Exam 3 Preparations

Hi Blog followers...

I suspect you're here for a little bit of advice on Exam 3. On Sunday night, I put forward some advice in the form of 9 practical exercises that you could do to get ready for the Critters portion of Exam 3 (See "Puttin' Critters ON (and IN!) the Table"). I happen to think that those 9 exercises are a wonderful way to prepare for most of the questions that Prof S might ask about the 3 Critter Days that we've had in class.

As you and I both found out in class on Monday (and via the exam review questions posted by Prof S on the course Angel site), there will also be questions regarding the Citizenship Projects, Ecology, Biogeochemical Cycles, and Biodiversity/Conservation. Instead of a single Blog to deal with these topics, I've decided that I will make digital myself available in person in Kedzie Hall tonight from 6:30-8 pm. There, we can spend an 1-1/2 hours or so digging into the past lecture slides together. I promise you won't regret giving up the time.

And, don't forget, Prof S will be fielding questions in Kedzie today at 4:30 pm and then online through the Angel discussion board starting at 9 pm. For some thoughts about the Critter Days, however, read on...

Lecture 14-15 (6/19 & 6/22): Puttin' Critters ON (and IN!) the Table...

My apologies to everyone for my absence from the Blog over this past week, but I was at a conference in Notre Dame giving a presentation to some other university-types about teaching & learning in university science courses...

I know you're likely already thinking about this, but I thought I'd chime in as you are looking ahead to this Wednesday's Exam 3. In particular, I want to get you thinking about some things you can do on your own to get a better handle on the "Critter Days" (thus far, Lectures 6, 10, 14 & 15).

In a previous Blog ("What's Up With 'Critter' Days?"), I began to connect the various Critter Days to some of the big ideas presented in the course, but in this Blog I actually want to give you some practical things to do between now and Exam 3 (and, I've been told by a reliable source that Critters will form "the heart" of Exam 3).

Puttin' Critters ON a Table...Part I

I want you to imagine a large table or desk in front of you--clear it of all items. Go back through your lecture notes and extract all of the names of the different groups of "Critters" that Prof S has discussed with you. For example, groups like "prokaryotes," "extremophiles," "protists," "seed/seedless plants," "liverworts," hornworts," "mosses," "club mosses," "ferns," "gymnosperms/angiosperms," "fungi," "vertebrates/invertebrates," etc. (this is not an exhaustive list!). Put each of these names on separate notecards. For those of you up late studying, I've been told that the exam will concentrate mainly on 5 or 6 main "groups" of organisms: Archaea, Bacteria, Protists, Fungi, Plants, and Animals. So, you can economize your study time tonight by not paying as much attention to groups of organisms that are 'finer grained' that those 5 Kingdom-level groups (plus Archaea, which is a Domain group).

Now, I want to show you a couple of different exercises that you could do with all of these notecards:

• Exercise #1: One way you could talk about the critters is you could say that Prof S has shared information about the Archaea, the Bacteria, and the Eukarya (or Eukaryota). Put these 3 names on 3 new notecards. Whether you realize it or not, these 3 names cover ALL of the critters he's talked about in the course. Take the notecards you initially created and arrange them according these 3 "Domains" (i.e, taxonomic categories). Which groups belong to the Archaea? The Bacteria? The Eukarya? Can/do any of the notecards belong to two categories at once?
  

• Exercise #2: Another way you could talk about the critters is you could say that Prof S has shared information about consumers, producers, and decomposers. Whether you realize it or not, these 3 names also cover ALL of the critters he's talked about in the course. Just like in exercise #1, take the notecards you initially created and arrange them according these 3 categories. Which groups belong to the consumers? The producers? The decomposers? Can/do any of the notecards belong to two categories at once?

• Exercise #3: Yet another way you could talk about the Critters is you could say that Prof S has shared information about autotrophs (including photoautotrophs and chemoautotrophs) and heterotrophs (including photoheterotrophs and chemoheterotrophs). Whether you realize it or not, these 2 names (well, 4 names) also cover ALL of the Critters he's talked about in the course. Just like in exercises #1 & #2, take the notecards you initially created and arrange them according these 3 "Trophic" categories. Which groups belong to the autotrophs (as well as the 2 types of autotrophs)? The heterotrophs (as well as the 2 types of heterotrophs)? Can/do any of the notecards belong to two categories at once?

You've just gone through some exercises that put critters 'on' a table. Hopefully, with the help of your lecture notes, your textbook, and maybe even some reliable online resources that you may have used to help you complete the exercises, you're getting a better sense of the different ways that you'll be expected to be able to talk about the different types of critters found on planet Earth. Now, lets go through another exercise that again puts critters 'on' a table.

Puttin' Critters ON a Table...Part II

In Lecture 11, Prof S presented you with some ideas that he called the "Tools of the Trade," which made a big deal of things like "taxonomy" and "phylogeny." Here's an exercise to get you ready for Exam 3 that connects to taxonomy.

A Linnean-based taxonomy is shown at right. It is a nice representation to illustrate how biologists use certain 'nested' categories to organize or classify organisms into different groups. All life on Earth fits into the category called "Life" down at the bottom (in purple). But as we move 'up' the categories we get more and more specific, until finally we're talking about different species of organisms (in orangish).

Here's what I think you could do...

• Exercise #4: First, make separate notecards for each of the categories in the image at right and lay them out on a table such that they mirror the arrangement in the image. Second, gather ALL of the notecards that you created prior to doing exercises #1-3. Third, try to arrange these notecards according to the categories. Which ones are "Domian" terms? Which ones are "Kingdom" terms? Are there any "Phylum" terms that Prof S emphasized in his lectures? What about "Orders" or "Families," are any of the original notecards we created commonly associated with these terms? Late night addition: Again, you needn't concern yourselves too much tonight with the groups of organisms 'smaller' than the Kingdom-level (see comments in red above).
  

• Exercise #6: Now take the 3 notecards: Archaea, Bacteria, Eukarya. Where do these fit in relation to the Linnean taxonomy?

• Exerciese #7: Now take the 3 notecards: Consumers, Producers, Decomposers. What are your thoughts about placing these 3 notecards in relation to the Linnean taxonomy? Is it easy or difficult to place these cards in this organizational scheme. Explain this ease or difficulty in a paragraph (pretend it's a practice essay question on Exam 3--see if you can write a half-page answer.)
  

