Earth 125 1st Edition Lecture 24 Outline of Last Lecture I. Predation as Cause of Extinctiona. Extinction in megafauna in past 100,000 yearsOutline of Current Lecture II. Today’s Biotic Crisis: 6th mass extinction?a. Overkill, introduction of species, habitat destructionCurrent LectureI. Review of Last Week: Megafaunal Extinction1. Climate or hunting?i. Paleolithic humans – hunting ii. Human arrival lines up with extinction, as does some drastic climate change2. Question of the week: How are megafaunal extinctions in Africa & Europe different from those in the Americas and Australia? Why?i. Megafauna co-evolved with humans in both Africa and Europe, so justlike with the Lynx and Hare, prey became “adapted” to human predation pressureii. Leads to co-existenceiii. Predation is not, in general, a strong mechanism for extinction, but it causes evolution1. Leads to strong natural selection for defensive strategiesa. Defensive behavior (speed, avoidance), toxins (biochemical defenses), sheer size, armor, crypsis, life history traits (birth rates)3. Our knowledge of extinctions, for the most part, comes primarily from fossilsi. And from biological/ecological evidenceII. Today’s Biotic Crisis1. Current Extinctionsi. Almost always (recently), humans are involved with these extinctions1. Overkill2. Introduced Species (predators, disease, competitors)3. Habitat Destruction2. Last Steller’s Sea Cow (1768)i. Sea cow was discovered in 1741 and hunted to extinction by 1768, meat from one adult could feed 33 sailors for a monthii. Today, 4 species of sirenians (include manatee, dugongs) are endangered or threatened3. Introduced speciesi. Polynesian Islands:1. Snails documented very well since early 20th century2. In the 1970s, 2 alien land snails were introduced sequentially to many Pacific islands, with disastrous consequences for endemic partulidsa. #1 giant African land snail, Achatina fulica, which quickly became an agricultural pesti. Because of its disturbances to agriculture, they introduced…b. #2 carnivorous snail, Euglandina rosea, which was meant to control the giant land snail which took over the islandi. But, the shell of Achatina fulica is too thick for Euglandina rosea, so instead, the carnivorous snail took over the smaller snailsii. Stephens Island wren1. wren, one time on mainland NZ, only flightless songbird in the worlda. Late 1800s: wren found only on Stephen’s islandb. 1895: “cats have become wild and are making sad havoc among all the birds”2. Extinction:a. The last wren was seen eaten by a cat (which was brought to the island by the lighthouse keeper)b. Human’s fault4. Habitat Destructioni. The Dodo bird1. Large flightless bird found around Indian Ocean, first sighted around 1600 and then extinct less than 80 years latera. No evidence of humans consuming the birdii. Size of habitat directly correlated with number of species found there,that can live there1. Species-Area effect and extinctioniii. The Amazon: a hotbed of diversity 1. 40,000 plant species, 427 mammals species, 1,294 bird species2. Extreme forest lossesa. Reducing area of habitat means we are decreasing modern-day diversity within that habitatIII. Are we in the 6th mass extinction?1. Is the magnitude of extinctions very high (much higher than background)?2. Is the rate of extinction high (much higher than background?)3. Are the organisms going extinct today similar to those for which we have a good fossil record? (kind)i. We’ve only wiped out 1.5 percent of these species – right?1. But what’s the rate of extinction?a. 3.8x10-3 % / yearb. Small number, so why worry? ii. What is the background rate?1. Take average of durations of species, take reciprocal to find average ratesa. Bottom line: what is the rate per year?i. 5x10-5 %/ year2. Means what is going on in the past 400 years is more rapid, much worse than what happened priora. 100% worse than pre-human conditioniii. As far as rates, it looks like we are well beyond background and into a mass extinction.1. BUT, there is a fundamental differencea. Today we can study even small populations, in the fossil record this is generally not the case. b. Generally, the fossil record does not preserve those species that have small populations or narrow geographic ranges, rather, we see the common and widespread2. Example of recently extinct common species (passenger pigeon)a. Previously – 2,000,000,000 pigeons (flock that was 240 miles long and a mile wide)b. Hunted for agricultural reasons, to eat, and because of habitat destruction4. What are some biological (intrinsic) correlates of extinction?i. Traits that makes species more prone to extinction:1. small population size2. small geographic ranges (island endemics)3. higher trophic levels4. certain life histories (smaller litters, later age of maturity)5. complex social structures6. large body size5. So far, although the rate is high, it has not been going on for very longi. time to reverse the trend and avoid a mass extinctionii. What if things don’t change?1. Projected extinction rate: 1,700 to 5,100 times higher than background rateIV. Perspectives on extinction1. Morals – is it right?2. Aesthetics – the “beauty” of biodiversity3. Economics – the cost/benefit of biodiversity4. Biology (evolution)i. loss of genomes (extinction is forever) no example of a species re-evolvingii. long-term loss of diversity: takes millions of years for diversity to bounce back)iii. identity of victims: extinctions are not deterministically predictable. We can only make probabilistic predictionsiv. incumbency: while disappearance of species, presents opportunities for other species (example: dinosaurs & mammals), again who will “benefit” evolutionarily in the long run is