Introduced lake trout alter nitrogen cycling beyond Yellowstone Lake

Abstract

Citation: Tronstad, L. M., R. O. Hall Jr., and T. M. Koel. 2015. Introduced lake trout alter nitrogen cycling beyond Yellowstone Lake. Ecosphere 6(11):224. http://dx.doi.org/10.1890/ES14-00544.1Abstract. Introduced predators can have large effects on the ecosystem in which they were introduced, but how much these effects extend to other ecosystems beyond the invaded one is less known. We compared how lake trout (Salvelinus namaycush) affected nutrient cycling in an invaded and adjacent ecosystem in Yellowstone National Park, Wyoming, USA. Introduced lake trout in Yellowstone Lake caused the native Yellowstone cutthroat trout (Oncoryhynchus clarkii bouvieri ) population to decline. Native cutthroat trout are a dominant animal in the lake and may alter nutrient cycling in both Yellowstone Lake where they reside and in tributary streams used for spawning. We estimated changes in nutrient transport and nutrient uptake in both Yellowstone Lake and Clear Creek, a spawning stream, before and after the invasion of lake trout. Annual area-specific excretion fluxes from cutthroat trout were nine times higher in Clear Creek compared to Yellowstone Lake when cutthroat trout were abundant. However, fluxes within the lake and stream were similar after cutthroat trout declined. In Yellowstone Lake, zooplankton excretion supplied 86% of ammonium (NH 4 þ ) that was taken up, but cutthroat trout only supplied ,0.3% after the introduction of lake trout. Conversely, NH 4 þ excreted by cutthroat trout was likely a major flux in ClearCreek, because NH 4 þ fluxes from cutthroat trout exceeded watershed export of NH 4 þ in years when .3000 cutthroat trout spawned. Furthermore, NH 4 þ excretion fluxes from spawning cutthroat trout in ClearCreek supplied up to 6.1% of the NH 4 þ demanded by microbes after the introduction of lake trout.However, based on modeled past NH 4 þ uptake, we estimated that up to 60% of NH 4 þ excreted by spawning cutthroat trout may have been taken up by stream microbes when cutthroat trout were abundant. Therefore, transported NH 4 þ from spawning cutthroat trout was likely an integral part of N cycling in tributary streams in the past. By comparing the effects of declining cutthroat trout on two ecosystems, we show that lake trout had a larger effect on N cycling within an adjacent stream ecosystem than the invaded lake ecosystem itself, because the migratory behavior of cutthroat trout concentrated them in spawning streams increasing their effect.

A Portfolio Framework for Prioritizing Conservation Efforts for Yellowstone Cutthroat Trout Populations

“…; Tronstad et al. ), suggesting that the overall conservation benefits far outweigh the considerable monetary costs to control invasive Lake Trout. This post hoc assessment supports the ongoing efforts (Syslo et al.…”

“…Within our framework, this population of Yellowstone Cutthroat Trout ranks in the top 10% of all populations, as it is genetically pure and occupies over 750 km covering a diversity of streams, including access to Yellowstone Lake, where thermal stratification provides an important contemporary and future coldwater refuge (Goyer et al 2014). Furthermore, this population of Yellowstone Cutthroat Trout has been documented to have high ecological value that extends across ecosystems (Crait et al 2015;Tronstad et al 2015), suggesting that the overall conservation benefits far outweigh the considerable monetary costs to control invasive Lake Trout. This post hoc assessment supports the ongoing efforts (Syslo et al 2011) and justifies further expenditures aimed at reducing the major threat to this important population.…”

Fisheries Volume 43 Number 10 October 2018

“…Within our framework, this population of Yellowstone Cutthroat Trout ranks in the top 10% of all populations, as it is genetically pure and occupies over 750 km covering a diversity of streams, including access to Yellowstone Lake, where thermal stratifi cation provides an important contemporary and future coldwater refuge (Goyer et al 2014 ). Furthermore, this population of Yellowstone Cutthroat Trout has been documented to have high ecological value that extends across ecosystems (Crait et al 2015 ;Tronstad et al 2015 ), suggesting that the overall conservation benefi ts far outweigh the considerable monetary costs to control invasive Lake Trout. This post hoc assessment supports the ongoing efforts (Syslo et al 2011 ) and justifi es further expenditures aimed at reducing the major threat to this important population.…”

Invasion of Hawaiian rainforests by an introduced amphibian predator and N2‐fixing tree increases soil N2O emissions

“…, Tronstad et al. ). Extensive evidence indicates that terrestrial and aquatic predators can indirectly affect carbon (C) and N cycling by altering the abundance or behavior of species at lower trophic levels (Dobson et al.…”

“…Non-native predators can also significantly alter ecosystem functioning (Wardle et al 2011, Tronstad et al 2015. Extensive evidence indicates that terrestrial and aquatic predators can indirectly affect carbon (C) and N cycling by altering the abundance or behavior of species at lower trophic levels (Dobson et al 2006, Schmitz et al 2010, Strickland et al 2013.…”