12: Biodiversity and The Extinction Crisis

Last updated
Save as PDF

Page ID: 103396

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

Figure \(\PageIndex{1}\): Shark fins in Hong Kong. by Cloneofsnake, CC-BY-SA 2.0

Sharks are declining rapidly on a global scale because humans have replaced them as the ocean's top predators. One way that humans hunt sharks is by using a practice called **shark finning**. This is the process of slicing off a shark’s fin and discarding the rest of the still-living body, often by dumping it back into the ocean. Shark fins are tempting targets for fishermen because they have high monetary and cultural value. They are used in a popular dish called shark fin soup, which is a symbol of status in Chinese culture. Approximately 100 million sharks are killed globally each year, and one of the major incentives for this is the shark fin trade. With their slow growth and low reproductive rates, sharks are highly susceptible to extinction, and it is difficult for many shark species to replenish their populations as quickly as they are being diminished.

Biodiversity loss refers to the reduction of biodiversity due to displacement or extinction of species. The loss of a particular individual species may seem unimportant to some, especially if it is not a charismatic species like the Bengal tiger or the bottlenose dolphin. However, biologists estimate that species extinctions are currently many times higher the normal, or background, rate seen previously in Earth’s history. This translates to the loss of tens of thousands of species within our lifetimes. This is likely to have dramatic effects on human welfare through the collapse of ecosystems. Loss of biodiversity may have reverberating consequences on ecosystems because of the complex interrelations among species. For example, the extinction of one species may cause the extinction of another. To measure biodiversity loss, scientists assess which species are at risk of extinction as well as survey ecosystem decline.

Learning Objectives

Define biodiversity
Describe types and patterns of biodiversity.
List reasons why biodiversity is important.
Explain how biodiversity has changed over Earth's history.
Compare the current rate of global extinctions to the average rate observed in the geological record.
Discuss how species are classified into categories based on their extinction risk.

12.1: Value of Biodiversity
Biodiversity is important to the survival and welfare of human populations because it has impacts on our health and our ability to feed ourselves through agriculture and harvesting populations of wild animals. Measuring biodiversity on a large scale involves measuring ecosystem diversity (the number of different ecosystems on Earth), Species diversity (the number of different species in a particular area and their relative abundance), and genetic diversity (a measure of the variability among ind
12.2: Patterns of Biodiversity
Biogeography, the study of the past and present distribution of species around the world, reveals high species richness in the tropics. Most of the world's biodiversity hotspots, which have high species richness and risk of species loss, are concentrated in the tropics. These regions also have many endemic species, which are occur occur locally.
12.3: Extinction
Extinction is the global loss of a species. Five mass extinctions have occurred in geological history, and extinction rates were particular high during these events. Earth is currently experiencing a sixth mass extinction, which is driven by human activities. When mass extinctions are not occurring, extinction still occurs at a low rate, the background extinction rate. The local elimination of a species (extirpation) is also of conservation concern.
12.4: Measures of Biodiversity Loss
A common means of assessing biodiversity loss involves classifying species based on extinction risk. The Red List includes nine such categories. The species at greatest risk of extinction are called critically endangered, followed by endangered, vulnerable, and near threatened species. Biodiversity can also be gauged at the ecosystem level, both in terms of area and ecosystem diversity.