Antagonistic interactions and their impact on species formation and biodiversity maintenance

Water quality, size, connectivity and other physical properties of hydrological systems might have different functions in the formation and maintenance of biodiversity, but this remains mostly unclear due to the lack of undisturbed sites for experimental modelling. Alpine freshwater habitats such as micro-waterbodies (MWB) represent a kind of natural system suitable for biodiversity research. In order to assess potential linkages between environmental factors, connectivity of MWBs and aquatic species richness, we conducted a pilot study in two separated MWB systems located in Gaoligong Mountain, northwest Yunnan province, China. A total of 27 MWBs have been analyzed, including 22 connected and 5 isolated bodies. 13 conventional environmental factors were tested while all kinds of aquatic macro-organisms were collected and classified. Results showed a high environmental heterogeneity among MWBs and significant differences between the two systems but only a few environmental variables such as the depth of soil bottom, total Nitrogen and altitude were related to species richness and the formation of the community structure. As a benefit from the high environmental heterogeneity, the cascaded MWB systems provided divergent habitats able to support species richness at a higher level than the same number of randomly selected MWBs. This finding supports the idea that habitat connectivity matters also in extremely small aquatic ecosystems. Moreover, although still a preliminary result, a polarization effect within connected chains where edge MWBs host higher taxa and endemic taxa richness as well as larger populations, was detectable. This study gives interesting insights on the spatial processes driving community structure and a new prospective for biodiversity conservation. Since alpine MWBs have significant effects on the maintenance of watershed biodiversity, further research on such small and crucial ecosystems is encouraged.

Refugia have been perceived as a major role in structuring species biodiversity, and understanding the impacts of this force in a community assembly with prey–predator species is a difficult task because refuge process can interact with different ecological components and may show counterintuitive effects. To understand this problem, we used a simple two-species model incorporating a functional response inspired by a Holling type-II equation and a prey refuge mechanism that depends on prey and predator population densities (i.e., density-dependent prey refuge). We then perform the co-dimension one and co-dimension two bifurcation analysis to examine steady states and its stability, together with the bifurcation points as different parameters change. As the capacity of prey refuge is varied, there occur critical values i.e., saddle-node and supercritical Hopf bifurcations. The interaction between these two co-dimension one bifurcations engenders distinct outcomes of ecological system such as coexistence of species, bistability phenomena and oscillatory dynamics. Additionally, we construct a parameter space diagram illustrating the dynamics of species interactions as prey refuge intensity and predation pressure vary; as the two saddle-node move nearer to one another, these bifurcations annihilate tangentially in a co-dimension two cusp bifurcation. We also realised several contrasting observations of refuge process on species biodiversity: for instance, while it is believed that some refuge processes (e.g., constant proportion of prey refuge) would result in exclusion of predator species, our findings show that density-dependent prey refuge is beneficial for both predator and prey species, and consequently, promotes the maintenance of species biodiversity.

One of the central questions in microbial ecology is how to explain the high biodiversity of communities. A large number of rare taxa in the community have not been excluded by abundant taxa with competitive advantages, a contradiction known as the biodiversity paradox. Recently, increasing evidence has revealed the central importance of antimicrobial toxins as crucial weapons of antagonism in microbial survival. The powerful effects of antimicrobial toxins result in simple combinations of microorganisms failing to coexist under laboratory conditions, but it is unclear whether they also have a negative impact on the biodiversity of natural communities. Here, we revealed that microbial communities worldwide universally possess functional potential for antimicrobial toxin production. Counterintuitively, the biodiversity of global microbial communities increases, rather than decreases, as the abundance of antimicrobial toxins in rare taxa rises. Rare taxa may encode more antimicrobial toxins than abundant taxa, which is associated with the maintenance of the high biodiversity of microbial communities amid complex interactions. Our findings suggest that the antagonistic interaction caused by antimicrobial toxins may play a positive role in microbial community biodiversity at the global scale.

Competition between species with asymmetrical interaction strength is thought to have a significant force in determining species biodiversity. Generally, competitive interaction has received a lot of attention among ecologists due to the important influences that interspecific competition played in the advancement of ecological theory and the development of population dynamics field. Mathematical modelling has been employed widely in the study of population dynamics and this tool can be used to better understand the influential roles of asymmetrical interaction in structuring community dynamics. To achieve this aim, we examine a multispecies Lotka-Volterra competition model consisting of asymmetrical interactions and environmental carrying capacity components. The significant influences of competitive interactions on multispecies community dynamics are investigated; in particular, we examine how the variation in competitive strength between multiple species leads to different outcomes of biotic interactions. To do this, we conduct a detailed bifurcation analysis of the model, as the strength of asymmetrical interaction varies, by means of dedicated continuation software. This allows us to discover regions of different types of attractors (e.g., limit cycles, alternative stable state communities, species coexistence and species exclusion) in the parameter space and to understand its bifurcation structures. Transcritical and Hopf bifurcations are observed in this ecological system and these bifurcations correspond to threshold values for asymmetrical interactions, which can lead to certain dynamics occur and disappear. Our bifurcation analysis also explains several previously published results, highlights parameter space with qualitatively different dynamics and uncovers some intriguing ecological phenomena concerning the interplay between asymmetrical competition and the maintenance of species biodiversity.

