Amphibian populations around the world are diminishing at unprecedented rates. In myriad diverse habitats, their once ubiquitous presence has become a trickle in spacetime. Attempts to find a single cause for this crisis have been as many and varied as the habitats themselves, as have results from scientific analyses spanning more than a decade. Data reveal fickle and disharmonious patterns, where intuition expects black and white conclusions. A large scale transition of some kind is in progress, most likely involving novel and damaging stoichiometric undertows and intrusions of uncontainable energy. An anthropogenic confluence of ecological and climatic dysfunctions is at the root of this mass decline, and solutions may be beyond the scope of nature (both human and non-human) to attain.
No one factor can be isolated and removed from the equation that will restore the chorus of the amphibians to the planet’s more moist locations. Pesticides and ozone depletion have been addressed, allegedly by scientists employing inadequate methods, according to recent reports1 (S. Jackson, C. Griffin, 1991; Hayes, 2002). Climate change and habitat destruction, on the other hand, remain as a two-pronged assault on natural systems everywhere, with a common origin – human growth.
This paper is not region-specific, but instead seeks to illustrate how synergistic effects are being duplicated across the North American continent, and how the damage pattern is emerging on ever-larger scales. Ultimately, the fate of human society is what is being discussed here, with amphibian trends used as an indicator of its health or otherwise. An attempt will be made to determine where human growth (and the processes it generates) fits into the amphibian decline puzzle, and how its basic tenets can be revised before the “amphibian song” is silenced forever.
Non-Human Environments.
The International Union for the Conservation of Nature (IUCN) recently embarked upon a project entitled the Global Amphibian Assessment2 – the first worldwide assessment of amphibians – and concluded that fully one third of all amphibian species can be considered “threatened”. This situation, which means that, of a reported 1,856 species, 32.5% are in danger, and could realistically undergo tens of thousands of years worth of extinctions in the next century alone, suggests that something peculiar is happening; some of these projected extinctions will be occurring in regions distant from direct human interference, possibly as a result of the fungal disease, chytridiomycosis, which some claim is a result of global climate change. This condition appears to afflict amphibians in regions where the impact of human activity isn’t immediately obvious, but could be considerable. (In densely human populated regions, where chytridiomycosis is non-existent, amphibians are also declining, such as in Europe.) It is fair to assume that the most effective large-scale surveys are not possible outside relatively developed regions, for a variety of reasons, and consequently “true” global amphibian decline data may not be available. Nevertheless, these indicator species are declining in massive numbers, and their last remaining refuge may be the heart of shrinking rainforests, in terms of preserved ecosystems if not species diversity. This is a time when life in general is being challenged, by conditions never before seen, or not seen for millions, if not billions of years, such as atmospheric alteration. Virtually no species is immune to the universal effects of phenomena such as UV-B increases because of thinning ozone, amphibians least of all. That amphibians have survived other mass extinctions so successfully, but are so readily crumbling in the face of the current one is a particularly dramatic factor. We will now survey some aspects of human growth that constitute an assault on several media, all of which are critical to the health of amphibians.
Pushing the Green Envelope
The United States, Europe and Australia are considered to have relatively stable populations as a result of their industrialised nature and culture. It could therefore be concluded that there was no requirement for physical intrusions into the natural environments surrounding conurbations in these countries.
Unfortunately, this is not the case. The industrialised culture composes a one-way thrust, outward from various physical and conceptual centres, as the economy expands. Human beings now possess an array of tremendous power, in the form of information/communications technologies, lifestyle choices, and fossil-fuelled vehicles and appliances, both utilitarian and recreational in form.
Development of rural land becomes necessary, as people leapfrog town boundaries and seek refuge from ageing town infrastructures in rapidly constructed suburban “neighbourhoods”. Communications technology and inexpensive fuels means that they can work from personal computers, or else brave long commutes back and forth from their distant suburban homes. This phenomenon, of instant, mushrooming cul-de-sacs in the woods, or among the farms, is bringing people closer to nature, but also closer to pesticides. Amphibians are an important indicator, then, of biological health status for humans living in these cultures
The “chemical society”, whose innumerable tendrils extend into all walks of modern life, has created a pseudo-sanitised and potentially lethal form of human growth, which threatens to engulf and poison the natural foundation from whence it sprung. The United States is globally recognised as the forerunner of this trend; America has more and worse types of swelling “islands” of toxicity, that are damaging to the ecological matrices of which they are but a part, than any other nation. A project by Defenders of Wildlife has worked to classify the states with the greatest numbers of endangered ecosystems3. Among the worst are California, Texas and Georgia.
