Jonathan Newman

The species comprising the fungal endophyte genus “Epichloë ”are symbionts of cool season grasses. About half the species in this genus are strictly vertically transmitted, and evolutionary theory suggests that these species must be mutualists. Nevertheless, Faeth and Sullivan (e.g., 2003) have argued that such vertically transmitted endophytes are ’usually parasitic,’ and Müller and Krauss (2005) have argued that such vertically transmitted endophytes fall along a mutualism-parasitism continuum. These papers (and others) have caused confusion in the field. We used a systematic review to show that close to half of the published papers in this field incorrectly categorize the interaction. Here, we develop the argument that advantages and disadvantages are not the same things as mutualism and parasitism and that experimental evidence must be interpreted in the context of theory. We argue that, “contra ”Faeth and Sullivan, it is highly unlikely that such strictly vertically transmitted endophytes can be parasites, and that, “contra ”Müller and Krauss, it is inappropriate to apply the continuum concept to strictly vertically transmitted endophytes. We develop a mathematical model to support and illustrate our arguments. We use the model to clarify that parasitism “requires ”some degree of horizontal transmission, and that while it is appropriate to use the continuum concept when referring to the genus as a whole, or to species that possess horizontal transmission, we argue that it is inappropriate to use the concept when referring to species that are strictly vertically transmitted.

Among the instrumental value defenses for biodiversity conservation is the argument that biodiversity is necessary to support ecosystem functioning. Lower levels of biodiversity yield lower levels of ecosystem functioning and hence the inference that we should conserve biodiversity. In our book Defending Biodiversity: Environmental Science and Ethics, we point out three problems with this inference. (1) The empirical support for such an inference derives from experiments conducted on a very small set of ecosystem types (mainly grasslands and fresh water aquatic) and ecosystem functions (mainly nutrient uptake, biomass production, and decomposition rates). These experiments suffer from a number of largely unavoidable logistical constraints making the generality of their results questionable. (2) Even if the experimental results were unequivocal, their lack of external validity would still raise significant questions about how (if at all) these results apply to real world conservation problems. And (3) even if the experimental results were unequivocal and completely applicable to conservation problems, relying on such defenses implies other rational policy commitments that are at odds with other positions that environmentalists commonly take. Odenbaugh and I disagree largely about what inferences follow from these points rather than about the points themselves. I think that what follows is that if environmentalists want to use instrumental value defenses, then we need to accept that not all biodiversity is useful to us, and parts that are useful are not necessarily more useful than alternatives that might threaten biodiversity. I also think that the unpalatable implied commitments need to be taken seriously. This may mean that we environmentalists have to accept that biodiversity should not always be conserved, and that parts of the environmentalist agenda are little more than strong personal preferences that others need not respect. If environmentalists are willing to accept these conclusions, then there are no problems with relying on these instrumental value defenses, but I suspect that environmentalists are likely to be unhappy with such conclusions.