Abstract
Competition and predation alter individual traits of organisms, and these effects can scale-up to have consequences on community structure and dynamics. The relative importance of competition and predation will depend largely on the local assemblage of species, the type of predators, or the degree of niche segregation. We experimentally investigated the interplay of competition and predation on the structure and trophic level (measured via stable isotope analysis) of a seven-species Neotropical freshwater guild using a mesocosm approach in central Panama. We tested the effect of two types of predators (dragonfly nymphs or adult water bugs) in combination with the presence/absence of a common competitor, the red-eyed treefrog (Agalychnis callidryas), on four core species of tadpoles. We also distinguished between consumptive and non-consumptive effects of each type of predator by presenting them to tadpoles caged or freely roaming. Dragonfly larvae were more efficient predators than water bugs, but these effects were not uniform for all tadpole species. All amphibian species grew bigger when raised in the presence of an uncaged dragonfly nymph, presumably due to reduced competition through thinning, but tadpoles were smaller when exposed to caged dragonfly nymphs indicating the existence of non-consumptive predator effects as well. Predator presence also altered the relative trophic position of the different amphibian species, causing some tadpole species to increase and others to decrease their trophic status. Despite the presumed ecological similarity of tadpole species in the guild, the interplay of competition and predation had varying effects on the trophic status of nearly every species. Our results indicate that community composition can greatly affect the trophic level of larval amphibians, and that predation may have a greater role than competition in structuring Neotropical larval amphibian guilds.
Highlights
The structure and dynamics of ecological communities is determined by just four basic processes: selection, drift, speciation, and dispersal (Vellend, 2010; Kozak and Wiens, 2012)
Survival was not affected by the three-way interaction between competition, predation and tadpole species (χ2 = 5.32; P = 0.95) but was strongly affected by predator treatment (χ2 = 262.93; P < 0.001), tadpole species (χ2 = 198.24; P < 0.001), and the interaction between them (χ2 = 189.65; P < 0.001)
Not all tadpole species were prone to predation, as noted by the significant “predator × species” interaction (Figure 2, Table 1)
Summary
The structure and dynamics of ecological communities is determined by just four basic processes: selection, drift, speciation, and dispersal (Vellend, 2010; Kozak and Wiens, 2012). Stochastic and Trophic Niche Partitioning in Tadpoles deterministic factors further influence temporal and spatial species turnover that in turn determine which species interact at any given time and their relative abundances (Legendre et al, 2005), creating broad-scale variation in community composition (Berg and Bengtsson, 2007; Soininen, 2010). On top of these factors, ecological interactions such as predation and competition are decisive in structuring community composition. Direct assessments of trophic interactions are needed to better understand community composition and shed light on the complex relationships between competition and predation that arise as different species are involved (Arribas et al, 2014, 2015)
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