The effect of warmer winters on the demography of an outbreak insect is hidden by intraspecific competition

Warmer climates are predicted to increase bark beetle outbreak frequency, severity, and range. Even in favorable climates, however, outbreaks can decelerate due to resource limitation, which necessitates the inclusion of competition for limited resources in analyses of climatic effects on populations. We evaluated several hypotheses of how climate impacts mountain pine beetle reproduction using an extensive 9‐year dataset, in which nearly 10,000 trees were sampled across a region of approximately 90,000 km², that was recently invaded by the mountain pine beetle in Alberta, Canada. Our analysis supports the hypothesis of a positive effect of warmer winter temperatures on mountain pine beetle overwinter survival and provides evidence that the increasing trend in minimum winter temperatures over time in North America is an important driver of increased mountain pine beetle reproduction across the region. Although we demonstrate a consistent effect of warmer minimum winter temperatures on mountain pine beetle reproductive rates that is evident at the landscape and regional scales, this effect is overwhelmed by the effect of competition for resources within trees at the site level. Our results suggest that detection of the effects of a warming climate on bark beetle populations at small spatial scales may be difficult without accounting for negative density dependence due to competition for resources.     

FGF1 improves functional recovery through inducing PRDX1 to regulate autophagy and anti‐ROS after spinal cord injury

Fibroblast growth factor 1 (FGF1) is thought to exert protective and regenerative effects on neurons following spinal cord injury (SCI), although the mechanism of these effects is not well understood. The use of FGF1 as a therapeutic agent is limited by its lack of physicochemical stability and its limited capacity to cross the blood‐spinal cord barrier. Here, we demonstrated that overexpression of FGF1 in spinal cord following SCI significantly reduced tissue loss, protected neurons in the ventricornu, ameliorated pathological morphology of the lesion, dramatically improved tissue recovery via neuroprotection, and promoted axonal regeneration and remyelination both in vivo and in vivo. In addition, the autophagy and the expression levels of PRDX1 (an antioxidant protein) were induced by AAV‐FGF1 in PC12 cells after H₂O₂ treatment. Furthermore, the autophagy levels were not changed in PRDX1‐suppressing cells that were treated by AAV‐FGF1. Taken together, these results suggest that FGF1 improves functional recovery mainly through inducing PRDX1 expression to increase autophagy and anti‐ROS activity after SCI.     

Enhanced reproductive success revealed key strategy for persistence of devastated populations in Himalayan food‐deceptive orchid,Dactylorhiza hatagirea

Anthropogenic disturbances adversely affect populations of rare and endemic plants, resulting in reduction of their population size and performance. Among different plant groups, deceptive terrestrial orchids are vulnerable and possess greater extinction risks because of rarity in occurrence. To understand the response of food‐deceptive terrestrial orchids to disturbances, we selected Dactylorhiza hatagirea as our representative species, which is endemic to Himalaya, and studied its natural populations. This species is rare for being habitat specific, pollination limited and threatened in its natural habitats. We tested the hypothesis that disturbances lead to reduction in population size and plant performance of food‐deceptive terrestrial orchids. For assessing the impact of disturbance, two contrasting groups, heavily devastated (HD) and lightly devastated (LD), were identified on the basis of frequency and intensity of disturbance (harvesting of plant for tubers) by interviewing local people, medicinal plant extractors and shepherds. HD sites, in comparison to LD sites, were found to have smaller population sizes, but showed an increase in plant growth traits (plant height, specific leaf area, leaf N and specific shoot length). Similarly, plants at HD sites were found to have invested less in inflorescence (inflorescence size, inflorescence length, inflorescence length fraction and flowers per length), but despite that showed higher reproductive success. This was a clear indication of enhanced performance of its populations driven by disturbances. Our findings suggested that food‐deceptive species in small populations tend to reduce the probability of population extinction and have the capability to recover rapidly if conserved in time.     

Fire effects on the soil seed bank and post‐fire resilience of a semi‐arid shrubland in central Argentina

Soil seed bank is an important source of resilience of plant communities who suffered disturbances. We analysed the effect of an intense fire in the soil seed bank of a semi‐arid shrubland of Córdoba Argentina. We asked if the fire affected seed abundance, floristic and functional composition of the soil seed bank at two different layers (0–5 cm and 5–10 cm), and if fire could compromise the role of the soil seed bank as a source of resilience for the vegetation. We collected soil samples from a burned site and from a control site that had not burned. Samples were installed in a greenhouse under controlled conditions. During 12 months, we recorded all germinated seedlings. We compare soil seed bank with pre‐fire vegetation in terms of floristic and functional composition. The high‐intensity fire deeply affected the abundance of seeds in the soil, but it did not affect its floristic or functional composition. Floristic and functional composition of soil seed banks – at burned and unburned sites‐ differed markedly from that of the pre‐fire vegetation, although a previous study at the same site indicated high resilience after fire of this plant community. Our results indicate that resilience of this system is not strongly dependent on direct germination from seeds buried in the soil. Other sources of resilience, like colonization from neighbouring vegetation patches and resprouting from underground organs appear to gain relevance after an intense fire.     

