Over 27 years in Great Salt Lake (GSL: Utah, USA), phytoplankton relative abundances of chlorophytes, diatoms and cyanobacteria varied dramatically (monthly < 10–90

Ecosystems are frequently considered to be controlled by predation (top-down). Experiments examined this in four bird/spider/grasshopper/prairie habitats over 34 years, employing in each habitat three 100 m2 bird exclosures and controls (121 habitat/year cases) where plant, grasshopper, and spider abundances were measured. Top-down control (plants decrease and grasshoppers increase with bird exclusion) was observed in only 13.2% of cases, while plants increased and grasshoppers decreased in 33.1% of cases, plants decreased and grasshoppers decreased in 25.6% of cases, and plants increased and grasshoppers increased in 28.1% of cases. Therefore, top-down control was not common and system responses were not constant, but varied among sites, years, and directionally over time with climate change. This diversity of responses is expected given the variety of underlying processes in complex ecosystems. For example, decision tree/discriminant analysis found that plant decreases and increases with bird exclusion were correctly identified in 78.3% of cases by grasshopper hatchling abundance, plant cover, and annual net primary production (ANPP), while grasshopper decreases and increases with bird exclusion were correctly identified in 76.7% of cases by edible plant biomass per grasshopper hatchling, grasshopper hatchling abundance, and large grasshopper abundance. Analysis of other system-wide terrestrial trophic experiments indicates that the variety of responses observed by us over time and space may be common so that system-wide trophic responses may, in general, be more variable than either top-down or bottom-up as often considered.

Wild herbivore responses to anthropogenic climate change are often projected to be habitat and geographic range shifts as warmer conditions reduce the quantity and nutritional quality of forage plants, which makes species presence/absence a focus. Since 1978, herbivore abundances at the National Bison Range, MT, USA, were measured for grasshoppers (catch-effort), microtine rodents (runway density), and ungulates (drives and round-ups), along with climate and vegetation quantity (biomass) and quality (nitrogen content and chemical solubility related to digestibility). Counter to expectation with warming and drying, forage biomass increased as grass biomass increased more than dicot biomass decreased, and forage quality (solubility) increased. Consequently, herbivores that consume a grass diet (>25% grass: certain grasshoppers, microtines, bighorn sheep, elk, bison) increased in abundance, while herbivores consuming less grass declined (certain grasshoppers, pronghorn, whitetail, and mule deer). The result is an 18% increase in herbivore abundance and herbivory, counter to climate change expectations. Historically, grasshoppers consumed 46% more vegetation than mammals; now, they consume only 14% more, as grasshoppers did not increase as expected with climate change. Therefore, herbivores respond rapidly to climate-induced vegetation changes, and this is not a simple loss/addition of species, but changing trophic dynamics, which requires more knowledge of ecosystem dynamics.

Hypersaline Great Salt Lake’s (GSL: Utah, USA) pelagic food web is dominated by the herbivore, Artemia franciscana. Artemia demographic responses (survival, developmental transition, and reproduction) to GSL salinities, temperatures, common phytoplankton and yeast, and food levels were examined by factorial experiment. Survival across developmental stages was best at 90 ppt salinity, and decreased as temperature increased. Transition between life stages was best at 45 ppt salinity, and increased as temperature increased. Food was most important with both survival and transitioning responding similarly to food types and increasing with amount of food. Artemia reproduce in two ways (diapausing cysts – oviparity, live young – ovoviviparity): ovoviviparous and total reproduction were greatest at 90 ppt salinity and 20 °C, while oviparous reproduction was weakly affected by salinity and greatest at 20 °C. Oviparity was greatest at low food availability, while ovoviviparity and total reproduction increased with food availability, so reproduction shifted from oviparity to ovoviviparity as food increased. Maternal effects were observed for cyst hatchability, and ovoviviparous nauplii survival and transitioning to the juvenile stage. Combinations of salinity, temperature, food taxa and food amount strongly affect demography, making single factor studies of limited value. Results explain Artemia abundance in different parts of GSL and among years.

