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1. Diet of a threatened endemic fox reveals variation in sandy beach resource use on California Channel Islands

   https://doi.org/10.1371/journal.pone.0258919  

   Page, Henry M.; Schamel, Juliann; Emery, Kyle A.; Schooler, Nicholas K.; Dugan, Jenifer E.; Guglielmino, Angela; Schroeder, Donna M.; Palmstrom, Linnea; Hubbard, David M.; Miller, Robert J. (October 2021, PLOS ONE)

   Hyrenbach, David (Ed.)

   The coastal zone provides foraging opportunities for insular populations of terrestrial mammals, allowing for expanded habitat use, increased dietary breadth, and locally higher population densities. We examined the use of sandy beach resources by the threatened island fox ( Urocyon littoralis ) on the California Channel Islands using scat analysis, surveys of potential prey, beach habitat attributes, and stable isotope analysis. Consumption of beach invertebrates, primarily intertidal talitrid amphipods ( Megalorchestia spp.) by island fox varied with abundance of these prey across sites. Distance-based linear modeling revealed that abundance of giant kelp ( Macrocystis pyrifera ) wrack, rather than beach physical attributes, explained the largest amount of variation in talitrid amphipod abundance and biomass across beaches. δ 13 C and δ 15 N values of fox whisker (vibrissae) segments suggested individualism in diet, with generally low δ 13 C and δ 15 N values of some foxes consistent with specializing on primarily terrestrial foods, contrasting with the higher isotope values of other individuals that suggested a sustained use of sandy beach resources, the importance of which varied over time. Abundant allochthonous marine resources on beaches, including inputs of giant kelp, may expand habitat use and diet breadth of the island fox, increasing population resilience during declines in terrestrial resources associated with climate variability and long-term climate change. 

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2. Population expansion, divergence, and persistence in Western Fence Lizards (Sceloporus occidentalis) at the northern extreme of their distributional range

   https://doi.org/10.1038/s41598-022-10233-9  

   Davis, Hayden R.; Des Roches, Simone; Anderson, Roger A.; Leaché, Adam D. (April 2022, Scientific Reports)

   Abstract Population dynamics within species at the edge of their distributional range, including the formation of genetic structure during range expansion, are difficult to study when they have had limited time to evolve. Western Fence Lizards (Sceloporus occidentalis) have a patchy distribution at the northern edge of their range around the Puget Sound, Washington, where they almost exclusively occur on imperiled coastal habitats. The entire region was covered by Pleistocene glaciation as recently as 16,000 years ago, suggesting that populations must have colonized these habitats relatively recently. We tested for population differentiation across this landscape using genome-wide SNPs and morphological data. A time-calibrated species tree supports the hypothesis of a post-glacial establishment and subsequent population expansion into the region. Despite a strong signal for fine-scale population genetic structure across the Puget Sound with as many as 8–10 distinct subpopulations supported by the SNP data, there is minimal evidence for morphological differentiation at this same spatiotemporal scale. Historical demographic analyses suggest that populations expanded and diverged across the region as the Cordilleran Ice Sheet receded. Population isolation, lack of dispersal corridors, and strict habitat requirements are the key drivers of population divergence in this system. These same factors may prove detrimental to the future persistence of populations as they cope with increasing shoreline development associated with urbanization. 

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3. Bioaccumulation of methylmercury in a marine copepod

   https://doi.org/10.1002/etc.3660  

   Lee, Cheng‐Shiuan; Fisher, Nicholas_S (December 2016, Environmental Toxicology and Chemistry)

   Abstract Methylmercury (MeHg) is known to biomagnify in marine food chains, resulting in higher concentrations in upper trophic level animals than their prey. To better understand how marine copepods, an important intermediate between phytoplankton and forage fish at the bottom of the food chain, assimilate and release MeHg, the authors performed a series of laboratory experiments using the gamma‐emitting radiotracer²⁰³Hg²⁺and Me²⁰³Hg with the calanoid copepodAcartia tonsa. Assimilation efficiencies of Hg²⁺and MeHg ranged from 25% to 31% and 58% to 79%, respectively, depending on algal diets. Assimilation efficiencies were positively related to the fraction of Hg in the cytoplasm of the algal cells that comprised their diet. Efflux rates of Hg²⁺(0.29/d) and MeHg (0.21/d) following aqueous uptake were similar, but efflux rates following dietary uptake were significantly lower for MeHg (0.11–0.22/d) than Hg²⁺(0.47–0.66/d). The calculated trophic transfer factors in copepods were >1 for MeHg and consistently low (≤0.2) for Hg²⁺. The authors used the parameters measured to quantitatively model the relative importance of MeHg sources (water or diet) for copepods and to predict the overall MeHg concentrations in copepods in different marine environments. In general, MeHg uptake from the diet accounted for most of the body burden in copepods (>50%). For an algal diet with a MeHg dry weight bioconcentration factor ≥10⁶, >90% of a copepod's MeHg body burden can be shown to derive from the diet. The model‐predicted MeHg concentrations in the copepods were comparable to independent measurements for copepods in coastal and open‐ocean regions, implying that the measured parameters and model are applicable to natural waters.Environ Toxicol Chem2017;36:1287–1293. © 2016 SETAC 

