Thursday, October 14, 2010
Discussion Question 6 (Primary Threats)
Control of invasive species may involve searching for specialized natural enemies, parasites, or predators of that species within its original range and releasing such organisms in an attempt to control the invasive species at the new location, For example, an attempt is currently underway to control exotic purple loosestrife in North America by releasing several European beetle species that eat the plant in its home area. As another example, biologists are talking about introducing an exotic fungus into Hawaii to eliminate the invasive Puerto Rican coqui frog. What if these biological control agents begin to attach native species rather than their intended host? How might such a consequence be predicted and avoided? Consider the biological, economic, and ethical issues involved in a decision to institute a biological control program.
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The use of biological control to manage invasive species has been a subject of hot debate. Past blunders, some receiving strong media coverage, have led to skepticism in both the general population and the scientific community about the efficacy of biocontrol and the possibility of negative effects on non-target species. Previous attempts at biocontrol have shown that generalized predators and herbivores have the potential to greatly decrease population sizes of non-target, native species (i.e. Italian mongoose introduced to tropical islands to control rat populations decimate native bird and reptile populations, Simberloff and Stiling 1996). Considering the possible ecosystem implications, it would be hard to argue for the control of invasive pests using generalist species. Today, much effort is put into finding control species that have little ecosystem effects outside of their targets. If such species are found, adequately tested, and closely monitored after introduction, biocontrol may be a good “last resort” to managing invasive species.
The purple loosestrife provides an interesting “careful biocontrol in progress” example. The invasive plant degrades wetland habitat in over a dozen states, affecting native plants and waterfowl. Traditional management techniques, including herbicides, proved ineffectual (Blossey et al 2001). Scientists identified host-specific insects from the plant’s native environment that were candidates for biocontrol. They studied the insects’ life cycles and conducted experiments which tested native plants’ susceptibility to the insects. Several insect species were introduced in 1992 (Blossey et al 2001). Since then several states report significant decrease in flowering, stem height, and stem number in purple loosestrife. Careful, long-term monitoring of the introduced species and the wetland ecosystems is essential in quantifying results and identifying any undesirable impacts on the native communities (Blossey and Skinner 2000).
Even with careful testing and monitoring, introducing non-native species to control invasive species is risky. Unforeseeable consequences are common in nature, particularly in the long-term. Introduced species may evolve or disperse beyond the intended region. However, when other management strategies have proven ineffective in the face of an aggressive invader that causes substantial damage to our ecosystems, biocontrol may be the only choice.
REFS
Blossey, B. and Skinner, L. 1999. Design and importance of post-release monitoring. Proceedings of the X international symposium on biological control of weeds, 4, 693-706.
http://www.invasive.org/proceedings/pdfs/10_693-706.pdf
Blossey, B., Skinner, L. and Taylor, J. 2001. Impact and Management of Purple Loosestrife in North America. Biodiversity and Conservation, 10, 1787-1807.
http://www.springerlink.com/content/m8l203167uv7037k/
Simberloff, D. and Stiling, P. 1996. How Risky is Biological Control? Ecology, 77, 1965-1974.
http://www.jstor.org/discover10.2307/2265693uid=3739256&uid=2&uid=4&sid=21101333608207
Invasive species are a major issue in today’s conservation efforts. Some people have even claimed that invasive species will exceed habitat destruction as the major cause of species loss. Invasive species may well already been the main cause on some island ecosystems (Cloud, Veitch).
An invasive species is any species of plant or animal that is “non-native”. Unfortunately, human activity has been the main vector for these species, be that through animal trade, horticulture trade, or stow-aways on ships and planes. Nonetheless, the responsibility of maintaining these invasive species appears to fall on humans. One main management method has been to use biological control.
