Field studies consist of manual counts of animals in the wild followed by the creation of species lists. Local wildlife officials in national parks and university research teams usually do the counting and they compile the data from the study areas to build a picture of species distribution in a habitat or across larger regions such as counties and states.
Species counts provide valuable information on areas containing a high degree of biodiversity, as well as areas with little biodiversity. Areas having the greatest biodiversity are called hotspots, and these places have drawn worldwide interest as the most critical for protection. Species counts also help biologists determine the effects of habitats damaged by reduction in size, fragmentation, pollution, and other forms of destruction.
Two methods provide biologists with useful information in addition to that received by manual counts. The first method, camera surveillance, enables scientists to observe animals that live secretive lifestyles or in remote places. The Wildlife Conservation Society currently has set up 15 cameras in northeastern Cambodia along trails used by rare Asian tigers. As an animal passes between paired cameras, it breaks a detection beam and triggers the cameras. (Two cameras are used for each tiger because tiger stripes are not symmetrical and the combined images from each
flank help researchers identify individual animals.) Despite this high-tech approach to species monitoring, cameras have caught only one tiger, but the project leader Ed Pollard dreams of the time when the tiger’s habitat is sufficiently preserved to sustain a population. “In twenty years,” he said in 2007 to the Associated Press, “people will come here and drive along the road and there’s a distinct chance there’ll be a tiger trotting along in front of you.” This of course represents the goal of every conservation project.
The second method, fossil records, provides fewer technological results than remote-controlled cameras but offers a historical view of species rise and decline. Fossils give evidence of ancient organisms as well as a physical description of these organisms. Fossil records do not, however, give scientists all the information they need today about biodiversity becaus today’s available fossil records may represent only about 1 percent of the species that have ever lived on Earth.
Global mapping techniques are used for building databases on plant diversity, which in turn provide clues to the likely animal diversity in specific habitats. Any confined study area may be mapped by combining field study data with high-resolution satellite images. On a larger scale, global plant diversity mapping depends on statistics to predict where biodiversity is rich and where it is scant.
Despite the varied manual and technological means of assessing biodiversity, putting a quantitative value on biodiversity remains a difficult task, and no single method does the entire job. For this reason the Convention on Biological Diversity introduced in 2005 a tool for describing biodiversity in a single, standard manner. This BII quantifies the abundance of a diverse population relative to a well-studied reference species. The BII requires only a few weeks to gather data, compared with previous databases on species that have taken decades to compile. Biologists then calculate an index value as a percentage and using three pieces of information: the current way an ecosystem is being used (wilderness, agriculture, ranching, etc.), the area of the land being measured, and the species richness in that area. Using the grasslands of Kansas as a hypothetical example, a BII of 80 percent means that, when averaged
against all plant and animal species in the region, Kansas’s grassland populations have declined to 80 percent of their preindustrial (about the year 1800) numbers.
The BII assesses general trends in biodiversity rather than exact values, so that biologists learn about functional groups like insect-eating birds, small burrowing mammals, large grazing mammals, or rain forest amphibians. The BII also takes into account the types of human activities on the land, which of course greatly impact the status of the species living in the region. In summary, the BII indicates where biodiversity is disappearing the fastest and where it might be increasing.
The BII may soon supplement the information already gained from field studies, fossil records, and mapping. To date, these methods have together shown the following trends in biodiversity:
- Populations have declined 84 percent since the preindustrial period.
- Mammals declined the most in this period, 71 percent.
- Species associated with a specific habitat declined the most, 26 percent, in grasslands.
- Ninety percent of habitat loss leads to the extinction of about 50 percent of the habitat’s species.
- Greatest biodiversity losses in Africa are in countries with the continent’s greatest population density: Lesotho and Swaziland.
Georgina Mace, director of science at the Institute of Zoology in the United Kingdom, explained to Nature magazine in 2005, “Biodiversity assessments need to move away from species lists and species extinction rates, because often the existence and proximity of local [human] populations matters more. [The] biodiversity intactness index makes a start in satisfying many requirements and provides a robust, sensitive and meaningful indicator.” For this reason comprehensive indicators such as the BII give the best picture of biodiversity losses and gains.
