Feeding Preferences of a Generalist Salt-Marsh Crab: Relative Importance of Multiple Plant Traits

Abstract

Few studies have evaluated the relative importance of multiple plant traits to herbivore diet choice, especially with an experimental approach. Moreover, although circumstantial evidence points to plant toughness and silica content as important determinents of diet choice, few studies have experimentally demonstrated that these factors actually deter feeding by herbivores. We examined feeding preferences of a generalist salt‐marsh crab, Armases cinereum, for all the common angiosperms in its habitat. We took an experimental approach to evaluating the importance of toughness, secondary chemistry, silica, salt, and protein in determining feeding preferences. Consumption of plants by Armases in two experiments was correlated with decreasing toughness. Consumption was more equitable when plants were ground up and reconstituted in agar discs, with reduced differences in toughness. In four pairwise choice tests, Armases always preferred the softer plant of the pair, but in three of four cases exhibited no preference when the same plants were presented in reconstituted discs. Several plant extracts significantly stimulated or deterred feeding by Armases, but these effects were not consistent with and could not be used to predict overall preferences for fresh plants. Salt in artificial diets stimulated feeding by Armases. Silica had no effect on feeding in two experiments and stimulated feeding in a third. Armases was mildly stimulated to feed by high levels of protein in artificial diets, but these levels were above those found in plants, and the protein content of plants did not correlate with feeding preferences. Our results point towards plant toughness as most important in determining feeding choices of Armases. Since Armases is omnivorous, it may escape dietary constraints that affect feeding choices of pure herbivores. The dogma that silica defends plants against herbivory needs to be re‐examined with additional experimental studies.

Macroalgas varadas sobre la superficie de una playa arenosa del sur de Chile: preferencias alimentarias y de habitat de juveniles y adultos de Orchestoidea tuberculata (Nicolet), (Amphipoda, Talitridae)

“…Por ejemplo Rothäusler & Thiel (2006) Conocer los factores que determinan las preferencias alimentarias de los consumidores herbívoros, es uno de los aspectos más complejos en este tipo de estudios (e.g., Pennings & Paul 1992, Penning et al 1998. Aspectos tales como la amplia variedad de rasgos (e.g., características nutricionales y estructurales) que presentan las macrófitas (Steneck & Watling 1982, Pennings et al 1998, McClintock & Baker 2001, o las diferencias inter e intraespecíficas de los requerimientos nutricionales de los herbívoros (Pennings et al 2000, Byrén et al 2006) dificultan la interpretación de los resultados. Por ejemplo, Gómez & Westermeier (1995) estudiaron los contenidos energéticos y constituyentes orgánicos (proteínas, lípidos, carbohidratos y manitol) en las mismas especies de macroalgas utilizadas en este estudio y encontraron que L. nigrescens tiene en general un valor nutritivo más bajo que el de las otras especies, con contenidos de proteínas, carbohidratos solubles y manitol significativamente más bajos que los de M. pyrifera y con valores de energía total y carbohidratos solubles y manitol significativamente más bajos que los de D. antarctica.…”

“…Por ejemplo, Gómez & Westermeier (1995) estudiaron los contenidos energéticos y constituyentes orgánicos (proteínas, lípidos, carbohidratos y manitol) en las mismas especies de macroalgas utilizadas en este estudio y encontraron que L. nigrescens tiene en general un valor nutritivo más bajo que el de las otras especies, con contenidos de proteínas, carbohidratos solubles y manitol significativamente más bajos que los de M. pyrifera y con valores de energía total y carbohidratos solubles y manitol significativamente más bajos que los de D. antarctica. El hecho de que los juveniles de O. tuberculata tengan un consumo preferencial de L. nigrescens por sobre las otras dos macrófitas, confirma la dificultad de entender y predecir los patrones de preferencia en estos consumidores marinos (Pennings et al 1998). Los factores que determinan el cambio ontogénico en el uso del alimento de O. tuberculata no son conocidos; sin embargo se proponen aquí algunas posibilidades.…”

“…Existe una amplia variedad de rasgos de las macrófitas que pueden influir sobre los patrones de preferencia de los consumidores herbívoros, tales como tipo y concentración de metabolitos secundarios, calidad nutricional, dureza y pH (Steneck & Watling 1982, Pennings et al 1998, McClintock & Baker 2001. Además, esos herbívoros pueden responder de manera diferente a un rasgo en particular (Pavia et al 1997, Zimmer 1999.…”

Relative importance of vascular plants and algal production in the food web of a Spartina-invaded salt marsh in the Yangtze River estuary

“…However, the trophic contribution of C 3 plants may overcome that of Spartina when they co-occur in a same marsh (Stribling & Cornwell 1997, Wainright et al 2000. More than 80% of the biomass of S. alterniflora is comprised of refractory structural lignocellulose, and it is among the toughest marsh plants and does not decompose easily (Pennings et al 1998). Stable carbon isotope analysis of microbial biomarkers also suggest the C 3 plant Scirpus maritimus is a more important carbon source for bacterial growth than C 4 Spartina (Boschker et al 1999), so that production from C 3 vascular plants can be utilized more easily through the bacterial pathway.…”

Disturbances as a Structuring Factor of Plant Palatability in Aquatic Communities

“…Plant palatability is regarded as a key functional trait, as it governs in part the competitive success of species , Rachich and Reader 1999, Gross et al 2001. Some plant species can effectively reduce herbivore consumption through morphological adaptations or deterrent chemical compounds (Newman et al 1996, Cronin 1998, Pennings et al 1998, Kubanek et al 2001. Such species should have the ability to persist in habitats where herbivore pressure is high, even under resourcelimited conditions (Coley et al 1985, Sheldon 1987.…”