Acta Oecologica-International Journal of Ecology最新文献

Competition can cause the loss of certain species and concurrent dominance of other species, especially with invasive species. Here we explore the mechanisms behind competition between an invasive grass species, smooth brome Bromus inermis, and two dominant native grass species, big bluestem Andropogon gerardi and little bluestem Schizachyrium scoparium. Bromus inermis is now found in all contiguous states in the United States and may outcompete native species in North America, particularly when grazed. Grazing was simulated by cutting the plants once per year and three times per year, done monthly in the summer (plus an uncut control treatment). We grew all three species in the greenhouse as monocultures, as well as in a mix of B. inermis + A. gerardi and B. inermis + S. scoparium. We found that there was considerable yield suppression when smooth brome competed with both big- and little bluestem mixes with B. inermis after three cuts. Non-structural carbohydrates and total nitrogen declined considerably aboveground for the B. inermis + A. gerardi mix after three cuts. The clearest overall impact was that of cutting frequency, with plants receiving three cuts per season having lowest biomass. We conclude that the maintenance of biomass in B. inermis, despite the level of simulated herbivory, was probably the reason that they remained competitively dominant over the two native bluestem species.

Forest litter is an important factor in shaping the soil environment. In the temperate climate zone, there is a lack of research on the impact of shrubs on the properties of forest soils. The aim of this study was to determine the effect of litter decomposition and nutrient release from litter with an admixture of shrubs on enzymatic activity and C/N/P stoichiometry of soils. The study included pine monocultures and pine stands with an admixture of rowan or alder buckthorn or European hazelnut. In our experiment, we determined the chemical properties of litter of various shrub species. We determined the chemical composition of leachates from decomposing litter and the rate of decomposition of litter of different species. We determined the C/N/P stoichiometry and enzymatic activity of soils affected by litter of various species of shrubs. The quality of litter and the rate of its decomposition is an important factor shaping the properties of forest soils. Components released from the decomposition of litter with the shrubs had a positive effect on the C/N/P stoichiometry of soils and enzyme activity. The results obtained in this experiment confirm the possibility of using shrubs, especially alder buckthorn and European hazelnut, to improve the properties of forest soils. As a result of the decomposition of alder buckthorn or European hazelnut litter, the soil becomes enriched with nutrients. The decomposition of litter with shrub admixture occurs much faster compared to pine litter, which has a positive effect on the C/N/P stoichiometry and the enzymatic activity of soils.

Numerous researchers have endeavored to discover a general explanation for elevational diversity gradients, but we remain unclear whether similar diversity patterns and driving factors exist for the same life-forms along different elevational gradients within the same region. In the Ili Valley of the Central Asia Biodiversity Hotspot, we selected four elevational gradients with similar species pools and evolutionary histories to assess the factors influencing of elevational diversity pattern. Our findings indicate distinct patterns of species diversity for the same life-forms along the four elevational gradients within the same region. The species richness and abundance of woody plants are primarily controlled by climate-based factors (i.e., minimum temperature, temperature seasonality, mean annual precipitation, and potential evapotranspiration) along four elevational diversity gradients in the Ili Valley, while the species richness and abundance of herbaceous plants are primarily influenced by both climate and soil nutrients (i.e., soil organic carbon). In conclusion, climate is an important driver of species diversity for woody plants, and that the driving mechanisms of herbaceous plant diversity along elevational gradients should consider both climate and soil nutrients.

In the vast majority of gall insects, solitary establishment of a gall is the rule, but the primitively social aphid Tamalia coweni exhibits communal gall occupation under conditions of increased competition for gall sites. Here we tested the hypothesis that gall-sharing rates are a function of variable population densities in galls and on leaves of the host plant. Current results, observed under natural density and temporal variation, demonstrate that population density is a strong predictor of co-occupation rates. Although basal leaf positions were more frequently chosen as gall-induction sites than distal ones, there was no evidence these sites were more likely to be co-occupied. In addition to spatial constraints, temporal constraints may be important in mediating primitive sociality in T. coweni.

