>> Hello students.  This is Plants and Animals of Southern California.  And we're on Dirt Mulholland in San--
[ Cheering ]
We're in Dirt Mulholland in the Santa Monica Mountains.  And it's fall.  Everything is dried all up.  Actually, what I want to talk to you today about is maybe not so much the things that we're seeing, but some of the organisms that you would have, you know, come in encountered throughout your life.  And in particular, I'm interested in the difference between a deer mouse and a porcupine.  Like a deer mouse--here's what a deer mouse does.  A deer mouse makes more deer mouse and fast and then dies.  And a porcupine, a porcupine, it takes its time and lives a long time to make more porcupines.  So that's the difference between like rushing the reproduction and delaying reproduction under circumstances where the animal has a long period of survival.  And we can have similar things in different groups of organisms, not just mammals, where there is this kind of tradeoff between reproducing early or surviving a long time and reproducing later on.  And I think it varies from group to group, like certain groups will have a certain kind of biology and then other groups have another kind of biology.  So, there is a certain kind of thing that it's implied by being a mamma, like you're going to have determinate growth, you're not going to keep on growing and growing like a redwood tree would and you're going to, you know, take care of your young a lot.  So you might think that all mammals have a tendency, maybe to be kind of at one end to the spectrum to begin with, but there's different gradations of it.  And the spectrum I'm referring to is the spectrum between what's called r-selected species and k-selected species.  So, r-selected species are species that are--their adaptation is centered around increasing the rate of reproduction.  And r refers to--little r, it refers to this famous logistic curve where under optimal conditions and no crowding, a population can grow at a rate, little r.  So, deer mice populations can grow at a very rapid rate because they reproduce right away and then those babies grow up pretty soon and they reproduce right away, and those babies grow up pretty soon and reproduce right away.  That's an r-selected strategy.  On the other flip side of the coin, you might think a porcupine is a little bit more of a k-selected species.  And k that refers to the same logistic model but it's emphasizing instead of the optimal natural rate of increase the size that the population could grow to or its carrying capacity, k is for carrying capacity.  And k-selected species, they don't particularly have a rapid rate of population increase but they're able to compete with other species.  And in a similar way, we could kind of think about plants, right?  And in plants, we would think maybe a redwood tree would be the ultimate k-selected species, it's super competitive.  Once a redwood tree grows, there's nothing is going to out-compete a redwood tree.  And then at the other end, annual plants, they grow during the winter and then they reproduce in spring and then they're dead, and they wait until the next rains or something.  Those would be very r-selected species.  Like wildflowers, like annual wildflowers in the desert or around here, there's a lot of annual wildflowers that--they just--they live just to reproduce that one year and they used up all their energy and it's gone.  So, this is--the topic here is Life History Diversity, a diversity in life histories from species that are annuals, the species that are long-lived perennials and often really good competitors.  And as we look at different species within a group, then we can often say relative to one another which is more r-selected and which is more k-selected.  It's not so much that there's two categories of r-selected and k-selected where you can just put species into them, because of course, you know, relative to a mountain lion or something a porcupine is r-selected.  But relative to deer mice, a porcupine is k-selected.  It's more that it's--it's a really important access of variation.  And it's one that we could think of as being a tradeoff access.  That is it's good to level on time, so natural selection would favor living a long time.  It's also good to reproduce early.  A natural selection would favor reproducing early.  It's just that in reality, organisms have to allocate between these two components of fitness that are both good things, and so they trade off from one another.  So it depends on what kind of environments in.  If it's in the desert and it starts out being a long-lived perennial plant, then there would be natural selection for it to become an annual, right?  If on the other hand it starts out being a cactus already, there would be natural selection for it to be k-selected.  So it's not that r-selected is better than k-selected or k-selected is better than r-selected, it completely depends on kind of which way selection goes for that particular environment.  And in any community, you'd end up with some species that are more r-selected and some species that are more k-selected.  The r-selected ones would be often once it lived in disturbances or little patches where other places things can't grow.  And then the k-selected ones would be more competitive species, like the shrubs you would think of as k-selected.  If we had a fire coming through here, then you'd have a bunch of r-selected stuff for a while before the k-selected stuff came back.  We might think of k-selected as being super cool because we are very k-selected, right?  We delay reproduction then we have a very small clutch, like one usually.  And then we take care of that baby till they're 30.  