Trait similarity patterns within grass and grasshopper communities: multitrophic community assembly at work

Area of Science:

• Ecology
• Community Ecology
• Trait-based Ecology

Background:

• Trait-based community assembly theory posits abiotic filtering promotes similarity in stressful environments and competition promotes dissimilarity in productive ones.
• Previous research on trait similarity along productivity gradients focused on single trophic levels.
• The influence of trophic interactions on trait similarity patterns across environmental gradients remains underexplored.

Purpose of the Study:

• To investigate how trophic interactions affect plant and herbivore trait similarity patterns along environmental gradients.
• To test hypotheses regarding environmental control, bottom-up control, and top-down control of trait variation in grasses and grasshoppers.
• To determine the drivers of trait similarity in grasses and grasshoppers within a South African savanna ecosystem.

Main Methods:

• Data collection on community composition and trait variation for 41 grass species and 53 grasshopper species across 50 savanna plots.
• Utilized structural equation models to analyze the response of trait values to rainfall and fire frequency gradients.
• Assessed the influence of trait similarity patterns of one trophic level on the other.

Main Results:

• Grass traits exhibited increased similarity under lower rainfall and higher fire frequency, indicating strong environmental control.
• Grasshopper trait range patterns were primarily influenced by vegetation structure and grass trait patterns (bottom-up control).
• Environmental factors had indirect effects on grasshopper traits, mediated through plant traits, with limited evidence for top-down control.

Conclusions:

• Environmental factors directly shape plant trait similarity, while trophic interactions primarily drive herbivore trait similarity.
• This research highlights the importance of considering trophic interactions to expand trait-based community assembly theory.
• The findings offer a more comprehensive understanding of community assembly dynamics in savanna ecosystems.