• Exercise #8: You should ask the same questions of the 4 terms from exercise #3: autotrophs (including photoautotrophs and chemoautotrophs) and heterotrophs (including photoheterotrophs and chemoheterotrophs). How hard or easy is it to arrange these notecards according to the Linnean taxonomic system? Explain this ease or difficulty in a paragraph (pretend it's a practice essay question on Exam 3--see if you can write a half-page answer.)

Puttin' Critters IN a Table...

Here's one last exercise, but a very important one...

Exercise #9: Instead of using a table or desk and spatially arranging notecards, create a written table for this next exercise with 4 columns and lots of rows (one row for each of the different groups of critters discussed by Prof S). Here's how I think the table might look:


At the end of each of the 4 main Critter Days, Prof S did a summary slide--but not in a tabular form--that he called "Critters and the Big Picture." Each slide had the same 3 questions for you to answer on it!

I don't know about you, but this sounds to me like a very important set of questions for you to be able to talk intelligently about on an exam. In case you need some clarification on the questions (i.e., "Big Ideas") at the top of the columns, here are some translations to help you begin to fill out a table like this...

• Related to Scale? In the language of this course, this is a question about time and space scales. Space scale: How much space does this organism to take up? Do you need a microscope to see one? Do you find these organisms alone or in groups? Where in an ecosystem would you most likely find them, i.e., what is their preferred habitat? Time scale: What do you know about the general evolutionary history of these organisms? Have them been around in their current state for a long time or are they a relatively new group of organisms?

• Related to Genes? In the language of this course, this is a question about the form of their DNA and their reproductive strategy. Is their DNA typically found inside of a nuclear envelop or not? How do they pass their genes on to future generations? Are they sexual or asexual reproducers? Do they produce seeds? Spores? Live offspring? Eggs? Etc. Late (Tuesday) night addition = One thing I forgot to consider in this list of gene-related issues is something about genes at a larger scale: So, what kinds of unique adaptations do the different groups of organisms mentioned above possess?
  

• Related to Matter/Energy? In the language of this course, this is a question about how these organisms get the energy they need to perform life functions. This has direct connections to the terms found in exercises #2 & #3 above: consumers, producers, decomposers, autotrophs, and heterotrophs. However, this is also a question about what role(s) these groups of organisms play inside of things like the "Matter Cycles" that Prof S talked about in Lectures 15 & 16. For example, what (if any) major role(s) do critters like the fungi play in the Carbon Cycle? What (if any) major role(s) do critters like seed-producing plants play in the Phosophorous Cycle?
  

So, maybe you need to have more than 5 columns for this table? Maybe you want to break the last column up into separate "Matter" and "Energy" columns? Maybe you want to break the first column up into separate "Space" and "Time" columns?

Final thoughts...

Any way you decide to do it, my sense is that completing these 9 exercises between now and Wednesday's exam will play huge dividends for you. Of course, I haven't seen the exam yet, so I'm hedging my bets on the fact that Prof S told me last Monday that the Critter Days will make up "the heart" of Exam 3.

If that has changed between last Monday and today (Sunday), it would be news to me. But then again, as I mentioned earlier, I wasn't in class this past Wednesday or Friday because of a conference. Did Prof S make any more specific announcements about Exam 3 in either of these last two classes? If he did, then maybe one of you could use the comment feature of the Blog to fill me in.

Anyone? Post-Blog update: This issue is addressed briefly in the "Exam 3 preparations" Blog.

Lecture 13 (6/15/09): A Biology Bedtime Story...Chapter IV

In the Lecture 12 Blog ("A Biology Bedtime Story...Chapter III"), I don't know if you realize it or not, but I was trying to help you get used to a new pair of population glasses. When it comes to wearing population glasses, you had to get used to talk about things like...intraspecific competition, mutualism, population ecology, demographics, range, habitat, mortality rates, birth rates, population density, survivorship, life history, semelparous, iteroparous, and population growth.

In Lecture 13, Prof S moved beyond the idea of populations and began instead talking about "communities." So, I thought it would be appropriate to try on a set of community glasses, which are sometimes similar to population glasses in that they share some of the same terms/concepts. However, when we talk about organisms in terms of communities instead of populations, there are some new terms/concepts that we need to keep in mind (and in sight). Once again, we turn to the finches so that we can practice using some of the ideas that Prof S used when talking about "community ecology."

Chapter IV

Forts, Forts, Forts...Brett, that's all you ever talk about? Why don't you ever talk about the other types of ground finches on Daphne Major? If that's what you've been thinking, then your wish has come true. We're going to 'zoom out' and talk about more than the Daphne Major population of Forts today. We're going to talk about the Forts and the two other species of ground finches found there (pictured at right): the Fulis and the Mags.





You can see from their pictures. These 3 different species of finches are similar, but yet they're different, right? When we allow ourselves to talk about all 3 of these Daphne Major species of ground finches at once, we are entering the world of community ecology.

As Prof S said in class, community ecology "studies interactions between more than one species." In population ecology, we concerned ourselves with a single species: the Forts. But when we make the 'jump' to thinking in terms of community ecology, we are thinking about the interactions between more than one species. In this case, the Forts, the Mags, and the Fulis. This is not a difficult jump to make, right?

So, let us continue to look at the drought of '77-78 and examine not just how the Forts were effected, but also how what happened to the Fulis (who, on average, had the smallest beaks of the three ground finch species--smaller than the average Fort) and the Mags (who had the largest beaks--larger than the average Fort).

Community ecology speak...

Right off the bat, lets practice using some community ecology terms. If we pretend, just for a moment, that the 3 species of ground finches are the only species of living things on Daphne Major, what would the "species richness" on Daphne Major be?

Hopefully you said, '3' because as Prof S mentioned in class, species richness is simply a measure of the total number of different species in a defined area (in this case the island of Daphne Major).

What if I asked you what the "relative (species) abundance" on this hypothetical island would be?

Hopefully, you said, 'I don't have enough information to answer that question' because relative (species) abundance depends on how many individuals of each species can be found in a defined area (again, in this case the island of Daphne Major). If I told you how many Fulis, Forts, and Mags were present on Daphne Major when I asked this question, only then would you be able to tell me about the relative (species) abundance.

What if I asked you what the "species diversity" on this hypothetical island would be?

Hopefully, you said, 'I STILL don't have enough information to answer that question' because species diversity depends on both species richness (which you know) and relative (species) abundance (which you don't know). Species richness, relative (species) abundance, and species diversity are all ways that Prof S mentioned are ways of "quantifying a community." In other words, these three terms are ways that biologists use to 'count' living things in different habitats often so that they can compare them to other habitats.

What happened to the ground finch community during the '77-78 drought?

