Abstract
ABSTRACT We analyzed the seasonal variation in the diet, trophic niche breadth (Levins index), the partitioning of food resources (Pianka’s symmetric index) and trophic level (weighed average of trophic level of each prey determined in FishBase and SeaLifeBase platform) of Plagioscion squamosissimus (Heckel, 1840) and Hydrolycus scomberoides (Cuvier, 1819) in the Machado River, Rondônia, Brazil. Fish samplings were conducted bimonthly from June 2013 to May 2015 in five sites, using eight sets of gillnets. The occurrence frequency and volumetric frequency were used to quantify the food items. We analyzed the stomach contents of 283 individuals, 134 of H. scomberoides and 149 of P. squamosissimus. Fish were the most consumed food item by both piscivorous species. However, H. scomberoides mostly ingested pelagic fish (e.g. Characiformes fishes and Prochilodus nigricas Spix & Agassiz, 1829), while P. squamosissimus mostly consumed benthic fish [e.g. Pimelodus blochii Valenciennes, 1840 and Tenellus trimaculatus (Boulenger, 1898)]. Hydrolycus scomberoides presented the trophic level 3.55 for both periods analyzed, while P. squamosissimus 4.01 in the flood period and 3.82 in the drought period. Seasonal variations in the diet of H. scomberoides and P. squamosissimus were observed (PERMANOVA). Specifically, P. squamosissimus consumed mainly “Siluriformes” fishes and P. blochii in the drought period. The trophic niche breadth of P. squamosissimus was greater than that of H. scomberoides in the flood period. The species P. squamosissimus and H. scomberoides had low (0.35) food niche overlap in both seasons analysed. The data indicated that P. squamosissimus has a generalist feeding habit, while H. scomberoides is specialized in prey selection. The overlap of food niche between the species in both periods of the hydrological cycle was low, indicating that niche partitioning was probably the main mechanism of coexistence of these species, with little relationship with variations of the hydrological cycle.
Highlights
Hydrolycus scomberoides (Cuvier, 1819), the dogtooth characin, is distributed throughout the Amazon basin (Queiroz et al, 2013), has a piscivore dietary habit, consumes entire fish, but has insignificant commercial importance (Santos et al, 2006). Considering their ecological importance, this study aimed to evaluate piscivorous fish feeding in a stretch of the Machado River, Amazônia, comparing flood and drought periods
Hydrolycus scomberoides consumed a total of 14 food items, while P. squamosissimus consumed a total of ten items
We highlight that H. scomberoides mainly ingested pelagic fish and P. squamosissimus mainly ate benthic fish
Summary
MacArthur (1965) described that gradients of richness could be explained by two contrary patterns of niche occupation: (i) the niche expansion model, where an increase in richness is linked to the occupation of new regions of niche space (habitat dimensions and resources), which are not available or still need to be explored by more assemblages (MacArthur, 1965; Karr & James, 1975); and (ii) the niche packing model that proposes higher diversity is associated to denser niche packing, which arises through more restricted specialization or greater overlap in resource use (Klopfer & MacArthur, 1961; Karr & James, 1975) that, in turn, may reflect differences in the ecological capacity of coexistence or regional differences in speciation rates (Hubbell, 2006)
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