A mast‐seeding desert shrub regulates population dynamics and behavior of its heteromyid dispersers

Granivorous rodent populations in deserts are primarily regulated through precipitation‐driven resource pulses rather than pulses associated with mast‐seeding, a pattern more common in mesic habitats. We studied heteromyid responses to mast‐seeding in the desert shrub blackbrush (Coleogyne ramosissima), a regionally dominant species in the Mojave–Great Basin Desert transition zone. In a 5‐year study at Arches National Park, Utah, USA, we quantified spatiotemporal variation in seed resources in mast and intermast years in blackbrush‐dominated and mixed desert vegetation and measured responses of Dipodomys ordii (Ord's kangaroo rat) and Perognathus flavescens (plains pocket mouse). In blackbrush‐dominated vegetation, blackbrush seeds comprised >79% of seed production in a mast year, but 0% in the first postmast year. Kangaroo rat abundance in blackbrush‐dominated vegetation was highest in the mast year, declined sharply at the end of the first postmast summer, and then remained at low levels for 3 years. Pocket mouse abundance was not as strongly associated with blackbrush seed production. In mixed desert vegetation, kangaroo rat abundance was higher and more uniform through time. Kangaroo rats excluded the smaller pocket mice from resource‐rich patches including a pipeline disturbance and also moved their home range centers closer to this disturbance in a year of low blackbrush seed production. Home range size for kangaroo rats was unrelated to seed resource density in the mast year, but resource‐poor home ranges were larger (P < 0.001) in the first postmast year, when resources were limiting. Blackbrush seeds are higher in protein and fat but lower in carbohydrates than the more highly preferred seeds of Indian ricegrass (Achnatherum hymenoides) and have similar energy value per unit of handling time. Kangaroo rats cached seeds of these two species in similar spatial configurations, implying that they were equally valued as stored food resources. Blackbrush mast is a key resource regulating populations of kangaroo rats in this ecosystem.     

Tree diversity,tree height and environmental harshness in eastern and western North America

Does variation in environmental harshness explain local and regional species diversity gradients? We hypothesise that for a given life form like trees, greater harshness leads to a smaller range of traits that are viable and thereby also to lower species diversity. On the basis of a strong dependence of maximum tree height on site productivity and other measures of site quality, we propose maximum tree height as an inverse measure of environmental harshness for trees. Our results show that tree species richness is strongly positively correlated with maximum tree height across multiple spatial scales in forests of both eastern and western North America. Maximum tree height co‐varied with species richness along gradients from benign to harsh environmental conditions, which supports the hypothesis that harshness may be a general mechanism limiting local diversity and explaining diversity gradients within a biogeographic region.     

Emergence and accumulation of novel pathogens suppress an invasive species

Emerging pathogens are a growing threat to human health, agriculture and the diversity of ecological communities but may also help control problematic species. Here we investigated the diversity, distribution and consequences of emerging fungal pathogens infecting an aggressive invasive grass that is rapidly colonising habitats throughout the eastern USA. We document the recent emergence and accumulation over time of diverse pathogens that are members of a single fungal genus and represent multiple, recently described or undescribed species. We also show that experimental suppression of these pathogens increased host performance in the field, demonstrating the negative effects of emerging pathogens on invasive plants. Our results suggest that invasive species can facilitate pathogen emergence and amplification, raising concerns about movement of pathogens among agricultural, horticultural, and wild grasses. However, one possible benefit of pathogen accumulation is suppression of aggressive invaders over the long term, potentially abating their negative impacts on native communities.     

Oxidative shielding and the cost of reproduction

Life‐history theory assumes that reproduction and lifespan are constrained by trade‐offs which prevent their simultaneous increase. Recently, there has been considerable interest in the possibility that this cost of reproduction is mediated by oxidative stress. However, empirical tests of this theory have yielded equivocal support. We carried out a meta‐analysis to examine associations between reproduction and oxidative damage across markers and tissues. We show that oxidative damage is positively associated with reproductive effort across females of various species. Yet paradoxically, categorical comparisons of breeders versus non‐breeders reveal that transition to the reproductive state is associated with a step‐change reduction in oxidative damage in certain tissues and markers. Developing offspring may be particularly sensitive to harm caused by oxidative damage in mothers. Therefore, such reductions could potentially function to shield reproducing mothers, gametes and developing offspring from oxidative insults that inevitably increase as a consequence of reproductive effort. According to this perspective, we hypothesise that the cost of reproduction is mediated by dual impacts of maternally‐derived oxidative damage on mothers and offspring, and that mothers may be selected to diminish such damage. Such oxidative shielding may explain why many existing studies have concluded that reproduction has little or no oxidative cost. Future advance in life‐history theory therefore needs to take account of potential transgenerational impacts of the mechanisms underlying life‐history trade‐offs.     

Investigating the environmental Kuznets curve hypothesis in seven regions: The role of renewable energy

The aim of this research is to investigate how renewable energy consumption effects pollution and whether the relationship between income and pollution formulates the inverted U-shaped relationship which signals the existence of the environmental Kuznets curve (EKC). To realize the aims of this study, non-stationary panel data techniques were utilized to examine the seven selected regions. According to Pedroni and Fisher type cointegration tests, the variables were cointegrated. Moreover, the dynamic ordinary least square (DOLS) and the vector error correction model Granger causality revealed that renewable energy consumption has a significant negative effect on pollution in Central and Eastern Europe, Western Europe, East Asia and the Pacific, South Asia, and the Americas. However, the tests revealed that renewable energy consumption has no significant effect on pollution in the Middle East and North Africa and Sub-Saharan Africa. In addition, the results in general indicated that the existence of the EKC hypothesis is determined by the significance of the renewable energy consumption. Therefore, the EKC hypothesis was only found in the regions where their renewable energy has a significant correlation with pollution in both the short run and the long run. Furthermore, a number of policy recommendations were provided for the investigated regions.     

Bedbugs Evolved before Their Bat Hosts and Did Not Co-speciate with Ancient Humans

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Energetic reserves, leptin and testosterone: a refinement of the immunocompetence handicap hypothesis

The immunocompetence handicap hypothesis (ICHH) assumes that testosterone (T), required for the expression of sexual traits, can also incur a cost due to its immunosuppressive properties. However, T-dependent immunosuppression could also arise as an indirect consequence of energy reallocation from the immune system to other metabolic demands. Leptin is mostly produced in lipogenic tissues and its circulating level is positively correlated with the amount of lipid reserves. Leptin also has an important role as immunoenhancer and we suggest that this hormone could play a role as a mediator of the immunosuppressive effect of testosterone. In particular, we propose that only the individuals able to maintain large lipid reserves (with high leptin levels), while sustaining high testosterone levels, might be able to develop sexual displays without an impairment of their immune defences. Here, we tested one of the assumptions underlying this extension of the ICHH: leptin administration should attenuate testosterone-induced immunosuppression. T-implanted and control male zebra finches (Taeniopygia guttata) received daily injections of leptin or phosphate buffered saline. T-implants initially depressed the phytohaemagglutinin-induced immune response. However, T-birds injected with leptin enhanced their immune response to the level of control birds. These results open a new perspective on the study of the ICHH.