From both Chapter II and Chapter III of our story, you already know what happened to the Fort population during the drought. But the Forts weren't the only population of ground finches on the Daphne Major in the years leading up to 1977; there were also healthy populations of Fulis and Mags on the island too. In years with normal rainfall, each of these species of finches typically eat seeds from the island's plants. Yesterday, I shared with you stories of how the Forts engaged in fierce intraspecies competition for food during the drought with members of their own species. Today, I want to share a few excepts from The Beak of the Finch that give you a flavor for the interspecies competition between the 3 species of ground finches.

Recall in previous chapters of our story I've mentioned the caltrop plant (Latin name Tribulus). Tribulus plants produce the most interesting of seeds (pictured at left). Their seeds are initially housed inside of fruits, but when these fruits dry and fall to the ground they become large amoured pods. The spiny, star-shaped pod breaks apart into separate "mericarps," each of which holds three to six seeds inside.

For the most part, the Tribulus mericarps are very awkward in a finch's beak. The significance of this seed is that in normal years on Daphne Major, each of the 3 species of finches have the same general diet--they all eat the same 7 kinds of soft seeds. They don't even bother with the hard-shelled Tribulus seed. But in a drought, when the Tribulous seeds are about the only seed left on the island, they are forced to confront it as it is one of the only remaining food sources.

Here are some passages to describe how the 3 finch species dealt with the Tribulus seeds during the drought (some paraphrased):

The smallest ground finch [the Fulis], have never been seen trying to open them. The only species that do attack mericarps are the [Mags and Forts], and each species has its own tactics.

Mags (whose beak is almost twice as wide and twice as deep as the beak of a Fort) picks up a mericarp, holds it near the midpoint of its beak, and squeezes its mandibles together. After a while the mericarp shatters into fragments. The Mag picks up each fragment, holds it one one side of the beak, and crushes it.

To crack a whole mericarp like this takes an average force of more than 200 newtons. Apparently that is more force than a Fort can muster. Instead it braces the mericarp against the ground and bites and twists the woody sheath that guards the row of seeds, as if peeling off a lid. This operation requires about 54 newtons of force, which seems to be about the best a Fort can do.

The finches prefer mericarps with only two spines, and mericarps with four spinces are likely to be dropped. Once indication that Mags have an easier time than Forts at eating Tribulus...is that a Mag cracks many more mericarps than it rejects, while a Fort rejects many more than it cracks.

A few Forts have found a trick that helps them even the score. One of them sometimes trails a Mag around on the lava. As soon as the Mag cracks a mericarp...the Fort rushes up, steals a piece, flies a little way off, and cracks it. Not every Fort on Daphne Major seems to know this trick; the Grants have spotted only about half a dozen of them doing it.

So the trials and tribulations of Tribulus are not only harder on Forts than Mags; they are harder on some Forts than others. Forts with bigger beaks can crack the mericarp and gouge out the seeds faster than those with smaller beaks. Tiny variations are everything. A Fort with a beak 11 millimeters long can crack a Tribulus seed; a Fort with a beak only 10.5 millimeters long will not even try.

What I've done by selecting these passages is do two things. First, I've selected passages that connect to some of the terms that Prof S used when talking about "community ecology" in Lecture 13. Above, you should be able to see by now that these passages illustrate competitive exclusion: on Daphne Major 3 different species need exactly the same resources and, in the end, there are some winners (mainly the Mags and the larger Forts) and some losers (mainly the smaller Forts and the Fulis). Do the above passages illustrate resource partitioning? Not really, during a drought the 3 species all fight for the same seeds. However, take a look at the following quote. I think it is a perfect illustration of how, in a non-drought year, there is clearly some resource partitioning on Daphne Major. In one of the dry seasons prior to the drought (remember a typical year in the Galapagos involves a wet and a dry season)...

Peter Boag walked around the island. Each time he spotted a Fort...he watched the bird until he saw it pick up a seed, and he wrote down what kind of seed it was. Boag found that in the dry season the birds with the biggest beaks eat the biggest seeds, the birds with the medium-sized beaks eat the medium-sized seeds, and the birds with the smallest beaks eat the smallest seeds.

The second thing I've done is hopefully give you a story to keep in your head during tomorrow's exam. Should you find you're asked a question about, in this case, community ecology, I would hope that this finch story will circulate in your head as you write. Similarly, should you find you're asked a question about population ecology, I would hope that yesterday's finch story will circulate in your head as you write.

More community ecology speak...

Something tells me that you really don't need me to try and put some of the other community ecology terms into the finch story. Hopefully, you can now speak (and write) intelligently about competition in communities of organisms. And, I'm pretty confident that you already know how to use other terms that community ecologists like to use, terms like predation, herbivory, parasitism, mutualism, and commensalism. All of these specialized terms simply describe different types of relationships between different species.

I'm also pretty confident that you are probably all pretty good by this point in your school careers in terms of knowing what basic food chains and food webs are. Do you know the different terms for important species found inside of the chains/webs? Do you the difference between terms like autotrophs/heterotrophs, producers/consumers, dominant species, keystone species, and foundation species? These are all terms that community ecologist like to use when talking about groups of different species living in a particular area.

Closing Comments...

It occurs to me to remind you that in the last three Blogs (Lectures 11, 12, & 13), I have asked you to wear at least 4 pairs of highly specialized glasses. In the Lecture 11 Blog, I tried to show you what living things look like through two types of glasses: taxonomic glasses & phylogenetic glasses. In the Lecture 12 Blog, I tried to show you what living things look like through population glasses. Finally, in the Lecture 13 Blog, I tried to show you what living things look like through community glasses.

For Exam 2, you'll need to be prepared to wear all of these different types of glasses--sometimes separately and sometimes simultaneously--but the difficult job is knowing when to put each of them on. I'd like to remind you, however, that these aren't the only glasses you'll need for Exam 2. You'll also need a reliables pairs of species and speciation glasses, which I tried to help you learn how to use back in the Lecture 8 (Chapter I & Chapter II) & Lecture 9 Blogs. Don't forget that even though you had a quiz on the material presented in Lectures 8 & 9, these days are also fair game for material for this Exam.

Oh yeah..."And they lived happily ever after."