Human-induced disturbances have a significant impact on populations of polypores. In the 20th century, Białowieża Primeval Forest (BPF) was strongly affected by harvesting disturbance. As a result of natural regeneration, forest stands are composed predominantly of pioneer species regenerated in harvested areas. We asked how substrate type, stand age, site conditions, substrate size, and decay stage of post-clearcut stands affect species richness and composition of polypore communities inhabiting aspen Populus tremula.

Data was collected in broadleaf stands representing two levels of site conditions (mesic and wet) and two categories of age (young 30–60 years and old 80–110 years old), seven stands for each factor combination, a total of 28. In each forest stand 11 sampling plots were systematically established where basidiomata were registered on a 4-m fragment of the nearest log and up to a 4-m height of the nearest living aspen tree, a total of 308 samples for each substrate category. Due to the hierarchical structure of data, the influence of environmental variables on number of species registered was modeled with mixed effect models. The influence of environmental factors on polypore composition was assessed with db-RDA models.

Twenty-five species of polypores were found, including seven red-listed and one legally protected in Poland. The number of observed polypore species was significantly higher on logs and in older stands, but site conditions did not influence it. The stand age influenced the number of species on living trees but not on logs. The increase in log diameter and moderately advanced decay stage positively affected species number. The same factors were found to impact polypore community composition. The results confirm the high importance of aspen for polypore diversity maintenance.

Urban green spaces are biological habitats that play an important role in maintaining urban biodiversity and are affected by artificial light at night (ALAN). Determining the effects of ALAN on predators in urban green spaces is important for promoting the maintenance and conservation of these functions of insect communities in urban green spaces. We investigated the effects of ALAN on a web-building spider species (Trichonephila clavata) in urban green spaces in the Tokyo metropolitan area, Japan. We used a GPS receiver to determine the positions of streetlights and spider webs and classified the webs into two groups: those within the reach of streetlights and those outside their range. We then measured the web distribution (web density), web size, female traits (femur length and body weight), and male presence. Web densities in the light conditions were higher and web sizes smaller than those of webs in the no light conditions. Female body weight and length were also significantly lower in the light conditions than in the no light conditions. However, female body condition and male abundance did not differ between the light and no light conditions. Our results showed that T. clavata maintains some degree of fitness in urban fragmented green spaces although their physical characteristics and behaviour are altered by ALAN. Therefore, we suggest that measures to improve the quality within green infrastructure are required to maintain the function of generalist predators such as web-building spiders in urban green spaces.

Insect herbivores can inflict substantial costs on plant reproductive success. Seed herbivory impacts directly by reducing the number of seeds and therefore the dispersal and reproductive potential of the plant. Fig trees, Ficus, provide keystone resources for tropical forests. The pollinating fig wasps develop inside figs, so consumption of unripe figs results in trees not only losing seeds but also their pollen dispersers. Selection to defend figs should therefore be strong. Seed herbivory is understudied in tropical forests and most data has been collected from fallen fruits. Here we use canopy sampling to identify fig-consuming larvae in central Panama and quantify both their consequences for the fig trees’ reproductive success and the defensive value that ants provide against these larvae. Field surveys of 46 crops from nine fig species revealed that larvae could destroy up to 80% of figs on a tree. From seven Ficus species we barcoded (using COI) 51 individual fig consuming larvae (mainly Lepidoptera) that grouped into seven molecular operational taxonomic units. Lepidopteran larvae formed two feeding strategies, either stationary within a fig or tunneling between figs. Within the context of our study, stationary larvae were specialists whereas tunneling larvae were either specialists or generalists found on different Ficus species. Trees with ants had significantly fewer figs consumed by larvae (9% ± 17% (mean ± SD) for trees with azteca ants and 16% ± 24% for trees with other ants) than did trees without ants (51% ± 27%). Our results corroborate earlier findings that hosting ants can be an effective defensive mechanism for trees against seed herbivores or other antagonistic insects. Our study contributes to a wider body of research around the networks of insects associated with figs that highlights the importance of a multitrophic approach for understanding mutualism stability and persistence in the face of antagonism.