Response of Five Miscanthus sinensis Cultivars to Grasshopper Herbivory: Implications for Monitoring of Invasive Grasses in Protected Areas

Introduced grasses can aggressively expand their range and invade native habitats, including protected areas. Miscanthus sinensis is an introduced ornamental grass with 100+ cultivars of various invasive potential. Previous studies have demonstrated that the invasive potential of M. sinensis cultivars may be linked to seed viability, and some of the physiological traits, such as growth rate. Little is known, however, about whether these traits are associated with response of M. sinensis to insect herbivory, and whether plant tolerance and resistance to herbivory vary among its cultivars; which, in turn, can contribute to the invasive potential of some of M. sinensis cultivars. To address this issue, in our study we explored the response of five cultivars of M. sinensis to herbivory by Melanoplus grasshoppers. We demonstrated that plant responses varied among the cultivars during a season; all the cultivars, but “Zebrinus”, demonstrated a significant increase in plant tolerance by the end of the growing season regardless of the amount of sustained leaf damage. Different patterns in plant responses from “solid green” and “striped/spotted” varieties were recorded, with the lowest plant resistance detected for “Autumn Anthem” in the cage experiment. Our results have important applications for monitoring low-risk invaders in protected areas, as well as for biotic resistance of native communities to invasive grasses.

Toxin gene profiles and antimicrobial resistance of Clostridioides difficile infection: a single tertiary care center study in Iran

Background and Objectives: Due to the reduced susceptibility of clinical Clostridioides difficile strains in hospitals to var- ious antimicrobial agents, the importance of antimicrobial susceptibility testing (ASTs) has increased. This study aimed to investigate the toxin gene profiles and the antimicrobial resistance of C. difficile isolated from hospitalized patients suspected of having Clostridioides difficile infection (CDI) in Tehran, Iran. Materials and Methods: The stool samples were obtained from a hospitalized patients. The samples were shocked by al- cohol and the patients cultured on cycloserine-cefoxitin-fructose agar in anaerobic Conditions. Toxin assay was performed for detection of toxinogenic isolates. An antibiotic susceptibility test was done. Furthermore, their genome was extracted for PCR to confirm C. difficile and detect toxin gene profile. Results: Toxigenic C. difficile were identified in 21 of the 185 stool samples (11.3%). PCR detected seven toxin gene profiles; the highest prevalence was related to tcdA+B+, cdtA+B- toxin gene profile (57.1%). There were 14.3% and 28.6% resistant rates of the isolates towards vancomycin and metronidazole with the toxin gene profiles; tcdA+B+, cdtA±B+; and tc- dA+B-, cdtA-B+. All resistant isolates to moxifloxacin, clindamycin, and tetracycline were belonged to the toxin gene profiles; tcdA+B+, cdtA+B+; tcdA+B+, cdtA+B-, and tcdA-B+, cdtA+B-. Conclusion: Relative high resistance was detected towards metronidazole and vancomycin, although, still have acceptable activity for CDI treatment. However, a proper plan for the use of antibiotics and more regular screening of C. difficile anti- biotic resistance seems necessary.

Experimental Tree Mortality Does Not Induce Marsh Transgression in a Chesapeake Bay Low-Lying Coastal Forest

