Habitat fragmentation is the main cause of extinction of animal and plant species worldwide.
Fragmentation occurs when a large ecosystem is transformed by human action into numerous fragments of reduced size, spatially isolated from each other.
Habitat loss manifests itself as a reduction in the total area of habitat available for flora and fauna.
Habitat loss and fragmentation are generally two correlated phenomena, which can occur at the same time, thereby increasing the deleterious effects on the natural environment. Like deforestation, the loss of biodiversity is both a cause and consequence of global warming who 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 significant loss of habitat but also degradation due to the pollution they generate or even the construction of infrastructure which induces fragmentation of habitats (example of roads crossing forests, roads are a barrier for many species). But to this we must add intensive fishing, aquaculture, forestry, tourist and industrial developments, 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 according to 4 mechanisms
- The “mechanical” effect is the destruction of habitat by humans, which manifests itself, for example, in deforestation. One of the quickest and most obvious effects of fragmentation is the elimination of species present only in the destroyed parts of the landscape. It can also cause an immediate loss of species endemic to the fragmented area. This can be explained by the disappearance of a certain number of elements, following the fragmentation, which was necessary for the survival of these species.
- A disruption of dispersal processes. Species that require a mosaic of habitats (presence of several different habitats) for their development can be driven towards extinction if a physical barrier separates one habitat from others. In addition, these species can be endangered when fragmentation causes the separation of a large population into several small populations which are no longer linked together 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 due to their low numbers, and due to 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 certain cases, species require the presence of a diversity of habitats to live: a habitat linked to nesting, another to feeding, one to reproduction, etc. A reduction in habitat potential will therefore lead to the disappearance of these species. Another factor to consider is the size of the animals. A large species often requiring more space for its survival than a small species. The fragmentation of environments causing the creation of several small fragments, the environment will therefore become unfavorable for species requiring large spaces.
- An edge effect: the share represented by the edge in the ecosystem increases in the event of fragmentation. Conditions ecological specific conditions are present in the edge ecosystem compared to the central zone: the sunshine, the wind regime and even the temperature regime will vary. These different conditions between the edge and the core zone induce the presence of different fauna and flora. The initial habitat will therefore be denatured due to the increase in the edge effect, which will alter local diversity patterns and population dynamics. A new procession of species will therefore be present in this space to the detriment of that of the core space. If the latter is home to endemic species, reducing the surface area of the habitat can 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 reduction in specific diversity and a change in the composition of communities. These species sensitive to fragmentation are:
- Naturally rare species that have a low population density or limited geographic distribution.
- Species that have low fecundity or a short life cycle.
- Species requiring a large area of habitat to ensure long-term population viability.
- Species with low dispersal capacity, and which will therefore not be able to reach an unfragmented habitat.
- Species that need unpredictably present resources to live.
- Species that can only live in core areas (and therefore not in edge areas) or species that will be vulnerable to predators present in edge areas.
- Species vulnerable to human exploitation.
The fragmentation of habitats through the creation of roads can also encourage the exploitation of species, and therefore their extinction, by making hitherto inaccessible areas accessible to humans.