How many buffalo does it take to change a savanna? A response to Bowman et al. (2008)

Bowman et al. (Journal of Biogeography, 2008, 35 , 1976–1988) aimed to explain observed increases in woody cover on floodplains and savannas of Kakadu National Park using estimates of buffalo (Bubalus bubalis) density as a causal variable. They found that buffalo were a minor model variable and concluded that buffalo are ‘not a major driver of floodplain and eucalypt dynamics’. However, the authors mislabelled the historical density of buffalo on their site, citing a period as high density instead of low density. Further, their results were not contextualized within the substantial body of scientific and historical evidence of the buffalo’s strong influence on vegetation in Kakadu. The authors instead postulated three unanalysed drivers of observed patterns of change: fire regime, rainfall and atmospheric CO₂. We suggest that further analyses of change in woody vegetation should make use of accurate historical records of grazers as well as available data sets on fire history.     

How many high production chemicals are rodent carcinogens? Why should we care? What do we need to do about it?

High production volume (HPV) chemicals are produced in or imported to the US in amounts greater than 1 million pounds per chemical per year. The EPA has identified thousands of HPVs. Due to their abundance, such chemicals bring a substantial risk for human exposure, and as a result some level of adverse consequences to health are to be expected. In order to examine the potential for cancer risk associated with HPVs, this paper examines HPVs that have been tested in the National Toxicology Program's rodent cancer bioassay. The chemicals tested in the bioassay represent a small sample of the universe of environmental chemicals to which people are exposed. Unexpectedly, 60% of the 128 HPVs evaluated in the bioassay proved to be rodent carcinogens. This value compares to a predicted prevalence of only 16.5% carcinogens in a previous study. The previous study concluded that HPVs were less likely to be toxic by a variety of other test criteria as well. However, the approach involved identifying putative carcinogens using quantitative chemical structure-activity relationships (QSAR) in contrast to the direct tabulation of bioassay test results performed here. Detailed examination of bioassay results reveals that test outcomes depend heavily on route of administration as well as on dose level, sex, strain, and species used. Since most of these factors have little or no apparent relationship to chemical structure, results of this study suggest that QSAR, as well as virtually all other alternative methods, may not generally provide accurate predictions of carcinogenic potential. As we wait for efficient and effective methods for predicting carcinogens to be developed, people continue to be exposed to environmental carcinogens. Progress on regulating environmental carcinogens as well as on developing more effective test methods has been minimal since "war on cancer" began approximately 30 years ago. The present study questions whether the current strategy for dealing with environmental carcinogens will ever be successful. Close examination of rodent cancer test results seems to suggest that almost all chemicals may have carcinogenic potential in some genotypes under some exposure circumstances. If this hypothesis is correct, it would explain the general lack of progress in developing methods to differentiate carcinogens from noncarcinogens. A completely new strategy for dealing with cancer caused by exposures to environmental chemicals seems to be needed.