which can cause rapid growth in population of the species in the new area, and cause more competition in an are -Biological Magnification: Since species become immune to certain pesticides or insecticides, causing them to adapt and grow stronger; thus affecting the community they live in. A community is an assemblage of populations of various species living close enough for potential interactions. Ex: trees and shrubs in Shenandoah national park. Interspecific interactions key relationships in the life of an organ is in its interactions with other species in the community. They include: competition, predation, herbivory, parasitism, mutualism, commensalism and disease. Interspecific competition is more likely to occur in our world today because so many resources are limited because of insecticides and harmful toxics. The animals that ate the plants quickly died which led second consumers to interspecific competition. Also chemicals pass through water which lead to a short supply of clean water which leads to interspecific competition. More then 200 basic chemicals have been made to kill “pests” which lead carnivores to a limited supply of meat which also lead to interspecific competition. Biological niche- organism’s job in the community since harmful chemicals were released to many types of organisms including bees, the balance of nature has been thrown out of control. The bee’s niche is to pollinate flowers but if the flowers were harmful to the bees then the bees will not be able to pollinate the flowers which lead to no fruition which leads to a decreased amount of food which leads to competition and competitive exclusion principle. Strontium used in nuclear explosions was planted in the soil which contaminated plants which caused interspecific competition. Food Webs In her novel, Silent Spring, Rachel Carson suggests ways in which DDT and other pesticides/insecticides are spreading to different species often causing death and illnesses amongst these species. Food webs are a series of food chains linked together which are used by ecologists to summarize the trophic relationships of a community (the feeding relationships between organisms). “And No Birds Sing” According to the novel, food webs play an important role of the spread of DDT and other pesticides/insecticides proven by real-life events. In 1954, Dr. Wallace and Mr. Mehner at Michigan State University researched robin populations during the spraying for the Dutch elm disease on campus. However, when the robins migrated back the following spring they were found dead and dying all over the campus because of insecticidal “And No Birds Sing” (continued) Dr. Roy Barker of the Illinois Natural History Survey at Urbana traced that the robins’ fate were in the hands of the food web with the elm tree as its primary producer. The DDT sprayed on the trees sent a streaming poison to all parts of the trees while forming a poisonous film over the leaves and bark. When the leaves fall to the ground, they become one with the soil which in turn is fed on by the earthworms; elm being one of its favorite foods. Thus, swallowing the insecticide into their bodies becoming “biological magnifiers” of “And No Birds Sing” (continued) One of the robins’ main foods are earthworms. Therefore, after the robin has consumed enough earthworms with DDT it was most likely to die resulting in the end of the food web. Poison Through The Web This example is one of many that have occurred during the naïve usage of DDT and other pesticides/insecticides. The spraying of this poison has contaminated plant life, the primary producers, which are consumed by animals and humans therefore creating a great “epidemic” throughout the trophic structure (feeding relationships) of life causing death and illnesses which could lead to extinction. Humans have the greatest impact on biological communities. A disturbance is an event, such as a storm, fire, flood, drought, overgrazing, or human activity, that changes a community, removes organisms from it, and alters resource availability. HUMAN DISTURBANCE: Effect on insects: Some are killed by the DDT & other insecticides, while others adapt and become immune, causing stronger, more harmful formulas to be developed. Effect on water: Runoff from the toxic soil caused rivers and other bodies of water to become contaminated Effect on died or because infected fish. birds: Many became ill they ate worms, and DDT is Sprayed Effect on fish: Many species of fish died and became ill. For example many trout died from cancer caused by DDT. Effect on humans: Drinking water becomes toxic and causes sickness. Predation- herbivory- since DDT is fat soluble it will build up as it moves in the food chain. The storage of DDT begins with the smallest conceivable intake of chemical and continues until quite high levels are reached. The fat storage depots act as biological magnifiers, so that an intake of a little as 1/10 of 1 part per million in the diet results in storage depots about 10 to 15 parts per million, an increase of one hundredfold or more. Diseases now are multiple-created radiation in all its forms. As we contaminate soil, water, and food we also poison the organism that uses them to survive and then eventually humans will be poisoned. Chemicals Affect the WHOLE Ecological Community [TAKEN FROM SILENT SPRING] “In less than two decades of their use, the synthetic pesticides have been so thoroughly distributed through the animate and inanimate world that that they occur virtually everywhere. Residues of these chemicals linger in soil to which they may have been applied a dozen years before. They have entered and lodged in the bodies of fish, birds, reptiles, and domestic and wild animals…They have been found in fish in remote lakes, in earthworms burrowing in soil, in the eggs of birds – and in man himself” (pgs 15 and 16) “The problem of water pollution by pesticides can be understood only in context , as a part of the whole system to which it belongs…” (pg39) “Water must also be thought of in terms of the chains of life it supports- from the small as green cells of the drifting plant plankton, through the minute water fleas to the fishes that strain plankton from the water and are in turn eater by other fishes or by birds, mink raccoon –in a n endless cyclic transfer of materials from life to life” (pg 46) The world may find that insects and rodents are pests but in reality, “pests” are part of our community and they contribute a niche and balance to all other life forms. So instead of trying to eliminate organisms we do not like, we should appreciate all living things because our lives are not able to exist without theirs.