User:LisaTruong3/Biodiversity loss

Human-driven biodiversity loss and ecological effects

Pollution

Air pollution

Water vapor, carbon dioxide, methane, and nitrous oxide are examples of natural greenhouse gases. In the past 250 years, concentration of carbon dioxide and methane have increased, along with the introduction of anthropogenic emissions such as hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride into the atmosphere. These pollutants are emitted into the atmosphere by the burning of fossil fuels and biomass, deforestation, and agricultural practices, which amplifies the effects of climate change. As larger concentrations of greenhouse gases are released into the atmosphere, this causes the Earth’s surface temperature to increase. This is because greenhouse gases are capable of absorbing, emitting, and trapping heat from the Sun and into the Earth's atmosphere. With the increase in temperature expected from rising greenhouse gas concentrations, there will be higher levels of air pollution, greater variability in weather patterns, intensification of climate change effects, and changes in the distribution of vegetation in the landscape.

Other pollutants that are released from industrial and agricultural activity are sulfur dioxide and nitrogen oxides. Once sulfur dioxide and nitrogen oxide are introduced into the atmosphere, they can react with cloud droplets (cloud condensation nuclei), raindrops, or snowflakes, forming sulfuric acid and nitric acid. With the interaction between water droplets and sulfuric and nitric acids, wet deposition occurs and creates acid rain. As a result, these acids would be displaced into various environments and vegetation during precipitation, having significant aerial distance (hundreds of kilometres) from the emission source. Sulfur dioxide and nitrogen oxide can also be displaced onto vegetations through dry deposition.

Sulfur dioxide and nitrous oxide concentration has many implication on aquatic ecosystems, including acidity change, increased nitrogen and aluminum content, and altering biogeochemical processes. Typically, sulfur dioxide and nitrous oxide do not have direct physiological effects upon exposure; most effects are developed by accumulation and prolonged exposure of these gases in the environment, modifying soil and water chemistry. Consequently, sulfur largely contributes to lake and ocean acidification, and nitrogen initiates eutrophication of inland and coastal water bodies that lack nitrogen. Both of these phenomena alter the native aquatic biota composition and influence the original food web with higher acidity level, minimizing aquatic and marine biodiversity.

Nitrogen deposition has also affected terrestrial ecosystems, including forests, grasslands, alpine regions, and bogs. The influx of nitrogen has altered the natural biogeochemical cycle and promoted soil acidification. As a result, it is likely that plant and animal species composition and ecosystem functionality will decline with increased soil sensitivity; contribute to slower forest growth, tree damage at higher elevations, and replacement of native biota with nitrogen-loving species. Additionally, sulfate and nitrate can be leached from the soil, removing essential nutrients such as calcium and magnesium, and be deposited into freshwater, coastal, and oceanic environments, promoting eutrophication.

Noise pollution

Noises generated by traffic, ships, vehicles, and aircrafts can affect the survivability of wildlife species and can reach undisturbed habitats. Although sounds are commonly present in the environment, anthropogenic noises are distinguishable due to differences in frequency and amplitude. Sounds for many species are a form of communication between one’s population, whether that is for reproduction purposes, navigation, or to notify others of prey or predators. However, due to anthropogenic noises, this inhibits species from detecting these sounds, affecting overall communication within one’s population. Species such as birds, amphibians, reptiles, fishes, mammals, and invertebrates, are examples of biological groups that are impacted by noise pollution. If species cannot communicate with one another, this would result in reproduction to decline (not able to find mates), and higher mortality (lack of communication for predator detection).