The Puerto Rican Coqui Frog is a good example of invasive species control. This frog was a dominating species in Puerto Rico for many years, outcompeting most of the other native amphibians. An introduction of the fungus, Batrachochytrium dendrobatidis, successfully brought down this population of coqui frogs in Puerto Rico by attaching to the frog and limiting its life-cycle. This fungus was incredibly effective because other native frogs in Puerto Rico were immune to the fungus. In Hawaii, the invasive coqui frog is now repeating its “terror” on the islands. It competes with endemic Hawaiian birds for insects, it outcompetes other amphibians, and there is fear of introducing Brown Snakes, the main coqui predator, on the islands. Ecologists are again interested in introducing the fungus to Hawaii to bring down the coqui frog. But what happens if other Hawaiian amphibians are not immune to the fungus as the one in Puerto Rico were?
Ecologists make mistakes. One famous example of this is the introduction of the Cane Toad in Australia. Sugar cane growing in Hawaii brought an increase in the population of the invasive Cane Beetle. This beetle was diminishing the crops and creating problems with sugar production. Ecologists introduced the cane toad, and successfully brought down the population of the beetle, increasing sugar cane production once again. When this problem began occurring in Australia, ecologists figured they could again introduce the cane toad to Australia to bring down the cane beetles there. Unfortunately, there were some critical differences between Hawaii’s situation and Australia’s situation. In Australia, the sugar cane grew taller, the beetles were at the top of the cane, and the toads could not even reach the beetles. The beetles there were diurnal, while the toads were mostly out hunting at night. Finally, the sugar cane in Australia grew in a much dryer climate than in Hawaii. The toads ended up leaving the sugar fields in search of wetlands. They migrated to other parts of Australia and became the dominating species. So overall, ecologists failed to bring down the cane beetle population, and introduced a very dangerous invasive species, the cane toad, effectively bringing down the populations of many other endemic Australian species.
This example is important to keep in mind when making decisions about invasive species control. Tests and trials should be performed to ensure success, because a mistake could change an entire ecosystem.
REF:
“Turning the Tide of Biological Invasion: The Potential for Eradicating Invasive Species”- MN Clout and CR Veitch
“Control of Coqui Frogs”- College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa
“Our Amazing Planet- Cane Toads Invade, Conquer Australia”- Brett Isreal
The term “invasive species” may give people the misconception that an invasive species is a large, aggressive predator. However and invasive species can be anything from a large mammal to a species of plant. An invasive species is a non-native species in an ecosystem that causes environmental or economic harm (1). Invasive species are introduced to a new environment through various methods, but humans are primary contributors. When humans travel from place to place, they often bring unwanted invaders with them. Other methods include cargo ships, pet trade, wood products, and ornamental plants (2).
Although this may not seem like a major problem facing our society, invasive species have proven to be highly detrimental. In fact, approximately 42% of threatened or endangered species are at risk because of the effects invasive species (2). Invasive species have direct and indirect effects on an ecosystem. They directly cause harm to an ecosystem by preying on native species, thus preventing native species from reproducing and growing. With a decreased rate of reproduction in a species leads to a decrease in biodiversity, which leads to inbreeding and eventually extinction. Invasive species out-compete native species for the limited resources in an ecosystem. They also cause a decline in native species by bringing disease into an environment. By causing a decline and an eventual extinction of the native species in an environment, invasive species are also indirectly effecting other organisms in an ecosystem by disrupting food webs.
Many efforts have been made to try to control invasive species in an environment. One method is the use of biological control, which attempts to control an invasive species by introducing natural enemies, parasites or predators of the invasive species into the invaded ecosystem. However, this method poses many consequences. Although the introduced species may be a natural predator to the invasive species in their natural environment, there is no way to be sure how these two species will interact in a completely new environment. Small scale tests can be used in order to make predictions on their interactions, but there is no way to be completely positive. Once this introduced species is put in the new environment, it could possibly become a second invasive species to the ecosystem, causing even more harm before its introduction. For example, the mongoose was introduced to the Hawaiian Islands in order to control the rat population. However, insignificant research was conducted prior to its introduction. The mongoose, being a day-time dweller, was not awake in the nighttime to kill the rats, which are nocturnal. This lead to the mongoose preying on many other species of animals like birds and other small mammals. The mongoose also introduced diseases such as leptospirosis and rabies to the Hawaiian islands (3).
