LATITUDINAL VARIATION IN PALATABILITY OF SALT-MARSH PLANTS: ARE DIFFERENCES CONSTITUTIVE?

Abstract

Biogeographic theory argues that consumer–prey interactions are more intense, and prey defenses better developed, at lower latitudes. Along the Atlantic Coast of the United States, low-latitude salt marsh plants are less palatable than high-latitude conspecifics. To test the hypothesis that latitudinal variation in palatability would occur in the absence of geographically different environmental cues (i.e., that differences in palatability are constitutive rather than induced by climate or herbivore damage), we grew high- and low-latitude individuals of three species of salt marsh plants from seeds (Solidago sempervirens) or rhizome cuttings (Distichlis spicata and Spartina alterniflora) in a common-garden greenhouse environment, and compared their palatability to herbivores over time. We also quantified leaf toughness and nitrogen content over time in order to help explain results of feeding assays. High-latitude plants were always more palatable to herbivores than low-latitude conspecifics. Latitudinal ...