Transgression into adjacent uplands is an important global response of coastal wetlands to accelerated rates of sea level rise. “Ghost forests” mark a signature characteristic of marsh transgression on the landscape, as changes in tidal inundation and salinity cause bordering upland tree mortality, increase light availability, and the emergence of tidal marsh species due to reduced competition. To investigate these mechanisms of the marsh migration process, we conducted a field experiment to simulate a natural disturbance event (e.g., storm-induced flooding) by inducing the death of established trees (coastal loblolly pine, Pinus taeda) at the marsh-upland forest ecotone. After this simulated disturbance in 2014, we monitored changes in vegetation along an elevation gradient in control and treatment areas to determine if disturbance can lead to an ecosystem shift from forested upland to wetland vegetation. Light availability initially increased in the disturbed area, leading to an increase in biodiversity of vegetation with early successional grass and shrub species. However, over the course of this 5-year experiment, there was no increase in inundation in the disturbed areas relative to the control and pine trees recolonized becoming the dominant plant cover in the disturbed study areas. Thus, in the 5 years since the disturbance, there has been no overall shift in species composition toward more hydrophytic vegetation that would be indicative of marsh transgression with the removal of trees. These findings suggest that disturbance is necessary but not sufficient alone for transgression to occur. Unless hydrological characteristics suppress tree re-growth within a period of several years following disturbance, the regenerating trees will shade and outcompete any migrating wetland vegetation species. Our results suggest that complex interactions between disturbance, biotic resistance, and slope help determine the potential for marsh transgression.

Localised population collapse of the invasive brown alga, Undaria pinnatifida: Twenty years of monitoring on Wellington's south coast

<p>Invasive species pose a significant threat to marine environments around the world. Monitoring and research of invasive species is needed to provide direction for management programmes. This thesis is a continuation of research conducted on the invasive alga Undaria pinnatifida following its discovery on Wellington’s south coast in 1997. By compiling the results from previous monitoring surveys (1997-2000 and 2008) and carrying out additional seasonal surveys in 2018, I investigate the distribution and spread of U. pinnatifida on Wellington’s south coast, how this may have changed over time and what impacts it may have had on native macroalgal and invertebrate grazer communities. Intertidal macroalgal composition and U. pinnatifida abundance was recorded on fifteen occasions between 1997 and 2018 at two sites at Island Bay and two sites at Owhiro Bay. In addition, the subtidal abundance of six invertebrate grazers was recorded eight times within the same sampling period. Microtopography was also measured at each site to determine if topography had an influence on macroalgal composition. From 1997 to 2000 U. pinnatifida abundance gradually increased per year, but its spread remained localised to Island Bay. In 2008 U. pinnatifida had spread westward to Owhiro Bay where it was highly abundant. However, in 2018 no U. pinnatifida was recorded at any of the sites indicating a collapse of the invasion front. Further investigation revealed that U. pinnatifida was still present along the south coast with the nearest population only 500 m away from the nearest study site. The cause of the U. pinnatifida collapse is not known for certain, but it is unlikely that biotic resistance in the form of competitive exclusion or grazing or a change in environmental parameters such as temperature or nutrient concentration were contributing factors. It is speculated that the collapse arose from a multitude of confounding effects of which further research is needed to identify the exact cause. U. pinnatifida had no impact on macroalgal or grazer community composition. Additionally, microtopography also had no significant impact on macroalgal composition. This study reports the first ever invasion front collapse of U. pinnatifida in the world, and as a result, provides a new insight on U. pinnatifida distribution and invasion ecology. These findings can assist in predicting the future spread of U. pinnatifida populations as well as aid in formulation of new management strategies.</p>

Localised population collapse of the invasive brown alga, Undaria pinnatifida: Twenty years of monitoring on Wellington's south coast

