The Threat of Invasive Species
An Interview with Dr. Michael Hutchins
By Jordan Schaul | National Geographic | December 25, 2012
In an ongoing series of interviews with renowned wildlife professional and ecologist Dr. Michael Hutchins, Newswatch Contributing Editor Dr. Jordan Schaul explores another threat to nature. In the last interview, Michael and Jordan discussed Nature-Deficit Disorder. Here is a complete bio for Dr. Michael Hutchins.
Jordan: People, including scientists, often confuse or misuse terminology applied to invasive species biology. For example, the words “exotic”, “non-indigenous” and “introduced” are used interchangeably, but their precise meaning usually warrants more conservative usage. The distinctions may seem trivial, but they are important in helping us understand how these “invaders” influence the world around us. Can you first provide some background information on invasive species with particular regard for the labels and terminology?
Michael: There are a few subtleties in definitions. The terms “exotic”, “alien”, “non-indigenous” and “introduced” are often used interchangeably to describe species that are non-native to a host ecosystem. More specifically, they refer to species that have not evolved in the host ecosystem or naturally colonized the area; but rather, to species that have been actively transported by humans past natural geographical barriers to dispersal (e.g., mountain ranges, oceans, rivers, etc.). Introductions can be either purposeful or accidental. Examples of purposeful introductions (i.e., those in which humans consciously decided to move animals from one place to another) include the nutria in the southeastern United States, the mongoose in Hawaii, and the European red deer and Himalayan tahr in New Zealand. Accidental introductions (i.e., those that were moved without human knowledge) include the brown tree snake on Guam, which arrived on ships from Australia or New Guinea during World War II, and European rats and mice, which also caught a ride on sailing ships during the colonization of North America. Of course, not all introduced species are invasive. A species becomes invasive when it successfully establishes itself within a host ecosystem subsequent to its introduction.
That being said, climate change may necessitate some re-evaluation of this terminology. Climate (e.g. temperature, rainfall, etc.), which has in the past, limited the dispersal and subsequent colonization of some areas by some species, may not be a barrier in the future. Thus, we may see unexpected movements of some flora and fauna into areas that were previously uninhabited by them. Climate change is a human-made phenomenon, so this may not technically be classified as “natural” colonization or change in distribution; however, since the organisms are moving on their own, it is still different from the human-caused purposeful or accidental species introductions across natural geographical barriers to dispersal.
One of the most commonly misused terms in our vocabulary is the term “feral”. By the term “feral” we are referring specifically to domesticated animals (i.e., those that have been shaped by many generations of selective breeding) that have “gone wild” and are no longer living under human care. Examples would include feral cattle, pigs, goats, sheep, horses, cats, and dogs. Feral animals are not considered “native” to their host ecosystems; however, their ancient progenitors can be (e.g. feral horses are not native in North America, nor are domesticated cats in Africa). Feral rats, cats, and pigs are especially serious pests.
Jordan: In Anchorage, where I lived most recently, there is a great concern for the impact northern pike has on trout and salmon populations. There is also a considerable concern for a plant invader that we are all familiar with—purple loosestrife. But we often forget the economic toll that results from not only the direct impact invaders and introduced species have on native flora and fauna, but the efforts to manage these populations of “invasive” species are also quite costly. What are your thoughts?
Michael: Yes, the financial cost of either eradicating or controlling introduced species is enormous. It is estimated that the United States Department of the Interior alone spends over $100 million annually on the management of the most destructive of these ecological interlopers. Of course, these expenditures must be weighed against the monetary and biological costs of inaction. It is estimated that introduced species are costing the U.S. $120 billion annually in lost crops, property damage, environmental degradation, etc. (Pimental, D., Lavch, R. and Morrison, D. 2000. Environmental and economic costs of non-indigenous species in the United States. BioScience 50: 53-65). This is why it is so critical for our nation to enact effective legislation that prevents additional introductions of destructive non-native flora and fauna before they occur. Some legislation currently exists to deal with specific circumstances (http://www.invasivespeciesinfo.gov/laws/main.shtml); however, existing laws are simply not sufficient. Currently, U.S. law is weak and our government has been slow to act. There is legislation pending, but it sits languishing in Congress (http://archive.truthout.org/article/invasive-species-bill-stuck-congress?print).
Jordan: The management of feral cats in North America has generated contentious debate among a number of factions, including conservation scientists and activist communities. Is there an easy answer?
