Germination traits explain soil seed persistence across species: the case of Mediterranean annual plants in cereal fields

Background and Aims

Seed persistence in the soil under field conditions is an important issue for the maintenance of local plant populations and the restoration of plant communities, increasingly so in the light of rapidly changing land use and climate change. Whereas processes important for dispersal in space are well known, knowledge of processes governing dispersal in time is still limited. Data for morphological seed traits such as size have given contradictory results for prediction of soil seed persistence or cover only a few species. There have been few experimental studies on the role of germination traits in determining soil seed persistence, while none has studied their predictive value consistently across species. Delayed germination, as well as light requirements for germination, have been suggested to contribute to the formation of persistent seed banks. Moreover, diurnally fluctuating temperatures can influence the timing of germination and are therefore linked to seed bank persistence.

Methods

The role of germination speed measured by T₅₀ (days to germination of 50 % of all germinated seeds), light requirement and reaction to diurnally fluctuating temperatures in determining seed persistence in the soil was evaluated using an experimental comparative data set of 25 annual cereal weed species.

Key Results

It is shown that light requirements and slow germination are important features to maintain seeds ungerminated just after entering the soil, and hence influence survival of seeds in the soil. However, the detection of low diurnally fluctuating temperatures enhances soil seed bank persistence by limiting germination. Our data further suggest that the effect of diurnally fluctuating temperatures, as measured on seeds after dispersal and dry storage, is increasingly important to prevent fatal germination after longer burial periods.

Conclusions

These results underline the functional role of delayed germination and light for survival of seeds in the soil and hence their importance for shaping the first part of the seed decay curve. Our analyses highlight the detection of diurnally fluctuating temperatures as a third mechanism to achieve higher soil seed persistence after burial which interacts strongly with season. We therefore advocate focusing future research on mechanisms that favour soil seed persistence after longer burial times and moving from studies of morphological features to exploration of germination traits such as reaction to diurnally fluctuating temperatures.     

Two ways of trapping seeds in alpine environments, Lapland, Sweden

Seed dispersal in two habitats was investigated in the mid-alpine Latnjajaure valley, in northernmost Swedish Lapland. The seed rain size was measured using artificial seed traps and natural snowbed at a heath and a meadow site, c. 1000 m a.s.l. The average seed rain size trapped in the snowbeds varied from 18 seeds m^-2 at the heath site, to 96 seeds m-² at the meadow site. On average, the heath trap station had 177 seeds m-² and the meadow station, 218 seeds m². At each site, the vegetation was inventoried within a circular area with a radius of 20 m. Overall, the species assembly in the seed rain reflected the surrounding vegetation. However, there were additional species in the seed rain as well. At the seed trap station on the wind-exposed heath, 78% of the seeds originated from sites outside the homogeneous vegetation around the trap. These seeds were dispersed from locations at least 150 m from the trap site. By trapping a higher number of species than artificial traps and a higher number of seeds per unit area, snowbeds served as effective 'seed traps'. However, the location of the sampling spot in the snowbed is crucial due to a decrease in seed density towards the edge. In this study, with the aim of trapping the main dispersing species in the area, the optimal artificial seed trap size appears to be - 1.5–2.0 m². There was also a positive correlation between the mean July and August temperature, the seed rain size, and the number of species found. Thus, through brief visits to remote locations, the study of seed dispersal can be accomplished effectively when snowbeds are present on the landscape.     

Seed traits and bird species influence the dispersal parameters of wetland plants

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Dropping rates of elaiosome-bearing seeds during transport by ants (Formica polyctena Foerst.): Implications for distance dispersal

