Factors causing loss of genetic, species and ecosystem diversity

Introduction - Factors causing loss of genetic, species and ecosystem diversity

Biodiversity refers to the totality of genes, species, individual organisms along with their ecosystem.  There are three types of biodiversity

Genetic diversity is the number of alleles of a single gene that are present in a species’ gene pool. If the genetic diversity is too small, a species may not be able to evolve to adapt to a changing environment.

Species diversity - About 13 million species of microbes, plants, and animals represent the planet’s species diversity, although most of them remain un-identified.  

Ecosystem diversity - The wide variety of the Earth’s ecosystems also known as ecosystem diversity, provide habitat for the enormous number of species.

Biodiversity loss is the extinction of species worldwide or the decrease in biodiversity within a species or an ecosystem or in a given geographic area or in the whole Earth. Biodiversity loss is the decline in the number, genetic variability, and variety of species, and the biological communities in an ecosystem. This loss result in the breakdown of the ecosystem.  Even minor changes in species composition will have dramatic influence on the food web and will further lead to an overall reduction in biodiversity.

Over geologic time, multitudes of species have gone extinct because they could not adapt fast enough to the changing environment since life began to flourish 600 MYA (million years ago). At least five times in the planet’s history, mass extinctions have occurred.  Those previous mass extinctions in the past were the Ordovician, the Devonian, the Permian, the Triassic, and the Cretaceous.  There are many possible causes for mass extinctions and in some cases, more than one factor may contribute to the termination of species. Some natural causes of mass extinctions are Plate tectonics, Climate change, Volcanic eruptions, Flood basalts, Asteroid impact, etc. 

After a mass extinction, the ecological niches stay empty for a period of time. Eventually, life continues in form of new organisms evolved to fill the abandoned niches. It takes between 20 and 100 million years for an ecosystem to reach the same level of biodiversity it had before the extinction.

The last mass extinction was 65 million years ago, when an asteroid impact propelled the planet from the Age of Reptiles, when dinosaurs and other reptiles dominated the niches in earth to the Age of Mammals, when mammals evolved different strategies for filling those same niches. Earth is presently in the midst of a sixth great extinction, the Holocene.  Unlike the others, this extinction is being caused by one of the planet’s species, resulting from human activities such as habitat destruction, soil and genetic erosion, and the introduction of alien species into established environments.

Intentionally or not, human activities alter and sometimes destroy organisms and ecosystems. Most biodiversity is lost as ecosystems are mowed down to make room for human landscapes—homes, farms, power plants, and industrial complexes, etc. Ecosystems are degraded by being fragmented, as when roads are carved through them, or by being polluted. Hunters and fishers overharvest the animals, loggers level forests for timber and herb collectors deplete the supply of herbaceous plants. Where humans go, other species—rats, cats, fish, and weeds, etc follow and these invaders devour, outcompete, or run out the ecosystem’s native organisms. Climate change also damages ecosystems and species such as when conditions change too rapidly for the organisms to adapt to them.  Global warming joined together with a bacterial pathogen wiped out many species of frogs and toads. As a result of all these factors species extinctions are occurring at a rate 10 to 100 times higher than was normal in the planet’s history.

Biodiversity loss

Even if a species is not eliminated or extinct from the ecosystem or from the biosphere, a decrease in its population size results in a decrease of its niche. If its niche is critical in the proper functioning of the ecosystem, there will be significant changes in the corresponding ecosystem structure. For example, clearing trees from a forest eliminates the shading, temperature and moisture regulation, animal habitat and nutrient transport services they provide to the ecosystem.

Natural Biodiversity Loss

The biodiversity in an area increases and decreases with natural cycles. Seasonal changes, such as the spring increase biodiversity as the populations of many species rise. Winter temporarily decreases an area’s biodiversity, as warm-adapted insects die and migrating animals leave. Natural ecological disturbances, such as wildfire, floods, and volcanic eruptions, change ecosystems drastically by eliminating local populations of some species and transforming whole biological communities. These disturbances are temporary since ecosystems adapt to the challenges resulting in ecological succession.

Human-Driven Biodiversity Loss

Biodiversity losses due to disturbances caused by humans tend to be more severe and long lasting. Humans, their crops, and their food animals take up a large` share of Earth’s land area. Half of the world’s habitable land has been converted to agriculture, for grazing by cattle, sheep, goats, and other livestock. This massive conversion has resulted in more than 60 percent decline in the number of vertebrates. A 2019 report by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services noted that up to one million plant and animal species are facing extinction due to human activities.

Forest clearing, wetland filling, stream channeling and rerouting, road and building construction also results in substantial change in the ecology of the area and are associated biodiversity losses.

The five important drivers of biodiversity loss are as follows

1.      Habitat loss and degradation – this includes thinning, fragmentation, or destruction of an existing natural habitat.  This will reduce or eliminate the food resources and living space for most species. Species that cannot migrate are often wiped out.  Examples are conversion of forests, wetlands, grasslands, and other natural areas for urban and agricultural uses

2.      Invasive species – These are non-native species that can significantly modify or disrupt the ecosystems where they colonize.  These species outcompete native species for food and habitat, resulting in a decline of native species population. Invasive species may arrive in new areas either through natural migration or may be introduced by human.

3.      Overexploitation-  This is the harvesting of animals, fish or other organisms to a greater extent.  This results depletion of such species to very low numbers and may even lead to extinction.

4.      Pollution – This is the addition of any substance or energy to environment at a rate faster than it can be dispersed, diluted, decomposed, recycled, or stored in a harmless form.  Pollution causes biodiversity loss by creating health problems in exposed organisms. This exposure may either kill the animals or create reproductive problems that threaten the species’ survival.

5.      Climate change associated with global warming – This is the modification of Earth’s climate caused by the burning of fossil fuels.  This is mainly due to human activities. Fossil fuel combustion produces greenhouse gases that enhance the atmospheric absorption of infrared radiation and trap the heat, influencing temperature and precipitation patterns.

Among these five factors, Habitat loss and invasive species are the primary drivers of biodiversity loss, and climate change is becoming an important primary driver as the 21st century progresses. All these five factors are strongly influenced by the continued growth of the human population and its consumption of natural resources.  Interactions between two or more of these drivers increase the pace of biodiversity loss.

 

 

References

• Emerging Consequences of Biotechnology - Biodiversity Loss and IPR Issues, Krishna Dronamraju, World Scientific Publishing Co. Pte. Ltd.
• Biosphere - Ecosystems and Biodiversity Loss, Dana Desonie, Chelsea House
• https://www.britannica.com