Monday, March 12, 2012

Globalization and the spread of Invasive Species

Imagine this, you find yourself in a dark almost pitch black enclosed space, surrounded by unfamiliar terrain and objects. The air tastes and feels different than you’re used to.  The sounds you have heard every day no long permeate the air around you, instead there is nothing but a repetitive splashing sound. The world around you rocks harmoniously swaying back and forth. These sights, sounds, and motions are all you know for the next few days, although time seems to slip away. Suddenly you are jarred away from this strange world as sunlight strikes your eyes, after adjusting for a few moments you realize you in the storage cargo of a boat. As soon as you possibly can you escape, leaving behind the boat that held you captive. Around you now, not unlike the boat, is not the home you once knew, instead you find a world that is full of food, delicious food. And much to your delight you find you were not the only one of your kind to have been transported, in fact a lot of you were aboard the ship. Suddenly a vicious hunger grips you and the other members of your home land, you begin to travel inward and eat all the food around you, and it pleases you that in this new world no one is trying to attack you, and so you begin to reproduce and eat and reproduce and eat. This story may seem like some sort of science fiction novel, but if you have not already guessed this is the tale of invasive species one that has played out at an increasing rate because of modern globalization.
 Does this map show products being shipped or travel destinations for invasive species? 

                Since the last 200 years global trade has been steadily increasing, this has been dueto the fact that economies have been growing. And not only have economies been growing but we have developed better technology that allow for bigger, stronger, and faster methods of transportation as well as technology that allows for easier excavation/depletion of resources. Since the first person set sail invasive species most likely came aboard as well, but within the last 50 years the scope of trade has increased by so much that invasive species have begun to travel to new lands, whether by accident or intentionally by humans, at an alarming rate. Because of globalization a healthy portion of invasive species has been wreaking havoc on the lands they have come into contact with. Increased global trade leads to more product shipping and it is within these products that some species travel, much like stowaways. Others cling the ship themselves to move from one ocean to the next, and therein lies the problem. Comparing the two graphs below it can be seen that as global shipping has increased so to have invasive species.
                                The graph above shows the increase in global shipping, this has increased as global economies increase

