Here is your paragraph on global ecological imbalance:
The constituent operating units of an ecosystem, various living organisms, live in a dynamic equilibrium with each other.
This equilibrium has evolved over millions of years and has the capacity to adjust to changes in the physical as well as the biological environment.
That is why the equilibrium is said to be dynamic. Among the plants, the cycle of nutrients between falling leaves, flowers etc. and their decomposition by bacteria and fungi is in a state of equilibrium. The amount of nutrients consumed gets replenished by the recycling processes, discussed earlier.
Even among the animal communities, the dynamic ecological equilibrium is maintained between various levels. The ecological efficiency of an ecosystem is only 10 per cent, i.e., only one- tenth of energy at a particular level can be transferred to the higher level. The herbivores and carnivores balance each other.
An increase in any one of these will lead to disruption of the ecosystem. For instance, an unnatural increase in herbivores can lead to depletion of plant species very fast, thus narrowing the base of the pyramid. Similarly, an unnatural growth of carnivores will increase plant population in relation to the animals, which again will strain the nutrient supply in the ecosystem.
In agriculture, monoculture cropping practices are narrowing the base of biodiversity. As a result, new diseases and deficiencies have crept in. Nutrient cycle of soil gets disturbed and the soil becomes impoverished. Excessive use of chemical fertilisers causes soil degradation and eutrophication.
Reckless deforestation, especially on slopes, exposes the soil to erosive forces which further lead to siltation of streams. Besides, the soil is deprived of leaf litter, leading to impoverishment of its structure. Thus, the abiotic components of the ecosystem are disturbed and an imbalance sets in. Overgrazing, especially on dry-land slopes, exposes the soil to wind erosion. These areas face the threat of desertification.
Introduction of alien varieties of plants and animals causes a chain of disturbances in the ecosystem. For instance, the introduction of rabbit into Australia led to the destruction of grasslands, as the rabbit had no predator in the new environment.
Changes in the physical environment also play a crucial role in altering the ecological balance. Global warming is expected to lead to melting of ice caps and a rise in sea level. The fish population, in that case, will move northwards.
The fertile agricultural fields will also be available northwards. This will cause northwards migration of populations. All this may end up making some species extinct, while evolving new species which would adapt to the changed environment.
This dynamic equilibrium between organisms is referred to as homeostasis.