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Premise of the study: Seedling establishment and early survivorship are crucial steps for the regeneration of plant populations because both have long-lasting effects on plant population dynamics. For species recruiting through facilitation, species-specific facilitative effects might affect early fitness, an overlooked aspect in studies of facilitation considering groups of nurse species. METHODS: We experimentally evaluated the roles of 10 nurse species and open space on the early performance of the columnar cactus Neobuxbaumia mezcalaensis. We measured establishment, survivorship, and growth of individuals over 3 years. Moreover, to study an extended period of the ontogeny of the interaction between this cactus and its nurse plants, we also monitored survivorship and growth rates of individuals between 3 to 12 cm tall during a 3-year period. Key results: Neobuxbaumia mezcalaensis performance varied significantly among nurse species, and only six yielded positive effects on early fitness. Densely canopied plants were the best nurses for this cactus. However, even among densely canopied species, some produced negative effects on the early fitness of N. mezcalaensis, indicating that similar nurse plants may elicit either facilitative or interference effects on beneficiary species. CONCLUSIONS: Our results emphasize the importance of species-specific facilitative interactions in the crucial early stages in the life cycle of N. mezcalaensis and how different nurse species modify the effect of seed-rain and contribute significantly to the population dynamics of the species.

Species assemblages often have a non-random nested organization, which in vertebrate scavenger (carrion-consuming) assemblages is thought to be driven by facilitation in competitive environments. However, not all scavenger species play the same role in maintaining assemblage structure, as some species are obligate scavengers (i.e., vultures) and others are facultative, scavenging opportunistically. We used a database with 177 vertebrate scavenger species from 53 assemblages in 22 countries across five continents to identify which functional traits of scavenger species are key to maintaining the scavenging network structure. We used network analyses to relate ten traits hypothesized to affect assemblage structure with the “role” of each species in the scavenging assemblage in which it appeared. We characterized the role of a species in terms of both the proportion of monitored carcasses on which that species scavenged, or scavenging breadth (i.e., the species “normalized degree”), and the role of that species in the nested structure of the assemblage (i.e., the species “paired nested degree”), therefore identifying possible facilitative interactions among species. We found that species with high olfactory acuity, social foragers, and obligate scavengers had the widest scavenging breadth. We also found that social foragers had a large paired nested degree in scavenger assemblages, probably because their presence is easier to detect by other species to signal carcass occurrence. Our study highlights differences in the functional roles of scavenger species and can be used to identify key species for targeted conservation to maintain the ecological function of scavenger assemblages.

This article is a Commentary on Scholz et al. (2021), 232: 2138–2151.

The vegetation that grows on coastal wetlands is important for ecosystem functioning, a role mediated by plant traits. These traits can be affected by environmental stressors and by the competitive environment the plant experiences. The relative importance of these influences on different traits is poorly understood and, despite theoretical expectations for how factors may interact, empirical data are conflicting. Our aims are to determine the effect of flooding, species composition and their interaction on plant functional traits, and assess the role of biodiversity and species composition in driving community-level responses to flooding. We conducted a factorial glasshouse experiment assessing the effects of species composition (all combinations of three saltmarsh species, Aster tripolium, Plantago maritima and Triglochin maritima) and flooding (immersion of roots) on a suite of functional traits. We also related biomass in mixed species pots to that expected from monocultures to assess how species interactions affect community-level biomass. Species composition frequently interacted with flooding to influence functional traits and community-level properties. However, there was also considerable intraspecific variability in traits within each treatment. Generally, effects of flooding were more pronounced for below-ground than above-ground biomass, while composition affected above-ground biomass more than below-ground biomass. We found both negative and positive interactions between species (indicated by differences in above- and below-ground biomass from expectations under monoculture), meaning that composition was an important determinate of community function. While the effect of flooding alone on traits was relatively weak, it interacted with species composition to modify the response of both individual plants and communities. Our results suggest that responses to increased flooding will be complex and depend on neighbourhood species interactions. Furthermore, intraspecific trait variability is a potential resource that may dampen the effects of changes in flooding regime.

