Biology subjects

Hall, R. O.

Publications and source records attributed to Hall, R. O..

3 recordsLinked to original sources

bioRxiv2023

Models of underlying autotrophic biomass dynamics fit to daily river ecosystem productivity estimates improve understanding of ecosystem disturbance and resilience

Directly observing autotrophic biomass at ecologically relevant frequencies is difficult in many ecosystems, hampering our ability to predict productivity through time. Since disturbances can impart distinct reductions in river productivity through time by modifying underlying standing stocks of biomass, mechanistic models fit to productivity time series can infer underlying biomass dynamics. We incorporated biomass dynamics into a river ecosystem productivity model for six rivers to identify disturbance flow thresholds and understand the resilience of primary producers. The magnitude of flood necessary to disturb biomass and thereby reduce ecosystem productivity was consistently lower than the more commonly used disturbance flow threshold of the flood magnitude necessary to mobilize river bed sediment. The estimated daily maximum percent increase in biomass (a proxy for resilience) ranged from 5% to 42% across rivers. Our latent biomass model improves understanding of disturbance thresholds and recovery patterns of autotrophic biomass within river ecosystems.

ecology↗

bioRxiv2022

Exploring the mismatch between the theory and application of photosynthetic quotients in aquatic ecosystems

Estimates of primary productivity in aquatic ecosystems are commonly based on variation in O2, rather than CO2. The photosynthetic quotient (PQ) is used to convert primary production estimates from units of O2 to C. However, there is a mismatch between the theory and application of the PQ. Aquatic ecologists use PQ=1-1.4. Meanwhile, PQ estimates from the literature support PQ=0.1-4.2. Here, we describe the theory on why PQ may vary in aquatic ecosystems. We synthesize the current understanding of how processes such as NO3- assimilation and photorespiration can affect the PQ. We test these ideas with a case study of the Clark Fork River, Montana, where theory predicts that PQ could vary in space and time due to variation in environmental conditions. Finally, we highlight research needs to improve our understanding of the PQ. We suggest departing from fixed PQ values and instead use literature-based sensitivity analyses to infer C dynamics from primary production estimated using O2. Scientific Significance StatementAccurate measures of primary production in aquatic ecosystems are necessary to quantify energy availability to higher trophic levels and biological effects on global CO2 concentrations, among other reasons. However, we commonly measure primary production using O2 because it is easier, despite our motivation to measure the rate of fixed C, and then use the photosynthetic quotient (the ratio of O2 release to CO2 fixed, PQ) to convert O2 based metabolism to CO2. This study provides a summary of the current mismatch between our current knowledge and the application of PQ, highlights our current knowledge gaps, and emphasizes the need to use literature-based sensitivity analysis rather than uninformed fixed PQ values.

ecology↗

bioRxiv2021

Ecological outcomes of hybridization vary extensively in Catostomus fishes

Hybridization has been studied extensively to learn about speciation and mechanisms of reproductive isolation, but increasingly we recognize that hybridization outcomes vary geo-graphically and can depend on the environment. At the same time, hybridization can reshape biotic interactions in an ecosystem, leading to ecological shifts where hybridization occurs. Identifying how hybrid individuals function ecologically would link evolutionary outcomes of hybridization to ecological consequences, but relatively few studies have focused on ecological traits of hybrids. We described the feeding ecology of several Catostomus fish species and their hybrids by using stable isotopes ({delta}13C and{delta} 15N) as a proxy for diet and habitat use, and compared two native species, an introduced species, and three interspecific hybrid crosses. We replicated this comparison spatially, including hybrids and parental species from seven rivers in the Upper Colorado River basin where parental species co-occur and the opportunity for hybridization exists. Although relationships between native species in isotopic space varied, individual native species did not fully overlap in isotopic space in any river sampled, suggesting little overlap of resource use between these historically sympatric species. The introduced species overlapped with one or both native species in every river, suggesting similar resource use and potential for competition. Hybrids occupied intermediate, matching, or more extreme (transgressive) isotopic space relative to parental species, and were isotopically variable within and among rivers. We suggest that ecological outcomes of hybridization, like genomic outcomes of hybridization, are likely to vary across locations where a pair of species hybridizes. This variation implies that hybridization might have large unpredictable, idiosyncratic ecological effects on fish assemblages where hybrids occur. Although we found little evidence that hybrids are at a disadvantage ecologically--there were no significant declines in body condition relative to parental species--it is nevertheless possible that abiotic or biotic attributes of a river might constrain the range of interspecific hybrids that are successful, thus contributing to variation in hybridization outcomes across rivers.

evolutionary biology↗