Hello students.  This is Plants and Animals of Southern California and we are at Paradise Falls next to this great creek that is flowing throughout the year.  So, it's an unnatural creek in a certain sense.  This creek didn't use to flow that much throughout the year.  It flows this much because people are adding water upstream.  And so even though it's in a Mediterranean climate where creeks are supposed to flood during the winter and then die down during the summer, and by fall just be a series of pools that are not even connected by any flowing water.  Even though it's in a climate where that's what happens to the creeks, this creek is not doing that because it's had its constant input of water throughout the year.  We can call this an urbanized creek even though it's flowing through the middle of a wild open natural area.  And so, what I want to do is kind of engage in a little bit of theorizing about how creeks like this might have changed from natural creeks that I'll call drought flood creeks.  Like they undergo drought and then they undergo flood and then they undergo drought and then they undergo flood.  And the amount of flood is different from year to year.  It's just a lot of stuff like that.  Those creeks are the types of creeks we would have had in the Mediterranean climate all over the place in Southern California.  And then some of those creeks have been changed to be urbanized creeks that have water in them flowing rapidly all year round.  So, the first thing that I think that happens is the algae do really well in these urbanized creeks because algae really don't like drying out that much.  Like drying out is not a good thing for an alga.  Also, these urbanized creeks tend to have more fertilizer in them, you know, like they're draining golf courses, they also have waste water discharge and so they'd have nitrates and phosphates and stuff like that in it.  And algae love those nitrates and phosphates and stuff or at least some algae do.  And so you kind of get a bit of an algal bloom going in these urbanized creeks.  They're a little bit eutrophied.  That means that they've had nutrients added, whereas oligotrophic streams are ones that don't have very many mineral nutrients in them.  And mosses and liverworts would really like to live in oligotrophic streams.  So if you look at the streams that are coming off of the Sierra Nevada, those--they're just lined with mosses.  There's lots and lots of mosses there.  And by September, there's almost no water in them.  There's a little bit, but you know, there's not that much water in compared to what there is in February and the mosses are all dried out.  Mosses don't mind drying out and they don't mind the fact that there's not that many nutrients in them.  Whereas this creek at Paradise Falls, it has water flowing throughout the whole year and there's quite a bit of nutrients in this water and it's got a lot of algae.  We would say that it's a eutrophic stream, whereas the Sierra Nevada streams are oligotrophic streams.  So, then let me sort of speculate about the difference between one of these drought flood streams versus an urbanized stream in Southern California.  And I'm basically kind of drawing this from logic and maybe the comparison of Mediterranean climate streams to streams that would be in some place like Georgia where, you know, it's raining in the middle of summer time and they have the same amount of rain in the summer time as they have in the winter time.  So the first thing is the nutrient inputs I think would be greater for the urbanized stream than for the drought flood stream.  The seasonal fluctuation and the height of the water would be greater in the drought flood stream than in the urbanized stream.  Like there's almost no water during the summer time.  The among year fluctuation in both nutrients and also floods, that would be greater in the drought flood stream than in the urbanized stream.  The connectivity of everything, especially during the summer would be greater in the urbanized stream than in the drought flood stream.  'Cause in the drought flood stream, you get little pools that are not very well-connected to one another during the summer time, whereas the urbanized stream, summer time same as winter time.  You know people keep on watering the golf courses.  It's all--The seasonality is much less.  So the connectivity structure would change.  I think also nutrient retention would kind of change.  That is, in the drought flood stream--and what happens is leaves fall down, but then they're dry so they don't mold very readily, right?  They just kind of sit there, all right, and then what happens?  Eventually it rains but then it rains too much and it just flushes the stuff all out.  So, nutrients are not really retained that much, whereas in the urbanized stream, stuff drops in, it gets wet, it gets moldy, things eat it.  You know, like the community just sort of starts recycling this stuff and it gets incorporated into the biotic lining of the stream before the floods come and wash stuff out.  So it's kind of held down a little bit better.  Nutrient retention I think would be greater for the urbanized stream, OK.  Now we might also think about the speed at which these allochthonous inputs, leaves and things are processed.  And I think that they're--be quickly processed when it's wet in the urbanized stream and whereas it would--the processing would be delayed during drought periods for the drought flood stream.  And then during the floods periods, you know, it's become this torrent of mud that's just coming down the stream and it's much more abiotic in its character.  We might also say that there would be a kind of a seasonal cycle or a heartbeat of the community of macroinvertebrates for the drought flood stream that would happen.  You know, like there would be a certain set or guild of animals that would be doing really well in the winter.  But then the--there's changes to the kind of stream it is pretty fast.  So by March, that wouldn't be the right stream for those kinds of organisms.  Other organisms would rise up and have more of a dominance.  