Fig 1.
Timeline of simplified trout diets.
Historical representations of Yellowstone cutthroat trout and >300 mm lake trout diets before lake trout invasion, and during two stages of lake trout density, with the current diet composition unknown during a moderate-density state of lake trout. Size, color intensity, and thickness of solid-lined boxes represents relative densities of organisms, thickness of lines represents relative contributions of organisms to predator diet, and size, color intensity, and thickness of dashed boxes represents inferred density of organisms based on previous research. Diet data for the 1950s are from Benson [44], data for 1989 are from Jones et al. [46], data for 1997 are from Ruzycki et al. [54], and data for 2012 are from Syslo et al. [53]. Relative abundances of lake trout are from Syslo et al. [55]. Lake trout absent is a state with no detectable density, low-density state is ~80,000 >300 mm lake trout, high density is ~450,000 >300 mm lake trout, and moderate-density state is ~300,000 >300 mm lake trout. Relative abundances of Yellowstone cutthroat trout are from Koel et al. [40]. Relative abundances of cladocerans are from Tronstad et al. [21], and relative abundances of amphipods are inferred from Wilmot et al. [52].
Fig 2.
Distribution of samples collected from Yellowstone Lake.
Map of Yellowstone Lake, Yellowstone National Park, Wyoming, USA showing the number and location of stable isotope samples and corresponding diet samples for Yellowstone cutthroat trout (a, purple hues) and lake trout (b, green hues) collected in 2018 and 2019. Base map sources can be accessed using the following: Yellowstone Lake border (https://pubs.usgs.gov/sim/2007/2973/); United States of America and individual state borders (https://www.sciencebase.gov/catalog/item/52c78623e4b060b9ebca5be5); Yellowstone National Park border (https://www.sciencebase.gov/catalog/item/4ffb3aebe4b0c15d5ce9fc0b).
Fig 3.
Simplified representation of Yellowstone cutthroat trout and >300 mm lake trout diets during the moderate-density state (~300,000 >300 mm lake trout; estimate of lake trout density from Syslo et al. [55]). Size and thickness of solid-lined boxes represents relative densities of organisms, thickness of lines represent relative contributions of organisms to predator diet, size and thickness of dashed boxes represents inferred density of organisms based on previous research.
Fig 4.
Comparisons of diet proportions.
Diet composition (proportion by weight) for Yellowstone cutthroat trout and lake trout in Yellowstone Lake (Cla = cladocerans; Cop = copepods; Amp = amphipods; Lee = leeches; Chi = chironomids; Ins = insects; Mol = mollusks; Yel = Yellowstone cutthroat trout; Fis = unidentified fish). Bootstrapped 95% credible intervals were drawn from a distribution of 1000 samples. Relative abundances of lake trout are from Syslo et al. [55], where absent is a state with no detectable density or complete absence of lake trout (1989), low-density state is ~80,000 >300 mm lake trout (1997), high-density state is ~450,000 >300 mm lake trout (2012), and moderate-density state is ~300,000 >300 mm lake trout (2019). No Yellowstone cutthroat trout diets were analyzed during the lake trout low-density state. aCurrent study. bSyslo et al. [53] averages among stratification seasons. cJones et al. [46]. dBenson [44]. eRuzycki et al. [54]. fIncludes Ephemeroptera, Tricoptera, Plecoptera, and non-chironomid dipterans. *Not included in table are diet items and proportions: 0.01 Leucisids, 0.02 organic matter. †Not included in table are diet items and proportions: 0.01 diatoms, 0.02 detritus. ‡Not included in table are diet items and proportions: 0.03 diatoms, 0.01 detritus. ±Not included in table are diet items and proportions: 0.01 diatoms, 0.03 detritus. +Not included in table are diet items and proportions: 0.06 diatoms, 0.03 detritus. **Not included in table are diet items and proportions: 0.04 lake trout eggs, 0.01 sucker. ***Not included in table are diet items and proportions: 0.01 wasps and beetles, 0.01 water mites. ****Not included in table are diet items and proportions: 0.03 wasps and beetles, 0.02 water mites, 0.02 gastropods.
Fig 5.
Comparison of diet overlap between two lake trout density states.
Schoener’s index of diet overlap values for lake trout moderate-density state (this study) (a) and a lake trout high-density state (Syslo et al. [53]) (b). Relative abundances of lake trout are from Syslo et al. [55], where high density is ~450,000 >300 mm lake trout, and moderate-density state is ~300,000 >300 mm lake trout. Schoener values >0.6 indicate a high degree of overlap (Wallace [67]), represented by boxes with black outlines.
Fig 6.
Comparison of stable isotope signatures and ellipse areas between native and invasive trout.
Individual stable isotope values (δ15N, δ13C) and standard Bayesian ellipse areas for Yellowstone cutthroat trout (YCT) length classes (circles; purple hues) and lake trout (LKT) length-classes (squares; green hues) sampled from Yellowstone Lake, 2018–2019, during moderate density state (a) and standard Bayesian ellipse areas for high-density state Yellowstone cutthroat trout (YCT) length classes (black) and lake trout (LKT) length-classes (grey) from Syslo et al. [53] (b). Note that the scales of x-axes on the panels are different.
Table 1.
Comparison of stable isotope signatures for native and invasive trout between lake trout density states.
Sample sizes (N) and mean δ13C and δ15N (95% confidence intervals in parentheses) and median posterior distribution value of standard Bayesian ellipse areas (SEAB) by lake trout density state (lake trout state) and length class for lake trout and Yellowstone cutthroat trout. Amphipods included to demonstrate basal isotope values. Lake trout state densities are from Syslo et al. [55].
Fig 7.
Stable isotope ellipse overlap for Yellowstone cutthroat trout in two lake trout density states.
Standard Bayesian ellipse area 40% core distribution of stable isotope signatures for Yellowstone cutthroat trout from a lake trout moderate-density state (purple-blue hues) and a lake trout high-density state (Syslo et al. [53]; grey hues) among length classes: 100–300 mm (a), 301–475 mm (b), 476–575 mm (c), and all length classes (d). Relative abundances of lake trout are from Syslo et al. [55], where high density is ~450,000 >300 mm lake trout, and moderate-density state is ~300,000 >300 mm lake trout.
Fig 8.
Stable isotope ellipse overlap for lake trout in two lake trout density states.
Standard Bayesian ellipse area 40% core distribution of stable isotope signatures for lake trout from a lake trout moderate-density state (green hues) and a lake trout high-density state (Syslo et al. [53]; grey hues) among length classes: 100–300 mm (a), 301–475 mm (b), 476–575 mm (c), 576–1000 mm (d), and all length classes (e). Relative abundances of lake trout are from Syslo et al. [55], where high density is ~450,000 >300 mm lake trout, and moderate-density state is ~300,000 >300 mm lake trout.
Fig 9.
Conceptual model representing dynamics of an apex invasive predator undergoing suppression and a native species of conservation responding to the diet plasticity of the invasive species.
Solid lines represent abundances over time from the start of invasive species expansion to the most recent time of suppression. Grey hues represent the diet plasticity of the invasive predator. Light grey polygons represent periods in which the invasive predator consumed their preferred prey, the native species of conservation, in high diet proportion. The dark grey polygon represents a period in which the invasive predator consumed a less-preferred prey in high diet proportion.