Grazing experiments were conducted for the zooplankton Artemia franciscana on three of its most common Great Salt Lake (Utah: USA) phytoplankton species (> 80–90

Microbialites are microbial communities that create a carbonate structure. They are abundant in the Great Salt Lake, a hypersaline lake in the arid Great Basin of the USA, where they contribute to overall primary production, seasonally up to 55%. While the microbial diversity of microbialites has been investigated, how abiotic factors affect the abundance of their primary constituents is not well understood. We examined how microbialite primary producers respond to varying levels of temperature, salinity, and nitrogen within ranges observed in the Great Salt Lake. All abiotic factors and their interactions significantly affected the maximum chlorophyll-a abundance, suggesting that these factors co-limit microbialite primary producers in the Great Salt Lake. Maximum chlorophyll-a concentrations increased with nitrogen additions and showed a parabolic relationship with salinity and temperature with peaks around 60 ppt and 20°C, respectively. While salinity had a strong effect on microbialite primary producers, we found that temperature and nitrogen were more impactful, accounting for 40 and 30% of the variance in maximum abundance, respectively, while salinity contributed just 15%. Our results show the importance of the interplay of abiotic factors on Great Salt Lake microbialites and highlight the need for increased study of benthic communities in inland saline lakes.

Over the past 109 years, a Montana intermountain bunchgrass prairie annually became warmer (0.7°C) and drier (27%). The temperature and precipitation trends continued since 1978, as we studied nitrogen availability, annual aboveground primary production (ANPP), plant phenology and species composition. Given the annual increase in temperature and decrease in precipitation, ANPP might be expected to decline; however, it increased by 110%, as the period of greatest production (late-May-June) became wetter and cooler, counter to the annual pattern, and this was strongest at lower elevations. Grass production increased by 251%, while dicot production declined by 65%, which increased grass relative abundance by 54%. Summer temperatures increased 12.5% which increased plant senescence by 119% and decreased fall plant regrowth by 68%. More intense summer senescence changed plant species composition in favor of more drought tolerant species. The greater ANPP and summer senescence may increase susceptibility for fire, but fire tolerance of the plant species composition did not change. Invasive plant species increased 108% over the study with annual grasses accounting for >50% of this increase, which further increased summer plant senescence. Therefore, seasonal climate changes at a smaller geographical scale (local), rather than average annual climate changes over a larger geographical scale (regional), may better reflect plant community responses, and this makes ecological forecasting of climate change more difficult.

Understanding drivers of ecosystem primary production is a foundational question in ecology that grows in importance with anthropogenic stresses (e.g., climate change). Traditionally, ecosystem production is considered to be abiotically controlled at large spatial scales (e.g., precipitation, temperature, etc.), which underlies forecasting climate change impacts. Using a "common garden" experiment over 10 years at two sites with the same plant and grasshopper species, we show that primary production is strongly influenced by biotic factors (herbivory and plant adaptations to it) at finer spatial scales by creating positive feedbacks, which reverse relative productivity of ecosystems expected from abiotic conditions alone. Our results without herbivory indicate that one site has 26% less annual net primary production (ANPP) than the other site. With herbivory, the sites reverse in ANPP, so the site with lower ANPP without herbivory now is 15% greater than the site with higher ANPP without herbivory, as they respectively increase by 6% and decline by 33%. This reversal is due to changing nitrogen availability (N), as N becomes 16% greater at the higher ANPP site with herbivory, respectively a 3% increase and 41% decline in N. The ANPP and N changes are observed, even though the sites are a few kilometers apart and have the same grasshopper and plant species.

Survivability of diapausing (cryptobiotic) life stages over time in nature, beyond maximum observed time for viability, is not well understood. Because these life stages are an adaptation to overcome harsh conditions, survivability over time is assumed to be high. Brine shrimp (Artemia franciscana) diapausing eggs (cysts) permit overwinter survival to initiate the population each spring. An experiment was designed to examine overwinter survival of brine shrimp cysts for 17 yr in Great Salt Lake (Utah, U.S.A.). Initial hatchability entering the winter (17.8-78.8%) and overwinter survivability (9.9-65.9%) of cysts varied dramatically among years. Better maternal nutrition increased initial hatchability. Overwinter survival of cysts decreased in part because some cysts hatch when it is too cold for the hatchlings to feed (0.8-39.4% among years), so they starve. However, overwinter cyst survival decreases the most with warmer waters in winter, and with better maternal nutrition, as both factors lead to diapause being easier to break. Annual variation in initial hatchability and survival is shown to be important to Great Salt Lake brine shrimp populations. Therefore, cryptobiotic life-stage ecology needs to be better understood, as these life stages may have highly variable hatchability and survivability with normal environmental stresses.

