Q.32. Explain types of Biodiversity. Explain
different threats of Biodiversity.
Ans. "Biodiversity"
is most commonly used to replace the more clearly defined and long established
terms, species diversity and species richness. Biologists most often define
biodiversity as the "totality of genes, species and ecosystems of a region".
An advantage of this definition is that it seems to describe most circumstances
and presents a unified view of the traditional types of biological variety
previously identified:
· taxonomic diversity (usually measured at the
species diversity level)
· ecological
diversity often viewed from the perspective of ecosystem diversity
· morphological diversity which stems from genetic diversity
· functional diversity which is a measure of
the number of functionally disparate species within a population (e.g. different
feeding mechanism, different motility, predator vs prey, etc.)
In 2003 Professor Anthony
Campbell at Cardiff University, UK and the Darwin Centre, Pembrokeshire,
defined a fourth level: Molecular Diversity.
Threats: -
In 2006 many species were formally classified as rare
or endangered or threatened; moreover, scientists have estimated that millions
more species are at risk which have not been formally recognized. About 40
percent of the 40,177 species assessed using the IUCN Red List criteria are now
listed as threatened with extinction—a total of 16,119.
Jared Diamond describes an "Evil Quartet"
of habitat destruction, overkill, introduced species and secondary extinctions.
Edward O. Wilson prefers the acronym HIPPO, standing for Habitat destruction,
Invasive species, Pollution, human over-Population and Over-harvesting. The
most authoritative classification in use today is IUCN's Classification of
Direct Threats which has been adopted by major international conservation
organizations such as the US Nature Conservancy, the World Wildlife Fund,
Conservation International and BirdLife International.
Habitat destruction: -
Habitat destruction has played a key role in
extinctions, especially related to tropical forest destruction. Factors
contributing to habitat loss are: overconsumption, overpopulation, land use
change, deforestation, pollution (air pollution, water pollution, soil
contamination) and global warming or climate change.
Habitat size and numbers of species are
systematically related. Physically larger species and those living at lower
latitudes or in forests or oceans are more sensitive to reduction in habitat
area.Conversion to "trivial" standardized ecosystems (e.g.,
monoculture following deforestation) effectively destroys habitat for the more
diverse species that preceded the conversion.
Co-extinctions are a form of habitat destruction.
Co-extinction occurs when the extinction or decline in one accompanies the
other, such as in plants and beetles.
Introduced and invasive
species: -
Barriers such as large rivers, seas, oceans,
mountains and deserts encourage diversity by enabling independent evolution on
either side of the barrier, via the process of allopatric speciation. The term
invasive species is applied to species that breach the natural barriers that
would normally keep them constrained. Without barriers, such species occupy new
territory, often supplanting native species by occupying their niches, or by
using resources that would normally sustain native species.
The number of species invasions has been on the rise
at least since the beginning of the 1900s. Species are increasingly being moved
by humans (on purpose and accidentally). In some cases the invaders are causing
drastic changes and damage to their new habitats (e.g.: zebra mussels and the
emerald ash borer in the Great Lakes region and the lion fish along the North
American Atlantic coast). Some evidence suggests that invasive species are
competitive in their new habitats because they are subject to less pathogen disturbance.
Others report confounding evidence that occasionally suggest that species-rich
communities harbor many native and exotic species simultaneously while some say
that diverse ecosystems are more resilient and resist invasive plants and
animals.
Not all introduced species are invasive, nor all
invasive species deliberately introduced. In cases such as the zebra mussel,
invasion of US waterways was unintentional. In other cases, such as mongooses
in Hawaii, the introduction is deliberate but ineffective (nocturnal rats were
not vulnerable to the diurnal mongoose). In other cases, such as oil palms in
Indonesia and Malaysia, the introduction produces substantial economic
benefits, but the benefits are accompanied by costly unintended consequences.
Finally, an introduced species may unintentionally
injure a species that depends on the species it replaces. In Belgium, Prunus
spinosa from Eastern Europe leafs much sooner than its West European
counterparts, disrupting the feeding habits of the Thecla betulae butterfly
(which feeds on the leaves). Introducing new species often leaves endemic and
other local species unable to compete with the exotic species and unable to
survive. The exotic organisms may be predators, parasites, or may simply
outcompete indigenous species for nutrients, water and light.
At present, several countries have already imported
so many exotic species, particularly agricultural and ornamental plants, that
their own indigenous fauna/flora may be outnumbered. For example, the
introduction of kudzu from Southeast Asia to Canada and the United States has
threatened biodiversity in certain areas.
