Invasive species wickedly impact ecosystems and simultaneously are inconvenient to immediate human wants and needs. No species better illustrates this than the domesticated cat (Felis catus) also known as the house cat. The housecat occupies one of the highest positions within the turbulent world of human engendered biological co-evolution. The perfect hunting generalist is at the same time the calming innocent purring ball of contentment and pleasure. The domesticated housecat is a killing machine that can successfully hunt many small mammals, birds and even fish. And being an opportunist like its human companions, the cat quickly adopts a home and adapts to the local food supply.
Many species have co-evolved with Homo sapiens such as horses, cows, dogs, mice, rats, wheat, rice, house flies, roaches, influenza, and E.coli. This bounded collection of species has spread across the earth, together, in a stochastic system of over-production and extreme competition for resources. Each species now needs the other and so while some increase for awhile a larger balance is maintained internally at the expense of endogenous ecological systems. Simply put, the human ecosystem can be imagined as a biological bulldozer re-engineering the biomes of Earth as it moves across the planet. This whirling ball of continuous change, this human ecosystem disturbance is analogous to a farmer plowing a field. A side-effect of this disturbance is the facilitation of biological invasion. The agents of invasion are referred to as invasive species. Moreover, by deft definitional sleight of hand we mostly eliminate many of the co-evolutionary exotics that give us companionship or food from our list of invasive species, because these friends-of-mankind species have been assigned a greater value to humanity as compared to their destructive outcome to nature (the local endogenous or native ecosystem).
The housecat reigns supreme in its seat of power. It brings aesthetic and emotional pleasure earning its keep in earlier ages by keeping some of the lesser denizens of the human ecosystem’s over-production capabilities in check. Mankind values the silo of grain for tomorrow’s dinner, and thus values the cat in the raging interaction of man versus mouse. The aloofness of the cat is translated as an expression of a partially “wild” animal; a poetic state that allows humans to think the cat belongs outdoors as a right accorded to wild beings and, therefore, is living in balance in nature doing good things for all.
The purring kitten sitting on one’s lap models the image of innocence. Like the sibling that swats its brethren and then smiles when those-who-must-be-obeyed arrive, the cat is beyond suspicion or reproach for any damage to an ecosystem. Because the emotional bond is so strong and so deep and so cultivated by both the cat and the humans who love the cat, the idea of any possible negative interaction that might be induced or caused by a cat lies beyond the pale of polite conversation. The occasional pet hamster or goldfish not-with-standing, the cat is seen as a defender of the home eliminating the scourge of pest and disease vectors (rats, mice). This idea then leads to a generalization that cats only help brings balance to the world – a good thing, naturally.
One trait of the domesticated cat is to reproduce (over-produce) with little concern for population excess. The human part of the equation may from time to time make the quick calculation that cat equals wild equals nature. For whatever the reason, the cats who fall from grace and live on the edge of the human ecosystem, are now referred to as “stray” by cats-as-a-benefit and “feral” by cats-as-destructive. The word feral allows humans to use a definition function that inputs friend of man and outputs a wild species undifferentiated as to origin or impact. In other words, the feral cat is now safely classified one step removed from the good or behaved house cat, and may even be labeled by a few as an invasive species, but only if the few are willing to risk thundering approbation. Just as labeling a garden ground cover like English ivy as a weed, labeling the house cat as feral is one step from recognition of invasive species status. Both the ivy and the cat when found outside their traditional expected position or use with in the human ecosystem are species on the edge of good and bad.
Along with the blurry definitional status of the cat, the reinforcing idea that natural ecosystems consists of free, “undeveloped” spaces and, therefore, a no cost solution to the challenge of human ecosystem excesses, allows for a quick disposal of the stray cat to a native ecosystem, side-stepping the impact question and blithely finding no harm in the action. The fuzzy opportunistic definition of a cat’s place in the greater and lesser schemes of things permits us to allow the cat to reside in any aspect of any ecosystem at the lowest immediate cost to the human agent. In other words we can throw the cat out and defend its unique place in the world at the same time and do so without any internal philosophic conflict.