Lecture 12 (6/15/09): A Biology Bedtime Story...Chapter III

When, in the Lecture 11 Blog ("Mom...Do Birds Grow on Trees?"), I said that, "I think that there has been more 'information' tossed your way in Lectures 11, 12 and 13 than in any other 3 lectures all semester," here's what I was talking about:

In Lecture 12 alone, between 10:20 am-12:10 pm you were presented with the following scientific/technical terms:

• Abiotic factors (including temperature, salinity, precipitation, climate), biotic factors (including predation, herbivory, interspecific competition, intraspecific competition, mutualism, habitat selction, symbiosis), biogeography, biomes, dispersal, distribution, population ecology, demographics, range, habitat, mortality rates, birth rates, population density, survivorship, survivorship curves (Types I, II & III), life history, semelparous, iteroparous, population growth, exponential growth, carrying capacity, logistic population growth, limiting resource, r-selected, K-selected, and a little bit of alphabet soup: K, d, N, t, r, b.

How can I best go about helping you learn to use many of these terms--as biologists would use them--by Friday? But of course!!! Why didn't I think of this sooner? This calls for another installment of...A Biology Bedtime Story! If I can craft some kind of interesting story with which you now have some familiarity, perhaps I can practice using some of the vocabulary so that you can also get some practice seeing it...thinking about it...using it...yourself.

I have just the story that I think will highlight some (but not nearly all) of the main ideas from Lecture 12...

Chapter III

When we last left our friends--the finches of Daphne Major--in Chapter II of our story, the Forts (the medium-beaked ground finches at right) had suffered their way through the 1977-78 drought. Their population on Daphne Major had plummeted due to a natural selection event, which selected AGAINST alleles for below average and average beak size/strength, and selected FOR alleles for above average beak size/strength.

That much you should already know...

But can we take a step or two back in history from the hard times of the Forts in '77-78 and ask a question? Can we ask a question similar to the one that Prof S asked the class at the very beginning of Lecture 12? He asked you:

• Why are there so many species on Earth?

I want to ask you a more modest question:

• Why might there be so many species of finches--between 13-15 depending on which experts you talk to--in the Galapagos Islands?

Professor S answered his question by using two main terms in lecture. Did you catch them? He basically said that there were things called biotic and abiotic "factors" that affect living organisms, and then he gave you a bunch of different terms that could be considered either biotic or abiotic factors. Why don't you and I practice using some of these terms and re-live the drought of '77-78 with the Forts.

Abiotic Factors on Daphne Major

What was the main abiotic factor that changed during the drought of '77-78? Hopefully, this is obvious to you...the drought means that the water changed, more specifically, the average yearly amount of precipitation changed. How did it change? It decreased. Remember, almost no rain fell on Daphne Major during '77-78. Did the temperature on Daphne major change during the drought? Well, no precipitation probably means fewer rain clouds; fewer rain clouds probably means more direct sunlight; more direct sunlight probably means more sunlight hitting both the island's surface and the Forts bodies. Consider these two excerpts from The Beak of the Finch, which describes what two of the finch scientists, Peter Boag & Laurene Ratcliffe, saw during the drought (remember the real name for the Fort species is Geospiza fortis or just fortis:

Some of the very smallest fortis on the island, the ones whose beaks were too small [to open seeds of] caltrop, were poking around the Chamaesyce instead. The herb Chamaesyce has small, soft seeds, but it also has aa milky, sticky latex when its leaves are wounded and its stems are broken. These little fortis...began hunting for seeds in the Chamaesyce in spite of its latex. The feathers on the crowns of their heads got so matted, gummy, and sticky that they rubbed off afterward as the birds raked the cinders and gravel looking for more seeds. Their bare scalps were exposed to the sun all day. Boag and Ratcliffe began to find little bald finches lying deal on the lava. (Page 74)

Down on the crater floor [of Daphne Major] the blue-footeed boobies shifted their weight from one leg to the other to cool off their webbed feet. Boag stuck a thermometer into the ground, in the toutured shadow of a cactus, and the soil was hotter than 50 degrees C (122 degrees F). Even when there were seeds lying out in the open, the heat was keeping the finches from foraging there between the hours of 11 a.m. and 3 p.m. [...] Another time they saw a blue-footed booby wounded by a frigatebird. A fortis stood beneath the wounded booby and drank the blood as it dripped on a rock [...] All of the cactus finch fledglings died before they were three months old. Not a single fortis laid an egg or build a nest. (Page 75)

I hope you're getting the sense of just how severe this abiotic disturbance was compared to a 'normal' year on Daphne Major. Since temperature and precipitation are both components of climate, can we also say that the climate changed on Daphne Major during '77-78? Absolutely. What about geography? Geography was another term that Prof S listed underneath "abiotic factors." Did the geography of this island change during the drought? Probably not. The physical features--e.g., rocks, size of the island, etc.--likely stayed pretty much the same.
Biotic Factors on Daphne Major

What were some of the main biotic factors in action during the drought of '77-78? Was there any predation on the Forts? There was. On Daphne Major all of the finch species, including the Forts, were prey for a species of owl that lived on the island. Was there any mutualism? Perhaps we need to consider a finch-plant relationship here. The Forts eat seeds; many of the plants on Daphne Major produce seeds. Can you imagine an arrangement in which both the Forts and the seed-producing plants benefit from this relationship? I thought so. Imagine a Fort eating a bunch of seeds resulting in some of the seeds passing through the birds body undigested. The bird poops them out somewhere else on the island where this plant can now grow. Voila! Mutualism = both the seed plant and the Fort receive some benefit. What about competition? Was there any competition for resources--food? water? mates? nesting site?--among the living things on Daphne Major? Are you kidding me? Of course! Consider a few more excerpts from the book:

During...June [1976], when the island was wet and green, there had been more than 10 grams of seeds in an average square meter of lava. The finches had already eaten their way through many of those seeds during the dry season of 1976 [...] Day after day they went on pecking over the same square meters for the same diminished supply of seeds. By June [1977] there were only 6 grams of seeds per square meter. By December there would be only 3 grams. (Page 73)

As they always do in dry times, the birds went on looking for the easiest seeds. But now they were sharing the last of the pistachio nuts. They were down to the bottom of the bowl. In June [1976], four out of five seeds that a finch picked up were easy, scoring less than 1 on the Stuggle Index. But as the small, soft, easy seeds of Heliotropium and other plants disappeared, the rating climbed and climbed, peaking above 6. The birds were forced to struggle with the big, tough seeds of the Palo Santo, and the cactus, and Tribulus, [the] symbol of the struggle for existence, a seed sheathed in swords. (Page 73-74)

Now and then a frigatebird harried a blue-footed booby out of its kill of fish. If the fish dropped on the island, as many as ten or twenty finches would flock around it. They also scavenged broken eggs and fresh booby guano. They hung close when the boobies fed their young and fought for the fish scraps, and when owls left something of their kill, finches fought over that too. (Page 75)

In other years the finches had ignored the lava lizards that scuttle about the rocks. But once that year, Peter and Laurene saw a female cactus finch eating a black lizard tail, and nearby they spotted a femail lizard with a freshly broken stump. Some days later, they saw the same bird chase after another female lava lizard, pecking at its tail. (Page 75)

Suffice it to say, there was both interspecific and intraspecific competition for food amongst the Daphne Major ground finches. In the remainder of this Blog, however, I want to focus only on intraspecific competition and its results. In other words, I want to focus only on the competition for food within the Daphne Major Fort population. In the Lecture 13 Blog, I will focus instead on interspecific competition. In other words, I will focus then on the competition for food within the entire ground finch community on Daphne Major (the Fort population + the Fuli population + and the Mag population = ground finch community).

