Résumé
It has been argued that the mechanisms structuring ecological communities
may be more generalizable when based on traits than on species identities.
If so, patterns in the assembly of community-level traits along
environmental gradients should be similar in different places in the
world. Alternatively, geographic change in the species pool and regional
variation in climate might result in site-specific relationships between
community traits and local environments. These competing hypotheses are
particularly untested for animal communities. Here we test the geographic
constancy of trait-based assembly patterns using a widespread
multi-trophic community: aquatic macroinvertebrates within bromeliads. We
used data on 615 invertebrate taxa from 1656 bromeliads in 26 field sites
from Mexico to Argentina. We summarized invertebrate traits with four
orthogonal axes, and used these trait axes to examine trait convergence
and divergence assembly patterns along three environmental gradients:
detrital biomass and water volume in bromeliads, and canopy cover over
bromeliads. We found no overall signal of trait-based assembly patterns
along any of the environmental gradients. However, individual sites did
show trait convergence along detrital and water gradients, and we built
predictive models to explore these site differences. Sites that showed
trait convergence along detrital gradients were all north of the Northern
Andes. This geographic pattern may be related to phylogeographic
differences in bromeliad morphology. Bromeliads with low detritus were
dominated by detritivorous collectors and filter feeders, where those with
high detritus had more sclerotized and predatory invertebrates. Sites that
showed the strongest trait convergence along gradients in bromeliad water
were in regions with seasonal precipitation. In such sites, bromeliads
with low water were dominated by soft-bodied, benthic invertebrates with
simple life cycles. In less seasonal sites, traits associated with
short-term desiccation resistance, such as hard exoskeletons, were more
important. In summary, we show that there are strong geographic effects on
the trait-based assembly patterns of this invertebrate community, driven
by the biogeography of their foundational plant species as well as by
regional climate. We suggest that inclusion of biogeography and climate in
trait-based community ecology could help make it a truly general theory.
(excerpted from Srivastava, DS et al. 2022. Geographical variation in the
trait-based assembly patterns of multitrophic invertebrate communities.
Functional Ecology)