Prosopis juliflora and Leucaena leucocephala are notable examples of invasive woody plants that can spread throughout similar habitats in India. However, little is known about how these two species may interact with one another if future rainfall pattern shifts, which is particularly concerning. Recognizing the pivotal role of eco-physiological parameters in deciphering the dynamics of interspecific competition, a study was devised to elucidate the interplay between L. leucocephala and P. juliflora under simulated rainfall conditions. At Botanical Garden, Banaras Hindu University, Varanasi, UP, India, three fixed rainout shelter plots were established, each receiving distinct precipitation levels: low rainfall (LR), normal rainfall (NR), and high rainfall (HR). Within each plot, three replicate subplots were dedicated to pure stands of L. leucocephala (L), pure stands of P. juliflora (P), and mixed stands of the two species (LP). The findings of the study underscore significant variations in soil Inorganic N, N-mineralization, based on precipitation levels, with maximum values observed in HR plot and L. Similarly, biomass, photosynthetic rate, and transpiration rate exhibited significant variability in response to precipitation treatment, reaching their highest values in HR plot and L. Conversely, root length, root-shoot ratio, and water use efficiency peaked in LR plot and P, presenting a contrasting trend. This study suggests that L. leucocephala may facilitate the growth of P. juliflora by improving the soil's nitrogen availability and, consequently, the eco-physiological characteristics of the plant in mixed plant stands. Furthermore, L. leucocephala is providing P. juliflora with favourable conditions for robust growth under water stress—a scenario indicative of Facilitative approach.

QUESTIONS: What is the community‐level consequence of biotic processes, in particular the importance of facilitation, in determining patterns of diversity in alpine plant communities of the Himalayan Hengduan Mountains? Does facilitation intensity change with environmental severity, and are these changes due to environmental severity or nurse trait effects? LOCATION: Eleven alpine plant communities dominated by cushion plants in the Himalayan Hengduan Mountains, within the mountain system of south‐central China. METHODS: We determined plant species richness and abundance in habitats created by cushions and cushion‐free areas, and assessed the cushion effects on species richness and abundance with rarefaction curves and the relative interaction index, respectively. We examined the relationship between cushion effects on diversity and habitat severity and tested if changes in the net cushion effects along the severity gradient were due to a change in the performance of species without cushions (environmental severity effect) and/or with cushions (nurse trait‐mediated effect). RESULTS: The presence of cushion plants increased species richness and abundance in most studied plant communities. The net facilitation effect of cushions increased with increasing habitat severity, an effect that could be attributed mainly to a reduction in species richness in cushion‐free areas with increasing severity. However, the changes in magnitude of facilitation of particular cushion species growing in high and low severity habitats could be attributed to both environmental severity and neighbour trait effects. Despite the overall positive effect of cushion plants on plant species richness, not all cushion species contributed to higher species richness. The deviation of individual cushion species from the general pattern of increasing facilitation with increasing severity indicated the species specificity of facilitation depends on the traits of nurse species. CONCLUSION: The presence of cushion plants generally increased species richness in alpine plant communities of the Himalayan Hengduan Mountains, with the importance of the cushion effect increasing with habitat severity due to a buffering effect by cushions of the negative effect of habitat severity on species richness observed in cushion‐free areas. This indicates the pivotal role of facilitative interactions among plant species in supporting high diversity in these severe environments.

The loss of biodiversity by the replacement of invasive species could lead to the loss of functional traits that maintain certain ecosystem services (ES). The ES method provides a conceptual framework to value changes of functional traits related to this loss of biodiversity. The Caribbean Sea offers a multifaceted seascape to evaluate this approach as native seagrass species (Thalassia testudinum, Syringodium filiforme or Halodule wrightii) cohabit this region together with the invasive seagrass Halophila stipulacea, native to the Indian Ocean. The functional traits of native seagrass species in the Caribbean are compared to different traits of H. stipulacea observed worldwide with the aim of evaluating the dimensions of this change in terms of the ES that seagrass meadows provide in the Caribbean. Under a changing seascape due to climate change and anthropogenic pressures that have driven the disappearance of most seagrass meadows in the Caribbean, we explore how this invasive seagrass could play a role in restoration attempts as a pioneer species where native species have been lost. The potential unintended consequences of the presence of H. stipulacea to replace services of native species are also noted.