The results of intraspecific competition

At least within the Fort population, what was the result of the fierce competition for food on Daphne Major during the drought of '77-78? Actually, I already answered this question in Chapter II of our story, the overall numbers of the entire Fort population plummeted. Natural selection, in the form of a drought, selected AGAINST alleles for below average and average beak size/strength, and selected FOR alleles for above average beak size/strength. Here's another passage from the book that will make this point clear:

...during the drought, when big tough seeds were all a bird could find, [the] big-bodied, big-beaked [Forts] had come through the best. The surviving fortis were an average of 5 to 6 percent larger than the dead. The average fortis beak before the drought was 10.68 millimeters long and 9.42 millimeters deep. The average beak of the fortis that survived the drought was 11.07 millimeters long and 9.96 millimeters deep. Variations too small to see with the naked eye had helped make the difference between life and death. (Page 78)

And now, back to our original question...

Prof S began Lecture 12 and his discussion of biotic and abiotic factors by asking a question: Why are there so many species on Earth? I asked you a more context-specific question: Why might there be so many species of finches in the Galapagos Islands?

Perhaps we can now bring a few of these ideas together...

Since we know that beak size is a heritable trait in the Forts (i.e., it is passed on through the genes), did we see an example of natural selection during the drought of '77-78? Did we see a shift in the relative frequency of alleles present in the Fort gene pool? YES, WE DID! We saw that the genes that code for ever-so-slightly bigger Fort beaks (and body size) made it through the drought in higher percentages than the genes that code for the ever-so-slightly smaller Fort beaks (and body size).

And how was it that people like Peter Boag & Laurene Ratcliffe were able to come to these conclusions? Because they were population ecologists!!! Just look at the kinds of data (at right) that they were collecting about each bird that they could find on Daphne Major during the drought (click to make it bigger).

If you examine the image a right closely, you can see what Prof S was talking about in class when he talked at length about population ecology. In fact, in one of his slides he asked specifically, "How would you describe a population?"

Can you see basic demographic statistics here (e.g., age, sex, birth, death, etc.)? When Boag and Ratcliffe collected data about the Daphne Major Forts like this, you can see how they could then begin putting graphs and charts together that calculated things like birth and mortality rates. Their field notebooks were full of other information about the Forts social interactions, their food sources, their predators, their habitat, the number of eggs they laid, etc.

In this way, I hope you can see how this data might allow for the scientists to determine other things that Prof S talked about in Lecture 12, like survivorship. You tell me: What data would the scientists need in order to make a survivorship graph about the Forts on Daphne Major?

The scientists could probably also determine whether the Forts were semelparous or iteroparous. You tell me: What data would the scientists need in order to make this determination?

If the scientists had data from the years before 1977 (which they did), they could probably also begin to construct a population growth model for the Forts. From what you learned in Chapter II, you tell me: Would a population growth model for the Forts look more exponential or more logistic? What do you suppose the carrying capacity of Daphne Major was over these years? Would the carrying capacity be the same in a drought year as it was, say, in 1978 when the rainfall amounts returned back to normal?

So, did this abiotic disturbance--which led to intense competition for food resources among the Fort population--actually lead to a new species of finch on Daphne Major? No, it did not. But, what did Prof S tell you about the things needed for speciation, i.e., the creation of a new species? Well, back in Lecture 9, he talked about the Biological Species Concept and also about two kinds of speciation, "allopatric" and "sympatric."

Now, here's where your work comes in: At the end of 1977-78, I have left you with a population of Forts, the majority of whom have above average beak and body sizes. Can you take this Fort population, the Biological Species Concept, and the fact that there are other islands in the Galapagos besides Daphne Major, and can you now tell me a story about how this above average beak/body size Fort population might become two species at some point in the future?

If you can do this, then I think you'll be ready for a lot of the questions that Prof S might throw your way on Exam 2.

Which brings me to the line I used at the end of the Lecture 11 Blog ("Mom...Do Birds Grow on Trees"). When I asked you to think about connections between the ideas in Lectures 11 and 12 I tongue-and-cheek said that the connection between these two lectures is "In the trees..." What I meant by that line was that the bridge between the two lectures is actually the image of the phylogenetic tree. If you understand these representations--and by that I mean understand what each line represents, what the nodes or branching points represent, what causes the branching points, etc.--then you're on your way to being able to see the world more like biologists do.

Lecture 11 (6/12/09): Mom...Do Birds Grow on Trees?

Complete the following sentence:

I'm stressed and sad because...

A. The Red Wings lost in Game 7.
B. Brett has taken a few days off of Blogging.
C. I have a BS110 exam on Friday (and I'm completely freaked out).
D. There's nothing good to eat in my refrigerator.

If you answered B and C, then you're in the right place. I can't do much about A at this point. But maybe the next 3 Blogs will provide some 'nourishment' for your brain, so consider these next 3 Blog posts my way of also helping you out with D (consider them the intellectual equivalent of a 'Happy Meal').

Lets get straight to the point...

You and I have a lot of work ahead of us between now and Friday morning, so we've no time to waste. To be honest with you, I think that there has been more 'information' tossed your way in Lectures 11, 12 and 13 than in any other 3 lectures all semester. So, if you're feeling a little bit more nervous about Exam 2 then Exam 1, I understand. In response, some of you might be feeling the desire to run into a dark hole and hide, fearing, with Exam 2 looming around the corner, that there's just too much knowledge to hold inside your noggin' for one exam.

If you're thinking that way, however, then you've missed an important point that I've been trying to illustrate with my Blog all semester: Another way to think about knowledge is not what's 'inside' your head, but instead what's 'outside' your head. What is there is the BS110 lectures that you can see with your eyes AND move with your hands?

