# Divergent Functional Roles of Shredder Size: Interspecific Versus Intraspecific Effects on Aquatic Leaf Litter Decomposition

## TL;DR

This study shows that different species and life stages of aquatic insects affect how quickly leaves break down in streams.

## Contribution

The study reveals that both species identity and larval ontogenetic stage significantly influence decomposition and organic matter processing in streams.

## Key findings

- Potamophylax, the largest shredder taxon, showed the highest decomposition and FPOM production rates.
- Younger larval stages within species exhibited higher processing rates than older stages.
- Shredder identity and ontogenetic stage significantly affect decomposition and particle size distribution.

## Abstract

Biodiversity underpins ecosystem functioning, and higher diversity of taxa and traits often enhances efficiency. However, such relationships may vary, as intraspecific variation—including differences across ontogenetic stages—can modulate a taxon's contribution to ecosystem functioning. We conducted laboratory experiments to examine the effects of shredder identity, diversity, and ontogenetic stage on leaf litter decomposition and fine particulate organic matter (FPOM) production. Three caddisfly shredder taxa (Allogamus, Potamophylax, and Sericostoma) were collected in two different months and fed with highly decomposable alder (
Alnus glutinosa
) leaves individually and in shredder combinations during 1‐week incubation periods. The experiments reflected distinct larval instars and were conducted with a time interval of 2 months. We hypothesized that decomposition and FPOM production would vary with taxon identity and ontogeny, with diversity enhancing processing rates. We further expected higher processing rates in younger larvae due to their greater metabolic demands. Results showed that both shredder identity and ontogenetic stage significantly affected decomposition, FPOM production, and particle size distribution. The largest taxon, Potamophylax, had the highest decomposition and FPOM production rates and produced the largest FPOM particles, while the smallest taxon, Allogamus, had the lowest rates and produced the smallest particles. Within taxa, younger and smaller larval stages exhibited higher rates than their older conspecifics. These results highlight the importance of shredder identity and ontogenetic stage in shaping both the magnitude and timing of key ecosystem processes.

Biodiversity enhances stream ecosystem efficiency, with greater taxonomic and trait diversity improving functions like decomposition. Shredder diversity arises from both species differences and ontogenetic variation. We experimentally examined these factors to reveal how they shape the magnitude and timing of organic matter processing in streams.