The Greater Atlanta area has in excess of 16,000 miles of roads4. Air and water quality in this region fall considerably short of Federal standards, as can be said of many other metropolitan areas. The Atlanta region has had federal highway funds cut as a result of non-compliance with air standards – a crucial blow to a region dependent on automobiles. It is the least densely populated metropolitan region in the United States, one quarter the density of Los Angeles. Georgia ranks third in the nation for amount of rural and wooded areas being converted to suburbs, with an average of 50 acres per day of tree cover being depleted since 19875. (Nationally, 1 million acres per year are lost to sprawl6.) Elsewhere, massive increases in storm-water run-off (along with its toxic load) have contaminated major watersheds such as the Chesapeake Bay, where 90,000 acres are engulfed by sprawl every year7. Developed wetlands and river networks – the former filled in and paved over by bulldozers, and the latter overwhelmed by the resultant increased run-off – are becoming unfit for habitation by America’s native species, with Delaware leading the nation in loss of native plant and animals8. Even “rural” Vermont lost 10% of its farmland to development over an average 2 years in the 1980’s9.
Sprawl means space, and space means driving. Driving creates untold quantities of poisonous gases, which have various negative effects on the atmosphere, on the soils and biota, after they have reacted and precipitated on the natural environment. Climate – change and acid precipitation have certainly conspired to alter the chemistry of current ecosystems to the detriment of amphibians, in greater measure than the bulldozers and tarmac-layers immediately connected to suburban developments. The sediments that are flushed into aquatic systems during construction and resultant globally dispersed gases that contribute to climate and pH change as by-products of excess driving and energy generation, are major contributors to the amphibian decline puzzle, as are the nitrate wastes from industrial effluents and wastewater treatment plants. The “modern” lifestyle has apparently formed a discontinuity from natural processes, one that threatens to unhinge previously unsuspected synergistic forces, releasing into the human environment a plethora of chaotic and undifferentiated health hazards. First, the issue of reliable data is discussed, with consideration to the often fragmented and variegated terrain facing herpetologists in the field.
Logistic and Methodological Difficulties.
Recent studies have unearthed datalogical hurdles concerning spatially isolated-yet-connected or inaccessible habitats, particularly with regard to obtaining accurate density and distribution data. Amphibians, being biphasic, occupy a huge variety of these types of environments, and issues regarding the validity of data have arisen in all avenues of field surveyance. It has become apparent that population composition and behaviour is extremely changeable over very short vectors of space and time, thus rendering projections across even moderate geographic scales irrelevant. Studies must be limited to the satisfaction of particular objectives (determination of population age, courtship patterns, etc) and little else, while creating as small an impact on the habitat as possible. Two methods, quadrat sampling and patch sampling, are among the most reliable for establishing density and distribution. Quadrat sampling, the random placing of small square-shaped areas of intense study, is not dependent on uniformity of habitat, and each quadrat is an independent source of data. It is difficult to place quadrats on overly steep ground or in places where vegetation is dense, however, and other methods and devices are required in these circumstances. Patch sampling within habitats (microhabitats) has become a favoured sampling method, with rocks, boards and logs all constituting individual “patches”, and accurate dimensional values being associated with each. Actual size of rocks and logs carry quantitative and qualitative significance, and comparison of microhabitats within a single area must be strictly limited to same-dimension patches. Any variation from these guidelines may create bifurcations in data-relevance that, if overlooked or extrapolated, result in gross inaccuracies. Until recently, amphibian surveys were performed with far less concern than might be appropriate for these highly sensitive organisms, and herpetologists have become well-aware of the levels of scientific expertise demanded of the task.
Species abundance and diversity are related concepts. Abundance is self-explanatory, but the concept of diversity has been criticised for its lack of an operational definition (McIntosh, 1967, Hurlbert, 1971). The concept has a mathematical basis, which is the abundance factor relative to the species-representation factor. “Richness” and “evenness” are its chief determinants.
Richness. Sample size effects present a problem when attempting to determine diversity; as the size of a sample increases, the diversity increases also. A species count is the most basic of data, but the sample size, micro-location, search-time, weather and attitude of participants can all radically affect the representative sample, which in turn will be factored into any calculations for biodiversity. Hurlbert differentiated between numerical species richness and areal species richness. The former is a value derived from number of species present in a sample of particular size, and the latter is taken from number of species relative to given area or volume of a sampling site. Sample size effect is a universally recognised problem, for which there have been suggested two solution formulae. One is to take the overall species count, reduce the value by 1, and divide it by the log of the total number of individuals in the sample: D = (s – 1)/log n (Gleason, 1922), where D is the index. Another way to arrive at an index is to divide the total species count by the square root of the total number of individuals: D = S
√ N (Menhinick, 1964). The problem with these methods lies in the fact that the values for total (expected) species E(s) and total individuals (n) must remain functionally constant across a variety of ecosystems, and that the relationship between them cannot deviate from the precise form. So, while establishing richness by relating numbers of individuals to species represented is scientifically credible, it is somewhat lacking as a method for characterising diversity. The concept of evenness seeks to factor into the overall equation the proportional abundance of the species.
Evenness. The measure of species distribution and proportion relies on a standard – the equal abundance of all species – against which divergences can be compared. There are innumerable ways in which this “balance” can be upset, and translation of data into graphic form constitutes non-linear, chaotic representations, which accurately reflect the spontaneity and complexity of living systems. Use of the word “dominance”, to describe greater proportionate abundance in communities is discouraged, due to its associations with competition, with each species being represented by a single value – observed abundance over species. There exist numerous more advanced equations which define evenness, but they tend to suffer from similar limitations as above. Heterogeneity indices, as they are called, express more equitable distribution among species in the form of higher index values.
