Patterns of Speciation Diversify in Bursts (punctuational) Diversify slowly (gradual) Time No...
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Transcript of Patterns of Speciation Diversify in Bursts (punctuational) Diversify slowly (gradual) Time No...
Patterns of Speciation
Diversify in Bursts(punctuational)
Diversify slowly(gradual)
Tim
e
No diversification(living fossil)
Evolutionary Changes
XX X
X
X = extinction
Adaptive Radiation
Adaptive Radiation
An adaptive radiation is a clade (group of related species) that has evolved into numerous, diverse forms
What causes adaptive radiations?
Pioneering a new habitat containing few competing organisms– remote islands, isolated large lakes
What causes adaptive radiations?
Mass extinction wipes out competitors• There have been 5 major catastrophic mass extinctions• The last is associated with the final extinction of
dinosaurs• Surviving forms radiate to occupy ‘niches’ left vacant
by the extinct forms • e.g. Radiation of mammals after extinction of
dinosaurs
What causes adaptive radiations?
Evolution of a key innovation• birds radiate after the evolution of flapping
flight• Angiosperms (flowering plants) radiate after
the evolution of reproduction via flowers
Why are there ‘living fossils’?
Organisms may be ‘well-adapted’, but there is little room for evolutionary change because of competitors or environmental constraints
Evolutionary Trends
• Little change in the number of phyla (higher taxonomic levels) in the last 500 million years
• The number of species has been steadily increasing (despite set-backs caused by mass extinctions)
Evolutionary TrendsConvergences are common - independent
radiations come to resemble each other Australia, South America & North America
evolved similar grazers, browsers & saber-toothed ‘cats….. All from different ancestors
Evolutionary Trends
Repeated patterns sometimes acquire names:
• Cope’s rule: Members of a clade tend to get larger in evolutionary time
• Bergman’s rule: Organisms get larger at higher latitudes (toward the poles)
• Islands: Large animals evolve to be smaller (dwarf elephants), Small animals evolve to be larger (giant tortoises)
Evolutionary Trends
Much of the diversification of species seems to be related to …..
(1) Arms Races (Red Queen): plants vs. herbivores vs. carnivoresgrass vs. horses, crabs vs. snails
(2) Mutualisms: flowering plants + pollinators + seed dispersers