Incorporating indirect pathways in body size-trophic position relationships

Area of Science:

• Ecology
• Ichthyology
• Food web dynamics

Background:

• Interrelationships between body size, trophic position (TP), and trophic niche width are debated.
• Previous studies often excluded non-carnivores and ignored indirect effects, interactions, and phylogeny.

Purpose of the Study:

• To analyze the relationships among TP, consumer size, food item size, trophic niche width, and functional traits (gut length, mouth width) in freshwater fishes.
• To investigate indirect pathways and mediating effects in size-based trophic relationships.

Main Methods:

• Confirmatory path analysis using an extensive dataset of freshwater fishes.
• Inclusion of both carnivorous and non-carnivorous species.
• Analysis of functional traits including gut length and mouth width.

Main Results:

• Consumer size was indirectly linked to TP through maximum food size, food size variation, mouth width, and gut length.
• Larger food items correlated with higher TP; longer guts correlated with smaller, homogeneous food items.
• Body size was not directly associated with TP in either carnivorous or non-carnivorous fish.

Conclusions:

• Functional traits and their intermediate pathways are crucial for understanding size-based trophic relationships across diverse feeding strategies.
• Relying solely on body size as a surrogate for TP is cautioned, especially in freshwater ecosystems with significant plant/detritus consumption.