In a deciduous forest, foraging ants collect elaiosome-bearing seeds and carry them to their nests. Some of the seeds reach the nest and are concentrated there. Others may be dropped by ants during transport. The dropped seeds enter the soil seed pool. However, they might be repeatedly removed by other ant individuals and carried again in the direction of the nest. Rates of seed dropping and repeated removals must be known to evaluate the effect of ant workers on dispersal distance of seeds. The rate of seed dropping is predicted to depend on size of seeds and of elaiosomes, both of which vary among plant species, and on the size of the ant workers. Mark-recapture experiments were used to evaluate dropping rates of seeds of five myrmecochorous and diplochorous plants (Chelidonium majus L., Asarum europaeum L., Viola matutina Klok., V. mirabilis L., V. hirta L.) during their transport by the ant Formica polyctena Foerst. In the series of species A. europaeum – V. hirta – V. mirabilis – Ch. majus – V. matutina, the dropping rate increased. Small workers dropped seeds of A. europaeum more often than did large ones, while seeds of V. hirta were dropped by ants of different size classes with the same frequency. Across species, dropping rates of seeds were negatively correlated with the rate at which ants removed them from the depot. The number of seeds which reach the nests is the other important parameter of seed dispersal. This parameter depends on dropping rates: seeds with lower dropping rates have higher chances of being deposited in nests. Diplochores usually produce many small seeds, which are characterised by low removal rates and high dropping rates during transport by ants. Obligate myrmecochores produce rather few large seeds, which have high removal rates and low dropping rates. To analyse the significance of seed dropping in the dispersal distance of seeds, a computer simulation based on two factors [(i) seed number produced by a plant; (ii) dropping rate of seeds] is proposed.     

Snowbeds trapping seed rain—a comparison of methods

The possibility of assessing seed rain by deposits in snowbeds was investigated in the Abisko area in northernmost Swedish Lapland. In late summer the "grey blanket" on the snowbed surface was skimmed off, melted and sieved through a filter paper. The debris contained on average 741 seeds m², making up 6.5% of the total debris dry mass. A total of 11,909 seeds, representing 69 species, were encountered in the study. Phyllodoce coerulea, Carex bigelowii and Juncus trifldus were the most abundant. The efficiency of the snowbeds as diaspore traps was compared with a set of artificial traps. Data from two years were compared. The snowbed proved to be more efficient than artificial seed traps, in particular for trapping seeds of graminoids and herbs. Both methods revealed considerable among-year variation in seed output as a possible result of differences in summer climate. The results also suggest that snowbed can be used for assessing aeolian inorganic deposition, in the present study on average 9.0 g m².     

Mammalian seed dispersal in Cantabrian woodland pastures: Network structure and response to forest loss

We evaluated the role of wild large mammals as dispersers of fleshy-fruited woody plants in woodland pastures of the Cantabrian range (N Spain). By searching for seeds in mammal scats across four localities, we addressed how extensive seed dispersal was in relation to the fleshy-fruited plant community, and applied a network approach to identify the relative role of mammal species in the seed dispersal process. We also tested the response of mammalian dispersers to forest availability at increasing spatial scales. Five carnivores and three ungulates dispersed seeds of eight fleshy-fruited trees and shrubs. Mammalian seed dispersal did not mirror community-wide fruit availability, as abundant fruiting trees were scarce whereas thorny shrubs were over-represented among dispersed species. The dispersal network was dominated by bramble (Rubus ulmifolius/fruticosus), the remaining plants being rarer and showing more restricted disperser coteries. Fox (Vulpes vulpes), badger (Meles meles), and wild boar (Sus scrofa) dispersed mostly bramble, whereas martens (Martes sp.) dispersed mostly wild rose (Rosa sp.). Ungulates occasionally dispersed holly (Ilex aquifolium) and hawthorn (Crataegus monogyna). The empirical network reflected a skewed distribution of interactions and some functional complementarity (as judged from the low levels of connectance and nestedness), but also some degree of specialization. Mammals overused uncovered microsites for seed deposition, and increased their disperser activity in those landscape sectors devoid of forest. Combined with previous findings on avian seed dispersal, this study suggest a strong functional complementarity coming from the low overlap in the main plant types that mammals and birds disperse – thorny shrubs and trees, respectively – and the differential patterns of seed deposition, with mammals mostly dispersing into deforested areas, and birds into forest-rich landscapes.     