                                This graph shows the increase in invasive species since 1500, showing a huge increase in the last 100 years
  Invasive species alter ecosystem resulting in a variety of negative consequences.  One of the biggest issues is that invasive species out compete native species, this results in the displacement of native species, if not extinction. This can have huge effects on the invaded ecosystem, if the native species that is driven out is a keystone species then the loss of that species can cause a trophic cascade, resulting in an even greater reduction in species within the area. Hence invasive species can lead to a reduction in biodiversity. This reduction in biodiversity can lead to a reduction in certain ecosystem services provided by the land, this is another problem related to invasive species. To fully see the scope that invasives can have it is best to highlight a few prominent cases of invaders.
                One of the most beautiful aspects of science to me is when two species co-evolve resulting in the dependence of one on the other. These mutualistic relationships evolve because somewhere in time the species began to have an increase in fitness when the two worked together. One stunning example of co-evolution is in South Africa where native species of ants carry and thus disperse the seeds of native plants; this mutualistic interaction is known as myrmecochory. The ants gain a food source, because what they actually are attracted to are food bodies attached externally to the seed, and the plants have their seeds dispersed. But in last the few decades this wonderful balance has been disrupted by an invasive species that was brought to South Africa on cargo ships, the invader is the Argentine ant, Iridomyrmex humilis. Argentine ants out compete native ants and they even attack and kill other species of ants. Where the Argentine ant is invasive it has been replacing indigenous species of ants and South Africa is no different. A study carried out by W. Bond and P. Slingsby looked at how the Argentine ant, by replacing indigenous ants, disrupts a coevolved dispersal system and reduces seedling establishment. The study found that the Argentine ant impacted the local vegetation negatively. They found that when native ants were exposed toseeds the rate of seed removal was 100% by the end of the first day, indicatingthat native ants are effective seed dispersers. The Argentine ants, on theother hand, only removed about 44% of the seeds after the first day; this showsa huge decline in the seed dispersal. The results were that Argentine ants caused a decline in approximately 170 species of plants. This decline was due to the fact that Argentine ants do not disperse seeds as far; do not gather as many seeds thus leaving them out in the open to be consumed by birds and rodents, and also by eliminating native ant species that do successfully disperse plant seeds. Like many invasive species brought about by globalization these ants lead to a decrease in native species.
The Argentine ant
                Another invasive species, the Asian longhorned beetle, was introduced to the United States by global trade with china. The Asian long horned beetle is native to eastern China, where it has recently has become a pest. The species was first reported in the United States in 1996 in a port in New York City. The Asian longhorned beetle was transported in solid wood packing materials, such as cargo crates, from Chinese ships. Once it escaped from the cargo ship it began to infest a large number of trees in the United States. The Asian longhorned beetle eats an enormous variety of tree species, effectively killing the tree. The adult Asian longhorned beetles does not do much more than chomp on a few twigs, the larvae however do a sever amount of damage. The larvae eat their way into the center of the tree eating away at the cambium and vascular tissues, after a year of burrowing they then eat their way out where they metamorphosis into an adult. The only method of removing the Asian longhorned beetle has been to cut down infested trees. In the United States approximately 42,000 treeshave been cut down and about 866,000 have been treated with insecticides tostop spread infection. This has cost the United States close to 375 milliondollars.
Asian Longhorned beetle
                These case studies exemplify the devastating environmental and economic impacts that the spread of invasives can have, and this spread is only worsened by increased global imports and exports. We know that invasive species are showing an upward trend because of increasing globalization, we know the affects the invasives can have, but what can be done to decrease their spread? The first idea to stop their spread would be to stop global trade, this however is not a reasonable solution. The next step is to stop invasives from getting into non-native lands or water ways. One of the most effective methods to stop invasives from getting into water from ships is called ballast water exchange, in which the tanks of a ship are pumped out and refilled in the open sea. Another method that was created to treat shipments that might contain the Asian Longhorned beetle is described as a phytosanitary measure. This involves a standard for heat treatment and fumigation of wood packaging materials. This standard has been adopted internationally, showing that the global community is beginning to try and combat the spread of invasives.
                Global trade is necessary for economic stability in most developed, and even in a lot of under developed, countries. What is not necessary is the re location of species from one country to another. To help deter this spread we need to develop policies and standards that are strict on detecting invasive species. We need to have the fore sight to search all shipped cargo to see if it contains any unwanted specimen, because even if a shipment has a species that is not invasive now it may become so in future. The negative impacts that invasive species can have is too great for us to not take action, we must take measures to ensure that global trade will no longer negatively impact the environment. So what can the average citizen do to stop invasive species, a few things. First off vote for legislation that will impose stricter security measures on trade ships. Next if you know a product was shipped carrying an invasive, don’t buy it. And most importantly if you see an invasive species in your community inform a local authority on the matter.

Relevant links
Invasive Species: Pathogens of Globalization
Trade, Transport and trouble: managing Invasive species in an era of globalization
Collapse of an Ant-Plant Mutualism
Managing Invasive Populations of Asian Longhorned Beetle and Citrus Longhorned Beetle: A Worldwide Perspective

1 comment:

  1. All of these blogs on invasive species complement each other well by emphasizing different aspects of the issue. This blog helped provide the global context of why invasions keep happening (global trade keeps increasing) and what methods (e.g. ballast exchange) might be effective in stopping invasives "at the point of attack."

    I also enjoyed the story-like introductory paragraph. It's easy to "demonize" invasive species and, indeed, they are a critical problem. But it's important to remember that they are essentially doing what their biological impulses compel them to be doing. As a land manager I recently interviewed about invasive species strategies told me, "They're just plants being plants, doing what plants are supposed to be doing." The problem is that we've upset the natural order and allowed them to happily enter a new paradise where there's lots of food and no one is attacking them.

    An interesting thing to think about is that from a biogeographical perspective, humans essentially acted as an "invasive species" when they crossed the Bering land bridge into North America and encountered a land where none of the species were adapted to human predators. That's what I thought about when I read the opening paragraph's story. In some ways, North America must have seemed like a paradise with easy prey and lots of food. Some scientists have theorized that the extinction of large mammals in North America was due to the rapid advance of humans into a region in which other species had not co-evolved with them.

    The example of the Argentian ant is a good one because it highlights this whole issue of how different species have coevolved, in this case the native ants coevolving with the plants in a beneficial way. In other cases, predators and prey and pathogens have coevolved in a way that keeps each actor in check.

    Lots of things to think about here