Disruptions to ecosystems
Introduced species and biodiversity
- [Narrator] At first glance it might seem that introducing new species the human act of taking species from somewhere else and dropping them in a different area, would be good for biodiversity. Let's face it, if you take a bunch of beautiful flowers and plant them in your garden you're increasing the biodiversity in your garden, right? You raised the species richness in your garden. But it's not a simple additive equation. It's more complicated than that. The term introduced species is synonymous with exotic species. The definition is, any species that through the activities of humans is knowingly or accidentally transferred from its native habitat into one in which it doesn't naturally occur. An introduced species is the opposite of a native species. Which is one that occurs in an area naturally. Without human intervention. Many introductions are intentional. We do it on purpose. And we've been doing that for a heck of a long time. Probably ever since humans came onto the scene and realized that they could pick something up that was alive and bring it somewhere else to serve their purposes. From goats and pigs to cattle and crops, mostly we transport organisms that will do some good for us through agricultural means. We've been introducing plants and animals to places where they weren't native for a long, long time. Usually when people think about introduced species they're really thinking more about the accidental ones. The things that happen coincidentally alongside human activities. When we introduce a species to a new area, everything that's living on, in, or with that species comes along with it. If you pick up a cow from one place and move it to another, it's gonna bring along all the parasites that those cows normally deal with. I think people immediately picture images of rats streaming off the ships when they pull into some beautiful Tahitian paradise. Or the snakes that came into Guam with military movements during World War Two. These animals are legendary in doing damage to native birds. They're very obvious ways that introduced organisms radically change biodiversity, in a single place. There are so many other subtle ways that introductions happen and cause problems. The bottom line is that the world economy is hit with an annual cost of 1.4 trillion dollars dealing with the negative impacts, obvious and not so obvious, of introduced species. That's a number I have a hard time wrapping my mind around. If you had an extra 1.4 trillion dollars to play around with there's a lot of possibility to do some good in the world. Because humans have been introducing new species for a long time, the concept of native habitat is a little bit slippery. The human activities that caused the transfer can happen long before we recognized that it actually happened. So that sometimes the history of an introduction can be lost. When we aren't sure of the history, up until the point we are sure, or have some reasonable evidence, we call those species cryptogenic. Crypto means hidden. Genic means origin. Solving the riddles of cryptogenic species underscores another reason why collections are so important. The only way to trace the origins of introductions is to know what was there beforehand. Collections can preserve that historical information and collections made today establish baselines for future reference. If those collections are maintained in perpetuity those baselines are gonna be good 100 years from now. Or 1,000 years from now, when we see a radically different and altered environment due to the introductions. So we can use collections to try and get answers to this problem. Not all species are in fact harmful. Clearly they're not all harmful to us. Because the ones that we introduce on purpose are ones that are there for our benefit. Some introduced species can provide new food sources or even habitats for native species. Native species aren't always helpless and harmed. They can make use of some of the newcomers. Introduced grasses and corn for example, are eaten by native species. And certain trees that've been introduced can serve as habitats for birds. Some introduced species live under our radar, we don't even know they're there. Doing little perceivable damage to the ecosystem, by reducing species richness. But some introduced species certainly go beyond just living peacefully, alongside the natives. They can do this because they have competitive advantages. They lack natural controls, such as the predators or diseases that keep them in check in their native habitats. Some invasive species are generalists. Which means they can tolerate, reproduce rapidly, and thrive in a wide range of environmental conditions. Allowing them to successfully compete with and overwhelm native populations. When introduced species take over an environment at the expense of native species, they're known as invasive species. All invasive species are introduced, but not all introduced species are invasive. Here's an example of consequences for humans as well as for species richness. In 1992, an introduced species of comb jelly was found in the Black Sea. Comb jellies are weird, transparent, jellyfish-like forms with a voracious appetite for fish larvae and eggs. Within months that single introduction resulted in the total collapse of the anchovie fisherie, in the Black Sea. Comb jellies tolerated the conditions in the Black Sea and their population exploded, at the expense of the anchovies. The bottom line here is that introduced species can out compete the natives for food, for space, and other resources. They alter the ecosystems food webs, disturbing crucial elements and interactions that would otherwise contribute to healthy ecosystem function. The comb jelly is a good example of that. Sure, your species list for the Black Sea is gone up by one, but it destroyed all the anchovies. You have to take a species off the list. Plus, perhaps whatever else was eating the anchovies. And before you know it, because there's nothing for the comb jellies to eat anymore, they're gone, too. So, not only have you not added a species, but in the end you've actually subtracted a whole bunch. So invasive species are ultimately, organisms that cause decreases in ecosystem function. That's another definition of invasives that we need to come to grips with. What's worse, invasives very seldom come by themselves. As I was saying with the cow example, they often come with new diseases, new parasites, new accompanying effects, that we can hardly predict. Another good example of invasives are pathagens. Something that we don't often consider as invasives. These include disease-causing organisms like, fungi, or bacteria, and even viruses. These are things that we also introduce to wild populations. And there are extinctions that come from that. In fact, in the past 500 years we've directly caused the extinction of more than 100 species of birds, partly through the introduction of disease and heck knows what damage we did to organisms that were depending on those birds. In the forest realm, Dutch Elm disease was something that, when I was growing up was a huge thing and actually it still is. In North America, Dutch Elm disease left skelatol trees for miles and miles. When I was a kid growing up in Toronto in the '60s 80% of the elms in the city were killed. And it was really sad. Those trees were not only gorgeous, they were very important lumber. Elm trees were a direct service to us, in so many different ways, from producing shade to furniture. The fungus was introduced by bark beetles, some of which were native and some of which were introduced. Both of which supported and co-evolved with the fungal pathogen. Which could not be stopped. This idea of being a generalist, the ability to reproduce and displace natives, the ability to become more abundant at the expense of other species, to introduce diseases, to proliferate in non-native habitats, that should sound pretty familiar. Because that's us. In some ways, we are the ultimate invasive species. We don't just introduce ourselves, we are invasive. The difference is that unlike the comb jellies and the bark beetles and cows, we're capable of recognizing that fact and maybe mitigating our impact. We can look at the world and the problems and start thinking about ways to control the invasives, to coral them, maybe to reduce their effects and not introduce them in the first place. We have to, not just for moral reasons, I think, but because ironically, and as we said earlier, the invasives that we're bringing with us accidentally or on purpose, can do a lot of harm to species upon which we depend. Worse, they can upset healthy ecological functions upon which all life depends. Including us.
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