Howdy doody, students?  This is Plants and Animals of Southern California.  And I thought we might talk a little bit about what a species is not.  I think it's difficult because in our common language, we think of a species kind of in the same way that we think of a triangle, you know, like we talked about species, and so they have essences.  And that they are kind of these fixed things in nature, it just kind of part of our language to speak of them typologically as though they were a type.  And yet, if we go and consider lots and lots of species, there's very little that we can say about them in general.  So, there are some species that can contain lots of variations, lots and lots of variation.  And there's other species that contain almost no variation.  There are some species that have a very broad geographic ranges and there's other species that have very, very narrow geographic ranges.  There are some species that are ancient.  As far as we can tell, the species or something like the species has existed for tens of millions of years, and there's other species that have arisen over the last 100,000 years.  So, it's kind of unfortunate that when Darwin figured out that species are not fixed, he didn't throw away the word species, because now we have to struggle on still using this word that has this kind of feeling of being a type like a triangle or pentagon, when in fact it's not.  One thing that's helpful to consider is if you were to kind of go across nature and pick two closest relatives, things that you thought were closest relatives and do that a hundred times, you know?  So it's us and chimpanzees, and the African elephant of Savannas and the African elephant of the forest.  You know, like you get a bunch of these pairs, a hundred of these pairs.  Then what could you say about this in this kind of thought experiment is that the depth where--that you have to go back in time to a common ancestor of these pairs could vary enormously.  Like in some in cases, like us and chimpanzees, you know, might be 8 million years.  In other cases, it might be 80,000 years.  In some cases, it might be 80 million years, you know, like be a huge amount of difference just in that.  How much you'll have to go back between members of sister species to find their common ancestor.  And then there's other kind of complications that immediately arise like the way that I post it is just based on the species that taxonomists would recognize.  But what if one of the species that you're thinking about, it actually consist of two different things that have been reproductively isolated from each other for a very, very long time but they haven't diverged morphologically or even ecologically very much.  And so taxonomists don't recognize in these different species.  That's certainly possible that one member of the pair could be that.  It could be--it could actually consist of two things that we choose not to call species because they haven't diverged very much.  But that--have been separated from each other for a very, very long time.  And when what if the other member of the pair has very recently evolved?  It very recently evolved from one of these two cryptic ancient lineages, like say you had the lineage being some fish that we're in the Atlantic Ocean and the Pacific Ocean.  And, you know, various [phonetic] fishes in the ocean, they look exactly the same, but one is right in the Atlantic and one is in the Pacific, and they haven't been interbreeding with each other for a very long time, like--since North America and South America crashed into one another.  And then from one of those lineages, say the pacific lineage, you had a little side branch that started going up the rivers.  And once it went up the river, of course, it was in a new niche and so it diverge radically, and nobody in their right mind wouldn't call the one that lives in the river, say in the Columbia River Gorge, a species.  But then you're kind of caught with this problem that the thing that it came from, its progenitor is both paraphyletic and anciently so.  I guess the, you know, like the message that I want to come across with this is this wouldn't be a very--this exercise of kind of going through and finding lots of pairs, what you would find is that the pairs have not diverge from each other in the same way at all, you know, like there would be a hundred different cases of how they diverged from each other.  So we can kind of think of like the human species is being this--species that's very broadly distributed and has lots of variations, it's probably due to sexual selection and there's a lots of clinal variation, but it has some really cool characteristics like we teach evolution to one another, which I think mostly the other species don't do that much.  Where there's other species like this Brickellia here, it's not very special.  You know, it's not that different from the next Brickellia over.  You know, like there's some characters, they've diverged from one another but it's not a character that's kind of moved into a new zone.  So, just be careful for the rest of your lives about the way use this word species 'cause--don't make it mean more than it actually means and don't interpret other people's use of it as though it means a lot.  It just sort of--I don't know, it's kind an ominous [phonetic] arbitrary thing that we use to keep track of things.  It's useful but I think people many will get in trouble by making it mean too much.  So, I would take--don't try to make it mean that much.  It means different things in each case.  OK, so we we're talking about what species is not.  