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)

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

The synergistic response of primary production in grasslands to combined nitrogen and phosphorus addition is caused by increased nutrient uptake and retention

Background and aims A synergistic response of aboveground plant biomass production to combined nitrogen (N) and phosphorus (P) addition has been observed in many ecosystems, but the underlying mechanisms and their relative importance are not well known. We aimed at evaluating several mechanisms that could potentially cause the synergistic growth response, such as changes in plant biomass allocation, increased N and P uptake by plants, and enhanced ecosystem nutrient retention. Methods We studied five grasslands located in Europe and the USA that are subjected to an element addition experiment composed of four treatments: control (no element addition), N addition, P addition, combined NP addition. Results Combined NP addition increased the total plant N stocks by 1.47 times compared to the N treatment, while total plant P stocks were 1.62 times higher in NP than in single P addition. Further, higher N uptake by plants in response to combined NP addition was associated with reduced N losses from the soil (evaluated based on soil δ15N) compared to N addition alone, indicating a higher ecosystem N retention. In contrast, the synergistic growth response was not associated with significant changes in plant resource allocation. Conclusions Our results demonstrate that the commonly observed synergistic effect of NP addition on aboveground biomass production in grasslands is caused by enhanced N uptake compared to single N addition, and increased P uptake compared to single P addition, which is associated with a higher N and P retention in the ecosystem

How do nutrients change flowering in prairies?

Farmers today apply more synthetic fertilizers to farm fields than ever before – but not all of these nutrients are used by crops: some fertilizer escapes through the air, soil, or water. Nitrogen, phosphorous, and potassium flow off farm fields when it rains, billow into the air when fields are plowed, and drift with the wind to other areas. Extra nutrients are also released to the air when people burn fossil fuels. We wanted to find out: what happens when these extra nutrients land on wild prairie ecosystems? How do its wild plants respond? Do they all just grow better? Or could there be any negative side effects? To answer these questions, we systematically added nutrients to experimental patches of prairie. We found that these added nutrients (specifically nitrogen) made early-season plants thrive while reducing the amount of late-season plants, but only in some prairie types. This change could have serious implications for the way prairie ecosystems function

Viral diversity and prevalence gradients in North American Pacific Coast grasslands

Host-pathogen interactions may be governed by the number of pathogens coexisting within an individual host (i.e., coinfection) and among different hosts, although most sampling in natural systems focuses on the prevalence of single pathogens and/or single hosts. We measured the prevalence of four barley and cereal yellow dwarf viruses (B/CYDVs) in three grass species at 26 natural grasslands along a 2000-km latitudinal gradient in the western United States and Canada. B/CYDVs are aphid-vectored RNA viruses that cause one of the most prevalent of all plant diseases worldwide. Pathogen prevalence and coinfection were uncorrelated, suggesting that different forces likely drive them. Coinfection, the number of viruses in a single infected host (alpha diversity), did not differ among host species but increased roughly twofold across our latitudinal transect. This increase in coinfection corresponded with a decline in among-host pathogen turnover (beta diversity), suggesting that B/CYDVs in northern populations experience less transmission limitation than in southern populations. In contrast to pathogen diversity, pathogen prevalence was a function of host identity as well as biotic and abiotic environmental conditions. Prevalence declined with precipitation and increased with soil nitrate concentration, an important limiting nutrient for hosts and vectors of B/CYDVs. This work demonstrates the need for further studies of processes governing coinfection, and the utility of applying theory developed to explain diversity in communities of free-living organisms to pathogen systems