Michael: No, there is no easy answer, primarily because of the human dimensions creating this growing ecological problem (Lepczyk, C.A., van Heezik, Y. and Cooper, R.J. 2011). An issue with all-too-human dimensions. The Wildlife Professional 5(1): 68-70). First, it is important to point out that domestic cats are a non-native species. No one knows for sure, but there are an estimated 30-80 million feral domestic cats in the United States. Add to that the number of house cats that are allowed outdoors and we are talking about tens of millions more.
A battle is ongoing between feral cat advocates and conservationists over how to address this issue. Cat advocates, represented by organizations, such as Alley Cat Allies, Best Friends Animal Society and the Humane Society of the United States, believe that the answer to feral cat control is Trap-Neuter-Release (TNR) programs. Such programs consist of “managed” cat colonies, where the animals are trapped, sterilized, vaccinated against rabies (in some areas), and then released back into the environment, ranging from natural areas to suburban and urban neighborhoods. Colony managers provision the cats with food and sometimes protect them from predation by building structures onto which they can escape. Cat advocacy groups have sold TNR as an effective way to control feral cat populations to a growing number of municipalities around the country. In fact, there is a movement in the U.S. to stop accepting stray and feral cats at shelters, to treat feral cats as protected wildlife, and to prevent private landowners from controlling feral cats on their properties. Under this scenario, shelters simply become revolving doors back into outdoor colonies.
So why do conservationists oppose TNR? First, domestic cats—even well-fed ones—are deadly predators, which are killing an estimated 1 billion birds and other small native animals annually. These numbers are extrapolated from studies that looked at the number of prey animals that were brought home by outdoor house cats. More recently, cat predation has been investigated by radio-tagging birds and monitoring cats with “Kittycams”, small video cameras mounted on the animals to track their activities (http://smithsonianscience.org/2011/03/alarming-number-of-fledgling-suburban-catbirds-fall-prey-to-domestic-cats-study-finds/; http://www.abcbirds.org/newsandreports/releases/120806.html). Predation by feral and free-roaming house cats has caused the extinction of endemic island bird species (Dauphine, N. and Cooper, R.J. 2011. Pick one: Outdoor cats or conservation. The Wildlife Professional 5(1): 50-56.), and when eliminated from oceanic islands, native birds have made dramatic comebacks (http://www.care2.com/causes/feral-cats-slaughtered-to-save-endangered-birds.html). Furthermore, when systematic studies have been conducted, TNR does not appear to be an effective method of controlling feral cat populations, primarily because of immigration into colonies or a failure to sterilize a sufficient percentage of the cats (http://onlinelibrary.wiley.com/doi/10.1111/j.1523-1739.2009.01174.x/abstract). Some of these managed colonies have been active for more than 20 years and artificial feeding of the animals likely increases the longevity of the cats. Unfortunately, municipalities that do implement TNR-only management do not require an independent evaluation of such projects to ensure that the number of cats is declining as a result. In fact, the goal appears not to reduce feral cat numbers, but to simply avoid euthanasia.
The diseases associated with feral cats are also problematic. The numbers of rabies cases in feral cats appear to be increasing, with new reports almost weekly (http://www.abcbirds.org/newsandreports/releases/110921.html). Rabies is not the only zoonotic disease carried by feral cats; others include typhus and hookworm (Gerhold, R. 2011. Cats as carriers of disease. The Wildlife Professional 5(1): 58-61). Among the most dangerous and underrated of these is Toxoplasma gondii, a protozoan that must pass through the gut of a cat to reproduce, which has, as an acute disease at the time of infection, been linked to fetal deformities and death in humans (http://www.pamf.org/serology/managementoftoxo.pdf). Once acquired, toxoplasmosis is a chronic infection, which has recently been linked to autism, schizophrenia, and even brain cancer in humans (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3035534/; http://rsbl.royalsocietypublishing.org/content/8/1/101; http://www.sciencedirect.com/science/article/pii/S175094670900097X). While some of these studies are correlational and thus do not imply causation, they are suggestive. Even more remarkable is that T. gondii is a parasite that may manipulate the behavior of its host. Rodents that carry the protozoan lose their fear of cat urine, which would normally cause them to flee, thus increasing the probability that they will end up in the gut of a cat; this may have some implications for human behavior as well (http://www.scientificamerican.com/article.cfm?id=common-parasite-linked-to-personality-changes). T. gondii coming from freshwater run-off from cat litter in landfills and feral cat colonies near our coasts has resulted in the death of thousands of marine mammals, including dolphins, whales, seals, sea lions, and sea otters. (http://microbiology2009.wikispaces.com/Marine+Sea+Otters+being+affected+by+Toxoplasmosis; http://www.nih.gov/news/health/may2011/niaid-25.htm). The connection to marine mammals may be through their diets: anchovies for seals, sea lions, whales, and dolphins (http://www.sciencedaily.com/releases/2008/06/080602103404.htm) and for sea otters, through filter-feeding mollusks (http://www.sciencedaily.com/releases/2002/06/020627004404.htm). Feline leukemia, a disease common to domestic cats, is a problem for the endangered Florida panther (http://www.vetscite.org/publish/items/001787/index.html).