Consumer effects on rainforest primary production are often considered negligible because herbivores and macrodetritivores usually consume a small fraction of annual plant and litter production, even though consumers are known to have effects on plant production and composition in nontropical systems. Disturbances, such as treefall gaps, however, often increase resources to understory food webs, thereby increasing herbivory and feeding rates of detritivores. This increase in consumption could lead to more prominent ecosystem-level effects of consumers after disturbances, such as storms that cause light gaps. We determined how the effects of invertebrate herbivores (walking sticks) and detritivores (litter snails) on understory plant growth may be altered by disturbances in a Puerto Rican rainforest using an enclosure experiment. Consumers had significant effects on plant growth, but only in light gaps. Specifically, herbivores increased plant growth by 60%, and there was a trend for detritivores to reduce plant growth. Additionally, plant biomass tended to be 50% higher with both consumers in combination, suggesting that herbivores may mediate the effects of detritivores by altering the resources available to detritivore food webs. This study demonstrates that disturbance alters the effects of rainforest consumers, and, furthermore, that consumer activity has the potential to change rainforest successional processes.

A fishery for brine shrimp (Artemia franciscana) cysts to supply the aquaculture industry considerably expanded in the late 1980s in the Great Salt Lake, Utah, USA. With this expansion, concerns emerged in the 1990s about the fishery's sustainability, especially its impact on the abundant western North American waterbirds that use the lake and feed on brine shrimp. We track the development of management strategies using adaptive management by the Utah Division of Wildlife Resources (UDWR), which focused on the biology of the system and development of biology-based harvesting models. The models and their rationale are presented, their success in forecasting is evaluated, and implications for managing the harvest and conserving waterbirds are examined. We view this as an interesting case study because it transpired over a short time in a relatively simple system. This permitted us to clearly track management from the onset of a harvest market, through realization that the harvest had to be managed in the absence of needed biological knowledge, to the adaptive development of management strategies as biological knowledge was accumulated. The outcome illustrates the success that harvest management can attain with careful monitoring of the resource and terminating the harvest when a necessary escapement stock is attained.

Over the past century at the National Bison Range, temperature has increased by 0.6 °C, and annual precipitation has decreased by 26%, despite increases in May–June precipitation over the past 35 years. Limited experimental work to date has explored plant responses produced by the interaction of changes in both temperature and precipitation, and of the existing studies, none have focused on the endangered bunchgrass ecosystem. Using a 2-year climate change manipulation experiment, we show that bunchgrass productivity increased with supplemental growing season precipitation, while warming alone exerted no significant effect. More importantly, the ratio of June precipitation to minimum temperature, a representation of the interaction of climate variables, predicted bunchgrass productivity better than either climate variable individually. This ratio acted as a surrogate index reflecting increased evapotranspiration with rising temperatures and thus better predicting soil moisture available for plant growth. Experimental warming over the summer led to significantly lower plant species richness and biodiversity, while increased precipitation, when applied over the entire summer, counteracted some of these declines. Warming also led to greater and more rapid plant senescence over the summer, resulting in greater litter production [an increase of 47.82 ± 17.82 (± SE) percentage points] and potential fire risk. Given the simultaneous changes in precipitation and temperature predicted for the next century, multi-factor experiments are essential to understand how ecosystems will respond to future climate scenarios.

