Effects of large herbivores on grassland arthropod diversity

Both arthropods and large grazing herbivores are important components and drivers of biodiversity in grassland ecosystems, but a synthesis of how arthropod diversity is affected by large herbivores has been largely missing. To fill this gap, we conducted a literature search, which yielded 141 studies on this topic of which 24 simultaneously investigated plant and arthropod diversity. Using the data from these 24 studies, we compared the responses of plant and arthropod diversity to an increase in grazing intensity. This quantitative assessment showed no overall significant effect of increasing grazing intensity on plant diversity, while arthropod diversity was generally negatively affected. To understand these negative effects, we explored the mechanisms by which large herbivores affect arthropod communities: direct effects, changes in vegetation structure, changes in plant community composition, changes in soil conditions, and cascading effects within the arthropod interaction web. We identify three main factors determining the effects of large herbivores on arthropod diversity: (i) unintentional predation and increased disturbance, (ii) decreases in total resource abundance for arthropods (biomass) and (iii) changes in plant diversity, vegetation structure and abiotic conditions. In general, heterogeneity in vegetation structure and abiotic conditions increases at intermediate grazing intensity, but declines at both low and high grazing intensity. We conclude that large herbivores can only increase arthropod diversity if they cause an increase in (a)biotic heterogeneity, and then only if this increase is large enough to compensate for the loss of total resource abundance and the increased mortality rate. This is expected to occur only at low herbivore densities or with spatio-temporal variation in herbivore densities. As we demonstrate that arthropod diversity is often more negatively affected by grazing than plant diversity, we strongly recommend considering the specific requirements of arthropods when applying grazing management and to include arthropods in monitoring schemes. Conservation strategies aiming at maximizing heterogeneity, including regulation of herbivore densities (through human interventions or top-down control), maintenance of different types of management in close proximity and rotational grazing regimes, are the most promising options to conserve arthropod diversity

An experimental study of the effects of pH and nitrogen on grassland vegetation

The response of plant species to a full-factorial experimental manipulation of soil pH and soil N in a Minnesota old field is compared to patterns observed in a chronosequence of old fields. Agropyron repens reached its greatest relative abundance in low pH but high N treatments. Schizachyrium scoparium was less affected by N, but was most abundant at low pH. Poa pratensis had its greatest relative abundance in high N and high pH treatments. Total biomass and species richness were also influenced by the treatments. Thus, the common plant species were differentiated in their responses to pH and N manipulations. However, these pH and N responses did not explain the patterns observed in the old field chronosequence unless the differential colonization abilities of the species and the relationships between soil pH, soil N and successional age were considered

Sex and Gender in Psychotrauma Research

BackgroundPosttraumatic stress disorder (PTSD) is two to three times more common in women than in men. To better understand this phenomenon, we need to know why men, women, and possibly individuals with other sex/gender identities respond differently to trauma. To stimulate sex and gender sensitive research, the European Journal of Psychotraumatology (EJPT) was the first journal to adopt a gender policy. In addition, a call for papers entitled Integrating and Evaluating Sex and Gender in Psychotrauma Research was announced. ObjectiveThis special issue synthesizes the past five years of psychotrauma research with regard to sex/gender differences. MethodSeventy-seven articles were identified from EJPT archives, including five systematic reviews. These articles examined sex differences and/or gender differences in exposure to trauma, posttraumatic stress responses, or how sex and gender impacts (mental) health outcomes or treatment responses. ResultsFindings from these studies outlined that: 1. sex and gender still need to be more clearly defined, also in relation to the context that codetermine trauma responses, like other ‘diversity’ variables; 2. in most studies, sex and gender are measured or reported as binary variables; 3. sex and gender are important variables when examining trauma exposure, responses to these events, symptoms trajectories, and mental and physical health outcomes across the life span; and 4. in PTSD treatment studies, including a meta-analysis and a systematic review, sex and gender were not significant predictors of treatment outcome.ConclusionFuture research must focus on sex and gender as important and distinct variables; they should include sex and gender in their statistical analyses plan to better clarify associations between these variables and (responses to) psychotrauma. To enhance reporting of comparable data across studies, we provide suggestions for future research, including how to assess sex and gender.</p