Mapping the ecological resilience of Atlantic postglacial heathlands.

Anthropogenic heathlands are semi-natural ecosystems with a unique cultural and biodiversity value, considered worthy of preservation across most of the world. Their rate of loss, however, is alarming. Currently, we know little about the heathlands' actual span of resilience affordances and their association with abiotic and anthropogenic factors, including how much additional intervention they need to persist. Consequently, we are missing out on vital knowledge for conservation, management and the historical persistence of heathlands.This paper develops a method to assess the ecological resilience affordances of Atlantic postglacial heaths in the absence of human management. We use 12 existing cases of heathland succession to establish a four-step resilience grade for each site, which we regress onto a series of explaining factors and use it in predicting heath resilience across postglacial Atlantic Northern Europe.We find that temperature, humidity, elevation and sandiness have a positive correlation with high heathland resilience. Our predictive mapping shows an uneven distribution of ecological heath resilience across Atlantic Northern Europe within an area of 1,000 × 1,200 km of 5 × 5 km resolution.Historic heathland distributions far exceed areas that afford high heath resilience, suggesting that heath distribution and persistence depend on both abiotic and anthropogenic factors. Policy implications: The map predicting the ecological resilience of Atlantic postglacial heaths can be used by managers working towards heath preservation and restoration to prioritize conservation efforts and to plan management practices across Atlantic Northern Europe. Together with the predictive model, it provides an important initial screening tool to assess heathland resilience in the absence of management as well as the impact of atmospheric nitrogen. The results are equally relevant for scholars who are interested in humans' role in increasing and decreasing ecosystem resilience. Our predictive method can be applied in other regions across the world by adding regionally specific variables.

Ongoing decline in insect-pollinated plants across Danish grasslands.

Loss of habitat, eutrophication and reduced grazing intensity are known drivers of landscape-level changes in plant species composition; however, consequences of the massive decline in insect abundance are still to be understood. Pollinator decline can reduce seed set in plants relying on insects for successful reproduction. This may result in a reduced recruitment of insect-pollinated plant species with associated changes in species composition. So far, large-scale studies addressing this issue have relied on few data points-typically consisting of 'historic' records of numbers of insect-pollinated plants compared to present-day records. Such comparisons can provide information as to whether the diversity of insect-pollinated plants has changed, but not whether the process is still ongoing. Here, we use nationwide monitoring data of plant species richness in Danish grasslands from the period 2004-2014, covering 244 grassland sites and encompassing more than 790 flowering plant species. We show an ongoing decrease in insect-pollinated, but not wind-pollinated, plant species across different habitat types. In both dry calcareous and Nardus grasslands, loss of insect-pollinated plants was greatest at sites with low grazing intensity. However, insect-pollinated plants also declined from sites with higher grazing intensity, and plants requiring more specialized insect pollination tended to decline most. In addition to changes in plant diversity driven by land-use intensification, loss of pollinators may also play a role in reducing the richness of insect-pollinated plants. Ongoing reduction in floral richness could further increase the threat to insects relying on these plants as a food source.

Disclosing the double mutualist role of birds on Galápagos.

Life on oceanic islands deviate in many ways from that on the mainland. Their biodiversity is relatively poor and some groups are well-represented, others not, especially not insects. A scarcity of insects forces birds to explore alternative food, such as nectar and fruit. In this way, island birds may pollinate and disperse seed to an extent unseen on any mainland; they may even first consume floral resources of a plant species and then later harvest the fruit of the same species. Through this biotic reuse, they may act as double mutualists. The latter have never been studied at the level of the network, because they are traditionally considered rare. We sampled pollination and seed-dispersal interactions on Galápagos and constructed a plant-bird mutualism network of 108 plant (12% being double mutualists) and 21 bird species (48% being double mutualists), and their 479 interactions, being either single (95%) or double mutualisms (5%). Double mutualists constitute the core in the pollination-dispersal network, coupling the two link types together. They may also initiate positive feedbacks (more pollination leading to more dispersal), which theoretically are known to be unstable. Thus, double mutualisms may be a necessary, but risky prerequisite to the survival of island biodiversity.

Distinct effects of the nephridial symbionts Verminephrobacter and Candidatus Nephrothrix on reproduction and maturation of its earthworm host Eisenia andrei.

