Pitcher plants possess extrafloral nectaries that secrete nectar containing sugars, amino acids, and water and which attract the potential prey that depend on the nectar for nourishment Pitcher plants also display intricate red and green patterns that have been hypothesized to play a role in attracting prey but few studies support this hypothesis
Thus, it remains an open question whether or not red coloration or patterning of pitcher plants is at all related to prey capture, or whether color interacts with nectar to enhance prey capture. We conducted a field experiment to test independent and interactive effects of red coloration and nectar availability on prey attraction by the northern pitcher plant, Sarracenia purpurea. We assessed prey capture by live pitchers ranging in color from almost entirely green to almost entirely red. We then measured independent and interactive effects of color and nectar using “pseudopitchers” (50-ml painted tubes), with and without added sugar solution. We hypothesized that both real S. purpurea pitchers and pseudopitchers with nectar would capture more prey than pseudopitchers without nectar. We further predicted that because ants have biochromatic vision, real or pseudopitchers with contrasting venation would capture significantly more ants than monochromatic pitchers.
Results/Conclusions
The number of ants captured was unrelated to the proportion of visible red areafor real pitchers and pseudopitchers with or without nectar. Presence of nectar significantly increased ant capture in painted and non painted pseudopitchers. The relationships between red coloration and number of ants captured by pseudopitchers or by real pitchers were virtually identical. Our experimental results clearly illustrate that pitcher plants use nectar to attract prey. These results also highlight the importance of studying prey capture in the field, of distinguishing among multiple possible attractants, and of employing experimental controls. Although many carnivorous plants exhibit contrasting patterns and nectar guides when photographed under ultraviolet light there is no evidence that potential prey in the field actually see these patterns. Ants, the primary prey of all pitcher plants, see ultraviolet and green and would see red as grey, only weakly contrasting with the pitcher’s green base color. Such a weak contrast is unlikely to be a strong attractor. We therefore conclude that nectar, not color, is the primary means by which pitcher plants attract prey.
