Asked by Bob
Explain why entering an interglacial period resulted in an increase in biodiversity on Earth.
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An interglacial is a warm interval between ice ages. Entering an interglacial increases biodiversity for several linked reasons:
- More and larger habitable area: Ice sheets retreat, exposing vast new land (and shallow continental shelves when sea level changes), so more area is available for plants and animals to colonize.
- More and more varied habitats: Deglaciation creates a patchwork of soils, wetlands, rivers, lakes, forests and coastal environments. Greater habitat heterogeneity supports more species and more ecological niches.
- Greater primary productivity and energy flow: Warmer temperatures, longer growing seasons and higher atmospheric CO2 raise plant productivity. More energy at the base of food webs supports larger populations and more trophic complexity.
- Population expansion and reduced extinction risk: Warmer conditions allow many populations to expand their ranges and increase in size, lowering local extinction probability and permitting species persistence.
- Increased opportunities for speciation and diversification: Range shifts, fragmentation into refugia during the previous cold period, and subsequent secondary contact during warming produce genetic divergence, hybridization and novel selection pressures that can foster speciation and adaptation.
- Expansion of productive marine habitats: Rising sea levels and warmer seas expand shallow marine habitats (estuaries, reefs, continental shelves) that are hotspots of marine biodiversity.
- Greater climatic stability and specialization: Relatively stable, warm conditions favor the evolution of specialized interactions (e.g., coevolutionary relationships) that increase community complexity and species richness.
(There are caveats: some groups—notably many Pleistocene megafauna—declined or went extinct around the last deglaciation, often because of human impacts. But overall the net effect of interglacial conditions is to raise global productivity, habitat diversity and capacity for species diversification, leading to higher biodiversity.)
- More and larger habitable area: Ice sheets retreat, exposing vast new land (and shallow continental shelves when sea level changes), so more area is available for plants and animals to colonize.
- More and more varied habitats: Deglaciation creates a patchwork of soils, wetlands, rivers, lakes, forests and coastal environments. Greater habitat heterogeneity supports more species and more ecological niches.
- Greater primary productivity and energy flow: Warmer temperatures, longer growing seasons and higher atmospheric CO2 raise plant productivity. More energy at the base of food webs supports larger populations and more trophic complexity.
- Population expansion and reduced extinction risk: Warmer conditions allow many populations to expand their ranges and increase in size, lowering local extinction probability and permitting species persistence.
- Increased opportunities for speciation and diversification: Range shifts, fragmentation into refugia during the previous cold period, and subsequent secondary contact during warming produce genetic divergence, hybridization and novel selection pressures that can foster speciation and adaptation.
- Expansion of productive marine habitats: Rising sea levels and warmer seas expand shallow marine habitats (estuaries, reefs, continental shelves) that are hotspots of marine biodiversity.
- Greater climatic stability and specialization: Relatively stable, warm conditions favor the evolution of specialized interactions (e.g., coevolutionary relationships) that increase community complexity and species richness.
(There are caveats: some groups—notably many Pleistocene megafauna—declined or went extinct around the last deglaciation, often because of human impacts. But overall the net effect of interglacial conditions is to raise global productivity, habitat diversity and capacity for species diversification, leading to higher biodiversity.)
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