Diplochory in western chokecherry: you can��t judge a fruit by its mesocarp

Western chokecherry (Prunus virginiana var. demissa, Rosaceae) is dispersed by frugivorous birds and carnivores, but it has large seeds that are potentially attractive to rodents that could act as seed predators and dispersers. Here, we quantify the benefits of primary dispersal by birds and secondary dispersal by scatter-hoarding rodents. In the fall, avian frugivores (mostly American robins, Turdus migratorius, and cedar waxwings, Bombycilla cedrorum) consumed 87% of the fruit crop and dispersed 67% of the fruit crop away from parent plants. Rodents removed 89% of seeds that simulated bird-dispersed seed rain from transects in riparian zones and 58% from transects in upland habitats. Rodents scatter-hoarded 91.6% of the seeds they removed, burying most in small caches (two to eight seeds) 8?C25?mm deep. About 39% of the seeds in spring caches produced seedlings. Inside rodent-proof exclosures, 52.1% of seeds buried to simulate rodent caches produced seedlings, 29.7% of which were still alive after 1?year. In contrast, only 3.8% of seeds placed on the soil surface, simulating dispersal by avian frugivores, produced seedlings. Seed dispersal by frugivorous birds likely contributes to colonization of unoccupied habitat through long-range dispersal and to escape from distance-dependent seed mortality near the parent plant. Despite seed losses, rodents offer short-range seed dispersal and bury seeds in more favorable sites for germination, improving seedling emergence and establishment. The combined mechanisms of seed dispersal significantly enhanced chokecherry seedling recruitment by providing more dispersal-related benefits than either frugivorous bird or scatter-hoarding rodents could provide alone.     

Odor of achlorophyllous plants’ seeds drives seed‐dispersing ants

Seed dispersal by ants is an important means of migration for plants. Many myrmecochorous plants have specialized appendages in their seeds called elaiosome, which provides nutritional rewards for ants, and enable effective seed dispersal. However, some nonmyrmecochorous seeds without elaiosomes are also dispersed by ant species, suggesting the additional mechanisms other than elaiosomes for seed dispersal by ants. The seeds of the achlorophyllous and myco‐heterotrophic herbaceous plant Monotropastrum humile are very small without elaiosomes; we investigated whether odor of the seeds could mediate seed dispersal by ants. We performed a bioassay using seeds of M. humile and the ant Nylanderia flavipes to demonstrate ant‐mediated seed dispersal. We also analyzed the volatile odors emitted from M. humile seeds and conducted bioassays using dummy seeds coated with seed volatiles. Although elaiosomes were absent from the M. humile seeds, the ants carried the seeds to their nests. They also carried the dummy seeds coated with the seed volatile mixture to the nest and left some dummy seeds inside the nest and discarded the rest of the dummy seeds outside the nest with a bias toward specific locations, which might be conducive to germination. We concluded that, in M. humile seeds, volatile odor mixtures were sufficient to induce seed‐carrying behavior by the ants even without elaiosomes.     

Evolution of seed dispersal in North American <Emphasis Type="Italic">Ephedra</Emphasis>

Related plants often produce seeds that are dispersed in very different ways, raising questions of how and why plants undergo adaptive shifts in key aspects of their reproductive ecology. Here we analyze the evolution of seed dispersal syndromes in an ancient group of plants. Ephedra (Gymnospermae; Gnetales; Ephedraceae) is a genus containing ≈50 species in semiarid ecosystems worldwide and with three distinct types of cones. We collected mature cones and seeds of ten species of Ephedra in southwestern United States and measured nine morphological traits for each species. Principal component analysis and other data characterized three types of Ephedra cones and seeds. Species with dry, winged cone bracts are dispersed by wind (i.e., E. torreyana and E. trifurca), those with succulent, brightly-colored cone bracts are dispersed by frugivorous birds (i.e., E. antisyphilitica), and those with small, dry cone bracts and large seeds are dispersed by seed-caching rodents (e.g., E. viridis and E. californica). Two species (E. funerea and E. nevadensis) have cone and seed morphologies intermediate between two seed dispersal syndromes. Seed and cones traits were mapped onto two recent phylogenies to help reveal the evolutionary history of seed dispersal syndromes. Bird dispersal is thought to be the ancestral form of seed dispersal in ephedras as it is common in the Old World where Ephedra originated, but the three North American species dispersed by birds are not monophyletic. The two wind dispersed species in North America also do not cluster together, suggesting separate origins. Seed dispersal by seed-caching rodents is common in North America and appears to have evolved several times, but this syndrome is absent form other continents. The evolutionary history of Ephedra in North America suggests that the means of seed dispersal has been malleable. Evolutionary shifts were likely linked to changes in ecological conditions.     

