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Tropical pitcher plants (Nepenthes) are carnivorous plants that trap and digest prey using highly modified fluid-filled leaves known as pitchers. Prey are digested by plant-secreted enzymes and pitcher symbionts. Pitchers exert control over abiotic properties of the digestive fluid such as pH levels that can influence its symbionts. Here we examine natural variation in pH and dissolved mineral concentrations in three sympatric Nepenthes species, assessing correlations between fluid properties and pitcher traits. We use addition experiments to investigate differences in protein digestion/absorption rates between species. Fluid pH and dissolved mineral levels both showed distinct patterns corresponding to pitcher developmental stages in N. gracilis and N. rafflesiana, whereas N. ampullaria differs from its congeners in exhibiting far less variation in fluid pH, as well as less clear evidence of protein depletion. This study further elucidates the properties of pitchers as habitats, revealing ways in which the host plant regulates that habitat. [ABSTRACT FROM AUTHOR]