Biological controls are risky and pose many consequences to an ecosystem. Once an invasive species establishes itself in an ecosystem it is almost impossible to eliminate it. The best method for controlling invasive species is by spreading awareness and through prevention. Many methods such as requiring immigration or customs forms when traveling to a new destination help prevent and control the introduction of invasive species.
REFERENCES:
(1) “Invasive Species”- U.S. Fish and Wildlife Service
http://www.fws.gov/invasives/
(2)“Invasive Species”- http://www.nwf.org/Wildlife/Wildlife-Conservation/Threats-to-Wildlife/Invasive-Species.aspx
(3)“The Mongoose: A Maui Menace”- Naturally Speaking: Nature Photography and Conservation
http://www.perlgurl.org/archives/2006/05/the_mongoose_a_maui_menace_1.html
The term “invasive species” may give people the misconception that an invasive species is a large, aggressive predator. However and invasive species can be anything from a large mammal to a species of plant. An invasive species is a non-native species in an ecosystem that causes environmental or economic harm (1). Invasive species are introduced to a new environment through various methods, but humans are primary contributors. When humans travel from place to place, they often bring unwanted invaders with them. Other methods include cargo ships, pet trade, wood products, and ornamental plants (2).
Although this may not seem like a major problem facing our society, invasive species have proven to be highly detrimental. In fact, approximately 42% of threatened or endangered species are at risk because of the effects invasive species (2). Invasive species have direct and indirect effects on an ecosystem. They directly cause harm to an ecosystem by preying on native species, thus preventing native species from reproducing and growing. With a decreased rate of reproduction in a species leads to a decrease in biodiversity, which leads to inbreeding and eventually extinction. Invasive species out-compete native species for the limited resources in an ecosystem. They also cause a decline in native species by bringing disease into an environment. By causing a decline and an eventual extinction of the native species in an environment, invasive species are also indirectly effecting other organisms in an ecosystem by disrupting food webs.
Many efforts have been made to try to control invasive species in an environment. One method is the use of biological control, which attempts to control an invasive species by introducing natural enemies, parasites or predators of the invasive species into the invaded ecosystem. However, this method poses many consequences. Although the introduced species may be a natural predator to the invasive species in their natural environment, there is no way to be sure how these two species will interact in a completely new environment. Small scale tests can be used in order to make predictions on their interactions, but there is no way to be completely positive. Once this introduced species is put in the new environment, it could possibly become a second invasive species to the ecosystem, causing even more harm before its introduction. For example, the mongoose was introduced to the Hawaiian Islands in order to control the rat population. However, insignificant research was conducted prior to its introduction. The mongoose, being a day-time dweller, was not awake in the nighttime to kill the rats, which are nocturnal. This lead to the mongoose preying on many other species of animals like birds and other small mammals. The mongoose also introduced diseases such as leptospirosis and rabies to the Hawaiian islands (3).
Biological controls are risky and pose many consequences to an ecosystem. Once an invasive species establishes itself in an ecosystem it is almost impossible to eliminate it. The best method for controlling invasive species is by spreading awareness and through prevention. Many methods such as requiring immigration or customs forms when traveling to a new destination help prevent and control the introduction of invasive species.
