Global pattern of biodiversity
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ByPRANAVATHIYANI GB.Sc Bioinformatics
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Biodiversity is the degree of variation
of life.
This can refer to genetic variation,
species variation, or ecosystem
variation within an area, biome, or
planet.
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ѻ Diversity is a function of
two factors: number of
species (Species
Richness) and number of
specimens belonging to
these species (Evenness).
ѻ Several indices
measuring diversity have
been proposed, giving
more or less weight to
either of these two
factors.
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PATTERN OF DISTRIBUTION
Both species occupy the same tree.(A) Apteryx australis occupies thefloor (B) Rhipidura fuliginosaoccupies the canopy branches
(A)
(B)
MICROHABITAT concept
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Geological history
Climate
Availability of food
Chemistry of Environment
Competition
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Global patterns of terrestrial vertebrate diversity analysed in the study.Each of the 32 bioregions is coloured by its vertebrate species richness (amphibian,reptile, bird, mammal richness combined; dark green represents the lowest valuesand dark red represents the highest values) (Jetz & Fine, 2012)
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Species introduction led to new patterns of distribution
Macropus eugenii was thought to be extinct in
Australia for 100 years. But it has been
rediscovered in an island in New Zealand (2000
species) where a former governor of that country
introduced the species in 1862.
Introduction of mahogany species in the Philippines
led to hectares of biodiversity-dead zones.
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Spatial and temporal isolation leads to
speciation
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Migration constitutes a special kind of dynamic pattern
Ancient human migration patterns as derived from mitochondrial DNA
analysis
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The tropics have the highest species diversity
Latitudinal gradients of species richness for swallow tail butterflies in three parts of the world. (Collin & Morris, 1985)
High species diversity is due to:
a. high productivity and food availability
b. high biomass and hence complex structure
c. past patterns of evolution
d. survival of fragments of habitats through the cold episodes of the last
2 million years.
e. degree of small-scale disturbance mosaic of successional processes
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Diversity involves species richness and evenness and
generally increases during the course of succession
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Species
Regulation
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The patterns of species diversity
in an area or at any one time
are set by some combination of
three factors:
Chance
History and
Necessity.
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Chance: random processes of birth, death and migration. A lizard
might arrive unpredictably on a remote island, for example, because
the log it was on happened to float in the right direction.
History: correlation through time as a function of reproduction. In
other words, if a species was abundant in the near past, chances are
that it will be abundant today. Also, progeny tend to cluster near the
parents, therefore, we tend to find organisms in "pockets" rather than
evenly distributed in space.
Necessity: The laws of growth, competition and interaction.
Different species flourish in different conditions. The number of
species that can coexist will depend on how complex the
environment is and on how strongly they compete with one another.
And, of course, the number of species of herbivores, predators and
parasites will depend on the number of plants, prey and hosts.
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