Fitness-associated consequences of an omnivorous diet for the mangrove tree crab Aratus pisonii

Abstract

Omnivory is a widespread trophic strategy with variable impacts on survival and reproduction, even within closely related taxonomic groups. In coastal ecosystems experiencing extensive environmental changes, many decapod crustaceans employ omnivorous feeding strategies. Because animals initially respond to environmental changes with behavioral modifications that can alter their foraging habits, a mechanistic understanding of how diet influences fitness is essential to predict the impact of future environmental changes on species fitness and population dynamics. We investigated the impact of an omnivorous diet on the consumption, survivorship, physiological condition, and reproductive effort of the mangrove tree crab Aratus pisonii, a major mangrove consumer. A. pisonii engaged in compensatory feeding on plant material; crabs consumed more food and digested it less efficiently as the proportion of plant material in their diet increased. Although there were relatively few deaths, survival appeared to be negatively impacted by the consumption of large quantities of animal material and marginally negatively influenced by high levels of plant consumption. Physiological condition improved due to consumption of both plant and animal material, while only consumption of animal material increased reproductive investment. These results demonstrate that the opportunistic inclusion of animal material in the diet of A. pisonii significantly improves physiological condition and reproductive effort, and suggests that vitellogenic individuals cannot fully compensate for a lack of animal material in their diet by increasing plant consumption. This study provides a mechanistic framework to understand how potential diet changes by omnivorous crabs such as A. pisonii, which are facing numerous changes in their environment, may impact their fitness and population dynamics.

An anthropogenic habitat within a suboptimal colonized ecosystem provides improved conditions for a range‐shifting species

“…This can be explored through the examination of the precise ways in which an analogous habitat provides improved conditions. For example, the quantity and quality of an individual's diet have a direct impact on several aspects of its ecology and life history including growth (Buck et al, 2003;Griffen, Guy, & Buck, 2008), offspring quantity and quality (Green, Gardner, Hochmuth, & Linnane, 2014;Millamena & Quinitio, 2000), and bioenergetics (Charron et al, 2015;Riley, Vogel et al, 2014). Thus, an improved diet may itself be the mechanism behind other benefits including increased size.…”

“…To examine the proportional energetic investment into energy storage by conspecifics in each habitat, we separated and dried the primary energy storage organ (hepatopancreas) (Parvathy, ) and the somatic tissue of each crab. To compare energetic investment between habitats, we calculated the hepatosomatic index (HSI) of each crab as the ratio of the dry weights of the hepatopancreas and the somatic tissue, which is a common measure of energy stores in crustaceans (Griffen, Vogel, Goulding, & Hartman, ; Kennish, ; Riley, Vogel et al., ; Sánchez‐Paz, García‐Carreño, Hernández‐López, Muhlia‐Almazán, & Yepiz‐Plascencia, ). However, HSI is dependent on both sex and reproductive stage (e.g., a female will have a lower HSI when carrying eggs; Belgrad, Karan, & Griffen, ).…”

“…Docks may fit this criterion within the salt marsh as they provide A. pisonii with a shaded habitat and vertical structure more similar to the historic mangrove as well as easy access to food in the form of abundant fouling communities. While mangrove leaves are not available in the dock habitat, animal material, which is abundant on docks in the form of fouling communities, is a high‐quality food source (Riley, Vogel, & Griffen, ) that is preferred by A. pisonii over mangrove leaves (Erickson, Feller, Paul, Kwiatkowski, & Lee, ). Easy access to a high‐quality food source could be a boon to A. pisonii as the quantity and quality of diet play crucial roles in the energetics and life history of an individual (Charron et al., ; Wen, Chen, Ku, & Zhou, ).…”

“…While mangrove leaves are not available in the dock habitat, animal material, which is abundant on docks in the form of fouling communities, is a high-quality food source (Riley, Vogel, & Griffen, 2014) that is preferred by A. pisonii over mangrove leaves (Erickson, Feller, Paul, Kwiatkowski, & Lee, 2008). Easy access to a high-quality food source could be a boon to A. pisonii as the quantity and quality of diet play crucial roles in the energetics and life history of an individual (Charron et al, 2015;Wen, Chen, Ku, & Zhou, 2006).…”

Inversión reproductiva de Aratus pisonii (Decapoda: Sesarmidae): diferencias entre hábitats y análisis de rutas

“…López & Conde (2013) encontraron una asociación directa entre la variedad de rubros consumidos por A. pisonii y la altura del manglar, pero sólo durante el periodo de lluvias, sugiriendo que existe una mayor oferta de recursos en los manglares con mayor desarrollo estructural visible durante esta temporada. Las lluvias generalmente ocasionan un incremento en la productividad de los manglares, apreciable sobre todo en regiones áridas y semiáridas (Day, Conner, Ley-Lou, Day, & Navarro, 1987;Rodríguez, 1987;McKee, 2002), como es el caso de los manglares de la península de Paraguaná de este estudio; esto toma más sentido si consideramos que A. pisonii es una especie catalogada como omnívora oportunista, cuyos individuos deben tomar ventaja estas condiciones para su beneficio (Beever, Simberloff, & King, 1979;Brogim, & Lana, 1997;Díaz, & Conde, 1988;Erickson, Feller, Paul, Kwiatkowski, & Lee, 2008;Riley, Vogel, & Griffen, 2014).…”