Environmental quality information does not necessarily surface in diversity data. It is possible for a habitat to accommodate great diversity and to be relatively polluted or disrupted, just as it is possible for a habitat to naturally contain a small diversity of species, regardless of disruption levels. Amphibians’ biphasic, migratory life-cycles, tightly-coupled to distribution of wetland and upland habitats, create an almost unique problem for scientists in the field. Great differences of environmental preference exist over minute physical distances, and field herpetologists note that many species live in close proximity to humans, unbeknown to them, as a result of camouflage, fossorial, seasonal and nocturnal behaviours.
Environmental Chemistry
The immense variety of chemical insults to aquatic and terrestrial systems which are home to amphibians is too broad and complex a subject to adequately tackle in this paper, but several of the better-known forms of environmental degradation will be addressed. Chemicals are working in concert with other factors, such as parasites, pathogens and ozone-depletion (increased UV-B) to threaten the existence of amphibian and other communities. Anthropogenic issues are centred on chemicals in all media, with pesticides, fossil-fuels and wastewater/fertiliser being three of the main sources of the problem.
Pesticides and Chemical Contaminants
It is estimated that private lawns in America cover between 20-30 million acres. The EPA believes that 70 million pounds of active pesticide ingredients10 are administered to lawns every year. That these chemicals migrate from their point of application to surrounding water bodies is a known fact. Precise migration routes and rates are largely unknown. Agricultural pesticides account for 939 million pounds per year, according to EPA estimates for 1995. This includes all forms of active ingredients. Hayes et al conducted an extensive study11 of the pesticide atrazine, of which 60 million pounds per year are applied in the United States by farmers alone. Atrazine is one of the world’s most-utilised agricultural chemicals. It was found to be present in regions outside application radii due to atmospheric transport in rainwater, suggesting its ubiquity. Hayes discovered that this chemical was responsible for hormonal disruption in frogs, due to the activity of the enzyme aromatase, which converted testosterone to estrogen after impact. Two experiments were performed, using the African Clawed-Toad, Xenopus;
1) Tadpoles exposed to concentrations of between 0.01ppb and 25ppb and morphological effects noted after metamorphosis.
2) Adults exposed to 25ppb directly and testosterone and estrogen levels measured. Results for Experiment 1 showed that, when exposed to as little as 0.01ppb, tadpoles developed androgynously, with abnormal reproductive features, such as mixtures of ovaries and testes or too many gonads generally. Results for Experiment 2 showed that males exposed to atrazine had testosterone levels equal to that of females. Control males in the experiment had normal levels of testosterone. This chemical is considered by the EPA to be safe for short-term human consumption at concentrations of 200ppb, and 3ppb in drinking water. Atmospheric transport ensured a background presence of 1ppb at locations where it wasn’t used in applications. Hayes’ findings revealed demasculinising effects at levels 10,000 to 30,000 times beneath levels considered non-toxic to frogs (3ppm). Levels of atrazine involved in exposure of Xenopus were one thirtieth the level allowed by the EPA in drinking water. Implications for human health are obvious, as well as one explanation for amphibian declines, given the tremendous quantities of atrazine applied to world environments.
Impacts of chemical contaminants at critical points in the life-cycle may influence such things as population size and density. Developmental toxicants such as polychlorinated biphenyls (PCB’s) and organochlorine pesticides have been found to correlate with ageing populations at particularly contaminated sites. Disproportionate numbers of adults exhibiting slight physical deformities suggests low survival rates of immature individuals suffering impacts12. Toxic stress early in the life cycle may impair individuals’ ability to respond to general environmental stressors, as a result of corticosterone-producing (stress-response) centres being compromised by exposure to persistent organochlorine pesticides.
The synergy associated with this and other forms of chemical poisoning may affect amphibians’ ability to avoid/fight off predators, as well as adapt to naturally changing conditions in familiar habitats. Metapopulations are dependent on two chief factors:
1) Numbers/density of individuals dispersing between ponds.
2) Density and distribution of wetlands in the landscape, which determines potential for populations to be adequately configured, for genetic and competitive reasons.
