Species: Meaning, Origin and Interaction | Ecology

In this article we will discuss about:- 1. Meaning of Species 2. Origin of Species 3. Interactions 4. Interdependence.

Meaning of Species:

A large variety and numerous individual organisms are found in nature. The organisms do not occur in isolation. Such organisms may be of a kind, as cats, rats, tiger, bean plants, humans, etc. The individual organisms aggregate and form population. A geographically localised group of individuals of the same kind form a species.

The individual organisms of a species may differ in structure and function depending upon their sex, stage of development or specialisation for specific functions.

For example, in many insects the adult, larval and pupal stages are considerably different. In frogs, toads and salamanders the adults and larval stages are quite different in structure and function. On the other hand, the sporophyte and gametophyte of a fern or moss are quite different in their structure and function.

On the other hand, in many organisms the males and females are different in size, form and colour. When two forms occur among the organisms of the same kind the phenomenon is called dimorphism.

The horse and the mare, the dog and the bitch, the lion and the lioness, man and woman, peacock and peahen are not alike. They exhibit sexual dimorphism. Plants such as the date palm and Cycas have male and female individuals and bear different types of flowers and sporophylls.

The individuals in a colony of honey bees and termites differ considerably in structure and function. When many forms of individuals occur within the same kind of organism, the phenomenon is called polymorphism. Various types of individuals occur in some coelenterate colonies.

For example, a colony of Physalia is made up of hundreds of individuals of different kinds comprising feeding, protective, reproductive and float forming individuals. A colonial form of Volvox (a green alga) consists of about 60,000 or more cells. In such colony only the peripheral cells bear flagella, and help in locomotion.

A few cells are reproductive, and the larger part of the colony is made of vegetative cells. Many wild species of flowers show colour polymorphism. To some extent, polymorphism helps in survival and adaptation of species.

Within a species, there are some populations which show some morphological characteristics. For instance, in South Africa, the people of Zulu tribe are short statured {i.e., 1.2 m) and those of Watusi tribe are tall (i.e., 2.2 m). The different human races show considerable physical differences.

The negroids, caucasoids and mongoloids, can be recognized by their peculiar faces. Similarly, the various breeds of dogs, cows, sheep, roses and other cultivated plants look quite different in size, colour and appearance (Fig. 11.4).

For example, there are several breeds of dogs, such as Keeshond, Eskimo, Cairn terrier, Indian greyhound, Welsh terrier. Chow, Dachshund, Dalmatian, Irish terrier, Yorkshire terrier, Buldog and Irish wolfhound, which are quite different in size, colour and appearance.

However, all these different looking individuals of the same species may interbreed among themselves. While the populations or individuals belonging to different species may appear quite similar but do not breed in natural conditions.

Thus, a species can be defined as a group of closely related, structurally and functionally similar organisms which interbreed with one another in nature, but not with organisms of other groups.

The inability to interbreed or reproductive isolation makes the most important distinction between different species. Thus, reproductive isolation is the main factor that maintains the distinctness of different species. But there are several examples where members of two species are alike and still do not interbreed.

However, members of two different species may breed under captivity or under artificial conditions. As we know, the horses and donkeys are of distinct species but they interbreed and produce sterile offspring, the mule (i.e., progeny of male donkey and mare) or hinny (i.e., progeny of stallion and female donkey).

The artificially produced hybrids between bull frog’s leopard frogs die before attaining the reproductive age. There are some examples of species that interbreed under captivity to produce fertile offspring, they are—the mallard and pintail duck, the tiger and the lion, the polar bear and the Alaskan brown bear, the platy and swordtail fishes.

The interbreeding between members of two different species can occur only when the isolating condition is removed artificially. There is great diversity in the living world. To study the diversity, the scientists have developed several hierarchical terms-many similar species make a genus; many related genera constitute a family, and several related families form the order.

Origin of Species:

It has already been mentioned in the preceding paragraphs that prevention of interbreeding between members of different species is essential for the maintenance of identity of the species. It is an established fact that life arises only from pre-existing life. It is also thought, that new species is derived from the par-existing ancestral species.

Now the question arises, how does a new species originate. Here, we will consider the origin of a terrestrial species which has a wide range of distribution. For example, due to development of a physical barrier, such as a high mountain range or a large body of water, it becomes impossible to maintain interbreeding between the members of the groups thus separated.

Sometimes the long distance between populations may act as a reproductive barrier between them. In the initial stages, interbreeding between the individuals of these two populations will be possible if the isolation factor is artificially removed. However, the absence of a reproductive contact for a long time will lead to a loss of capacity for interbreeding.

