Matching the scale of trait measurement to the ecological
processes disrupted by global change
Ultimately, trait-based analyses of ecological variance strive for
generality in explaining ecological processes, for example size-based
relationships in predator-prey interactions (Rice et al. 1993) or
thermo-tolerance in species responses to environmental gradients of
change (e.g. using naturally occurring climate resilient corals to
construct bleaching-resistant nurseries; Morikawa and Palumbi 2019).
However, relevance and specificity drive the need to down-scale
trait-based approaches to the system and questions, while maintaining
scalable analytical frameworks. The resolution at which traits are
measured and associated with the constituents of biological communities
(i.e. by individual, life stage, population, or species) determines the
level of inference that can be achieved in evaluating their role in
mediating outcomes across environmental and ecological contexts. We
suggest that the scale at which traits should be measured depends on 1)
the ecological scale of the research question (individual, population,
community, or ecosystem), 2) the focus on ecological patterns or
process, 3) the extent to which intra- and inter-specific variation is
hypothesized to play an important role in mediating the focal
environmental filtering process in question, and 4) the analytical
method used to generate inference.
Trait variation can be measured for a community of organisms or at the
species-level, as well as at subpopulation to individual level. It must
be clear whether intra-specific variation in trait values within species
or groups of taxa that share measurable traits is the required currency
for predictive modeling. But species’ trait information is typically
available to analysts at either broad (species- or metapopulation-)
scales or very specific geographic scales, with a rate-limiting middle
ground of information on spatially and temporally explicit
subpopulations. Where the consequences of species interactions are the
focus of investigation, and food web traits are conserved at a species
or population level, trait-based linkages between species groups may be
most appropriately coded at that level (i.e., one value per species or
population). Trait variation can be measured at a subpopulation to
individual level, where intra-specific variation in trait values within
species or groups of taxa that share measurable traits is the required
currency for a model. For example, across large longitudinal or
latitudinal gradients of change that span multiple species’
subpopulations. However, traits of interest were typically represented
using a single value/level per species in the predictive global change
studies identified here (Figure 7), regardless of study type, ecosystem,
or taxonomic focus.