Effects of seed traits on the potential for seed dispersal by fish with contrasting modes of feeding

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Seed dynamics of resprouting shrubs in grassy woodlands: Seed rain,predators and seed loss constrain recruitment potential

Abstract Measuring the fate of seeds between seed production and seedling establishment is critical in understanding mechanisms of recruitment limitation of plants. We examined seed fates to better understand the recruitment dynamics of four resprouting shrubs from two families (Fabaceae and Epacridaceae) in temperate grassy woodlands. We tested whether: (i) pre‐dispersal seed predation affected seed rain; (ii) post‐dispersal seed predation limited seed bank accumulation; (iii) the size of the seed bank was related to seed size; and (iv) viable seeds accumulated in the soil after seed rain. There was a distinct difference in seed production per plant between plant families with the legumes producing significantly more seeds per individual than the epacrids. Seed viability ranged from 43% to 81% and all viable had seed or fruit coat dormancy broken by heat or scarification. Pre‐dispersal predation by Lepidopteran larvae removed a large proportion of seed from the legume seed rain but not the epacrids. Four species of ants (Notoncus ectatomoides, Pheidole sp., Rhytidoponera tasmaniensis and Iridomyrmex purpureus) were major post‐dispersal seed removers. Overall, a greater percentage of Hardenbergia (38%) and Pultenaea (59%) seeds were removed than the fleshy fruits of Lissanthe (14%) or Melichrus (0%). Seed bank sizes were small (<15 seeds m^?2) relative to the seed rain and no significant accumulation of seed in the soil was detected. Lack of accumulation was attributed to seed predation as seed decay was considered unlikely and no seed germination was observed in our study sites. Our study suggests that seed predation is a key factor contributing to seed‐limited recruitment in grassy woodland shrubs by reducing the number of seeds stored in the soil.     

Frugivory by introduced black rats (Rattus rattus) promotes dispersal of invasive plant seeds

Oceanic islands have been colonized by numerous non-native and invasive plants and animals. An understanding of the degree to which introduced rats (Rattus spp.) may be spreading or destroying seeds of invasive plants can improve our knowledge of plant-animal interactions, and assist efforts to control invasive species. Feeding trials in which fruits and seeds were offered to wild-caught rats were used to assess the effects of the most common rat, the black rat (R. rattus), on 25 of the most problematic invasive plant species in the Hawaiian Islands. Rats ate pericarps (fruit tissues) and seeds of most species, and the impacts on these plants ranged from potential dispersal of small-seeded (≤1.5 mm length) species via gut passage (e.g., Clidemia hirta, Buddleia asiatica, Ficus microcarpa, Miconia calvescens, Rubus rosifolius) to predation where <15% of the seeds survived (e.g., Bischofia javanica, Casuarina equisetifolia, Prosopis pallida, Setaria palmifolia). Rats consumed proportionally more seed mass of the smaller fruits and seeds than the larger ones, but fruit and seed size did not predict seed survival following rat interactions. Although invasive rat control efforts focus on native species protection, non-native plant species, especially those with small seeds that may pass internally through rats, also deserve rat control in order to help limit the spread of such seeds. Black rats may be facilitating the spread of many of the most problematic invasive plants through frugivory and seed dispersal in Hawaii and in other ecosystems where rats and plants have been introduced.     

The Response of the Alpine Dwarf Shrub Salix herbacea to Altered Snowmelt Timing: Lessons from a Multi-Site Transplant Experiment

