Lecture #2 Speciation Unit 6: Evolution

These are all members of a single species. Macroevolution What is a Species? 9/14/2018 These are all members of a single species. G. Podgorski, Biol. 1010

There is only one extant (existing) human species. Macroevolution What is a Species? 9/14/2018 There is only one extant (existing) human species. G. Podgorski, Biol. 1010

Macroevolution Determining What Is and What Isn’t a Distinct Species Can Have Economic Consequences 9/14/2018 Northern spotted owl (left) and barred owl (right). G. Podgorski, Biol. 1010

What exactly IS a species? Species - a group of organisms that look alike and are capable of producing fertile offspring in nature.

About 2 million species have been described. Macroevolution 9/14/2018 How Many Species Are There? We don’t know. About 2 million species have been described. Estimates of existing species number range from 4 million to 100 million (with 10-15 million being a more commonly considered upper estimate). G. Podgorski, Biol. 1010

Question: How do new species arise? Speciation – The process whereby a population achieves reproduction isolation and results in the formation of new species.

The key to speciation is reproductive isolation of populations. Macroevolution 9/14/2018 The key to speciation is reproductive isolation of populations. Geographic isolation is an example of a reproductive isolating mechanism. G. Podgorski, Biol. 1010

Other ways to achieve reproductive isolation (different habits within an overlapping range)

Isolation is not enough however! Populations of the same species that live in different locations will only evolve in different directions if they are exposed to slightly different selective pressures.

As isolated populations of the same species become more different over time, they may eventually be unable to breed with one another. The two populations are then considered to be different species.

Harris’ antelope squirrel White-tailed antelope squirrel Macroevolution 9/14/2018 Example I Harris’ antelope squirrel White-tailed antelope squirrel Two species of ground squirrel are believed to have descended from a common ancestral population that was separated by formation of the Grand Canyon. G. Podgorski, Biol. 1010

Example II Darwin’s Finches   Darwin hypothesized that the Galápagos finches had descended from a common ancestor. These ‘founders’ were probably blown over from the South American mainland in a storm. The ancestral finch was a ground-dwelling, seed-eating finch.

There are now 13 species of finch living on the Galapagos Islands.

Darwin’s Finches are an example of Adaptive Radiation. Adaptive Radiation - The diversification of several new species from a recent ancestral source. ‘Recent’ meaning in the last 100,000 years in the case of Darwin’s finches.

Darwin proposed that natural selection shaped the beaks of different bird populations as they became adapted to eat different foods.

Take 2 minutes to summarize what you have learned regarding what is necessarily in order for a new species to arise. Give an example of speciation as well.

Three Types of Evolution Divergent Evolution Convergent Evolution Parallel Evolution

1. Divergent evolution - speciation in which sub- populations of a species split to form 2 or more new species When species have undergone divergent evolution, there is a common ancestral form. Example: Darwin’s Finches

Another example Eohippus (common ancestor to all the rest) gave rise to several species of horse, all of which are currently extinct except for modern day Equus.

similar environmental pressures. Convergent Evolution The independent evolution of similar structures among distantly related species due to similar environmental pressures. Example: body plan of shark & dolphin

Convergent Evolution

Example - Marsupials vs Placental Mammals. Parallel Evolution - the independent evolution of similar traits, starting from a similar ancestral condition. Example - Marsupials vs Placental Mammals. Parallel Evolution is similar to convergent evolution in that similar features evolve in two species independently. They differ in the fact that two species are DISTANTLY related in convergent evolution. (Ex: dolphins vs. sharks)

Examples of parallel evolution Marsupials and placental mammals most recently shared a common ancestor 125-150 million years ago, yet these similar features appeared in each of the distant relatives!

Is this an example of Convergent, Parallel or Divergent Evolution? http://evolution.berkeley.edu/evolibrary/home.php Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

Take 2 minutes to summarize what you have learned about the three types of evolution that can occur.

At what rate does evolution occur? Gradualism - the model of evolution in which gradual change over a long period of time leads to species formation. For decades, gradualism was the model of evolution that most biologists agreed on.

Some biologists in recent times suggested a different theory; in which successful species remain UNCHANGED for long periods of time. (‘If its not broke, don’t fix it!’) They hypothesize that major environmental changes in the past have caused evolution to occur in spurts.

Punctuated Equilibrium – The model of evolution in which periods of rapid change in species are separated by periods of little to no change.

Extinction and Evolution Rapid bursts of evolution tend to follow in the wake of extinctions. Extinction - when a species disappear permanently. Best estimates from the fossil record indicate that greater than 99% of species that have ever existed are now extinct.

Why does extinction occur? If the environment changes beyond the capacity of a species to survive that change, extinction is inevitable.

According to the fossil record, a large percentage of the organisms on Earth suddenly became extinct 440 million years ago. This was the first of five major mass extinction’s that have occurred on Earth. Mass extinction - the death of all members of many different species, usually caused by an ecological disaster. Ex of natural events that may trigger extinction Volcanic eruption, climate change, Meteor crashing in to the earth.  

After each of the 5 mass extinctions, species that are better suited to the new conditions may replace those that became extinct. There is always a burst of evolution following a mass extinction as the survivors recolonize the habitats unoccupied due the mass extinction. There are many resources available and little competition, so populations grow readily.

Example The extinction of the dinosaurs was followed by the ‘rise of mammals’. http://www.history.com/topics/why-did-the-dinosaurs-die- out/videos#what-killed-the-dinosaurs

Is the 6th mass extinction happening now? Humans are currently accelerating the rate of extinction! The leading cause of species extinction today is habitat loss. Much of this is due to human activity. We are disrupting many of the earth’s ecosystems (ex: logging, mining, farming, housing development). This displaces many species and leads to extinction.

Are We Now Causing a Mass Extinction? Macroevolution 9/14/2018 Are We Now Causing a Mass Extinction? G. Podgorski, Biol. 1010

Take 2 minutes to summarize what you have learned regarding the rate at which evolution occurs and the relationship between extinction and evolution.