Pitcher plants (Sarracenia purpurea L.) attract insects to pitchers and then capture them in fluid-filled, pitfall traps, but how efficient are pitcher plants at capturing prey in their natural environment? We monitored insect activity by videotaping pitchers and analyzing videotapes for several variables including identity of each visitor and outcome of each visit (e.g., departure or capture). Efficiency of capture (i.e., number of captures per number of visits) was low. Overall efficiency of capture was 0.83-0.93%, depending on whether potential prey were broadly or narrowly defined. Ants constituted 74% of the potential prey. Efficiency of capture of ants was even lower at 0.37%. Potential prey were more likely to visit pitchers with greater red venation and less water in the pitcher. There was no correlation between number of potential prey visiting a pitcher and pitcher age, length, or mouth width. Also, number of potential prey visits did not correlate with plant size, air temperature, time of day or date of videotaping. While the overall efficiency of prey capture was very low, pitcher plants may still benefit from the additional nutrients. However, the relationship between ants and S. purpurea remains an enigma, since it is unclear whether the plants capture enough ants to compensate for nectar lost to ants.
Reproductive strategies of herbaceous plants were analyzed in three successional communities. The communities were a 1—yr old—field, 10—yr old—field, and forest. Analyses included measurement of community—wide reproductive effort (reproductive dry wt/total dry wt) at 3—wk intervals throughout one growing season. Reproductive effort was highest in the 1—yr field. There was essentially no difference in reproductive effort between plants in the 10—yr old—field and forest communities; both exhibited relatively low reproductive effort. Reproduction in the 1—yr and 10—yr fields was highly synchronous; there was little synchrony of reproduction in the forests. This may indicate a more efficient utilization of resources throughout the growing season in the forest. Analyses also included measurement of numbers of seeds per plant produced by dominant species in each community. Number of seeds per plant in the 1—yr and 10—yr fields was relatively high, while number of seeds per plant was comparatively low in the forest. The ratio of root:total biomass increased with successional age, reflecting a proportionately larger expenditure of energy on competitive structures in the forest. Also, goldenrods, dominants in the 10—yr field, were found to possess 1 characteristic of an r—strategy (i.e., large number of small seeds) and a characteristic of a K—strategy (i.e., low reproductive effort). This apparent paradox was explained by relating these characteristics to the selective pressures that might produce them. In addition, the empirical data provide support for expanded concepts of reproductive strategies.
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