Reduced metamorphic mass and impaired motor functions are commonly noted sublethal effects of pesticides, particularly organophosphates and carbamates. It is significant that under natural conditions, only 3-5% of offspring survive to metamorphosis, and that metamorphic production is an episodic phenomenon. Impacts from chemical contamination can interrupt this tenuous process, reducing recruitment to critical levels. Habitat succession is dependent on dispersal of metamorphose juveniles from aquatic sources to surrounding terrestrial locations (and on to colonise new ponds), and chemical contamination diminishes the likelihood that this age-old cycle will occur, as a result of low survival rates, compromised motility and lack of suitably healthy available ponds.
pH
Much has been written on the subject of acidity in aquatic ecosystems, and there is great latitude in interpreting the data. Many factors, such as acid precipitation, snowmelt, groundwater composition and lake-basin geology contribute to overall pH values, and any one factor may raise a spike in these values. There is no question that the single greatest contributor to acid-rain is petrochemicals, or fossil fuels. The embryonic phase is the most sensitive to acidification in amphibians, and different species exhibit different levels of tolerance, with lethal effects ranging from pH 6.1 to 4.6 (Hecht, 1993). Jackson and Griffin (1991)13 studied pond chemistry in the Connecticut Valley and concluded that adult Ambystoma salamanders were unable to survive in the Connecticut Valley in ponds with pH < 4.5. They stated that earlier suggestions (Cook, 1978, 1983) were incorrect with regard to ongoing acidification of water-bodies, and that pH was variable over time, with different quantities of [H+] present from year to year. This contradicts the belief that a trend towards lower pH is occurring generally, but doesn’t necessarily indicate diminished rates of impact; constant shifts up and down the scale could actually be more damaging than a single, smooth descent in values. This applies to both aquatic and terrestrial habitats.
Lowered pH means greater metal ion content, which is toxic. There is a buffering range scale in soils, where different cations dominate the chemical make-up. When soils reach the (lowest) iron buffering range (pH < 3.8) there is a marked decline in terrestrial amphibian density and richness (Wyman and Jancola, 1992). A complex electrochemical relationship between accumulated acid anions and the dominant cations of the buffering ranges takes place, whereby the dominant ions are leached away, taking other cations with lower valence along with them. Sodium, with its small atomic weight, is often deficient in these soils. Wyman (1988) appears to have discovered an important correlation between this Na+ deficiency in soil and the density and distribution of certain salamander species: The skin of amphibians is extremely sensitive and constitutes a two-way membrane that conducts exchange between the organism and its environment, of fluids and gases. Highly-acidic aquatic environments cause amphibian larvae to lose Na+ through the epidermis (Freda and Dunson, 1985), resulting in the loss of essential neurological and cellular functions. Over several laboratory and field experiments, Frisbie and Wyman (1991, 1992, 1995) found evidence for sodium disruption in salamanders living on substrates with low pH, using eastern red-backed, Allegheny Mountain Dusky and northern two-lined salamanders. Radioactive sodium was injected into the subjects, and they were placed on buffered low pH substrates, ranging from 5 to 3. Concentrations of Na were determined after 24 and 48 hours, revealing higher Na efflux at lower pH for the Allegheny and northern two-lined, with the opposite being true for the eastern red-backed. Acidified environments were thus found to be detrimental to amphibians, both aquatic and terrestrial.
The University of California, Los Angeles also performed a study, for California EPA Air Resources Board14, on the effects of acidity on amphibians in the Sierra Nevada. The aquatic habitats of the Sierra compose extremely low ionic concentrations, heightening the sensitivity of the community. Adult specimens of four species of amphibian were collected, and the larvae resulting from their fertilised eggs used in dose-response studies, involving low pH and aluminium. Embryos and hatchlings were kept for 7 days in water with pH as low as 4.0 and as high as 6.0. Inorganic aluminium was introduced to reconstituted water at concentrations of 75 μg/L in pH 6.0, 5.5 and 5.0, respectively. This produced values of 39, 70 and 80 μg/L. The organisms were exposed to various pH levels and three solute levels, before being evaluated for post-treatment survival, hatching time, and total body length. At the same time, lakes from the sample area were surveyed for amphibian characteristics. 141 water samples were taken from sites where amphibians were breeding, and 94 samples taken from potential breeding sites, where no amphibians were found. Water chemistry was analysed for all samples.
Results showed that embryos and larvae in all species were reduced in total length, with embryos being more sensitive than larvae. Individuals were smaller as pH values declined, and higher ionic aluminium concentrations caused high mortality on the one species tested for this. pH of breeding habitat samples was 5.4 to 7.9, and the acid neutralising capacity ranged from -1.5 to 1100 μeq/L. Composition of amphibian populations appeared unrelated to pH or dissolved solids. Amphibian declines have certainly been occurring in the Sierra, but it seems that acid precipitation is not the cause. Increased sensitivity, due to low ionic concentrations at these sites, may have contributed to the forms of drastic lethal and sublethal effects achieved in the laboratory. These conditions represent a “lose-lose” situation for the organisms; if they already live in low pH-high ionic environments, they are definitely affected, and if they are living in “pristine” environments they will be impacted more dramatically by these forms of chemical shifts when they occur. There is no way to determine the quality of the sampling and analysis aspect of this project, and bias on the part of the governing body (Air Resources Board) is a matter for conjecture. The subjects were taken from a high-altitude environment, which could have been beyond the radius of impact from the Greater Los Angeles area, whose smog tends to collect against the western face of the Sierra. The two surveys described above took place close to major conurbations in the northeast and southwest United States, in the Catskills and the Sierra Nevada Mountains.
