“Paul CordovaL. LehrDecember 11, 1995Freedman defines a pollutant as “the occurrence of toxic substances or energy ina larger quality then the ecological communities or particular species cantolerate without suffering measurable detriment” (Freeman, 562). Although theeffects of a pollutant on an organism vary depending on the dose and duration(how long administered). The impact can be one of sublethality to lethality, alldependent upon the factors involved. These factors need to be looked at whendetermining an ecosystem’s disturbance by a pollutant. Some of the most frequent pollutants in our ecosystem include: gases such assulphur dioxide, elements such as mercury and arsenic, and even pollution bynutrients which is referred to as eutrophication.Order now
Each of these pollutants posea different effect on the ecosystem at different doses. This varied effect iswhat is referred to as dose and duration. The amount of the pollutantadministered over what period of time greatly affects the impact that thepollutant will have on an ecosystem and population. Pollutants can affect both a population and an ecosystem. A pollutant on apopulation level can be either non-target or target. Target effects are thosethat can kill off the entire population.
Non-target effects are those thateffects a significant number of individuals and spreads over to otherindividuals, such is the case when crop dusters spread herbicides, insecticides. Next we look at population damage by a pollutant, which in turn has adetrimental effect on the ecosystem in several ways. First, by the killing of anentire population by a pollutant, it offsets the food chain and potentiallykills off other species that depended on that organism for food. Such is thecase when a keystone species is killed.
If predators were the dominant specieshigh on the food chain, the organisms that the predator keep to a minimum couldmassively over produce creating a disturbance in the delicate balance ofcarrying capacity in the ecosystem. Along with this imbalance another potentialproblem in an ecosystem is the possibility of the pollutant accumulating in the(lipophilic) fat cells. As the pollutant makes it way through the food chain itincreases with the increasing body mass of the organism. These potentialproblems are referred to as bioconcentration and biomagnificaiton, respectively.
Both of these problems being a great concern of humans because of their locationon the food chain. These are only a few of the impacts that a pollutant can haveon a population and ecosystem. Another factor to consider is the carrying capacity when evaluating the effectsof a pollutant on an ecosystem. A carrying capacity curve describes the numberof individuals that a specific ecosystem can sustain. Factors involved includeavailable resources (food, water, etc. ), other members of the species ofreproductive age and abiotic factors such as climate, terrain are alldeterminants of carrying capacity.
This curve is drawn below:# of individualsYearsIf a pollutant is introduced into an ecosystem , it can affect the carryingcapacity curve of several organisms (Chiras, 127). This effect on the curve iscaused by the killing off of the intolerant and allowing more room for both theresistant strain and new organisms. In some cases the pollutant will createunsuitable habitats causing migration. Another important part of the idea of a carrying capacity is the Verholst(logistic) equation: The actual growth rate is equal to the potential growthrate multiplied by the carrying capacity level.
Three major characteristicsexist for this equation. First, that the rate of growth is density dependent,the larger the population, the slower it will grow. Secondly, the populationgrowth is not limited and will reach a stable maximum. Lastly, the speed atwhich a population approaches its maximum value is solely determined by the rateof increase (r).
In a population with a stable age structure this would be thebirth rate minus the death rate, but this is almost impossible. If any of thevariables in this equation are affected by a pollutant then the growth rate ofan organism can be seriously affected which can in turn affect the entireecosystem (Freeman, 122). Now using the approach of classical toxicology we study the poisoning effects ofchemicals on individual animals resulting in lethal or sublethal effects. Effects on individuals may range from rapid death (lethal) through sublethaleffects to no effects at all. The most obvious effect of exposure to a pollutantis rapid death and it is common practice to assess this type of toxicity by theLD50 (the lethal dose for 50%