Subsidies of long‐chain polyunsaturated fatty acids from aquatic to terrestrial environments via amphibian emergence

Abstract

Resource subsidies across aquatic‐terrestrial boundaries can alter predator distribution and biomass and elicit trophic cascades. Most studies have focused on the size of cross‐boundary fluxes, but the impact of a subsidy is also mediated by quality and relative abundance of similar resources in the recipient habitat. Long‐chain polyunsaturated fatty acids (LC‐PUFAs) are necessary for proper physiological function, are unevenly distributed across the landscape, and animals differ greatly in their ability to synthesize them from biochemical precursors, which creates the potential for limitation and increases their possible importance as a subsidy. We examined whole‐body LC‐PUFA content and export in eight species of emerging amphibian metamorphs across eight temporary ponds in a wetland complex. We found that whole‐body content and export of LC‐PUFAs varied across species, but were generally within the ranges of other amphibian studies and several freshwater fish and aquatic insects. Anurans exported higher amounts of LC‐PUFAs than salamanders, largely due to the higher emergence biomass of anurans. As such, the export of LC‐PUFAs closely mirrored the biomass export for each species. Larger ponds exported higher amounts of eicosapentaenoic acid and docosahexaenoic acid, but some smaller ponds exported more per unit wetted area, indicating the potential importance of small ponds at a landscape scale. Given their vital physiological roles, the uneven distribution of aquatic‐origin LC‐PUFAs could have far reaching effects on terrestrial predators.

Cross-Ecosystem Linkages: Transfer of Polyunsaturated Fatty Acids From Streams to Riparian Spiders via Emergent Insects

“…In fact, aquatic ecosystems have been suggested to be the principal source of LC-PUFAs and a net transfer from aquatic to terrestrial systems has been recognized (Moyo et al, 2017). Emergent aquatic insects represent an important vector for LC-PUFA transfer across the ecosystem boundary to terrestrial consumers (Gladyshev et al, 2013;Martin-Creuzburg et al, 2017;Popova et al, 2017;Fritz et al, 2019) and some riparian predators might have specialized on exploiting this high-quality prey. Indeed, low dietary LC-PUFA provision can cause impaired development or lower breeding success of certain species (e.g., tree swallows), even with an abundance of other food sources (Twining et al, 2016a(Twining et al, , 2018.…”

Bottom‐up effects of fungicides on tadpoles of the European common frog (Rana temporaria)

“…The retarded growth in the leaching treatment seems mainly related to food of low quality (Table 2), more specifically the lack of dietary provisioning of highly unsaturated fatty acids such as ARA, EPA, and DHA. Since tadpoles sampled after 49 days from all treatments show, however, no difference in the concentration of these three fatty acids, despite partly substantial deviations in dietary concentrations, it may be assumed that tadpoles are capable of converting ALA to EPA and DHA as well as LIN to ARA-a process that is suggested to be rare in organisms (Fritz et al, 2019), inefficient and thus energetically costly (Twining et al, 2016).…”

Reciprocal subsidies between temporary ponds and riparian forests

“…Amphibian emergence across ponds was generally larger than aquatic insect emergence which has been demonstrated to be important as prey in terrestrial food webs. Amphibian emergence also represents a high-quality subsidy of both elemental nutrients and essential complex nutrients to the terrestrial food web which can have fitness consequences for terrestrial predators (Fritz et al 2017(Fritz et al , 2019Fritz and Whiles 2018). Furthermore, this subsidy of predators may elicit strong trophic cascades, especially in spatially heterogenous complexes of ponds and influence nutrient cycling (Beard et al 2002;McCoy et al 2009).…”

“…Conversely, energy accrued in the terrestrial environment by adults is transferred across habitat boundaries when eggs are deposited in the aquatic environment (Regester and Whiles 2006; Reinhardt et al 2013; Fritz and Whiles 2018). This is especially true for amphibians, as their eggs can constitute a substantial flux of material and nutrients (Capps et al 2015; Fritz and Whiles 2018; Fritz et al 2019), and the emergence of postmetamorphic amphibians can constitute a substantial prey subsidy to surrounding forest (Pechmann et al 1989; Gibbons et al 2006). Aquatic insect emergence can also constitute a considerable energy subsidy to the surrounding terrestrial environment, and its importance to terrestrial consumers is well established ( see review in Baxter et al 2005).…”