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Idiosyncrasy in ecology – What’s in a word?
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WHG Hol1*, KM Meyer2, WH van der Putten1,3
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Wageningen, The Netherlands
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Büsgenweg 4, 37077 Göttingen, Germany
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Netherlands
Netherlands Institute of Ecology (NIOO-KNAW), Droevendaalsesteeg 10, 6708 PB
Göttingen University, Faculty of Forest Sciences and Forest Ecology, Ecosystem Modelling,
Wageningen University, Laboratory of Nematology, P.O. Box 8123, 6700 ES Wageningen, The
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Netherlands Institute of Ecology, Droevendaalsesteeg 10, 6708 PB Wageningen, The
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Netherlands. Email: g.hol@nioo.knaw.nl
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Phone: +31 317473610, Fax: +31 317473675
Corresponding author: WHG (Gera) Hol
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Running headline: Idiosyncrasy in ecology
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Ecological research aims at finding general rules and principles, but the variation in nature is
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seemingly endless. General ecological rules are rare and they apply best to large-scale patterns
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(Lawton 1999). At small to intermediate scales, effects can depend on species identity or
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environment and are often called ‘idiosyncratic’. We noticed that idiosyncrasy is becoming used
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more frequently in ecological papers. This observation triggered a literature study of the word
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idiosyncrasy to answer the following questions: Is idiosyncrasy in ecology a new trend? What is
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idiosyncrasy used for? In which journals do we find idiosyncrasy? Should we welcome a further
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increase of the use of idiosyncrasy in ecology?
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We used Web of Science® to search for papers in ecological journals containing the
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word “idiosyncrasy” or “idiosyncratic” in title, summary or keywords. The idiosyn* papers in
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ecological journals increased from 4 (average 1991-1996) to 21 (average 2005-2010) per year.
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The same increase is also visible when looking at the proportion of idiosyn* papers in ecological
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journals (Fig. 1), showing that the increase in idiosyncrasy papers is not just due to an increase in
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the total number of ecological papers per year. The correlation between year and proportion
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idiosyn* papers is significant (Spearman rank correlation rs = 0.81, P < 0.001) and the best fit is
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an exponential curve, growing by 7% per year. This confirmed our personal observation:
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idiosyncrasy in ecology is a new trend.
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What is then idiosyncrasy? According to the Oxford Dictionary, idiosyncrasy is
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something peculiar to an individual, e.g. a feeling, view or mode of expression. It can also be
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used for a distinctive characteristic of something and in medicine it is used for individuals with
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an allergic reaction. We screened all idiosyn* papers in ecological journals up to date to find out
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what idiosyncrasy was used for exactly. The first ecological paper using idiosyncrasy also
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applied it at the level of individuals, i.e. chemical variation in individual grasshoppers (Jones
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1986). In the other idiosyn* papers in ecology it has been used for aggregation levels from
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individuals, species, families, functional groups and ecosystems up to landscapes, but the species
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levels is most common. The phenomena that were described can be grouped arbitrarily into three
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common forms of idiosyn* usage: scatter, interactions and outliers. Scatter includes positive,
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negative and neutral effects of individuals or species to a treatment or environment (e.g.
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Boecklen et al. 1991). Non-additive or nonlinear relationships (Brinkman et al. 2005; Hoorens et
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al. 2010) between treatment and response are often reported as idiosyncratic effects. Consistent
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deviations from the norm, which are visible as outliers in plots of experimental data, indicate
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unique behaviour of individual species and are also labelled as idiosyncratic effects (Kappeler
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1997; Edwards et al. 2001). We realize that one word can have multiple meanings and
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sometimes the intended meaning can be deducted from the context. However, the use of
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idiosyncrasy may result in confusion or even contradiction. For most authors idiosyncrasy seems
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to be a synonym of “unpredictable” or “lack of patterns”, while others argue that idiosyncrasies
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can be predictable (Emmerson et al. 2001). Quite a few papers use idiosyn* as an alternative for
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species-specific; yet we also found the notion “species-specific and somewhat idiosyncratic”,
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suggesting that the two terms are not the same. Unfortunately, 25% of the papers use
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idiosyncrasy in the abstract only which makes it nearly impossible to pinpoint what kind of
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idiosyncrasy the authors refer to.
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In Web of Science® we found 74 source titles (mostly journals) for the 220 ecological
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papers containing idiosyn*. The list is headed by Oikos, followed by Ecology, Global Ecology
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and Biogeography, Evolution and Oecologia. This raised the question whether high impact
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journals are more likely to publish idiosyn* papers than lower impact journals, which is indeed
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the case (Supplementary Material, Fig. S1). It will be difficult to determine whether high impact
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journals have different vocabulary or whether this positive relation between impact and
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idiosyncrasy is due to the difference in topics between journals. Many papers appear to have no
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links with other idiosyn* papers via shared authors or via citation and this shows idiosyncrasy as
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a widespread, but disconnected label (Fig. 2). The lack of context and definition severely
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hampers interpretation. There are a few clusters with five or more papers (Fig. 2) and within the
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contexts of those clusters it might be clearer what is meant by “idiosyncrasy”. The two largest
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clusters are in the area of biodiversity-ecosystem functioning and biogeography.
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We conclude that currently idiosyncrasy is not a very meaningful label, given the non-
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defined use and difficulties to deduct which of the many meanings is referred to by the authors.
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The obvious solution is, when ecologists can not agree on a common definition for idiosyncrasy,
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to define it when used, or to replace idiosyncrasy by less ambiguous terms. Scientific writing
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should match the accuracy of data collection and analysis.
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Acknowledgements
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W.H. is supported by the EU FP7 project SOILSERVICE. This is publication XXXX of the
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NIOO-KNAW.
