Hello, students. This is Plants and Animals of Southern California, and we're at Vasquez Rocks, which is kind of on the edge of the desert, and we might call this vegetation Juniper woodland, which is sometimes also lumped in with Pinyon pine woodland.  So remember there's Juniper and Pinyon pine, and those live on the mountaintops that are kind of rimming around the desert.  Okay so today I wanted to kind of clear up a few things.  One little set of terminology I need to introduce is how different types of organisms interact, and I'll call these species interactions, although I'm not specifically paying attention to species, like don't dwell on the rank of species.  It's like interactions between different kinds of organisms.  So there's sort of a classification of these types of interactions if two organisms are having negative effects on each other's populations.  So kind of think... try to think of it as the population level.  If the two actors are having negative effects, we'll call it competition.  So, for instance, if these Junipers are having a negative effect on the chamois and the chamois is having a  negative effect on the Junipers, then that would be competition.  If either population would grow if the other one was cut back, then that's kind of a sign of competition, and then in contrast we have other types of interactions that are positive interactions.  So you  might have positive interactions between two organisms.  For instance, there's bees out here, right, and the bees would be visiting flowers, and if the flowers are getting pollinated by the bees, then that's good for the flowers, and if the bees are getting food from the flowers, that's good for the bees, and so that would be a win-win, and win-win's we'll call mutualisms.  So negative-negative is competition, and positive-positive is mutualism, and then of course you have situations that are positive for one of the actors and negative for another actor, and those are variously called predation or parasitism.  So if a coyote comes up and eats a jackrabbit, then that's predation, like outright killing it and then eating it.  That's predation, whereas if you have say on these Juniper plants you have mistletoes, and the mistletoes are not really outright killing the Juniper plant, they just make it a little less healthy, then we'll call it parasitism, and the Juniper plants, of course, have lots of parasites.  Some of the parasites are plants, mistletoe, but then they also have parasites that are animals that are, you know, eating the Juniper just a little bit but not killing it, probably lowering its fitness some and lowering the population's, you know, health a little bit.  Now in addition... so those are kind... that's a positive-negative interaction.  Now, in addition you can have interactions that might be positive for one of the actors and then not have much of an effect on the other actor, and that's sometimes called commensalism. So, I don't know if it's the case, but let's say that there's birds that need these Junipers.  There's certain birds that need these Junipers, and it has no effect on the Juniper.  It's just basically no effect on the Juniper or very, very little effect on the Juniper, but it's essential for the bird to have the Junipers.  If the Junipers disappear, the bird's population would be drastically cut back.  That's what I would call commensalism.  Okay, now if that's not complicated enough then there's some other words that we also sometimes throw in.  There's this word called facilitation, and that's a word that includes both mutualisms that are plus-plus reactions... interrelationships, positive for both actors, and interactions that are commensalisms that are kind of neutral for one actor and then very positive for another actor.  So facilitations are interactions that on the whole might be considered positive as opposed to antagonistic relations, which are ones that are more like the predation or parasitism or competition.  So antagonistic relations versus facilitative relations are a kind of coarser way to classify things, and you might really, you know, kind of debate how much in, say, a plant community is it facilitation and how much of it is antagonism, and that might even change from plant community to plant community, and ecologists go out and measure stuff like that.  So a possible facilitation might be that underneath the Junipers there are certain plants that profit from the shade of the Junipers, right, and that would be a facilitative reaction... interaction.  And then this community's also been invaded by some alien plants... alien plant... alien plants from the Mediterranean, and these alien plants, like for instance there's a grass here called Bromus tectorum.  There's a lot of it out here.  Then they are sometimes... some of these alien plants are very invasive, and they'll go, and they'll make a lot of seeds, and those seeds germinate really fast after the rains come, the Bromus tectorum, and then they grow up and they both disturb the soil some and take over, and they also take resources away from other plants that might have a somewhat slower life cycle.  So we'd probably view that as a very antagonistic relationship, that invasion of Bromus tectorum.  Okay now it's important to understand that these interactions between species, they are not necessarily always the same.  They can be very conditional where, you know, under certain circumstances bees are mutualistic to  flowers and then on other circumstances a certain kind of bee might be a parasite, a conditional parasite of the flowers, like for instance, let's say we have a flower out here that can be pollinated by either hummingbirds or bees.  If there's no hummingbirds around, then the bees would be a mutualist.  They'd be carrying pollen, but it turns out that people have measured the quality of pollination provided by hummingbirds, and it's often a lot better than the quality of pollination provided by bees.  Under those circumstances, a bee that comes and removes nectar and removes pollen is taking pollen out of the system, pollen that would have been transported by a hummingbird, which would have been a better pollinator, and so if there's a lot of hummingbirds in the ecological community, then the bees become conditional parasites, and so you have to kind of like always be thinking of it in a fluid way, like depending on what else is happening within the ecological community, something can flip from being facilitative to being antagonistic.  Okay, now another word that you'll come across is symbiosis, and symbiosis is a relationship between organisms that's very intimate, that's very close where they're interacting with each other sending specific signals and then reacting to those specific signals, and symbioses could be mutualistic, like you have some symbioses that are mutualistic, and I guess we'd call those mutualistic symbioses where both actors are getting a net benefit.  So like in lichens we have the algae that are providing photosynthates, the sugars that result from photosynthesis, and the fungi that are providing a home for the algae.  Those algae wouldn't be able to live all over those rocks without the fungi, and so I think on the whole we usually think of algae and fungi and lichen as being mutualistic symbiosis.  In contrast when we go out and look at the Junipers, we'll see that there are these galls that are formed, and those galls are formed  because something like a midge, a mother midge, laid an egg and on the  bud of a Juniper and then that midge, that baby midge, would secrete chemicals that are like the hormones of the Juniper, and the Juniper then reacts to those hormones and grows a whole house around the baby midge.  That's a gall, and so that's a symbiosis.  It's a very intimate relationship between the Juniper and the midge, but it's not a mutualistic symbiosis.  It's a parasitic symbiosis, and then we also have to realize that this, too, is potentially conditional, that under certain circumstances a symbiosis can be mutualistic and then under other circumstances it can be antagonistic, and over evolutionary time, you might even think that things would coevolve in ways that would change whether the relationship was mutualistic or antagonistic.  So those terms I'll be using a lot, and they're kind of like the building blocks of understanding how the community functions ecologically, and that's all that I have to say about that.