Climate warming exerts profound effects on plant community composition. However, responses to climate warming are often reported at the community and functional type levels, but not at the species level. To test whether warming-induced changes are consistent among community, functional type, and species levels, we examined the warming-induced changes at different levels in an alpine meadow from 2015 to 2018. The warming was achieved by deploying six (open top) chambers [including three non-warmed chambers and three warmed chambers; 15 × 15 × 2.5 m (height) for each] that resulted in a small increase in mean annual temperature (0.3–0.5°C, varying with years) with a higher increase during the non-growing season (0.4–0.6°C) than in the growing season (0.03–0.47°C). The results show that warming increased plant aboveground biomass but did not change species richness, or Shannon diversity and evenness at the community level. At the functional type level, warming increased the relative abundance of grasses from 3 to 16%, but decreased the relative abundance of forbs from 89 to 79%; relative abundances of sedges and legumes were unchanged. However, for a given functional type, warming could result in contrasting effects on the relative abundance among species, e.g., the abundances of the forb species Geranium pylzowianum, Potentilla anserine, Euphrasia pectinate, and the sedge species Carex atrofusca increased in the warmed (compared to the non-warmed) chambers. More importantly, the difference in species identity between warmed and non-warmed chambers revealed warming-induced species loss. Specifically, four forb species were lost in both types of chambers, one additional forb species (Angelica apaensis) was lost in the non-warmed chambers, and two additional species (one forb species Saussurea stella and one sedge species Blysmus sinocompressus) were lost in the warmed chambers. Consequently, changes at the species level could not be deduced from the results at the community or functional type levels. These data indicate that species-level responses to climate changes must be more intensively studied. This work also highlights the importance of examining species identity (and not only species number) to study changes of community composition in response to climate warming.

Climate warming is often seasonally asymmetric with a higher temperature increase toward winters than summers. However, the effect of winter-biased warming on plant reproductive phenology has been seldom investigated under natural field conditions. The goal of this study was to determine the effects of winter-biased warming on plant reproductive phenologies. In an alpine meadow of Tibetan Plateau, we deployed six large (15 m × 15 m × 2.5 m height) open top chambers (three warmed chambers and three non-warmed chambers) to achieve winter-biased warming (i.e., a small increase in annual mean temperature with a greater increase towards winter than summer). We investigated three phenophases (onset and offset times and duration) for both the flowering and fruiting phenologies of 11 common species in 2017 and 8 species in 2018. According to the vernalization theory, we hypothesized that mild winter-biased warming would delay flowering and fruiting phenologies. The data indicated that the phenological responses to warming were species-specific (including positive, neutral, and negative responses), and the number of plant species advancing flowering (by averagely 4.5 days) and fruiting onset times (by averagely 3.6 days) was higher than those delaying the times. These changes were inconsistent with the vernalization hypothesis (i.e. plants need to achieve a threshold of chilling before flowering) alone, but can be partly explained by the accumulated temperature hypothesis (i.e. plants need to achieve a threshold of accumulative temperature before flowering) and/or the overtopping hypothesis (i.e. plants need to reach community canopy layer before flowering). The interspecific difference in the response of reproductive phenology could be attributed to the variation in plant traits including plant height growth, the biomass ratio of root to shoot, and seed mass. These results indicate that a mild winter-biased warming may trigger significant change in plant reproductive phenology in an alpine meadow.

Global warming challenges predators by changing their abiotic and biotic environment. Although predators may adapt by virtue of behavioral plasticity, few studies have explored this behavior under field conditions. We conducted a field warming experiment in an alpine meadow using six large open-top chambers that increased mean annual temperature by 0.6°C. We monitored the abundance and behavior of two web-building spider species differing in size and their prey for four consecutive years. Warming reduced the prey biomass and decreased the abundance of short-bodied prey more than long-bodied ones for the larger spiders, and increased the abundance of long-bodied prey for the smaller spiders. As a consequence, warming reduced the abundance of the larger spider and increased the abundance of the small spider by an average of -47.4% and +128.3%, respectively. The web mesh-size of the larger spider decreased by -43.6%, whereas the mesh-size of the smaller spider increased by +79.8%. Structural equation models showed that the behavior of both spider species was the result of warming-induced changes in the prey size spectrum. Our data reveal that predators can behaviorally adapt to warming-induced shifts in the composition and size distribution of complex communities, which is likely to result in altered community metabolism, energy fluxes, and thus ecosystem functioning.

1. Invertebrates contribute largely to the decomposition of animal carcasses in natural ecosystems. However, we currently lack experimental evidence for the impact of predatory ants on carrion decomposition. Provided that many ant species display their role in the necrophilous community as predators but not as decomposers, we hypothesized that the ants would negatively affect the carrion decomposition rates by predating on other insect decomposers.2. In a Tibetan alpine meadow, we conducted a one-factor designed field experiment involving three treatments, that is, 20, 60, and 500 cm of yak (Bos grunniens) carrion plots away from anthills (Camponotus herculeanus), which mirrored the high, intermediate, and low ant abundance, respectively. 3. Our results show that the necrophilous community assemblage differed significantly along the distance gradients from anthills, with the dominance of the necrophilous community shifting from ants in the 20 cm treatment to maggots in the 500 cm treatment.The ants significantly decreased the number of maggots through predation, resulting in a significant decrease of the carrion decomposition rates. However, ants did not change the number of other scavengers albeit they attacked them.4. These results suggest that the predatory ant C. herculeanus can modify the carrion decomposition rates through generating a strong consumptive effect on decomposers, which is important to understand the necrophilous community assemblage and the decomposition of animal-based materials.

It has been suggested that the importance of network architecture to species diversity and stability should be based on preference networks (comprised of niche differentiations), rather than observational networks, because species abundance may significantly affect interaction frequencies. Considering that resource abundance is usually greater for herbivores than parasites, we hypothesized that the abundance effect is stronger for parasitic than herbivory interactions. To test this hypothesis, we collected 80 quantitative observational networks including 34 herbivorous and 46 parasitic networks from the published literature, and derived preference networks by removing the effects of species abundance. We then determined the network nestedness using both weighted NODF and spectral radius. We also determined species degree distribution, interaction evenness, weighted connectance and robustness for both observational and preference networks. The observational networks (including both herbivory and parasitic networks) were more nested judged by weighted NODF than spectral radius. Preference networks were less nested for parasitic than herbivory networks in terms of both weighted NODF and spectral radius, possibly because removing the abundance effect increased interaction evenness. These trends indicated that the abundance effect on network nestedness was stronger for parasitic than herbivory networks.Weighted connectance and robustness were greater in most preference networks than observational networks, indicating that preference networks may have higher network stability and community persistence compared to observational ones. The data indicate that future network analyses should not only address the structural difference between mutualistic and antagonistic interactions, but also between herbivory and parasitic interactions.