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1. Competition shapes individual foraging and survival in a desert rodent ensemble

   https://doi.org/10.1111/1365-2656.13583  

   Manlick, Philip J.; Maldonado, Karin; Newsome, Seth D. (September 2021, Journal of Animal Ecology)

   Abstract Intraspecific variation, including individual diet variation, can structure populations and communities, but the causes and consequences of individual foraging strategies are often unclear.Interactions between competition and resources are thought to dictate foraging strategies (e.g. specialization vs. generalization), but classical paradigms such as optimal foraging and niche theory offer contrasting predictions for individual consumers. Furthermore, both paradigms assume that individual foraging strategies maximize fitness, yet this prediction is rarely tested.We used repeated stable isotope measurements (δ¹³C, δ¹⁵N;N = 3,509) and 6 years of capture–mark–recapture data to quantify the relationship between environmental variation, individual foraging and consumer fitness among four species of desert rodents. We tested the relative effects of intraspecific competition, interspecific competition, resource abundance and resource diversity on the foraging strategies of 349 individual animals, and then quantified apparent survival as function of individual foraging strategies.Consistent with niche theory, individuals contracted their trophic niches and increased foraging specialization in response to both intraspecific and interspecific competition, but this effect was offset by resource availability and individuals generalized when plant biomass was high. Nevertheless, individual specialists obtained no apparent fitness benefit from trophic niche contractions as the most specialized individuals exhibited a 10% reduction in monthly survival compared to the most generalized individuals. Ultimately, this resulted in annual survival probabilities nearly 4× higher for generalists compared to specialists.These results indicate that competition is the proximate driver of individual foraging strategies, and that diet‐mediated fitness variation regulates population and community dynamics in stochastic resource environments. Furthermore, our findings show dietary generalism is a fitness maximizing strategy, suggesting that plastic foraging strategies may play a key role in species' ability to cope with environmental change. 

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2. Heterochronic Shifts Mediate Ecomorphological Convergence in Skull Shape of Microcephalic Sea Snakes

   https://doi.org/10.1093/icb/icz033  

   Sherratt, Emma; Sanders, Kate L; Watson, Amy; Hutchinson, Mark N; Lee, Michael S; Palci, Alessandro (May 2019, Integrative and Comparative Biology)

   Abstract Morphological variation among the viviparous sea snakes (Hydrophiinae), a clade of fully aquatic elapid snakes, includes an extreme “microcephalic” ecomorph that has a very small head atop a narrow forebody, while the hind body is much thicker (up to three times the forebody girth). Previous research has demonstrated that this morphology has evolved at least nine times as a consequence of dietary specialization on burrowing eels, and has also examined morphological changes to the vertebral column underlying this body shape. The question addressed in this study is what happens to the skull during this extreme evolutionary change? Here we use X-ray micro-computed tomography and geometric morphometric methods to characterize cranial shape variation in 30 species of sea snakes. We investigate ontogenetic and evolutionary patterns of cranial shape diversity to understand whether cranial shape is predicted by dietary specialization, and examine whether cranial shape of microcephalic species may be a result of heterochronic processes. We show that the diminutive cranial size of microcephalic species has a convergent shape that is correlated with trophic specialization to burrowing prey. Furthermore, their cranial shape is predictable for their size and very similar to that of juvenile individuals of closely related but non-microcephalic sea snakes. Our findings suggest that heterochronic changes (resulting in pedomorphosis) have driven cranial shape convergence in response to dietary specializations in sea snakes. 

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3. Invasive species invoke a lifetime of trophic change in native stream fishes

   https://doi.org/10.1002/ecs2.70304  

   Diallo, Jessica O; Olden, Julian D (June 2025, Ecosphere)

