Resource availability and ecosystem size predict food‐chain length in pond ecosystems

Abstract

Food‐chain length (FCL) in ecosystems has been studied extensively, and numerous hypotheses to predict FCL, productivity, ecosystem size, and productive space have been proposed. For example, the productivity hypothesis suggests that resource availability limits FCL, whereas the productive‐space hypothesis predicts that per‐unit‐size resource availability and ecosystem size equally limit FCL. However, previous studies have only measured total productivity to test FCL and have never tested the impact of resource availability within a system on FCL. Therefore, we estimated FCL in 15 ponds using stable isotope techniques to test the most common hypotheses for predicting FCL. We also measured total productivity, pond volume (ecosystem size), and edible microalgal carbon (resource availability) in each pond. We found that productive‐space (edible carbon+pond volume) was the best model to predict FCL, and FCL was significantly correlated with edible carbon and pond volume. However, factors such as total productivity did not directly predict FCL of the ponds. Therefore, our results suggest that both resource availability and ecosystem size predict FCL in pond ecosystems and play significant roles in maintaining longer FCLs. Furthermore, the productive‐space hypothesis appears to be particularly important for determining the FCL of ponds.

Food-chain length and adaptive foraging

“…Recent empirical studies have shown that food-chain length is positively correlated with habitat size (Spencer & Warren 1996;Post et al 2000a;Takimoto et al 2008;Doi et al 2009). Our model provides two possible explanations for these observations: one is related to changes in species richness and the other to interspecific spatial segregation.…”

“…This value can be estimated in natural ecosystems by using the stable isotope technique (Vander Zanden et al 1999;Post et al 2000a;Takimoto et al 2008;Doi et al 2009). For runs with multiple top predators and/or basal species, we used the maximum value among all combinations of top predator and basal species.…”

“…Pimm (1982) summarized four hypotheses of food-chain length: (i) food-chain length is limited by available energy and should increase with increasing resource availability (the energy limitation hypothesis; Elton 1927;Lindemann 1942;Hutchinson 1959); (ii) a longer food chain is less persistent under disturbed environments (the dynamic stability hypothesis; Pimm & Lawton 1977; but see Sterner et al 1997); (iii) optimal diet choices of individual species determine the food-chain length (the optimal foraging hypothesis; Hastings & Conrad 1979);and (iv) food-chain length is limited by the constraint that a predator should be larger than its prey (the design constraint hypothesis). In addition, empirical evidence from both aquatic (Spencer & Warren 1996;Vander Zanden et al 1999;Post et al 2000a;Doi et al 2009) and terrestrial ecosystems (Schoener 1989;Takimoto et al 2008) suggests that food-chain length is positively correlated with habitat area (Cohen & Newman 1988), raising another possible determinant of food-chain length.…”

Resource availability determines food chain length in Chinese subtropical rivers

“…Although productivity generally increases FCL (Thompson and Townsend 2005;Hoeinghaus et al 2008;Doi 2012), the effects of the magnitude of ecosystem size could positively (Post et al 2000;Takimoto et al 2008;Doi et al 2009;McHugh et al 2010;Sabo et al 2010) or neutrally (Thompson and Townsend 2005;Warfe et al 2013) influence FCL. Furthermore, the effects of disturbance on FCL are highly variable and could be positive (Calizza et al 2012), neutral (Walters and Post 2008;Warfe et al 2013), or even negative (McHugh et al 2010;Sabo et al 2010).…”

C and P in aquatic food chain: A review on C:P stoichiometry and PUFA regulation

“…Certainly, available energy as resource must set some upper limit to the number of trophic levels proportionately to the space available on which the successive top trophic levels can forage (Schoener, 1989). On verifying a productivity-space hypothesis, Doi et al (2009) demonstrated longer food chain length at high C level (as productivity) and maximum ecosystem size (space). These coupling factors would have maximum affect on food chain in river or lakes rather than ocean.…”