Biosphere Lecture 4

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Biogeography
Is the science that attempts to document and understand spatial patterns of biological diversity (from genes to communities and ecosystems).
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Factors affecting the distribution of species
Climate Topography Interactions with other species Humans
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Main Earth Terrestrial Biomes
A biotic community extending over a large geographical area that presents similar climatic and abiotic conditions
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Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a large area, creating a typical ecosystem over that area. Such major ecosystems are termed as
biomes.
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Polar desert can seem
lifeless
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Tropical rainforest is
full of life
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Controls on plant productivity
Climate affects productivity In general productivity is positively related to temperature, water and light. All tend to be high in the tropics and low at high latitudes
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Climatic Variables control biome distribution
Air Temp, Precipation , Net radiation
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Bioclimatic variables are derived from the
monthly temperature and rainfall values in order to generate more biologically meaningful variables.
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BIOCLIMATIC variables control biome distribution:
Precipation , runoff/water surplus and soil moisture
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Bioclimatic variable: seasonality
Increases with latitude Increases with distance from sea (continentality) In parts of Siberia, there is a 60oC difference between average January and July temperatures
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PAR
– photosynthetically active radiation
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Holdridge life zones system (1947)
a global bioclimatic scheme for the classification of land areas The system has found a major use in assessing the possible changes in natural vegetation patterns due to global warming
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Theory of Island Biogeography
Kill all the animals on an island Allow island to be re-colonised Number of species reaches a predictable equilibrium
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Theory of Island: is a field within biogeography that examines the factors that affect the species richness of isolated natural communities. The theory was originally developed as
island biogeography
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Biogeography or Island Biogeography is used in reference
to any ecosystem (present or past[2]) that is isolated due to being surrounded by unlike ecosystems, and has been extended to mountain peaks, oases, fragmented forest, and even natural habitats isolated by human land development.
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Species richness of an island depends
on its size and isolation MacArthur & Wilson (1960s)
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The rate of extinction once a species manages to colonize an island is affected by island size; this is the
species-area curve or effect
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rescue effect.
Populations on islands that are less isolated are less likely to go extinct because individuals from the source population and other islands can immigrate and "rescue" the population from extinction
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target effect
Species may actively target larger islands for their greater number of resources and available niches; or, larger islands may accumulate more species by chance just because they are larger
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Approximately, if area increases by a factor of ten the number of species
doubles
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Positive relationship between biodiversity and
temperature
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Positive relationship between biodiversity and
precipitation
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Number of species declines with
altitude
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Number of species peaks at low
latitudes (the tropics)
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Tropics are a larger proportion of
the Earth’s surface than any other region
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10-fold change in area =
double the number of species
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High latitude ecosystems are
younger
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These high latitude ecosystems have undergone repeated re-colonisation after
ice-age events
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There has been more time for speciation in tropics however
Climate change may have created opportunities for speciation rather than caused extinctions
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In the history of the Earth, there was more land in the
tropics
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Higher productivity can support more
trophic levels
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High temperatures in the tropics led to :
Faster metabolic rates Shorter generation times More generations, so more evolution
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Climate envelope is the range of climatic conditions that a species is found in
Temperature Precipitation
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Conditions species experiences in tropics are
more constant
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Constant climate in tropics results in:
Species adapt to local conditions - niches Species ranges can be small (low tolerance) Do not need to migrate = reduces gene flow
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Impacts on dispersal rates
‘Mountain passes are higher in the tropics’ Daniel Janzen (1967) Local adaptation may reduce the ability of organisms to disperse Small change in conditions could result in a species being at a disadvantage compared with a species that already lives
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Why are there more species in the tropics?
Speciation rates are high and extinction rates are low
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Card 2

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Factors affecting the distribution of species

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Climate Topography Interactions with other species Humans

Card 3

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Main Earth Terrestrial Biomes

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Card 4

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Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a large area, creating a typical ecosystem over that area. Such major ecosystems are termed as

Back

Preview of the front of card 4

Card 5

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Polar desert can seem

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