Biodiversity Sections 18.4. 16.4, and 30.1

Biodiversity The total number of species in a region is known as biodiversity. Besides the number of species, the numbers within each species is important. If one population grows in size and dominates an ecosystem, that ecosystem can lose biodiversity.

Different areas of the world differ in their relative amounts of biodiversity. Why?

E.O. Wilson on Biodiversity TED Presentation

Studying Biodiversity The number of named species falls far behind the estimated number of actual species. Some groups, such as insects are studied far more than others. Why? Notice this is just Eukaryotes!

Estimates vary about the number of species yet to be discovered and named, but it’s clear that we have a long way to go!

Species richness: the number of species in a given area. A species area curve plots the number of species encountered as a function of sampling area size.

Species richness: Often used to describe species within the same trophic level. In many ecosystems, most species are present in small numbers of individuals. Only a few species are present in high numbers of individuals.

Species equitability: another measure of evenness of distribution of individuals among the species in a community. Both of these “ecosystems” are equally diverse. Which is more equitable?

High species diversity is found in tropical rainforests and coral reefs. Why?

Extinction Risks Specialization and resource partitioning increase diversity. However, the tradeoff is that organisms become more vulnerable to extinction if the environment drastically changes.

Localized Distribution By living in a limited area, a population avoids competition with other populations. The risk is that a natural disaster will destroy the limited habitat. The Devil’s Hole Pupfish lives in a single waterhole in Nevada.

Fender’s Blue Butterfly feeds only on Kinkaid’s Lupine. Overspecialization Organisms that have specialized feeding habits reduce competition with other species. If the limited food source goes extinct, so does the species feeding on it. Fender’s Blue Butterfly feeds only on Kinkaid’s Lupine.

Interactions Isolation reduces competition and predation. If a new predator or competitor is introduced, a formerly isolated species may be hunted or out- competed to extinction. Many Hawai’ian birds were driven to extinction by introduced predators.

Habitat Loss The greatest cause of extinction is habitat loss. Organisms with highly specialized habitat needs may avoid competition, but risk extinction if their habitat is threatened. Tropical rain forests are being logged at an alarming rate, mostly for grazing cattle.

Humans and Biodiversity Humans change ecosystems: deforestation, use of land for farming, pollution, altering rivers, and more. Habitat destruction reduces biodiversity. Ecosystems also impact humans: Loss of forests, farmland, clean water, flood protection, and more can directly impact human life.

Habitat destruction worldwide threatens – or may have destroyed – many species that have not even been named. Recent discoveries of new mammal species have found the animals already on the brink of extinction.

Ecosystem services Directly used substances • food plants and animals • building materials • fiber and fabric materials • fuel • medicinal plants • oxygen replenishment Indirect, beneficial services • maintaining soil fertility • pollination • seed dispersal • waste decomposition • regulation of local climate • flood control • erosion control • pollution control • pest control • wildlife habitat • repository of genes “Ecosystem services” are direct and indirect benefits humans receive from the environment.

Humans have directly benefitted from biodiversity. Drugs derived from plants and animals.

A diverse ecosystem yields a diversity of foods. Forest mushrooms Tropical fruits Andean Potatoes A diverse ecosystem yields a diversity of foods.

Modern agriculture relies on vast monocultures of crop plants; the exact opposite of diversity. Monocultures are easier to harvest, but more vulnerable to diseases and pests than mixed crops.

Permaculture and mixed-crop agriculture supports a diverse soil food web, which supports the crops. These methods tend to be more labor-intensive.

Humans also benefit indirectly from intact, diverse ecosystems. Natural rivers meander, creating a richly diverse wetland ecosystem.

Channelizing rivers, reducing wetlands, and cutting down trees along rivers changes the ecosystem. Loss of wetland diversity means loss of species. Sediments that would be deposited along the river system and in islands around the mouth of the river flows straight out to sea.

New Orleans was once protected by the many islands in the Mississippi Delta. Much of the sediment that built those islands now runs out to the sea. The islands have eroded, leaving less protection against hurricanes.

Recap Biodiversity refers to the number of different species in an ecosystem. Measures of biodiversity also take into account the relative population sizes of different species. Humans have a powerful effect on the biodiversity of many ecosystems. Loss of biodiversity can affect humans in turn.