Variable contribution of inquilines to prey digestion in <i>Nepenthes</i> pitcher plants: the role of pitcher traits

While prey capture has been extensively studied in pitcher plants, prey digestion, particularly the role of pitcher inhabitants in prey decomposition, has received little attention. We tested and compared prey decomposition among four Nepenthes species, which vary in pitcher traits and associated inquiline guilds. In a field experiment, 15 prey items were introduced into the digestive fluid of 120 newly opened pitcher tanks of four Nepenthes species and 30 water-filled artificial tanks. Half of the tanks of each type were bagged with insect-screening net and after 1 month prey count and degradation were compared between treatments. Whereas prey was recovered from all bagged tanks, a significant part was missing from the unbagged lidless artificial and N. ampullaria tanks. The probability of prey recovery also increased with tank height but did not decrease with the abundance of any inquiline guild, suggesting that missing prey was removed by external visitors. Prey degradation was greater in unbagged tanks, varied across species and increased significantly with the abundance of saprophages and plant detritus. These results highlight the involvement of inquilines and falling debris in prey breakdown in these carnivorous plants, with species-specific relative contributions, and they suggest a role of pitcher shape in protecting against kleptoparasitism. This article is part of the theme issue 'Life in natural microcosms'.