Community: Structure and development

Community (समुदाय):- When several populations share a common habitat and its resources, they interact among them­selves and develop into a biotic community or sim­ply, a community.

(जब कई आबाड़ियाँ एक समान निवास स्थान और उसके संसाधनों को साझा करती हैं, तो वे आपस में बातचीत करते हैं और एक जैविक समुदाय या बस, एक समुदाय में विकसित होते हैं।)

Structure of Community:- Structure describes characteristics of ecological niches, species richness and species composition.

1. Ecological niches:-

Characreristics of niche:-

i. Interactions:- A niche may also involve what that individual eats, how it interacts with other living things, and also how it connects with the non-living factors.

ii. Energy flow:- Niche consumes the flow of energy from one species to another, and thus it is very important to accept how a species eats or interacts with other organisms in an ecosystem to maintain ecological balance.

iii. Balance:- Without ecological niches, there would be less biological variety, and the ecosystem would not be in balance. For example, a population in an environment make use of the resources and breeds to produce more animals or organisms, which then escalate the resources for the predators.

iv. Factors:- The full span of biotic and abiotic factors utilized by species for duration form the fundamental niche, and the element that limits the population, like competition and predators, are called limiting factors.

Types of Niches:- 5 types

i. Habitat Niche (Spatial Niche):- It accounts for the physical space occupied by an organism. This explains the different microhabitats owned by several species having similar general habitats. E.g. seven species of millipedes reside in the same general habitat of the forest floor of a maple oak forest, and all are decomposers, i.e. occupy the same trophic level but predominate in their specific microhabitat that is created by several gradients in the decomposition stage.

ii. Trophic Niche:- It tells about the functional role or trophic position occupied by a species. It explains how different species share the same habitat but occupy different trophic niches. E.g. Darwin’s finches of the Galapagos islands. These birds belong to the same genera and live in the same general habitat but differ in their eating habits, i.e. trophic position. One species is vegetarian, feeding on buds and fruits, and, others are insect eaters, feeding on insects of different sizes. There is a woodpecker finch, which has a wood-pecking beak.

iii. Hypervolume Niche (Multidimensional Niche):- It represents the position of a species in the environmental gradient. There are a large number of environmental factors, both abiotic and biotic, that affect the population. This is the fundamental niche of the species and refers to the totality of abiotic and biotic factors to which a given species is uniquely adapted.

iv. Fundamental Niche:- It is recognized by Hutchinson. The fundamental niche of a species is the hypervolume that a population can fill in the absence of competitors. So each species has a fundamental niche within a community.

v. Realized Niche:- It is also recognized by Hutchinson. Because of competition, due to similar essentials along the niche dimension, the competitor niches will be overlying one another. As a result of these biotic constraints, only a part of the niche is realized by the species. These smaller hyper volumes occupied by a species are termed the realized niche.

2. Species richness:- The number of distinct species in a community is referred to as species richness.

> If we identified less species in one community and more species in another, the second community would have significantly more species diversity than the first.

> The most diverse communities are found around the equator, where there is abundant solar energy (supporting high primary productivity), mild temperatures, abundant rainfall, and little seasonal variation.

> The communities with the least diversity of species are found in the poles, which receive less solar energy and are therefore colder, drier, and less conducive to life.

> Species richness is calculated only for mammal species and not for all species.

3. Species composition:- The number of species in a community is a measure of its complexity.

> It is determined by the number of distinct species in the community (species richness) as well as the relative abundances of those species (species evenness).

> Species diversity is increased when there are more species and their abundances are more evenly distributed.

> Ecologists believe that ecological groups with greater diversity are more stable (i.e., better able to rebound after a disruption) than those with less diversity.

> However, the association between diversity and stability isn't uniform, and in some circumstances, other factors (besides species diversity) are more essential in defining community and ecosystem stability.

> Some species have extremely powerful effects on community structure, keeping the community's equilibrium or even allowing it to exist.

i. Foundation Species:- It is a species that has a strong role in structuring a community. Biologists describe foundation species as “engineers of ecosystems.”

ii. Keystone Species:- It is a species that has a disproportionately large effect on community structure relative to its biomass or abundance. Keystone species differ from foundation species in two main ways: 

i. They are more likely to belong to higher trophic levels (to be top predators).

ii. They act in more diverse ways than foundation species, which tend to modify their environment.

Development of Community:-

> Communities are never stable, but dynamic, changing more or less regularly over time and space. 

> Communities are developed by ecological succession.

> Ecological Succession:- The occurrence of relatively definite sequence of communities over a period of time in the same area is known as ecological succession. It has following steps -

- In a barren area there reach the seeds and propagules of the species which is known as migration.

- These seeds or propagules after germination develop into the seedlings which then develop into adults. But only a few of these survive and are capable of successful growth, and this process of seedling establishment and successful growth is called ecesis.

- As a result of migration and subsequent ecesis, species colonise the new areas—colonization. 

- By this time with the changing environment due to plants growth several other species of both plants and animals start colonising the area and sooner or later the area is colonised by a definite community.