The characteristics associated with prey attraction and capture in pitcher plants are not well understood. Because of physiological constraints due to growth patterns and resource availability, pitcher characteristics should vary among seasonal cohorts and with pitcher age. We measured age-related changes in characteristics (funnel diameter, extrafloral nectar guides, extrafloral nectar concentration) and in prey capture of early- and mid-season cohorts of Sarracenia alata pitchers. Pitchers achieved their mature height before opening, and pitchers of the mid-season cohort were smaller than those produced early in the growing season. In both cohorts, extrafloral nectar concentration on the lip of the pitcher and the number of “secondary nectar guides” (an indication of hood coloration) were highest approximately 3 wk after pitchers opened. The rate of insect capture in both cohorts was highest approximately 3 wk after pitchers opened, corresponding with the peak in nectar concentration and the maximal number of secondary nectar guides observed. The mean intact insect capture from the four main collections (the three sampling periods for Cohort A and the single period for Cohort B) was significantly positively related to mean nectar concentrations for those collections. When pitchers were capturing at their maximal rate (3 wk after opening), prey capture per unit size per unit time was higher in the mid-season cohort even though nectar concentration was not significantly different than that in the early-season cohort. Furthermore, ants comprised a significantly greater proportion of intact insects captured by the mid-season cohort. The results of this study show that characteristics of pitchers and their effect on prey capture vary between seasonal cohorts and with pitcher age. Nectar appears to be an important attractant, and foraging insects may be attracted by nectar, coloration, or most likely by some combination of these and other characteristics. The physiological constraints and evolutionary pressures leading to these differences need to be examined.
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