Alteration and loss of habitats

One of the greatest threats for the survival of the species are the changes, loss and fragmentation of their habitat. Human beings, in fact, have deeply modified the territory, as a result of a large growth in the population, industrial development, the expansion of transportation networks, and agriculture and fishing on an industrial scale. An example of the consequences of the changes in the habitats can be seen In the Mediterranean Sea. Posidonia oceanica is an endemic marine plant in the Mediterranean that forms submerged sea grass meadows on the sandy bottom, which are a fundamental component of the equilibrium and of the richness of the sea coast environment. This plant has a great environmental value, in fact, one square metre of sea grass meadow can produce 10 to 15 litres of oxygen per day. Furthermore the meadows give shelter to a great variability of biological species, both vegetable and animal, (400 vegetable species and approximately 1000 animal species), in fact many animals find food and shelter there. Another important function carried out by Posidonia is to protect the sea coast, where it guarantees stability, acting as a protection from sea currents and the waves. It has been calculated that a regression of only one metre of the sea grass meadows can lead to a loss of about 15-18 metres of sandy coastline. Among the principal causes of danger for the Posidonia sea grass meadows is the fishing activity with bottom trawling nets that tear away the plants leaving the subsoil uncovered; and subsequent recolonization of these plants becomes difficult. If the meadows disappear, the principal effects will be: a loss of biodiversity, a change in the trophic network, a decrease in productivity with consequent damage to fishing itself, a change in the metabolizing process of trophic chains, an increase in coastal erosion, and the consequent decrease in the quality of the environment. During the last century, changes in the territory consisted mainly of an increase in the surface area taken by agriculture and livestock farming, an increase in the urban areas, the development of road networks and the related infrastructures, the construction of hydroelectric plants and hydraulic plants, exploitation of underground deposits and fishing with more powerful boats and more efficient nets. Due to these changes, the natural environments are changed, destroyed and subdivided, which cause the loss, and division into small parts, of the habitats. The importance of the loss of the habitats is surely intuitive, while the concept of “fragmentation” is more difficult to understand. Fragmentation of the habitat is a division of the territory into various smaller areas that can remain, in some way connected to each other or may be totally isolated. The consequence of this leads to the subdivision of populations distributed in that particular area which are, therefore, less consistent than the original population. For this reason populations become more vulnerable to external stress, to climatic changes, to anthropic disturbance, epidemics and genetic deterioration due to cross- breeding among the population that is “related”. For example, it is calculated that every year approximately one million specimens of amphibians in the region of Lombardy, are affected by car traffic. In particular, the species that are most affected by this problem are the green frogs (Rana kl. esculenta) and the common toads (Bufo bufo). When these animals move toward the reproduction areas, they are forced to cross a number of asphalted roads that are often found around the waterways in Lombardy. Therefore the adult breeder specimens face mass extermination due to their slow and clumsy movement at dusk or during the night hours, before they have laid their eggs. It has been shown that the impact of roads can cause the extinction of these populations of amphibians.

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