Although parasites are increasingly recognized for their ecosystem roles, it is often assumed that free‐living organisms dominate animal biomass in most ecosystems and therefore provide the primary pathways for energy transfer. To examine the contributions of parasites to ecosystem energetics in freshwater streams, we quantified the standing biomass of trematodes and free‐living organisms at nine sites in three streams in western Oregon, USA. We then compared the rates of biomass flow from snails The trematode parasite community had the fifth highest dry biomass density among stream organisms (0.40 g/m2) and exceeded the combined biomass of aquatic insects. Only host snails (3.88 g/m2), sculpin (1.11 g/m2), trout (0.73 g/m2) and crayfish (0.43 g/m2) had a greater biomass. The parasite ‘extended phenotype’, consisting of trematode plus castrated host biomass, exceeded the individual biomass of every taxonomic group other than snails. The substantial parasite biomass stemmed from the high snail density and infection prevalence, and the large proportional mass of infected hosts that consisted of trematode tissue ( Estimates of yearly biomass transfer from snails into trematodes were slightly higher than the combined estimate of snail biomass transfer into the three vertebrate predators. Pacific giant salamanders accounted for 90% of the snail biomass consumed by predators. These results demonstrate that trematode parasites play underappreciated roles in the ecosystem energetics of some freshwater streams.
Agricultural expansion is predicted to increase agrochemical use two to fivefold by 2050 to meet food demand. Experimental evidence suggests that agrochemical pollution could increase snails that transmit schistosomiasis, a disease impacting 250 million people, yet most agrochemicals remain unexamined. Here we experimentally created >100 natural wetland communities to quantify the relative effects of fertilizer, six insecticides (chlorpyrifos, terbufos, malathion, λ‐cyhalothrin, permethrin and esfenvalerate), and six herbicides (acetochlor, alachlor, metolachlor, atrazine, propazine and simazine) on two snail genera responsible for 90% of global schistosomiasis cases. We identified four of six insecticides (terbufos, permethrin, chlorpyrifos and esfenvalerate) as high risk for increasing snail biomass by reducing snail predators. Hence, malathion and λ‐cyhalothrin might be useful for improving food production without increasing schistosomiasis. This top‐down effect of insecticides on predators was so strong that the effects of herbicides on schistosomiasis risk were masked in the presence of predators because there were so few snails. In the absence of snail predators, herbicide effects on snails were generally negative by reducing submerged vegetation Like insecticides, fertilizer had strong positive effects on snail populations. Fertilizer increased both snail habitat (submerged vegetation) and snail food (periphyton), but of these two pathways, the increases in snail habitat resulted in greater snail population growth. Total snail biomass was positively associated with both infected snail biomass and parasite production and thus human infection risk.
- PAR ID:
- 10369111
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Applied Ecology
- Volume:
- 59
- Issue:
- 3
- ISSN:
- 0021-8901
- Page Range / eLocation ID:
- p. 729-741
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Juga plicifera into trematode parasites relative to aquatic vertebrate predators (sculpin, cutthroat trout and Pacific giant salamanders).M = 31% per snail). -
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