Relationships between body size and trophic position of consumers in temperate freshwater lakes

Abstract

Animal body size is a driving force behind trophic interactions within biological communities, yet few studies have explored relationships between body size and trophic position (based on d 15 N) at a broad-scale in freshwater lakes. Therefore, our goals were to (1) determine whether body size is a good predictor of trophic position for multiple pelagic zooplankton taxa and fish communities, and (2) examine how body size-trophic position relationships at the community level compare to species level for fish. Zooplankton and fish were collected from 12 and 7 lakes, respectively, located in the Kawarthas, southern Ontario, Canada. The results indicated that for zooplankton, significant positive but different relationships were found between body size and trophic position for cladocerans, in general, and Daphnia, but not Holopedium. For fish, at the lake community level six out of seven relationships were positive and significant, but again, different among lakes. In contrast, at the species level only three of eight species-specific relationships were significant. Furthermore, for two widespread species, Perca flavescens and Micropterus dolomieu, significant differences were found between community-and lakespecific species relationships. Our community-level models and most species-level models provide evidence that trophic interactions in freshwater lakes are size-based. These results demonstrate that general species models should be applied with caution when using body size to predict trophic position. Additionally, the predictive power of some relationships found here is questionable since, albeit significant, their strengths are generally low. Together, our results suggest that body size may have limited use in predicting trophic position of some biota in temperate freshwater lakes.

Linking secondary structure of individual size distribution with nonlinear size–trophic level relationship in food webs

“…Here, we focus on the nonlinearity of size-TL relationships as a critical determinant of the secondary structure of ISD. In the generalized MTE model, we assume trophic level as a nonlinear function of body size, TL ¼ s(log M ), approximated by an mth-order polynomial, s(log M ) ¼ P m i¼0 b i log i M. This assumption is motivated by empirical observations (Barnes et al 2010, Persaud et al 2012). In addition, the polynomial assumption provides the flexibility to model the potential omnivory occurring somewhere in a size-based food web.…”

“…With the two baselines, the averaged TL of each size fraction can be calculated. The TL of each size fraction was calculated from the weighted average of TLs with respect to each baseline, which are weighted by the relative contribution of each baseline to the size fractions in question by the twosource mixing model (Vander Zanden and Rasmussen 2001), assuming the trophic enrichment factors of the stable isotope d 13 C as e C ¼ 1% (Post 2002) and d 15 N as e N ¼ 2.35% for freshwater plankton (Persaud et al 2012). Here, the TL of each size fraction was estimated for each individual sampling date.…”

“…For aquatic microbial food webs, small protists grazing on bacterivorous flagellates are secondary consumers that are likely to occupy higher trophic levels than large, herbivorous zooplankton (primary consumers) (Azam et al 1983). Actually, omnivory and microbial interactions also can be found in other types of food webs (Coll andGuershon 2002, Bonkowski 2004), and may explain many naturally occurring examples of nonlinear size-TL relationships (Layman et al 2005, Hechinger et al 2011, Persaud et al 2012. Indeed, some mechanistic dynamic models incorporating omnivory can generate diverse secondary structure in ISD (Fuchs andFranks 2010, Banas 2011).…”

Turnover and fractionation of nitrogen stable isotope in tissues of grass carp Ctenopharyngodon idellus

“…), is widely used for assessing the feeding ecology of organisms (Guelinckx et al 2007, Overmyer et al 2008) and the trophic interactions in food webs (Murchie & Power 2004, Persaud et al 2012. In contrast with traditional gut content analysis, which captures a snapshot of consumer food sources recently consumed (Jones & Waldron 2003), stable isotope analysis (SIA) as a dietary tracer provides an integrated estimate of long-term food utilization (Gao et al 2006(Gao et al , 2011 and reflects the isotopic signature of diet sources with a fractionation factor by analyzing the entire organism or a specific tissue (Phillips & Gregg 2003).…”

Zooplankton predators and prey: body size and stable isotope to investigate the pelagic food web in a deep lake (Lake Iseo, Northern Italy)

“…Carbon and nitrogen stable isotope analyses are increasingly used to trace conveyance of carbon sources through lake food webs and identifying zooplankton taxa roles and relationships Mazumder, 2005, 2006;Persaud et al, 2012). A major concern is that I cannot address prey available for a given predator, as I do not actually know all actors in the scene of the lake theatre, nor I know all possible roles they might play (Hutchinson 1965).…”