Geology topics

Stanley D. Smith

Publications and source records attributed to Stanley D. Smith.

4 recordsLinked to original sources

USGS2011

Shifting species interactions in terrestrial dryland ecosystems under altered water availability and climate change

Species interactions play key roles in linking the responses of populations, communities, and ecosystems to environmental change. For instance, species interactions are an important determinant of the complexity of changes in trophic biomass with variation in resources. Water resources are a major driver of terrestrial ecology and climate change is expected to greatly alter the distribution of this critical resource. While previous studies have documented strong effects of global environmental change on species interactions in general, responses can vary from region to region. Dryland ecosystems occupy more than one-third of the Earth's land mass, are greatly affected by changes in water availability, and are predicted to be hotspots of climate change. Thus, it is imperative to understand the effects of environmental change on these globally significant ecosystems. Here, we review studies of the responses of population-level plant-plant, plant-herbivore, and predator-prey interactions to changes in water availability in dryland environments in order to develop new hypotheses and predictions to guide future research. To help explain patterns of interaction outcomes, we developed a conceptual model that views interaction outcomes as shifting between (1) competition and facilitation (plant-plant), (2) herbivory, neutralism, or mutualism (plant-herbivore), or (3) neutralism and predation (predator-prey), as water availability crosses physiological, behavioural, or population-density thresholds. We link our conceptual model to hypothetical scenarios of current and future water availability to make testable predictions about the influence of changes in water availability on species interactions. We also examine potential implications of our conceptual model for the relative importance of top-down effects and the linearity of patterns of change in trophic biomass with changes in water availability. Finally, we highlight key research needs and some possible broader impacts of our findings. Overall, we hope to stimulate and guide future research that links changes in water availability to patterns of species interactions and the dynamics of populations and communities in dryland ecosystems.

Biological Reviews↗

USGS2007

Dynamics of cover, UV-protective pigments, and quantum yield in biological soil crust communities of an undisturbed Mojave Desert shrubland

Biological soil crusts are an integral part of dryland ecosystems. We monitored the cover of lichens and mosses, cyanobacterial biomass, concentrations of UV-protective pigments in both free-living and lichenized cyanobacteria, and quantum yield in the soil lichen species Collema in an undisturbed Mojave Desert shrubland. During our sampling time, the site received historically high and low levels of precipitation, whereas temperatures were close to normal. Lichen cover, dominated by Collema tenax and C. coccophorum , and moss cover, dominated by Syntrichia caninervis , responded to both increases and decreases in precipitation. This finding for Collema spp. at a hot Mojave Desert site is in contrast to a similar study conducted at a cool desert site on the Colorado Plateau in SE Utah, USA, where Collema spp. cover dropped in response to elevated temperatures, but did not respond to changes in rainfall. The concentrations of UV-protective pigments in free-living cyanobacteria at the Mojave Desert site were also strongly and positively related to rainfall received between sampling times ( R 2 values ranged from 0.78 to 0.99). However, pigment levels in the lichenized cyanobacteria showed little correlation with rainfall. Quantum yield in Collema spp. was closely correlated with rainfall. Climate models in this region predict a 3.5–4.0 °C rise in temperature and a 15–20% decline in winter precipitation by 2099. Based on our data, this rise in temperature is unlikely to have a strong effect on the dominant species of the soil crusts. However, the predicted drop in precipitation will likely lead to a decrease in soil lichen and moss cover, and high stress or mortality in soil cyanobacteria as levels of UV-protective pigments decline. In addition, surface-disturbing activities (e.g., recreation, military activities, fire) are rapidly increasing in the Mojave Desert, and these disturbances quickly remove soil lichens and mosses. These stresses combined are likely to lead to shifts in species composition and the local extirpation of some lichen or moss species. As these organisms are critical components of nutrient cycling, soil fertility, and soil stability, such changes are likely to reverberate throughout these ecosystems.

Mojave Desert↗

USGS2001

Leaf conductance decreased under free-air CO2 enrichment (FACE) for three perennials in the Nevada desert

A common response of plants to elevated atmospheric CO 2 concentration (CO 2 ) is decreased leaf conductance. Consequently, leaf temperature is predicted to increase under elevated CO 2 . Diurnal patterns of leaf conductance and temperature were measured for three desert perennials, the C 3 shrub Larrea tridentata , C 3 tussock grass Achnatherum hymenoides and C 4 tussock grass Pleuraphis rigida , at the Nevada Desert FACE facility. Measurements were made on ambient and c . 550 µmol mol −1 CO 2 plots through both a wet and dry year. Reductions in conductance were 35%, 20% and 13% for Pleuraphis , Achnatherum and Larrea , respectively. Decreased conductance occurred throughout the day only for Pleuraphis . Both C 3 species had smaller CO 2 effects during dry periods than wet. Leaf temperature did not differ significantly between elevated and ambient CO 2 for any species. Comparisons of blower-control and nonring plots indicated that the FACE apparatus did not confound our results. All three species exhibited decreased leaf conductance under elevated CO 2 , although reductions were not uniform during the day or among years. Nonetheless, leaf energy balance was only minimally changed for these microphyllous desert perennials.

Nevada↗

USGS1979

Mortality of experimentally descaled smolts of coho salmon (Oncorhynchus kisutch) in fresh and salt water

Removal of slime from 25% of the body caused no deaths among smolts of coho salmon in fresh water or in seawater (28&permil;). Removal of slime and scales from the same percentage of body area caused no deaths in fresh water, but 75% mortality within 10 days in seawater. The 10-day median tolerance limit was 10% scale removal immediately before the smolts entered seawater. Mortality was highest when the scales were removed from the area of the rib cage. Recovery of smolts in fresh water from a loss of scales that would be lethal in seawater occurred rapidly; 90% of the fish regained tolerance to seawater within 1 day.

Transactions of the American Fisheries Society↗