Sunday, April 28, 2013

California Tiger Salamander: Habitat & Scarcity

Yeah, yeah, it's been a while since I posted, I know. I've been tinkering with this one (and a couple others) for a while, but decided to break it into two or more posts just to finally get something up, to let any interested readers know I'm still alive. So, since I was asked to talk about about California Tiger Salamanders (CTS) a bit, here goes. I worked on a number of projects with CTS concerns in my years in consulting in California. I learned a lot about them, and I really enjoy talking about ecology, so these guys are particularly interesting to me.

California Tiger Salamanders are a fantastic example of adaptation to weird circumstances, so before I can describe them and their life cycle, I have to describe their most essential habitat: Vernal Pools. Oh, how I love vernal pools. A vernal pool is a depression in clay, or in regular soils underlain by bedrock, in such a way that it sometimes fills with water and then dries out. The exact timing of that varies from place to place, but a lot of them are like clockwork, flooding every year and staying full for several months before they dry up, regular enough that a whole ecological system has sprung up around the resources they provide.

See, when a vernal pool fills with water, plants adapted to that specific type and timing of inundation start to spring up. Plants that want to bloom earlier are in the outer ring, where the water first begins to recede, while plants that like more summery weather bloom closer to the center, or sometimes in the very middle after the pool has entirely dried up. The spring bloom of vernal pools is gorgeous, and you get concentric rings of flowers adapted to different timing, in different colors, spreading across a landscape. Frogs and birds and other creatures are attracted, and the birds often carry in insects or insect eggs. Little egg-like things called "cysts" that have lain dormant in the soil for as long as it took for the pool to become inundated again (in some places this takes years) hatch, and the pool suddenly becomes full of freshwater crustaceans called "fairy shrimp," also specially adapted to vernal pool habitat, and also highly endangered.

Think mail-order sea-monkeys, except you'd get thrown in jail for mailing these.

In some places, the meadows are full of these pools, just because the soils are clay-filled and clay swells to a waterproof muck layer when it gets wet. Whole networks of vernal pools and little swales are formed by one topping its basin and its water flowing downhill to form another. In some areas, the clay layer is fairly thin, and if someone were to dig a hole just a few feet deep in the middle of a vernal pool it would drain like a bathtub and possibly never fill up again. Vernal pools tend to occur more in meadows and grasslands than in forests, because trees can penetrate the clay or break up the rock layer, or just suck up all the water before any creatures can take advantage of it as anything more than a short-term watering hole. If it isn't there regularly enough and long enough, it isn't actually a vernal pool, it's just a puddle, and no vernal pool species can either find their way to it on the backs of animals or evolve adaptations to it. If it's there too long, it's a pond, and you get fish and plants adapted to permanent water. And since meadows and grasslands are prime building, farming, and cattle grazing space, vernal pools got fairly well wiped out. There's not a ton of them left.

Because the habitat is so rare and delicate, lots of the highly specialized plants and animals adapted to their conditions are endangered. So it is with the California Tiger Salamander. Something you have to understand is that being endangered doesn't mean that the creature lives a lonely life, searching across an empty landscape for a mate. It just means that there's not a lot left, and often this is measured in comparison to the former geographic range of the species. In some rural patches around Santa Rosa, CA, for example, when the right time in the rainy season hits, and they get a good drenching, if you went out for a walk you'd be hard pressed NOT to find a California Tiger Salamander. I've heard people grumble about this. But Santa Rosa just happens to be one of the last remaining areas that hasn't been overly developed, and also happens to have the right kind of clayey soils in a thick enough layering to hold vernal pools, enough so that agriculture and ranching haven't destroyed it.

The point is, there used to be many, many more places that could support this species. When a species gets winnowed down to just a few populations, even if they're incredibly dense ones, a single bad year can wipe it out. One too many droughts in a row, one outbreak of disease, one too many stressors imposed by climate change, and they don't come back. That's why the Endangered Species Act exists.

Anyway, CTS live in vernal pools for part of their life, and in mammal burrows for the rest, and return later when it's time to breed. That's all I've got for now. Next time I'll tell you all about the life cycle of the species, how the males and females approach mating differently, touch again on their fantastic gills, all that.