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Example research essay topic: Million Years Ago Permian Extinction - 1,401 words

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Anthropology Is human extinction possible? Why does this happen? What causes a species to be extinct? Can human race prevent it? To answer these questions we must first define what extinction means, what types are there and why do they occur.

As extinction is a continual product of natural selection, since the dawn of competition spawned by the first meiosis event, natural selection has altered all life on earth, precariously engaging in life experiments some that work and some that dont. Those experiments that do not work are those who have so far been extinct, and in fact 99 % (Kiernan 1996: 574) of all species that have ever engaged in the life battle have met their fate and are now extinct. Some people define extinction, as the disappearance of a plant or animal from the wild. Meaning that creatures surviving only in zoos or natural reserves could also be considered extinct. Other people use the terms regional extinction and local extinction to refer to the elimination of a creature from a specific geographical area but not from the whole planet Kiernan 1996: 574). These types of extinctions are rather common and are usually caused by human intervention in the form of over hunting, introduced competitors and destruction of habitat.

Another type of extinction refers to the very dynamic way nature interrelates, where the extinction of one creature can lead to the extinction of another. This phenomenon is known as co extinction. Animals in the food chain depend on other animals for food thus when one animal becomes extinct those who prayed upon it, must find other means of food if they are unable to do so their fate is surely written. Another type of extinction deals with extinction caused by evolutionary change where through the process of speciation results in the development of a new species Elliot 1998: 2931). This type of extinction is not as devastating to the biodiversity on earth in that though we loose a species, genetic heritage of the extinct species is passed on its evolutionary descendants (Kiernan 1996: 574) thus maintaining diversity in genetic characteristics. The last and better-known type of extinction is the most devastating form of all.

In studying the fossil record scientist have found evidence of what they call Human extinctions. This type of extinction is characterized by rapid decline of biodiversity followed by periods of explosive development. At least five times in the earths geological history have there been acute mass extinctions. The most know eras of human extinction are the Ordovician, 440 million years ago; the Devonian, 365 million years ago; the Permian, 245 million years ago; the Triassic, 210 million years ago; and the Cretaceous, 65 million years ago (Freedman 1996: 1431). The decline of diversity within a species or a taxon is so great found in these periods that such drastic decline could have not possibly been caused by genetic changes.

One of the most devastating mass extinctions took place at the end of the Permian period. This rapid extinction has been puzzling to the scientist trying to understand these phenomenon. Various explanations for such change have been proposed which has been the cause of many debates. Attempts to explain the causes of human extinction have centered on terrestrial phenomena such as sea-level changes, climatic changes, or volcanic activity. In Richard Monastersky's lifes closest call he outlines one of the leading theories behind the cause of the Permian extinction. Soda water as it harmlessly sounds suggest Monastersky along with Andrew Knoll and Richard Bambach (Monastersky 1997: 75) was the cause along with other geological events of the great Permian extinction.

In this model Knoll, suggest that toxic concentrations of carbon dioxide accumulated in the deep ocean and then surged to the surface, extinguishing much of the life in the shallow seas (Monastersky 1997: 75). (Most of the extinction in the Permian was of shallow sea creatures). This theory builds upon the concept of plate tectonics, which hoarded all of the continents together earlier in the Permian. With this arrangement coupled with the absence of the polar ice caps suggest Knoll, ocean currents would have grown sluggish preventing oxygen rich water to sink to the bottom of the ocean in a process called thermocline (Monastersky 1997: 75). It is this process which was triggered by the onset of global cooling caused by lack of carbon dioxide in the air during this Permian which suggest knoll caused the release of toxic carbon dioxide and other gases that caused havoc on animals and plants filling the upper reaches of the ocean (Monastersky 1997: 75). Perhaps one of the most known extinctions is the one that happened during the Cretaceous period bringing about the extinction of those great creatures we are so enthralled with: the dinosaur. This particular extinction has been the cause of much debate mainly because is the first extinction where an extraterrestrial cause may have been the culprit.

The scientists were investigating how does population dynamics play a role in the possible extinction of the human race? There are various models of population growth that incorporate density dependence (Dennis and Taper 1994, Hotel 1995). These models are mostly stochastic versions of deterministic differential equations models. Estimation of the parameters in these models is crucial for various applied problems and management decisions. Unfortunately, the commonly available length of the time series for parameter estimation is short, in the range of 10 - 30 yr. Shorter time series lead to larger variability in parameter estimates.

However, in many ecological situations, spatial replications are available and should be utilized (Cigliano et al. 1995, Dennis et al. 1997) to improve parameter estimation. These spatial replications can be utilized to improve the estimators in three different ways. One can consider the spatial replications identical and independent replications of the time series and combine the information under that hypothesis. This, in effect, assumes that the phenomenon is spatially homogeneous, the environmental noise is spatially uncorrelated, and that there is no dispersal. Another approach is to assume that spatial replicates are related to each other only because they share the environment.

This leads to the "joint density dependence" (JDD) model by Dennis et al. (1997), which assumes that the environmental noise is spatially correlated, but there is no immigration and emigration between the spatial locations. In this paper we explore a third approach which is to explicitly take into account the effects of dispersal in addition to the effects of shared environment. There have been a number of theoretically interesting and biologically sensible models for population dynamics that explicitly accommodate spatial aspects. When the information on fluctuations in resource availability, dynamics of natural enemies and other density-dependent factors is unavailable, models with time-varying parameters and high-order lags can be used to describe the influence from these unknown density-dependent factors on population dynamics.

Mathematically, a time series with dynamics described by a nonlinear stochastic dynamic function with autoregressive moving average terms can, under certain assumptions, be approximated by a linear time-varying-parameter model via standard Taylor series linearization techniques The structural population dynamic process developed in the study incorporates time-varying growth rate and density dependence parameters. This process also incorporates population dynamics as a function of these parameters and previous population density. A fourth class of models arises when time-varying density dependence parameters are considered. The population dynamics are termed indeterminate if the density dependence parameters take on values during the time from two or more of the following categories: b [less than] 0, b [greater than] 0, and b = 0 (Strong 1986, Brown 1989).

Little attention has been paid in the literature to the formulation of models for indeterminate density dependence. As humans we should do everything to prevent our extinction. However, the result will depend totally us and on our actions. Words: 1 292 Bibliography: 1) Elliot, D.

K 1998 Extinctions and evolutionary explosions. In Magills survey of science, edited by L, Hope, pp. 2931 - 22936. Salem press. New Jersey. 2) Freedman, B 1996 Extinction.

In The gale encyclopedia of science, edited by B, Travers, pp. 1430 - 1434. Gale research. New York. 3) Hildebrand, A. R. , and Boston, W.

V 1991 Cretaceous ground zero. Natural history 46 - 54. 4) Kiernan, V 1996 Extinctions. In Encyclopedia of life sciences, edited by M, Cavendish, pp. 574 - 576. New York. 5) Monastersky, R 1996 lifes closest call. Science news 151: 74 - 76.


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Research essay sample on Million Years Ago Permian Extinction

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