Animal parasites can also alter ecosystem energetics through a variety of indirect mechanisms including population reduction of herbivores that control primary production (Sinclair 1979), alteration of secondary production through reduced fecundity or growth of hosts (Hurd 2001), behavioural modification of habitat-forming species leading to changes in local production (Mouritsen & Poulin 2005, 2006), and manipulation of host behaviour resulting in increased energetic subsidies from terrestrial to aquatic ecosystems (Sato et al. For example, plant foliar fungal pathogens can exert strong top-down control on primary production, sometimes surpassing the impacts of herbivores in certain grassland ecosystems (Mitchell 2003). These findings suggest that parasites can play important roles in trophic interactions and energy flow and several studies have shown that parasites can alter primary and secondary production through population-level effects on their hosts. 2008) and comprise a large component of biodiversity (Hudson, Dobson & Lafferty 2006). Despite being cryptic and small in size, parasites are involved in a disproportionately high number of species interactions in some ecosystems (Lafferty, Dobson & Kuris 2006 Lafferty et al. The rich literature on freshwater ecosystem energetics has largely omitted the roles of infectious agents, despite the increasingly recognized importance of parasites in ecosystem structure and function (Loreau, Roy & Tilman 2005 Tompkins et al. Lindeman 1942 Odum 1957) and most methods of quantifying secondary production have been pioneered with aquatic macroinvertebrates (Benke 1984 Downing & Rigler 1984).
Throughout the development of the field of production ecology, freshwater lakes, ponds and streams have proven especially useful as model systems (e.g. Hall, Wallace & Eggert 2000) and as metrics of population success (Benke & Huryn 2010). ratios of production to biomass Waters 1977), in constructing food webs with quantified interaction strengths (e.g. More recently, biomass and production measurements have proven useful in studies of biomass turnover (i.e. The early use of such methods led to fundamental ecological concepts including the designation of trophic levels, the corresponding decrease in trophic-level biomass with increasing trophic position, and the efficiency of energy transfer between consumers and resources (Elton 1927 Lindeman 1942). Quantifying the biomass and production of populations, communities and entire trophic levels has been a central tool in understanding how energy moves through ecosystems (Odum 1971).
Our results suggest that a significant amount of energy moves through trematode parasites in freshwater pond ecosystems, and that their contributions to ecosystem energetics may exceed those of many free-living taxa known to play key roles in structuring aquatic communities.Given that infected snails release cercariae for 3–4 months a year, the pond trematode communities produced an average of 153 mg m −2 yr −1 of dry cercarial biomass (range = 70–220 mg m −2 yr −1). On average, each trematode taxon produced between free-swimming larvae (cercariae) infected snail −1 24 h −1 in mid-summer.Mid-summer trematode dry biomass averaged 0♱0 g m −2, which was equal to or greater than that of the most abundant insect orders (coleoptera = 0♱0 g m −2, odonata = 0♰8 g m −2, hemiptera = 0♰7 g m −2 and ephemeroptera = 0♰3 g m −2). Between 18% and 33% of the combined host and parasite biomass within each infected snail consisted of larval trematode tissue, which collectively accounted for 87% of the total trematode biomass within the three ponds. An average of 33♵% of mature snails were infected with one of six trematode taxa, amounting to a density of 13 infected snails m −2 of pond substrate. Snails and amphibian larvae, which are both important intermediate trematode hosts, dominated the dry biomass of free-living organisms across ponds (snails = 3♲ g m −2 amphibians = 3♱ g m −2).Using quantitative surveys and dissections of over 1600 aquatic invertebrate and amphibian hosts, we calculated the ecosystem-level biomass and productivity of trematode parasites alongside the biomass of free-living aquatic organisms in three freshwater ponds in California, USA.This omission is particularly important considering the roles that parasites sometimes play in shaping community structure and ecosystem processes. Despite the central role of such studies in the advancement of freshwater ecology, there has been little effort to incorporate parasites into studies of freshwater energy flow.
Ecologists often measure the biomass and productivity of organisms to understand the importance of populations and communities in the flow of energy through ecosystems.
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