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

  • ️Fri Jan 01 2021

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

Henry M Page et al. PLoS One. 2021.

Abstract

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. δ13C and δ15N values of fox whisker (vibrissae) segments suggested individualism in diet, with generally low δ13C and δ15N 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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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Locations of the study beaches on Santa Rosa and Santa Cruz Islands off the California, USA, coastline (inset).

Abbreviations: SP—Sandy Point, SO—Soledad, AS—Arlington Springs, BB—Bechers Bay, WC—Water Canyon, SE—Southeast Anchorage, FP—Ford Point, CC—China Camp, FC—Forney’s Cove, CB—Christy Beach, CP—Coches Prietos. Attribution: Map tiles by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under OdbL.

Fig 2
Fig 2. Abundance and biomass of upper beach and wrack associated invertebrates across beaches.

(A) Abundance and (B) biomass values for talitrid amphipods, Megalorchestia spp., isopods Alloniscus perconvexus and Tylos punctatus, and staphylinid beetle Thinopinus pictus combined for each study beach. Mean ± SE, n = 5 (Santa Rosa Island) and n = 3 (Santa Cruz Island) transects. Site abbreviations as in Fig 1.

Fig 3
Fig 3. Contribution of beach material to island fox scat.

(A) Proportion (as percent) of island fox scat containing terrestrial (solid brown) and endemic beach (hatched-blue) material, (B) mean percent (± SE) of individual scat (by dry weight) consisting of beach material from each beach. Site abbreviations as in Fig 1.

Fig 4
Fig 4. Relationships between beach material in scats and endemic beach invertebrate abundance and biomass.

Proportion (as percent) of scat with endemic beach invertebrates and (A) invertebrate abundance and (B) biomass, and mean percent of invertebrates per gram scat versus (C) invertebrate abundance and (D) biomass at Santa Rosa and Santa Cruz Island study sites. Mean values for (C) and (D) ± 95% confidence intervals. Regression fits weighed for differences in sample size among sites. Dashed lines show 95% confidence intervals around regression lines. Site abbreviations as in Fig 1. *Santa Cruz Island.

Fig 5
Fig 5. δ13C and δ15N values of island fox whisker segments.

Values from individual foxes trapped at (A, B) Soledad (n = 10 foxes), (C, D) China Camp (n = 8 foxes), and (E, F) Arlington Springs (n = 5 foxes). Date of whisker collection provided in lower left of each figure pair. Whiskers varied in length and therefore number of segments. Segment 1 is most proximal to the face. Each segment represents an approximate two week time period.

Fig 6
Fig 6. Bivariate plots of island fox whisker segment δ13C and δ15N values for Soledad and China Camp beaches.

(A) Soledad and (B) China Camp beaches, and (C) comparison of populations from the two sites. The two beaches were sampled within two weeks of each other. Isotopic niche width visualized as standard ellipses enclosing 40% of the isotope space for individual foxes and for populations at each site. Dashed gray lines enclosing values for males, solid black lines enclosing females. Standard ellipse areas (SEAC and SEAB) for individuals and each population are given in Table 3. Mean δ13C and δ15N values of potential foods, included for context, are adjusted upward to account for expected trophic discrimination between fox and food (TDFs: Δ13C = 2.6‰ and Δ15N = 3.4 ‰).

Fig 7
Fig 7

Comparison of (A) body weight (kg) and (B) condition index for female and male adult foxes between Soledad (SO) and China Camp (CC) locations. Mean ± SD.

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HMP JS JED RJM: U.S. Department of Interior, Bureau of Ocean Energy Management (BOEM) (https://www.boem.gov/), Environmental Studies Program, Washington D.C. Co-op Agreement #M15AC00012 RJM: National Aeronautics and Space Administration (https://www.nasa.gov/), Biodiversity and Ecological Forecasting Program (Grant NNX14AR62A), Co-op BOEM Agreement MC15AC00006, and the National Oceanic and Atmospheric Administration (https://www.noaa.gov/) in support of the Santa Barbara Channel Marine Biodiversity Observation Network RJM: National Science Foundation's (https://www.nsf.gov/) funding of the Santa Barbara Coastal Long Term Ecological Research program (OCE 1232779, OCE 1831937). JED, RJM: National Science Foundation (OCE 1458845) Funder: DMS. The funder participated in the fieldwork and proofed the paper.