Prey size diversity hinders biomass trophic transfer and predator size diversity promotes it in planktonic communities

Abstract

Body size exerts multiple effects on plankton food-web interactions. However, the influence of size structure on trophic transfer remains poorly quantified in the field. Here, we examine how the size diversity of prey (nano-microplankton) and predators (mesozooplankton) influence trophic transfer efficiency (using biomass ratio as a proxy) in natural marine ecosystems. Our results support previous studies on single trophic levels: transfer efficiency decreases with increasing prey size diversity and is enhanced with greater predator size diversity. We further show that communities with low nano-microplankton size diversity and high mesozooplankton size diversity tend to occur in warmer environments with low nutrient concentrations, thus promoting trophic transfer to higher trophic levels in those conditions. Moreover, we reveal an interactive effect of predator and prey size diversities: the positive effect of predator size diversity becomes influential when prey size diversity is high. Mechanistically, the negative effect of prey size diversity on trophic transfer may be explained by unicellular size-based metabolic constraints as well as trade-offs between growth and predation avoidance with size, whereas increasing predator size diversity may enhance diet niche partitioning and thus promote trophic transfer. These findings provide insights into size-based theories of ecosystem functioning, with implications for ecosystem predictive models.

Modified FlowCAM procedure for quantifying size distribution of zooplankton with sample recycling capacity

“…In addition, body size has been demonstrated to play an important role in mediating predator-prey interactions [1–3]. In fact, size has been designated as the “meta-trait” integrating several plankton functional traits into a single measurement [4, 5].…”

“…In fact, size has been designated as the “meta-trait” integrating several plankton functional traits into a single measurement [4, 5]. Since the pioneering works of Sheldon and colleagues [6, 7], size distribution has also figured prominently in the studies of plankton community structure and dynamics [3, 8–10]. …”

“…The ZooScan is suitable for imaging particles ranging in size from 200 μm to several centimetres [14] and the FlowCAM is preferable for analysing smaller plankton. In practice, scientists have used the FlowCAM to obtain cell counts [15, 16], size structure [3, 9, 13, 17], and community composition [13, 18]. Nonetheless, most of the researches using the FlowCAM have been limited to unicellular plankton, namely phytoplankton and protists (even though the FlowCAM manufacturer has suggested its application for measuring zooplankton for some time [18]).…”

Size diversity and species diversity relationships in fish assemblages of Western Palearctic lakes

“…Woodward et al 2005), it might be possible to draw links between the variations in size diversity and changes in the structure and functioning of communities (Ye et al 2013, García-Comas et al 2016. For example, according to the Niche Diversification Hypothesis (Connell 1978), which suggests that systems of higher diversity could take greater advantage of the niche opportunities in an environment, a highly size-diverse community may be able to capture a greater proportion of resources relative to a less size-diverse one.…”

“…Body size has been used as a trait in several functional diversity indices, but usually it refers to just one estimate of the size of the adult per species. A simple and intuitive way to assess variation in the individual body size structure of a community is to use its size diversity (Brucet et al 2006, Quintana et al 2008, Ye et al 2013, García-Comas et al 2016. Size diversity, based on the Shannon diversity index (Pielou 1969), integrates the amplitude of the size range and evenness in the same way as the Shannon species diversity index integrates the number of species and their relative abundance.…”