Functional response of Neoseiulus barkeri Hughes on two-spotted spider mite (Acari: Tetranychidae)

Generalist predatory mites are the common phytoseiid fauna in many agroecosystems, but little attention has been paid to their potential as biological control agents. In this study, we determined the functional responses of adult females of the generalist predator Neoseiulus barkeri Hughes on eggs, larvae, and adults of the two-spotted spider mite, Tetranychus urticae Koch, in the laboratory. Predation experiments were conducted on pepper leaf discs over a 24 h period at 25±1°C, 70–80% RH and 16L:8D photoperiod. Prey densities ranged 5 to 80 eggs, or 5 to 40 larvae, or 1 to 8 female adults of T. urticae per disc. The predation rate of N. barkeri adult females on T. urticae eggs was the same as on its larvae, but the predation rate on adult females was much lower. The role of generalist predatory mites in integrated and biological control of greenhouse pests was discussed.     

Population and evolutionary dynamics in spatially structured seasonally varying environments

Increasingly imperative objectives in ecology are to understand and forecast population dynamic and evolutionary responses to seasonal environmental variation and change. Such population and evolutionary dynamics result from immediate and lagged responses of all key life‐history traits, and resulting demographic rates that affect population growth rate, to seasonal environmental conditions and population density. However, existing population dynamic and eco‐evolutionary theory and models have not yet fully encompassed within‐individual and among‐individual variation, covariation, structure and heterogeneity, and ongoing evolution, in a critical life‐history trait that allows individuals to respond to seasonal environmental conditions: seasonal migration. Meanwhile, empirical studies aided by new animal‐tracking technologies are increasingly demonstrating substantial within‐population variation in the occurrence and form of migration versus year‐round residence, generating diverse forms of ‘partial migration’ spanning diverse species, habitats and spatial scales. Such partially migratory systems form a continuum between the extreme scenarios of full migration and full year‐round residence, and are commonplace in nature. Here, we first review basic scenarios of partial migration and associated models designed to identify conditions that facilitate the maintenance of migratory polymorphism. We highlight that such models have been fundamental to the development of partial migration theory, but are spatially and demographically simplistic compared to the rich bodies of population dynamic theory and models that consider spatially structured populations with dispersal but no migration, or consider populations experiencing strong seasonality and full obligate migration. Second, to provide an overarching conceptual framework for spatio‐temporal population dynamics, we define a ‘partially migratory meta‐population’ system as a spatially structured set of locations that can be occupied by different sets of resident and migrant individuals in different seasons, and where locations that can support reproduction can also be linked by dispersal. We outline key forms of within‐individual and among‐individual variation and structure in migration that could arise within such systems and interact with variation in individual survival, reproduction and dispersal to create complex population dynamics and evolutionary responses across locations, seasons, years and generations. Third, we review approaches by which population dynamic and eco‐evolutionary models could be developed to test hypotheses regarding the dynamics and persistence of partially migratory meta‐populations given diverse forms of seasonal environmental variation and change, and to forecast system‐specific dynamics. To demonstrate one such approach, we use an evolutionary individual‐based model to illustrate that multiple forms of partial migration can readily co‐exist in a simple spatially structured landscape. Finally, we summarise recent empirical studies that demonstrate key components of demographic structure in partial migration, and demonstrate diverse associations with reproduction and survival. We thereby identify key theoretical and empirical knowledge gaps that remain, and consider multiple complementary approaches by which these gaps can be filled in order to elucidate population dynamic and eco‐evolutionary responses to spatio‐temporal seasonal environmental variation and change.     

Root exudates and their ecological consequences in forest ecosystems: Problems and perspective北大核心CSCD

Researches on rhizosphere ecological processes and the underlying mechanisms have become one of the most active and sensitive hotspots in soil science. Root exudates have specialized roles in mediating the nutrient cycling and signal transduction within root-soil-microbe interactions. They are the key driving factors in regulating the functions of rhizosphere micro-ecosystem, and serve as a major premise for the concept and ecological processes in rhizosphere. However, due to the instinctive advantages of crops, such as short life cycles and convenient operation, most previous studies on root exudation mainly focused on agricultural ecosystems and were primarily targeted at providing practical guidelines. In contrast, there have been relatively few investigations on root exudates of trees, which highly limited the comprehensive knowledge of the potential mechanisms of root exudates in mediating soil biogeochemical processes in forest ecosystems. Hence, in this review, based on the main findings in our previous studies and the emerging frontiers in rhizosphere ecology, we specifically reviewed the ecological consequences and key remaining challenges in researches on root exudation in forests. Finally, we identify several topics and research outlooks for guiding future work to facilitate studies on root exudation and its ecological consequences in forest ecosystems. © Chinese Journal of Plant Ecology