Ecological community- Definition, Concept, Characteristics
What is Ecological Community?
Most species are on content, a number of different types of living things. We usually recognised a farm hills, a forest, a desert by the dominant plants and animals on it. This association of population of different organisms are referred to as ecological community.
The community concept is one of the most important principles in ecological thought and practice. A biotic community is an assemblage of a number of organism usually of different species living in a prescribed area of a physical habitat, while only assemblage of plant is considered, it is called plant community. Similarly, when assemblage of animal is considered, it is called animal community. However in any biological organisation of plants and animals are interdependent on same (condition) habitat and environmental conditions. The community is thus essentially a biotic community. It is a closely organised unit because its characteristic in addition to the living path of the ecosystem.
The idea of community concept is important and the fact that diverse organism live together in an orderly manner with mutual tolerance and beneficial interaction in a natural area and the impact of a community to be recognised is that the organism grow as a community grows.
The organisation of community is intricate enough which of the concept regarding is organisation that have developed firstly by observation and the secondly by experiment. Biotic community is an organised super organised unit. This particular idea is difficult to proof and Disproof. There are variation in biotic community as we observed in nature.
Communities are association of population, which characteristic are greatly physical environment and by the interaction to the population with in the community.
Therefore, community ecology deals with the groups of different kinds of population in the area. A community specially defines includes all the population within its boundary. It is important to appreciate difference between an ecosystem and community ecosystem include all the interacting physical and biological components of an area. Community includes all the organisms.
The pattern of species abundant and population interaction within the community structure. The community structure involves both the description more or less static features of communities and experimental analysis of population interaction. An appreciation of the complexity of population interaction is essential. If we are to gain an understanding community structure and features of community that determined the human disturbance. For this reason the dynamics of community structure is a very active field of ecological study.
Characteristics of Ecological Community
Like a population, a community too has its own characteristic which are not shown by its individual components species. This characteristic which are meaning only with reference to community level of organisation are as follows-
A. species diversity
B. growth form and structure
C. dominance
D. succession
E. trophic structure (self-sufficiency)
F. self-reliance
G. relative abundance
Species diversity-
The biotic community is a natural assemblage of a large number of plants and animals, microbes in an area which differ taxonomically from each other. The number of species and population abundance in community also vary greatly. Actually, it is a part of larger whole ecosystem in which living and non-living component interact and bring about circulation, transformation and accumulation of energy and matter.
Because in any particular habitat there is no considerable variation in environmental condition. The plants growing together in a community so unique, uniformity in their behaviour vegetation, therefore, is reflection of climate in general widely separated areas having similar climate and have similar aspect of landscape.
Species diversity is a fundamental characteristic of plant communities. The older and more stable the community, the more will be the species diversity. Nature favours high species diversity while men prefers monoculture and bring about uniformity. Natural communities with high species diversity are less vulnerable to environmental vagaries, while man-made community as for example, crossfield orchids nurseries etc. are open to greater damages by environmental hazards for epidemics and may be completely destroyed. High diversity is found in communities in which have larger food chain that is natural mature communities where more cases of symbiosis and parasitism exists.
Species diversity is a very useful parameter for comparison of two communities specially to study the influence of biotic disturbance or to know the step of succession and stability in the community. Species diversity is quantified by calculating species diversity index, which is the ratio between the number of species and importance value and the number of biomass for productivity of the individual.
Dominance:
Species which exerts controlling influence on the community by virtue of their size, number, production or other activities are called dominance. A relatively few species exert the major controlling influence on the entire communities, such as species groups which control the physical habitat and the community are known as ecological dominance. In a grassland dominant species are few, in tropical rainforest many as for example the grassland community at Pobitora Wildlife Sanctuary is dominated by Imperata cylandrica.
In a teak forest communities, the teak plants dominates other species cover and population density are the qualities determining the dominance. The removal of dominance would result important changes in a community.
Clements and Shelford in 1939 characterised
the ecological dominant as-
I. They receive the full impact of the climate.
II. They are best adjusted to the climate and habitat. Therefore they are more abundant in terms of density as well as average.
III. They react directly upon the climate and modify the water and light relation on land and gas and salt content in the sea.
Stratification of Ecological Community-
Another aspect of structure that is more common in stratification which involves vertical rather than horizontal changes within the community. In other words, it refers to profile structure or vertical disposition of organism or their parts of different levels in a community. All plants in a community are not of the same size and do not occupy the space there.
The stratification of a community is determined largely by the life form of plants, their size, branching and leaves which in turn influences and it influenced by the vertical gradient of light. The stratification allows the plant to exploit the incoming radiation and the space to the maximum according to their differential requirements. The crowding effect is mitigated through adjustment in height. Sometimes, the stratification is very complex where community passes a number of vertical layer of spaces. Each made up of a characteristic growth form. In grassland community there is a subterranean floor containing basal portion of a vegetation as rhizome of grass covered by debris of plants as well as animals and herbaceous substratum consisting of upper parts of grasses and herbs with a characteristic fauna.
However, stratification in a forest community is most complicated where as many as five vertical subdivision may be recognised and these subdivision are as follows-
I. subterranean subdivision
II. Forest floor
III. Herbaceous vegetation
IV. Shrubs
V. Trees
In some tropical rainforest there may be as many as eight vertical strata. Thus based upon the light and relative humidity requirements we find stratification in above ground parts, the maximum light is available to the plants of top layer and minimum light reaches the ground vegetation. Similarly stratification may also be found in the underground parts like roots, rhizome and other structure below the soil. The roots may be spread nearer the ground or may be deep penetrating. This placing among the roots permits the plants to grow their water and nutrient requirement from different level of the soil without affecting each other.
The number of stata above ground vary according to the kind of community. In the early stage of succession usually one stratum is present and is comprised by lichen, mosses Or annual herbs but as succession proceeds new stata are gradually added.
It is interesting to note that associated within the plant communities stratification is also observed in the animal community. Various insects, birds and other animals occupy a different position along the vertical space in the plant community. Different groups of birds may be found feeding and resting near the ground, in the shrubs and small tree foliage beneath the canopy itself. Different arthropods species occur at different levels from the canopy downwards to the herb layer and on the ground or below the ground surface.