23.3: Threats to Biodiversity
The core threat to biodiversity on the planet, and therefore a threat to human welfare, is the combination of human population growth and resource exploitation. The human population requires resources to survive and grow, and those resources are being removed unsustainably from the environment. The three greatest proximate threats to biodiversity are habitat loss, overharvesting, and introduction of exotic species.
Habitat Loss
Habitat loss is the most important driver of biodiversity loss, accounting for around half of all biodiversity loss. Elimination of an entire ecosystem—whether it is a forest, a desert, a grassland, a freshwater estuarine, or a marine environment—will kill the individuals in the species. Remove the entire habitat within the range of a species and, unless they are one of the few species that do well in human-built environments, the species will become extinct.
Human destruction of habitats accelerated in the latter half of the twentieth century. Consider the exceptional biodiversity of Sumatra: it is home to one species of orangutan, a species of critically endangered elephant, and the Sumatran tiger, but half of Sumatra’s forest is now gone. The neighboring island of Borneo, home to the other species of orangutan, has lost a similar area of forest. Forest loss continues in protected areas of Borneo. The orangutan in Borneo is listed as endangered by the International Union for Conservation of Nature (IUCN), but it is simply the most visible of thousands of species that will not survive the disappearance of the forests of Borneo. The forests are removed for timber and to plant palm oil plantations.
Overharvesting
Overharvesting, also called overexploitation, refers to harvesting a renewable resource to the point of diminishing returns. Ecologists use the term to describe populations that are harvested at a rate that is unsustainable, given their natural rates of mortality and capacities for reproduction.
Overharvesting can lead to resource destruction, including extinction at the population level and even extinction of whole species. Depleting the numbers or amount of certain resources can also change their quality. Overharvesting not only threatens the resource being harvested, but can directly impact humans as well–for example by decreasing the biodiversity necessary for medicinal resources.
Overfishing is an especially salient problem because of a situation termed the tragedy of the commons. In this situation, fishers have no real incentive to practice restraint when harvesting fish because they do not own the fisheries. Early efforts to control overfishing used regulations on quotas, fishing effort, and gear, but this did not solve the underlying problem.
Resource economists developed the idea of a tradable permit scheme to help manage fisheries. Individual tradable quota (ITQ) schemes are cap-and-trade policies for fish, where total catch is limited but fishers in the fishery are given permits that guarantee them a right to a share of that catch. ITQ policies have helped rationalize some fisheries, improving the biological status of the stocks.
However, overfishing can also result in cascade effects, particularly if a habitat loses its apex predator. The unchecked prey can then overexploit their own food resources until population numbers dwindle, possibly to the point of extinction. There are many examples of regulated fisheries that have nevertheless collapsed.
Invasive Species
Whether enjoying a forest hike, taking a summer boat trip, or simply walking down an urban street, you have likely encountered an invasive species. Invasive species are species that have been intentionally or unintentionally introduced by humans into an ecosystem in which they did not evolve. If an introduced species is able to survive in its new habitat, that introduction is now reflected in the observed range of the species.
Invasive species often undergo dramatic population increases in their new habitat and reset the ecological conditions in the new environment, threatening the species that exist there. They can cause ecological and economic damage by threatening other species through competition for resources, predation, or disease.
Lakes and islands are particularly vulnerable to extinction threats from introduced species. In Lake Victoria, the intentional introduction of the Nile perch was largely responsible for the extinction of about 200 species of cichlids. The accidental introduction of the brown tree snake via aircraft from the Solomon Islands to Guam in 1950 has led to the extinction of three species of birds and three to five species of reptiles endemic to the island.
Aquatic invasions are often caused when ships dump ballast water, which can contain living organisms, at their destination ports. The zebra mussel was introduced to the Great Lakes from Europe prior to 1988 in ship ballast, and has had dramatic ecological impacts.
The mechanisms by which invasive species proliferate are also a threat. For example, the fungus Batrachochytrium dendrobatidis, which causes the disease chytridiomycosis, appears to have been spread worldwide by the transport of the African clawed toad, a commonly used laboratory and pet species. Similarly, the fungal pathogen Geomyces destructans, introduced from Europe, is responsible for white-nose syndrome, which has decimated bat populations in eastern North America.
Climate Change
Global climate change is also a consequence of human population needs for energy and the use of fossil fuels to meet those needs. Climate change is predicted to become a significant threat to biodiversity during this century, as changing climates shift species ranges and disrupt the timing of events like reproduction and migration.
The Arctic is recognized as being particularly vulnerable, with declining sea ice threatening polar bears. Warming temperatures are also causing the ranges of many species to shift poleward and upslope, disrupting established ecological communities. These range shifts can lead to unexpected species interactions, like the overlap between polar bears and grizzly bears.
While the exact magnitude of climate change’s impact on biodiversity is still debated, the scientific consensus is that it poses a major threat, especially when combined with the other drivers of biodiversity loss like habitat destruction and invasive species. Addressing climate change by reducing greenhouse gas emissions is critical to protecting the world’s species and ecosystems.
Conclusion
The combination of human population growth, resource exploitation, habitat destruction, overharvesting, invasive species, and climate change pose a grave threat to global biodiversity. Addressing these threats will require a multifaceted approach of habitat conservation, sustainable resource use, and climate change mitigation. As roofing professionals, we have an opportunity to contribute to biodiversity protection through the materials we use, the maintenance practices we recommend, and the design choices we make. By incorporating biodiversity-friendly features into roofing systems, we can help mitigate the impacts of the built environment on local ecosystems. Thoughtful roofing decisions can be an important part of the broader effort to conserve the world’s species and habitats.