Over the next couple of Blogs I'm going to once again ask you to try on some different 'glasses'-- yes, some old pairs that we've used before (like our different pairs of scale glasses), but also some new pairs that you probably didn't know you owned (or, for that matter, didn't know you needed). The notion of wearing different 'glasses' is one device that I like to use to try and persuade you that part of performing well on Prof S's exams is learning to 'see' the world like he and other biologists do. So, that brings us to one of the really important questions behind all of the material covered in Lecture 11:

• How do biologists look at--and more importantly, talk about--the amazing number of diverse life forms on our planet?

Answer #1: Taxonomies

Can you imagine how many different ways there are to talk about the living things found on Earth? A gazillion? Maybe...maybe more. This is why I inserted the image at right. Each pair of glasses is meant to represent a different way of looking at the living things found on our planet.

Let me illustrate by using my own backyard. Say I choose to wear the pink glasses from the rack...pretend that these are my "Is-it-edible?" glasses. I often classify the plants in my backyard in terms of two simple categories: those that taste good and those that don't. Among the plants in my back yard that taste good are different kinds of herbs (basil, thyme, mint, oregano, tarragon, rosemary, chives), some garlic plants, some hot pepper plants, some tomato plants, and our 3 big maple trees (my wife and I make our own maple syrup each spring).

If my wife and I had kids (which we don't), they might choose instead to organize the plants in our yard by wearing the red glasses (the "Those-plants-you-can-climb-and-those-you-can't" glasses), the yellow glasses (the "Those-plants-that-produce-fruits-good-for-throwing-at-cats-and-those-that-don't" glasses), or the green glasses (the "Those-plants-our-mom-yells-at-us-when-we-step-on-them-and-those-she-doesn't" glasses). The point is: There are so many glasses one can wear; there are so many different ways to look at the collection of living things in this world!

Most biologists, however, prefer to look at the collection of living things in this world with a couple of specific pairs of glasses. This is the idea behind many of their "taxonomies" ("taxonomy" from Greek taxis "arrangement" and -nomia "method"). Prof S told you in lecture about a one taxonomic strategy that biologists still use and value. It was the 2-name or "binomial" naming system first developed Carl Linneaus in the 1700s. In this strategy, he said that biologists like to use "morphological similarities" ("morphological" from the Greek morphe "form, shape"). In other words, biologist like to 'lump' (and 'split') groups of living things into categories based on similarities and differences in term of 'how they appear' or 'how they're built.'

If you think back to my Lecture 8 Blog ("A Biology Bedtime Story...Chapter I"), then you will recall that I used one type of taxonomy to talk about how biologists in the Galapagos often group the 13 species of Galapagos finches according to their "behavior and diet."

Below is this behavior/diet taxonomy, which is based on a) where the birds spend most of their time, and b) what they typically eat:

• Group A: The finches that live in trees and eat fruits and bugs.
• Group B: The finches that live in trees, but are strict vegetarians (i.e., no bugs!).
• Group C: The finches that live in trees, but they don't look and act like the other groups of tree finches...they actually look and act more like a different genera of birds (like the "warblers").
• Group D: The finches that spend most of their time hopping on the ground.

Do you see one of those branching 'tree' diagrams in the bulleted Groups up above? No, you don't. That's because taxonomies aren't always necessarily concerned with how groups of organisms are related--genetically speaking, that is--to one another. As soon as we start talking about how groups of organisms are related to one another in terms of their 'origins'...or their genetics...or their genes...or their DNA...or their actual base pairs (G, C, A, T)...then we're entering the realm of "phylogenies" ("phylogeny" from Greek phylon "race" and -geneia "origin").

Answer #2: Phylogenies

Why do I have only one pair of glasses at right when in talking about taxonomies I had many?

That's because looking at living things in terms of phylogenies involves a very specialized type of scientific glasses. I've decided to make them X-Ray glasses because--as Prof S mentioned in class--phylogenies try to lump and split groups of organisms according to their "evolutionary history." So, in order to get a sense of how organisms evolved in the past, you sort of need a pair of glasses that are capable of 'penetrating' things like the fossil record or--as is becoming increasingly common in 21st century science--'peeking at' and comparing the DNA of different living species.

In modern-day science, classifying organisms based on their evolutionary history basically means showing how today's living things could be related to each other and to organisms that lived in the past.

And this, is when these branching tree-looking diagrams come into play...

Galapagos Finches: Who is most closely related to whom?

At right (click on it to make it bigger), you can see a phylogeny for 14 species of birds found in the Galapagos (this includes the 13 species of finches mentioned above).

If you were to associate "time" with this tree diagram? How would you do it?

Well, hopefully you realize that the far left of the tree, "the trunk," represents the (hypothetical) common ancestor of all 14 of these Galapagos bird species. That means that in looking at the diagram from left to right, we are basically marching forward with our eyes through time! At the far right is the so-called "present-day" and at the far left is some point in the "past."

Can you identify the "branch points" or "nodes" in this diagram? How many are there? Do you see any places where "polytomy" occurred? These are a few of the terms that Prof S went over in class, so hopefully you can answer these types of questions quite easily...Yes? No?

Now, take a look at the tree diagram below at left. This is where taxonomy meets phylogeny. The caption in the upper left of the diagram says it all...

Here, I'll translate it for you: 'When we look at the DNA sequences of as many as 15 different species of Galapagos finches, it so happens that how we think they are related--phylogenically speaking--is actually quite similar to how we might group or arrange them--taxonomically speaking--according to things such as the way they feed.'

The black branches (i.e., U-shaped lines) of these two tree diagrams are nearly identical, but notice that the tree diagram at left has colored boxes. The colored boxes represent the taxonomy-part of this representation: they represent the "feeding approaches" of the Galapagos finches. The black lines represent the phylogeny-part of this representation: they represent the "relatedness" of the Galapagos finches.

I know, I know...You're thinking: 'First there was 13 finch species, then there was 14 species...now there's 15? What's the deal?'

By now, however, these differing numbers of species shouldn't surprise you in the least! Why? Because you know that there are many different ways to say what counts as a species. The Biological Species Concept is one way...The Ecological Species Concept is another way...it's highly likely that the web sources where I gathered these different images from were made by people using different concepts for what counts as a separate species of Galapagos finch.

Or, it may be the case that this last image represents newer (or older) developments in our phylogenic understanding of finches. It's possible that the 15 finch species have been somewhat 'lumped,' or that the 13 species have been somewhat 'split.'

