Fig. 1 Topological placement of taxa in the Yellowstone Lake food web before (left) and after (right) invasion by nonnative lake trout. The conceptualization (nonmathematical) emphases are the cutthroat trout (YCT) and other components known (black arrows) or hypothesized (orange arrows) to be affected by the introduction of lake trout (LKT). Thick arrows indicate that the consumption of that food item is high by predator or herbivore, and thin arrows indicate that the consumption is low, within the aquatic (below the blue line) and across terrestrial (above the blue line) ecosystems. Letters represent consumption of (A) phytoplankton, (B) zooplankton, (C) amphipods, (D to G) cutthroat trout, (H) longnose suckers, (I) elk calves, and (J) common loon, trumpeter swan, American white pelican, double-crested cormorant, and Caspian tern. Organisms are not drawn to scale, although the size of the fish, osprey, and otter depicts observed shifts in abundance between periods. California gulls were present before lake trout invasion but no longer nest on Yellowstone Lake.
Fig. 2 Response of planktivorous and benthivorous fish to invasion of Yellowstone Lake by an apex predator. (A) Lake trout abundance estimated by a statistical catch-at-age model markedly increased between 1998 and 2012 when suppression gillnetting effort became great enough to curtail further population growth, (B) long-term decline in the average catch per unit effort (CPUE) of cutthroat trout, and (C) long-term decline in average CPUE of longnose suckers during annual fish population netting assessments on Yellowstone Lake, with 95% confidence intervals, from 1980 to 2017.
Fig. 3 Changes in plankton due to decline of planktivorous cutthroat trout. Between 1977–1980 (before lake trout introduction), 2004 (10 years after lake trout were found), and 2016–2017 (>20 years later), the biomass of (A) small zooplankton (L. ashlandi, Diacyclops, and nauplii) declined and (B) large zooplankton (D. pulicaria, D. schødleri, and H. shoshone) increased. (C) Chlorophyll a concentration, an indicator of phytoplankton biomass, was more than two times higher in 1972 (17) than in 2004 (16) or 2016–2017. Letters (a, b) indicate differences (P < 0.05) among means.
Fig. 4 Decline of spawning cutthroat trout and response by bears, eagles, and osprey. (A) Mean number of spawning adult cutthroat trout observed (solid line) and proportion of visits where activity by black and grizzly bears was found (dashed) during weekly spawning visual surveys of 9 to 11 tributaries located along the western side of Yellowstone Lake (1989–2017). (B) Number of nests (solid line) and nest success (dashed) during May to August 1987–2017 for osprey and (C) during April to June 1985–2017 for bald eagles, within approximately 1 km of the Yellowstone Lake shoreline, connected tributaries, and forested islands.
- Table 1 The effect size of predatory lake trout on aquatic and terrestrial ecosystems.
The response variables for the past (before lake trout population growth) and present (after) were compared using a log response ratio of means [log10(Xpresent/Xpast)]. Lake trout enhanced the variable when the ratio was positive and reduced the variable when the ratio was negative; ratios near zero indicate that the variable was similar between the two time periods. CI, confidence interval.
Variable Past* Present Log ratio Year(s) Mean 95% CI Year(s) Mean 95% CI Fish population responses Lake trout abundance (total number × 1000) 1998–2002 95.3 2.8 2013–2017 843.9 6.0 0.95 Cutthroat trout abundance (CPUE) 1980–1984 44.6 4.2 2013–2017 22.1 1.2 −0.31 Longnose sucker abundance (CPUE) 1980–1984 30.0 1.5 2013–2017 4.6 0.4 −0.82 Cutthroat trout spawners (mean number observed) 1989–1993 52.8 7.1 2013–2017 5.3 0.5 −1.00 Aquatic ecosystem effects Small zooplankton biomass (mg/liter) 1977–1980 67.8 27.3 2017 30.3 17.0 −0.35 Large zooplankton biomass (mg/liter) 1977–1980 8.5 5.0 2017 102.9 24.0 1.08 Chlorophyll a concentration (μg/liter) 1972 2.2 0.3 2017 0.5 0.2 −0.64 Large zooplankton [H. shoshone length (mm)] 1977–1980 2.4 0.2 2017 4.4 0.2 0.26 Large zooplankton [D. pulicaria length (mm)] 1977–1980 1.9 0.1 2017 2.7 0.0 0.16 Small zooplankton [L. ashlandi length (mm)] 1977–1980 0.7 0.0 2017 0.9 0.1 0.12 Secchi disk depth (m)† 1976 9.9 0.1 2005 11.4 0.1 0.06 Terrestrial ecosystem effects Bear occurrence on spawning streams (proportion of visits) 1989–1993 0.5 0.0 2013–2017 0.2 0.0 −0.30 River otter use of cutthroat trout (prevalence in scat) 2002–2003 0.73 0.06 2006–2008 0.53 0.14 −0.14 Osprey nest count (total number) 1987–1991 37.6 2.2 2013–2017 3.2 0.1 −1.07 Osprey nest success (proportion that fledged) 1987–1991 58.8 3.4 2013–2017 31.4 7.1 −0.27 Bald eagle nest count (total number) 1985–1989 6.4 0.3 2013-2017 7.6 0.7 0.07 Bald eagle nest success (proportion that fledged) 1985–1989 56.0 6.1 2013–2017 70.4 3.6 0.10 *All data were collected before significant lake trout population growth with the exception of river otters, which were collected later during a period of lake trout population growth and cutthroat trout decline (24).
†Secchi depth was calculated using the model in fig. S6 based on 15 August (Julian day 227) 1976 and 2005.
Supplementary Materials
Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/3/eaav1139/DC1
Supplementary Text
Fig. S1. The watershed (>3200 km2) of Yellowstone Lake and tributary streams in Yellowstone National Park and the Bridger-Teton wilderness, Wyoming.
Fig. S2. Gillnetting effort expended and biomass of lake trout netted.
Fig. S3. Shift in size structure of prey fish populations during the period of lake trout invasion.
Fig. S4. Changes in plankton due to decline of planktivorous cutthroat trout.
Fig. S5. Phytoplankton biomass in the West Thumb of Yellowstone Lake.
Fig. S6. Secchi disk depths in the West Thumb of Yellowstone Lake.
Fig. S7. Depths of isotherms (°C) in the West Thumb of Yellowstone Lake.
Fig. S8. Surface water temperatures of Yellowstone Lake.
Table S1. Results of Prais-Winsten time series regressions.
Table S2. Fish explanatory variables used in time series and trend analyses.
Table S3. Bear and bird response variables used in time series analyses.
References (66–77)
Additional Files
Supplementary Materials
This PDF file includes:
- Fig. S1. The watershed (>3200 km2) of Yellowstone Lake and tributary streams in Yellowstone National Park and the Bridger-Teton wilderness, Wyoming.
- Fig. S2. Gillnetting effort expended and biomass of lake trout netted.
- Fig. S3. Shift in size structure of prey fish populations during the period of lake trout invasion.
- Fig. S4. Changes in plankton due to decline of planktivorous cutthroat trout.
- Fig. S5. Phytoplankton biomass in the West Thumb of Yellowstone Lake.
- Fig. S6. Secchi disk depths in the West Thumb of Yellowstone Lake.
- Fig. S7. Depths of isotherms (°C) in the West Thumb of Yellowstone Lake.
- Fig. S8. Surface water temperatures of Yellowstone Lake.
- Table S1. Results of Prais-Winsten time series regressions.
- Table S2. Fish explanatory variables used in time series and trend analyses.
- Table S3. Bear and bird response variables used in time series analyses.
- References (66–77)
Files in this Data Supplement:
