Terrestrial invertebrates respond to food subsidies in dry streambeds of non-perennial rivers: effects of subsidy type and their moisture condition

Non-perennial streams alternate between wet and dry phases, with dry streambeds attracting high diversity of terrestrial invertebrates, likely due to accumulated aquatic food subsidies. However, this aspect is only beginning to be explored. We examined how different food subsidies (leaf litter, macrophytes, macroinvertebrates, and fish) attract terrestrial invertebrates in dry streambeds and how their moisture condition (wet vs. dry) influences this attraction. Field experiments were conducted in two Mediterranean non-perennial streams by adding these subsidies separately in each moisture condition and analyzing invertebrate responses (community structure and composition). We hypothesized that food subsidies attract terrestrial invertebrates, with structural and compositional responses varying by subsidy type and moisture condition. Subsidies affected terrestrial invertebrates only in one stream, influencing abundance and composition but not richness. Fish carrion in wet condition attracted the highest invertebrate abundance across all subsidies and moisture conditions. Community composition varied depending on subsidy type, regardless of moisture: fish carrion attracted mainly scavengers, while plant-based subsidies favored herbivores and detritivores. Our findings highlight the role of food subsidies in structuring terrestrial communities in dry streambeds and the complex interplay between community composition, subsidy type, and moisture conditions.