   Abstract Trophic interactions operate across the lifetime of an individual organism, yet our understanding of these processes is largely limited to a single life stage or moment in time. Management and conservation implications of this knowledge gap are particularly important, given the mounting number, spread, and ecological impacts of invasive species. Biotracers, such as carbon and nitrogen stable isotopes of animal muscle, are commonly used to characterize the trophic ecology of an individual but fail to capture intraindividual variation and ontogenetic dietary shifts. However, recent work suggests that eye lenses may facilitate the reconstruction of individual lifetime trophic trajectories for fishes, including the chronology of past trophic positions of and carbon flow to consumers. By combining stable isotope analysis of fish eye lens tissue with aging techniques (otolith growth measurements), this study is the first to ask how the lifetime trophic niches of individuals vary within different community contexts. The results provide evidence for asymmetric competition causing differing trajectories in lifetime trophic niches for native and nonnative fishes along an invasion gradient in Burro Creek, Arizona, USA. Native roundtail chub, Sonora sucker, and desert sucker all displayed a coordinated displacement of lifetime trophic trajectories to a lower trophic level and reliance on aquatic, rather than terrestrial, resources as indicated by a shift to lower δ¹³C and δ¹⁵N in mixed, relative to native‐only, communities. By contrast, the trophic trajectories of nonnative green sunfish and bullhead species remained consistent between native and nonnative dominated communities. The presence of nonnative species led to a significantly greater decrease in δ¹³C through ontogeny for roundtail chub, a species of conservation concern in Arizona. These results demonstrate the prolonged trophic impact of nonnative fishes on native fishes beyond a single life stage. Displacement of ontogenetic dietary shifts by native fishes through interactions with nonnative species may lead to reduced fish growth and fitness, with implications at the population and ecosystem levels. Stable isotope analysis of fish eye lens tissue offers new opportunities to study the lifetime chronology of individual feeding habits and allows for exploration of the impacts of invasive species and environmental change throughout ontogeny. 

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4. The influence of biopsy site and pregnancy on stable isotope ratios in humpback whale skin

   https://doi.org/10.1002/rcm.9746  

   Fraleigh, Devin_C; Pallin, Logan_J; Friedlaender, Ari_S; Barlow, Jay; Henry, Annette_E; Waples, Danielle_M; Oglesby, Teris; Fleming, Alyson_H (April 2024, Rapid Communications in Mass Spectrometry)

   Abstract RationaleStable isotope analysis (SIA) of free‐swimming mysticetes using biopsies is often limited in sample size and uses only one sample per individual, failing to capture both intra‐individual variability and the influence of demographic and physiological factors on isotope ratios. MethodsWe applied SIA of δ¹³C and δ¹⁵N to humpback whale (Megaptera novaeangliae) biopsies taken during the foraging season along the western Antarctic Peninsula to quantify intra‐individual variation from repeatedly sampled individuals, as well as to determine the effect of biopsy collection site, sex, and pregnancy on isotope ratios. ResultsThere was substantial variability in δ¹³C from multiple biopsies taken from the same individuals, though δ¹⁵N was much more consistent. Side of the body (left versus right) and biopsy location (dorsal, anterior, ventral, and posterior) did marginally affect the isotopic composition of δ¹⁵N but not δ¹³C. Pregnancy had a significant effect on both δ¹³C and δ¹⁵N, where pregnant females were depleted in both when compared to non‐pregnant females and males. ConclusionsThese results indicate that isotopic signatures are influenced by multiple endogenous and exogenous factors and emphasize value in accounting for intra‐individual variability and pregnancy status within a sampled population. Placed within an ecological context, the endogenous variability in δ¹³C observed here may be informative for future isotopic analyses. 

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5. Contracting eastern African C4 grasslands during the extinction of Paranthropus boisei

   https://doi.org/10.1038/s41598-021-86642-z  

   Quinn, Rhonda L.; Lepre, Christopher J. (March 2021, Scientific Reports)

   Abstract The extinction of theParanthropus boiseiestimated to just before 1 Ma occurred when C₄grasslands dominated landscapes of the Eastern African Rift System (EARS).P. boiseihas been characterized as an herbivorous C₄specialist, and paradoxically, its demise coincided with habitats favorable to its dietary ecology. Here we report new pedogenic carbonate stable carbon (δ¹³C_PC) and oxygen (δ¹⁸O_PC) values (nodules = 53, analyses = 95) from an under-sampled interval (1.4–0.7 Ma) in the Turkana Basin (Kenya), one of the most fossiliferous locales ofP. boisei. We combined our new results with published δ¹³C_PCvalues from the EARS dated to 3–0 Ma, conducted time-series analysis of woody cover (ƒ_WC), and compared the EARS ƒ_WCtrends to regional and global paleo-environmental and -climatic datasets. Our results demonstrate that the long-term rise of C₄grasslands was punctuated by a transient but significant increase in C₃vegetation and warmer temperatures, coincident with the Mid-Pleistocene Transition (1.3–0.7 Ma) and implicating a short-term rise inpCO₂. The contraction of C₄grasslands escalated dietary competition amongst the abundant C₄-feeders, likely influencingP. boisei’s demise. 

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