How many species? 5 - 9 million non-bacterial species estimated Some estimates have ranged up to 100 million because of potential insect diversity 1.5 million cataloged, but many are only descriptions or a museum specimen Number of species reflects a balance between extinction and speciation, the evolution of new species Identification of new species and the confirmation of extinctions also shape estimates of the number of species
Extinctions Lose between 1-5% of species per year Calculations suggest that the current rates of extinction are 100 to 1,000 times natural background levels
Extinctions Rates today in the sixth global extinction event are comparable to the mass extinctions in the geological past – Permian extinctions (225 million years ago) 95% of marine species extinct because of climate change and volcanism – Cretaceous extinctions (65 mya) 70 % of all species, including dinosaurs, due to meteorite impact in Yucatan peninsula of Mexico that resulted in global cooling
Extinction is not necessarily easy to conclude. Sometimes species thought to be extinct are still present in small isolated populations
Extinction There is evidence that contemporary extinctions, while very high, have not been as high as some had predicted, for several reasons: – Effective conservation efforts – Species surviving on their own in secondary habitats and anthropogenic land covers Distinctive patterns to extinctions in the Anthropocene – Faunal homogenization – Faunal size bias
Faunal homogenization Same species present at one location as another Increased numbers of species locally due to human-aided dispersal of generalist species Overall declines in richness over larger extents because specialists and rare species extinct.
Species richness (the number of species) higher today due to generalist species becoming more widely distributed.
Diminished turnover in kinds and numbers of species from location to location for 1951- Present. In graph, size of circle indicates relative similarity in the kinds and numbers of species present. There are more differently sized circles in the earlier period (1896-1950), indicating greater distinctiveness to species and their numbers among the different parks. Today, more of the parks have the same kinds of species. Net overall loss of species over entire region, even though local park diversity has increased over time.
Faunal size bias Defaunation in the Anthropocene is size-specific Large-bodied mammals and birds are more susceptible to extinction
Relatively large, conspicuous species are still being discovered in remote or poorly studied areas. Shown are (a) an undescribed jay species from the Amazon basin, (b) a recently discovered fruit bat and (c) monitor lizard from the Philippines Taxonomic identification of new species
Speciation versus taxonomic identification of new species Speciation is the evolutionary process by which new species arise New species may arise in the Anthropocene, particularly plants as they hybridize New species get counted when they are identified 30,000 to 40,000 taxonomists worldwide 16,000 new species identified per year However, overall there are fewer species being described per taxonomist, suggesting that it may already be harder to discover new species
Extinction versus identification At current rate of identification, if there are 5 million species, then most will have been described by the year 2220 If extinction rates are as high as 5% per decade, then regardless of how many species exist on Earth, more than half will be extinct within 150 years, 2164 At the rates considered more realistic (i.e., <1% per decade) the rate of species description greatly outpaces extinction rates whether there are 2 or 10 million species on Earth.
How many species? Actual extinction rates may become nonlinear if their causes act synergistically. Number of species is a reflection of larger ecological dynamics. Two examples – Extinction debt – Trophic cascades
Extinction debt Lock in of future extinction of species due to human impacts that occurred as some earlier point in time. Time delay between human impact and extinction
Trophic cascade Because of trophic webs, loss or reintroduction of a large predator species can have disproportionately large effects on the abundances of other organisms