And then, you know, by May that wouldn't be the good stream for the stream organisms that were doing well in March.  So throughout the year, there just be a more of a seasonal change in the composition of the stream invertebrates whereas in the urbanized stream, it would be of little more constant in the way that they are handling it.  Overall, we might say that there would be more grazers in the urbanized stream than in the drought flood stream because there's more algae.  The algae are doing great in the urbanized stream.  So, there should be more grazers in the urbanized stream than shredders in the urbanized stream.  We might take the ratio of grazers to shredders and say it would be higher in the urbanized stream than in the drought flood stream.  I would think that the importance of K-selected species would be greater for the urbanized stream.  The urbanized stream, it has a lot of algae growing on it and things are not changing a lot.  So, probably biotic competition among those organisms that are able to live in that kind of climax situation would be much greater, whereas in the drought flood stream, the ability to take advantage of some resource quickly would be important.  So, it would be--our selected species would be a bigger deal in the species' composition for the drought flood stream and for the urbanized stream.  I don't have any data on any of this, but you know, I'm willing to speculate.  Let's think about this a little bit.  There are certain features of organisms, let's call them adaptations, that do well in a Mediterranean climate.  So, for stream invertebrates, a quick lifecycle would be an important one.  You know, just being able to get through your lifecycle pretty quickly because the stream is changing.  And so, the stream might be a great moment now for your species, but it's probably not going to be a great moment six months from now for that particular species, be great for some other species.  These organisms often then have more than one generation per year, whereas in a kind of a climax community like in Georgia, stream is always the same, being able to compete might be more important.  And so, they have fewer generations and put more of their energy into each individual being able to fight out its space. Asexual reproduction tends to be more important in the Mediterranean climate.  It's constantly seasonally changing than I think it would be in this urbanized stream.  And if the species has some kind of stage like an egg stage or a pupal stage that can survive with almost no water, then that species has a much better chance in a Mediterranean climate than some species that constantly needs water washing over it, you know, 365 days a year.  And the ability to kind of burrow down in the gravel and find little bits of moisture even when there's not water flowing on the riffles is something that's favored on the Mediterranean climate.  The ability to disperse between the pools is, you know, a big feature of our species.  And it wouldn't be a big feature of species in streams in Georgia because there's no problem going between the pools, you just let go and then grab on a little bit later and you're in a different pool, whereas our organisms are not that well-connected among the pools.  The ability to breathe air, so air-breathing species might do better in our communities because these pools are going to dry up, right?  We're talking about kind of small streams, they dry up and then an organism that can breathe air is going to do better than one that's relying on oxygen exchange through its skin because there might not be that much oxygen in this little pool at the end of the season.  Now we might also note that in a Mediterranean climate, we have a lot of endemism and rarity and kind of unusual stuff, that is accentuated by the differences in the streams.  Like each little part and reach of a stream, it dries up at a different rate.  And so you're starting out with, you know, this torrent and then it starts drying out a little bit.  And the things that are in the riffles, they're out of luck.  But the things that are in the pools are still doing OK.  And they might be shredders that are eating stuff.  And you might have this big boom of shredders for a while but then that's going to dry up.  And then predators are kind of eating all of the shredders up.  And this is not all happening exactly simultaneously in the different streams.  So among stream biodiversity is really great in Mediterranean climate.  You go from stream to stream to stream you find different stuff in a Mediterranean climate, whereas I think in these urbanized streams, you go from stream to stream to stream and you find the same stuff in every urbanized stream because they're all just flowing all the time.  Anyway I would think that the urbanized streams are going to ultimately contain less of these rare, weird, wonders, these endemic species that kind of live on the fact that the stream is constantly changing.  And then they would contain more of kind of climax species.  They would also maybe contain more alien species.  I would expect that the drought flood stream would be resistant to alien species, whereas the urbanized stream, it's a kind of unnatural stream, right?  It wouldn't have existed here before we started adding water.  And so other species that are adapted to other places have come here and live in our urbanized streams, alien species.  And then finally the mosses don't like the urbanized stream.  So mosses and liverworts are not going to do well in urbanized stream, whereas I think they do well in a drought flood stream.  All of these are just predictions, you know, like nobody has gone out and tested this.  We know a very little bit about the stream ecology around here, like we know that California newts and California tree frogs are really doing very poorly in the streams that have become very urbanized.  But those are the big charismatic animals.  And when a tree frog is a big charismatic animal, you know that you don't know anything.  I'm talking about the little, teeny organisms in the ecosystem.  Okay, and that's all that I have to say about that this year.