Question

1. Describe the various ways extinction rates are measured, in other words how do we estimate the loss of biodiversity on our planet.

2. What are the principal threats to biodiversity? Describe the decline of two species in which multiple threats have contributed to their decline.

Answer 1

Answer for question 1:

An indirect method used to measure biodiversity loss is species-area relationship.

This is by estimating the number of species found in a given area and how the number of species is increasing as the area expands. By this method, and conservation scientists h estimated how species will remain and disappear during habitat loss.

other methods is by measuring Species richness and evenness, Simpson's index and Shannon-Weiner Index before and after habitat loss.

Species Richness -measure of the number of different kinds of organisms present in a particular area.

Each species contributes one count to the total regardless of whether the species population is 1 or 1 million

Species Evenness- measure of the relative abundance of the different species making up the richness of an area.

Evenness can be calculated as: Relative abundance = number of individuals of a species/ total number of individuals

Simpson’s Index - measure of diversity which takes into account both richness and evenness of species.

n = the total number of organisms of a particular species N = the total number of organisms of all species

The value of D ranges between 0 and 1.

With this index, 0 represents infinite diversity and 1 represents no diversity.

The greater the value of D, the lower the diversity&The less the value of D, the higher the diversity.

Shannon-Weiner Index(H)

Mostly used in freshwater ecology

The higher the value, between 0 and logS, the higher the species diversity.

H- logarithamic measure of diversity

Pi - proportion of each species

s- no. of species in a community

Answer for question 2

Threats to biodiversity include Habitat loss and fragmentation, over exploitation, alien species invasions and co-extinction.

HABITAT LOSS AND FRAGMENTATION

1. It is the most important cause of extinction, e.g. The tropical rain forests, once covering 14 per cent of the land surface of Earth, but now they cover only 6 per cent of the land area.
2. The Amazon rain forests (called the ‘lungs of the planet’) are cleared for cultivation of soybeans or are converted into grasslands for raising beef-cattle.
3. The loss of a habitat deprives many animals and plants their homes and they face extinction.
4. Degradation of many habitats by pollution threatens the survival of many species.
5. When a large habitat is broken up into fragments, the populations of mammals and birds with migratory habits or requiring large territories are badly affected

OVER –EXPLOITATION

When ‘need’ turns to ‘greed’, it leads to over- exploitation of natural resources; many species become extinct, e.g. Steller’s sea cow, passenger pigeon, many marine fises became extinct due to over-exploitation by humans.

ALIEN SPECIES INVASION

1. When alien species are introduced in an area, some of them become invasive and may cause extinction of indigenous species, e.g.Introduction of Nile Perch into Lake Victoria (East Africa) caused extinction of more than 200 species of cichlid fish in lake.
2. Invasive weed species such as Parthenium (carrot grass), Lantana and Eichhornia (water hyacinth) causing environmental damage and posing threat to our native species.
3. The illegal introduction of the African catfish (Clarians gariepenus) for aquaculture purposes, is posing threat to the indigenous catfishes in our rivers.

CO-EXTINCTION

1. When a species becomes extinct, the plant and animal species associated with it also become extinct, e.g. When a host fish becomes extinct, its unique parasites also become extinct.
2. Similarly, when one partner of a co-evolved pollitator mutualism becomes extinct, the other partner also have the same fate.

Examples of the decline of two species in which multiple threats have contributed to their decline.

1. Sandplain gerardia:

• Annual hemiparasitic plant . It is a native to Maryland, Massachusetts, Rhode Island, Connecticut, and Long Island, New York.
• Endangered due to habitat loss due to establishment of human settlements in its natural population.
• The second reason is the natural disturbances caused by fire, flood, drought and storm patterns

2. San Joaquin kit fox:

The San Joaquin kit fox was common in california until the 1930s.

Endangered due to habitat loss due to increase in human activities when people began to convert grasslands to farms, orchards and cities.

It's existence was also threatened by pesticides and rodenticides associated with intensive agricultural use and industrial activities.