Fertilisers and Nitrates
Modern human habitats necessitate complex waste-water systems, which frequently fail to perform to anticipated standards, resulting in nitrogen compounds being introduced into systems that lack the capacity to cope with the quantities involved. Additionally, agricultural run-off of fertilisers contributes high concentrations to waterways, causing algal blooms and subsequent anoxic conditions. Nitrogen appears in aquatic systems in four forms: Ammonia (NH3), ammonium ion (NH4+), nitrite (NO2) and nitrate (NO3-). The most toxic form is ammonia, followed by nitrite and nitrate. Nitrates, from wastewater treatment, agricultural run-off, and industrial effluence, represent a substantial source of disruptive chemicals. Data on nitrate effects on amphibians, their prey and predators, are widely available. Nitrates are universally understood to have negative impacts on aquatic systems in general, and especially in amphibian systems. Laboratory conditions dictate that lethal and sublethal effects occur at concentrations between 2.5 and 100 mg/L15. These values are attained with some frequency across North America; nitrogen-based fertiliser use increased from 2.5 million tons in 1960 to approximately 11.9 million tons in 1985. It has been postulated that habitat loss and nitrate levels in wetlands are more closely correlated with lack of biodiversity than are pesticides.
Andrew Blaustein, a zoology professor at Oregon State University, is an expert on global amphibian declines. He has investigated the many causes behind the declining amphibian population, and has performed studies on the effects of nitrogen compounds on four species of amphibians, including the Oregon spotted frog – on the brink of local extinction. Researchers discovered that concentration levels of NO2 and NO3- commonly found in agricultural regions was high enough to kill some species. The concentration levels are considered safe for human consumption by the EPA. The Oregon spotted frog was four times more sensitive to the effects of NO3- than the other species, and is almost extinct in its native habitat, where agricultural practices are intense. Blaustein has also found a correlation between nitrogen run-off and amphibian deformities – another piece in the puzzle. The deformities are thought to be caused by a trematode known as a fluke, a parasite which spends some of its life-cycle in a snail. The snails eat algae, which grows prodigiously when nitrogen fertilisers are introduced into the aquatic habitat, creating a huge food reserve for the snails. An enlarged snail population means more trematodes, which results in greater incidence of amphibian deformity. In ponds where nitrogen levels were in excess of EPA drinking water standards, 67% of the frog population had multiple legs.
A variety of symptoms are associated with the presence of nitrogen. It has been suggested (Hecnar) that reduced feeding, which results in weight loss and ultimately death, is being caused by disruptions between tadpoles and gut bacteria involved in digestion. The condition in human infants is called methemoglobinemia, or “blue-baby syndrome”. The bacteria convert NO3- to NO2 (nitrate to nitrite) which oxidises iron in haemoglobin and forms methemoglobin which cannot bind oxygen. A certain diversity of bacterial forms is necessary to reduce the nitrite and metabolise the nitrate, which young children and tadpoles apparently lack. Consequently, the tadpoles are forced into uncharacteristically shallower water than usual in an attempt to obtain oxygen, causing them to become “beached” or exposed to predators. Urban areas contribute massively to these problems, with elevated nitrogen concentrations being the norm for many decades.
Enter the System
Experts around the world have convened and discussed all of the above issues and many more in some depth. One thing everybody agrees on is that there is no single remedy available to redress the balance in the amphibian saga.
Andrew Blaustein has been a pioneer in experimenting with the effects of high-level UV-B radiation, whose effects include reduced growth rates and damaged immune systems16. Ozone-depletion is anthropogenic in nature, a consequence of chlorofluorocarbons, and it may be many years before its full impact is able to be assessed. Despite years of study, no definite link between increased UV-B in the natural setting and amphibian declines has been established. This is true of several potential causes.
Others have speculated that global climate change is a major contributor to the declines – that human beings are making too great demands on the systems of other species by forcing them to adapt to changing conditions at rates hitherto unknown – and that the cycle of extinction has barely even begun. It has been observed that species’ behaviours are altered as a result of climate change, with amphibians being more affected than most as a result of their biphasic life-cycles. An organism which occupies niches in the moist zones between the aquatic and the terrestrial is caught in the most extreme aspects of this transition, and several instances are noted where frogs have become disoriented and somewhat confused by the lack of moisture in their environments, and are forced to search out situations where they might find it17. Behavioural adaptations around these changes are contributing to over-stressed organisms being overrun by parasites of various forms (such as flies, which are increased as a result of climate change) that may be unfamiliar to amphibians undergoing behavioural modifications. Unusual drought conditions, as well as heavy frosts in places where none had occurred before, are also related to climate change, and to local extinctions of frogs and toads.