Long-term effect of sheep and goat grazing on plant diversity in a semi-natural dry grassland habitat

Symbioses with mycorrhizal fungi and nitrogen-fixing bacteria (NFB) enhance nitrogen (N) acquisition in host plants and may promote N transfer to neighbouring plants through mycorrhizal networks (MN). Nevertheless, the extent and mechanisms of this transfer remain unclear. On the basis of a synthesis of 15N labeling studies, we show that MN and NFB synergistically enhanced interplant N sharing. In the presence of MN, N transfer from N-fixing donors to non-N-fixing receivers increased by an average of 9.7-fold, accounting for 5.61% of the total N in receiver plants. Moreover, greater amounts of N were transferred from N-fixing plants towards their phylogenetically distant plants. Source-sink gradients driven by differences in N content between neighbouring plants further promoted N transfer. Together, our findings highlight the ecological significance of an expanded MN framework in explaining interplant N sharing and provide new insights into how symbiotic guild interactions promote species coexistence and biodiversity maintenance.

Host‐specific pathogens have long been suggested to act as a major driver of species diversity in tropical forests. However, determining the degree of host specificity of potential pathogens coupled to key cellular characteristics of infection is difficult and time‐consuming. These challenges have delayed progress in relating the functional specificity of pathogenic fungi to ecological consequences. We tested the pathogenicity of 27 (of 215) fungi that were isolated from surface sterilized roots of seedlings from four common tree species in a diverse subtropical forest. Inoculation experiments showed that six fungi exhibited strong pathogenicity on the host seedlings. Five of these only infected their specific hosts (i.e. host‐specific pathogen species). Green fluorescent protein labelling revealed that in three host‐specific pathogens fungal hyphae were able to grow into the vascular tissues only in their specific host plant, in contrast to other fungal‐host combinations that exhibit non‐pathogenic interactions. This fluorescent labelling technique allows direct tracking of the progress of fungal infection in different host tissues. Synthesis. By coupling the green fluorescent protein technique with standard host inoculation experiments, we determined the developmental differences between infections by pathogenic and non‐pathogenic fungi in a relatively simple and straightforward way. Our work provides a useful tool for rapidly screening and categorizing host–fungal interactions, reflecting the functional basis of host specificity of pathogenic fungi. More broadly, this technique can contribute to understanding the roles of pathogens in species coexistence and biodiversity maintenance in forest communities.

Pollinator-mediated plant–plant interactions have traditionally been viewed within the competition paradigm. However, facilitation via pollinator sharing might be the rule rather than the exception in harsh environments. Moreover, plant diversity could be playing a key role in fostering pollinator-mediated facilitation. Yet, the facilitative effect of plant diversity on pollination remains poorly understood, especially under natural conditions. By examining a total of 9371 stigmas of 88 species from nine high-Andean communities in NW Patagonia, we explored the prevalent sign of the relation between conspecific pollen receipt and heterospecific pollen diversity, and assessed whether the incidence of different outcomes varies with altitude and whether pollen receipt relates to plant diversity. Conspecific pollen receipt increased with heterospecific pollen diversity on stigmas. In all communities, species showed either positive or neutral but never negative relations between the number of heterospecific pollen donor species and conspecific pollen receipt. The incidence of species showing positive relations increased with altitude. Finally, stigmas collected from communities with more co-flowering species had richer heterospecific pollen loads and higher abundance of conspecific pollen grains. Our findings suggest that plant diversity enhances pollination success in high-Andean plant communities. This study emphasizes the importance of plant diversity in fostering indirect plant–plant facilitative interactions in alpine environments, which could promote species coexistence and biodiversity maintenance.

Plant nitrogen (N) uptake is affected by plant-plant interactions, but the mechanisms remain unknown. A 15N-labeled technique was used in a pot experiment to analyze the uptake rate of ammonium (NH4+) and nitrate (NO3-) by Abies faxoniana Rehd. et Wils and Picea asperata Mast. in single-plant mode, intraspecific and interspecific interactions. The results indicated that the effects of plant-plant interactions on N uptake rate depended on plant species and N forms. Picea asperata had a higher N uptake rate of both N forms than A. faxoniana, and both species preferred NO3-. Compared with single-plant mode, intraspecific interaction increased NH4+ uptake for A. faxoniana but reduced that for P. asperata, while it did not change NO3- uptake for the two species. The interspecific interaction enhanced N uptake of both N forms for A. faxoniana but did not affect the P. asperata compared with single-plant mode. NH4+ and NO3- uptake rates for the two species were regulated by root N concentration, root nitrate reductase activity, root vigor, soil pH and soil N availability under plant-plant interactions. Decreased NH4+ uptake rate for P. asperata under intraspecific interaction was induced by lower root N concentration and nitrate reductase activity. The positive effects of interspecific interaction on N uptake for A. faxoniana could be determined mainly by positive rhizosphere effects, such as high soil pH. From the perspective of root-soil interactions, our study provides insight into how plant-plant interactions affect N uptake, which can help to understand species coexistence and biodiversity maintenance in forest ecosystems.

