Inter‐population differences in feeding ecology under nitrogen‐limited diets: Field growth and the role of cannibalism in limiting/improving reserve accumulation

Abstract

Growth is determined by an organism's physiology, physical environment, and biological conditions, including food availability and any intra‐ and inter‐specific interactions that can affect feeding activity. To analyse how all these factors interact to produce final growth in the herbivorous/detritivorous crab Neohelice granulata, we performed field and laboratory experiments with juveniles and adults from three populations which differed genetically as well as in their physical environment and the organic matter (OM) content in the soil that serves as food. We evaluated (a) growth in the field: Juveniles of the three populations were cross‐transplanted in exclusion cages; (b) effect of the presence of adults on juvenile feeding: We measured the feeding activity of small juveniles in presence/absence of an adult male as potential predator in the field; and (c) effect of diet on cannibalism: We analysed the cannibalistic behavior of adult males from two of the populations in the laboratory after they had received protein‐rich (24%) and protein‐poor (3%) diets. In experiment (a), final size was similar for the crabs from all three origins but growth differed between sites. Experiment (b) showed that the presence of adults interfered with feeding activity at the two sites with lower weight indicators. In experiment (c), we observed that low protein diet increased the cannibalistic behavior of adult males, and this effect was more intense in crabs from the poorest food site. Our results contribute to understanding the set of factors and interactions involved in the response of individuals to the prevailing conditions in natural environments in order to maintain a growth rate, perhaps at the expense of different reserve accumulation. They also enable discussion of the limitations of approaches used in laboratory experiments.

Visual determinants of prey chasing behavior in a mudflat crab

“…Recently, we discovered that Neohelice displays a robust visually guided chasing behavior (Tomsic et al, 2017). In fact, this crab preys on smaller crabs of its own species and also on sympatric fiddler crabs of the species Leptuca ( previously Uca) uruguayensis (Daleo et al, 2003;Bas et al, 2019). Preliminary studies in the field have shown that the predatory behavior of Neohelice can readily be evoked by using a small dummy moved at ground level (Tomsic et al, 2017).…”

Annual cycle of growth and population structure of the estuarine crabHemigrapsus crenulatus(Brachyura: Varunidae) off central Chile

“…salinity, temperature and oxygen) and ecological factors (e.g. competition, predation, mortality and food availability) by exhibiting differences in size frequency distributions (SFD), sex ratios, reproductive periods, size of maturity and recruitment (Lardies et al ., 2004; Posey et al ., 2005; Spivak et al ., 2016; Vina et al ., 2018), as well as migratory movements, lifespan, physiology and growth rates (Baeta et al ., 2005; Posey et al ., 2005; Koolkalya et al ., 2006; Lagos et al ., 2014; Theuerkauff et al ., 2018; Bas et al ., 2019). Depending on the environment and species, these effects can be expressed equally or differentially in males, females, ovigerous females and juveniles (Bas et al ., 2005; Posey et al ., 2005; Taylor & Seneviratna, 2005).…”