REFERENCES:
(1) “Invasive Species”- U.S. Fish and Wildlife Service
http://www.fws.gov/invasives/
(2)“Invasive Species”- http://www.nwf.org/Wildlife/Wildlife-Conservation/Threats-to-Wildlife/Invasive-Species.aspx
(3)“The Mongoose: A Maui Menace”- Naturally Speaking: Nature Photography and Conservation
http://www.perlgurl.org/archives/2006/05/the_mongoose_a_maui_menace_1.html
An invasive species is any organism that is not native. Usually, an invasive species has a negative impact on the habitat it invades. Some effects are increased competition for resources, lack of natural predators, predation on native species and alterations to the ecosystem’s natural processes. Invasive species are also harmful economically by destroying crops and agriculture. Some habitats are more vulnerable to invasive species then others. For instance, isolated islands such as Guam and Hawaii have been bombarded with invasive species from snakes, frogs, insects, and plants. Many tropical/sub-tropical islands are gold mines for invasive species because the climate provides favorable conditions/resources and there is a lack of natural predators. Before humans, these islands were so isolated that it was nearly impossible for an invasive species, or any species, to come over and colonize. However, with increased human activity, many foreign species are brought over seas to islands unintentionally. Once an invasive species is brought over and begins to reproduce, it is extremely difficult to eliminate them. Biological control programs have been put into place, but many times they are not 100% effective. For instance, in the late 1800s mongooses were brought over to Hawaii to help control the rat population. This did not work out as planned considering rats are nocturnal and mongooses are diurnal (active during the day). The mongoose had no effect on the rats, and they began to populate rapidly. Instead of rats, they began to prey on the native Hawaiian birds which has nearly drove them to extinction. Biological control programs can be helpful, but extensive research must go to studying a specific species before placing them in a different ecosystem. The best way to control an invasive species is to not let them get there in the first place. Precautions must be taken in order to stop an invasive species from colonizing. For example, Hawaii hires teams of inspectors that check tourist’s luggage and containers on ships for any species that someone brought or that accidentally boarded. They also force tourists to fill out agriculture forms to declare that you are not smuggling any type of foreign species into the state of Hawaii. Many fear that the Brown Tree Snake which has wreaked havoc in Guam, killing almost all of it’s native bird species may find it’s way over to Hawaii. I believe that these precautions must be implemented to prevent invasive species so we can limit the use of Biological control programs. These programs are not 100% effective and usually cause more harm by introducing another invasive specie unintentionally.
Sources:
http://www.invasivespecies.gov/global/prevention/prevention_index.html
http://www.huffingtonpost.com/2012/04/12/hawaii-invasive-species-cargo-inspectors_n_1419896.html
http://www.instanthawaii.com/cgi-bin/hawaii?Animals.mongoose
Invasive species pose a serious threat to biodiversity. When an invasive species is brought to a new environment, either accidentally or deliberately, it tends to have a significant competitive advantage because native species are not used to dealing with this new threat. This often leads to the extinction of many native species. Recently, efforts have been made to stop the spread of invasive species, such as using dogs to try and sniff out stow-away Brown Tree Snakes from reaching Hawaii and treating ballast water to prevent the transport of marine organisms from harbor to harbor. However, there are already many cases of invasive species causing havoc on native populations.
In order to try and control invasive species many different techniques have been implemented, from traps to chemical warfare. But invasive species can be remarkably persistent. When all else fails, should biological control be considered? Biological control is a controversial technique that involves introducing a second invasive species to an environment that is already infected by an invasive species in an attempt to limit the population of the first invasive species. Though this sounds simple enough, it is actually an incredibly complex process. It is usually not too difficult to find a predator for the invasive species from its natural environment; the main problem is finding the right predator. In order to ensure that there are no unintended side effects from the introduction of a new invasive species, the target environment has to be studied intensively.
There are many cases were biological control has gone horrendously wrong. These include the introduction of cane toads to Australia, Papua New Guinea, and other Caribbean islands. The plan was for the cane toads to control pests that preyed on sugar cane crops; however, the cane toads instead severely hurt the local environment. Many predators die as a result of eating the cane toad because they are unaware of the cane toad’s poison (Winkel and Lane, 2012).
But not all biological control initiatives have been unsuccessful. Purple loosestrife is an invasive plant species that severely hurts local plant biodiversity. In order to try and control this invasive species, leaf-beetles were introduced to populations of Purple loosestrife (Davalos and Blossey, 2011). These beetles have been successful in limiting the population of Purple loosestrife so that these plants are no longer the dominant plant in many habitats.
