- Sabrina Danial Leong
Discrete entities or continuum community best describes current Ecology?
A number of species assembled to form a pioneer community. Commonly, community is the assemblage of any populations in a habitat. They can consists of many sizes and could be from a taxonomic group or different types of taxonomic group (Krebs 2014). These species were capable of immigrating rather rapidly and can withstand unfavorable environmental conditions in a new zone. The seeds from the earliest plants were dispersed either through wind, carried by animals to a new area or even seeds that were already embedded in the soil for many years. These seeds germinate and developed as plants that can resist harsh states of environmental factors and also direct sunlight (Brewer 1994).
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Succession is a global event where the composition of species change due to naturally occurring circumstances or even human activity. Succession was originally defined by plant ecologists who focused on the adjustment of flora. Normally, these plant assemblage on uninhibited sites that were formed through geological events such as glaciation and volcanism or even other interferences. Succession is an outcome of reciprocal changes in the community composition of different kingdoms (animals, plant, fungi, protists, and bacteria)
The physical adjustment in community composition is not just certain process running at that community of level but is considered as a natural effect of species interacting with dissimilar life history strategies (Morin 2011). According to McIntosh (1985), the early controversies about the succession process has involved many bitter debates in the community of ecology. There were two very different view from the famous ecologists; Fredrick Clements and Henry Gleason.
Clements assumed that the ecological communities were comparable to superorganisms where interactions of different species boost a direct pattern of the evolution of community. He views superorganisms as a fundamental element of web of life and changes will occur repeatedly throughout the entire community. He also compared primary succession with embryonic development and secondary succession with healed organisms. Hence, Clements established seres, a term that explained succession through array of intermediate stages.
Clement came out with 6 main phases in the succession process. Firstly, nudation, where an open area is created. Secondly, the migration of species to a new place. Thirdly, ecesis, the adaptation of those plants to that new environment which subsequently carries out normal processes like germination, reproduction and growth. Next, competition within the community will take place. Both intra- and interspecific organisms in that particular area will fight for resources. Fifthly, the plants and the animals will react to and with each other. This will result in the formation of shade and nutrient-rich by the young trees. Finally, the stabilization, where the community eventually reaches a climax. At this stage, it is equilibrium with the environment (Pakcham 1982).
He suggested that the different environmental establishments as well as all types of disturbances such as fire were the factors influencing the formation of different climax communities which subsequently maintained them in a disclimax level, a steady state.
On the other hand, Gleason went totally opposite of Clements. He believed that the abundance of species fluctuates independently of one another through successional period and not mutually beneficial associations. His idea was termed individualistic, a group of species having similar physical and chemical niche requirements. Gleason took account of the patterns and how each and every one of species react individualistically to the biotic and abiotic factors. He also defended that early arrivals of a species tend to control a site and they could hinder the survival of the later arrivals. They are recognized as competitors and thus restrict the new species once that particular area is dominated by their own kind. This proves that groups as well as communities can be consisted of organisms of the same species.
The view on individualistic community evolution was nothing more than just the assemblages of species whole its biology requirements permit them to utilize certain locations. Individualistic is a species-scale event where the individual of dissimilar species’ tolerance is different to the conditions of the local environment. He concluded that community is the sum of all species living in an area and they do not participate in developing special community characteristics.
Individualistic has explained a better description of the vegetation succession growth. The spore of Rhizopus can be an example in this matter. Rhizopus spore grows well and reproduce without depending on other organism if the environment itself is conducive to survive. This simply means that a plant need a proper environment for them to carry out their normal operations and functions. These performance variation in function and also the morphological structure of the plants are influenced by the differences in the environment. Each plant have the ability to exist under different types of environmental states.
A fixed environment is not always the case in the life of all individuals within a species. External factors are what made the environment of a particular plant. Hence, individuals from the same species tend to inhibit different habitats and also have different associates in different situations. Environment that has certain limitations to one part of the range of a species can result in variation in its structure and contribute to the theory of species evolution (Gleason 1917).
