The Best Way to Assure the Future is to Invent It: the UND Wellness Center

This departmental history was written on the occasion of the UND Quasquicentennial in 2008.https://commons.und.edu/departmental-histories/1086/thumbnail.jp

NOTES: RANGE EXTENSION OF THE VIRGINIA OPOSSUM (DIDELPHIS VIRGINIANA) IN NORTH DAKOTA

The Virginia opossum (Didelphis virginiana) is broadly distributed across North America from Costa Rica in the south to southern Ontario in the north and from the southern Great Plains in the west to the eastern United States. The Virginia opossum also was introduced multiple times to thePacific Coast beginning in the late 1800s and has established populations in that region (Gardner and Sunquist 2003). This species is a habitat generalist known to frequent wetland and hardwood habitats but also can be found in grasslands, along forest edges, and in agricultural and suburban settings throughout its range (Gardner and Sunquist 2003, Beatty et al. 2014). However, the Virginia opossum is adapted poorly to winter, limiting its northern distribution to more tolerable warmer climates. It does not hibernate or exhibit torpor, and it will remain in its den rather than forage on nights when temperatures are below freezing or when there is deep snow, risking starvation if more than 54 days of winter are too harsh to forage (Brocke 1970). Despite these limitations, the Virginia opossum has expanded north in recent decades (Myers et al. 2009) and has been documented in novel areas of the Upper Midwest and New England (e.g., Dice 1927, Goodwin 1935, Jackson 1961). Both climate change and human land use alteration have been identified as contributing factors to their current range expansion. A recent study conducted across Michigan and Wisconsin identified reduced days of snow on the ground and increased agricultural land as two key factors facilitating the opossum’s expansion in the Midwest (Walsh and Tucker 2017). As generalist omnivores, opossums benefit from increased road kill and resources provided by agricultural practices (Beatty et al. 2014). Humans are further ameliorating winter conditions by providing shelter and easily accessible food, as evidenced by opossums in urban areas weighing more than individuals in adjacent natural habitats (Kanda 2005, Wright et al. 2012)

Constraints on the Establishment of Plants Along a Fluctuating Water-Depth Gradient

We used simulation modeling to investigate the relative importance of current environmental conditions and factors affecting establishment of different plant species on the formation of vegetative zonation patterns. We compared the results from a series of six models that incorporated increasing amounts of information about key factors affecting species\u27 ability to adjust to water-level fluctuations. We assessed model accuracy using aerial photographs taken of a 10-yr field experiment, in which 10 wetlands were flooded to 1 m above normal water level for 2 yr, drawn down for 1 or 2 yr, and reflooded for 5 yr to three different water levels (normal, +0.3 m, +0.6 m). We compared each model\u27s ability to predict relative areal cover of five dominant emergent species and to recreate the spatial structure of the landscape as measured by mean area of monospecific stands of vegetation and the degree to which the species were intermixed. The simplest model predicted post-treatment species distributions using logistic regressions based on initial species distributions along the water-depth gradient in the experimental wetlands. Subsequent models were based on germination, rhizomatous dispersal, and mortality functions implemented in each cell of a spatial grid. We tested the effect on model accuracy of incrementally adding data on five factors that can alter the composition and distribution of vegetative zones following a shift in environmental conditions: (1) spatial relationships between areas of suitable habitat (landscape geometry), (2) initial spatial distribution of adults, (3) the presence of ruderal species in the seed bank, (4) the distribution of seed densities in the seed bank, and (5) differential seedling survivorship. Because replicated, long-term data are generally not available, the evaluation of these models represents the first experimental test, of which we are aware, of the ability of a cellular-automaton-type model to predict changes in plant species\u27 distributions. Establishment constraints, such as recruitment from the seed bank, were most important during low-water periods and immediately following a change in water depth. Subsequent to a drop in water level, the most detailed models made the most accurate predictions. The accuracy of all the models converged in 1–2 years after an increase in water level, indicating that current environmental conditions became more important under stable conditions than the effects of historical recruitment events

General destabilizing effects of eutrophication on grassland productivity at multiple spatial scales

Fil: Hautier, Yann. Utrecht University. Department of Biology. Ecology and Biodiversity Group. The Netherlands.Fil: Zhang, Pengfei. Utrecht University. Department of Biology. Ecology and Biodiversity Group. The Netherlands. - Lanzhou University State. School of Life Science. Key Laboratory of Grassland and Agro - Ecosystems. People’s Republic of China. - Institute of Eco-Environmental Forensics of Shandong University. People’s Republic of China. - Ministry of Justice Hub for Research and Practice in Eco - Environmental Forensics. People’s Republic of China.Fil: Loreau, Michael. Centre for Biodiversity Theory and Modelling. Theoretical and Experimental Ecology Station.CNRS. France.Fil: Wilcox, Kevin R. University of Wyoming. Department of Ecosystem Science and Management. Laramie, WY, USA.Fil: Seabloom, Eric W. University of Minessota. Department of Ecology, Evolution, and Behavior. Minessota, USA.Fil: Tognetti, Pedro Maximiliano. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA). Buenos Aires, Argentina. - CONICET – Universidad de Buenos Aires. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA). Buenos Aires, Argentina.Eutrophication is a widespread environmental change that usually reduces the stabilizing effect of plant diversity on productivity in local communities. Whether this effect is scale\ndependent remains to be elucidated. Here, we determine the relationship between plant diversity and temporal stability of productivity for 243 plant communities from 42 grasslands\nacross the globe and quantify the effect of chronic fertilization on these relationships.\nUnfertilized local communities with more plant species exhibit greater asynchronous dynamics among species in response to natural environmental fluctuations, resulting in greater local stability (alpha stability). Moreover, neighborhood communities that have greater spatial variation in plant species composition within sites (higher beta diversity) have greater spatial synchrony of productivity among communities, resulting in greater stability at the larger scale (gamma stability). Importantly, fertilization consistently weakens the contribution of plant diversity to both of these stabilizing mechanisms, thus diminishing the positive effect of biodiversity on stability at differing spatial scales. Our findings suggest that preserving grassland functional stability requires conservation of plant diversity within and among ecological communities.grafs