Remarkably, even with all of this evidence, cat advocacy groups continue to claim that the animals have little impact on native wildlife, that they are not significant carriers of disease, and that TNR is the most and only effective way to manage feral cat populations (http://www.alleycat.org/page.aspx?pid=1253; http://cat-chitchat.pictures-of-cats.org/2012/03/bird-lobby-still-conspiring-against.html#!/2012/03/bird-lobby-still-conspiring-against.html). Then why have several conservation organizations and scientific societies, including The Wildlife Society, National Audubon Society, the American Bird Conservancy, the American Association of Wildlife Veterinarians, the American Society of Mammalogists, and the National Wildlife Federation, developed policies that oppose the practice? (e.g., http://joomla.wildlife.org/documents/cats_tnr.pdf). Unfortunately, we know full well that even when presented with contradictory evidence, many people have a very difficult time changing their worldview (http://www.motherjones.com/politics/2011/03/denial-science-chris-mooney) and the values of cat advocates and conservationists are very different. While the former is focused solely on the lives and welfare of individual cats, the latter are generally concerned about animal welfare and the survival of native wildlife populations and their habitats. What is fascinating and paradoxical, however, is that the welfare of domestic cats is not improved by allowing them to roam free. Outdoor cats are hit by cars, contract diseases, and are killed by predators. One study found that 42% of the items consumed by 8 coyotes living in Tucson, AZ, over a 5-month period were domestic cats (http://www.bioone.org/doi/abs/10.2193/2008-033). Even People for the Ethical Treatment of Animals (PETA), among the most strident of animal rights organizations, opposes TNR management for feral cats based on humane considerations (http://www.ammoland.com/2010/06/11/peta-agrees-trap-neuter-release-is-bad-for-cats/#axzz2F9KlvaLv).
So what are the potential solutions? There are many things that could be done immediately to address this growing ecological problem, the root of which is irresponsible pet ownership. The first thing would be to establish required pet owner education programs, which stress the problems associated with cats going outdoors. Second, pet cats should be licensed, sterilized, and banned from roaming without supervision, and the fines for violations should be substantial. Third, there should be a limit on the number of cats that can be maintained per household. Fourth, there should be a ban on feeding feral cats, and as many feral cats as possible should be taken out of the environment through live trapping and removal. Feral dogs can also pose a serious problem for wildlife (http://www.aphis.usda.gov/wildlife_damage/nwrc/publications/11pubs/young112.pdf). However, we have rules against dogs being allowed to be off-leash or roaming without supervision, so why not cats? Last but not least, feral cats should immediately be removed from all island ecosystems, or other environmentally sensitive areas, such as wildlife refuges or parks.
To help resolve this contentious issue, it is critical that state and federal government agencies get involved in the debate. State fish and wildlife agencies and the U.S. Fish and Wildlife Service have a legal and moral obligation to protect our native wildlife (http://www.capemaycountyherald.com/article/8627-fish-and-wildlife-service-eyes-cats). Similarly, the Public Health Service and the Centers for Disease Control have a responsibility to protect public health. Decisions to engage in TNR are being made by local politicians who have little or no knowledge about the situation, are only told one side of the story, or are just taking the easy way out. However, some municipal and company leaders have stood up to the feral cat lobby and either rejected or discontinued TNR when they discovered that it was not doing the job that it was intended to do (http://www.daily-times.com/ci_21745958/city-farmington-stops-feeding-local-feral-cat-colony; http://www.connectamarillo.com/news/story.aspx?id=760182#.UM-e8m_AcrU; http://triblive.com/x/pittsburghtrib/news/westmoreland/s_734329.html#axzz2FLq6PwSk; http://articles.orlandosentinel.com/2012-03-29/business/os-loews-hotels-cat-colony-20120329_1_feral-cats-community-cats-wild-cats; http://articles.mcall.com/2011-10-13/news/mc-easton-feral-cats-20111013_1_feral-cats-animal-health-and-welfare-euthanize-animals).
Jordan: Recently, some ecologists have argued that we should begin to accept the fact that many exotic species are here to stay, not all exotics are destructive, and some could be beneficial. Further, they suggest that some ecologists are prejudiced against exotics and we should just accept the” new normal.” What do you think about that?