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Figure legends
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Figure 1. Proportion of papers using idiosyn* in ecological journals between 1991-2010; based
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on ISI Web of Knowledge (Thomson Reuters 2010), Topic: idiosyn*, Years: 1991-2010, Subject
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area: ecology).
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Figure 2. Network showing links between idiosyn* papers in ecological journals 1986-2011.
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Each dot represents a paper (n=216) and papers can be linked via authors or via citations. Single
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arrows indicate a citation; double arrows indicate papers that share at least one author and these
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can also be linked via citation.
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Fig 1
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Fig 2
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Supplementary Material
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Figure S1. The relation between the 5 Year Impact Factor of a journal and the number of
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observed – expected idiosyn* papers per journal. Numbers refer to journal titles, listed at the end
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of the section below.
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To correct for the number of publications per journal, we calculated the expected number of
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idiosyn* papers as if they were occurring at random throughout all ecological journals. Journals
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publishing more papers would thus be more likely to have more idiosyn* papers.
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With help of Web of Science® the total number of publications in ecological journals was
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calculated between 1986-2010. A total of 149 ecological journals were selected based on the
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subject category Ecology in the Journal Citation Reports®. Together these journals published
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241310 papers between 1986-2010. In this period 213 idiosyn* papers were published in
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ecological journals (Topic = idiosyn*; Subject area = ecology). The observed idiosyn* papers
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per journal was obtained using the Analyze Results option based on Source Title. The expected
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number of idiosyn* papers per journal was calculated as follows: (total number of idiosyn*
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papers/total number of ecological publications) x total number of publications per journal. The
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difference between observed and expected idiosyn* papers per journal was plotted against the 5-
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Year Impact Factor 2009. We preferred the 5-Year Impact Factor over the yearly impact factor
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as a more robust measure of impact. Since not all 149 journals had a 5-Year Impact Factor 2009,
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only 124 points are plotted in the figure. Each number refers to a journal. 1: Trends Ecol Evol, 2:
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Annu Rev Ecol Evol S, 3: Ecol Lett, 4: Ecol Monogr, 5: B Am Mus Nat Hist, 6: Global Change
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Biol, 7: Front Ecol Environ, 8: ISME J, 9: Mol Ecol, 10: Global Ecol Biogeogr, 11: Ecology, 12:
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Evolution, 13: J Ecol, 14: J Appl Ecol, 15: Am Nat, 16: Perspect Plant Ecol, 17: Conserv Biol,
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18: P Roy Soc B-Biol Sci, 19: Ecography, 20: Ecol Appl, 21: J Biogeogr, 22: J Anim Ecol, 23:
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Ecosystems, 24: Divers Distrib, 25: Heredity, 26: Funct Ecol, 27: J Evolution Biol, 28:
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Oecologia, 29: Oikos, 30: Biol Conserv, 31: Biol Letters, 32: Biogeosciences, 33: Wildlife
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Monogr, 34: Biol Invasions, 35: Landscape Ecol, 36: Paleobiology, 37: Agr Ecosyst Environ, 38:
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Behav Ecol, 39: Microb Ecol, 40: Ecol Eng, 41: Behav Ecol Sociobiol, 42: J N Am Benthol Soc,
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43: Ecol Soc, 44: Mar Ecol – Prog Ser, 45: Evol Ecol, 46: J Veg Sci, 47: Basic Appl Ecol, 48:
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Ecotoxicology, 49: Landscape Urban Plan, 50: Ecol Econ, 51: Adv Ecol Res, 52: J Chem Ecol,
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53: Aquat Microb Ecol, 54: Mol Ecol Notes, 55: Anim Conserv, 56: Restor Ecol, 57: Ecol
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Complex, 58: J Exp Mar Biol Ecol, 59: Ecol Model, 60: Biotropica, 61: Biodivers Conserv, 62:
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Plant Ecol, 63: Theor Popul Biol, 64: Chemoecol, 65: Austral Ecol, 66: J Arid Environ, 67:
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Pedobiologia, 68: Popul Ecol, 69: Ecol Ecol Res, 70: Acta Oecol, 71: Appl Veg Sci, 72:
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Wetlands, 73: J Wildlife Manage, 74: J Trop Ecol, 75: Ecohyddrology, 76: Polar Biol, 77:
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Ecoscience, 78: Oryx, 79: Ecol Res, 80: Aquat Ecol, 81: Ann Zool Fenn, 82: Eur J Soil Biol, 83:
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Ecol Inform, 84: Environ Biol Fish, 85: Theor Ecol-Neth, 86: J Soil Water Conserv, 87: Polar
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Res, 88: Eur J Wildlife Res, 89: Mol Ecol Resour, 90: Wildlife Res, 91: Biochem Syst Ecol, 92:
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Compost Sci Util, 93: Mar Biol Res, 94: Wildlife Biol, 95: Rangeland Ecol Manag, 96: Rev Chil
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Hist Nat, 97: New Zeal J Ecol, 98: Rangeland J, 99: Am Midl Nat, 100: Afr J Ecol, 101: Fungal
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Eco, 102: Nat Area J, 103: S Afr J Wildl Res, 104: Vie Milieu, 105: Community Ecol, 106: J Nat
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Hist, 107: Int J Sust Dev World, 108: P Acad Nat Sci Phila, 109: Pol J Ecol, 110: Southeast Nat,
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111: Polar Rec, 112: Northeast Nat, 113: Northwest Sci, 114: J Freshwater Ecol, 115: Russ J
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Ecol+, 116: Southwest Nat, 117: West N Am Naturalist, 118: Interciencia, 119: Amazoniana,
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120: Rev Ecol – Terre Vie, 121: Can Field Nat, 122: Ohio J Sci, 123: Contemp Probl Ecol, 124:
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Nat Hist.
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