Ecosystem is a self-sustaining unit of nature. It is defined as a functionally independent unit (of nature) where living organisms interact among themselves as well as with their physical environment. In nature two major categories of ecosystems exist: terrestrial and aquatic. Forests, deserts and grasslands are examples of terrestrial ecosystem.
Ponds, lakes, wet lands and salt water are some example of aquatic ecosystem. Crop lands and aquarium are the example of man-made ecosystems.
The interaction between the living organisms and their environment can be studied in a puddle of water or a hole in a tree, which are very small ecosystems or in large ecosystems such a forest, river or ocean. Irrespective of their sizes all ecosystems share many common characteristics. Let us study moderate sized pond ecosystem.
Theories of Evolution
Jean Baptiste de Lamarck was the first evolutionist to believe that organisms change over time. Using fossil records as a guide, Lamarck was able to develop three theories; one is The Theory of Need which states that organisms change in response to their environment.
Their ability to survive helped them develop characteristics necessary for them to adapt in a given environment.
Next is The Theory of Use and Disuse; which according to Lamarck, organs not in use will disappear while organs in use will develop.
Lamarck believed that giraffes before have short necks, but because of the need to survive and in order to reach tall trees for food, they kept stretching their necks until these became longer and able to reach taller trees.
These acquired characteristics were believed to be inherited by their offspring and propagated by the next generation of giraffes. Lamarck called it as The Theory of Acquired Characteristics.
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If you change the color of your hair from black to blond, do you think your child can inherit the blond color of your hair? A young lady keeps on using whitening soap and becomes fair? Can her child inherit her acquired fairness? Many scientists rejected the theories of Lamarck.
They understood that if there were changes in cell or body structure, there could be changes in the genetic information of the species.
The more popular Theory of Evolution proposed by Charles Darwin based on natural selection is different from the theories of Lamarck. According to Darwin, giraffe species originally had varying neck lengths but natural selection favored the survival of giraffes with longer necks that could feed on taller trees that were available.
Giraffes with short neck were eliminated due to lack of accessible food supply. Fifty years after Lamarck‘s Theory of Use and Disuse, Charles Darwin suggested the Theory of Natural Selection, after his voyage to the Galapagos Island in HMS Beagle.
He was fascinated by the diversity of organisms he found along the journey. In Galapagos Island, he observed that finch species have different beak structures for different food types. The abundance of certain finch species in an island was somehow related to the type of available food for these birds.
Darwin suggested that selection also takes place in nature. In selective breeding, farmer identifies and selects the best and desirable trait to propagate. In natural selection, environmental factors promote the survival of the fittest and eliminates the less fit.
Organisms struggle for existence in order to survive; they compete for food and space. Organisms with favorable and advantageous characteristics survive and reproduce.
Fitness refers to the ability of an organism to survive and produce offspring. Different individuals in a population possess different characteristics and abilities. This is called variation.
Variation among individuals in the population would likely bring greater chance of survival. An organism that is adapted and has structures fitted to survive in a given environment would likely produce offspring.
Variation increases the chance of survival of living things. Organisms with the best and desirable traits would likely adapt to environmental changes and may gradually become better suited to survive in a given environment.
Organisms which are best adapted to the environment will continue to reproduce and perpetuate their own kind. Mating between surviving populations of the same species may shift the abundance of a new breed of organism because of mutation, gene combination, and natural selection. This then leads to speciation and may subsequently increase biodiversity
In summary, Jean Baptiste de Lamarck was the first Evolutionist to believe that organisms change over time using Fossil records as a guide.
Worthy of notice also is the popular theory of Evolution proposed by Charles Darwin based on natural selection which is different from the theory of Lamarck.
According to Darwin, giraffe species originally had varying neck lengths but natural selection favored the survival of giraffes with longer necks that could feed on taller trees that were available.
Basically there are two theories of Evolution viz are: Jean Baptiste de Lamarck theory of evolution and Charles Darwin theory of evolution.
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