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4. Dietary shifts across biogeographic scales alter spatial subsidy dynamics

   https://doi.org/10.1002/ecs2.2980  

   Ziegler, Shelby_L; Able, Kenneth_W; Fodrie, F_Joel (December 2019, Ecosphere)

   Abstract Over heterogeneous landscapes, organisms and energy move across ecological boundaries and this can have profound effects on overall ecosystem functioning. Both abiotic and biotic factors along habitat boundaries may facilitate or impede key species interactions that drive these energy flows—especially along the land–sea interface. We synthesized the literature detailing estuarine fish diets and habitat characteristics of salt marshes from U.S. East and Gulf coasts to determine patterns and drivers of cross‐boundary trophic transfers at the land–sea interface. Notably, marsh‐platform species (i.e., killifishes, fiddler crabs) appear virtually absent in the diets of transient estuarine fishes in the Gulf of Mexico, while along the South Atlantic and Mid‐Atlantic Bights, marsh‐platform species appear regularly in the diets of many transient estuarine fishes. Tidal amplitude varied across these three biogeographic regions and likely regulates the availability of marsh‐platform species to transient estuarine fishes via both access to the marsh surface for marine predators and emergence of marsh‐resident prey into the adjacent estuary (i.e., higher tidal amplitude increases predator–prey encounter rates). Surprisingly, marsh shoot density was positively correlated with the presence of marsh‐platform species in the diet, but this pattern appears to be mediated by increased tidal amplitude, suggesting the mode and periodicity of abiotic cycles drive diet structure of transient estuarine fishes more so than local habitat structural complexity. Subsequently, these processes likely influence the degree to which “trophic relay” moves energy from the marsh toward the open estuary. Understanding the dynamics that determine energy flows, spatial subsidies, and ultimately, ecosystem‐level productivity, is essential for implementation of holistic ecosystem‐based approaches to conserve and manage complex landscape mosaics. 

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5. Trophic niche of a nonnative invader and environmental drivers of its increasing populations in the coastal Everglades

   https://doi.org/10.1007/s10530-024-03444-w  

   Kahmann, Grace; Rehage, Jennifer_S; Massie, Jordan_A; Nelson, James_A; Santos, Rolando_O; Viadero, Natasha_M; Ryan_James, W.; Boucek, Ross_E; Crane, Derek_P; Rezek, Ryan_J (September 2024, Biological Invasions)

   Abstract The Florida Everglades is a critically important, but highly threatened ecosystem that is becoming increasingly susceptible to the invasion of non-native species. This study investigated the ecological role of the invasive peacock eel (Macrognathus siamensis) within this ecosystem using 15 years of electrofishing data and stable isotope analysis. We investigated the population trends of peacock eels at the marsh-mangrove ecotone of the Shark River Estuary, the environmental factors contributing to their abundance, and the potential interactions they may have with native fish assemblages and coastal food webs. We used stable isotope analysis to provide insights into the basal resource contribution to peacock eels and hypervolume analysis to determine peacock eel trophic niche size and overlap with native species. Results of this study found that peacock eel abundance has rapidly increased, and their populations are strongly related to hydroclimatic regimes. Peacock eel abundance was positively associated with warmer water temperatures and greater marsh inundation periods. The trophic niche of peacock eels was significantly smaller in volume than that of native sunfishes (Lepomisspp.) indicating lower intraspecific resource use variability and suggesting a limited potential for inter-specific competition with these taxa. However, in recent years, the catch of peacock eels has outnumbered the catch of all native sunfishes combined. The feeding habits and pervasiveness of peacock eels in the coastal Everglades could lead to a decrease in abundance of benthic prey items targeted by peacock eels and alter food web dynamics in the system. Based on these data, peacock eel populations are predicted to continue to increase, highlighting the importance of continued monitoring of their potential impact on native fish assemblages and food webs. 

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