Noise pollution is common in marine ecosystems, affecting at least 55 marine species. For many marine populations, sound is their primary sense used for their survival; able to detect sound hundreds to thousands kilometers away from a source, while vision is limited to tens of meters underwater. As anthropogenic noises continue to increase, which has been doubling every decade, this compromises the survivability of marine species. One study discovered that as seismic noises and naval sonar increases in marine ecosystems, cetaceans, such as whales and dolphins, diversity decreases. Noise pollution has also impaired fish hearing, killed and isolated whale populations, intensify stress response in marine species, and changed species’ physiology. Because marine species are sensitive to noise, most marine wildlife are located in undisturbed habitats or areas not exposed to significant anthropogenic noise, limiting suitable habitats to forage and mate. Whales have changed their migration route to avoid anthropogenic noise, as well as altering their calls. Noise pollution also impacts human livelihood. Multiple studies have noticed that fewer fishes, such as cod, haddock, rockfish, herring, sand seal, and blue whiting, have been spotted in areas with seismic noises, with catch rates declining by 40-80%.

Noise pollution has also altered avian communities and diversity. Anthropogenic noises have a similar effect on bird population as seen in marine ecosystems, where noises reduce reproductive success; cannot detect predators due to interferences of anthropogenic noises, minimize nesting areas, increase stress response, and species abundances and richness declining. Certain avian species are more sensitive to noises compared to others, resulting in highly-sensitive birds to migrate to less disturbed habitats. There has also been evidence of indirect positive effects of anthropogenic noises on avian populations. In a study conducted by Francis and his colleagues, nesting bird predators, such as the western scrub-jay (Aphelocoma californica), were uncommon in noisy environments (western scrub-jay are sensitive to noise). Therefore, reproductive success for nesting prey communities was higher due to the lack of predators.

Invasive species

Invasive species have major implications on biodiversity loss and have degraded various ecosystems worldwide. Invasive species are migrant species that have outcompeted and displaced native species, altered species richness and food webs, and changed ecosystems’ functions. According to the Millennium Ecosystem Assessment, invasive species are considered one of the top five factors which result in biodiversity loss. In the past half century, biological invasions have increased immensely worldwide, resulting in biodiversity loss. Ecosystems that are vulnerable to biological invasions include coastal areas, freshwater ecosystems, islands, and Mediterranean-climate location. One study conducted a meta-analysis on the impacts of invasive species on Mediterranean-type ecosystems, and observed a significant loss in native species richness. Invasive species are introduced to new habitat, either intentionally or unintentionally, by human activities. The most common methods for the introduction of aquatic invasive species are by ballast water, hull of ships, and attached to equipment such as fishing nets. Furthermore, global warming has changed typical conditions in various environments, allowing greater migration and distribution of species dependent on warm climate. This phenomenon could either result in greater biodiversity (new species being introduced to new environments), or reduce biodiversity (promotion of invasive species). A biological invasion is deemed successful if the invasive species can adapt and survive in the new environment, reproduce, disperse, and compete with native communities. Some invasive species are known to have high dispersal rates and have major implications on a regional scale. For example, in 2010, muskrat, raccoon dog, thrips, and Chinese mitten crab, was identified and have affected 20 to 50 regions in Europe.

Invasive species can become financial burdens for many countries. Due to ecological degradation caused by invasive species, this can alter the functionality and reduce the services that ecosystems provide. Additional costs are also expected in order to control the spread of biological invasion, to mitigate further impacts, and to restore ecosystems. For example, it has been estimated that the cost of damages caused by 79 invasive species between 1906-1991 in the United States would approximate to US$120 billion. In China, invasive species has reduced the country's gross domestic product (GDP) by 1.36% per year. Management of biological invasion can also be costly. In Australia, the expense to monitor, control, manage, and research on invasive weed species was approximately AU$116.4 million per year, with costs only directed to central and local government. In some situations, invasive species may have benefits, such as economic returns. For instance, invasive trees can be logged for commercial forestry. However, in most cases, the economic returns are far less compared to the cost caused by biological invasion.

Not only have invasive species cause ecological damages and economical losses, but it can also affect human health. With the alteration in ecosystem functionality (due to homogenization of biota communities), invasive species have resulted in negative effects on human well-being, which includes reduced resource availability, unrestrained spread of human diseases, recreational and educational activities, and tourism. With regard to human health, alien species have resulted in allergies and skin damage to arise. Other similar diseases that invasive species have caused include human immunodeficiency virus (HIV), monkey pox, and severe acute respiratory syndrome (SARS).

