Ecological interactions between spiders and the purple pitcher plant, Sarracenia purpurea

Spiders and harvestmen are commonly captured by or reside upon the carnivorous purple pitcher plant, Sarracenia purpurea. Although spiders and harvestmen are often known to be prey of S. purpurea, other ecological interactions between these arthropods and the plant are poorly understood. Studies were undertaken at three pitcher plant populations, two in Virginia and one in North Carolina, to assess the ecological relationships between spiders and harvestmen and S. purpurea. Multiple plots containing pitcher plants (treatment) and plots lacking pitcher plants (control) were created at these locations. Spiders and harvestmen were collected through five different techniques. Spatial, temporal, and interspecific variation in spider diversity and density among these techniques was calculated. To assess the attractive and/or retentive ability of the morphological features of S. purpurea, a field experiment was carried out whereby pitcher plant types and models were placed in a large area and their capture abilities were compared. Sticky traps at various proximities from the plant were used to test the plant's influence on local insect density. The propensity of spiders and harvestmen to consume S. purpurea nectar was also examined, and the species of spiders that commonly oviposit in the pitchers were recorded. Finally, stable isotope signatures were used to determine if spider residents contribute nutrients to the plant. Significant correlations were found between the density and diversity of spiders captured by S. purpurea and those found in the environment. There was no difference in spider diversity or density between control and treatment plots. Pigment-lacking, peristome nectar-lacking, and control pitchers did not differ in arthropod capture, but models captured less prey. Furthermore, newer pitchers captured more prey than older pitchers. These data indicate that attraction and/or retention of spiders by S. purpurea is similar to attraction and/or retention of insects. Spiders and harvestmen readily consumed S. purpurea nectar and often used the plant for oviposition. Spider residents of the genus Agelenopsis contributed nitrogen to the pitchers. Finally, there was no difference in insect density between control and treatment sticky traps, suggesting that S. purpurea does not influence nearby insect density.