The ecological imbalance is defined as a state, observable in ecological communities, or in the ecosystems that host them, in which the composition and abundance of species is unstable indefinitely.
Ecological theory has been strongly influenced by the notion of competition between species for resources, as well as by the assumption that populations and communities are typically found in environments saturated with individuals and species, under conditions of equilibrium..
However, it is now known that in all kinds of organisms it is common that competition is not decisive, or that populations and communities suffer irregular and severe fluctuations. This causes that there are, even naturally, unstable ecosystems, therefore ecologically unbalanced..
This has led to a growing interest, both from a theoretical and a practical point of view, in the issue of ecological instability..
Article index
Ecological imbalance may be due to the inability of ecological communities to reach a stable state (homeostasis) through the competitive interactions that determine ecological succession..
In these cases, after suffering disturbances, the changes in the composition and abundance of species in the community are not directional; that is, the community does not go through defined successional stages and, therefore, does not reach the final stable stage of the succession, or ecological climax.
If the species that make up a community cannot maintain a relatively constant population size, situations of ecological imbalance are generated. Often the species involved are non-native organisms introduced by humans that become dominant in invaded communities..
Non-native organisms have been separated from their competitors and natural pathogens present in their regions of origin, so their population size is not limited by interactions with native species..
When the cause of the ecological imbalance is native species whose population size is not limited by other species, the cause is usually stochastic or asynchronous oscillations of biotic and abiotic factors, often poorly understood, that alter the composition and abundance of these species.
Like the ecological balance, the ecological imbalance is affected by external disturbances that cause changes in the composition and abundance of species. These external disturbances can be natural or of human origin.
However, in ecological disequilibrium, external disturbances, having more variable means and variances greater than those of equilibrium, have such a strong effect that they make the population growth of certain species independent of their density..
Competitive interactions fail to counteract the effect of such external shocks.
Another factor, in this case entirely biotic, that can cause ecological imbalance is the great longevity of certain species, native or non-native. This makes their competitive displacement by species belonging to more advanced successional stages very slow, causing a delay in the appearance of the ecological climax..
The delay, which can last more than a hundred and even up to a thousand years, mainly affects plant communities, both natural, for example tropical forests, and man-made, for example grasslands..
Certain authors, whose opinions are often magnified by the media, have proclaimed that the popular concept of ecological balance, or "balance of nature", has lost its validity and has been replaced by the concept of ecological imbalance, according to which the typical condition of ecosystems is instability.
Depending on the ecological characteristics of the species that compose them, natural communities can be ordered in a continuous sequence that goes from those with a randomly determined composition and with a low level of ecological balance, to those with a highly deterministic composition and with a high level of balance. ecological.
Species with low mobility and low population size, such as some plants, sessile animals, and ectoparasites, are subject to lower levels of competition than large species with high mobility and dense populations, such as large mammals, birds, and insects. flying.
When the ecological imbalance is caused directly by human activity, it tends to cause habitat degradation, economic losses and a decrease in environmental quality..
When it is caused by the presence of non-native organisms, generally introduced by humans, the environmental and economic consequences can be very negative. For example:
1) They compete with advantage with native species, causing their displacement or extinction.
2) Alter predator / prey cycles, to the detriment of native species.
3) Due to their uncontrolled population growth, they can cause habitat degradation, which is detrimental to agriculture, livestock and native species.
4) When introduced species are vectors of parasites or pathogenic organisms, they produce epidemics that can affect humans, their domestic animals and plants, and native flora and fauna..
5) Non-equilibrium conditions can be very long-lasting, so it may take a very long evolutionary time for a biodiversity equivalent to the original to recover, if this is possible..
When the ecological imbalance is caused by human activity, it almost invariably has deleterious effects on the biodiversity of the invaded ecosystem. It can even cause the total extinction of species.
When ecological imbalance is a natural property of communities or ecosystems, it not only has no negative consequences, but can help maintain higher diversity.
For example, it is known that in terrestrial and aquatic communities, such as tropical rainforests or kelp forests, the imbalance caused by frequent and relatively strong natural disturbances, such as the fall of a tree, allows the survival of competitively inferior species..
These competitively inferior species under equilibrium conditions, for example plants of early successional stages, allow the existence of species co-adapted to them, such as herbivorous, nectarivorous and frugivorous animals..
These plants also generate the necessary environmental conditions for the establishment of more competitive plants..
There is evidence of ecological balance at all levels, in space and time. For example, island bird communities and some insect communities commonly live under apparent conditions of dynamic equilibrium..
However, at all these levels, periods of stability often alternate with even longer periods of instability. At the population level, the high frequency of environmental disturbances means that many species do not live in ecological balance most of the time: the reestablishment of the same can take years.
At the community level, the existence of vacant niches frequently determines the absence of competition and therefore that the species do not live in ecological balance..
In evolutionary time, the existence of large numbers of vacant niches caused by mass extinctions and by the presence of vast habitats not yet colonized has led to the permanent configuration of completely new communities and ecosystems. This has led to an increase in biodiversity.
In Rothamsted, England, certain plant communities have not reached ecological equilibrium for over a hundred years. The reason is that most of the species that establish after environmental disturbances are perennial and very long-lived thanks to clonal reproduction through underground tissues..
In South Africa, pines planted almost two hundred years ago with seeds brought from climatically similar environments in the Northern Hemisphere are not attacked by herbivorous insects and native pathogens. Under these conditions, they do not live in ecological balance with native plants, which are attacked by these enemies..
In 1932, 107 sheep were brought to the Scottish island of Hirta (638 ha), with no human population. In 1948, 1961-1967 and 1985-1990, the number of sheep ranged between 600 and 1600. The abundance of food allows the multiplication of sheep in summer. Hunger kills them in winter. Climatic seasonality prevents an ecological balance from being reached.
Similarly, in the Australian outback, red kangaroo populations, despite continually reproducing, suffer large fluctuations caused by variability in rainfall. Droughts, unpredictable in time, prevent an ecological balance from being reached by causing high mortality in these mammals.
In order to conserve biodiversity, promote sustainable development and maintain environmental quality, in general the ideal would be to alter as little as possible the situations of ecological balance or imbalance present in nature..
Humanity is characterized by creating and maintaining extensive artificial ecosystems lacking ecological balance. In these ecosystems, the biotic components have been determined by humans for specific purposes, such as agricultural and livestock production..
The areas occupied by agricultural monocultures, or by cattle and planted pastures, are among the most extreme examples of environments in ecological imbalance that the planet has known.
The incessant growth of the human population requires the expansion of artificial ecosystems to the detriment of the natural world. Therefore, it has been suggested that it is necessary to reduce this growth through education and voluntary family planning.
Other recommended measures would be to reduce food waste, and promote the consumption of foods of plant origin instead of those of animal origin since, per unit mass of food produced, agriculture requires less space than livestock.
Yet No Comments