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Ballistic seed dispersal (ballochory) involves the autonomous explosive release of seeds from adult plants. The unconventional mechanics of this strategy have understandably drawn considerable scientific attention. The explosive release of seeds is achieved by a variety of physical mechanisms but broadly involves the rapid coiling or shattering of seed pods to transfer kinetic energy to seeds, facilitated largely by either the evaporation or absorption of water in seed pod tissues. There has been a bias toward researching physiological and physical aspects of ballistic plants, with the evolutionary ecology being comparatively neglected. Although ballochory is represented in 23 plant families, it has never become common. This fact should invite curiosity regarding the selective pressures that encourage its evolution. Previous research has been unable to correlate ballochory with plant traits such as morphology, generation time or habitat preferences, and so we take an alternative approach in considering the evolutionary advantages that can provide insight on the shared set of circumstances that favour the evolution of this strategy. We review the known selective advantages that ballistic dispersal can confer to plants and promote a hypothesis that ballochory may be particularly selected for in instances of concentrated predation pressure on parental canopies. For plants in static and patchy landscapes, such a strategy could balance a trade‐off between escaping concentrated natural enemies while maximising the probability of transport to suitable habitat. We account for its rarity by considering the major opportunity cost that may only be justified when other seed dispersal mechanisms are limited. Moving forward, we suggest experimental manipulations to test this hypothesis and promote a research agenda in the field of ballistic seed dispersal that illuminates its intriguing evolution. This viewpoint article describes an initial hypothesis regarding the evolutionary ecology of explosive seed dispersal. Although the physical mechanisms of this unconventional process are well understood, the evolution of this plant trait has received comparatively little attention. We suggest that predation pressure on or beneath the parent plant could help explain the repeated evolution of this trait and hope to stimulate experimental manipulations to test this.

Seed dispersal is a critical process in plant colonisation and demography. Fruits and seeds can be transported by several vectors (typically animals, wind and water), which may have exerted strong selective pressures on plant’s morphological traits. The set of traits that favour dispersal by a specific vector have been historically considered as seed dispersal syndromes. As seed dispersal syndromes have a great potential to predict how seeds move (i.e. the relative importance of the standard mechanisms of seed dispersal), they have attracted the attention of naturalists and researchers for centuries. However, given that observations of actual dispersal events and colonisation are seldom reported, there is still much confusion in current studies failing to properly discriminate between seed dispersal syndromes (i.e. sets of traits that favour a particular mechanism) and actual seed dispersal (i.e. the vector that moves a given seed in one dispersal event). This distinction is important because the presence of any seed dispersal syndrome does not preclude the seed being occasionally dispersed by other non-standard mechanisms (i.e. different from the one predicted). Similarly, the absence of seed dispersal syndromes does not prevent seeds from being dispersed. The correct coding of seed dispersal syndromes thus requires a systematic and evolutive, rather than a phenomenological approach. Unfortunately, such approach has rarely been implemented at a community-level and no comprehensive datasets of seed dispersal syndromes are yet available for any entire flora. This database contains categorisation of the native European flora into eight seed dispersal syndromes. Information for a total of 9,874 species retrieved from the volumes of Flora Europaea were analysed. Earlier versions of this database, which only coded for the presence of four long-distance dispersal syndromes (endozoochorous, epizoochorous, thalassochorous and anemochorous diaspores), were used in four previous studies. Here, we present a fully revised and expanded database, including the presence of four additional short-distance dispersal syndromes (myrmecochorous, vertebrate hoarding, freshwater hydrochorous and ballochorous diaspores), a nomenclatural update for all species and the codification of 416 additional species. Roughly half (51.3%) of the native European flora produce diaspores without traits clearly associated with facilitating seed dispersal. The other half (48.7%) of the European plant species produces diaspores with some specialised traits associated with seed dispersal, most of which (79.9%) with a potential to facilitate long-distance dispersal events. The most common diaspores are those with anemochorous (23.5%), epizoochorous (8.0%), endozoochorous (7.8%), myrmecochorous (7.2%), thalassochorous (2.3%), freshwater dispersal (2.1%), ballochorous (4.6%) and vertebrate hoarding associated traits (0.2%). Two-thirds (66.3%) of the European shrub and tree species have diaspores with some specialisation for biotic seed dispersal.

