What are they? Where do they come from? Where are they now? Where are they going? What can be done about them?

Poster presented May 1999, at the South Florida Restoration Science Forum

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High potential for species sharing with South Florida Excluded from analyses; elev. > 500m Low potential for species sharing with South Florida Climate values fall beyond limit of discriminant function Zero potential for species sharing with South Florida

* For Eurasia, high potential exists in the central and southern Indian subcontinent, southern Indochina, and the Malay Peninsula.

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Preventing invasion or establishment of noxious species is more cost effective than post-establishment control. Ideally, land managers would have a 'hot list' of species to watch for and eradicate should they appear. Thus, the many attempts to develop models that predict potential invaders (Williamson 1996). I test the hypothesis that similarity in climate between the invaded (host) region and the native region of plant species can be used to predict the magnitude of risk that the host region would be subject to from various places around the world. This is the first step of a multi-faceted effort to predict plant species invasions of the natural lands of south Florida. South Florida is home to the Everglades ecosystem. In addition to being source of freshwater for a burgeoning human population, south Florida is home to Everglades National Park which is a World Heritage Site (UNESCO 1972), an International Biosphere Reserve (IGBP 1988) and the focus of one of the most ambitious ecosystem restoration efforts ever undertaken (for information see http://www.sfrestore.org). Controlling non-native species invasions is an important part of the effort to save the Everglades (Doren and Jones 1997).

I performed a discriminant analysis of the number of species that occurred in both Australia and south Florida using climatic variables as predictors. For each of 16 variables included, I calculated the absolute value of the difference between the south Florida mean value and the value for each half degree block in Australia. Thus, the lower the resulting number, the more similar the two areas are in climate.

The first two canonical discriminant functions accounted for 48% and 22% of the variance. A plot of the centroid values for the three species classes shows that the model discriminates clearly high species values from low and zero. To validate the predictive power of the model I constructed a classification matrix using the results from the analysis sample. The hit ratio (the percent of units correctly classified by the analysis) was 78.9%.

The maps at the top of the page show the distribution of areas with climates similar enough to south Florida's that they could harbor potential exotic species. I excluded from the analyses all areas north of 40°N latitude as well as areas with elevations greater than 500 m. Of the remaining areas, each continent holds at least some regions with high potential for species sharing with south Florida. These areas can serve as sources for exotic plant species introductions into south Florida and as hosts for plants native to south Florida.

But the degree of adaptation of species to the climates under which they live is often overrated. We may infer this from our frequent inability to predict whether or not an imported plant will endure our climate, and from the number of plants and animals brought from warmer countries which here enjoy good health. We have reason to believe that species in a state of nature are limited in their ranges by the competition of other organic beings quite as much as, or more than, by adaptation to particular climates.

Of course, Charles Darwin was right. Climate alone will not predict which species will invade where. My work is meant to serve as a first, course sieve to narrow the scope of future investigations. By identifying areas that harbor the most climatically pre-adapted species, scientific efforts can be focused to determine which of those species pose serious threats as invaders.

In considering the literally countless terrestrial species spread over the 15 billion ha of land on the earth one easily succumbs to despair in attempting to predict what the next wave of non-native species will be comprised of. By using host-area specific climatic-matching I have limited the search area to a few well-defined, albeit large, regions. The next step is to look within regions with predicted high numbers of climatically pre-adapted species. Do species within similar climatic regions persist in similar habitats? Are they invasive? These and other questions can be addressed with climate as a controlled variable. By first delineating a search area using host-area specific climatic matching, then cataloguing which species are there and in which habitat types they persist, one can begin to develop the ideal "hot list" of species that natural area managers can use to prevent future non-native invasions.

A more immediate application of my results would be in restricting the importation to a host area of species from regions with high potential for climatically pre-adapted species. Current national and state regulations should be strengthened to address the threat posed to biodiversity by climatically pre-adapted nonindigenous species. Also, we should fight to stem the human-facilitated movement, both intentional and unintentional, of species around the world. From an ecological perspective the obvious first action would be to prohibit the introduction of all non-indigenous species to any host area. This does not sit well with commerce, however, especially with the current trend toward global free trade (Jenkins 1996, Yu 1996). Host-area specific analyses could play a major role in determining which species pose risks for specific regions of a state or a country. Perhaps, in the absence of an all-out ban, targeted restrictions could be developed and implemented.

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