Transcript Extinctions
THE REAL WORLD... Context for extinction How many species are there? How do we find out? Context for extinction 1. Extrapolate numbers based on observation that for every temperate species, there are two tropical counterparts = 3-5 million. 2. Use information on rate of discovery of new species to project forward, group by group = 6-7 million. 3. Species size:species richness relationship – in terrestrial animals (~ 1 cm to a few meters), approximate empirical rule for each 10-fold reduction in length there are 100 x the number of species = 10 million. 4. Do intensive counts in small areas of each taxa, extrapolate to rest of available habitat Estimates of beetle species richness (more than 1000 species recorded in one tree) in the canopies of tropical trees (about 50,000 species), and assumptions about the proportion of non-beetle arthropods that will also be present in the canopy, plus others that do not occupy the canopy – 30 million arthropods. http://www.youtube.com/watch?v=gZRgibEVXJU Total Phylum Order E&T Chordates Mammals 361 Birds 316 Reptiles 124 Amphibians 35 Fishes 165 Arthropods Insects 71 Crustaceans 22 Plants Flowering plants 783 Conifers and cycads 5 Ferns and allies 30 Molluscs 126 Cnidaria Corals 2 # Described species 5,702 9,956 9,347 15,000 40,000 1,065,000 40,000 272,655 980 13,025 70,000 2,175 Total Phylum Order E&T Chordates Mammals 361 Birds 316 Reptiles 124 Amphibians 35 Fishes 165 Arthropods Insects 71 Crustaceans 22 Plants Flowering plants 783 Conifers and cycads 5 Ferns and allies 30 Molluscs 126 Cnidaria Corals 2 Viruses 0 Bacteria 0 Protists 0 Fungi 0 Platyhelminthes 0 Rotifera 0 Bryozoa 0 Nematoda 0 # Described species 5,702 9,956 9,347 15,000 40,000 1,065,000 40,000 272,655 980 13,025 70,000 2,175 5,000 4,750 80,000 80,000 25,000 1,800 5,000 25,000 Total Phylum Order E&T Chordates Mammals 361 Birds 316 Reptiles 124 Amphibians 35 Fishes 165 Arthropods Insects 71 Crustaceans 22 Plants Flowering plants 783 Conifers and cycads 5 Ferns and allies 30 Molluscs 126 Cnidaria Corals 2 Viruses 0 Bacteria 0 Protists 0 Fungi 0 Platyhelminthes 0 Rotifera 0 Bryozoa 0 Nematoda 0 # Described % species Described 5,702 99 9,956 99 9,347 99 15,000 99 40,000 75? 1,065,000 12 40,000 ? 272,655 55 980 1 13,025 87 70,000 35 2,175 ? 5,000 1 4,750 0.5 80,000 5 80,000 5 25,000 ? 1,800 ? 5,000 ? 25,000 ? How many species are there?? http://ocean.si.edu/oceancensus So far, the Census of Marine Life comprised 15,304 species of fish and 194,696 to 214,696 species of animals and plants, estimated to be roughly 10 percent of the world's total. The census is adding about 150 to 200 species of fish and 1,700 species of animals and plants each year. Total Endangered & Threatened Species US Foreign Total Mammals Birds Reptiles Amphibians Fishes Molluscs Insects Arachnids Crustaceans Corals Animal totals 85 93 36 26 153 123 67 12 22 2 619 276 223 88 9 12 3 4 0 0 0 615 361 316 124 35 165 126 71 12 22 2 1,234 Flowering plants 782 Conifers and cycads 3 Ferns and allies 30 Lichens 2 Plant totals 817 1 2 0 0 3 783 5 30 2 820 Grand totals 1,436 618 2,054 Context for extinction How many species are there? How do we find out? How many have recently gone extinct? Are current rates of extinction higher than historic (pre-human) rates? Trends in recorded animal species extinctions since 1600, for which a date is known • All extant species will become extinct eventually – more than 99% of species that ever existed are now extinct. • Individual species last on average 1- 10 million years. If we assume 10 million species, we would then predict 100 to 1000 extinctions each century. • Current rate: birds and mammals = 1% per century (100-1000 x background rate). Nene - Branta sandvicensis Extinction: happens to all species eventually Extinction stochastic results from normal, random changes; more important for smaller populations conservation solution: maintain large population sizes deterministic consequence of some progressive change in environment - addition of predator, loss of food source, degradation/loss of habitat conservation solution: identify and manage causes Extinction Probability of extinction increases as population size decreases Probability increases with length of time Extinction higher probability per unit time for species with: • • • • • smaller range fewer subpopulations low migration among subpopulations highly stochastic environment low genetic diversity? Extinction primary species of concern tend to be large animals • • • • no clonal propagation long generation time small number of progeny low dispersal rates – inability to recolonize or escape catastrophic events • species in stable environments Causes of extinction Population extinctions occur due to: • intrinsic factors – demographic stochasticity – changes in sex ratio, reproduction, survival Causes of extinction Population extinctions occur due to: • intrinsic factors – demographic stochasticity – changes in sex ratio, reproduction, survival Allee effect - threshold density or N below which population goes to extinction • due to social interactions, physical alterations of environment, probability of finding a mate, etc. stanfordalumni.org Causes of extinction Population extinctions occur due to: • intrinsic factors – demographic stochasticity – genetic stochasticity - founder effect, genetic drift, inbreeding – genetic load Causes of extinction Population extinctions occur due to: • intrinsic factors – demographic stochasticity – genetic stochasticity • extrinsic factors – environmental stochasticity • variation in predators, pathogens, food supply (biotic) – catastrophe • fires, floods, droughts (abiotic) 900 Heath hen extinction, Martha's Vineyard 800 700 N 600 500 400 N ~ 50 refuge established fire reduces habitat, followed by heavy goshawk predation and severe winter 1927, N =13, mostly males 300 200 disease 100 1932 extinction 0 1900 1903 1906 1909 1912 1915 1918 1921 1924 1927 1930 extrinsic factors intrinsic factors Most extinctions are due to multiple factors interacting simultaneously For example: causes of fish extinctions in N. America: physical habitat alteration (73%) introduced species (68%) chemical pollution (38%) hybridization (38%) overharvest (15%) Extinction vortices Extinction vortices A vortex F vortex Extinction vortices R vortex (demographic, based on intrinsic rate of increase, r) • chance decrease in N increases variance of the population growth rate Var(r) • population becomes more vulnerable to environmental stochasticity normal demographic fluctuations decline in N – small catastrophe N increased pop’n variance Time Extinctions are forever - ? ivory-billed woodpecker smoky madtom blue pike spoonhead sculpin deepwater sculpin Extinctions are forever - ? ivory-billed woodpecker smoky madtom blue pike spoonhead sculpin deepwater sculpin 1942 – last seen in US waters of L. Ontario 1972 – last seen in Canadian waters 1999 – 3 caught in targeted trawls 2004 – 1 2005 – 17 in standard assessment trawls 2009 > 75 (depth > 90 m) Lazarus effect… When is population size too small (hopeless)? Przewalski’s horse Guam rail black-footed ferret European bison Speke’s gazelle dusky seaside sparrow 13 10 6 6 4 2…1..…0 note: these are all captive (regulated) populations….