Variable and complex food web structures revealed by exploring missing trophic links between birds and biofilm

Abstract

Food webs are comprised of a network of trophic interactions and are essential to elucidating ecosystem processes and functions. However, the presence of unknown, but critical networks hampers understanding of complex and dynamic food webs in nature. Here, we empirically demonstrate a missing link, both critical and variable, by revealing that direct predator-prey relationships between shorebirds and biofilm are widespread and mediated by multiple ecological and evolutionary determinants. Food source mixing models and energy budget estimates indicate that the strength of the missing linkage is dependent on predator traits (body mass and foraging action rate) and the environment that determines food density. Morphological analyses, showing that smaller bodied species possess more developed feeding apparatus to consume biofilm, suggest that the linkage is also phylogenetically dependent and affords a compelling re-interpretation of niche differentiation. We contend that exploring missing links is a necessity for revealing true network structure and dynamics.

To What Extent Do Food Preferences Explain the Trophic Position of Heterotrophic and Mixotrophic Microbial Consumers in a Sphagnum Peatland?

“…Body size is thus a fundamental indicator of trophic level in food webs because it places constraints on many biological variables, including crucial foraging traits (energy content of resources, handling times, attack rates, and prey density) [57][58][59][60]. However, a strong relationship between body size (here, testate amoebae shell length or diameter) and TP cannot be found for consumers that exploit a wide range of prey body sizes [7,59], as shown here with H. papilio and N. tincta. Nevertheless, we found that the size of shell aperture and biovolume were inversely proportional to the TP of testate amoebae in the microbial network, while usually these morphological traits are considered as indicators of high trophic level [12,25,27].…”

“…Microbial communities are composed of numerous (and often poorly described or altogether unknown) species that can form complex food webs with numerous feeding links. Discovering the structure of these food webs is important because they may affect processes occurring at the population, community, and ecosystem levels [7]. The true trophic position (TP) and diversity in trophic roles of different microbial species and/or species group of different species were, until recently, all but impossible to determine.…”

“…Identifying how and to what extent these webs are structured is necessary if we hope to move beyond a "black box" approach and toward a more mechanistic understanding of the ecosystem processes and functions that they drive [2][3][4][5][6]. However, the presence of incompletely described feeding relationships hampers our understanding of complex and dynamic food webs in nature [7]. A clear example is the scarcity of existing data on microbial food webs, which, for practical reasons, are often limited to experimental studies using a very limited number of taxa and often in combinations that do not reflect any natural system [8][9][10][11].…”

Diet-tissue Stable Isotopic Fractionation of Tropical Sea Cucumber, Holothuria scabra

“…Fecal stable isotopes are widely used in diet studies in mammals and birds 6,23 , since fractionation is not considered to occur during food assimilation 14 . However, a recent study 7 indicated that while fecal δ 13 C is a reliable proxy for diet in mammals, δ 15 N is altered by digestion for unidentified reasons contingent on diet composition.…”

Shorebirds along the Yellow Sea coast of China face an uncertain future—a review of threats

“…S29 in Supplementary material) for use in the production of 'fish' feeds (Y. Chen and D. S. Melville, unpublished data), which are part of a growing market for probiotics in aquaculture (Qi et al 2009). The extent of such harvesting and the potential implications for coastal ecology are not known but are potentially significant (Kuwae et al 2012).…”