I attempted to respond to Cats are Invasive Species, 20 May 2007 by Sally, but found that comments were restricted to the team. Her contention is that by strictly construing the opening of the federal defintion, and more importantly, setting aside certain human needs and values in the consideration, that, then, by definition, house cats are invasive species. While true at a surface level understanding, as usual, invasive species matters never quite hold still for our particular desired outcomes.
Of course, the federal definition goes a little further, and has certain implied and stated qualifiers. I hold that this is not a world of absolutes, but, a world entwined with issues laden with value judgements; it is a wicked inconvenience that the invasive species issue is wrought with such complexities that individual stakeholders start with their end game results in mind and then define the term to suit their desired outcome. I have written much about invasive species as a wicked problem: Invasive Species; Wicked Inconvenience: part two. http://ipetrus.blogspot.com/2007/02/invasive-species-wicked-inconvenience_18.html
I have included excerpts from a federal white paper and a link thereto: "An invasive species is a non-native species whose introduction does or is likely to cause economic or environmental harm or harm to human, animal, or plant health. The National Invasive Species Management Plan indicates that NISC will focus on non-native organisms known to cause or likely to cause negative impacts and that do not provide an equivalent or greater benefit to society. In the technical sense, the term ‘invasion’ simply denotes the uncontrolled or unintended spread of an organism outside its native range with no specific reference about the environmental or economic consequences of such spread or their relationships to possible societal benefits. However, the policy context and subsequent management decisions necessitate narrowing what is meant and what is not meant by the term invasive species. Essentially, we are clarifying what is meant and not meant by “causing harm” by comparing negative effects caused by a non-native organism to its potential societal benefits.For a non-native organism to be considered an invasive species in the policy context, the negative effects that the organism causes or is likely to cause are deemed to outweigh any beneficial effects. Many non-native introductions provide benefits to society and even among species that technically meet the definition of invasive, societal benefits may greatly exceed any negative effects (for example crops and livestock raised for food). However, in some cases any positive effects are clearly overshadowed by negative effects, and this is the concept of causing harm. For example, water hyacinth has been popular in outdoor aquatic gardens but its escape to natural areas where its populations have expanded to completely cover lakes and rivers has devastated water bodies and the life they support, especially in the southeastern U.S. And, there are some organisms, such as West Nile virus, that provide almost no benefits to society at all. Such organisms constitute a small fraction of non-native species, but as a consequence of their ability to spread and establish populations outside their native ranges, they can be disastrous for the natural environment, the economies it supports, and/or public health. Because invasive species management is difficult and often very expensive, these worst offenders are the most obvious and best targets for policy attention and management." excerpt from http://www.invasivespeciesinfo.gov/docs/council/isacdef.pdf