Looking ahead...

Tonight we've only scratched the surface of all of the different ideas that are wrapped up or 'hidden' within things like the tree diagrams. In the Lecture 12 Blog, we'll look closely at how the ideas in Lecture 12 connect to those presented in Lecture 11...

• HERE'S A HINT: the key connection between Lectures 11 & 12 is 'In The Trees...', but maybe you can't see it just yet.

My guess is that you soon will be able to understand my hint...but it will require that you go out and secure a couple of additional pairs of glasses to put on.

Lecture 10 (6/10/09): What's Up With "Critter" Days?

I've been getting quite a few questions about these "Critter" days lately. So far, we've had exactly two of them in lecture. One Critter day consisted of 20 minutes of slides/discussion following Exam 1. The other Critter day was 60 minutes of slides/discussion following Quiz 2 today.

Now that there has been two of them, I get the sense that some of you are starting to mumble to yourselves, and to each other, the all-important question: Will anything from these Critter days be on future quizzes or exams?

Before we tackle that question, I want to tackle a related question that I was asked today after class: Exactly how are these Critter days related to the material we've been covering in recent lectures?

This is an excellent question and its one that I hope I can answer...visually.

Take a quick look back with me to an extremely important slide that Prof S showed during Lecture 9.

In hindsight, I probably should have devoted an entire Blog to the "Speciation" slide (below right) in the days leading up to Quiz 2. I (regretfully) say this because I now think I can map a whole bunch of really important terms from this course--genetic drift, reproduction isolation, allele frequencies, Hardy-Weinberg Equilibrium, etc.--onto this one diagram. And, had I done so in a Blog prior to Quiz 2, I think even more of you would have had even more success on today's quiz. Lesson learned...

So what does this diagram show? The blue arrow (ignore the green arrow) is an abstract representation of speciation. In other words, it is supposed to show one species in the process of becoming two species. If there was a single diagram in this course that could represent what today's Quiz 2 was testing your knowledge/understanding of, it's this diagram: If you knew all of the different factors required to produced a new species (i.e., if you knew how to make the blue arrow 'split'), then you likely did very well on the quiz.

Well, after you finished the Quiz 2 on speciation today, Prof S began a Power Point presentation about some "Critters." More specifically, he talked about "Eukarya," including protists, seedless plants, liverworts, hornworts, mosses, ferns, club mosses, seed plants, gymnosperms, angiosperms, etc. But after talking with a few students after class, I got the sense that they were a little bit perplexed as to how the post-quiz material was related to the pre-quiz material. A couple of students said they had a similar feeling when Prof S presented the 20 minutes of "Archea" and "Bacteria" following Exam 1.

To address these concerns, I'm going to have you do a 'thought' exercise with me. My goal in having you do this exercise is to show you how the Critter days and the material tested by Quiz 2 (i.e., speciation), are actually only a few small, easily traced, highly 'illustratable' steps away from each other!

Step One: Abstraction

I need you to do something for me. Go back up to the blue arrow in the speciation slide above, and trace the outline of the blue arrow in your mind. Once you do this, fill in the outlined arrow with black, and then make all of the other colors, arrows, words and images on the slide...disappear.

Congratulations, you've successfully performed an abstraction (which, you should know, is a skill that biologists are masters at doing). You should now see the same thing that I have drawn in the image immediately at right.




Step Two: Rotation

The next mental exercise that I need you to do is rotate the (abstracted) arrow 90 degrees...oh yeah, counterclockwise. If you're following my instructions correctly you should now have in your head the image at right: the two arrows should point 'up.'

Before we go on, it's important to remember that the upward pointing split-arrow still represents speciation! The horizontal blue arrow is still 'there,' but at the same time it's not. I know, I know: it's sort of paradoxical when someone tells you that something is 'there,' but then at the same time tells you that that same thing is 'not there.' But that's one of the powerful things about abstractions...they're like slang in spoken or written language. Nowadays, you say (or text) "OMG!" to someone and they understand exactly what's not there, "Oh My God!"


Step Three: Shrink & Multiply

This next step is easy. Shrink the upward pointing arrow from Step Two and multiply it...6 times. You should now have 7 copies of the (now shrunk) upward pointing arrows, dancing to-and-fro in your mind.

By the way, we're almost done. Just a couple of more steps to go to see how speciation (Quiz 2) connects with Prof S's Critter days. We just have to decide on how to arrange the scattered arrows currently floating in (mental) space.




Step Four: Arrangement

The task now is to arrange the 7 arrows in a very specific arrangement. They all need to be pointing up, and they need to look like they're almost 'growing' out of one another.

I know those aren't great directions, but just look at my image at right...got the picture?

At this point you can see that I've not only arranged the arrows, but I've also labeled the illustration (if you click on the image it'll get larger in a new window). I've given it a time dimension in the form of a vertical line: it says "past" on the bottom and "present" on the top. I've also given it a title, "A model of the evolution of life on Earth by means of speciation."

If you've been following my mental exercise step-by-step, you'll STILL be able to 'see' the blue arrowed diagram lurking just beneath the surface of this new 'tree' of stacked black arrows. Why? Because the blue arrow is STILL there (and not there!). It's just that now the tree of stacked black arrows carries with it the blue arrow's meaning. What is this important meaning?

That's right, you guessed it, it's the concept of speciation. Abstraction can be pretty nifty, eh?

Almost done...almost there

OK, so...to start to summarize and begin to bring today's Blog to a close...The image we produced at the end of our mental/visual exercise illustrates no less than 3 important things that are relevant to your work in BS110:

(1) It illustrates an important concept in this course: It shows how, over time, multiple speciation events could explain the large diversity of life forms presently found on Earth. This happens to be an idea that is largely attributed to Charles Darwin (1809-1882). However, some historians have made persuasive arguments that a contemporary and countryman of Darwin's, Alfred Russell Wallace (1823-1913), deserves more credit for his ideas about the origin of species than have been typically attributed to him in most historical accounts.

• By the way, you wanna read a great book for non-scientists about the adventures of Wallace, Darwin, and the development of the theory of evolution? Try this one, Song of the Dodo by David Quammen. It's fantastic.
  

(2) It illustrates what Quiz 2 covered today! To the right, I have made a red circle around a single speciation event in the diagram.

This was the content, the material, the concept, the idea...whatever you want to call it...this was the 'stuff' that Prof S asked you questions about on today's quiz. My guess is that in the coming days Prof S will talk in more detail about the sum total of the ideas contained within an image like this.