In the due course of time, the individuals of these populations undergo physical and physiological changes depending upon their environment, so that, they become morphologically different from each other. They would gradually go away from each other in structure and function and ways of living, and become as different as to give rise to a new species.

Interactions between Members of a Species:

The individuals of a species interact with each other in several ways, such as cooperation, communication and competition.

Cooperative Interaction:

This type of interaction is essential for reproduction and perpetuation of the species. Organized social interactions offer the advantages of cooperation in reproduction, caring for the young, obtaining food and in defence. A herd of musk oxen form a circle for protection. Social organization may be very simple or very complex. The simplest social behaviour is herding, schooling or flocking.

The individuals are less likely to be captured by a predator while in a school than if alone. Social organization also aids in reproduction and rearing. For the seal, meeting at the breeding area makes contact between male and female easier.

The baboons and monkeys live together for such advantages as grooming each other and caring for the young. Herding, rank establishment and territory and other interactions are restricted to certain animals only.

Group Formation:

Family life or group formation in different animals varies. It is found only in few types of animals. Foxes, wolves and swans are monogamous, i.e., once a male and female come together the partnership lasts throughout life.

However, in sparrow the partnership breaks down at the end of a breeding season, and the male and female birds find new partners in the subsequent years. Seals, walruses and deer’s are polygamous. A male keeps a harem of many females. Rats, mice and some other animals do not have any fixed partners.

Many animals, such as geese, ducks, parrots, antelopes, deer, zebras, elephants and monkeys live in groups or herds. Members of each herd cooperate for mutual protection and for finding food and water for the herd.

For example, it has been observed in the Bandipur Santuary of Karnataka that when a group of cheetals is attacked by a predator, such as the wild dog, panther or tiger, the stag with the best antlers is closely surrounded by other individuals so that it is saved from destruction. This is a unique example of the self-sacrifice of a few individual deer allowing them-selves to be killed in the interest of the species.

Usually a community has a few populations that are more important in determining the nature of community than the others. These dominant species strongly influence the food supply and the environment of the other species.

In a forest, the large trees are usually dominant species. Large trees dominate forests because their canopy of leaves over the other populations determines how much light is available to other plants.

On the other hand, within the herd there is a social organisation and ranking of individuals. Usually the females are subordinate to males and the young are subordinate to the adult. In the red deer the female is the leader of the herd. Dominance or ranking of individuals is generally settled by battles.

Dominance is also established by an aggressive posture or display of feathers by birds. In most species, the individuals of the highest rank have the first choice of mate and food followed by individuals of subsequent ranks.

The honey bees, ants and termites form well organised societies having division of labour among its members showing polymorphism. In these social insects (honey bees) the individuals of different kinds (i.e., polymorphic) live together in a colony and work together for the benefit of the group.

Here the insect societies are formed of different castes such as workers, males (drones) and queen. All of them are specialized for different kinds of work. The workers collect and store food. They also build houses of complicated design, and also do other special tasks. The males and the queen are mainly involved in reproduction and act as the progenitors of future colony.

In the termites incomplete metamorphosis is found, which shows that the insects hatched from eggs are very similar to adults and develop into adults through growth and moulting. Most of these function as worker termites, and have perpetual adolescent phase and do not develop into adults. Only the king and the queen reach the adulthood and produce future colony through sexual reproduction.

The insect societies are quite different from the human society. They differ both in origin and organisation. Human societies show more psychosocial evolution than biological evolution. The members are made of numerous family units composed of males and females, adults and juveniles.

However, the insect societies are the products of biological evolution based on learnt behaviour. All the members of the colony are derived from common parents.

Home Range and Territory:

Individuals, pairs or groups of vertebrates and higher invertebrates, commonly restrict their activities to a definite area. This area over which the animals wander in search of food and mates, is called their home range.

Variations in home range are associated with the species, sex, age, season and with such ecological condition as availability of food, shelter and intraspecific struggle. Home range provides an animal with its necessities of life, such as food, cover, shelter and to rear young ones.

A number of breeding groups that is pairs and herds inhabit a home range. Each breeding group, or an individual occupies a particular territory. The home range of different groups can overlap but not the territory. Each territory centres round the individuals or group’s home, nests, holes, burrow or other types of shelter.

The special odours of the urine or faeces delineate the territory of animals like dogs and tigers. The territory is defended by its members. The territorial concept is most developed in birds where the male first establishes a territory. It drives off all other males of the same species from this territory and sometimes also females other than its mate.