Humans have been transporting species around the globe and introducing them to exotic systems for centuries, as well as stocking water-bodies with fish for recreational purposes, many of which prey on eggs and larvae of salamanders, frogs and toads. Ironically, one of the chief threats to amphibian systems is an amphibian itself. The common bullfrog, Rana catesbeiana, has been encroaching upon the habitats of amphibians across the United States18. In many cases, reduced ability of species to avoid predators, compromised motility in adults and larvae, reduced body size and instinctual faculties have meant increased predation by the bullfrog, resulting in bullfrog ranges being expanded markedly, both naturally and by human involvement. Bullfrogs were introduced west of the Rockies by humans, and in almost all areas where bullfrogs have succeeded in “removing” the native amphibian population, conditions are degraded as a result of human activity; bullfrogs are not simply preying on other species, but are basically more tolerant of these changes, and are thriving in the face of other species’ inability to cope.
Interconnected causes lie at the heart of the situation; wetlands are paved over, disrupting the configuration of natural water-bodies on the landscape, opening new access routes to motor vehicle traffic and its attendant toxic emissions, enabling sudden new concentrations of humanity to sprout in recently isolated places. Migration corridors are being churned up by development, and millennia-old breeding ponds are disappearing, while those that remain are receiving large inputs of acids – by-products of vehicle use and increased output by power-stations. Amphibians that live in “pristine” environments are also declining, and nobody can point to any one cause, though most can cite several causes that most likely are working in tandem. It has even been suggested that acid rain can increase amphibian populations. Karen Clark (Canadian Ministry for the Environment) found that highly acidified aquatic environments were able to support certain species of salamander, but no fish. These fish might otherwise have preyed on the salamanders’ eggs, but were unable to tolerate the acidic conditions. As a result, salamander populations were increased. Another researcher, Clive Cummings (Institute of Terrestrial Ecology, Monks Wood), found that highly acidified water killed some frog eggs but the tadpoles that survived, once adapted to the conditions, were able to thrive as a result of the less ferocious competition for resources. It is not difficult to envision how such increases in food supplies might affect bullfrog populations, however, assuming that higher numbers of metamorphose individuals were able to be sustained (they are minor and insignificant in truth).
Distribution of species is difficult to predict for amphibians, as large numbers of species occupy small areas while small numbers of species may occupy large areas. It is clear that all habitats destroyed for human habitation will never be restored, and that developers are not inclined to be educated on the subject of biodiversity and genetics. Fragmentation combined with climate change and increased UV-B radiation represents a considerable barrier to organisms attempting to overcome sudden environmental changes. Construction of roads creates what are termed “road zone effects”19 (Forman et al, 1995), degraded ecology in the linear regions adjacent to roads. Roads tend to breed more roads, as well as provide passageways for undesirable elements, such as oil and salt run-off, non-native species and illegal use of trails by recreational vehicles.
Wetlands and wetland buffer-zones constitute a scientific and legal issue, largely centred around the fact that buffer-zones are not large enough to accommodate amphibians as they live out their life-cycle. Circular drawn buffer zones around patches of wetland may not accurately reflect the shape of migrations, and need to be several times larger. Conservation commissions across the U.S. engage developers in a complex legal dance with regard to these edge effects, with matters of economy often being the deciding factor. Farmers, hemmed in by swelling suburbs, may plough to the very edge of wetlands, while using various chemicals to increase yields, thereby utterly poisoning the complex ecology of the area in order to meet financial needs. All is dovetailed to all else.
Frogs, toads and salamanders that have evolved effective forms of camouflage (and other types of) mimicry may find themselves defenceless against non-native predators, as a result of natural rocks, native species and flora being stripped away around them. C. K. Dodd and L. L. Smith define habitat destruction as “the complete elimination of a localised or regional ecosystem leading to the total loss of its former biological function”, and they stress that “altered” habitats may well constitute worse damages than “destroyed” habitats, as the invisible effects of chemicals mask grossly distorted conditions while hardier species are able to move into suburban areas. It has been discovered recently that disturbed or degraded habitats are more likely to be the site of ranaviral epizootics on five continents20. Frogs infected with fungal viruses have been successfully treated with fungicides developed in the laboratory, but in nature no such defence exists, and once again the attempts to determine the actual cause of diseases like chytridiomycosis run aground in the face of ecological chaos.
The American dependence on automobiles (and the fuels they require to function) is the keystone in the maelstrom. Zoning laws, cultural stubbornness and the need for an expanding economy are working together to grind what remains of our natural resources into dust. It is to the automobile culture that we must direct most of the penetrating questions, to those responsible for designing a world around the motor-car, a world that appears acceptable when viewed impassively through glass at approximately fifty miles-per-hour.
Post-war America enjoyed a brief spell of seeming prosperity, before plunging into a culture based on planned obsolescence. Articles in common use were designed by industrial chemists to be thrown away having failed after a short time. This appeared to be the key to an ever-expanding economy; construct non-durable goods in vast quantities, advertise them on television and on highway billboards, and pump the economy full of them until there is little option but for every manufacturer to follow suit, in order to compete at the “new low prices”. The huge abundance of petrochemicals meant that not only plastics, pesticides and other hazardous compounds could be freely available, but that their transport across the continent was not a problem. Entire economies were built on storage and haulage. People began to neglect the inner core of established cities and towns, moving out into the “country”, to live in larger houses that sported two-car garages on their fronts; domiciles began to resemble loading docks, and automobiles grew in size, coming to resemble delivery rather than personal vehicles, as the politics of planned obsolescence gripped America. Local landfills were capped and vented, filled to capacity, and peoples’ refuse now delivered to “transfer stations”. The hugely increased garbage volumes were shipped off to points unknown, managed by private companies whose sole involvement was for profit. Skirmishes erupted in Congress over the garbage problem, and states were banned from refusing other states’ garbage through the Interstate Commerce Clause. The effects of garbage leachate on ground- and surface-water are little understood with regard to the mid-future, but many problems involving heavily mineralised effluence have surfaced, especially in aquatic systems.
