COMMUNITY Its Origin, Structure & Organization of Bio-Community
One of the earliest formal definitions of community ecology was suggested by Cornell professor Robert Whittaker in 1975. Whittaker characterized community ecology as an assemblage of living organisms that interact and form a community with a unique structure and species composition. Knowing how a community function is vital to promoting and preserving biodiversity.
Community:
By definition, community represents the population of all species living and interacting in an area at a particular time. The population can, within limits, adapt to changes in environmental conditions. The major driving force of adaptation to environmental changes is believed by most biologists to be biological evolution, the change in a population’s genetic makeup through successive generation.
Concept of Community:
A group of organisms constitutes the population. Each population has characteristics like natality, mortality, age structure, growth dynamics, and so on. But when several populations share a common habitat and its resources, they interact among themselves and develop into a biotic community or simply, a community.
Microorganisms, plants, and animals populations sharing a common habitat and interacting among themselves develop into biotic communities. The composition of a biotic community in any habitat is dependent upon the prevalence of environmental conditions in that habitat and the ecological amplitude of species populations.
Thus, the climate and other abiotic, as well as biotic conditions of a habitat, determine the type of community which survives and develops. The organisms of a community usually exhibit trophic (feeding) relationships among themselves. They also interact in sharing the space and there may be interactions at a reproductive and behavioral level.
Each biotic community exhibits a number of characteristics, such as diversity, density, dominance, composition, and stratification. Each community has a special limit. Sometimes the boundary between two communities may be very sharp or gradual.
The transitional zone or junction between two or more diverse communities is called “eco-tone”. The eco-tone harbors a community termed eco-tonal community with organisms of overlapping communities and some of the unique types.
Structure of Community:
Communities may be small, consisting of few species populations in a small space, or large, comprising several species populations in a large area. The community structures, composition and other characteristics can be readily described by visual observation without actual measurement.
This is a qualitative approach that is easier than the quantitative population analysis where measurements are actually made. Communities usually categories by the ecologists in various ways primarily based of habitat features like water availability, high exposure, or other habitat features.
For instance, depending on the amount of water availability, plant communities may be hydrophytic (aquatic habitats), mesophotic (moderately moist soil habitat), and xerophytic (dry or arid habitat).
Similarly, communities growing on conditions of abundant light are called halophytic and those growing in shade Scio phytic. Identically communities growing on various habitats designated as desert communities, mountain communities and estuarine communities, and so on.
In general, a community is dynamic since it changes over time. This dynamic nature is reflected in the succession of organisms in a habitat. A series of changes results in the development of a relatively stable community, which maintains its structure and influences the climate of the area.
Such a stable and mature community is called a climax community, while communities of successional stages are called seral communities. The plant community structures, composition and other characters can be described in both qualitative or quantitative means.
Community Dynamics:
Communities are dynamic systems constantly interacting with another system, the environment, which is equally dynamic. The community charges are gradual and imperceptible at any time but easily recognizable if observed at regular intervals over a long period of time. Seasonal changes in plant communities always occur at every place, particularly in areas where temperature variation is significant.
However, in the course of a very long period of time in many places the communities have reached a peak stage and attained a dynamic balance with the environmental changes. The process of change in communities and their environment at one place in the course of time is called “ecological succession”.
Community Ecology Examples-
Community ecology encompasses many types of ecological interactions that continue to change over time. A forest community includes the plant community, all trees, birds, squirrels, deer, foxes, fungi, fish in a forest stream, insects, and all other species living there or migrating seasonally.
Similarly, a coral reef community includes a vast number of different species of corals, fish and algae. Abundance and distribution are strong forces that shape the biological community.
A coral reef
Community ecology focuses on how interactions between different species affect health, growth, dispersion, and abundance of the ecological system. At the community level, species are often interdependent. Several short food chains are common in most biological communities. Food chains often overlap and form food webs of producers and consumers.
Community Ecology Structure:
Community ecologists study the interaction between structure and organisms. Structure describes the characteristics of ecological niches, species richness, and species composition. Species interact with each other and with their environment in many different ways, such as competing for finite resources or working together to trap game. Population dynamics play a pivotal role in communities.
The energy pyramid shows how energy is made and transferred by organisms that comprise the food chain. Heterotrophic producers of usable food energy from the sun form the broad base of the pyramid.
Primary consumers such as herbivores cannot make food to fuel their cells and must eat producers to live. Secondary consumers are carnivores that eat primary consumers. Tertiary consumers devour secondary consumers, but the apex predator at the top of the pyramid has no natural enemies.
A food chain represents the flow of food energy in a community. For instance, phytoplankton is eaten by fish that may be caught and cooked by a human. Only 10 percent of the energy consumed is transferred at each trophic level, which is why the energy pyramid is not inverted. Decomposers play a role by breaking down dead organisms to release nutrients back into the environment.
