Habitat fragmentation is the main cause of extinction of animal and plant species in the world.
Fragmentation occurs when a large ecosystem is transformed by human action into many small fragments, spatially isolated from each other.
Habitat loss is manifested by a reduction in the total area of habitat available for wildlife.
Habitat loss and fragmentation are generally two interrelated phenomena that can occur at the same time, thereby increasing the deleterious effects on the natural environment. Like deforestation, biodiversity loss is both a cause and consequence of global warming that threatens us.
The human species bears a heavy responsibility
These phenomena are linked to a large number of human activities: urbanization and agriculture which lead to a significant loss of habitat but also to degradation because of the pollution they generate, or the construction of infrastructures which induce a fragmentation of habitats (for example, roads which cross the forests, roads are a barrier for many species). But to this we must add intensive fishing, aquaculture, forestry, tourism and industrial development, extraction of materials (such as quarries), and of course the absurdity of hunting... the list of activities causing an impact is very long.
The fragmentation of natural environments affects biodiversity through 4 mechanisms
- The "mechanical" effect is the destruction of habitat by humans, which manifests itself for example in deforestation. One of the most rapid and obvious effects of fragmentation is the elimination of species present only in the destroyed parts of the landscape. It can also result in an immediate loss of species endemic to the fragmented area. This can be explained by the disappearance of a number of elements, as a result of fragmentation, that were necessary for the survival of these species.
- Disruption of dispersal processes. Species that require a mosaic of habitats (the presence of several different habitats) for their development can be driven to extinction if a physical barrier separates one habitat from the others. In addition, these species may be endangered when fragmentation causes a large population to split into several small populations that are no longer connected and whose numbers are no longer large enough to have a viable population. These populations will not be able to survive in the long term because of their small size, and because of the genetic uniformity that this will induce which will make them more sensitive to external conditions.
- Reduced habitat diversity with restricted populations. Habitat diversity contributes to species diversity. In some cases, species require a diversity of habitats to live: one habitat for nesting, one for feeding, one for breeding. Another factor to be considered is the size of the animals. A large species often requires more space for its survival than a small species. The fragmentation of the environment causes the creation of several small fragments, the environment will thus become unfavorable to the species needing large spaces.
- An edge effect: the share represented by the edge in the ecosystem is increased in case of fragmentation. Conditions ecological Specific conditions are present in the edge ecosystem compared to the core area: sunlight, wind regime and temperature regime will vary. These different conditions between the edge and the core zone lead to the presence of different fauna and flora. The initial habitat will therefore be distorted due to the increased edge effect, which will alter the local diversity patterns and population dynamics. A new set of species will therefore be present in this area to the detriment of the core area. If the latter is home to endemic species, the reduction in habitat area may endanger these populations and cause their extinction
The most sensitive species are the first to be affected by fragmentation
A loss of habitat will therefore cause a decrease in species diversity and a change in community composition. These species sensitive to fragmentation are:
- Naturally rare species that have low population density or limited geographic distribution.
- Species with low fecundity or short life cycles.
- Species that require a large area of habitat to ensure long-term population viability.
- Species with low dispersal ability, and therefore will not be able to reach unfragmented habitat.
- Species that need to live on unpredictably present resources.
- Species that can only live in core areas (and therefore not in edge areas) or species that will be vulnerable to predators in edge areas.
- Species vulnerable to human exploitation.
Fragmentation of habitats through the creation of roads can also encourage the exploitation of species, and thus their extinction, by making previously inaccessible areas accessible to humans.