Currently, the planet is losing species rapidly. Countless creatures have vanished both before and after humans’ emergence. Delord’s team believes that extinction is the greatest threat to biodiversity. Maintaining diversity is crucial in maintaining the balance of the ecosystem. An increase in the number of prey and a decrease in the number of predators may lead to the extinction of one species. Therefore, it will take time for the prey and predator to adjust to a new dietary structure. Before the equilibrium is achieved again, the extinction of a particular species may thread the population of the upstream and downstream food cycles.
In the past 65 million years, there have been five mass extinctions. During the mass extinction, 90% of all marine creatures and 70% of all terrestrial animals perished. Abiotic factors have been primarily responsible for the earlier five major extinctions. The most significant factors put forth by academics are asteroid impacts, volcanic eruptions, or earthquakes. These factors may also indirectly cause the extinction of animals by causing a rapid rise in temperature in the organisms’ habitat. Scientists argue that another significant extinction is occurring, also called the sixth mass extinction.
Three-quarters of species, including amphibians, mammals, arthropods, insects, birds, etc., have survived since the last major extinction. The species that are most in danger of going extinct are amphibians. The International Union for Conservation of Nature’s Red List of Threatened Species indicates that 41% of endangered animals are amphibians. We must research the factors behind amphibian extinction and work to decrease the extinction rate to maintain the balance of biodiversity.
Biologists believe the current extinction is more complex than the previous five mass extinctions. As stated in the opening paragraph, the causes of the past five mass extinctions are primarily environmental. However, environmental factors play a less significant role in the sixth extinction. Instead, the primary cause of the sixth extinction is human involvement. Scientists are currently attempting to comprehend the extinction of amphibians using the following three human-driven influences: habitat destruction, invasive species, and overexploitation of animal resources.
Habitat destruction
The first cause of amphibian extinction is habitat destruction. A US research team studied the wetland in urban and agricultural regions of central and southwestern Minnesota. They discovered a connection between the depletion of wetlands in the area and a decline in amphibian populations. Human activity today is accelerating the loss of natural habitat. For example, people reclaim the tidal flats to acquire more land, cut the trees to get wood resources, and destroy the natural habitat to create more urban architecture and infrastructure space. According to scientists, the amphibian group has several traits that make it easier for them to go extinct due to habitat loss, including a narrow geographic distribution and habitat degradation.
Sodhi’s team discovered that frogs with a narrow geographic distribution are more likely to go extinct (Sodhi et al., 2008). The team’s research involves data analysis on more than 3000 species to look for a correlation between geographic distribution and extinction rate. Let’s say a species only inhabits a tiny region. Geographically restricted species typically exhibit higher habitat specialization, which implies that they can only live in regions that share the same characteristics as the restricted area. Because they can only exist in areas with features similar to the specified territory, species with confined geographic ranges typically exhibit higher habitat specialization. Any slight change in any factor (such as temperature, altitude, and humidity) has a significant impact on whether they can survive in the new habitat. The species is more likely to go extinct since it can only survive in this region and finds it difficult to adapt to other environments.
The team also investigates other potential factors contributing to species extinction in this paper. A significant factor they discovered was body size: the statistical model revealed a significant correlation between the extinction rate and body size. If an organism has a larger body size, it requires more energy sources to support its daily metabolism. If their habitat is destroyed, they will go extinct rapidly since they cannot meet their daily needs for food and shelter. The research also suggests that other variables, such as climate seasonality, may affect extinction in concert with body size. The elements interact and combine to cause the extinction of the species. However, it is only when a species has a narrow geographic range that people realize how much body size affects extinction rates. People still do not fully understand how other factors—like climate seasonality—affect extinction and what will happen when various elements coexist to varying degrees.
Pollution in the ecosystem also reduces the abundance of particular species. The assertion is supported by research on amphibians in Central America. One of the primary businesses in Central America is agriculture. Agrochemical pesticides aid agricultural product growth but can endanger adjoining amphibians’ lives (Whitfield et al., 2016). The research team discovered that extinction is impacted by agricultural chemicals both directly and indirectly. Some agricultural pesticides may harm amphibians’ health, impairing organ function.
Additionally, the chemicals can contaminate the environment, leaving less food, shelter, and water resources. The research team also discovered that the toxic constituent of agrochemical pesticides might be detected 20 kilometers from the plantation at a dose that drastically shortens the lives of nearby amphibians. Therefore, contemporary human agricultural activity poses not only a hazard to amphibians living on the plantation but also to amphibians living in the neighborhood.
However, the author mentions that certain amphibian species have evolved to be resistant to artificial agricultural toxins.