Communication:

The survival and well-being of an animal population is largely dependent upon the communication among the members of the population. Even simple organisms have developed methods of communication, such as sight, sound, chemicals or contact.

Through these methods of communication, members of a population indicate dominance, submission, the source of food, the presence of danger, hunger, the urge to mate, and the limits of territory.

Visual Displays:

Animals may use visual displays to communicate. This is the way where the animal stands, moves, or shows body colouring.

For example, an aggressive cobra arches its back, bares its fangs, and displays the neck hood. Male birds are often brightly coloured to attract females of their species and to draw the attention of enemies away from the female and young. Honey bees perform various dance movements to indicate the distance and direction of the food source.

Communicating by Sound:

Animals may also communicate by making sounds. Each call or cry carries its own special message. Some animals have as many as two dozen different sound signals indicating hunger, fear, threat, annoyance, desire for mating and parental concern. Even animals such as rabbits and giraffes, utter sounds when they are intensely afraid.

Use of Chemicals:

Certain special chemical compounds such as pheromones, secreted by animals transmit message to other members of the species. Pheromones are detected by smell or taste. These chemicals communicate territorial rights, fear, or a desire to mate. The territory making compounds in urine and faeces as already mentioned in preceding paragraphs are also pheromones.

Ants release chemicals containing pheromones, which enable the members of colony to find their path from the colony to the source of food and back. The sex pheromones are used by bitch during the breeding season to attract the male dog. A dog can smell a bitch from a distance of one kilometre.

Chemicals can also be produced and secreted by specialized glands or tissues and may be included in the urine or saliva. The male lion marks his territory by spraying urine at points along the outer edge of his territory. Among social animals, the dominant males have large scent- marking glands as compared to the others on the group and use them more often.

Physical Contact:

To convey concern, hunger, play or aggression, animals may use physical contact. A young “bird pecks at the parent’s bill to communicate hunger. A pet cat will rub up against a person to communicate pleasure. Giraffes use their long necks in struggles for dominance by knocking heads and necks.

Competition:

The amount of food, light, space, minerals and water that are available in a particular habitat is limited. With the result, organisms are in competition with one another for one or more of these factors. Competition can be defined as rivalry between two or more organisms for obtaining the same resources.

For example, sparrows fight with each other for shelter, and wall lizards chase each other to catch insects. Populations may compete directly, leading to the extinction or adaptation of one of them.

Plants also compete for space, light, water and minerals. The dense mass of seedlings competes among themselves. Some seedlings grow faster than the others and survive; others remain weak and eventually die.

However, proper seed dispersal reduces the competition. In some xerophytic plants the roots secrete certain compounds which inhibit the germination of seeds within a certain distance. The many interactions among the members of a species, such as group formation, territorial maintenance, communication and competition have a common function and that is survival of species.

Species Interdependence:

Members of the biotic community in an area are dependent on each other. The interdependence is usually observed in their interaction, mainly for food, space, reproduction and protection. Such interactions are important for survival of different species and the biotic community as a group. Food interactions are reflected in food chains, which consist of plants, animals and microbes.

Plants and animals have well established interdependence for reproduction. For example, insects are flower-specific and have structures suitable for nectar sucking and pollination. Contrary to it, some flowers are insect-specific.

For example, snapdragon flower possesses lip-like petals, which facilitate insect entry and landing. Here, both flowers and insects have developed and evolved in a way leading to their interdependence.

The nectar of flowers is main attraction for insects. Insects visit the flowers in search of nectar and pollination is effected. The fluctuations in insect pollination would affect pollination that leads to plant reproduction.

Birds and mammals help in the dispersal of seeds and fruits. Interdependence may also be shown by certain other specific examples. For example, cuckoo lays eggs in the nest of other birds, and gall wasps bury their eggs deep into the tissues of plants that ensure hatching and protection.

Camouflage:

Some members of biotic community, particularly animals, .sometimes camouflage to avoid detection. For example, butterflies and moths have colours which match the colours of flowers, and therefore, their detection becomes difficult. The camouflage can be observed in praying mantis and leaf insect, which mimic the shapes of leaves and branches.

Mimicry:

For example, orchids mimick the butterfly, as their colours are concerned. Generally, weaker members of animals, mimic the strong, fast moving species and which have a fewer natural enemies. For example, non-poisonous snakes mimic the poisonous snakes to avoid their enemies. Usually, birds mimic voice of other animals.