It's--all the grad school maybe 35.  And so anyway, we--you know, we kind of think of k-selection as being a great way to live because your individual is doing great for a long time.  But that doesn't really mean that, you know, like natural selection doesn't exactly care about individuals, natural selection is just favors whatever gets the genes for those characters into the future.  And if it means burning through the individual and the individual dies but its offspring go on, and its offspring go on to make grand-offspring and great-grand-offspring really fast, then that can be the way that natural selection operates.  And it just sort of depends on, you know, the exact evolutionary trajectory of that lineage.  Now, it's the case that if you look at a particular group of organisms and you measure these life history characteristics for each species and then kind of take the average of each species.  So like for a whole bunch of these plants, you would measure how long it takes them to get to reproduction, how many seeds they make when they eventually reproduce, how big the seeds are and stuff like that.  When you measure those things and then you do it for a bunch of species, then the different components of fitness like age at first reproduction and longevity, they turned out to be negatively correlated.  Like in species that have long longevities they'll have delayed reproduction, and species that have short longevities they'll have fast reproduction.  So, that's some evidence about this tradeoff.  Another bit of evidence about this tradeoff is often if you take experimental populations, say fruit flies, and in these fruit flies you impose artificial selection for, say early reproduction and you only let the ones that reproduce early, you know, make the next generation.  Then you'll get correlated response to selection in longevity and they won't live as long.  Even though you didn't select for them to not live as long, it's just that those two things are related to one another by some kind of internal allocation of resources and time, of time and energy and all that stuff.  And so that's another way in which you can get clues about these tradeoffs.  It turns out, however, that if you just go into a population and you measure individuals and their life history traits, then it turns out that there is not always a negative correlation, often there's a positive correlation that is some individuals they are just super lucky.
^M00:10:10 They had good genes and they had--they landed in the right place, they were born at the right year and, you know, they just have everything going for them.  And then there's other individuals that are kind of losers, you know?  And I would call that access, an access of acquisition as supposed to allocation.  That is some individuals have been able to require more resources and so they're good in all sorts of ways and other individuals have not been able to acquire resources either because of their genes or something else.  And they don't have a lot of resources to devote to anything, any of the different components of fitness.  And it's this balance between allocation and acquisition that determines whether the relationship between components of fitness would be negative or positive.  It would be negative if allocation dominates in determining what the variation is and it would be positive if acquisition dominates in determining what the variation is.  Now, there's other components of fitness besides just age at first reproduction and longevity.  Those are just ones I've kind of pulled out of the hat.  And they're import--you know, they are important ones.  But there are some other things like that vary sometimes and that we also think are involved in tradeoffs.  One is how big the babies or seeds are and how many seeds or babies there are, like a plant might have a certain amount of energy, it can devote to reproduction.  And it could divide those up into a bunch of little tiny seeds or it could divide them up into a small number of great big seeds.  And that would be another one of these allocation things.  If you want to come back to animals, a case might be the number of eggs.  They are laid at any one reproduction episode.  So like an albatross which is a bird that lives for a long, long time, an albatross would often lay just one egg at a time and an albatross can kind of--you could think of it as the average albatross is going to live a long time and have lots of reproductive episodes whereas if you have some bird that doesn't live for a very long, a robin, then it would tend to lay several eggs at a time.  Now, it actually turns out that birds are a bit conservative.  And on the whole, birds tend to lay fewer eggs than they're actually able to maintain.  Like if you take other eggs and you stick them in there they're actually able to raise one more chick than they could, and the ideas that natural selection has acted on these birds to kind of save a little bit of their energy for a subsequent reproductive episode so that they don't completely exhaust themselves with that clutch.  And then next year they'll have--they'll start out strong and be able to command another clutch.  I guess the things to remember from these are, that they're already sort of access [phonetic] of variation where organisms can't kind of get the best of both worlds as species diversify.  And so they tend to shift along an envelope of a tradeoff towards one life history trait or another life history trait.  And life history traits, just like teeth and claws and fur, they are characteristics of the species, so natural selections acts on them and such.  So, that's all that I have to say about that.
[ Laughter ]