Michael: This is unfortunately true. Some ecologists have apparently conceded defeat in our battle with invasive wildlife and plants, declaring exotic species the winners. For example, Mark Davis of Macalester College in St. Paul, Minnesota, and his colleagues have suggested that it will be a “never-ending battle to keep a habitat pure.” They contend that non-native species are really not all that bad and that we should take a new approach to the fast-blending biosphere or so-called “Anthropocene” (the proposed term for the present geological epoch—from the time of the Industrial Revolution onwards—during which humanity has begun to have a significant impact on the environment) (http://www.academia.edu/678134/Dont_judge_species_on_their_origins). As Davis et al. have said, “We should accept this coming change as inevitable and simply begin managing for what is desirable and undesirable, not for what is ‘natural.’ There certainly are some introduced species that are beneficial, including our domesticated food crops. However, it has also been estimated that some 80% of introductions have been detrimental, thus earning them the term “biological pollution.” Consequently, the vast majority of biologists and ecologists believe that the views expressed by Davis et al. to be counterproductive (Simberloff, D. 2012. There’s nothing benign about invasions. The Wildlife Professional 6(2): 39). Ignoring these growing problems, they say, will greatly reduce our future options and result in the extinction of many native species, including those of great ecological and cultural importance (see below).
There is no doubt that it will be difficult to control or eradicate some invasive species once they have become established. However, it is critical that the most destructive of invasive species be targeted for action, and that new technology is developed to get the job done and added to the already-existing arsenal (http://www.invasive.org/control/index.cfm). The U.S. government is taking this issue very seriously. A new bill, HR 669, the “Non-native Wildlife Prevention Act”, introduced into Congress in 2009, seeks to classify all imported species as to their probability of becoming invasive, and to ban the importation of all species deemed a significant threat. Additional steps are being taken to build governmental capacity to prevent the introduction of invasive species at our borders and other points of entry. A recent study published by IUCN-The World Conservation Union, identified trade and travel as the “primary drivers of biological invasion, both into and out of the United States” and determined prevention measures to be “the most cost-effective means of minimizing the introduction of and thus impact of invasive species” (http://cmsdata.iucn.org/downloads/barcelona_ias_paper___low_quality_pdf.pdf).
Jordan: What kind of impact can invasive species have on human health?
Michael: There are many potential impacts of introduced species on human health. Introduced species are not just limited to larger animals and plants; they can include pathogens as well. Who can forget the introduction of smallpox to the New World and its devastating impact on Native American cultures? Perhaps the best known of recent introductions to the United States is the West Nile Virus, a pathogen spread by mosquitoes that have killed millions of native birds but also afflict humans (http://www.cdc.gov/ncidod/dvbid/westnile/wnv_factsheet.htm). In fact, a potential new disease vector, the Asian tiger mosquito, was imported accidentally to the U.S. in tire casings intended for recapping. The insect carries and transmits many diseases in its native range (http://www.idph.state.il.us/envhealth/pctigermosquito.htm). Introduced vertebrates are carriers of potentially dangerous diseases (see comments on feral cats, above). For example, feral swine carry brucellosis, a potentially serious disease that can be passed to humans, domestic animals, and wildlife (http://www.knoe.com/story/20329404/feral-hogs-at-felsenthal-sick-with-brucellosis; http://www.medicinenet.com/brucellosis/article.htm).
Jordan: I’m most interested in the future of wildlife conservation. Can you talk about the threats to biodiversity and global species preservation in the context of invasive species biology?
Michael: The introduction of non-native species has had a devastating impact on North America’s native fauna and flora and their habitats (http://www.actionbioscience.org/biodiversity/simberloff.html). Of the nearly 2,000 imperiled species in the United States, close to one-half are endangered due to the impact of invasive species. It is important to note that many anthropogenic factors have contributed to the decline of our native fauna and flora (e.g., habitat loss, pollution, etc.), but these impacts are cumulative. Thus, alien species, working in concert with many other factors, are driving many native animals to the brink of extinction. In fact, introduced species have been identified as a greater threat to our native biodiversity than pollution, over-harvest and disease combined.
The effects of invasive species on native wildlife, plants, and their habitats vary widely. For example, introduced animals often compete with native species that have similar dietary needs. Introduced carnivores may prey on native animals, whereas herbivores frequently alter the composition of native plant communities, or reduce vegetative cover so that native wildlife becomes more susceptible to predation. Exotic plant species compete with native ones for space and light and can crowd natives out of their own habitats. New and sometimes deadly diseases carried by alien interlopers have sometimes swept through indigenous populations. In cases where the introduced species is closely related to a native species, interbreeding can alter the genetic composition of the native populations and decrease their survivability. A failure to eradicate or control the most destructive of alien species is therefore likely to result in the widespread extinction of many native animals and plants. Is this the heritage we want to leave our children and grandchildren?
