Common ant species dominate morphospace: unraveling the morphological diversity in the Brazilian Amazon Basin

Rare plant and vertebrate species have been documented to contribute
disproportionately to the total morphological structure of species
assemblages. These species often possess morphologically extreme traits
and occupy the boundaries of morphological space. As rare species are at
greater risk of extinction than more widely distributed species,
human-induced disturbances can strongly affect ecosystem functions related
to assemblage morphology. Here, we assess to what extent the distributions
of ant morphological traits are supported by morphologically extreme
species and how they are distributed among habitats in a global
biodiversity hotspot, the Brazilian Amazon. We used a morphological
database comprising 15 continuous morphological traits and 977
expert-validated ant species distributed across the Brazilian Amazon. We
produced species range estimates using species distribution models or
alpha hulls (when few records were available). Next, we conducted a
principal components analysis to combine traits into a space with reduced
dimensionality (morphospace). Then, we identified morphologically extreme
species in this space and quantified their contributions to morphological
diversity across different habitat types in the Brazilian Amazon Basin. We
identified 114 morphologically extreme ant species across the Amazon ant
morphospace. These species also accounted for a large percentage of
morphospace filling, exceeding 99% representation in the most disturbed
habitats in the Amazon. Our results suggest that a few morphologically
extreme species capture most of the variation in ant morphology and
therefore, the spectrum of ecosystem functions performed by ants in the
Brazilian Amazon Basin. Further, unlike for many other groups, these
extreme morphologies were represented by the set of most common species.
These results suggest greater functional redundancy and resilience in
Brazilian Amazon ants, but more broadly, they contribute to our
understanding of ecological processes that sustain ecosystem functions.