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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. Exploitation of a marine subsidy by a terrestrial invader

   https://doi.org/10.1007/s10530-024-03500-5  

   Winters, Christopher; Jurgela, Grace; Holway, David (December 2024, Biological Invasions)

   Abstract Intertidal environments receive energy from marine ecosystems in the form of marine wrack, which makes up the base of a food web that includes both intertidal and terrestrial consumers. Consumption of wrack by terrestrial consumers can elevate their abundance and alter how they interact with organisms in adjacent terrestrial environments. Although rarely documented, terrestrial invaders may exploit marine wrack subsides and potentially disrupt intertidal and terrestrial food webs. Here, we examine consumption of marine wrack resources by the introduced Argentine ant (Linepithema humile), which occurs commonly on beaches in southern California. In controlled trials the Argentine ant readily scavenged arthropod detritivores (amphipods and flies) abundant in wrack. In spite of obvious risks (e.g., exposure to tides, desiccation, thermal stress) associated with intertidal foraging, Argentine ant activity on beaches was comparable to that in spatially-paired, scrub environments. Foraging on beaches allowed ants to access higher densities of arthropod prey and carrion compared to those found in scrub environments. Stable isotope analyses provide evidence for extensive assimilation of marine-derived resources. Values of δ¹⁵N and δ¹³C for the Argentine ant were higher at beach sites than at scrub sites, and Argentine ant δ¹⁵N values broadly overlapped those of intertidal consumers at beach sites. Although ants are known to forage in intertidal environments, this study provides a novel example of an introduced ant species exploiting a cross-boundary subsidy. 

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3. 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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4. Shark teeth zinc isotope values document intrapopulation foraging differences related to ontogeny and sex

   https://doi.org/10.1038/s42003-023-05085-6  

   McCormack, Jeremy; Karnes, Molly; Haulsee, Danielle; Fox, Dewayne; Kim, Sora L. (July 2023, Communications Biology)

   Abstract Trophic ecology and resource use are challenging to discern in migratory marine species, including sharks. However, effective management and conservation strategies depend on understanding these life history details. Here we investigate whether dental enameloid zinc isotope (δ⁶⁶Zn_en) values can be used to infer intrapopulation differences in foraging ecology by comparing δ⁶⁶Zn_enwith same-tooth collagen carbon and nitrogen (δ¹³C_coll, δ¹⁵N_coll) values from critically endangered sand tiger sharks (Carcharias taurus) from Delaware Bay (USA). We document ontogeny and sex-related isotopic differences indicating distinct diet and habitat use at the time of tooth formation. Adult females have the most distinct isotopic niche, likely feeding on higher trophic level prey in a distinct habitat. This multi-proxy approach characterises an animal’s isotopic niche in greater detail than traditional isotope analysis alone and shows that δ⁶⁶Zn_enanalysis can highlight intrapopulation dietary variability thereby informing conservation management and, due to good δ⁶⁶Zn_enfossil tooth preservation, palaeoecological reconstructions. 

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5. 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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