<p>Invasive species pose a significant threat to marine environments around the world. Monitoring and research of invasive species is needed to provide direction for management programmes. This thesis is a continuation of research conducted on the invasive alga Undaria pinnatifida following its discovery on Wellington’s south coast in 1997. By compiling the results from previous monitoring surveys (1997-2000 and 2008) and carrying out additional seasonal surveys in 2018, I investigate the distribution and spread of U. pinnatifida on Wellington’s south coast, how this may have changed over time and what impacts it may have had on native macroalgal and invertebrate grazer communities. Intertidal macroalgal composition and U. pinnatifida abundance was recorded on fifteen occasions between 1997 and 2018 at two sites at Island Bay and two sites at Owhiro Bay. In addition, the subtidal abundance of six invertebrate grazers was recorded eight times within the same sampling period. Microtopography was also measured at each site to determine if topography had an influence on macroalgal composition. From 1997 to 2000 U. pinnatifida abundance gradually increased per year, but its spread remained localised to Island Bay. In 2008 U. pinnatifida had spread westward to Owhiro Bay where it was highly abundant. However, in 2018 no U. pinnatifida was recorded at any of the sites indicating a collapse of the invasion front. Further investigation revealed that U. pinnatifida was still present along the south coast with the nearest population only 500 m away from the nearest study site. The cause of the U. pinnatifida collapse is not known for certain, but it is unlikely that biotic resistance in the form of competitive exclusion or grazing or a change in environmental parameters such as temperature or nutrient concentration were contributing factors. It is speculated that the collapse arose from a multitude of confounding effects of which further research is needed to identify the exact cause. U. pinnatifida had no impact on macroalgal or grazer community composition. Additionally, microtopography also had no significant impact on macroalgal composition. This study reports the first ever invasion front collapse of U. pinnatifida in the world, and as a result, provides a new insight on U. pinnatifida distribution and invasion ecology. These findings can assist in predicting the future spread of U. pinnatifida populations as well as aid in formulation of new management strategies.</p>

Biotic resistance or invasional meltdown? Diversity reduces invasibility but not exotic dominance in southern California epibenthic communities

High community diversity may either prevent or promote the establishment of exotic species. The biotic resistance hypothesis holds that species-rich communities are more resistant to invasion than species-poor communities due to greater interspecific competition. Conversely, the invasional meltdown hypothesis proposes that greater exotic diversity increases invasibility via facilitative interactions between exotic species. To evaluate the degree to which biotic resistance or invasional meltdown influences marine community structure during the assembly period, we studied the development of marine epibenthic “fouling” communities at two southern California harbors. We found that fewer exotic species established as total and exotic richness increased during community assembly and that this effect remained after accounting for space availability. We also found that changes in exotic abundance decreased over time. Throughout the assembly period, gains in exotic abundance were greatest when space was abundant and richness was low. Altogether, we found greater support for biotic resistance than invasional meltdown, suggesting that both native and exotic species contribute to biotic resistance during early community development. However, this resistance may not reduce the total dominance of exotic species.

Long-Term Coexistence of Two Invasive Vespid Wasps in NW Patagonia (Argentina)

In Patagonia (Argentina) two non-native vespid wasps became established in the last decades. Vespula germanica was first detected in 1980 while V. vulgaris arrived some 30 years later. Both species can have a strong negative impact on agriculture, natural environment and on outdoor human activities. Invasion success -the establishment and spread of a species- may be influenced negatively by the degree of interaction with the resident native community, and alien species already present. The sequential arrival of these two wasps allows us to understand key questions of invasion ecology. Additionally, recognizing the outcome of the invasion by vespids in Patagonia -a region lacking native social wasps-, may help plan species-focused mitigation and control strategies. We explored long term species coexistence through the deterministic Lotka-Volterra competition model, using site-specific field data on prey captured (to estimate niche overlap) and current nest densities in sites. Food items carried by workers were similar but there is some degree of segregation. V. germanica nest density in shared sites, and in sites without coexistence, were 3.14 and 3.5 respectively, being higher for V. vulgaris with 4.71 and 5.33. The model predicts stable co-existence of both species in the invaded range, yet a higher abundance of V. vulgaris should be expected. Added to evidence on other foraging behavioral attributes of both wasp species and the invasion patterns observed in other regions, it is likely that the prior presence of V. germanica does not contribute significantly to the biotic resistance of the invaded range for V. vulgaris

A two-phase plant-soil feedback experiment to explore biotic influences on Phragmites australis invasion in North American wetlands

