Major Threats to Biodiversity by Human Activities (Simple, Easy Ecology Lecture Notes)


Causes of biodiversity loss degradation

‘It is that range of biodiversity that we must care for – the whole thing –
rather than just one or two stars’

David Attenborough


What are major threats to biodiversity?

Major threats to biodiversity are:

1.  Habitat destruction/Deforestation

2.  Introduced and invasive species

3.  Genetic pollution

4.   Over exploitation

5.   Hybridization

6.   Climate change

7.   Diseases

8.   Human over-population

(1). Habitat destruction/Deforestation:

Ø  Habitat destruction and deforestation has played a key role in extinction

Ø  Habitat loss occurs when natural habitats are modified for human needs

Ø  Factors causing habitat destruction are: Over-population, Deforestation, Pollution and Global warming

Ø  Habitat size and number of species are systematically related

Ø  Physically larger species and those living at lower latitudes or in forests or oceans are more sensitive to reduction in habitat area

Ø  Major reasons for habitat destruction are: Large scale industrial and commercial activities, Mining, Cattle rearing, Commercial fishing, Plantation cropping & Agriculture, Dam construction and Encroaching

Ø  Habitat loss can leads to habitat fragmentation

Ø  Habitat fragmentation: large natural habitats were get fragmented by human construction activities

Ø  Habitat fragmentation is very critical for large and territorial animals such as elephants

Ø  The breeding behavior of these animals are strongly depends on the size of the habitat they lives

Effect of Eichornia on Environment and Biodiversity

Eichornia overgrowth over the water body

(2). Introduced and invasive species:

Ø  Large barriers such as mountains, or seas support diversity in the area surrounded by these barriers

Ø  This is by enabling independent evolution by allopatric speciation

Ø  Invasive species: species that breach the natural barriers that would normally keep them away

Ø  Invasions therefore can reduce diversity

Ø  Invasive species eliminate native species by:

@. Occupying their niches

@. By using resources of native species

@. By competing with native species

@. Causing diseases to native species

 (3). Genetic pollution:

Ø  Endemic species can be threatened through the process of genetic pollution

Ø  Genetic pollution occurs by the uncontrolled hybridization

Ø  Genetic pollution causes: homogenization the genome of individuals and replacement of local genomes

Ø  Hybridization is the side-effects of introduction and invasion

Ø  Genetic pollution is more detrimental to rare species that come into contact with more abundant ones

Ø  Abundant species immediately colonize new areas by vanishing the rare species

(4). Over exploitation

Ø  Over exploitation occurs when a resources are consumed at an unsustainable rate

Ø  Over exploitation of biodiversity occurs in the form of (1). Overhunting, (2). Excessive logging, (3). Poor soil conservation in agriculture, and (4). Illegal wildlife trade

Ø  Illegal wildlife trade is the “largest threat” to biodiversity in Asia

Ø  25% of world fisheries are now overfished to the point where their current biomass is less than the sustainable mass

(5). Hybridization: (fusion of unrelated plants)

Ø  Green Revolution popularized hybridization for increased yield

Ø  Hybrid breeds originated in developed countries further hybridized with local varieties in developing countries

Ø  This is to create high yield strains resistant to local climate and diseases

Ø  High yielding breeds causes genetic erosion and gene pollution in wild species

Ø  Genetic erosion and genetic pollution may destroy unique genotypes

Ø  This creates a hidden crisis which could result in a severe threat to our food security or health

(6). Climate change:

Ø  Global warming is one of the major threat to global biodiversity

Ø  Coral reefs (biodiversity hotspots) will be lost in 20 to 40 years if global warming continues at the current trend

Ø  Carbon dioxide concentration in atmosphere affects morphology of plants

Ø  Higher carbon dioxide concentration acidify oceans

Ø  In 2004, an international collaborative study on four continents estimated that 10% of species would become extinct by 2050 due to global warming

Ø  Climate change induces change in raining pattern

Ø  Climate change also affects migratory animals and birds

Ø  Biodiversity in polar and mountain region are more vulnerable to climate changes

(7). Diseases:

Ø  Diseases can eliminate species from earth

Ø  The cause of disease may be natural or anthropological

Ø  Human activities sometimes speedup the severity of natural diseases

Ø  Introduced species may carries pathogens along with them

Ø  Viral epidemics in animals is major threat to biodiversity

Ø  Animals are more prone to disease than plants

Ø  Animals in captivity are also prone to diseases

Countries by Population Density in 2015

Click on the image for details (Source wikipedia)

(8). Human over-population:

Ø  World population (as of July, 2015) is 7.3 billion

Ø  In 1950 the population was 2.5 billion

Ø  Population will reach 9 billion during the 21st century

Ø  Increase in population leads to over exploitation of resources

Ø  Forest area will be reduced in the future

Ø  Population increase ultimately cause pollution increase

Ø  Population explosion thus form the prime factor biodiversity depletion

Ø  Population increase can cause the other 7 main threats of biodiversity mentioned above


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