Understanding disproportionately high densities of stream macroinvertebrates in size-density relationships

Author(s)

Braga, Julia M. ; Mello, Jose L. S. ; Shimabukuro, Erika M. ; Venuso, Laura J. ; Guerra, Pedro P. B. ; Perkins, Daniel M. ; Saito, Victor S.

• Document type: Journal article
• Source: Hydrobiologia; v. N/A, p. 16-pg., 2025-10-07.

Abstract

Metabolic scaling theory provides a framework to understand energy flows in ecosystems, predicting a negative relationship between body mass and density, where smaller species tend to occur in higher densities than larger ones. We assessed disproportionately high densities in tropical stream macroinvertebrates through size-density relationships (SDR), focusing on taxa exceeding expected densities for their body mass. We hypothesized that unique functional traits allow singular niche exploitation and reduced competition, resulting in high net energetic gains. To test this, we sampled Atlantic Forest stream communities monthly for over a year, estimating individual body mass via allometric equations. Positive SDR residuals indicated disproportionate densities, which we related to functional traits. As expected, size and density were negatively related, with some taxa showing greater density in time than predicted by their body mass. However, contrary to our hypothesis, functional uniqueness was not associated with higher densities, suggesting that traits alone may not drive disproportionate densities. Instead, disproportionate densities appeared in taxa with high redundancy with congenerics. Additionally, taxa with higher densities showed greater temporal variability, indicating a fluctuating dynamic of dense populations. Our results suggest that high densities could be linked to a combination of niche preemption and modification mechanisms of community assembly. (AU)

• FAPESP's process: 23/08252-0 - The phenology of aquatic insects in tropical regions - scholarship 2
• Grantee: Laura Joia Venuso
• Support Opportunities: Scholarships in Brazil - Technical Training Program - Technical Training
• FAPESP's process: 23/00574-9 - The role of stochastic community assembly on the size structure of aquatic metacommunities under global change
• Grantee: José Leonardo da Silva Mello
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 23/15982-5 - Understanding the aquatic macroinvertebrat disproportionality in the biomass-abundance relationships in Atlantic Forest streams
• Grantee: Julia Maria Braga
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• FAPESP's process: 24/02873-6 - Relationship between stability and complexity in ecological networks of stream communities in tropical and temperate zones
• Grantee: Pedro Pontes Bueno Guerra
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 22/01452-1 - Understanding the role of stochasticity in metacommunity assembly under global changes
• Grantee: Victor Satoru Saito
• Support Opportunities: Regular Research Grants