Jordan: Does the public have a role in helping to control invasive species?
Michael: There are a number of things the public can do to assist in controlling destructive non-native species and preventing future introductions. In the case of invasive vertebrates, members of the public can inform state or federal wildlife authorities when they spot strange or unusual animals in their neighborhoods or in local parks. Often the first step in eradication or control is identifying that a non-native animal is present. The invasive snakehead fish, a species native to Asia, was first detected by the public who caught the species while fishing (http://www.csa.com/discoveryguides/snakehead/overview.php). Last, but not least, responsible people, who own pet cats and dogs can keep the animals indoors or under their supervision at all times and have them sterilized so that they cannot reproduce. Similarly, people who have exotic reptiles, amphibians or fish, should not release them into nature, as these can be a source of species introductions. The public can also become involved by contacting their elected representatives and expressing concern about invasive species and the many ecological problems they cause.
Jordan: Yes, exotic fish can have a devastating impact on aquatic ecosystems. Farmed exotic species for food consumption can present potential hazards, but so do aquarium fish sold to aquarium hobbyists, as you mentioned. I recently addressed this in a recent post highlighting the work being done by the Shedd Aquarium and its partners to address exotic species introduced to the Great Lakes Ecosystem (http://newswatch.nationalgeographic.com/+2012/11/29/shedd-aquarium-studies-invasive-fish-species-impacting-the-great-lakes-ecosystem/).
I’m glad you mention citizen involvement. There are many opportunities out there for people to learn about invasive species so that they can participate in efforts to control or eradicate them. Here at the Orange County Zoo, we display native animals from the region. My hope is that we can select some invasive species for display as other natural history institutions have done. The more the public knows about invasive animals, the more we can curb the growth of those that are deemed most damaging to our native ecosystems. What about invasive plant species?
Michael: In the case of invasive plants, many schools, gardening clubs, conservation organizations, citizen science programs, and zoos and aquariums, have programs that allow the public to get directly involved in invasive plant control. For example, David Havens, a teacher at St. Luke’s School in New Canaan, CT—a member of the Green Schools Alliance (http://greenschoolsalliance.org/about-us)—designed and taught a high school course in environmental research, which engaged students in invasive plant removal. This is a great way to get students outdoors, to familiarize them with the identification of both non-native and native plants, and to get them directly involved in conservation.
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MEET THE AUTHOR
Jordan Carlton SchaulWith training in wildlife ecology, conservation medicine, and comparative psychology, Dr. Schaul's contributions to Nat Geo Voices have covered a range of environmental and social topics. He draws particular attention to the plight of imperiled species highlighting issues at the juncture or nexus of sorta situ wildlife conservation and applied animal welfare. Sorta situ conservation practices are comprised of scientific management and stewardship of animal populations ex situ (in captivity / 'in human care') and in situ (free-ranging / 'in nature'). He also has a background in behavior management and training of companion animals and captive wildlife, as well as conservation marketing and digital publicity. Jordan has shared interviews with colleagues and public figures, as well as editorial news content. In addition, he has posted narratives describing his own work, which include the following examples: • Restoration of wood bison to the Interior of Alaska (As Animal Curator at Alaska Wildlife Conservation Center and courtesy professor at the University of Alaska) • Rehabilitation of orphaned sloth bears exploited for tourists in South Asia (As executive consultant 'in-residence' at the Agra Bear Rescue Center managed by Wildlife SOS) • Censusing small wild cat (e.g. ocelot and margay) populations in the montane cloud forests of Costa Rica for popular publications with 'The Cat Whisperer' Mieshelle Nagelschneider • Evaluating the impact of ecotourism on marine mammal population stability and welfare off the coast of Mexico's Sea of Cortez (With Boston University's marine science program) Jordan was a director on boards of non-profit wildlife conservation organizations serving nations in Africa, North and South America and Southeast Asia. He is also a consultant to a human-wildlife conflict mitigation organization in the Pacific Northwest. Following animal curatorships in Alaska and California, he served as a charter board member of a zoo advocacy and outreach organization and later as its executive director. Jordan was a member of the Communication and Education Commission of the International Union for the Conservation of Nature (CEC-IUCN) and the Bear Specialist Group of the IUCN Species Survival Commission (BSG-SSC-IUCN). He has served on the advisory council of the National Wildlife Humane Society and in service to the Bear Taxon Advisory Group of the Association of Zoos and Aquariums (AZA Bear TAG). In addition, he was an ex officio member of the council of the International Association for Bear Research and Management.