Ch 6: Mass Extinction & Global Change

Extinction Inevitable Living fossils Rate of extinction not constant 99.9% of species that ever lived have gone extinct Some species changed enough to be considered a new species Others were evolutionary dead ends Living fossils persist, unchanged for millions of years Rate of extinction not constant At least 5 mass extinctions Are we in the middle of the 6th?

History of Life on Earth Prokaryotes 1.9 BYA: Eukaryotes 600 MYA: Cambrian Explosion macroscopic organisms! 5 mass extinctions since then Overall, biodiversity increasing

Cretaceous-Tertiary Extinction 315 mya: the amniotic egg 280 mya: reptiles dominate 65 mya: dinosaurs extinct (except birds), mammals dominate This marks the end of the Cretaceous and the beginning of the Tertiary. Meteorite strike thought to be root cause dust blocks solar radiation tidal waves fires acid rain

Permian Extinction 251 mya Four times as many extinctions as the other mass extinction events only known mass extinction of insects Root cause unknown Meteorite Volcanic activity Continental drift Pangea, unstable climate Drop in sea level dries out shallow marine areas Low oxygen limits terrestrial life to low elevations Hypoxic oceans

Recovery After Extinctions Takes tens of millions of years So while we won’t destroy the planet, we will be extinct before it recovers

Estimate the Rate of Extinction Challenges Hard to be sure a species is extinct Most of the world’s species are undescribed Attempts World Conservation Monitoring Centre Most comprehensive list, ~ 90 species of plant, ~ 726 species of animal Coendangered species ~ those we know little about, but are closely associated with endangered species Species-Area relationship

Species Area Relationship S = CAz S, species; C & z, constants depending on taxa and island set; A, area Combine with an estimate of tropical forest decline Use that to estimate yearly extinction rate

Background Extinction Rate Typical lifespan of a species is one million years, each year 1 of every million species should go extinct if 10 million species, 10 species per year Extinction rate from species-area curve is 27,000 species each year Assuming human population stabilizes between 10-15 billion We may lose between 10-25% of species

Global Climate Change What makes glacial and interglacial periods? Tilt of Earth on its axis 22-25o Shape of Earth’s orbit precession of equinoxes, where in orbit solstices and equinoxes occur Together, a 100,000 year cycle of glacier and inter-glacial periods Other factors solar flares/variation in solar output ocean currents and jet streams presence of glaciers, CO2, greenhouse gases that affect solar radiation (absorbed) and radiant energy (reflected) Variations in global and local trends in temperature

Historic Responses to Climate Change Range shifts toward poles or equator well-documented in fossil record Contract range to refugia, remnant habitat Species tend to respond individually, not by whole-community shifts

Future Climate Currently in an interglacial period The role of CO2 enter an extended, super-interglacial period? The role of CO2 greenhouse gas concentration rising, 30% over pre-industrial levels methane has doubled corresponding rise in temperatures even if CO2 isn’t the culprit, not a bad idea to curtail use of fossil fuels

Adapting to Future Changes Cycles repeat every 100,000 years, biota survived those changes  evidence of adaptability Limits to adaptability populations already stressed by habitat loss, overexploitation… amount of available habitat limited barriers to dispersal including roads, urban areas, agricultural lands Unprecedented changes? Greater increase in temperature geographic bottleneck, can only change range so much mountain-top species Between the devil and the deep blue sea Rate of change too fast mobility, dispersing and sedentary stages, philopatric spp. Range and phenology changes already detected

Between Generational Mobility Key Mobile Between Generations Sedentary Between Generations Mobile as Individuals Migratory birds Insects in ephemeral ponds Pelagic fishes Philopatric migrants Insects in deep lakes Anadramous fishes Sedentary as Individuals Territorial fishes with planktonic larvae Early-successional plants; self-incompatible annuals Intertidal molluscs Desert-spring fishes Late-successional plants; self-compatible perennials Terrestrial molluscs