by Whit Gibbons

December 15, 2013

One of my grandsons brought me a book last week and said, "Grandpa, I want you to write about this. I think it's important." I looked at the book, "The 10 Most Destructive Ecosystem Invaders" (by Lisa Cheung), and decided that maybe it was.

The book is part of a series by Rubicon Publishing that focuses "primarily on educational publishing for K-12." I like their stated goal of improving "the literacy skills of all kinds of readers ... by creating material that is bold, creative and engaging, but also has instructional value."

The series has excellent photographs and catchy modules of information. In this book the ecological facts are enlightening and entertaining. Not everyone will agree that the 10 species chosen are the "most destructive" ones. Indeed, the author notes that opinions will vary about which species should be on the list and in what order. Your opinion might be influenced in part by where you live, but the critical point is that ecosystems worldwide are under siege by destructive invasive species.

The animals listed in the book include some I have written about before. For example, the zebra mussel. Listed as no. 10, it is an invasive species accidentally introduced from the Black Sea into the Great Lakes via cargo ships. One of the negative impacts is on native mollusks, which the zebra mussels outcompete. I can tell you from experience that these little shelled intruders have sharp edges, and when you step on them barefooted in a lake it hurts.

An amphibian I have talked about is the cane toad (aka marine toad) from tropical America that has been introduced to Australia and other regions with devastating environmental effects. Not only do these giant toads, which can reach over a foot in length, eat other amphibians they are even deadly to some would-be predators. A cane toad has huge glands on the top of its head that produce poisonous compounds. An animal that tries to eat one of these invaders ingests toxic chemicals. When cane toads are introduced into a habitat where native predators have no experience with them, the results can be deadly. The cane toad is given the rank of No. 3.

The brown tree snake is listed as No. 2. This quintessential invasive and destructive species, found naturally in the Australian and Indonesian regions, was unintentionally introduced onto the island of Guam in the western Pacific during World War II. It has become such a serious threat to local wildlife that Guam's native forest birds have been declared "virtually gone." At least a dozen birds known only from Guam are now extinct.

The book lists the Asian long-horned beetle as the No. 1 destructive ecosystem invader in the world. Native to China, these black and white beetles have been introduced in Europe, Canada, and the United States. The noticeable impact of the invasive beetles is the destruction of hardwood trees. The larvae burrow into native trees and eventually kill them because trees outside the beetle's geographic range have no natural defenses against them.

Why some alien species become rampant pests whereas others do not remains a mystery.

A record of all accidental or intentional releases of alien species would reveal that most never survive for more than a few generations if that long.

Others may persist but never reach high population levels; they simply become an inconsequential part of the flora and fauna of a region. For example, many southern cities have small, but persevering, colonies of inoffensive gecko lizards native to tropical Africa, Asia, and the West Indies. To my knowledge, none of them have become predators or competitors of any of our native species.

Some may quibble about the book's top-10 list, rearranging the order or substituting one invasive species for another. But there can be no argument that the uncontested, hands-down, indisputable leader in ecosystem destruction is humans. It's important to remember that.

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