Introduction
Identifying general principles that govern the distribution and
abundance of species across Earth’s ecosystems is a fundamental pursuit
in ecology. Over the past three decades, ‘trait-based’ ecology—focused
on the role that measurable characteristics of organisms play in
mediating geographic distribution and abundance—has emerged as a major
conceptual lens through which to describe general processes that might
drive patterns of biodiversity across the biosphere (Hansen and
Urban1992; McGill et al. 2006; Mindel et al. 2016). Traits-based theory
stemmed from descriptive correlations between the frequency of
phenotypic traits hypothesized to affect individual and population level
success across taxa and environmental contexts (e.g. Grime 1988; Diaz
and Cabido 1997). But the ultimate potential of traits-based approaches
might allow scientists to predict ecological outcomes in new contexts
(i.e. functional traits; McGill et al. 2006).
The need for predictive trait-based approaches is increasingly urgent
due to mounting evidence that stresses like climate change, biological
invasion, and over-exploitation are having profound effects on
ecosystems and the socioeconomic benefits they provide. While ecological
communities are inherently dynamic, with species membership and relative
abundance varying over time and space (Cottenie 2005, Dornelas et al.
2014), unprecedented levels of anthropogenic stress are now driving
species range and density changes that far exceed historical levels
(Chapin et al. 2000, IUCN 2008). Effects are proving to be unequal
across species (Zavaleta et al. 2009, Sunday et al. 2012, Bates et al.
2014), so ecological communities are essentially being pulled apart, and
reassembled with new member combinations (Hobbs et al. 2009, García
Molinos et al. 2015). What will future species assemblages look like,
and how will they function, in the face of these major disturbances?
Identifying species’ characteristics that recur across unrelated taxa
and confer information about species performance under a range of
environmental and biotic interactions offers the potential to predict
ecological dynamics as novel ecosystem configurations form under global
change. For example, as abiotic conditions defining the fundamental
niche shift under climate change, biotic traits that confer species’
dispersal and survival abilities help define the shape of realized
niches they are likely to occupy (McGill 2006; Early and Sax 2011;
Estrada et al. 2018).
Here we present a quantitative review
of trait-based biodiversity research and its application to global
change ecology to address the following questions: (1) Which traits
offer promising insights into the outcomes of environmental and biotic
filtering across ecosystem types and taxonomic groups? (2) To what
extent (and in what contexts) are traits-based insights being applied to
predict the ecological outcomes of global change? (3) What are the
potential barriers to predicting the outcome of environmental and biotic
interactions using traits? (4) What research techniques and conceptual
frameworks can help us move beyond describing ecological patterns and
towards prediction? Our review is framed from the perspective that
species’ behavioural, morphological, physiological, and life history
attributes mediate scale-dependent environmental and biotic filters on
distribution and abundance across land and seascapes (Figure 1).
Species’ characteristics that confer success under abiotic environmental
conditions such as temperature, light, acidity, moisture (in terrestrial
systems) and dissolved oxygen (in aquatic systems) provide the coarsest
filter on species distribution (i.e. Filter 1 in Figure 1; the
boundaries of the fundamental niche). Traits that influence the outcome
of biotic interactions within local environments further mediate species
persistence and co-existence (i.e. including trophic interactions;
Filter 3 in Figure 1). A host of traits that confer information on
species’ dispersal ability mediate feedbacks between the effects of
abiotic and biotic interactions on species’ range and relative
abundances (i.e. dispersal-limited controls on redistribution; Filter 2
in Figure 1). Knowledge of the role that traits play in filtering across
these scales facilitates prediction about species persistence and
relative abundance in new contexts such as altered environmental
conditions (e.g. climate-mediated shifts in thermal regimes; Figure 1A
vs B).