DOI: 10.5061/dryad.d5f6h00
title: Data from: Threshold elemental ratios and the temperature dependence of herbivory in fishes

description: 1. Herbivorous ectothermic vertebrates are more diverse and abundant at
 lower latitudes. While thermal constraints may drive this pattern, its
 underlying cause remains unclear. We hypothesized that this constraint
 stems from an inability to meet the elevated phosphorus demands of bony
 vertebrates feeding on P-poor plant material at cooler temperatures
 because low gross growth efficiency at warmer temperatures facilitates
 higher P ingestion rates. We predicted that dietary carbon:phosphorus
 (C:P) should exceed the threshold elemental ratio between carbon and
 P-limited growth (TERC:P) for herbivores feeding at cooler temperatures,
 thereby limiting the range of herbivorous ectothermic vertebrates facing
 P-limited growth. 2. We tested this hypothesis using the Andean
 suckermouth catfishes Astroblepus and Chaetostoma. Astroblepus are
 invertivores that inhabit relatively cool, high-elevation, streams while
 Chaetostoma are grazers that inhabit relatively warm, low-elevation
 streams. We calculated TERC:P for each genus across its elevational range
 and compared these values to measured values of food quality over an
 elevational gradient in the Andes. We also broadly summarized measurements
 of TERC:P across diverse groups of fishes. 3. Supporting our hypothesis,
 we found that dietary C:P was predicted to exceed the TERC:P for the
 grazer Chaetostoma near the highest elevation where this genus has been
 recorded. Conversely, the TERC:P for the invertivore Astroblepus was
 consistently higher than that of Chaetostoma and thus its dietary C:P
 never approached the TERC:P. We found that, among all fishes, omnivores
 had higher average TERC:P than invertivores, and TERC:P did not vary with
 temperature. 4. Our results suggest that, at least for Andean suckermouth
 catfishes, cool temperatures constrain herbivory at higher elevations.
 Increased gross growth efficiency at cooler temperatures evidently
 restricts the ability of P-limited consumers to meet P demand. However,
 our survey of fish TERC:P estimates suggests that some fishes are able to
 circumvent this constraint through behavioral and life history adaptations
 that reduce P demand or increase P use efficiency. 5. The physiological
 tradeoffs underlying these functional shifts reveal that geographic
 dietary patterns can be predicted by stoichiometric theory, but variation
 in food quality and consumer traits that reduce P demand and/or increase P
 efficiency can create exceptions to these patterns.
description: Astroblepus and
 Chaetostoma collection recordsSearch parameters used
 in FishNet2 to obtain geographic distribution data which were used in
 analyzing elevational range and for parameterizing TER models. We present
 these search parameters rather than the full datasets due to data sharing
 restrictions in the FishNet2 user agreement.DRYAD fishnet2
 parameters.docxAstroblepus and
 Chaetostoma body stoichiometry dataBody stoichiometry data
 collected for Astroblepus and Chaetostoma in this study, including
 locality information and corresponding museum catalog numbers for voucher
 specimens when applicable.Table S1-Astroblepus and
 Chaetostoma-all specimens.xlsx