Because the ecosystem is so complex, it can be incredibly difficult to predict all of the consequences of introducing an invasive species to a new environment. Many past attempts at biological control have gone wrong and forever scared the local habitat. Biological control should not be attempted without a lot of research on the environment, target species, and biological control agent. Even with extensive research and controlled tests accidents happen. But sometimes the potential benefits may outweigh the risks.
References
Winkel, Dylan and Lane, John. 2012. The invasive cane toad (Bufo marinus) in West New Britain, Papua New Guinea: observations and potential impacts on native wildlife. Biological invasions. 14(10):1985-1990.
Davalos, A., and Blossey, B. 2011. Matrix Habitat and Plant Damage Influence Colonization of Purple Loosestrife Patches by Specialist Leaf-Beetles. Environmental entomology. 40(5):1074-1080.
Swain et al. 2011. Monitoring Invasive Species: Detecting Purple Loosestrife and Evaluating Biocontrol along the Niobrara River, Nebraska. Giscience & Remote Sensing. 48(2): 225-244
To begin answering this question, I first want to define biological control as the intentional introduction of an exotic species into an area with the intent of controlling an invasive species, whether it be plant or animal. With this, question 6 asks about the potential negative effects of implementing biological control and after careful research I found that the most threating potential side effect of biological control is host shifting. Meaning that the introduced species begins to feed on or affect species other than the intended species. This could cause a huge number of problems, especially by altering the food web and potentially knocking out competitiors and allowing the invasive species to grow even further. The threats if host shifting are even more severe because the process of biological control is all but impossible to reverse due to both ecological and ethical issues. Another potential negative effect of implementing biological control comes from the introduction of an exotic species itself. This process can lead to a lot more than the spread of that species, there is also the possibility of the spread of disease and parasites that can go onto affect native species. This could result from introducing an infected species or even having contaminants when moving the species. As I saw it, these were the major potential negative consequences of biological control, but the next part of the question asked about how these things can be avoided. The number one answer to this is host specificity. When choosing an exotic species to introduce, a ton of research is done on that species. In order for it to be a candidate to be introduced the species must show extremely high host specificity. This reduces the chances of host shifting. The species must also have natural enemies/ competitors present in order to ensure that its numbers are controlled. In addition to all of this, the process of introduction is heavily structured and guarded, so as to reduce the possibility of introducing contaminants. There has been a lot of debate about biological control because of the reasons mentioned above, but overall I am personally for it. In my opinion the positive aspects far outweigh the negatives. Biological control is natural, so unlike pesticides and herbicides it is environmentally friendly. It is also a lot less expensive, and even though it takes on average 2-3 years to fully go into action it has the potential for the most long term control.
Projects based around biological control are extremely relevant even here at UCSB. The parisitology is currently involved in a project to control the spread of Schistosomes by using crayfish as biological control agents for the snails that expel the schistosome larvae into the water that many people in Africa have no choice but to consume. This is actually the second process of biological control that has been done by the Kuris lab, the first was done in Kenya and was very successful. Biological control is extremely important and the fact that is has been shown to reduce the spread of the second most devastating human parasite in the world is huge evidence that the positives far outweigh the negatives. Although in the past there have been failed attempts such as the 1884 introduction of the Mongoose to Australia as a way to control the rabbit population, very few have gone devastatingly wrong. The process has evolved and since then the amount of research and evidence that is legally required before biological control can be implemented has made the possible negative consequences extremely unlikely.
References
http://www.fws.gov/invasives/staffTrainingModule/methods/biological/impacts.html
lamar.colostate.edu/~hufbauer/Pages/biologicalcontrol.html
The mongoose in Australia: failed introduction of a biological control agent
David PeacockA,C and Ian AbbottB
Kuris, A. M., K.D. Lafferty and M.E. Torchin. 2005. Biological control of the European green crab, Carcinus maenas: natural enemy evaluation and analysis of host specificity.
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