1、Let the concept of trait be functional!,Cyrille Violle, Marie-Laure Navas, Denis Vile, Elena Kazakou, Claire Fortunel, Irene Hummel and Eric Garnier,Abstract,In its simplest definition, a trait is a surrogate of organismal performance. We therefore give an unambiguous definition of plant trait, with
2、 a particular emphasis on functional trait. A hierarchical perspective is proposed, extending the performance paradigm to plant ecology. Functional traits are defined as morpho-physiop-henological traits which impact fitness indirectly via their effects on growth, reproduction and survival, the thre
3、e components of individual performance. We finally present an integrative framework explaining how changes in trait values due to environmental variations are translated into organismal performance, and how these changes may influence processes at higher organizational levels.,Introduction,Following
4、 Darwins (1859) proposal, traits were initially mainly used as predictors (proxies) of organismal performance. Over the last threedecades, developments in community (Grime 1974,Petchey and Gaston 2002, McGill et al. 2006) and ecosystem (Chapin 1993, Grime 1998, Lavorel and Garnier 2002, Eviner and C
5、hapin 2003) ecology have forced the concept of trait beyond these original boundaries, and trait-based approaches are now used in studies ranging from the level of organisms to that of ecosystems. Within each discipline, diverse types of traits are thus used to assess inherent components involved in
6、 the explanation of complex processes defined at higher organizational levels (Fig. 1),A further complication has arisen with the introduction of functional traits, an expression coined with the emergence of functional ecology as a discipline(Calow 1987, Keddy 1992a). Current attempts to devise func
7、tional classifications of organisms (Noble and Gitay 1996, Woodward and Cramer 1996, Lavorel et al. 1997), define the functional diversity of communities (Walker et al. 1999, Petchey and Gaston 2002,Mason et al. 2005) and assess species effects on ecosystems (Lavorel and Garnier 2002, Eviner and Cha
8、pin 2003), all advocate the use of functional traits. The aims of this paper are to propose unambiguous definitions of traits and functional traits, and to suggest a framework on how traits could be used to address current issues in community and ecosystem ecology.,Plant traits: definitions,In the f
9、irst one, Petchey et al. (2004) tested how different indices of functional diversity could explain differences in biomass production. Theseindices were calculated using a number of so-calledtraits: eight were measured at the individual plant level (four leaf traits, three traits describing the statu
10、re of the plants and seed mass), while three were measured at a plot level (standing biomass, vegetation cover and canopy height). In the second one, Eviner (2004) characterized the influence of plant standing biomass,soil conditions and microbial phosphorus, all defined asplant traits.,In many case
11、s, a trait is defined at the level of the individual (Table 1, 2).,This definition of a trait requires further precisions:(1) the particular value or modality taken by the trait at any place and time is called an attribute (Lavorel et al.1997); (2) within a species, the trait, either continuous or c
12、ategorical, may show different attributes along environmental gradients (Fig. 2) or through time; (3)the attribute for a trait is usually assessed for one population (average of attributes of a set of individuals) in space and time (i.e. for a single value of the x-axis of Fig. 2). This has two cons
13、equences. First, there is not a single trait attribute for any particular species (Fig. 2). Second, information on the local environment where the trait has been measured is essential to interpret the ecological meaning of trait attributes.,A hierarchical perspective on plant traitsArnolds framework
14、 applied to plants,Such performance traits are a key concept of the morphology,performance, and fitness paradigm proposed by Arnold (1983) for animals. According to this paradigm,morphological traits influence (directly and indirectly)performance traits, which in turn influence (directly or indirect
15、ly) fitness. We suggest that the three components of plant fitness (growth, reproduction and survival) be assessed by the measure of onlythree performance traits: vegetative biomass, reproductive output and plant survival (Fig. 3). The value of these three performance traits is influenced by morphol
16、ogical, physiological and phenological(M-P-P) traits, operating from the cell to the whole plant levels (Fig. 3).,In the case of vegetative biomass, a convenient framework may be used to unravel relationships between M-P-P traits and performance traits. Vegetative biomass at any time t (VMt) can be
17、written as:,The special case of functional traits,Plant functional trait is a currently widely used expression in plant ecology (Daz and Cabido 2001,Lavorel and Garnier 2002, Hooper et al. 2005), but its actual meaning varies substantially among authors. This is the case of functional effect traits,
18、 defined as those traits that have an impact on ecosystem functioning (Daz and Cabido 2001, Lavorel and Garnier 2002). Hodgson et al. (1999) and Weiher et al. (1999) have introduced the hard/soft dichotomy in the functional trait terminology.,Plant traits and environment,Thus an ecological performan
19、ce can be defined as the optimum and/or the breadth of distribution of performance traits along an environmental gradient (Fig. 5).,Scaling-up from organisms to population,community or ecosystem,The standing biomass of a monospecific community is: This can be written as: We propose the term communit
20、y functional parameter (CFP) for such a community-aggregated feature:,Conclusions,For the concept to be functional, we suggest to stick to the terminology summarized in Table 3.,The main points are: . a trait is a feature measurable at the level of the individual, which does not require additional i
21、nformation from the environment or at any otherorganizational level; . a hierarchy is recognized among traits, expanding Arnolds (1983) morphology, performance, fitness paradigm to plant ecology: performance traits are those which contribute directly to fitness,while functional traits are those morpho-physiophenological traits which have an impact on performance traits (and thus indirectly on fitness); . integration functions among organization levels should be made explicit when scaling-up to the levels of populations, communities and ecosystems.,Thanks!,
