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Lecture 27

NATS 1940 Lecture 27: Mass Extinction Cont'd & Diversity Gradient + Species Diversity Equation

Natural Science
Course Code
NATS 1940
Mark Vicari

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Lect 27:
*Mass Extinctions cont’d & Diversity Gradients:
Species richness:
Diversity declines moving away from the equator
Patterns of Diversity: Latitudinal Gradients
Species richness:
Tropics > Temperate > Polar
Why is there more diversity near the equator than near the poles?
Latitude alone does not account for the observed patterns
Temperature alone was not a good predictor of local species
richness in 2 tests done
Therefore metabolic theory not well supported
More photosynthesis → more plant material → more animals
So what do plants need?
Sunlight is more intense near the equator
Precipitation is higher near the equator
Why the desert has little diversity
Mineral nutrients (available everywhere)
CO2 (available everywhere)
Land area in the tropics may also be a contributing factor
to its high diversity rates
Primary productivity:
The total mass of plants produced per unit area and time via
A better predictor of diversity than latitude or temperature
World distribution of plant productivity:
The energy hypothesis:
Amount of solar energy captured by photosynthesis
( due to water availability and sunlight) accounts for
latitudinal species richness gradient
Temperature and photosynthesis:
Rate of photosynthesis increases with increasing temperature..
up to a point
Max rate of photosynthesis is higher and occurs at a
higher temperature for tropical than temperate plants
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