Proliferations of “Big box” stores, fast-food restaurant chains, pharmacies and auto-service industries, line the new highways of the green envelope with their familiar signage and architecture. The commercial outlets are often modelled on rural culture, such as the Red Barn or Colonial Inn. The only difference is that the real red barns and colonial inns were made of wood, while the new ones are made of plastic. One of the main selling points of this shift away from more urban, retail ways of life was the attractions of “nature”; housing subdivisions, where people actually live, have spread their cul-de-sac tendrils into previously uninhabited forest, mountain and desert land. Hydrocarbon-fuelled labour-saving devices are “must have” items, by which people may control and enjoy this novel playground more easily.
Innumerable species of plants and animals were disrupted or threatened by this mass emigration away from established city centres. The application of pesticides, fertilisers, paints, sealants and other chemicals have permeated the fragmented wilderness. Indicator species such as amphibians began to decline immediately, but poorly understood field methods prevented scientists and others from addressing this in the early stages. Food production has gradually become centralised, with giant agribusinesses controlling the majority of food crops, creating vast monocultures of a limited genetic stock across the middle of the country. The move from the old urban centres was conducted chiefly by white, middle-class Americans, and the vacuum left behind has been rapidly filled by minority groups, creating racial economic disparity and resultant friction.
Solution: Throw Away the Sprawl – Keep Communities Intact
Sprawl is designed to be negotiated by the motor-car. It is not constructed on a scale evolutionarily familiar to homo-sapiens, a relatively gregarious but territorial creature. A low-density population spread across quite vast distances has never been the norm, except in extreme circumstances; we are living like pioneers in well-settled country, with the perception that space is unlimited. The continual extraction of fossil-fuels from the earth’s crust is the only thing that can maintain sprawl in its current functioning state. Fossil-fuel production will probably peak sometime in the next decade, effectively rendering sprawl redundant; its source of power is the source of its own and others’ destruction. Amphibians have been called “green sentinels”, for hundreds of millions of years exhibiting resilience in the face of all manner of environmental calamity. Some people are aware of what the present declines indicate, namely that change is a necessity.
The Smart Growth network is an organisation devoted to altering the nature of that which is termed “growth”. Architects, planners, scientists, and environmentalists across the nation have united and formed groups, to resist the tide of suburban development and enlighten the American populace as to what is happening to their land. Numerous coalitions have formed, with sustainable living at the core of their ideology. New Urbanism is another movement, associated with regional planners and state governments, in places that where there is a commitment to revolutionising American suburban life. These groups, along with others such as the Biodiversity Partnership, have set a clear agenda, which is based on sound ecological principles, designed to restore our natural landscape back to its proper condition.
The most oft-heard prerequisite for a solution is that people must learn to live in more compact, high-density, mixed-use situations – in short, the zoning laws would have to be drastically revised. Gone would be the single house-per-acre, the approximations of neighbourhoods, making way for the real thing21. Assistance from state agencies would be required, with priority going to those areas where growth is directed away from watersheds and forest communities. Agricultural operations would be given adequate space to function without overuse of chemicals, as new growth would be better planned and less automobile dependent. Bicycle paths and sidewalks would complement the mixed-use zoning requirements, as retail outlets, built into the ground floors of apartment buildings, make themselves available to people choosing not to drive. Where there is existing infrastructure, it would be enhanced and modernised, rather than ignored and leapfrogged in the flow outward into the green envelope. City centres, if financed properly and creatively, combined with neighbouring brownfields sites, would become vibrant, as human inventiveness would prevail when faced with no alternative. What James Kunstler has termed “the Autoslum” would cease to exist.
It is unreasonable to assume that suburban America can be transformed overnight, but it is a fact that one-quarter of states are currently implementing “moderate to substantial statewide comprehensive planning reforms”22. Biodiversity planning means recognising and protecting entire communities of wild animals and plants, at what is called the landscape scale. Landscape scale planning knows no legal boundaries, making land acquisition for conservation a strategic rather than haphazard business. The ways in which resource managers value sites under consideration can be more informed and effective, relying on input from wildlife biologists and environmental scientists. Only when landscape-scale conservation plans are incorporated into local council comprehensive plans can biodiversity be protected in sprawl’s edge zones. In turn, this local comprehensive plan can be built into the regional or state plan, thereby achieving a legal blanket-buffer for sensitive ecosystems. With refined methods utilised by trained professionals, these areas can be identified and documented, and the information fed into the planners’ database of smart growth, guiding the shape of proposed community projects. This will actually save developer’s time and money in the long-run, helping them avoid legal wrangles and expensive scientific reports for conservation commissions.
