Response of Armadillidium vulgare to elemental imbalance

Ecological stoichiometry offers important insights into how the elemental composition of food resources affects their consumers. As plant detritus is typically comprised of refractory, carbon-rich and nutrient-limited compounds, detritivorous consumers face a challenge to meet their nutritional demands and developed strategies to decrease the imbalance between the elemental composition of their bodies and that of their food resources. Here we evaluate if Armadillidium vulgare, a common and widespread detritivorous invertebrate, compensates for the elemental imbalance of food resources. We assessed consumption, growth and survival with four food resources varying in C:N:P ratios in a 4-week feeding experiment and measured C:N:P ratios in the food resources, the consumers, and their faeces. The results suggest that A. vulgare uses three complementary strategies to deal with low-quality food resources: (1) compensatory feeding to maximize intake of N, (2) stoichiometric shift in C:N ratio to decrease elemental imbalance, and (3) differential assimilation of P during digestion. There was increased consumption of food resources with low C:N and C:P ratios to take advantage of an abundant source of nutrients, and there was increased consumption of high C:N and C:P food resources to compensate dietary deficiencies. Somatic C:N ratios increased with increasing C:N ratios, but not with C:P or N:P ratios of food resources. Finally, A. vulgare selectively assimilated phosphorus, but not nitrogen, from the ingested food, producing faeces with C:P ratios unrelated to the respective ratios of the food resources and maintaining somatic C:P and N:P ratios relatively constrained.