Leaf color polymorphism as a mechanism of within-individual resource partitioning in the purple pitcher plant, Sarracenia purpurea.

Abstract

Resource partitioning occurs when two or more species have evolved traits that allow them to use a shared limiting resource in different ways, thereby reducing competition and promoting coexistence. In principle, the same phenomenon could occur between tissues of a single individual, if those tissues shared a limiting resource. In nitrogen deficient environments, like bogs, carnivorous plants such as Sarracenia purpurea, the purple pitcher plant, have evolved leaves modified to capture insects and acquire nitrogen from insects. Unlike most plants, whose leaves are nearly identical in appearance, individual pitcher plants have leaves (pitchers) that differ substantially in relative amounts of red and green coloration, i.e. they display leaf color polymorphism. This study addresses the possibility that pitcher plants use leaf color polymorphism as a mechanism of within-individual resource partitioning. I sampled the contents and photographed the hoods of 31 S. purpurea (five pitchers per plant) in Mud Lake Bog in Cheboygan, MI in order to determine the relationship between within-plant color variation and the biomass and types of prey captured. Plants with greater leaf color polymorphism captured significantly more overall prey biomass, hymenopteran biomass, and dipteran biomass, and more species of Hymenoptera, Coleoptera, Hemiptera, and Arachnida. In no case was biomass or number of species negatively correlated with within-plant color variation, suggesting that there is no substantial cost of leaf color polymorphism. These results suggest that purple pitcher plants have pitchers that vary in color, at least in part, because such variation is a mechanism of within-individual resource partitioning