However, through the process of stakeholder consensus, housecats are not considered an invasive species. Some stakeholders, recognizing the prolific reproductive capabilities of the now stray or feral cats, propose a program of trap, alter and return. This is an attempt to protect the sanctity of all life couched in terms of a live free and let live policy. It does nothing for the impact on ecosystem resources that the now altered cats still wreak, but it does mitigate the reproductive pressure. It does highlight an environmental dichotomy between protecting life directly and protecting the ecological systems that provide the structure for life. There is an inherent collision of desires between the immediate microscopic desire to protect life now, and the large macroscopic drive to protect the ecological systems that provide the resources for the species involved in the first place. The resulting chicken and egg squabble, a collision of desired outcomes allows the much broader portion of the public as disinterested traditional cat companions to rise above the fray guaranteeing no political movement towards an ecological solution whatsoever. The result is that we have groups that claim to protect habitat, rights and welfare from human exploitation, but engender the destruction of the ecosystems they are trying to protect by making no distinction to the strong and weak ecological interactions. In the case of cats, we get a decrease in the extremely important weak interactions at the expense of the cat induced strong interactions. In other words non-indigenous cats are more successful at hunting indigenous species and so, changing the internal balances of the ecosystems thereby adding considerable stress.
At some level of the dialogue surrounding policy choices, if cats were classified as invasive species, serious consideration of H. sapiens as an invasive species by analogy might take place. Doing this would make the politics of climate change look like a weekend walk in the park. Invasive species definitions are constructed from an anthropocentric lens or point of view. The idea and reality of cat is ingrained in human societal expectations which by definition are good for the continuation of humanity. The practical outcome is, of course, that human societal choices are not always in the interest of all individual humans in the long term, but for the species as a whole in the long run. And even that assumption of species benefit of individual action does not necessarily guarantee species continuation.
The negative impact of cats on indigenous species with in endogenous ecosystems especially in the urban interface with what is left of natural areas may be significant. In one study in the United States suggests that “…rural free-ranging domestic cats in Wisconsin may be killing between 8 and 217 million birds each year.” The large number of bird deaths should be compared to the total number of birds, but the enormity of the slaughter is enough to outrage defenders of natural areas from the predation of the cute and cuddly killing machine. This conflict of intentions sets up a us-or-them boundary and a classic wicked problem matrix (February 18, 2007, Invasive Species; Wicked Inconvenience: part two) where in stakeholders arrive at the complex issue with predetermined outcomes in mind that frame each constituency’s position and definition. An inability to actually address or even define the problem is the result of this process.
So the problem is one of perception. Is it alright to keep a house cat locked up inside away from the great outdoors for which it pines? Is there any responsibility on the part of human companions for the natural area destruction that domesticated cats can wring out of native ecosystems? Is there a role for house cats outside of strict sterile confinement? What is a natural ecosystem anyway, especially in a dense urban setting filled with mice and rats and other gems of human co-evolutionary pressures? Could we realistically ban cats in the same fashion as we attempt to ban plants or animals? To what geographic location exactly is a domesticated, co-evolved-with-humanity species native? Are housecats not native to wherever human live?
In spite of our desires for a linear simple straight to the point answer to any or all of these questions, there are no simple answers. If we intend to preserve unique, native ecosystems, then domesticated cats must be removed. On the other hand if we judge the cost of “natural” ecosystems beyond our resources to maintain, then perhaps cats have a role in the new novel unexplored ecosystems that we are unintentionally creating. We cannot have it both ways. If there are to be native species preserves, then they must be protected from the biological cloud of disturbance that is the human ecosystem including pet cats gone astray. In the end allowing pet cats or any other human companions beneficial or otherwise to wander uncontrolled in natural areas is as destructive as just paving over the green space.
On the other hand, killing our excess species, native or domesticated, because we did not take time to consider the consequences of our human actions devalue the worth of all life. Life is sacred or it is not. Treating life like we treat our plastic cups is setting up a feedback loop that will overwhelm us. We cannot build a viable, suitable life on the idea that everything has a cost-free disposable use.
 Definitions Subcommittee of the Invasive Species Advisory Committee (ISAC). (2006).Invasive Species Definition Clarification and Guidance White Paper. http://www.invasivespecies.gov/global/ISAC/ISAC_documents/ISAC%20Definititions%20White%20Paper%20%20-%20FINAL%20VERSION.pdf .
“It is also essential to recognize that invasive species are not those under human control or domestication; that is, invasive species are not those that humans depend upon for economic security, maintaining a desirable quality of life, or survival.”
 In Defense of Animals Press Release. (2000). Boeing Co. Cats To Be Killed
Fate Of Trapped Wildlife Unknown. http://cats.about.com/library/weekly/aa090400c.htm
 John S. Coleman, Stanley A. Temple, and Scott R. Craven. (1997). Cats and Wildlife:
A Conservation Dilemma. http://wildlife.wisc.edu/extension/catfly3.htm