Types of Interspecific Interactions-
In biology, interspecific interactions refer to the ways in which species interact in their community. The effect of such interactions on different species may be positive, negative or neutral for one or both. Many types of interactions occur in an ecological community and influence population dynamics.
These are a few examples of those types of interactions:
• Mutualism: both species benefit from the interaction, such as bacteria in the gut that speed digestion (+/+).
• Commensalism: one species benefits without affecting the other, such as a spider spinning a web on a plant (+/0).
• Parasitism: one species benefit, but the other is harmed, such as pathogenic microbes (+/-).
• Predation: one species prey on the other for survival (+/-).
• Competition: two species fight over limited resources (-/-).
Species and Structure Interactions:
Even small changes in nature can have big effects on community ecology. For instance, the structure is influenced by factors such as slight temperature changes, disturbances to habitat, pollution, weather events, and species interaction.
The relative abundance of food is a stabilizing factor in communities. Normally, there is a check-balance system of food and consumption.
Types of Species in Community Ecology:
Foundation species, like coral in a coral reef community, play a pivotal role in community ecology and shaping structure. Coral reefs are commonly called “rainforests of the sea” because they provide food, shelter, breeding areas, and protection for up to 25 percent of all marine life, according to the Smithsonian Museum of Natural History. Threats to coral reefs include climate change, pollution, overfishing, and invasive species.
Keystone species like wolves profoundly affect community structure relative to the abundance of the other species. If removed, the loss of key predators dramatically changes the entire community. Predators keep other populations in check that would otherwise overgraze and threaten plant species resulting in a loss of food and habitat. Overpopulation can also lead to starvation and disease.
Invasive species are invaders that are not native to the habitat and disrupt the community. Many types of invasive species like the Zebra Mussel, destroy native species. Invasive species grow rapidly and reduce biodiversity, which weakens the overall animal and plant community within that niche.
Community Ecology Definition of Succession:
Ecological succession is a series of changes over time to community structure that affects community dynamics and encourages the assembling of plants and animals. Primary succession starts with the introduction of organisms and species, usually on newly exposed rock. Pioneer species like lichens on rock come first.
Secondary succession happens when orderly recolonization occurs in an area that was previously inhabited before a disruption. For instance, after a wildfire decimates an area, bacteria modify the soil, plants sprout from roots and seeds, bushes and shrubs establish, followed by tree seedlings. Vegetation provides a vertical and horizontal structure that attracts birds and animals to the biological community.
How do we measure community structure?
Two important measures ecologists use to describe the composition of a community are species richness and species diversity
Species richness:
Species richness is the number of different species in a particular community. If we found 303030 species in one community, and 300300300 species in another, the second community would have much higher species richness than the first.
Communities with the highest species richness tend to be found in areas near the equator, which have lots of solar energy (supporting high primary productivity), warm temperatures, large amounts of rainfall, and little seasonal change. Communities with the lowest species richness lie near the poles, which get less solar energy and are colder, drier, and less amenable to life. This pattern is illustrated below for mammalian species richness (species richness calculated only for mammal species, not for all species). Many other factors in addition to latitude can also affect a community's species-richness.
Global species richness as calculated for mammal species.
Species diversity:
Species diversity is a measure of community complexity. It is a function of both the number of different species in the community (species richness) and their relative abundances (species evenness). Larger numbers of species and more even abundances of species lead to higher species diversity.
For example:
⇨ A forest community with 202020 different kinds of trees would have greater species diversity than a forest community with only 555 kinds of trees (assuming that the tree species were even in abundance in both cases).
⇨ A forest community with 202020 different kinds of trees in even abundances would have greater species diversity than a forest community with the same number of species in very uneven abundances (for instance, with 90% of the trees belonging to a single species).
In general, ecologists think that more diverse ecological communities are more stable (that is, more able to recover after a disturbance) than less diverse communities. However, the diversity-stability relationship isn't a universal rule, and there are some cases where other factors (besides species diversity) are more important in determining community and ecosystem stability.
What factors shape community structure?
The structure of a community is the result of many interacting factors, both abiotic (non-living) and biotic (living organism-related). Here are some important factors that influence community structure:
⇨ The climate patterns of the community's location.
⇨ The geography of the community's location.
⇨ The heterogeneity (patchiness) of the environment
⇨ The frequency of disturbances, or disruptive events.
⇨ Interactions between organisms.
A community's structure can also be shaped by the chance events that happened during its history. For instance, suppose that a single seed blows into the dirt of a particular area. If it happens to take root, the species may establish itself and, after some period of time, become dominant (excluding similar species). If the seed fails to sprout, another similar species may instead be the lucky one to establish itself and become dominant.
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