Abstract
Freshwater crabs are not commonly considered to be an important group in trophic webs, and this might be due to a lack of knowledge about their trophic roles in aquatic ecosystems. Trichodactylus borellianus is one of the most common and widely distributed freshwater crabs in the floodplains of the southern South American rivers. The main objective of the present study was to examine the trophic role of T. borellianus , in the floodplain of the Parana River, and its relationships with the freshwater littoral community. The trophic spectrum of this species was characterized for both sexes and individuals of different sizes (adults and juveniles), throughout daily and seasonal cycles. Samples were collected from the aquatic vegetation of three shallow lakes. The diet composition and the feeding activity of T. borellianus were evaluated through the examination of the stomach contents and their degree of emptiness. This crab species consumed several plant and animal items, including amoebas, rotifers, oligochaetes, copepods, cladocerans, and insect larvae. Moreover, this species consumes filamentous and unicellular algae, diatoms, fungi, and macrophytic remains. The predatory habits varied with the season and time of day, and variations in the feeding activity of the juveniles and adults were detected and documented. The diversity of food items eaten by this crab suggests that its trophic role in the community as an omnivore and opportunistic predator provides a connection among several trophic levels from both aquatic and terrestrial communities.
Highlights
Trophic webs are considered some of the main forces that structure aquatic communities (Pascual & Dunne, 2006)
All of the sampling sites showed aquatic vegetation, including Eichhornia crassipes, E. azurea (85% approximately), and Salvinia sp. (7%), with the remainder represented by Limnobium sp., Azzolla sp., Pistia sp., Ludwigia sp., Paspalum repens, and Hydrocotyle ranunculoides
The size of the crabs differed between autumn and the other seasons (one-way analysis of variance (ANOVA)(3; 79): 3.13; P = 0.036) in that smaller specimens were common in autumn
Summary
Trophic webs are considered some of the main forces that structure aquatic communities (Pascual & Dunne, 2006). Studies of the feeding ecology of animals contribute to the knowledge of the nutritional requirements of species, interactions with other organisms, and community organization patterns over evolutionary time (Lampert et al, 1992). Freshwater communities are complex assemblages influenced by the interactions and dynamics among the food web components (Kerfoot & DeMott, 1984). In such an habitat, assessing diversity is one possible way to analyze the condition of an environment. Data on ecological interactions and functions of the species are considered as an alternative measurement for ecosystem studies (Woodward et al, 2005; Woodward, 2009). Data on ecological interactions and functions of the species are considered as an alternative measurement for ecosystem studies (Woodward et al, 2005; Woodward, 2009). Fulton et al (2003), noted that information on predation is a crucial tool for modelling an ecosystemlevel analysis because this parameter shows the direction of the flow of matter and energy that determines the organization of communities
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