The ability to disperse individuals and seeds among subpopulations is required for the sustainability of plant metapopulations. Understanding the mechanism of seed dispersal is essential for the conservation and restoration of plant diversity. In this study, Euphorbia adenochlora growing on floodplains was used as a research target to obtain new knowledge about hydrochory and ballochory and estimate potential dispersal range related to hydrological regimes. A wetland spreading around the Omi Maiko Inner Lake in Minami‐Komatsu, Otsu City, Shiga Prefecture, Japan, was the study site. Euphorbia adenochlora bear capsules, which have a three‐chambered hollow structure and which float on water up to 14 days, they can be dispersed by hydrochory. The capsule of E. adenochlora splits open when it dries, and ejects the seeds at a maximum distance of 4.1 m, indicating that the drifting capsule is capable for secondary dispersal by ballochory. At the study site, 2% of E. adenochlora subpopulations were within the range where fallen capsules could be dispersed by hydrochory, and 33% of E. adenochlora subpopulations could have been formed by ballochory from the drift line. Practical implications. These subpopulations are crucial for the conservation of E. adenochlora population at the study site. Furthermore, the fluctuating and maximum water levels from late May to mid‐June for E. adenochlora were considered important to the formation of new subpopulations. Euphorbia adenochlora capsules split open when dry, and seeds are found to disperse by ballochory up to 4.1 m. Therefore, after drifting to the drift line (hydrochory), the seeds can be dispersed further landward by ballochory as secondary dispersal. The findings of this study, which spatially and explicitly demonstrate the potential seed dispersal range associated with the hydrological regime in addition to the seed dispersal mechanism of E. adenochlora, will contribute significantly to the conservation and restoration of the metapopulation of E. adenochlora at the study site.

1. The dispersal capabilities of most plant species remain unknown. However, gaining basic dispersal information is a critical step for understanding species' geographical distributions and for predicting the likely impacts of future climate change. Dispersal mechanisms can indicate short- or long-distance dispersers, and highlight important biological interactions. 2. To predict dispersal mechanisms for species where information is limited, we used generalized linear mixed models with basic life-history and ecological traits. Sets of models were created (using Australian species) for six dispersal categories: wind, unassisted, water, ant, vertebrate-ingestion and vertebrate-attachment dispersal mechanisms. We validated our models on the dispersal mechanisms of 50 Australian, 30 Californian, 30 Swiss plant species and a global compilation of 70 species. 3. Growth form, seed mass and vegetation type were the main predictor variables. Our models predicted dispersal mechanisms for Australian and Californian plant species equally well (c. 70% correct) and to a lesser extent for the Swiss flora (c. 50% correct). Our models predicted observed dispersal mechanisms (c. 50% correct) equally well to inferred dispersal mechanisms (based on seed morphology). 4. Synthesis. Our approach of using easily obtainable traits for predicting dispersal mechanisms of species allows dispersal information to be predicted for species where little is known. From here, the application of realistic dispersal curves to the predicted dispersal mechanisms will further understanding on the dispersal capabilities of species.

Many field studies on plant seed dispersal teach us that we cannot judge the effective dispersal mode of plants by examining only the morphologies of the fruits and seeds. In the present study, we explored the seed dispersal process of an evergreen tree, the Japanese star anise Illicium anisatum , which is highly toxic, containing neurotoxins in both the fruits and seeds. The fruits exhibit ballochory, a mode of seed dispersal characterized by explosive fruit dehiscence, and the extreme toxicity apparently seems to deter fruit and seed consumption by animals. However, we found that the dispersal distance afforded by this mode was very short (≤ 6 m). In the field, we confirmed that a passerine species, the varied tit Poecile varius , was the only consumer of the seed in foliage, and the bird actively transported seeds or fruits to either cache or consume them. Seeds setting on the forest understory were removed by the small Japanese field mouse Apodemus argenteus , and were also dispersed by this animal. Analysis of seedling spatial distribution revealed that seedlings were highly aggregated near standing trees or fallen logs, suggesting that caching facilitated seed dispersal. This study warns that plant toxicity and the ecological function thereof should not be evaluated based only on limited knowledge of the effects on humans and mammals. Our results pose further questions on the evolution of toxin tolerance in seed-caching animals and on the mutualism between toxic plants and animals.