Seth D. Newsome

Animals influence biogeochemical processes by consuming other organisms, transferring energy from basal resources up the food chain. Energy is routed through plant, fungal and bacterial channels, and the relative importance of these pathways can shift across space and time. Variation in these pathways may be particularly pronounced in highly seasonal environments where resource availability fluctuates throughout the year. Spatiotemporal variation in the transfer of plant‐ versus microbial‐derived energy to higher trophic levels is poorly understood but can affect bottom‐up and top‐down processes. For example, seasonal shifts in herbivore versus microbivore availability (bottom‐up) may alter prey choice by generalist‐feeding predators and lead to changes in top‐down predator control on primary production and decomposition. We tested how spatiotemporal variation in primary production influences the use of different energy channels by a widely distributed generalist invertebrate predator in the Arctic tundra. We sampled wolf spiders across four sites spanning a productivity gradient in the Alaskan Arctic during peak summer and on a weekly basis at one focal site throughout the growing season. Using essential amino acid (EAA) carbon isotope (δ ¹³ C) fingerprinting, we traced the flow of plant‐, bacterial‐ and fungal‐derived EAAs to spiders and quantified the use of plant‐ versus microbe‐based energy channels between sites and across summer. Wolf spiders were associated with more plant‐ and less fungal‐derived carbon assimilation when larger or collected from sites with higher normalized difference vegetation index (NDVI). Across the growing season, spiders shifted from primarily assimilating fungal‐based resources in early summer to plant‐derived resources in late summer, aligning with seasonal increases in NDVI. These patterns demonstrate spatiotemporal variation in carbon flow through different energy channels and suggest subsequent top‐down predator effects may also vary with basal resource availability. Our findings also suggest wolf spider body size may predict whether predation indirectly influences primary production or decomposition. As climate change alters seasonality, resource dynamics and invertebrate body sizes, these insights provide a basis for predicting spatiotemporal variation in predator impacts on ecosystem processes. Finally, our work demonstrates the utility of compound‐specific stable isotope analysis for integrating ecological and biogeochemical theory through the conceptual lens of zoogeochemistry.

Resource use links ecological context to organismal performance, yet whether dietary breadth or trophic position is more closely associated with physiological state in wild birds remains unclear. We used a natural trophic gradient in a sympatric passerine assemblage to test whether trophic position and isotopic niche breadth are associated with integrated physiological phenotypes. We studied three co-occurring passerine species in central Chile spanning a trophic spectrum (granivorous, omnivorous, insectivorous). Using blood δ13C and δ15N, we quantified isotopic niche width and estimated trophic position, then compared these metrics with physiological variables measured in free-living birds (n = 60), including differential leukocyte counts, antioxidant capacity, and enzymatic markers of oxidative metabolism, glutathione-related physiology, and plasma esterase activity. Isotopic niche width differed among species but was weakly associated with physiological variation. By contrast, estimated trophic position showed stronger species-level correspondence with multivariate physiological organization. Metabolic and enzyme-based variables contributed most to interspecific physiological differentiation, whereas baseline non-enzymatic antioxidant buffering was conserved. Overall, estimated trophic position showed a stronger correspondence with coordinated physiological variation than isotopic niche breadth. These findings highlight species-level physiological differences associated with trophic position and provide a basis for broader comparative analyses of ecological and evolutionary influences on avian physiology.

1. The effective conservation of migratory animals requires knowledge of their migratory connectivity or links between breeding stopover and wintering sites [1–3]. This fundamental information is g...

The adoption of maize as a dietary staple shaped human societies. While a reliable carbohydrate-rich source, its inherent nutritional limitations posed substantial challenges. Maize is deficient in lysine, an essential amino acid crucial for maintaining balanced health. Maize-dependent diets, therefore, necessitated complementary dietary strategies. We report amino acid stable carbon isotope data from 39 directly dated humans from southern Belize [6100 to 1100 before present (B.P.)] to investigate how early populations mitigated nutritional deficiencies. Concentration-dependent mixing model results indicate that protein supplementation from maize-eating animals contributed maize-derived lysine to human diets through trophic magnification (elevated proportions of isotopically distinct nutrients in tissues from trophic transfer). Our results indicate that such strategies were in place by 6100 B.P., consistent with evidence of early maize cultivation but predating reliance by ~2000 years. Our findings highlight early coevolutionary dynamics linking maize cultivation and human-animal provisioning relationships, deepening understandings of adaptive food systems during agricultural transitions and offering insights into nutritional strategies underpinning sustainable subsistence.