Consumers can alter decomposition rates through both feces and selective feeding in many ecosystems, but these combined effects have seldom been examined in tropical ecosystems. Members of the detrital food web (litter-feeders or microbivores) should presumably have greater effects on decomposition than herbivores, members of the green food web. Using litterbag experiments within a field enclosure experiment, we determined the relative effects of common litter snails (Megalomastoma croceum) and herbivorous walking sticks (Lamponius portoricensis) on litter composition, decomposition rates, and microbes in a Puerto Rican rainforest, and whether consumer effects were altered by canopy cover presence. Although canopy presence did not alter consumers' effects, focal organisms had unexpected influences on decomposition. Decomposition was not altered by litter snails, but herbivorous walking sticks reduced leaf decomposition by about 50% through reductions in high quality litter abundance and, consequently, lower bacterial richness and abundance. This relatively unexplored but potentially important link between tropical herbivores, detritus, and litter microbes in this forest demonstrates the need to consider autotrophic influences when examining rainforest ecosystem processes.

Using experiments and monitoring, we find that grasshoppers in a grassland ecosystem impact ecosystem functioning (nutrient cycling and primary production) in different ways among sites in the ecosystem. Experiments conducted over many years at two sites (21 and 15years, respectively) with the same grasshopper and plant species demonstrated that grasshoppers increased nitrogen availability (N) and consequently annual plant production (ANPP) at one site, and decreased N and consequently ANPP at the other site. Comparing the two sites, N increased on average by 8% and up to 21.6%, and resulting ANPP increased on average by 18.6% and up to 33.3%. Grasshoppers increase N and ANPP by preferentially feeding on slower decomposing plants, and the opposite occurs by preferentially feeding on faster decomposing plants. Monitoring 20 random sites in the ecosystem, grasshoppers consistently increased N and ANPP over 3years at 40% of sites, consistently decreased N and ANPP at 35% of sites, and sometimes increased and decreased N and ANPP at 25% of sites. Therefore, grassland grasshoppers, and insects in many ecosystems, may strongly affect ecosystem functioning.

The grasshopper, Camnula pellucida Scudder (Orthoptera: Acridae), is a severe pest of small grains and rangeland forage in North America. In a field experiment using cages containing C. pellucida in northwestern Montana, United States of America, we manipulated exposure to the fungal entomopathogen, Entomophaga grylli Fresenius (Entomophthorales: Entomophthoraceae) pathotype 1, temperature using small greenhouses, and moisture for the pathogen with water pillows. Treatment effects on fungal infection (mycosis) rates and grasshopper survivorship were assessed. Water pillows provided additional moist habitat for E. grylli without having an impact on grasshopper performance or the plant biomass and nitrogen content. Number of fungal spores, pathogen-induced mortality rates, and treatment effects on grass biomass and nitrogen content were also measured. Water pillows benefited the pathogen by increasing fungal spore levels by eightfold, which in turn shortened pathogen- exposed grasshopper survival time by half. In contrast, warming reduced fungal spore levels by 50% and subsequently reduced mortality from E. grylli by 67%. However, warmed pathogenexposed grasshoppers did not exhibit enhanced survival, which may be due, in part, to intraspecific competition among the surviving grasshoppers.

We examined the grazing rate of brine shrimp from Great Salt Lake, Utah (USA) at different life stages under varying water temperatures, salinities, and concentrations of two of their common phytoplankton foods: Dunaliella viridis and Coccochloris elabens. Trials for a brine shrimp life stage at a specific temperature, salinity, and food concentration occurred within 50 mL test tubes for 1 h; the difference between initial and final food concentrations represented grazing rate. General trends indicated grazing rate significantly increased with progressive life stages, increased with temperature, increased with food concentration, and decreased with salinity. Grazing rates for all life stages were greater on D. viridis compared to C. elabens. Brine shrimp life stages respond differently to environmental conditions. Specifically, while juveniles and adults varied their grazing rates in response to different food concentrations and salinities, nauplii grazing rate was not affected. Only adult grazing rates increased with increasing temperature. Differences in grazing rates under varying environmental conditions have implications for brine shrimp phenology, because brine shrimp populations in the Great Salt Lake are food limited in this highly variable environment.

