Lusha M. Tronstad

Body Size: How body size mediates the role of animals in nutrient cycling in aquatic ecosystems

Introduction Aquatic ecosystems have been fertile ground for understanding the extent to which animals can alter nutrient cycling. Although animals have been included in ecosystem models for years (for example, Teal, 1962), it is only more recently that investigators have looked at animals, either as individuals, single species, or assemblages, as agents regulating nutrient cycling (Kitchell et al., 1979; Meyer, Schultz & Helfman, 1983; Grimm, 1988; Jones & Lawton, 1995). A recent review details how animals can affect nutrient cycling in freshwater ecosystems (Vanni, 2002), but the next step is to understand the controls on which animals are important regulators of nutrient dynamics in ecosystems. One controlling factor is determined by attributes of the animals themselves, such as their body size. Animals can regulate nutrient cycling directly or indirectly (Kitchell et al., 1979; Vanni, 2002). Direct regulation is the transformation and transportation of nutrients by animal ingestion, egestion, production and excretion. For example, animal excretion can constitute the largest source of plant-available nitrogen (N) within an ecosystem (Hall, Tank & Dybdahl, 2003) and animals can move nutrients between habitats (Meyer et al., 1983). Perhaps more common are indirect controls, whereby animals alter nutrient cycling by changing the biomass, production or distribution of the plants or microbes that take up nutrients. For example, predatory fish can regulate phosphorus (P) dynamics or nitrogen retention via a trophic cascade (Elser et al., 1998; Simon et al., 2004).

Introduced Lake Trout Produced a Four-Level Trophic Cascade in Yellowstone Lake

Abstract Introduction of lake trout Salvelinus namaycush into a system can add a trophic level, potentially affecting organisms at lower trophic levels. Similar to many lakes and reservoirs in the western United States, lake trout were introduced into Yellowstone Lake, Wyoming. Previous studies showed that lake trout reduced the population and altered the size structure of native Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri in Yellowstone Lake, but we sought to determine the degree to which lake trout predation changed lower trophic levels. We predicted that the structure of lower trophic levels would change in conformance with trophic cascade theory because Yellowstone cutthroat trout consume zooplankton. We compared zooplankton and phytoplankton assemblages between the period when Yellowstone cutthroat trout were abundant and the period after they declined. As predicted by trophic cascade theory, zooplankton biomass shifted from being dominated by copepods before lake trout introduction to ...

Introduced lake trout alter nitrogen cycling beyond Yellowstone Lake

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 la...

Longitudinal changes in stream invertebrate assemblages of Grand Teton National Park, Wyoming

High elevation ecosystems are predicted to be strongly impacted by climate change; however, little is known of extant biodiversity in mountain streams. For this study, five streams in Grand Teton National Park, Wyoming were sampled along a longitudinal gradient to establish a baseline of invertebrate assemblages and environmental conditions. Five Surber samples were collected from low, middle and high elevation sites along each stream. Nearly 10 000 ind m−2 lived in these streams on average, but the density (mixed effects model, P = 0.54) and richness (P = 0.18) of invertebrates did not vary significantly by elevation. Total density of invertebrates was positively related to the amount of visible biofilm (anova, P = 0.03) and oxidation‐reduction potential (P = 0.05) and taxa richness was negatively related to specific conductivity (P = 0.009). Invertebrate assemblages and environmental conditions were more similar at low versus high sites when compared using non‐metric multidimensional scaling and tests of multivariate dispersion indicating that higher elevation sites harboured more environmental and species diversity. These results can help target which aquatic invertebrates to monitor as stream temperatures rise, and highlight the biotic and abiotic factors that structure aquatic ecosystems in the Teton Range of Grand Teton National Park.

Using Species Distribution Models to Guide Field Surveys for an Apparently Rare Aquatic Beetle

Abstract Surveying for rare animals can be difficult but using models to predict suitable habitat can guide sampling efforts. We used models to predict suitable habitat for the Narrow-footed Hygrotus Diving Beetle Hygrotus diversipes (diving beetle hereafter), a dytiscid beetle that is known from 10 streams in central Wyoming. The diving beetle was a category-2 Candidate species for listing as Threatened or Endangered in the Endangered Species Act between 1989 and 1996, and was petitioned for listing in 2007, 2008, and 2013. Suitable habitat for the diving beetle was predicted using Maximum Entropy and Random Forest models in Wyoming. Both models predicted that the diving beetle was more likely to occur in intermittent streams with a gentle gradient, shallow water table, variable precipitation pattern, and high soil electrical conductivity, and in the warmest areas of Wyoming. We conducted surveys for the diving beetle at sites where the species had previously been found, and in new areas that were predic...

Macroinvertebrate richness is lower in high-elevation lakes vs nearby streams: evidence from Grand Teton National Park, Wyoming

ABSTRACT Mountain ecosystems will be strongly impacted by climate change, yet little is known of extant biodiversity in high-elevation lakes, particularly in North America. In this study, we sampled the littoral zone of six alpine and subalpine lakes in Grand Teton National Park (GRTE), Wyoming, to characterise invertebrate diversity and environmental variation in these climate change-threatened ecosystems. Overall, we collected 19 aquatic invertebrate taxa, and found that each lake harboured a unique assemblage of invertebrates despite close geographic proximity in some instances (e.g. less than 5 km). The results of this study complement previous efforts focused on macroinvertebrate diversity of streams in the Teton Range, highlighting much lower diversity in montane lakes vs nearby streams. Taken together, the two studies establish an important baseline understanding of mountain freshwater biodiversity in GRTE. With rapidly changing hydrologic inputs to mountain lakes driven primarily by the recession of alpine glaciers, these results may help target aquatic invertebrates to monitor as climate change affects the region. Moreover, these data clarify habitat factors, both biotic and abiotic, that influence high-elevation lake assemblages of the Teton Range.

Range extension of Neoporus superioris (Balfour-Browne, 1944) (Insecta: Coleoptera) into Wyoming, USA

We report a new state record of Neoporus superioris (Balfour-Browne) from Crook County, Wyoming, USA. This new record represents the most southern extent of N. superioris known.

Flea Beetle (Altica spp.) Herbivory on a Threatened Plant, F.E. Warren Air Force Base, Wyoming

ABSTRACT: Colorado butterfly plant (Oenothera coloradensis (Rydb.) W.L. Wagner & Hoch ssp. coloradensis [syn. Gaura neomexicana Woot. ssp. coloradensis (Rydb.) Raven & Gregory]) in the Onagraceae; Primrose family) is a Threatened plant whose population declined in a protected area in southeastern Wyoming in 2007–2008, setting record low numbers in 23 years of the annual population census. This trend was accompanied by pervasive flea beetle herbivory (Altica spp.) in 2007. The most frequent flea beetle species collected in 2008–2009 was Altica foliaceae LeConte, a native species. Altica foliaceae favors members of Onagraceae, and A. foliaceae adults were collected on browsed Oenothera plants. The Oenothera population returned to pre-infestation numbers in 2009–2010, evidence that it survived by vegetative plants and seed bank. Results point to the importance of repeated long-term monitoring, without which this event could have been interpreted as a disaster or have gone unnoticed. It also documents an event that can inform population viability analysis.