Genetic pollution: -
Endemic species can be threatened with extinction
through the process of genetic pollution, i.e. uncontrolled hybridization,
introgression and genetic swamping. Genetic pollution leads to homogenization
or replacement of local genomes as a result of either a numerical and/or
fitness advantage of an introduced species. Hybridization and introgression are
side-effects of introduction and invasion. These phenomena can be especially
detrimental to rare species that come into contact with more abundant ones. The
abundant species can interbreed with the rare species, swamping its gene pool.
This problem is not always apparent from morphological (outward appearance)
observations alone. Some degree of gene flow is normal adaptation and not all
gene and genotype constellations can be preserved. However, hybridization with
or without introgression may, nevertheless, threaten a rare species existence.
Overexploitation: -
Overexploitation occurs when a resource is consumed
at an unsustainable rate. This occurs on land in the form of overhunting,
excessive logging, poor soil conservation in agriculture and the illegal
wildlife trade.
About 25% of world fisheries are now overfished to
the point where their current biomass is less than the level that maximizes
their sustainable yield.
The overkill hypothesis, a pattern of large animal
extinctions connected with human migration patterns, can be used explain why
megafaunal extinctions can occur within a relatively short time period.
Hybridization, genetic
pollution/erosion and food security: -
In agriculture and animal husbandry, the Green
Revolution popularized the use of conventional hybridization to increase yield.
Often hybridized breeds originated in developed countries and were further
hybridized with local varieties in the developing world to create high yield
strains resistant to local climate and diseases. Local governments and industry
have been pushing hybridization. Formerly huge gene pools of various wild and
indigenous breeds have collapsed causing widespread genetic erosion and genetic
pollution. This has resulted in loss of genetic diversity and biodiversity as a
whole.
(GM organisms) have genetic material altered by
genetic engineering procedures such as recombinant DNA technology. GM crops
have become a common source for genetic pollution, not only of wild varieties
but also of domesticated varieties derived from classical hybridization.
Genetic erosion coupled with genetic pollution may be
destroying unique genotypes, thereby creating a hidden crisis which could
result in a severe threat to our food security. Diverse genetic material could
cease to exist which would impact our ability to further hybridize food crops
and livestock against more resistant diseases and climatic changes.
Climate change: -
Global
warming is also considered to be a major potential threat to global
biodiversity in the future. For example, coral reefs - which are biodiversity
hotspots - will be lost within the century if global warming continues at the
current trend.
Climate change has seen many claims about potential
to affect biodiversity but evidence supporting the statement is tenuous. Increasing
atmospheric carbon dioxide certainly affects plant morphology and is acidifying
oceans, and temperature affects species ranges, phenology, and weather, but the
major impacts that have been predicted are still just potential impacts. We
have not documented major extinctions yet, even as climate change drastically
alters the biology of many species.
Human overpopulation
From 1950 to 2011, world population increased from
2.5 billion to 7 billion and is forecast to reach a plateau of more than 9
billion during the 21st century. Sir David King, former chief scientific
adviser to the UK government, told a parliamentary inquiry: "It is
self-evident that the massive growth in the human population through the 20th
century has had more impact on biodiversity than any other single factor."
At least until the middle of the 21st century, worldwide losses of pristine
biodiverse land will probably depend much on the worldwide human birth rate.
According to a 2014 study by the World Wildlife Fund,
the global human population already exceeds planet's biocapacity - it would
take the equivalent of 1.5 Earths of biocapacity to meet our current demands.
The report further points that if everyone on the planet had the Footprint of
the average resident of Qatar, we would need 4.8 Earths and if we lived the
lifestyle of a typical resident of the USA, we would need 3.9 Earths.
Q.33. Explain Pyramid, Bell and Urn shape of
population with examples.
Ans. Broad-based Pyramid or Expanding-age
Pyramid: -
In a
rapidly growing population, birth rate is high, and population growth is
exponential. So each successive generation will be more numerous than preceding
one, and the shape of the age structure is like a pyramid.
Bell-Shaped Polygon: -
As the rate
growth of a population slows and stabilises, the reproductive and
pre-reproductive group is the smallest and thus a stable age pyramid or
bell-shaped polygon is formed.
Urn-Shaped Pyramid: -
If the
birth rate is drastically reduced, the prereproductive group decreases in
proportion to the reproductive and post-reproductive groups and thereby, an
urn-shaped pyramid is formed. This type of age pyramid is also known as a
diminshing-age pyramid and it is representation of a that is dying off.
