Who gets hit first by extinction? The Extinction Vortex Who gets hit first by extinction?

What are background extinction rates? Vary, for different groups of organisms Species longevities range from 2-10 million years (4 my ave.) Marine invertebrates: 2-5 families lost every million years …but many other species not found in fossil record must appear & disappear at even higher rates…

Mass Extinction Events:

What makes species susceptible to extinction? What is the ultimate thing that makes a species more likely to go extinct? Small population size In other words, rare species are the most at risk

What does it mean to be a “rare species?” Describe 3 kinds of rarity Wilson uses 3 bird species to illustrate the “layers” of rarity (p. 228-229) Each group member review & describe what makes each of these three birds rare: Bachman’s warbler Kirtland’s warbler Red-cockaded woodpecker

Types of Rarity Show the distribution on an imaginary “range map” for each species Compare among species… How do species get to be so rare in the first place? Be prepared to report back to class

What are the main causes of rarity? Specialization (e.g. red-cockaded woodpecker) Small geographic range (endemic species) (e.g. Kirtland’s warbler) Sparse population within range (e.g. Bachman’s warbler) Large body size (= small population size) Top predators always rare – nature of food chains & energy transfer Chance events can isolate a population (…this may lead to speciation…)

What are two kinds of chance events that can isolate a population? Most of individuals die/are destroyed somehow (disease, cataclysmic event…) This is called the “Bottleneck Effect” A small group of individuals gets separated from the rest – e.g. birds blown off course during migration This is called the “Founder Effect”

What does it do to the species, when population size gets very small? Each group get a bag of M&M’s (don’t eat them yet!!) For our purposes, assume that M&M color represents individual phenotype/genotype Is there “genetic” variation in your population? Are all genotypes equally represented?

What happens when population size gets very small? In the worldwide “population” of M&M’s, the relative abundance of colors is: brown:orange:yellow:green:blue:red 6 : 6 : 3 : 3 : 3 : 1 If your bag (small population) of M&M’s was a perfect representation of this color mix, and it had a total of 110 M&M’s, how many of each color would you expect to have?

What happens when population size gets very small? How many M&M’s of each color would you expect to have? How many do you actually have? Has there been a change in “gene frequency” in your smaller population?

What happens when population size gets very small? Has there been a change in “gene frequency” in your smaller population? NOW – someone in your group should close their eyes, and take a random sample of 10 M&M’s from the bag. What is the color distribution now? Now has there been a change in gene frequency??

What happens when population size gets very small? Has there been a LOSS of “genetic” diversity?? Usually the color distribution in your new, very small population, is very different than it was in the whole population, & some colors are missing This phenomenon of random change in gene frequency & loss of diversity is called “random genetic drift”

What happens when population size gets very small? Two genetic problems arise in very small populations: One is genetic drift, as we have just seen with the M&M’s (random loss of genetic diversity, just based on who survives & leaves offspring) The other is… Inbreeding!

Problems at the genetic level in small populations These two problems for small populations lead to a phenomenon known as… “The Extinction Vortex”

The Extinction Vortex: