Evidence for nutrient-specific foraging of invertebrate predators under field conditions

Nutrient-specific foraging is the ecological theory that generalist consumers select food resources based on their nutritional content. While laboratory experiments support this, it has not yet been demonstrated in invertebrate predators in the field. We combined dietary metabarcoding with prey abundance and macronutrient content data to analyze nutrient-specific foraging in the field. Spider nutrient intake and prey choice deviated from random. Through a novel nutrient-based taxonomy and null modelling, we reveal a stable average macronutrient intake and disproportionate foraging for different macronutrients by individual spiders. This aligns with the expectation that individual spiders at different stages of nutrient balancing will be biased toward prey rich in different nutrients. This finding suggests that spiders are redressing nutritional deficits to obtain a target nutrient intake, as expected of nutrient-specific foraging. This evidence for nutrient-specific foraging under field conditions significantly extends our understanding beyond lab-based behavioral assays to resolve complex real-world systems.