Adaptation in Animals | Biology

In this article we will discuss about:- 1. Meaning of Adaptation 2. Adaptation—a Biological Process 3. Adaptive Convergence and Diver­gence 4. Structural and Functional 5. Organisms in Relation to Environ­ments.

Contents:

1. Meaning of Adaptation
2. Adaptation—a Biological Process
3. Adaptive Convergence and Diver­gence
4. Structural and Functional Adapta­tions
5. Adaptation by Organisms in Relation to Environ­ments

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1. Meaning of Adaptation:

Adaptation to environment is one of the basic characteristics of the living organisms. Living organisms are plastic and posses the inherent properties to respond to a particular environment. Adaptation to environmental dynamics is a biological process eternally operating in nature.

It is a facet of evolution and involve structural diversities amongst living organisms that are heritable. Organisms exhibit numerous structural and functional adaptations that help them to survive as species and to overcome the tremendous competition in nature.

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2. Adaptation—a Biological Process:

Living organisms show two basic pro­perties:

(i) Adaptability leading to

(ii) Adap­tation.

The term adaptability is applied to the power of orientation of the organisms to new environmental condition. All organisms possess the power of adaptability to a limited extent to various environmen­tal changes. Mammals are adaptable to various climatic conditions.

Adaptability and adaptation are two quite separate biological processes. Adaptation is defined as the permanent moulding in organisms to such an extent that they can live in a particular environment suitably.

It is a characteristic of living forms which deve­lop over a length of time, when certain morphological and physiological modifica­tions are initiated that enable them to survive within the jurisdiction of a parti­cular environmental condition.

A survey of the biological world reveals that all animals are harmoniously living in different ecological conditions. Every region has a peculiar and characteristic physical condition, which indirectly gives rise to varied forms. The island fauna re­present the typical examples. The evolu­tionary history of the animals also gives a large number of instances of adaptive changes.

Fishes are the primary aquatic vertebrates which show all the basic adaptations to their primal aquatic home. From fishes the amphibia, the first tetra- pod evolved. Having appeared on land they had to modify to live in a completely different environment. The amphibians show adaptive duality. They show modi­fications for aquatic medium as well as for terrestrial living.

The reproductive system in amphibia is not adjusted for terrestrial life, they had to come back to the watery home for the purpose of reproduction. The reptiles are the true land adapted forms in the phylogenetic history of vertebrates.

The reptiles hold the pivotal position from which both birds and mammals evolved and underwent parallel evolution. These living organisms have shown all the possible ways of living and furnish exten­sive adaptive radiations.

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3. Adaptive Convergence and Diver­gence:

As a result of living in a similar environment, organisms of quite distant and unrelated groups show close struc­tural and functional convergence. The reverse is also true in nature, where organisms, originating from the same stock exhibit adaptive divergence as a response to living in completely diff­erent environment. All secondary aquatic vertebrates show adaptive convergence (Fig. 4.1).

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4. Structural and Functional Adapta­tions:

The adaptations exhibited by orga­nisms to a particular environment are both structural as well as functional in nature. In a particular environment the structural and functional adaptations are almost in­separable. The structural adaptations are more obvious than functional ones. The instances of structural adaptations are plenty in nature.

The typical case of functional adaptation is the modifications of the gastro-intestinal tract in vertebrate body which is due to adaptation to diff­erent types of food. But both these modi­fications work harmoniously in an orga­nism to suit a particular environment.

So in our present discussion on adaptations of animals to different environments, the terminology ‘adaptation’ is used to mean both morphological and physiological modifications.

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5. Adaptation by Organisms in Relation to Environ­ments:

The different adaptations exhibit­ed by the organisms depend upon their surroundings. The environment of an organism is not only the physical environ­ment, but also includes the biogeochemical (biological, geological and chemical) and biotic environments. Of all these, light, temperature and water are the three main factors.

Light causes modifications of the eyes in vertebrates, temperature plays a very important role and the water seems to be a very important physical factor, especially from the ecological point of view. Some animals are adapted en­tirely within watery medium and others are adapted to land. Structural adapta­tions for living in these environments are quite obvious and contrasting.

Besides these important factors such as light, tempera­ture and water, other chemical and nutritional factors also play great role in adaptations. These impelling factors have caused the adaptive radiations amongst animals. Most of the vertebrates except fishes and some secondarily aquatic forms are adapted to terrestrial life. The terres­trial forms also exhibit divergent adaptive lines.

The ways through which the orga­nisms manifest their adaptations are:

a. Cursorial adaptation:

Cursorial animals show adaptations for living over the hard surface of the earth.

b. Fossorial adaptation:

Fossorial animals exhibit profound adaptations for living beneath the surface of the earth and lead subterranean life.

c. Scanaorial or arboreal adaptation:

The organisms have chosen to lead life above the surface of the earth onto the trees and become adapted accordingly.

d. Desert Adaptation:

The organisms living in deserts show, in addition to primary cursorial adaptations, the special adapta­tions against extreme temperature, lack of moisture, lack of vegetation characterising the deserts.

e. Volant Adaptation:

The organisms show extreme adaptations for aerial life.

f. Aquatic adaptation:

This adaptation made the animals suited for living in watery medium.

g. Cave adaptation:

Adaptations for living in caves.

h. Deep-Sea adaptation:

The organisms, in addition to aquatic adaptations, show adaptations for living at the extreme depth of the sea. In all adapted animals, the structures of the body which are in direct influence of the environment become extremely modi­fied, while the internal structures which are more conservative become less modi­fied.