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Studying for a test? Prepare with these 8 lessons on Ecology.
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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 raise 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 on to 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 happened coincidentally alongside human activities when we introduced 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 going to 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 and 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 I've introduced species that's a number I have a hard time wrapping my mind around if you had an extra one point four 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 cause the transfer can happen long before we recognize 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 going to be good a hundred years from now or a thousand 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 introduced 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 of the newcomers introduced grasses and corn for example are eaten by native species and certain trees that have 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 anchovy fishery 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 has 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 pathogens 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 lat 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 skeletal 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 were 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 invasive to corral 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