To measure intraspecific and interspecific interaction coefficients among tree species is the key to explore the underlying mechanisms for species coexistence and biodiversity maintenance in forests. Through the response surface experimental design, we established a long-term field experiment by planting 27,300 seedlings of four tree species (Erythrophleum fordii, Pinus massoniana, Castanopsis fissa, and Castanopsis carlesii) in 504 plots in different species combinations (six pairwise combinations of four species), abundance proportions (five abundance proportions of two species, i.e. A: B = 1:0, 3:1, 1:1, 1:3, 0:1), and stand densities (25, 36, 64, and 100 seedlings per plot). In this initial report, we aimed to quantify the relative importance of biotic and abiotic factors on seedling survival at the early stage of growth, which is a critical period for seedling establishment. We found that plot-level seedling survival rate was determined by species combination and their abundance proportion rather than stand density. At the individual level, individual survival probability was mainly explained by species identity, initial seedling size, and soil conditions rather than neighborhood competition. Our study highlights that the seedling intrinsic properties may be the key factors in determining seedling survival rate, while neighborhood effects were not yet prominent at the seedling life stage.

Live under strong power: A third plant species alters interspecific interactions between two plant species

Fine-scale spatiotemporal variation in seed-rodent interactions: A potential contribution to species coexistence

Abstract. 1. Altitudinal gradients offer a unique scenario to elucidate how the increase in harsh climatic conditions towards the top of the mountain interacts with other environmental factors at regional and local scale to influence the spatial variation in local species composition and biodiversity maintenance. We analysed the altitudinal variation in the taxonomic composition of epigaeic beetle assemblages across five mountains in north‐western Patagonia (Argentina) to address whether substantial change in species composition was associated (i) at regional spatial scale, with changes in vegetation types, and the presence of dry and moist mountains, and (ii) at local spatial scale, with variation in temperature, plant cover and richness and several soil characteristics.2. We collected beetles using 486 pitfall traps arranged in fifty‐four 100‐m2 grid plots of nine traps settled at about 100 m of altitude apart from each other, from the base to the summit of each mountain. We used multivariate analyses to identify beetle assemblages and to evaluate their association with environment.3. We identified different beetle assemblages, associated more with vegetation types rather than with mountains; indicator species showed higher degree of fidelity and specificity to vegetation types rather than to mountains. Local variation in temperature, plant cover and richness, and soil characteristics influence the variation in species composition.4. Our study suggests the existence of a regional beetle fauna that is shared across these mountains. Major regional changes in vegetation types and local variation in environment drive the variation in the species composition of beetle assemblages at these latitudes.

Cities are expanding worldwide and urbanisation is considered a global threat to biodiversity. Urban ecology has provided important insights on how urban environmental changes might affect individuals, populations, and species; however, we know little about how the ecological impacts of urbanisation alter speciesinteractions. Species interactions are the backbone of ecological communities and play a crucial role in population and community dynamics and in the generation, maintenance and structure of biodiversity. Here, I review urban ecological studies to identify key mechanistic pathways through which urban environmental processes could alter antagonistic and mutualistic interactions among species. More specifically, I focus on insect predation, parasitoidism and herbivory, competition, insect host-pathogen interactions, and pollination. I furthermore identify important knowledge gaps that require additional research attention and I suggest future research directions that may help to shed light on the mechanisms that affect species interactions and structure insect communities and will thus aid conservation management in cities.

Interactions between species are widely understood to have promoted the diversification of life on Earth, but how interactions spur the formation of new species remains unclear. Interacting species often become locally adapted to each other, but they may also be subject to shared dispersal limitations and environmental conditions. Moreover, theory predicts that different kinds of interactions have different effects on diversification. To better understand how species interactions promote diversification, we compiled population genetic studies of host plants and intimately associated herbivores, parasites, and mutualists. We used Bayesian multiple regressions and the BEDASSLE modeling framework to test whether host and associate population structures were correlated over and above the potentially confounding effects of geography and shared environmental variation. We found that associates' population structure often paralleled their hosts' population structure, and that this effect is robust to accounting for geographic distance and climate. Associate genetic structure was significantly explained by plant genetic structure somewhat more often in antagonistic interactions than in mutualistic ones. This aligns with a key prediction of coevolutionary theory that antagonistic interactions promote diversity through local adaptation of antagonists to hosts, while mutualistic interactions more often promote diversity via the effect of hosts' geographic distribution on mutualists' dispersal.