Overexploitation

Fossil fuel

Due to human dependency and demands, fossil fuel remains as the dominant energy source globally. This trend is expected to rise, with oil, natural gas, and coal demands increasing by 30%, 53%, and 50%, respectively, by 2035. Extraction, processing, and burning of fossil fuels indirectly impacts biodiversity loss by contributing to climate change effects, while directly causing habitat destruction and pollution. At fossil fuel extraction sites, land conversion, habitat loss and degradation, contamination, and pollution impacts biodiversity beyond terrestrial ecosystems; it impacts freshwater, coastal, and marine environments. Once fossil fuels have been extracted, they are transported, processed, and refined, which also impacts biodiversity as infrastructure development requires removal of habitats, and further pollution is emitted into the environment. Currently, fossil fuel exploitation tends to occur in areas with high species richness and abundances, usually located in coastal and terrestrial environments. In one study, Harfoot and his colleagues identified 181 possible “high-risk” areas for fossil fuel exploitation, which were areas that also supported high levels of biodiversity. Out of the 181 identified locations, 156 of these high-risk fields were not protected areas, indicating that further biodiversity could be lost with fossil fuel exploitation. It is predicted that future exploration for fossil fuel will occur in areas with low species richness and rarity, such as the oceans and in the Arctic. However, this prediction does not apply to Western Asia, Asia-Pacific, Africa, South America, and the Caribbean, where fossil fuel and coal exploitation is expected to occur in areas with high species richness. For example, the Western Amazon (located in Brazil) is known to have high biodiversity. However, this region is also threatened by exploitation due to the large quantity of oil and natural gas reservoirs. Typically, areas with large fossil fuel reservoirs have a greater likelihood of being extracted (based on the country's priorities). This is of concern as tropical environments contain high levels of biodiversity, which will indirectly result in greater deforestation for agricultural purposes and financial gains (e.g., exporting timber).

Biodiversity loss in marine environment

Marine biodiversity encompasses any living organism which resides in the ocean, and describes various complex relationships within marine ecosystems. On a local and regional scale, marine communities are better understood compared to marine ecosystems on a global scale. In 2006, it was estimated that approximately 300,000 marine species have been documented. However, the number of described marine species remains low compared to terrestrial species due to various factors, which includes the assignment of different names for the same species, and insufficient taxa classification. It is likely that many undocumented species has already disappeared. Because not all marine species have been described, it is difficult to provide an accurate estimate of global extinction in marine ecosystems. As a result, abundances of marine species remain uncertain, with estimates ranging between 178,000 to 10 million oceanic species.

With anthropogenic pressure, this results in human activities to have the strongest influences on marine biodiversity, with main drivers of global extinction being habitat loss, pollution, and overexploitation. Other indirect factors that have resulted in marine species to decline include climate change and change to oceanic biochemistry.

Overexploitation has resulted in the extinction of over 20 described marine species, which includes seabirds, marine mammals, algae, and fishes. Examples of extinct marine species include the Steller’s sea cow (Hydrodamalis gigas) and the Caribbean monk seal (Monachus tropicalis). However, not all extinctions were due to anthropogenic causations. For example, in 1930, the eelgrass limpet (Lottia alveus) became extinct once the Zostera marina population declined upon exposure to a disease. The Lottia alveus were greatly impacted as the Zostera marina were their sole habitats.

Changes in species abundances are more evidencable in some species compared to others. For example, fishes are commonly used as a global indicator for changes in population size. Reduction in global fish populations were first noticed during the 1990s. Currently, many commercial fishes have been overharvested; approximately 27% of exploited fish stocks in the United States are classified overfished. Furthermore, in Tasmania, it have been observed that over 50% of major fisheries species, such as the eastern gemfish, southern rock lobster, southern bulkefin tuna, jack mackerel, and trumpeter, have declined over the past 75 years due to overfishing.