Of urgent importance to both community ecology and conservation biology is the need to better understand the factors shaping the diversity and distribution of different taxonomic groups across broad environmental gradients. These concerns are especially pressing in hyper-diverse ecosystems such as tropical forests, where little is known about the diversity and ecology of many taxonomic groups, as well as on the underlying biotic and abiotic trophic interactions shaping community assembly.
To shed light on the subject, we used a rare standardized coordinated inventory carried out in French Guiana between 2012 and 2018. The latter consists of 36 1.9-ha plots with precise soil measurements and composition data for five taxonomic groups of major ecological importance – trees, ants, spiders, fungi and earthworms – of which some remain critically understudied in the tropics. We tested (i) the congruence of taxonomic composition among groups, and (ii) whether coordinated taxonomic turn-over among pairs of groups was explained by soil properties, using a combination of co-inertia analyses and a constrained randomization procedure accounting for spatial autocorrelation.
Results/Conclusions
We found remarkable diversity in all groups including >1000 species of trees and >400 species of ants. All species group pairs exhibited significant compositional associations, regardless of soil conditions. For five out of the ten pairs, the co-inertia between the two groups was also significantly explained by the overall soil heterogeneity, with P availability being the most influential variable. Tree and ant species were the most strongly associated groups, a result that possibly reflected the influence of the litter quality on the habitat structure and the community of ant preys. We further discussed the nature of interactions that could explain the significant associations observed among the other groups.
Our study provides strong evidence for coordinated turnover among taxa beyond simple relationships with environmental factors, thereby refining our understanding regarding the nature of interactions occurring among ecologically important groups. It paves the way for deeper investigations of biotic interactions in the tropics, and may bring new hypotheses to understand biodiversity patterns and even diversification processes. Our results also confirm the usefulness of trees but also ants as proxies for assessing the composition of other groups, which will improve the design and impact of conservation programs in tropical forests.