Interactions among bacterial-feeding nematode species at different levels of food availability

Abstract

Accurate prediction of the biodiversity-ecosystem functioning relationship requires adequate understanding of the interactions among species in a community. Effects of species diversity on ecosystem functioning are usually considered more pronounced with increasing functional dissimilarity, although species within functional groups may also perform non-identical functions and interact with each other. Here we present results of a laboratory experimental study aimed at elucidating whether interspecific interactions among species within a single nematode trophic group, bacterivores, (1) affect population development and community structure, and (2) depend on food availability. We studied the population growth of Rhabditis (Pellioditis) marina, a rhabditid nematode known to favour very high food densities when in monoculture, and of Diplolaimelloides meyli and D. oschei, congeneric Monhysteridae known to perform better in monocultures at intermediate food availability. Both Diplolaimelloides species showed significantly different patterns of food-density dependence in combination culture compared to monoculture. At very high food availability, the rhabditid nematode facilitated growth of both monhysterid species, probably as a result of down-regulation of bacterial density. At the lowest food availabilities, the presence of even low numbers of monhysterid nematodes lead to exclusion of the rhabditid, which at such low food availability has a very inefficient food uptake. At intermediate food availabilities, abundances of both Diplolaimelloides species were strongly depressed in the combination culture, as a result of food depletion by the rhabditid, indirect inhibitory interactions between the two congeneric species, or both. The complexity of the species interactions render predictions on the outcome and functional consequences of changes in within-trophic-group diversity highly problematic

Populations of two prey nematodes and their interaction are controlled by a predatory nematode

“…The latter abound on macroalgal wrack and in salt-marsh sediments with relatively high silt content (dos Santos et al 2009), whereas the former is typical of fine-to mediumgrained sandy sediments with very low silt percentages . At the Paulina site, they occur at very nearby stations (separated by only a few tens of meters).…”

“…(4) They are easy to culture in the lab, and their life history and mutual interactions have been well studied (Moens & Vincx 2000a,b, dos Santos et al 2008. They are in fact 2 of the only 3 marine nematode species for which interspecific inhibitory interactions have been well documented (De Mesel et al 2006, dos Santos et al 2009). (5) They are suitable prey to Enoploides (Moens et al 1999.…”

“…In combination with the inhibitory interactions among both prey species (De Mesel et al 2006, dos Santos et al 2009), we expected predation to further emphasize the dominance of D. meyli over D. oschei in the MIX experiment. D. oschei indeed attained lower abundances than its congener in the MIX experiment, whereas it was equally or even slightly more abundant than D. meyli in the SS experiment.…”

“…Moreover, the local diversity of nematode assemblages tends to be (very) high (Heip et al 1985, Wall & Moore 1999, Yeates et al 2009, and competitive, facilitative, and inhibitory interactions, even among closely related species, are important in shaping these assemblages (Mikola 1998, Ilieva-Makulec 2001, PostmaBlaauw et al 2005, De Mesel et al 2006, dos Santos et al 2009). It is unclear whether, and to what extent, predatory forces interfere with these horizontal interactions and affect assemblage structure and diversity.…”

“…These 2 bacterivorous species negatively affect each other's population development in laboratory microcosm experiments in the absence of predators, with D. meyli having a stronger inhibitory effect on D. oschei than vice versa (De Mesel et al 2006, dos Santos et al 2009. They have been shown to be very suitable prey for Enoploides (Moens et al 1999, 2000.…”