The main conflict between the ideology of Clements and Gleason was whether communities developed by depending on each other or whether as an aftermath of the individualistic set of natural inhibitor inflicted by a location. In the twentieth century, the ecologists did not really pay their attention on the fact that community occurred repeatedly, naturally and were organized in units of considerable degree of integration that ruled their succession, function, development and also its structure. This had been an ongoing debate among ecologist from all over the country. They also thought that organisms lived together in a habitat and interact among themselves to create communities or natural entities.
The current views believes that succession is not an individual process. Succession is considered a product of complex interactions which began with interferences that made opportunities for these community to establish. The characteristics of life history and also interactions between interspecific species combined to construct repeatable adjustments in the composition of community over time. Clement’s discrete entities community was viewed as very well ordered by previous evolution and ongoing cooperation between species. This unity was made up of combined characteristics and interactions of species within a community which were recurring. May (1989) suggested that an individual cannot have stability or succession, so the evolution of these kinds of phenomena cannot be explained at the level of individuals.
However, according to Real and Brown (1991), the individualistic view was said to be one of the ‘classic papers in the foundations of ecology’ but Gleason’s hypothesis is much more suitable for animal communities. Taylor (1979) reported that a bactivorous ciliates in a pond study suggested that the species distribution is random and independent. In separate study by Sousa (1979) claimed that a study of rocky intertidal communities were non-equilibrium and disturbance-based view was close to Gleason’s idea. Levin (1988) suggested that the mathematical theory of animal ecologists developed from Clementsian approach and ‘emphasized equilibrium, predictability, homogeneity and constancy’. According to Colwell (1985), back in the 1960 and 1970s, these were the key elements of the new ecology, with a little of Gleason’s individualistic view, that influenced the animal ecology.
The properties of the individuals is the key item of organization. Some ecologists disagree on the fact that succession, stability and resilience are part of emergent properties which are significant at community level only and consequently can only be used in ecological community phrase. Gleason’s continuum community was viewed as a self-standing behavior of that particular species. Communities are supposed to change continuously and gradually. Continuum is a concept that is more than one aspect. Their distribution is the response to aspects a part from other important factors.
Some ecologists also argued that stability and succession are both unsuitable in an individual because the process of these events cannot be justified. Westman (1983) proposed that the argument lasts because empirical existence of evidence underpins both views. Robert (1987) then suggested that those two views on community were consistent with mechanistic view of vegetation development.
There are data confirming that species are distributed according to their tolerances. Normally, the area of each species is different and this gave such data. The ordination, direct gradient analysis and classification showed that species lives that particular location mainly because of its physical characteristics. Nevertheless, each species that occurs in an association is probable linked with another group of species under different states (Begon 1996).
This has led to lengthy research and study which subsequently, the studies on animal community and plenty of discussions and works on the nature of animal communities has been developed ever since. According to McIntosh (1993), the differences and discussions are acknowledged under five general categories; evolution and community theory, individualistic concept, community definition, questions from community ecology and empirical studies.
On top of that, he stated that the empirical studies have recently take various assessments about community ranging from deterministic, integrated and organismic to individualistic with various suggestions for compromise into account. McIntosh (1993) also claimed that recent work perpetuates the original dichotomy between integrated organismic community concept and individualistic non-integrated concept.
Ecologists should be aware of the current agreed views and their theories must not be different from it. This is because evolutionary theory must be consistent and match the current accepted perspective on the inheritance mechanisms matter. In order for the ecological theories to pass, compatibility with natural selection must be taken into account. Besides, ecologists must also mind that the organization or classification should be based on individual, not on communities and ecosystems.
The views on discrete entities and continuum are complementary and the views on community can be expressed in equally valid ways. It is not the fundamental considerations whether the communities have clear boundaries or not. It is not compulsory to have discrete boundaries between communities in order to study ecological community.
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