Biology » Conservation Biology and Biodiversity » The Biodiversity Crisis

Summarizing the Biodiversity Crisis

Summary

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. The number of described species is estimated to be 1.5 million with about 17,000 new species being described each year. Estimates for the total number of species on Earth vary but are on the order of 10 million. Biodiversity is negatively correlated with latitude for most taxa, 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.

Glossary

adaptive radiation

rapid branching through speciation of a phylogenetic tree into many closely related species

biodiversity

variety of a biological system, typically conceived as the number of species, but also applying to genes, biochemistry, and ecosystems

biodiversity hotspot

concept originated by Norman Myers to describe a geographical region with a large number of endemic species and a large percentage of degraded habitat

chemical diversity

variety of metabolic compounds in an ecosystem

ecosystem diversity

variety of ecosystems

endemic species

species native to one place

extinction

disappearance of a species from Earth; local extinction is the disappearance of a species from a region

extinction rate

number of species becoming extinct over time, sometimes defined as extinctions per million species–years to make numbers manageable (E/MSY)

genetic diversity

variety of genes in a species or other taxonomic group or ecosystem, the term can refer to allelic diversity or genome-wide diversity

heterogeneity

number of ecological niches

megafauna

large animals

species-area relationship

relationship between area surveyed and number of species encountered; typically measured by incrementally increasing the area of a survey and determining the cumulative numbers of species

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