WHAT DETERMINES THE STRENGTH OF A TROPHIC CASCADE?

Trophic cascades have been documented in a diversity of ecological systems and can be important in determining biomass distribution within a community. To date, the literature on trophic cascades has focused on whether and in which systems cascades occur. Many biological (e.g., productivity:biomass ratios) and methodological (e.g., experiment size or duration) factors vary with the ecosystem in which data were collected, but ecosystem type, per se, does not provide mechanistic insights into factors controlling cascade strength. Here, we tested various hypotheses about why trophic cascades occur and what determines their magnitude using data from 114 studies that measured the indirect trophic effects of predators on plant community biomass in seven aquatic and terrestrial ecosystems. Using meta-analysis, we examined the relationship between the indirect effect of predator manipulation on plants and 18 biological and methodological factors quantified from these studies. We found, in contrast to predictions, that high system productivity and low species diversity do not consistently generate larger trophic cascades. A combination of herbivore and predator metabolic factors and predator taxonomy (vertebrate vs. invertebrate) explained 31% of the variation in cascade strength among all 114 studies. Within systems, 18% of the variation in cascade strength was explained with similar predator and herbivore characteristics. Within and across all systems, the strongest cascades occurred in association with invertebrate herbivores and endothermic vertebrate predators. These associations may result from a combination of true biological differences among species with different physiological requirements and bias among organisms studied in different systems. Thus, although cascade strength can be described by biological characteristics of predators and herbivores, future research on indirect trophic effects must further examine biological and methodological differences among studies and systems. © 2005 by the Ecological Society of America

Seed and establishment limitation contribute to long-term native forb declines in California grasslands

The effects of exotic species invasions on biodiversity vary with spatial scale, and documentation of local-scale changes in biodiversity following invasion is generally lacking. Coupling long-term observations of local community dynamics with experiments to determine the role played by exotic species in recruitment limitation of native species would inform both our understanding of exotic impacts on natives at local scales and regional-scale management efforts to promote native persistence. We used field experimentation to quantify propagule and establishment limitation in a suite of native annual forbs in a California reserve, and compared these findings to species abundance trends within the same sites over the past 48 years. Observations at 11 paired sites (inside and outside the reserve) indicated that exotic annual plants have continued to increase in abundance over the past 48 years. This trend suggests the system has not reached equilibrium >250 years after exotic species began to spread, and 70 years after livestock grazing ceased within the reserve. Long-term monitoring observations also indicated that six native annual forb species went extinct from more local populations than were colonized. To determine the potential role of exotic species in these native plant declines, we added seed of these species into plots adjacent to monitoring sites where plant litter and live grass competition were removed. Experimental results suggest both propagule and establishment limitation have contributed to local declines observed for these native forbs. Recruitment was highest at sites that had current or historical occurrences of the seeded species, and in plots where litter was removed. Grazing history (i.e., location within or outside the reserve) interacted with exotic competition removal, such that removal of live grass competition increased recruitment in more recently grazed sites. Abundance of forbs was positively related to recruitment, while abundance of exotic forbs was negatively related. Thus, exotic competition is likely only one factor contributing to local declines of native species in invaded ecosystems, with a combination of propagule limitation, site quality, and land use history also playing important and interactive roles in native plant recruitment.This is the publisher’s final pdf. The published article is copyrighted by Ecological Society of America and can be found at: http://www.esa.org/.Keywords: Recruitment limitation, Community assembly, Livestock grazing, USA grasslands, Exotic species, California, Competition, Invasion, Propagule limitationKeywords: Recruitment limitation, Community assembly, Livestock grazing, USA grasslands, Exotic species, California, Competition, Invasion, Propagule limitatio

A cross‐ecosystem comparison of the strength of trophic cascades

Although trophic cascades (indirect effects of predators on plants via herbivores) occur in a wide variety of food webs, the magnitudes of their effects are often quite variable. We compared the responses of herbivore and plant communities to predator manipulations in 102 field experiments in six different ecosystems: lentic (lake and pond), marine, and stream benthos, lentic and marine plankton, and terrestrial (grasslands and agricultural fields). Predator effects varied considerably among systems and were strongest in lentic and marine benthos and weakest in marine plankton and terrestrial food webs. Predator effects on herbivores were generally larger and more variable than on plants, suggesting that cascades often become attenuated at the plant - herbivore interface. Top-down control of plant biomass was stronger in water than on land; however, the differences among the five aquatic food webs were as great as those between wet and dry systems