When Species Invade

Adapted from photo by Michael Durum 

     This week’s World Wide Wednesday* features 3 stories about invasive species, which are non-native plants, animals, or other organisms that have been introduced to a particular ecosystem usually through human activity.  Invasive species generally cause ecological and economic damage to their new habitat by competing for resources or preying on native species. This week we’ll explore examples of harmful invasive species as well as an invasive species that’s playing nice with its new neighbors.

Beware soft fruits, the Drosophila suzukii are coming!

D. suzukii male

     Most Drosophila species, including the popular lab strain D. melanogaster, are attracted to rotting fruit in which to lay their eggs, but not Drosophila suzukii. Otherwise known as the spotted-wing drosophila, D. suzukii prefer to inject their eggs directly into the flesh of fresh fruit. Once hatched, D. suzukii larvae will eat the fruit from the inside and is therefore an economic threat to fruit crops such as cherries, blueberries, raspberries, blackberries, peaches, nectarines, apricots and grapes:

D. suzukii larvae in a strawberry. (adapted from photo by Hannah Burrack)

     Unlike other Drosophila species, female D. suzukii have a rather diabolical (to fruit at least), saw-like adaptation of their ovipositor, the external organ that deposits eggs, which allows it to pierce the skin of soft fruits:

Left: D. suzukii ovipositor. Right. D. simulans ovipositor. Adapted from image by Martin Hauser.

     Originally identified in Japan and Asia in the early 20th century, D. suzukii first appeared in California in 2008 and quickly spread across the Pacific Northwest. It has since found its way to  Southeastern US states, Michigan, Wisconsin, and even Maine. More recently, the spotted-wing drosophila has been spotted in European countries as well. The spread of D. suzukii is most likely due to the export and import of affected fruits.

A smug nutria asks, “When is an invasive species no longer invasive?”

Screenshot from Hi. I’m a Nutria. 

     Last week, the New York Times posted this Op-Doc animated short by filmmaker Drew Christie that explores the existential question facing all invasive species,  “How long does it take to become a native?” The short video provides a brief history of how nutria were originally brought to America to start fur farms and rightfully lays the blame on human activity for the introduction of the over-sized rodents to the Pacific Northwest. As nutria fur demand declined, many farmers simply released nutria into the wild. Drawing comparisons to other invasive species to the Pacific Northwest such as the American bullfrog, grey squirrels, house sparrows, and oh yeah humans, the nutria asks, “why do I get all the grief?”

Photo credit: Petar Milošević

     The answer of course lies outside of the video. Nutria are capable of destroying vast areas of wetland through their destructive feeding and burrowing habits. In sensitive ecosystems, such as the Louisiana wetlands, the havoc that nutria wreak can exacerbate existing degradation thereby increasing the threat and potential damage of flooding due to hurricanes and sea level rise. Various population control methods have been implemented with varying success. The Louisiana Dept. of Wildlife and Fisheries runs a nutria hunting and trapping incentive program.  Nutria has also been marketed for human consumption (although that has not gained much traction) as well as “guilt-free” fur.

Not all invasive species from Asia are bad…

Asian Shore Crab (Hemigrapsus sanguineus)

     You might remember from the end of last year the story of Samantha Garvey, the recently (at the time of the story) homeless 18-year-old Brentwood High School senior whose research project made her an Intel Science Talent Search semifinalist. The subject of her research? How the presence of the Asian shore crab, an invasive predator, affected the thickness of the shells of its prey, the ribbed mussels native to Long Island Sound. Although at first glance this might make the Asian shore crab seem like another bad invasive species story, research from Brown University scientists suggest otherwise. Appearing on US shores over 20 years ago, most likely by piggybacking on commercial ships originating from Asia, the Asian shore crab has populated almost the entire eastern seaboard without disrupting native ecosystems. In fact, the Brown University researchers found that the success of the Asian shore crab did not come at the expense of indigenous inhabitants since the study found a positive correlation between the number of invasive crab and a greater number of native species.

     Asian shore crabs also make great bait for tautog, one of my favorite fish to catch in RI:

     Til next week!

Related Reading:

Rats the Size of House Cats Invade the Florida Keys

CABI invasives blog

Toxicomania: Poisonous Invasive Plant Protects Australian Lizards from Poisonous Invasive Cane Toads

Globe-trotting hitchhikers: invasive species assault U.S. waters

*I was strongly advised to change the name to World Wide Wednesdays.