evolutionary history of tropical forests. geologic eras: a revision
TRANSCRIPT
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Evolutionary history of tropical forests
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Geologic eras: a revision...
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Jurassic135 million years ago
Cretaceous65 million years ago
Triassic200 million years ago
Permian225 million years ago
Present day
The Earth:always changing
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Rainforest distribution under various climate regimes
RAINFOREST FROST LIMITS
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Leaf morphology tells us about past temperature
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mil. yrs
Angiosperm revolution:90 million years ago
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Late Cretaceous: origin of many rainforest plant taxa
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Paleocene: first closed canopy rainforests, in three tropical belts
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Oligocene: after Eocene cooling, rainforests only around the equator
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The sudden warming probably triggered by massive CO2 discharge from ocean
see vents, or deep-ocean gas hydrates?
Paleocene/Eocene thermal maximum: “super greenhouse” distributionof rainforests, resulting in many important dispersal events
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Miocene: “greenhouse” distribution of rainforests in a single wide belt
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Last glacial maximum 16-20,000 yr ago: rainforests fragmented
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Latitudinal extent of tropical rainforest climates is highly variable
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The oldest rainforests:New Caledonia, Madagascar, East Australia
New Caledonia managed to stay in tropicalclimatic zone for the past 70 mil years
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Changes in distribution patterns: Nypa fructicans, one of the oldest contemporary palm species known from fossil records (70 mil years old)
Fossil Nypa roots
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Land bridge between the Americas: 3 million years ago
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Our unstable times: geologically fast changes in temperature and see level
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This and following vegetation maps: Jonathan Adams,University of Adelaide
Closed forest retreat during last glacial maximum
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Vegetation change between last glacial maximum and present
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22-16 ya - glacial maximum
Vegetation change between last glacial maximum and present
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Vegetation change between last glacial maximum and present
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Glacial maximum: SE islands connected with the continent
Old rivers
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Changes in altitudinal zonation from the last glacial maximum
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Colombian Andes
New Guinea East Africa
Changes in the upper forest limitduring late Quarternary
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Continental altitudinal profiles: high elevations in Africa lead to smaller lowland rainforest areas during glacial maximum
The curve shows % of land area below a particular elevation in km
During the last glacial maximum,only 15% of land area in Africa was in the lowland rainforest zone,compared to 35% in S. Americaand 40% in AsiaANDtropical forests in Africa are now the least diverse...
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Byrsonima Curatella
Variable proportion of forests and grasslands in S. America during past 10,000 years [based on pollen analysis]
grasses and sedges
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Forest area changein past 20,000 yrin Africa
pollen from lake sediments
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Do species boundaries correspond to glacial forest refugia?
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Reconstructed species richness maxima [Pleistocene glacial refugia] for butterflies, lizards and birds only partially overlap
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Conclusions:
The present distribution of tropical forests is very recent and most species evolved in different places than those they are facing now.
Current decrease in rainforest area has a recent precedent - during past glacial maximum, only 18,000 years ago.
The present-day rainforest ecosystems are therefore notvenerable finely-tuned systems, but rather hastily assembledmakeshift contraptions.
This last point is well explained in:Daniel H. Janzen (1985) On ecological fitting. Oikos 45: 308.