Verminephrobacter, the most common specific symbionts in the nephridia (excretory organs) of lumbricid earthworms, have been shown to improve reproduction of the garden earthworm Aporrectodea tuberculata under nutrient limitation. It is unknown how general this beneficial trait is in the Verminephrobacter-earthworm symbiosis, whether other nephridial symbionts also affect host fitness and what the mechanism of the fitness increase is. Here we report beneficial effects of Verminephrobacter and Candidatus Nephrothrix on life history traits of the compost worm Eisenia andrei, which in addition to these two symbionts also hosts Agromyces-like bacteria in its mixed nephridial community: while growth was identical between control, Verminephrobacter-free and aposymbiotic worms, control worms produced significantly more cocoons and offspring than both Verminephrobacter-free and aposymbiotic worms, confirming the reproductive benefit of Verminephrobacter in a second host with different ecology and feeding behavior. Furthermore, worms with Verminephrobacter and Ca. Nephrothrix, or with only Ca. Nephrothrix present, reached sexual maturity significantly earlier than aposymbiotic worms; this is the first evidence for a beneficial role of Ca. Nephrothrix in earthworms. Riboflavin content in cocoons and whole earthworms was unaffected by the presence or absence of nephridial symbionts, suggesting that nutritional supplementation with this vitamin does not play a major role in this symbiosis.

Intraspecific genetic variation and species coexistence in plant communities.

Many studies report that intraspecific genetic variation in plants can affect community composition and coexistence. However, less is known about which traits are responsible and the mechanisms by which variation in these traits affect the associated community. Focusing on plant-plant interactions, we review empirical studies exemplifying how intraspecific genetic variation in functional traits impacts plant coexistence. Intraspecific variation in chemical and architectural traits promotes species coexistence, by both increasing habitat heterogeneity and altering competitive hierarchies. Decomposing species interactions into interactions between genotypes shows that genotype × genotype interactions are often intransitive. The outcome of plant-plant interactions varies with local adaptation to the environment and with dominant neighbour genotypes, and some plants can recognize the genetic identity of neighbour plants if they have a common history of coexistence. Taken together, this reveals a very dynamic nature of coexistence. We outline how more traits mediating plant-plant interactions may be identified, and how future studies could use population genetic surveys of genotype distribution in nature and methods from trait-based ecology to better quantify the impact of intraspecific genetic variation on plant coexistence.

Competition Is a Strong Driving Factor in Wetlands, Peaking during Drying Out Periods.

The aim of the study is to investigate the relative importance of plant-plant interactions with regard to flooding and drought effect on perennial plant performances in wetlands. Flooding is expected to be the major driver and, accordingly, the importance of drought is hardly if ever taken into account. Focusing on five widespread species, the growth, the survival and the competitive ability of plants were monitored on permanent plots spread along two elevation gradients. Flooding duration and drought intensity were found to vary substantially along the ~ 0.5 meter range elevation gradient. Flooding and drought alternate over the hydrological year and the pin-point surveys were thus conducted over the course of one year. The data were modeled taking into account survival, recruitment and competitive growth throughout flooding and drying out periods. Flooding and drought both directly impacted the plant performances and their competitive effect, with the effect of drought being much more general among species and of higher magnitude than flooding. The importance of competition was found to be high for all species, particularly during the drying out period. It varied more along the flooding gradient than along the drought gradient. The higher flooding tolerance shown by the studied species compared to drought may be related to species specific growth timing together with efficient response traits. These results offer new insights into the filters operating over the species pools. This suggests that the drying out period and drought conditions may be even more important for species' relative success and the importance of competition than the flooding pattern. The general applicability of this result, obtained in mild Atlantic climate and fertile wetlands, remains to be studied.

The role of biotic interactions in shaping distributions and realised assemblages of species: implications for species distribution modelling.

Predicting which species will occur together in the future, and where, remains one of the greatest challenges in ecology, and requires a sound understanding of how the abiotic and biotic environments interact with dispersal processes and history across scales. Biotic interactions and their dynamics influence species' relationships to climate, and this also has important implications for predicting future distributions of species. It is already well accepted that biotic interactions shape species' spatial distributions at local spatial extents, but the role of these interactions beyond local extents (e.g. 10 km(2) to global extents) are usually dismissed as unimportant. In this review we consolidate evidence for how biotic interactions shape species distributions beyond local extents and review methods for integrating biotic interactions into species distribution modelling tools. Drawing upon evidence from contemporary and palaeoecological studies of individual species ranges, functional groups, and species richness patterns, we show that biotic interactions have clearly left their mark on species distributions and realised assemblages of species across all spatial extents. We demonstrate this with examples from within and across trophic groups. A range of species distribution modelling tools is available to quantify species environmental relationships and predict species occurrence, such as: (i) integrating pairwise dependencies, (ii) using integrative predictors, and (iii) hybridising species distribution models (SDMs) with dynamic models. These methods have typically only been applied to interacting pairs of species at a single time, require a priori ecological knowledge about which species interact, and due to data paucity must assume that biotic interactions are constant in space and time. To better inform the future development of these models across spatial scales, we call for accelerated collection of spatially and temporally explicit species data. Ideally, these data should be sampled to reflect variation in the underlying environment across large spatial extents, and at fine spatial resolution. Simplified ecosystems where there are relatively few interacting species and sometimes a wealth of existing ecosystem monitoring data (e.g. arctic, alpine or island habitats) offer settings where the development of modelling tools that account for biotic interactions may be less difficult than elsewhere.