Thursday, October 26, 2006

Frogs and chytrid/(chrytid(sic)), natural and exotic, evolution and succession. global warming and carbon sequestration.

The demise of the Panamanian gold frog to the unchecked spread of chytrid fungus brings several invasive species questions to light. One question would be the issue as to whether chytrid is in invasive species. A search online of the Global Invasive Species Database produced the following: Batrachochytrium dendrobatidis is a non-hyphal parasitic chytrid fungus that has been associated with population declines in endemic amphibian species in upland montane rain forests in Australia and Panama. It is causes cutaneous mycosis (fungal infection of the skin), or more specifically chytridiomycosis, in wild and captive amphibians. First described in 1998, the fungus is the only chytrid known to parasitise vertebrates. B. dendrobatidis can remain viable in the environment (especially aquatic environments) for weeks on its own, and may persist in latent infections.

As I continue to search for the “native” habitat of the disease, I begin to find that it is wide-spread and may, by definition lie on the fringe of the current definitions. Chytridiomycosis has now been reported from 38 amphibian species in 12 families, including ranid and hylid frogs, bufonid toads, and plethodontid salamanders. Although chytridiomycosis is found in a range of species and habitats (including African frogs in lowland regions in Africa) it has caused population declines of amphibians species confined to montane rain forests (Weldon et al. 2004; Daszak et al. 1999). The fungus prefers lower temperatures which may explain the high precedence of the fungus in high elevations in the tropics. In culture conditions optimum growth occurred at 23°C, with slower growth occuring at 28°C and (reversible) cessation of growth occuring at 29°C (Longcore, Pessier, Nichols, 1999, in Daszak et al. 1999).

The issue here whether this is truly a directly introduced by human activity invasive species, or whether it is part of the natural ecological evolution and succession. The claim is made that it is directly the result of human activity which is causing an unnatural warming. “Global warming is wiping out frog populations and threatening many species with extinction by driving epidemics of disease.” (Mark Henderson: The Times, January 12, 2006). If the spread of species by changes in weather is a criterion for defining an invasion, then what would be the paradigm for normal ecological succession? The hand of mankind can be seen in the studies of carbon sequestration. “Carbon sequestration refers to the provision of long-term storage of carbon in the terrestrial biosphere, underground, or the oceans so that the buildup of carbon dioxide (the principal greenhouse gas) concentration in the atmosphere will reduce or slow. In some cases, this is accomplished by maintaining or enhancing natural processes; in other cases, novel techniques are developed to dispose of carbon.” (Office of Science: US Dept of Energy)

When multiple variables are introduced, the task of defining an invasive species becomes complex and ever-shifting. “Every species has a set of environmental conditions under which it will grow and reproduce most optimally. In a given ecosystem, and under that ecosystem's set of environmental conditions, those species that can grow the most efficiently and produce the most viable offspring will become the most abundant organisms. As long as the ecosystem's set of environmental conditions remains constant, those species optimally adapted to those conditions will flourish. The "engine" of succession, the cause of ecosystem change, is the impact of established species have upon their own environments. A consequence of living is the sometimes subtle and sometimes overt alteration of one's own environment. The original environment may have been optimal for the first species of plant or animal, but the newly altered environment is often optimal for some other species of plant or animal. Under the changed conditions of the environment, the previously dominant species may fail and another species may become ascendant.” To complicate understanding further, “(t)here is a concept in ecological succession called the "climax" community. The climax community represents a stable end product of the successional sequence.” So it could be said that invasive species control is premised upon the stability of the overall environment which is not stable and changes over time.

So a reduction in the reach of the invasive species definition to direct human introduction may lead to a more manageable set of parameters. Species introduced by climate change may not be invasive. As in my previous post, the fuzzy, changeable edges of definition makes invasive species issues difficult to explain to a general audience. And the nature of scientific inquiry would demand a flexibility in the definition depended on current and on-going research.

The necessity to accept a changeable definition causes reluctance by the public to take action for a lack of “definite” science. This stance in turn causes friction and misunderstanding about the concept of invasive species as a whole, and therefore limits the finding of further research and control programs. Activists straining to protect ecosystems as currently occurring rush to push legislation, while others reject action until there is definitive science, which is in itself a misunderstanding of the scientific process. We wind up in a quagmire of a definition conundrum..

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