Many marine animals migrate thousands of kilometers, yet the spatial extent of dietary resources acquired along these routes remains poorly understood. Ide

Dechlorane Plus (DP), a widely produced yet only recently regulated chlorinated flame retardant, poses emerging environmental concerns due to its persistence and bioaccumulation potential. Its occurrence in terrestrial avian predators, especially in the Southern Hemisphere, remains poorly documented. Here we analyzed 108 secondary feathers from Andean condors (Vultur gryphus) across a ~2,500 km latitudinal gradient in Chile for syn-DP and anti-DP isomers and stable isotopes (δ13C, δ15N). Anti-DP predominated, with concentrations approximately threefold higher in the industrialized central zone compared to austral regions, revealing a marked north–south gradient. DP levels correlated positively with δ13C and negatively with δ15N across the full dataset, but these relationships disappeared within individual zones, indicating that regional contamination patterns override finer-scale dietary signals. No age-related differences were detected, suggesting that DP levels in feathers are more strongly influenced by recent, spatially variable exposure than by long-term bioaccumulation. These findings provide the first evidence of DP in a Southern Hemisphere scavenger, highlighting the Andean condor's role as a sentinel for contaminants and underscoring the need to assess potential toxicological risks in long-lived terrestrial raptors.

Protein is the main structural and functional component of cells, making it crucial for the survival of all living organisms. Yet mammalian herbivores and omnivores often consume diets deficient in the amount of protein required for growth, homeostasis, and reproduction. To compensate, mammals likely rely on their gut microbiota to synthesize essential amino acids (AAESS), particularly during periods of dietary protein limitation. We quantified the contribution of microbially synthesized AAESS to skeletal muscle in captive, wild-derived deer mice (Peromyscus maniculatus) fed diets varying in macromolecular quantity and quality. Using amino acid carbon isotope (δ13C) analysis combined with genetic sequencing, we assessed the origin of AAESS incorporated into host muscle and identified gut microbial taxa with the genetic potential for AAESS biosynthesis. We estimate that up to 25% of host muscle AAESS were microbially derived, with greater microbial contributions in mice fed diets containing low protein or more complex macronutrients. Gut microbial populations with the genetic potential for AAESS biosynthesis were more abundant in mice with larger contributions of microbially-derived AAESS in their tissues. These results demonstrate the crucial and likely pervasive role the gut microbiome plays in host protein metabolism, especially in mammals facing seasonal or persistent dietary protein limitation.

In river food webs, the energetic coupling of nutrient‐rich “fast” autochthonous (algal) and recalcitrant “slow” allochthonous (terrestrial) resources may confer stability. Additionally, microbial biofilms may enhance the nutritional quality of allochthonous resources for macroinvertebrate consumers, potentially facilitating trophic linkages within slow energy channels. We used 16S and 18S rRNA gene sequencing and essential amino acid (AA _ESS ) carbon isotope (δ ¹³ C) analysis to characterize microbial biofilms and quantify proportional contributions of AA _ESS derived from algae, terrestrial plants, and microbes (archaea, bacteria, fungi) to macroinvertebrates across a series of mesocosm and field leaf pack experiments in the middle Rio Grande of central New Mexico, USA. In our 12‐week mesocosm experiment, leaves of native Rio Grande Cottonwood trees ( Populus deltoides wislizeni ) contributed greater mean estimated proportions of AA _ESS (0.41–0.81) to Chironomidae larvae than those of nonnative Russian Olive trees ( Elaeagnus angustifolia ; 0.18–0.50). Microbes were notable sources of AA _ESS to macroinvertebrates inhabiting native C ₄ grass (Spike Dropseed; Sporobolus contractus ) leaf packs (0.08–0.26). Our field experiment demonstrated river sediment was the main source of microbes colonizing submerged Cottonwood leaves and that allochthonous resource use varied across macroinvertebrate taxa, such that Chironomidae assimilated the highest mean estimated proportions of AA _ESS from leaves (0.36–0.65), while Ephemeroptera and Trichoptera assimilated the highest mean estimated proportions of AA _ESS from algae (0.82–0.94). Our work indicates terrestrial tree leaves are important sources of AA _ESS to Chironomidae, while algae are the dominant source of AA _ESS to other macroinvertebrates in the middle Rio Grande.

Understanding variations in the routes by which wild animals gain and lose water is challenging, and common methods require longitudinal sampling, which can be prohibitive. However, a new approach uses Δ ′ ¹⁷ O _BW ( Δ ′ ¹⁷ O of animal body water), calculated from measurements of δ ′ ¹⁷ O and δ ′ ¹⁸ O in a single sample, as a natural tracer of water flux. Δ ′ ¹⁷ O _BW is promising, but its relationship to organismal variables such as metabolic rate and water intake have not been validated. Here, we continuously measured oxygen influxes and effluxes of captive deer mice ( Peromyscus maniculatus ), and manipulated their water intake and metabolic rate. We used these oxygen flux data to predict Δ ′ ¹⁷ O _BW for the mice and compared these model predictions with Δ ′ ¹⁷ O _BW measured in blood plasma samples. As expected, Δ ′ ¹⁷ O _BW positively correlated with drinking water intake and negatively correlated with metabolic rate. All predicted Δ ′ ¹⁷ O _BW (based on measured oxygen fluxes) values differed from measured Δ ′ ¹⁷ O _BW values by Δ ′ ¹⁷ O _BW among mammals, birds and fish.