Human activities and Biodiversity T

2 Human activities and Biodiversity

There are three general levels of biodiversity on earth. Ecosystem diversity is the variation within and between ecosystems. Species diversity is the number of species that exist in an area. Genetic diversity is the variation in the genes within a population of organisms.

In this activity, you will look at some examples of how human activities have altered the biodiversity of groups of taxa. Taxa (singular taxon) are levels of classification, for example species or genus.

Challenge

00 How do humans alter the biodiversity of groups of taxa?

Human Activities that Affect Biodiversity

habitat destruction

Humans change natural habitats through such activities as agriculture, building, mining, forestry, and pollution.

introduced species

Humans intentionally or accidentally move species from their native locations to new areas. When an introduced species causes or is likely to cause harm to the environment, the economy, or human health, the species is considered an invasive species.

o v e r e x p l o i tat i o n

Humans harvest animals or plants for ecosystem services, such as for food, medicine, lumber, collecting, and trading. The harvesting is considered overexploitation when the rate of harvest exceeds the ability of the population to recover.

Clearcutting of the Zambian rainforest.

422

Japanese beetles were accidentally introduced into the United States in 1916, and have since been severely destructive to turfgrass and ornamental plants.

So many striped narrow-headed softshell turtles have been taken from the wild for food and the international pet trade that natural populations are at risk.

HuMan activitieS and BiodiverSity ? activity 2

Procedure

1. In your science notebook, copy the following chart. Give it an appropriate title.

Scenario

Type(s) of human impact

Type(s) of biodiversity altered

2. Follow your teacher's directions for which scenario(s) to read.

3. Work by yourself to read your assigned scenario(s). As you read, fill in the columns on the chart.

4. In your group, take turns summarizing your assigned scenario(s). As you listen, fill in the columns on the chart for each scenario that you did not read.

disruption of networks

Ecosystems encompass a network of interdependent interactions. If the population of one species declines or goes extinct, that affects others in the network. An example of a network that could be disrupted is a food web.

breeding and cloning

People breed and clone populations of other organisms for various purposes. In doing so they might, for example, decrease genetic diversity in species of edible plants to create uniformly desirable crops.

A harmful algal bloom causes illness or death in fish, seabirds, marine mammals, and humans who eat seafood contaminated with a neurotoxin from the algae. Algal blooms also reduce the oxygen levels in bodies of water.

A geneticist checks an ear of experimental corn for genetic changes.

423

Science & Global iSSueS/bioloGy ? evolution

Vast amounts of rainforest in Borneo were cleared to plant oil palm trees.

The Rainforests of borneo

From an airplane above the island of Borneo, you can see the sudden divide between the rainforest and the straight rows of oil palm trees that have displaced the forest.

Borneo is a large island of more than 427,000 sq km (165,000 sq mi) between the South China and Java seas. On it are more than 15,000 known species of plants and some of the tallest tropical rainforests in the world. The rainforests are filled with an array of animals, including some that glide as they leap from tall trees, such as flying lizards, flying frogs, and flying snakes. Two species of gibbons and eight species of monkeys inhabit and climb in the trees. Sun bears, clouded leopards, elephants, orangutans, and rhinoceroses also live in and roam the rainforest. Even today scientists continue to discover species on the island that were never seen by other scientists before.

The greatest threat to the biodiversity of Borneo is forest destruction. Over the past two decades, approximately 40 million acres of forest have been cleared. Parts of the forests were cleared to plant palm trees, the fruits of which produce oil for cooking, body lotions, and fuel. The forests have also been extensively logged for timber to use for building and making paper. At the rate at which the forests of Borneo are being cut, the risk of current and future loss of biodiversity on the island is high.

The Potato in ireland

After the potato was brought to Ireland from Spain in the 17th century, the Irish found they could grow more food in a smaller area with less labor when they planted just one variety: the lumper potato. That potato turned out to be a good source of nutrition and became a staple crop for Irish peasants. Like other living organisms, however, the potato is susceptible to microbes that cause disease, and lumpers are particularly susceptible to the fungus Phytophthora infestans, which causes potato blight. Making the Irish food supply more vulnerable, the lumper

424

HuMan activitieS and BiodiverSity ? activity 2

In Ireland in the 1800s, potato blight killed whole crops of geneti-

cally identical lumper potatoes, causing widespread famine.

potatoes were all genetically identical to each other. In 1845, spores of the potato blight fungus were carried by the wind from England. A putrid stench hit the air as entire fields of potatoes died in just a few days.

While the potato blight reached all of Europe, only Ireland experienced devastating famine and suffering. One in eight Irish people died in three years.

Cichlids and nile Perch

Within the last 200,000 years in Africa's huge Lake Victoria,

a

more than 300 species of cichlid fish evolved to live in the

various habitats in the lake. Some cichlids, such as tilapia,

are edible, and some larger species are popular sport fishing

prey. Genetic evidence suggests that the cichlids evolved

from a common ancestor.

In the 1950s, the British government introduced the large Nile perch into the lake with the idea that the perch would provide the local people with a new protein source and a new commercial fishery.

Unfortunately, the perch ate the cichlids and other fish. Because cichlids were also fished along with the perch, introducing the perch appears to be the reason for the extinction of as many as 200 species of cichlids and the decline of other fish, such as catfish and lungfish.

b

When the Nile perch (a) was introduced into Lake Victoria, they ate the cichlids (b) and other fish that lived there.

425

Science & Global iSSueS/bioloGy ? evolution

In a further threat to the lake's biodiversity, the loss of the cichlid species that ate algae allowed the amount of algae in the lake to rise. Because algae consume oxygen, their abundance made it difficult for other small plants and animals in the lake to get enough oxygen for themselves. The Lake Victoria ecosystem is adjusting to these changes, but will not likely reach the level of biodiversity that existed before the introduction of Nile perch.

The dodo bird

The small Indian Ocean island of Mauritius was once home to populations of the large, flightless dodo bird, which had evolved over several million years on the island. Mauritius is isolated, and because they had little competition from other organisms the dodos had freely fed on fruit that had fallen to the ground. Those dodos with the ability to store large amounts of fat in times when food was scarce were better able to survive and reproduce. Eventually, over generations, the dodos increased in size. Flightlessness also evolved. As plant eaters in an environment with no predators, the inability to fly would have had no effect on the dodo's ability to survive. In the 16th and 17th centuries, Portuguese and Dutch explorers sailed to the island. The flightless dodos could not flee from humans who hunted them for food and for their eggs. The sailors also brought with them pigs, monkeys, and rats that fed on the dodos' eggs and chicks, and perhaps even adult dodos. On a small island, the relatively small dodo population could not survive under these changed conditions. In a small population, the genetic diversity of the population is relatively low. When genetic diversity is low, there is a low probability that any individual in the population will have the trait(s) required for survival and reproduction if the environment changes. Eighty years after humans arrived, dodos became extinct.

Dodo fossil bones confirm that the bird was flightless.

426

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download