Ecologists have already started rebuilding community ecology from functional traits

Update TRENDS in Ecology and Evolution Vol.21 No.9 481

Letters

Corresponding authAvailable online 10

www.sciencedirect.com

Ecologists have already started rebuilding communityecology from functional traits

Michael Kearney1 and Warren P. Porter2

1 Department of Zoology, The University of Melbourne, Parkville, VIC 3010, Australia2 Department of Zoology, University of Wisconsin, Madison, WI 53706, USA

McGill et al. [1] have recently called for a major change inhow researchers approach community ecology, whereby

organisms, including their surface area, feeding and diges-tive systems, and nutrient requirements, affect key eco-

the interaction between functional traits of organismsand environmental variation through space and time isconsidered against a background biotic ‘interactionmilieu’. They suggest that this can be achieved througha mechanistic approach to the fundamental and realizedniches, using general performance currencies such asenergy and nutrients. Although we agree entirely, wewould like to point out that the tools required to approachcommunity ecology in this way are well developed andare already being applied under three different guises:dynamic energy budget models, the geometrical frame-work of organismal stoichiometry, and biophysicalecology.

Dynamic energy budget models and the geometric fra-mework address two of the four research themes outlinedby McGill et al.: functional traits and performance curren-cies. Dynamic energy budgetmodel theory [2–4]models therelationship between surface area, feeding behaviour andenergy acquisition through partitioning the organism intostructural body mass and reserves (i.e. stored energydensity). Thus, it relates functional traits to a performancecurrency of energy. The ‘supply-side’ nature of dynamicenergy budget models is especially attractive because itprovides a link between organism traits, food availability,and energy for growth, maintenance and reproduction.This enables relatively easy integration of dynamic energybudget models with individual-based models of populationdynamics; a ‘long-term’ goal discussed by McGill et al. [1]that has in fact recently been achieved with considerablesuccess [5].

Whereas dynamic energy budget models often focus onenergy as a performance currency, the geometrical frame-work focuses particularly on nutrient stoichiometries [6,7].The basic process of the geometrical framework is to modelthe nutrient relationships of an organism as an n-dimen-sional hyperspace whose axes comprise carbohydrates,lipids proteins and other key nutrients (with obvious simi-larities to Hutchinson’s niche concept [8]). Nutrient intake,assimilation and output rates are modelled dynamically asan organism grows and reproduces, with the organismtracking a moving maximum-fitness target within thenutrient hyperspace. The dynamic energy budget modeland geometrical framework theories therefore enablemechanistic analysis of how functional traits of individual

or: Kearney, M. (mrke@unimelb.edu.au)July 2006

system-level processes using the performance currencies ofenergy and mass acquisition.

Recent developments in the field of biophysical ecologynow provide the opportunity to link functional traits andperformance currencies to McGill et al.’s third theme,environmental gradients, under their suggested frame-work of fundamental niches. Biophysical ecology [9]applies the principles of heat and mass transfer to calcu-late how different environmental conditions interact withfunctional traits, such as body size and behaviour, toaffect the performance currencies of energy, nutrientand water exchange. It thus enables the calculation, fromfirst principles, of the climatic component of the funda-mental niche [10]. Integration of biophysical ecology withGIS data sets on climatic conditions, topography andvegetation [10–12] then enables visualisation of the dis-tribution of the fundamental niches of species acrossenvironmental gradients through space and time [10].This functional trait-based approach to modelling thedistributions of species goes beyond correlative habitatmodels [13] to tackle McGill et al.’s second major researchquestion ‘What traits and environmental variablesare most important in determining the fundamentalniche?’.

The three approaches that we describe have developedindependently and there is enormous potential for theirintegration to obtain a truly mechanistic view of thefundamental niches of organisms. An addition to thisintegration challenge will be to find ways of incorporatingthe fourth theme of McGill et al., the biotic ‘interactionmilieu’, and its effect on constricting fundamental nichesto realized niches. Although we applaud McGill et al.’sappeal for a functional-trait approach to community ecol-ogy, we hope to have shown that we are in fact furtheralong the path to realizing their vision than they mighthave appreciated.

References1 McGill, B.J. et al. (2006) Rebuilding community ecology from functional

traits. Trends Ecol. Evol. 21, 178–1852 Kooijman, S.A.L.M. (2000) Dynamic Energy and Mass Budgets in

Biological Systems, Cambridge University Press3 van derMeer, J. (2006)Metabolic theories in ecology.Trends Ecol. Evol.

