19 Chapter 47
Learning Objectives
- Define biodiversity and mass extinction
- Recognize threats to biodiversity
- Identify efforts to preserving biodiversity
Conservation Biology and Biodiversity
In many ecosystems, the bottom of the food chain consists of photosynthetic organisms (plants and phytoplankton), called primary producers. The organisms that consume the primary producers are plant eaters, the primary consumers. Secondary consumers are usually carnivores that eat primary consumers. Tertiary consumers are carnivores that eat other carnivores. Higher-level consumers feed on the next lower tropic levels, up to the organisms at the top of the food chain — the apex consumers. Remember, decomposers support the energy cycle by converting dead plants and animals into the elements (CHONPS) that participate in the ecosystem again.
Biodiversity exists at multiple levels of organization and is measured in different ways depending on the goals of those taking the measurements. These measurements include numbers of species, genetic diversity, chemical diversity, and ecosystem diversity. Estimates for the total number of species on Earth vary but are on the order of 10 million. Biodiversity is negatively correlated with latitude, meaning that biodiversity is higher in the tropics. The mechanism for this pattern is not known with certainty, but several plausible hypotheses have been advanced.
Five mass extinctions with losses of more than 50 percent of extant species are observable in the fossil record. Biodiversity recovery times after mass extinctions vary, but have been up to 30 million years. Recent extinctions are recorded in written history and are the basis for one method of estimating contemporary extinction rates. The other method uses measures of habitat loss and species-area relationships. Estimates of contemporary extinction rates vary, but some rates are as high as 500 times the background rate, as determined from the fossil record, and are predicted to rise.
Percent extinction occurrences as reflected in the fossil record have fluctuated throughout Earth’s history. Sudden and dramatic losses of biodiversity, called mass extinctions, have occurred five times.
Humans use many compounds that were first discovered or derived from living organisms as medicines: secondary plant compounds, animal toxins, and antibiotics produced by bacteria and fungi. More medicines are expected to be discovered in nature. Loss of biodiversity will impact the number of pharmaceuticals available to humans.
Catharanthus roseus, the Madagascar periwinkle, has various medicinal properties. Among other uses, it is a source of vincristine, a drug used in the treatment of lymphomas. (credit: Forest and Kim Starr)
Crop diversity is a requirement for food security, and it is being lost. The loss of wild relatives to crops also threatens ability of breeders to generate new varieties. Ecosystems support human agriculture through pollination, nutrient cycling, pest control, soil development and soil maintenance. Loss of biodiversity threatens these supports and risks making food production more expensive or impossible. Wild food sources are mainly aquatic, but few are being managed for sustainability. Fisheries’ ability to provide protein to human populations is threatened when extinction occurs.
Biodiversity may provide important psychological benefits to humans. Additionally, there are moral arguments for the maintenance of biodiversity. The core threats to biodiversity are human population growth and unsustainable resource use. To date, the most significant causes of extinctions are habitat loss, introduction of exotic species, and overharvesting. Climate change is predicted to be a significant cause of extinctions in the coming century. Habitat loss occurs through deforestation, damming of rivers, and other activities. Overharvesting is a threat particularly to aquatic species, while the taking of bush meat in the humid tropics threatens many species in Asia, Africa, and the Americas. Exotic species have been the cause of a number of extinctions and are especially damaging to islands and lakes. Introduction of exotic species increase with increased human mobility and growing global trade. Climate change is forcing range changes that may lead to extinction. It is also impacting resource availability negatively in seasonal environments. Climate changes are greatest in the arctic. Global warming will also raise sea levels, eliminating some islands and reducing the area of all others.
New technological methods such as DNA barcoding and information processing are facilitating our catalog of biodiversity. There is also a legislative framework for biodiversity protection. International treaties such as CITES regulate the transportation of endangered species across international borders. Legislation within individual countries protecting species and agreements on global warming have had limited success. In the US, the Endangered Species Act protects listed species but is hampered by procedural difficulties and a focus on individual species. The Migratory Bird Act is an agreement between Canada and the United States to protect migratory birds. The non-profit sector is also very active in conservation efforts in a variety of ways.
Conservation preserves are a major tool in biodiversity protection. Presently, 11% of Earth’s land surface is protected in some way. The science of island biogeography has informed optimal design of preserves. Climate change will limit the effectiveness of preserves in the future. A downside of preserves is that they may lessen the pressure on human societies to function more sustainably outside the preserves.
Habitat restoration has the potential to restore ecosystems to previous biodiversity levels before species become extinct. Examples of restoration include reintroduction of keystone species and removal of dams on rivers. Zoos have attempted to take a more active role in conservation and can have a limited role in captive breeding programs.
Exercises
Key Takeaways
- Biodiversity can be measured in species, genetic, chemical and ecosystem diversity. Mass extinction events with losses >50% have been described five times in the fossil record.
- Threats to biodiversity include habitat loss and overharvesting.
- Efforts to preserve biodiversity include DNA barcoding, conservation and habitat restoration.