Seagrass meadows are facing structural degradation worldwide, losing both area and biodiversity. Habitat restoration could reverse this degradation, but so far, the success rate of seagrass restoration has been low. Incorporating facilitative interactions between plants and mussels into habitat restoration projects could potentially improve restoration success by increasing eelgrass survival and growth. In this study, we tested whether co-restoring two ecosystem engineers, namely eelgrass Zostera marina and blue mussels Mytilus edulis/trossulus would increase eelgrass restoration success in different sites. We also tested the rope method of eelgrass transplantation in sites where eelgrass was known to have previously existed. These small-scale field experiments were conducted in 2017–2019, in the northeastern Baltic Sea where the eelgrass reproduces only vegetatively. We found that co-restoration of eelgrass and mussels did not work at small scales because mussels were washed away within the first growing season. However, the shoot density of eelgrass increased over time, especially over the second growing season in the sheltered site, indicating that restoration is possible in these areas. Similarly, the restoration was most successful with the rope method in the sheltered site, suggesting that this method also has potential at larger spatial scales. Our results suggest that in such dynamic ecosystems abiotic factors, particularly exposure, play a larger role compared to biotic interactions, and thus the success of habitat restoration largely depends on local environmental conditions.

Longitudinal distribution and niche partitioning phenomena have been extensively reported for streams containing two salmonid species but remain poorly understood for streams containing three or more salmonid species. Herein, we examined the abiotic environmental variables and population densities of fishes, including three salmonids, in 30 reaches of the Setose River, Hokkaido, Japan, across altitudes (120–450 m) and maximum water temperature (15–26 °C) gradients to determine the distribution of major fish species in this system. The densities of white-spotted charr Salvelinus leucomaenis , southern Asian Dolly Varden Salvelinus curilus , masu salmon Oncorhynchus masou , fluvial sculpin Cottus nozawae , and stone loach Barbatula oreas varied along environmental gradients despite their wide distribution sympatrically. We further investigated the interspecific interactions between three potentially competitive salmonids, white-spotted charr, Dolly Varden, and masu salmon. We observed that in the three-species system, including upstream Dolly Varden, salmon occupied upstream areas colder than those inhabited by charr, which is contrary to the pattern reported for charr and salmon two-species systems, wherein charr are found in the colder upstream areas. In underwater observations, salmon preferred faster water velocities than charr and Dolly Varden. Dolly Varden were found exclusively on the riverbed, followed by charr, whereas salmon occurred further away from the riverbed. Analysis of the stomach contents revealed that all three salmonids depended on terrestrial insects, but only Dolly Varden consumed benthic aquatic insects. In our three-species system that included Dolly Varden (preadapted to benthos foraging), no difference was observed in the degree of terrestrial insect consumption between charr and salmon. These results are in striking contrast to the reports of charr preying on relatively more aquatic insects than those consumed by salmon in charr and salmon two-species systems. Therefore, we speculate that Dolly Varden and salmon influence interspecific interactions between charr and salmon and between charr and Dolly Varden, respectively, explaining the distinct longitudinal distribution and feeding habits observed in two- vs. three-species systems. These variant interspecific interactions among the three competing species may have driven the expansion of their sympatric zones.

The brown marmorated stink bug, Halyomorpha halys, is a polyphagous species from eastern Asia, which has spread to America and Europe where it damages many crops. In recently colonized areas, facilitative interactions between H. halys and native insects are poorly investigated. In this study, we report for the first time facilitation of native wasp and ant feeding by H. halys in Europe. The facilitation was related to the outflow of plant exudates caused by H. halys feeding on manna ash trees, where they have aggregated in response to an aggregation pheromone, which then attracted species of Hymenoptera to the infested trees. Trees other than manna ash were not involved in the facilitation between these two taxa. The species that frequently visited infested manna ash were Polistes dominula, Vespa crabro, Formica (Serviformica) cunicularia and Lasius emarginatus, while Polistes cf. nimpha, Vespula germanica, Crematogaster scutellaris and Tapinoma subboreale were occasional visitors. The numbers of wasps and ants feeding on plant exudates differed at different times in a day, with more Hymenoptera foraging in the afternoon, when more H. halys individuals were actively feeding. Facilitative interactions, such as those recorded in this study, are important for furthering our understanding of the ecology of invasive species in terms of creating sources of food for native organisms.