21, 136–1404 Nisbet, R.M. et al. (2000) From molecules to ecosystems through

dynamic energy budget models. J. Anim. Ecol. 69, 913–9265 Klanjscek, T. et al. Integrating dynamic energy budgets into matrix

population models. Ecol. Model. (in press)

482 Update TRENDS in Ecology and Evolution Vol.21 No.9

6 Raubenheimer, D. and Simpson, S.J. (2004) Organismal stoichiometry:quantifying non-independence among food components. Ecology 85,1203–1216

7 Simpson, S.J. et al. (2004) Optimal foraging when regulating intake ofmultiple nutrients. Anim. Behav. 68, 1299–1311

8 Hutchinson, G.E. (1957) Concluding remarks. Cold Spring Harb.Symp. Quant. Biol. 22, 415–427

9 Gates, D.M. (1980) Biophysical Ecology, Springer-Verlag10 Kearney, M. and Porter, W.P. (2004) Mapping the fundamental niche:

physiology, climate and the distribution of nocturnal lizards acrossAustralia. Ecology 85, 3119–3131

DOI of original article: 10.1016/j.tree.2006.06.019.

Corresponding author: McGill, B.J. (mail@brianmcgill.org)Available online 10 July 2006

www.sciencedirect.com

11 Porter, W.P. et al. (2000) Calculating climate effects on birds andmammals: impacts on biodiversity, conservation, populationparameters, and global community structure. Am. Zool. 40, 597–630

12 Porter, W.P. et al. (2002) Physiology on a landscape scale: plant-animalinteractions. Integr. Comp. Biol. 42, 431–453

13 Kearney, M. Habitat, environment and niche: what are we modelling?Oikos (in press)

0169-5347/$ – see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.tree.2006.06.019

Letters Response

Response to Kearney and Porter: Both functional andcommunity ecologists need to do more for each other

Brian J. McGill1, Brian J. Enquist2, Evan Weiher3 and Mark Westoby4

1 Department of Biology, McGill University, Montreal, QC, Canada, H3A 1B12 Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA3 Department of Biology, University of Wisconsin – Eau Claire, Eau Claire, WI 54702, USA4 Department of Biological Sciences, Macquarie University, NSW 2109, Australia

Kearney and Porter [1] have correctly identified one of our the types of physiological ecology put forth by Kearney

In our paper [2], we made three other points that gobeyond Kearney and Porter’s point of identifying work infunctional ecology that is of use to community ecologists.First, we emphasized three types of quantitative mea-sures (traits, performance currencies and environment)and the need to explore all possible combinations ofthese factors. Thus, in addition to the combinationsfound in the work highlighted by Kearney and Porter,we emphasize, for example, exploring how traits varyalong environmental gradients and which morphologicaltraits link to which physiological traits. Second, we alsoemphasized exploring not only the fundamental, but alsothe realized niche processes (i.e. the interaction milieu orspecies interactions). Most of Kearney and Porter’s exam-ples [1] do not address these realized niche processes:for example, we encourage asking which traits affectspecies interactions and how do species interactionschange with the environment? Finally, we emphasizeda shift in approach away from ANOVA-based ecologytowards looking at the mathematical relationshipsbetween quantitative measures of traits and environ-ment. None of these three agendas necessarily requires

and Porter [1]. These research agendas are currently stillin a necessary pattern-finding phase and tend to notexplicitly include any mechanism. The search formechanism in these areas in the future might lead toKearney and Porter’s physiological ecology, but it couldequally well lead to evolutionary ecology or behavior.

We suggest that functional ecology has not yet solved allof the needs of community ecologists. We addressed ourpaper to community ecologists and the changes that theyneed to make. The examples that we and Kearny andPorter provide not to the contrary, an equally long andnecessary paper could have been written calling for selectbranches of functional ecology to pay more attention tocommunity ecology [8] and thereby achieve more relevanceto applications in conservation. We do not attempt thishere, but briefly suggest that to achieve maximal useful-ness and relevance to the larger field of ecology areas offunctional ecology with aspirations to informing commu-nity ecology need to come out of the laboratory and into thefield by:� Becoming more comparative between species.Community ecologists study 5–200 species at a time.Physiological data need to have the same span.� Placing more emphasis on measures of fitness thathave an influence on the fate of the species overmultiplegenerations, instead of focusing on factors such asinstantaneous energetic requirements, leaf carbonassimilation rates, or single clutch size.� Building more links between physiological traitsand more easily measured, ecologically relevanttraits. The links between metabolism and body size[2] and between carbon assimilation rates and leaflife span [9] are good examples that need to beexpanded.