Monday, September 26, 2016

Exchanging Aliens

Alien species are becoming more and more commonplace around the globe. As our lives become more globalized, plants and animals are exchanged between countries and continents at an ever increasing rate. Often, these alien species, which can become a menace in their introduced environments because of their ecological and economic effects, are relatively benign in their natural habitats. This global movement of invasive species is illustrated by the exchange of two species, shampoo ginger and lantana, between Central America and South Asia.

Shampoo ginger (Zingiber spectabile) was brought to Las Cruces by the Wilsons who planted it, along with thousands of other species from around the world, into their botanical garden. Gradually, the seeds of these plants were dispersed into the surrounded rainforest by the myriad birds that traversed the garden. Of all the dispersed seeds, the ginger was one of very few species that had the physiology to flourish in the forest. It quickly took over the most vulnerable parts of the forest: the edges of the paths and began to out-compete its native relatives. When we visited the research station, the plant had spread throughout most of the secondary rainforest and was threatening to enter the primary forest areas. It was unmistakable: a spiky, fire engine-red intruder that was almost omnipresent in the forest. I found myself wondering what the future of its reign would hold; would an insect herbivore stumble upon its nutritive properties and take full advantage of the large population or would it continue to flourish unchecked? Only time can tell.
Zingiber spectabile. Picture from A Costa Rican Almanac.

Shampoo ginger is a highly prized medicinal plant in it’s native habitat: the Malayan rainforest. Alien species often are rather innocuous in their native habitats, where coevolved predation keeps their populations in check.

Lantana camara is another example of an alien invader, this time moving in the opposite direction - from Central America to Southeast Asia. It is a Central American shrub which was introduced to India by the colonizing British, who used it to make hedges and attract butterflies. In the South Indian scrub forest where I live its flowers, like those of the ginger, out-competed the native species for insect and butterfly pollinators and it was soon able to spread throughout the scrub forests of the Deccan Plateau. The dense bushes choked off native vegetation and it soon became omnipresent in the forest. Today, it threatens several national parks and has been near impossible to eradicate despite continued efforts. Walking through the forest, it is often the only plant that can be seen.
Lantana camara. Picture from

To me, this global exchange of species is indicative of the huge impacts anthropogenic activities have on every aspect of natural ecosystems around the world. Biodiversity is being disrupted, rearranged with consequences we can only guess at. Efforts to mitigate this movement of species and the upheavals it causes in ecosystems have also rarely worked. Perhaps the only response we can have is acceptance of these changes?

Avehi Singh
Reed College

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