Jonathan Silvertown

For successful colonization of host roots, ectomycorrhizal (EM) fungi must overcome host defense systems, and defensive phenotypes have previously been shown to affect the community composition of EM fungi associated with hosts. Secondary metabolites, such as terpenes, form a core part of these defense systems, but it is not yet understood whether variation in these constitutive defenses can result in variation in the colonization of hosts by specific fungal species. We planted seedlings from twelve maternal families of Scots pine (Pinus sylvestris) of known terpene genotype reciprocally in the field in each of six sites. After 3 months, we characterized the mycorrhizal fungal community of each seedling using a combination of morphological categorization and molecular barcoding, and assessed the terpene chemodiversity for a subset of the seedlings. We examined whether parental genotype or terpene chemodiversity affected the diversity or composition of a seedling's mycorrhizal community. While we found that terpene chemodiversity was highly heritable, we found no evidence that parental defensive genotype or a seedling's terpene chemodiversity affected associations with EM fungi. Instead, we found that the location of seedlings, both within and among sites, was the only determinant of the diversity and makeup of EM communities. These results show that while EM community composition varies within Scotland at both large and small scales, variation in constitutive defensive compounds does not determine the EM communities of closely cohabiting pine seedlings. Patchy distributions of EM fungi at small scales may render any genetic variation in associations with different species unrealizable in field conditions. The case for selection on traits mediating associations with specific fungal species may thus be overstated, at least in seedlings.

Questions: Are communities structured on a hydrological (soil moisture) gradient? Is there spatial segregation into hydrological niches? What is the shape of the hydrological niches of individual species? Controlling for spatial autocorrelation, how much of the spatial structure in the community is due to variation in hydrology? Do annuals and perennials behave alike with respect to the above questions?Locations: La Mina in Moscosa Farm, Salamanca, western Spain (dehesa community) and Laguna Larga in the Urbión Peaks, Soria, central‐northern Spain (alpine grassland).Methods: The presence of plant species was sampled in two contrasting field sites, for which we also built hydrological models. First, we reduced the dimensionality of the plant distribution data (non‐metric multidimensional scaling) and measured the correlation between the resulting ordination and the hydrological gradient. Then we defined hydrological niches and tested niche segregation of plant species against null models (Pianka metrics). Finally, we characterized the hydrological niche of each species using generalised additive mixed models and partitioned the species distribution variance into (1) a hydrological component, (2) a linear trend component and (3) and a spatial component, defined through sets of spatial variables (Moran's eigenvector maps).Results: Both plant communities were primarily structured along hydrological gradients, and spatial segregation into hydrological niches occurred among perennial species, although not among annuals in the dehesa community. Dehesa annuals were spatially aggregated in the driest niches. Hydrological variation shaped the responses of 60% of the annual and about 70% of the perennial species in both the dehesa meadow and the alpine community. Most responses were either monotonic or hump‐shaped. Finally, spatially structured hydrological variation proved to be the main driver of spatially structured species composition in all cases.Conclusions: Linearly (gradient of slope) and topographically (at a fine scale) structured variation in hydrology is the main driver of spatially structured species composition in both communities. Our results support the ecological hypothesis that spatial niche segregation on soil moisture gradients is an important mechanism of co‐existence for perennials in both test communities, although not for the species‐rich sub‐community of annuals in the dehesa meadow.

Accurate species identification is fundamental to biodiversity science, but the natural history skills required for this are neglected in formal education at all levels. In this paper we describe how the web application ispotnature.org and its sister site ispot.org.za (collectively, “iSpot”) are helping to solve this problem by combining learning technology with crowdsourcing to connect beginners with experts. Over 94% of observations submitted to iSpot receive a determination. External checking of a sample of 3,287 iSpot records verified > 92% of them. To mid 2014, iSpot crowdsourced the identification of 30,000 taxa (>80% at species level) in > 390,000 observations with a global community numbering > 42,000 registered participants. More than half the observations on ispotnature.org were named within an hour of submission. iSpot uses a unique, 9-dimensional reputation system to motivate and reward participants and to verify determinations. Taxon-specific reputation points are earned when a participant proposes an identification that achieves agreement from other participants, weighted by the agreers’ own reputation scores for the taxon. This system is able to discriminate effectively between competing determinations when two or more are proposed for the same observation. In 57% of such cases the reputation system improved the accuracy of the determination, while in the remainder it either improved precision (e.g. by adding a species name to a genus) or revealed false precision, for example where a determination to species level was not supported by the available evidence. We propose that the success of iSpot arises from the structure of its social network that efficiently connects beginners and experts, overcoming the social as well as geographic barriers that normally separate the two.

Summary: Despite the fundamental significance of water to plants and the persisting question of how competing species coexist, this is the first review of hydrological niches. We define hydrological niche segregation (HNS) as: (i) partitioning of space on fine‐scale soil‐moisture gradients, (ii) partitioning of water as a resource and/or (iii) partitioning of recruitment opportunities among years caused by species specializing on particular patterns of temporal variance of water supply (the storage effect). We propose that there are three types of constraint that lead to the trade‐offs that underlie HNS. (i) An edaphic constraint creates a trade‐off between the supply to roots of O₂ on the one hand vs. water and nutrients on the other. (ii) A biophysical constraint governs gas exchange by leaves, leading to a trade‐off between CO₂ acquisition vs. water loss. (iii) A structural constraint arising from the physics of water‐conducting tissues leads to a safety vs. efficiency trade‐off. Significant HNS was found in 43 of 48 field studies across vegetation types ranging from arid to wet, though its role in coexistence remains to be proven in most cases. Temporal partitioning promotes coexistence through the storage effect in arid plant communities, but has yet to be shown elsewhere. In only a few cases is it possible to unequivocally link HNS to a particular trade‐off. Synthesis. The field and experimental evidence make it clear that HNS is widespread, though it is less clear what its precise mechanisms or consequences are. HNS mechanisms should be revealed by further study of the constraints and trade‐offs that govern how plants obtain and use water, and HNS can be mechanistically linked to its consequences with appropriate community models. In a changing climate, such an integrated programme would pay dividends for global change research.