Latitudinal Differences in Plant Palatability in Atlantic Coast Salt Marshes

Abstract

A central hypothesis of biogeography is that consumer-prey interactions are more intense at lower latitudes, leading to increased defenses of prey. Because plants vary in many traits that might affect palatability to herbivores, however, studies of latitudinal variation in single plant traits such as secondary chemistry provide only circumstantial evidence to test this hypothesis. We directly compared the palatability of 10 salt marsh plants from seven northern (Rhode Island and Maine) and eight southern (Georgia and Florida) coastal salt marshes by flying fresh plant material back and forth and allowing 13 species of herbivores direct choices between northern and southern conspecific plants in laboratory assays. In 127 of 149 assays (85%), herbivores showed a significant or marginally significant preference for northern plants. In only one assay did herbivores prefer southern plants. These results occurred regardless of the geographic location of the assay, herbivore species, year, or season of plant collection, although there were hints that latitudinal differences became less pronounced for two plant species late in the growing season. Our results provide the most comprehensive evidence to date for a latitudinal gradient in plant palatability in any community. The proximate plant traits and the ultimate evolutionary factors responsible for this pattern remain to be determined.

Biogeography of sponge chemical ecology: comparisons of tropical and temperate defenses

“…Predation also seems to be negatively related to latitude, as supported by data from both terrestrial and marine systems (Pianka 1966;Bertness et al 1981;Menge and Lubchenco 1981;Coley and Aide 1991;Warren and Gaston 1992;Coates 1998). Coupling these latitudinal gradients in levels of defenses and predation has resulted in a general acceptance that organisms living in environments with higher levels of predation have evolved better defensive mechanisms than have those living in environments with lower levels of predation, despite the paucity of direct evidence available (Bolser and Hay 1996;Cronin et al 1997;Pennings et al 2001). In marine systems, this hypothesis was first proposed for sponge chemical defenses over 25 years ago (Bakus and Green 1974) but, to date, there are no experimental data for or against the idea that tropical sponges are chemically better defended than temperate sponges.…”

“…In addition, several studies have not found support for a latitudinal gradient in chemical defenses (McCaffrey and Endean 1985;McClintock 1987;Steinberg and Paul 1990;Van Alstyne and Paul 1990; Van der Vyver et al 1990;Targett et al 1992;Van Alstyne et al 1999), which reinforces the need for direct tests of this hypothesis (Bolser and Hay 1996;Pennings et al 2001) and suggests that factors other than predation may act as evolutionary forces on these chemicals (Schmitt et al 1995;Bolser and Hay 1996;Becerro et al 1997).…”

Interpopulational differences in the female reproductive cycle of the southwestern Atlantic estuarine crab <i>Chasmagnathus granulatus Dana</i>, 1851 (Brachyura: Grapsoidea: Varunidae)

“…Food quality and productivity may vary between sites as a consequence of differences in temperature, salinity, substrate, nutrient supply, photoperiod and also the chemical composition of the cordgrass species. Plant palatability may also be different, as in the USA Atlantic coast salt marshes (Pennings et al, 2001). No comparative studies of productivity or palatability between SA and MC saltmarshes are available.…”

Evolution of insect‐plant relationships: chemical constraints, coadaptation, and concordance of insect/plant traits

“…Geographic mosaics of local specialization in insect behavior (Gould, 1991;Bernays & Chapman, 1994;Bernays, 1998), detoxification physiology (Nitao et al, 1991;Hoy et al, 1998), and other insect genetic adaptations (Thompson, 1994;Mopper & Strauss, 1998) seem likely in most communities. However, these specialized herbivore traits are poorly known in relation to the underlying geographic variation in plant phytochemistry or palatability (Rausher, 1992;Johnson & Scriber, 1994;Pennings et al, 2001).…”