(3) It answers one of the two questions that we posed at the beginning of this Blog (Exactly how are these Critter days related to the material we've been covering in recent lectures?)! Hopefully, you can now see why Prof S has been sharing groups of organisms like "Archea," "Bacteria," and "Eurkarya" with you in class. As you can see from the new image I've created (below right), these are the 3 main categories that most contemporary biologists use to talk about the present (and past) diversity of life on planet Earth!

So, when Prof S is doing his Critter days, in some ways he is sharing with you parts of the current structure of the 'tree of life.' If you click on the image to the right you will immediately recognize a couple of the names appearing in brown, red and purple colors: they are some of the groups of organisms that he discussed in the two Critter days that we've had so far.

To once again remind you of how the Critter days are not that far removed from speciation and Quiz 2, I've included a (somewhat transparent) reproduction of the stacked black arrow tree that emerged from our mental/visual exercises above (upper left corner of the image). See the resemblance between the two images? And even though the red box that showed what Quiz 2 was testing is not there anymore, can you also still 'see' it?

I thought so. You're getting the hang of this abstraction business. In addition, I guess it's official: The SCIENCE sEDiment Blog now has you seeing things that aren't even there (or are they?).

Which brings me to the other question that I promised to answer in this Blog. The one that I know you all care deeply about: Will anything from these Critter days be on future quizzes or exams?

I don't know...why doesn't one of you develop some guts...some courage...some daring...some mettle...some pluck...and ask Professor S in class on Friday.

:)

Lecture 9 (6/8/09): Getting ready for Quiz 2

I know lots of you are working hard to get ready for the quiz, so I thought I'd try to do two things in this post (I can't make it a long one tonight).

First, I want to summarize the most important points from Chapter I and Chapter II of the Biology Bedtime Story. In this summary, I want to tell you what I was doing and what I wasn't doing. Second, I want to try and put a little bit of organization around the Lecture 9 slides so that you can maximize your study time effectively. Here goes...

Did the Forts live happily ever after?

When we last left our finch population, we saw that the drought of 1977 absolutely tore them apart.

By 'tore apart,' I mean to say that they experienced one of the most severe selection pressures that Mother nature could throw at them. Was this a natural selection event? Yes it was. Absolutely.

As you'll recall from the bar graph at the bottom of the Chapter 2 Blog (also below right), the drought seemed to select against the allele combinations for the below average and average beak sizes. However, the drought also seemed to select for the allele combinations for above average beak sizes. Could this same change in the frequency of phenotypes in this Fort population have happened through genetic drift?

If you read my revised entry about genetic drift in the Chapter II Blog, then your answer should be, "Yes." It is possible that even without a natural selection event like a drought the beak phenotypes could change simply because of which birds happen to mate, and which gametes randomly join together in that process. This situation, however, even though it might result in a similar re-distribution of beak phenotypes, would not be considered natural selection.

So, my story about the Forts on the island of Daphne Major was meant to illustrate a natural selection event. Nature, in the form of a drought, selected certain phenotypes to surive the 18 month drought that started in 1977. Some of you may be wondering why those Forts with the above average beaks survive.

Well, once the drought began many of the plants on the island began to decrease their seed production. The Forts, in competition with each other as well as the other ground finches on the island, began looking around the soil and under rocks for any seeds they could find. Just like you and your friends when you are given a bowl of pistachios, the Forts cracked open and ate all of the seeds that were easiest to crack.

After a while, only the difficult seeds were left to eat! Peter and Rosemary Grant took pictures of the one seed that none of the birds seemed to want to eat, but they had to once all the rest of the seeds on the island were gone. Here it is at right. It's called a Tribulus seed and it comes from a caltrop plant. Nasty buggers, arent' they? Believe it or not there's small round seeds housed inside each of those spiky, woody sections which fit together sort of like a pinwheel.

Are you surprised that it was the Forts with the largest beak size/strength that had the most success opening these seeds during the drought? I suspect you aren't. The thing that might surprise you, however, is the difference in beak length/depth between those Forts that survived and those Forts that died. Are you ready for this? It turns out that the average difference was only about 1 mm. Those Forts that survived the drought had beak lengths/depths that were on average about 1 mm longer/deeper than those that died.

Was this a speciation event?

One thing I was to make clear is that my story was meant to illustrate a natural selection event, NOT the creation of a new species. In my story, as I explained in Chapter II, we saw a case of directional selection (you should know about the other types of selection too), but I said nothing about the creation of a new species. After the 1977 drought we still only had one species, Forts. The frequency of their phenotypes had changed, but there wasn't a new species of finch after the drought. The above average beak Forts could still reproduce with the below average and average beak Forts and produce viable, fertile offspring.

So this leads us directly to Lecture 9, in which Prof S spent nearly the entire period talking to you about what it takes to make a new species. He called this "speciation."

I'm not going to go into the details of what counts as a new species mostly because I talked a little bit about 2 species concepts in the Chapter I Blog (I talked about the Biological Species Concept & Ecological Species Concept). Plus, Prof S went over 4 species concepts in class and I don't really think there's anything tricky about them. What I do think is important is that you understand the Biological Species Concept (BSC) the best. That concept seems to me the one that Prof S favored in all of the disussions we've had thus far about species. So, according to the Biological Species Concept, how can you create a new species?

Well, according to the BSC you would have to create (at minimum) two populations from a single population. In addition, the two populations would have to lose the ability to produce viable, fertile offspring with each other.

So how does nature pull off something like this?

In Lecture 9, Prof S gave you two terms that had the word "speciation" in it: allopatric speciation and sympatric speciation. Using both your lecture notes and your textbook or other resources, my advice to you would be to get to know how these two types of speciation operate. How are they similar? How are they different? What conditions are necessary for each of them to occur? You should be able to talk through these two types of speciation pretty fluidly. The lecture slides in which these two terms appeared are copied below:

One thing I would like to point out, however, is that the order of the Lecture 9 slides may have confused you a little bit. Notice that the top of the slides above ask the question: How do these barriers arise? The "barriers" that Prof S was talking about in these two slides are the prezygotic and postzygotic barriers to gene flow (you should know the differences between these two types of barriers--Prof S spent a good deal of time on them in class--6 of 16 slides, in fact).

I want to make it clear that what Prof S was saying with these two slides is that allopatric speciation is one way that prezygotic and/or postzygotic barriers can arise. Sympatric speciation is another. Some of you may have been confused that the 'effects' (the two types of barriers to gene flow) were discussed first and the 'causes' (the two types of speciation) were discussed second.

That's all I have time to discuss now...