Plants can cultivate soil microbial communities that affect subsequent plant growth through a plant-soil feedback (PSF). Strong evidence indicates that PSFs can mediate the invasive success of exotic upland plants, but many of the most invasive plants occur in wetlands. In North America, the rapid spread of European Phragmites australis cannot be attributed to innate physiological advantages, thus PSFs may mediate invasion. Here we apply a two-phase fully-factorial plant-soil feedback design in which field-derived soil inocula were conditioned using saltmarsh plants and then were added to sterile soil mesocosms and planted with each plant type. This design allowed us to assess complete soil biota effects on intraspecific PSFs between native and introduced P. australis as well as heterospecific feedbacks between P. australis and the native wetland grass, Spartina patens. Our results demonstrate that native P. australis experienced negative conspecific feedbacks while introduced P. australis experienced neutral conspecific feedbacks. Interestingly, S. patens soil inocula inhibited growth in both lineages of P. australis while introduced and native P. australis inocula promoted the growth of S. patens suggestive of biotic resistance against P. australis invasion by S. patens . Our findings suggest that PSFs are not directly promoting the invasion of introduced P. australis in North America. Furthermore, native plants like S. patens seem to exhibit soil microbe mediated biotic resistance to invasion which highlights the importance of disturbance in mediating introduced P. australis invasion.

Invasion Impact and Biotic Resistance by Invertebrate Communities

<p>Invasive species have been recognized as one of the greatest threats to global biodiversity and can have dire economic consequences. Yet rates of invasion are increasing due to the fast and growing network of transportation across the globe. The establishment, spread and impact of invasive species are affected by environmental conditions as well as resident species. Species respond differently to the same abiotic factors and different native species can respond either positively or negatively to invasion. The interaction between invasive and resident species, as well as the effect of temperature on invasive species, has gained much attention. The synergistic effect of suboptimal temperature and biotic resistance could have a much stronger limiting or controlling effect on invasive species than either factor alone. Linepithema humile (Argentine ants) are invasive species originally from a Mediterranean climate, but successfully spreading into extra range habitats. The establishment and spread of these ants in temperate New Zealand represents an ideal model system for studying invasion biology in terms of temperature limits and biotic resistance effects. I investigated the changing distribution of the invasive species the Argentine ants over multiple years at five sites in New Zealand. To test whether their rate of spread corresponds with microclimate I investigated their fine-scare distribution patterns and evaluated the number of generations they may develop seasonally and annually in different microhabitat types. I also evaluated their impact on other arthropod species. I conducted a laboratory experiment to evaluate the effect of temperature on their aggression towards other species, walking speed, and foraging abundance. Similarly, I tested the effect of biotic resistance from other ant species (Monomorium antarcticum and Prolasius advenus) with varying colony sizes. I investigated whether there was any interactive effect of temperature and biotic resistance on the Argentine ants. The distribution of Argentine ants had declined across many invasion fronts over the past 7-8 years. They were more likely to be found in concrete, short grass and sandy habitats, which provide warm microsites. Degree-day calculations predicted that they could develop between 2.5 to 3 generations in each of the above microhabitats per year in urban and rural sites while they were predicted to be unable to develop one generation under tree habitats. In tall grass microhabitats they were predicted to develop between 1-1.5 generations per year. The Argentine ants were hypothesised to adversely affect many other arthropod species. Richness and abundance of resident beetle species were negatively correlated with the invasion of the Argentine ants. Areas invaded by the Argentine ants were also associated with a greater number of exotic beetle species, which may imply secondary invasion. Laboratory experiments showed that lowering temperatures below 17°C negatively affected the Argentine ants‟ walking speed, foraging abundance, aggression and their resource control. A high colony size of M. antarcticum (the competing ant species) affected the foraging success of Argentine ants, and the effect was stronger when coupled with unsuitable temperature (17°C and below). Therefore, Argentine ants are weak competitors at low temperature levels. The results of my thesis underline the importance of biotic and abiotic resistances, their interactive effect as well as the effect of the Argentine ants on other species. Based on climatic considerations and the habitat preferences of resident species it may be possible to predict future spread of the Argentine ants. More importantly, knowledge of microhabitat preferences and biotic resistance may help future control measures against Argentine ants based on management of vegetation structure and microhabitat availability.</p>