Parasites are thought to play a role in ecosystem energetics, in part because some ecosystems harbor a substantial amount of parasite biomass. Nevertheless, the extent to which parasite biomass accurately reflects the flow of energy from hosts to parasites, and the linkages between their energetics, remain unclear. Here, we estimate parasite community energetics at the host and ecosystem-level and test predictions for parasite energetics using the metabolic theory of ecology. Across 27 host species, parasite community abundance declines with average individual parasite energy use R_p as R_p^-0.50 and increases with host metabolic rate R_h as R_h ^0.63, which is inconsistent with metabolic theory. We next test whether the fraction of host energy that is allocated to parasitism is invariant across hosts. Our empirical analysis demonstrates that 85% of the variation in parasite community energy use can be explained by differences in host metabolic rate. However, parasite community energy use increases allometrically with host metabolic rate   as   suggesting that the fraction of host energy used by parasites declines with host metabolic rate. At the ecosystem-level, we show that the energy flowing through parasite communities scales allometrically with the total rate of energy use by their fish hosts across three ecosystems. Importantly, directly examining energy flux revealed variation in parasite energy use among ecosystems that was not apparent when examining differences in biomass. Taken together, these results establish strong empirical links between host and parasite energetics, but our findings often did not align with predictions based on metabolic theory.

ReadMe.txt file for data deposited for:
Host energetics explain variation in parasite productivity across hosts and ecosystems

Four datasets are providing as .csv files.

Data S1. 'DataS1.parasite_community_abundance_data'
This is a .csv file containing data pertaining to Figure 1.
In Figure 1 plotted are the partial residuals of the linear model: np ~ avg_alpha + mh_alph_no_temp
Note. Data S1 is filtered by absolute maximum community abundance; see Table S2 for comparison of model coeffs.  

Data S2. 'DataS2.parasite_community_flux_data'
This is a .csv file containing data pertaining to Figure 2.
In Figure 2 plotted is parasite_flux ~ mh_alpha
Note. Data S2 is filtered by absolute maximum community flux; see Table S3 for comparison of model coeffs.   

Metadata for Data files S1 and S2:
Column_headers.

host_species: genus and species of host taxa
code: unique identifier of host individual used in the analysis
parasite_flux:  unit watts; temperature corrected parasite community flux following equation 6 in the main text; parasite flux = [(a*parasite body mass (kg) ^b)* exp((E_parasite/0.0000862)*(-((Temp_O+273.15)^-1) + ((Temp+273.15)^-1))))] * parasite abundance) and summed across all parasite species, where a = phylum specific normalization constant from table 1 in maint text and b = phylum specific scaling exponenet from table 1.  
mh_alpha: unit watts; temperature corrected host metabolic rate following equation 5 in the maint text; host metabolic rate = (a * host body mass (kg) ^ b) * exp((E_host/0.0000862)*(-((Temp_O+273.15)^-1) + ((Temp+273.15)^-1))))
mh_alpha_no_temp: unit watts; host metabolic rate following equation 5 in the maint text; host metabolic rate = (a * host body mass (kg) ^ b)
mh: units grams; host body mass
np: total parasite abundance, which is all parasite individuals within a host
n: number of hosts dissected; using a min. of 15 individuals per host species
avg_alpha: unit watts; mean energy usage within a parasite community see main text for calculation (note this is not temp corrected)
host_taxon: host taxonomic group, pertains to metabolic scaling parameters in table 1
Temp_O: units celsius; environmental temperature during collection period (notes needs to transforemd to kelvin for temperature correction)
Data_source: where the data came from, new data= unpublished data first used in this manuscript

Data S3. 'DataS3.energy_flux_ecosystem'
This is a .csv file containing data pertaining to figure 3.
In Figure 3A plotted are log_parasite_flux ~ log _host_flux + river
In Figure 3B plotted are log_parasite_biomass ~ log_host_biomass +river

Metadata for Data file S3.:
Column_headers.

river: name of river ecosystem; Passaic, Raritan, Mullica
season: seaon fall, winter, spring, summer
plot: site within river ecosystem
log_parasite_flux: units watts/m^2; log10 transformed parasite community flux within a sample
log_host_flux: units watts/m^2; log10 transformed host community flux within a sample
log_parasite_biomass: units g/m^2; log10 transformed parasite biomass density within a sample
log_host_biomass: units g/m^2; log10 transformed host biomass density within a sample

Data S4. 'DataS4.platyhelminthes_scaling'
This is a .csv file containing data used to estimate platyhelminthe metabolic scaling parameters given in Table 1, further details are provided in Supplmental materials Appendix II.

Metadata for Data file S4:
Column_headers.

species: parasite species; genus species
stage: parasite lifecycle stage; adult, larvae, sporocyst, redia
Temperature C: temperature at which metabolic rate was taken in degrees celsius
Body mass in original units: body mass of parasite in orignal units from study
Mass original units: units of mass  in study
Mean Respiration Rate in original units: metabolic rate in orignal units from study
respiration_units: units of metabolic rate in study
Notes on conversion: all conversions used
ln(body mass) (kg): units kg; natural log transformed body mass in wet weight
ln(metabolic rate) (Watts): units watts;  natural log transformed metabolic rate
Source: citation of study
Host type: host used in the study given as genus species/'free-living' indicates free living larval stage used