And so, let's then bring this back into our consideration of coevolution and really here what I want to do is take the "co" out of coevolution, it just evolution most of the time.  I think that what's meant by coevolution is a situation where--let me characterized it.  Where you have one species and that species adapts to a second species.  Say you have a host species and a parasite species.  The host species adapts to the parasite species and the parasite species adapts the host species, and the host species adapts to the parasite species, and the parasite species adapts to a host species, in other words, it's reciprocal, back and forth and back and forth.  And the implication of coevolution is that it's at the specie's level, that these species are adapting to one another.  But remember, I told you that you shouldn't take too much stock in the implication that species are units in nature, and let's see how that's plays itself out because if we're talking about host and parasites, then it could well be that you have a species of parasite that parasitizes several different species of host.  So, you could have a species of parasite like the mistletoe parasites that infect juniper and they infect not just California juniper but also Utah juniper and occasional [inaudible].  In this case, you would have the parasites that are maybe specializing on one kind of plant or another but it's kind of hard to see how the plants would be specializing on that particular species of parasite.  And so, the kind of that lock step reciprocal coevolution that we're imaging it wouldn't quite be at the specie's level.  Now if we take some other types of interactions that are less symbiotic, so it's just sort of your ordinary mutualism like a pollination mutualism.  Then, yes, of course, bees are adapted to flowers and flowers and flowers are adapted to bees.  But it didn't happened that a particular species of bee adapted to a particular species of flower and that particular species of flower adapted that that particular species of bee and it went back and forth doing the two-step all around the dance floor.  No, not at all.  What happened is a long, long, long, long time ago, there were some flowers and those flowers were adapted to beetles.
^M00:09:58  And then there were wasps that ate the beetles or something like that and started going and visiting the flowers, and then started being pollinators to those flowers.  And those wasps then started eating pollen of a whole bunch of different species of flowers, you know, they weren't particular to any type of flower.  And the flowers at that point were not adapted to the wasps at all.  And so, then this lineage of wasps adapted to eating pollen and they became what we now call bees.  And they radiated onto a whole bunch of different flowers and became lots of different lineages of bees.  Then eons later, after that has all been established, then--yes, there were times when there are particular lineages of flowers, that kind of find tuned what it means to be a flower and adapted to bees, but they didn't adapt to any particular species of bee or maybe they did adapt to particular species of bee but that's not the particular species of bee that any longer pollinates them.  You know, like other bees moved in, those bees died out when extinct.  So, if we just talking about the kind of non-symbiotic interactions that we find as mutualisms or antagonistic ones also, then it's what you might call diffused coevolution, which is coevolution without the "co".  It just that organisms are adapted to their biotic surroundings.  And over the long course of history, they've adapted to different biotic surroundings and those biotic surroundings have adapted to them, but it wasn't reciprocal exactly, it wasn't simultaneous, and it wasn't at all species-specific.  OK, so that's on array [phonetic] in which we shouldn't kind of take this word species too seriously, that is we should imagine that some of the evolution that happened between different forms of life was evolution that was not specific to the species, and instead was at the higher level than species.  Pretty big groups, you know, great big groups of lots of species of flowers, great big groups of lots of species of bees.  It's also the case that sometimes we should think of coevolution way below the species' level.  If you'll remember the newts and the garter snakes, it's not really that garter snakes are adapting to newts, and the California newt is adapting to that particular species of garter snake.  And really what happened is that a long, long, long time ago before garter snakes were an issue, newts evolved this tetrodotoxin in their skin.  That was already established.  And then we get this particular group of garter snakes which actually includes not one species but several species and these species are all in different populations.  Now, what you come on the scene and you realized, "Oh, there's co-differentiation of the populations of newts and the populations of garter snakes."  And so, that's coevolution, yeah, but it's kind of mosaic coevolution that's well below the species level.  It's different populations are adapting to the partner that they're with.  The newts are increasing their toxin level because they lived with garter snakes that are more tolerant of it.  It's just that there's been evolution to increase the strength of the toxicity in populations where garter snakes had become tolerant.  So, in other words, I think that this thing that I call biotic evolution, it's what everybody else calls coevolution and it's--sometimes above the species' level and sometimes below the species' level, and it's rarely just at the species' level, and that is all that I have to say about that.