Invasive species
Invasive species refer to the species that are not indigenous yet coexist alongside native species. Invasive can be either beneficial, neutral, or detrimental. However, invasive species typically have a detrimental impact on native species. First of all, invasive species share food resources with the local species. Local species cannot have adequate food if an invasive species shares some of the available food resources. As a result, a greater percentage of indigenous species experience food shortages when they coexist with invasive species. Second, invasive species may compete with local species for the same habitat. For local species with high habitat specialty, invasive species pose a significant threat since finding alternative habitats is challenging. Losing shelter jeopardizes spawning by making it easier for predators to take their eggs. Reduced reproduction lowers a species’ population, indirectly contributing to certain species’ extinction. Thirdly, invasive might spread illness within the local community. A symbiotic relationship between the parasite and host may already exist in the invasive species. However, when the parasite or virus comes into contact with the local species, it becomes easier for the local species to contract the infection and weaken its immune system.
The research on northern leopard frogs lends credence to the idea that invading species may cause local species to become extinct (Dueas et al., 2021). Amphibians of the northern leopard frog species inhabited North America. The scientists discovered a link between the number of bullfrogs and fish introduced into the area and the number of northern leopard frogs. Northern leopard frogs are less likely to be found where there are more invasive fish and bullfrogs. Additionally, the researchers still believe there is a connection between the newly introduced virus and the drop in local species, even though the statistical model does not indicate the existence of the fungus Batrachochytrium dendrobatidis (Bd), which causes infections in amphibians. The team asserts that invasive species adversely affect various species in different ways. To better protect native species, it is crucial to understand which species are severely affected by invasive species.
Exploitation
Amphibians are considered precious commercial goods in the market. Humans capture certain amphibians to use as medicine, while they capture and keep others as pets. As amphibians are continuously considered valuable to humans, their exploitation has become a significant concern since humans constantly look for new species to hunt and make more money.
In a study on the amphibian trade market in Indonesia, the team tracked over 5000 amphibian pet deals, and over 40% were illegal and unregulated (Natusch ET.AL, 2012). For the industry, the illegal pet hunting sector has several advantages. Pet trading has a minimal cost if there is no official regulation. Since amphibians are creatures of the natural world, amphibian dealers do not need to spend money on their care, food, or certification. Because of the significant profit margin for the illegal pet trade, more people join it in an effort to increase their income. The population of wild amphibians is a limited natural resource; thus, if more individuals enter this market while the amphibian population remains the same, the number of amphibians will eventually decline and go extinct.
According to a study on the Chinese frog industry, there are much fewer frogs available for medicinal purposes. The team hypothesizes that a frog’s size may determine whether the pet trade or human consumption impacts it more.
Conclusion
Even though scientists are still arguing whether the sixth mass extinction exists, it is undeniable that a significant number of species are lost due to human influences. Various factors, such as habitat destruction, invasive species, and human consumption, cause species extinction. To determine the most effective strategy for protecting vulnerable species, academia must still investigate a wide range of specific issues and theories.
References
Delord, Julien. (2007). The nature of extinction. Studies in history and philosophy of science, 38(3), 656-667. doi: 10.1016/j.shpsc.2007.06.004
Dueñas, Manuel-Angel ; Hemming, David J. ; Roberts, Amy ; Diaz-Soltero, Hilda. (2021). The threat of invasive species to IUCN-listed critically endangered species: A systematic review. Global ecology and conservation. Elsevier B.V, 26, e01476-. Doi: 10.1016/j.gecco.2021.e01476
LEHTINEN, RICHARD M ; GALATOWITSCH, SUSAN M. (2001). Colonization of Restored Wetlands by Amphibians in Minnesota. The American midland naturalist, 145(2), 388-396. Doi: 10.1674/0003-0031(2001)145[0388:CORWBA]2.0.CO;2
Natusch, Daniel J. D. ; Lyons, Jessica A. (2012). Exploited for pets: the harvest and trade of amphibians and reptiles from Indonesian New Guinea. Biodiversity and conservation, 21(11), 2899-2911. Doi: 10.1007/s10531-012-0345-8
Sodhi, Navjot S ; Bickford, David ; Diesmos, Arvin C ; Lee, Tien Ming ; Koh, Lian Pin ; Brook, Barry W ; Sekercioglu, Cagan H ; Bradshaw, Corey J A. (2008). Measuring the meltdown: drivers of global amphibian extinction and decline. PloS one, 3(2), e1636-. Doi: 10.1371/journal.pone.0001636
Whitfield, Steven M ; Lips, Karen R ; Donnelly, Maureen A. (2016). Amphibian Decline and Conservation in Central America. Copeia, 104(2), 351-379. Doi: 10.1643/CH-15-300
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