نطق سوم

Lecture 3:

listen to part of a lecture. in a biology class.

Okay, i’d like to get started, please. Today we’re gonna look at some very unusual plants and animals that have evolved on some remote ocean islands. And of course, when I say that, the first thing that probably comes to mind is. the galapagos islands. right? The galapagos islands, which are located. in the pacific ocean, off the coast of. south America. That’s right, about 600 miles off the coast and being so isolated from the mainland.

the species that developed there were quite different from those that developed on the mainland. and of course, after charles darwin observed all of this, it got his wheels turning. And he eventually came up with his famous theory of natural selection. And that’s why you’ve all heard of the galapagos silence. but we’re not gonna talk about the galapagos silence today. No. no way. Out in the middle of the indian ocean, somewhere between Africa and India, there’s another little cluster violence, not nearly as famous, but every bit is fascinating, in my opinion. um. A little group of islands called the seychelles. how many have heard of them? ok, a few of you then. well, it just so happens that I spent some time in the seychelles a few years ago. so they’re kind of close to my heart. um, and and just like in the galapagos islands, an amazing variety of unusual species have evolved there, things you won’t find anywhere else in the world. for example, one of the things I saw there was a tiny frog that’s not a whole lot bigger than an ant.

in fact, it’s one of the smallest vertebrates on earth. ok. Here’s a little mystery for you. you rarely get frogs colonies on remote ocean islands like the seychelles. um, you have some other animals that an ocean current could carry out there from the mainland. but frogs are too delicate. They couldn’t withstand the salt and the sun and so on for that length of time. so how do you think the ancestors of these little frogs got there, ken? people brought them. Um, good guess. People have been responsible for transporting a lot of species from one place to another. no. oh, maybe there used to be some kind. of law. land bridge that used to connect the islands to the. uh and you. you know, like the one that used to connect asia and North America. a that’s close, ken, actually, the theory is millions and millions of years ago, the earth had only two huge land masses to super continents. and then around 200 million years ago, part of one of these land masses broke away and began to move slowly out into the ocean. And as that chunk moved away, fragments of it also broke off and were left behind. and that’s how the seychelles formed. and so the theory goes, many of the plants and animals living on these islands were stranded out there in the middle of the ocean and isolated from the mainland. these tiny frogs are just one of the species descended from those stranded species. diane, I’m just curious.

How did they figure out that the seychelles were once part of one big continent?

okay, that’s a fair question. well, there are two ways that I know of. first you have some species in the seychelles who’s closest relatives are in asia, and then you have others there that have distant relatives in both asia and Africa. now, of course, various species of animals and plants can drift or fly from island to island, so that in itself doesn’t prove anything. um. And then I’m not a geologist, so I I don’t know all the details, but I do know that part of how they came to that conclusion was because the seychelles are made up of solid granite. Bedrock granite is a type of rock that’s typical of continents. Islands are typically made of volcanic rock. so if an island’s made of granite, that suggests that it once was part of a continent. in fact, the seychelles are the only islands in the middle of an ocean made of solid granite, the galapagos islands, the hawaiian islands, their products of underwater volcanoes, their compositions very different from that of the seychelles.

uh, okay, where was I. oh oh oh okay. ok. So then you had a relatively small number of plants and animals isolated for a long time out in the middle of the ocean. uh, maybe with a few new comers drifting in. Now and then. and so you got some very interesting things evolving. And speaking of that, I just happened to have with me a few hundred slides I took when I was there. No, no, just kidding.

but I do have a few slides of some things you’ve probably never seen before.

alright? Would someone get the lights please?

go out for 12 hours in Quebec, Canada.