Download Ecogeographic Rules

Ecogeographic Rules
Outline
• What are “ecogeographic rules”?
• Rules in terrestrial biomes
– Bergmann’s rule
– Allen’s rule
– Gloger’s rule
• Rules in marine biomes
– Jordan’s rule
– Thorson’s rule
Ecogeographic Rules
Variations in the traits of organisms (mainly
morphological) over geographical gradients
Rules in terrestrial biomes
• Bergmann’s rule (body size)
• Allen’s rule (length of appendages)
• Gloger’s rule (color)
Bergmann’s Rule
• Correlates body mass with latitude in animals
(specially vertebrates)
• Body mass increases towards higher latitudes
• Inter and intra-specific
White-tailed deer
Intra-specific variation of Moose (Alces alces) in Sweden
Bergmann’s rule
Hypothesized Causes:
• Thermal independence hypothesis
– Larger animals can withstand harsher climate
conditions than small animals
– Larger animals have larger reserves
Bergmann’s rule
Hypothesized Causes:
• Competition hypothesis
– Interspecific competition favors small body size, but
intraspecific competition favors large body size
– So, small body size is an advantage in high diversity
communities (tropics)
– At high latitudes, diversity & competitive pressure
are low, so larger body sizes favored
Allen’s Rule
Endothermic vertebrates from colder climates have
shorter appendages than closely related species from
warmer climates
Hypothesized cause: Thermoregulation shorter appendages conserve heat and longer
appendages are more effective in dissipating
heat
Rules in marine biomes
• Jordan’s rule (number of vertebrae)
• Thorson’s rule (developmental mode)
Jordan’s Rule
Number of vertebrae in marine fish increases along a
gradient from the tropics to cooler waters at higher
latitudes
Galaxias brevipinnis (salmonoid) populations
How might Jordan’s Rule be related to Bergmann’s Rule?
Hypothesized cause: likely related to a body size
gradient (similar to Bergmann’s rule)
Number of vertebrae is greater in larger fish
Tropical latitudes
Northern latitudes
Thorson’s Rule
• Development mode of marine
invertebrates (pelagic vs. direct
development) influences rate of speciation
• More direct than pelagic invertebrates at
high latitudes
• Higher number of species with direct development at higher
latitudes than in the tropics
• Higher biodiversity of marine invertebrates at higher latitudes
Gradients in predation and morphological
defenses
Shells from lower latitudes tend to be thicker, and more
sculpted, with a thicker lip, smaller opening
Ecogeographic rules summary
• Generality of rules questioned
• All have exceptions
• No definitive explanations on the
mechanisms generating these
patterns, mostly hypothesized
causation