Public transportation would have to be reinstituted, on a modernised basis, similar to the bus, tram and local train systems of Europe. “Transit-oriented development” (TOD) is forecast to become more common over the next several decades. In a TOD study of 3.971 transit stations, it was found that 14.6 million people were likely to want to own or rent property within a half-mile by 202523, “a staggering figure”, according to CTOD Director Shelley Poticha, which would require the construction of 2,100 additional residential units at each of the transit stations studied. The findings were reported in a speech at the Federal Transit Administration Railvolution Conference by Administrator Jennifer L. Dorn. With mixed-use neighbourhoods being planned across America, it is likely that this figure is actually much higher. Current trends suggest that many buses will run on hydrogen or bio-diesel in the future, which will cut emissions and remove pollutants from the air in cities.
Decentralisation is as much a prerequisite as compact communities. Community Supported Agriculture, an organic form of decentralised food-cropping, is spreading through the regions where smart growth is also likely to occur, providing healthy food without poisoning surrounding ecosystems with pesticides and fertilisers. People are beginning to become aware of the versatility of alternative energy sources such as the methane from the capped and vented old landfills, which can power thousands of residencies simultaneously without emitting compounds that contribute to dangerous pH levels in animal habitats.
All of these suggestions and realities are in their infancy, and it will be several years before the above methods are the norm. As we enter the post-industrial age, it is up to us in the west to set the standard, so to speak, as regards the state of our national wilderness. Industrialisation is currently passing through the third world, being digested by successive members of the human race, on its way towards a cleaner future. That one day industrialisation in its present form will be expelled, to be replaced by more mindful organisational structures, is perhaps humankind’s only meaningful goal today. The chemical society, particularly the petrochemical sector, has been identified in this paper as the chief cause of amphibian declines, and the greatest threat to the maintenance of human civilisation as we know it. Almost daily, new scientific discoveries concerning amphibian diversity, habits and extinctions are being made, as are discoveries towards alternatives to current fuel sources. Decentralisation of food-production in tandem with greater expertise and foresight on the part of planners is crucial if our wildlife communities are to survive, to be there to warn us of future problems, as they are doing today. Human growth in America will have to alter beyond recognition, as will the American consciousness. Environmental historians can point to other times when indicators were not heeded, but with today’s remarkable information technology there is no excuse for ignorance. Our destiny lies in our own hands. We have been warned.
Sources & Notes:
1 Hayes, 2002. Atrazine study revealed effects at 30,000 times beneath levels known to cause effects in frogs.
2 World Conservation Union; “500 scientists in 60 countries, etc…”
3 Earth Island Institute; Citizen Action to Preserve Wildlife Habitat in the United States.
4 New Georgia Encyclopedia
5 New Georgia Encyclopedia
6 The American Farmland Trust
7 Chesapeake Bay Foundation
8 Sierra Club; the Costs of Sprawl in Delaware.
9 Sierra Club; the Dark Side of the American Dream
10 Watershed Protection Techniques, article 5
11 Hermaphroditic, demasculinized frogs after exposure to herbicide, atrazine, at low ecologically relevant doses, Hayes, TB, A Collins, M Lee, M Mendoza, N Noriega, AA Stuart, and A Vonk. 2002.
12 Impact of Reproductive and Developmental Toxicants on Populations of Mudpuppies, Andree D. Gendron, Dept des Sciences Biologiques, Universite du Quebec, Montreal, Quebec.
13 Effects of Pond Chemistry on Two Syntopic Mole Salamanders, Ambystoma Jeffersonianum and A. Maculatum, in the Connecticut Valley of Masachusetts, 1991, UMass, Amherst.
14 California Environmental Protection Agency, Effects of Aquatic Acidity on Sierra Nevada Amphibians, David F. Bradford, Malcolm S. Gordon.
15 Nitrogen Pollution: An Assessment of Its Threat to Amphibian Survival, Jeremy David Rouse; Christina A. Bishop; John Struger.
16 The Complexity of Deformed Amphibians, Andrew R Blaustein and Pieter TJ Johnson.
17 Solving the Mystery of Amphibian Decline, Laura Girardeau.
18 Conservation of North American Stream Amphibians, Paul Stephen Corn, R. Bruce Bury and Erin J. Hyde.
19 Historical Trends and Future Prospects for Amphibians, C. K. Dodd and L. L. Smith.
20 Pathogens, Infectious Disease and Immune Defences, C. Carey, A. P. Pessier and A.D. Peace.
21 The Geography of Nowhere; the Rise and Decline of America’s Man-Made Landscape, and Home From Nowhere, James Howard Kunstler, Touchstone, 1993, 1996.
22 Planning for Smart Growth, 2002 State of States, American Planning Association.
23 Hidden in Plain Sight, Reconnecting America, Federal transit Administration, 2004.