Selective harvesting can cause evolutionary responses in populations via shifts in phenotypic characteristics, especially those affecting life history. Brine shrimp (Artemia franciscana) cysts in Great Salt Lake (GSL), Utah, USA are commercially harvested with techniques that select against floating cysts. This selective pressure could cause evolutionary changes over time. Our objectives are to (1) determine if there is a genetic basis to cyst buoyancy, (2) determine if cyst buoyancy and nauplii mortality have changed over time, and (3) to examine GSL environmental conditions over time to distinguish whether selective harvesting pressure or a trend in environmental conditions caused changes in cyst buoyancy and nauplii mortality. Mating crosses between floating and sinking parental phenotypes with two food concentrations (low and high) indicated there is a genetic basis to cyst buoyancy. Using cysts harvested from 1991-2011, we found cyst buoyancy decreased and nauplii mortality increased over time. Data on water temperature, salinity, and chlorophyll a concentration in GSL from 1994 to 2011 indicated that although water temperature has increased over time and chlorophyll a concentration has decreased over time, the selective harvesting pressure against floating cysts is a better predictor of changes in cyst buoyancy and nauplii mortality over time than trends in environmental conditions. Harvesting of GSL A. franciscana cysts is causing evolutionary changes, which has implications for the sustainable management and harvesting of these cysts. Monitoring phenotypic characteristics and life-history traits of the population should be implemented and appropriate responses taken to reduce the impacts of the selective harvesting.

Foraging data collected for beaver (Castor canadensis) at Isle Royale National Park, Michigan, during the summer of 1973 provided basic natural history information pertaining to diet, food preferences, rates of consumption and activity cycle. Beaver foraging was consistent with a linear programming model of herbivore optimal foraging. The model was used to predict beaver diet, the maximum distance a beaver foraged from its pond, and the manner in which the minimum and maximum diameters of beaver-cut woody vegetation changed with distance from the pond. INTRODUCTION Although many investigators have studied beaver (Castor canadensis), few quantitative data have been collected on food preferences and the basis for observed preference (see Jenkins and Busher, 1979, for review). Beaver appear to change preferences of both the species and diameters of plants they cut with increasing distance from their pond Uenkins, 1975, 1978, 1979, 1980) and Jenkins (1980) points out that this behavior might be explained by contingency models of optimal foraging (Schoener, 1971; Pyke et al., 1977) and "central place foraging" [extension of contingency foraging models to species that return, like the beaver, to a nest or "home" (Schoener, 1979; Orians and Pearson, 1979)]. In this paper, preference for certain plant species exhibited by beaver and the diverse mixture of plant foods in their summer diet will be examined to determine whether they can be predicted using a quantitative optimal foraging model, a linear programming model of optimal foraging developed specifically for herbivores (Belovsky, 1978). Finally, this herbivore foraging model is modified to include "central place foraging" to account for beaver plant choice with increasing distance from the pond. The model is applied, with limited data, to the foraging of beaver at one site; however, the results indicate that the model might be of value to the study of beaver at other sites and in other seasons. STUDY AREA Data were collected at three sites (two ponds and Lake Superior) in a forest at Isle Royale National Park, Michigan. Isle Royale is a 520 km2 archipelago in Lake Superior, 28 km from the nearest mainland. The upland forest surrounding all the sites is dominated by Betula allegheniensis, but the forest canopy in the lowlands immediately surrounding the two pond sites is primarily composed of Thuja occidentalis and Picea sp. These forests are more fully described by Belovsky and Jordan (1978). The two pond sites are located on Grace and Washington creeks. The third site is Washington Harbor on Lake Superior. The Grace Creek pond is 3.5 ha and the Washington Creek pond 1.5 ha; each of these sites maintained a single beaver family and lodge. The Washington Harbor site is larger (20 ha) and contains several lodges. All three sites contain aquatic macrophytes and are surrounded by abundant terrestrial vegetation. The pond sites have soft bottoms but the lake site bottom is primarily sand and gravel. These substrate differences lead to different aquatic macrophyte production, species and species diversity. METHODS Data collected on beaver include: (1) use of woody vegetation in relation to availability by species and by distance from the water's edge, and (2) diet and behavioral observations. All measurements were made between 20 May and 31 August 1973.