Investigating trophic ecology and dietary niche overlap among morphs of Lake Trout in Lake Superior

Four morphs of Lake Trout (Salvelinus namaycush, Walbaum 1792) have been identified in Lake Superior: leans, siscowets, humpers, and redfins. In this comprehensive study, the trophic ecology of Lake Trout morphs were characterized using stomach content, fatty acid, and stable isotope data. Stomach content results indicated a predominately piscivorous diet for leans, siscowets, and redfins, whereas humper diets were comprised of 50% fish and 50% Mysis by mass. Humper and siscowets were most similar in their dietary fatty acid profiles, whereas redfins had the most distinct dietary fatty acid profile. Results from stable isotope analysis revealed some among-morph differences along a pelagic-profundal consumption gradient (34S), but there were no significant differences in trophic position (15N) or basal carbon sources among morphs (13C). Using the recently developed nicheROVER software package, 4-dimensional trophic niches for each morph were quantified using stable isotope ratios (δ13C, δ15N, and δ34S) and fatty acid profiles (30 dietary fatty acids, condensed to one axis). Humpers had the largest 4-dimensional niche regions of all four morphs, and redfins had the smallest. Pairwise probability of overlap among morphs in these four-dimensional niche regions was determined to be < 50% in most cases. Overall, stomach content results indicate that humpers diets were more planktivorous than the other morphs, consistent with previous research. Results of the niche overlap analysis suggests some degree of generalist feeding for all morphs. Better characterization of seasonal variation in diet using tracers that reflect more recent feeding (e.g., fatty acids, stomach contents, and/or stable isotope analyses performed on tissues that turnover more quickly than muscle) are needed to further elucidate among-morph differences and similarities in diet and trophic ecology

From Locke to Materialism: Empiricism, the Brain and the Stirrings of Ontology

My topic is the materialist appropriation of empiricism – as conveyed in the ‘minimal credo’ nihil est in intellectu quod non fuerit in sensu (which interestingly is not just a phrase repeated from Hobbes and Locke to Diderot, but is also a medical phrase, used by Harvey, Mandeville and others). That is, canonical empiricists like Locke go out of their way to state that their project to investigate and articulate the ‘logic of ideas’ is not a scientific project: “I shall not at present meddle with the Physical consideration of the Mind” (Essay, I.i.2, in Locke 1975; which Kant gets exactly wrong in his reading of Locke, in the Preface to the A edition of the first Critique). Indeed, I have suggested elsewhere, contrary to a prevalent reading of Locke, that the Essay is not the extension to the study of the mind of the methods of natural philosophy; that he is actually not the “underlabourer” of Newton and Boyle he claims politely to be in the Epistle to the Reader (Wolfe and Salter 2009, Wolfe 2010). Rather, Locke says quite directly if we pay heed to such passages, “Our Business here is not to know all things, but those which concern our Conduct” (Essay, I.i.6). There would be more to say here about what this implies for our understanding of empiricism (see Norton 1981 and Gaukroger 2005), but instead I shall focus on a different aspect of this episode: how a non-naturalistic claim which falls under what we now call epistemology (a claim about the senses as the source of knowledge) becomes an ontology – materialism. That is, how an empiricist claim could shift from being about the sources of knowledge to being about the nature of reality (and/or the mind, in which case it needs, as David Hartley saw and Denis Diderot proclaimed more overtly, an account of the relation between mental processes and the brain). (David Armstrong, for one, denied that there could be an identification between empiricism and materialism on this point: eighteenth-century history of science seems to prove him wrong: see Armstrong 1968 and 1978.) Put differently, I want to examine the shift from the logic of ideas in the seventeenth century (Locke) to an eighteenth-century focus on what kind of ‘world’ the senses give us (Condillac), to an assertion that there is only one substance in the universe (Diderot, giving a materialist cast to Spinozism), and that we need an account of the material substrate of mental life. This is neither a ‘scientific empiricism’ nor a linear developmental process from philosophical empiricism to natural science, but something else again: the unpredictable emergence of an ontology on empiricist grounds