Climate change is altering spring snowmelt patterns in alpine and arctic ecosystems, and these changes may alter plant phenology, growth and reproduction. To predict how alpine plants respond to shifts in snowmelt timing, we need to understand trait plasticity, its effects on growth and reproduction, and the degree to which plants experience a home-site advantage. We tested how the common, long-lived dwarf shrub Salix herbacea responded to changing spring snowmelt time by reciprocally transplanting turfs of S. herbacea between early-exposure ridge and late-exposure snowbed microhabitats. After the transplant, we monitored phenological, morphological and fitness traits, as well as leaf damage, during two growing seasons. Salix herbacea leafed out earlier, but had a longer development time and produced smaller leaves on ridges relative to snowbeds. Longer phenological development times and smaller leaves were associated with reduced sexual reproduction on ridges. On snowbeds, larger leaves and intermediate development times were associated with increased clonal reproduction. Clonal and sexual reproduction showed no response to altered snowmelt time. We found no home-site advantage in terms of sexual and clonal reproduction. Leaf damage probability depended on snowmelt and thus exposure period, but had no short-term effect on fitness traits. We conclude that the studied populations of S. herbacea can respond to shifts in snowmelt by plastic changes in phenology and leaf size, while maintaining levels of clonal and sexual reproduction. The lack of a home-site advantage suggests that S. herbacea may not be adapted to different microhabitats. The studied populations are thus unlikely to react to climate change by rapid adaptation, but their responses will also not be constrained by small-scale local adaptation. In the short term, snowbed plants may persist due to high stem densities. However, in the long term, reduction in leaf size and flowering, a longer phenological development time and increased exposure to damage may decrease overall performance of S. herbacea under earlier snowmelt.     

Mating systems of snowbed plant species of the northeastern Calcareous Alps of Austria

Predicted climate warming will likely reduce the area and increase the fragmentation of alpine snowbed habitats. The ability of snowbed plants to cope with such fragmentation will, among other things, depend on their reproductive strategy. With respect to the mating system, as a key component of reproductive strategies, the environmental conditions in arctic and alpine snowbeds have been hypothesized to select for high selfing ability due to short growing seasons and unpredictable pollinator service. In this study we evaluate whether the mating system strategies of seven typical snowbed forbs of the northeastern Calcareous Alps in Austria are in line with this hypothesis. Field-pollination experiments were conducted in order to study the effects of pollinator exclusion (bagging; all study species), emasculation and manual self- and cross-pollination (subset of study species) on seed set. Additionally, data on floral traits associated with the reproductive system such as anther and ovule numbers and pollen:ovule ratios were collected. Results demonstrate that selfing is not uncommon but by no means obligatory for snowbed plants: the study species display a wide range of mating system types, from predominately outcrossing to predominately selfing. The different reproductive strategies of regional snowbed plants are discussed in relation to their ability to cope with climate warming induced habitat fragmentation.     

The ecophysiology of seed persistence: a mechanistic view of the journey to germination or demise

Seed persistence is the survival of seeds in the environment once they have reached maturity. Seed persistence allows a species, population or genotype to survive long after the death of parent plants, thus distributing genetic diversity through time. The ability to predict seed persistence accurately is critical to inform long‐term weed management and flora rehabilitation programs, as well as to allow a greater understanding of plant community dynamics. Indeed, each of the 420000 seed‐bearing plant species has a unique set of seed characteristics that determine its propensity to develop a persistent soil seed bank. The duration of seed persistence varies among species and populations, and depends on the physical and physiological characteristics of seeds and how they are affected by the biotic and abiotic environment. An integrated understanding of the ecophysiological mechanisms of seed persistence is essential if we are to improve our ability to predict how long seeds can survive in soils, both now and under future climatic conditions. In this review we present an holistic overview of the seed, species, climate, soil, and other site factors that contribute mechanistically to seed persistence, incorporating physiological, biochemical and ecological perspectives. We focus on current knowledge of the seed and species traits that influence seed longevity under ex situ controlled storage conditions, and explore how this inherent longevity is moderated by changeable biotic and abiotic conditions in situ, both before and after seeds are dispersed. We argue that the persistence of a given seed population in any environment depends on its resistance to exiting the seed bank via germination or death, and on its exposure to environmental conditions that are conducive to those fates. By synthesising knowledge of how the environment affects seeds to determine when and how they leave the soil seed bank into a resistance–exposure model, we provide a new framework for developing experimental and modelling approaches to predict how long seeds will persist in a range of environments.     

Two-phase seed dispersal: linking the effects of frugivorous birds and seed-caching rodents

Frugivorous birds disperse the seeds of many fruit-bearing plants, but the fate of seeds after defecation or regurgitation is often unknown. Some rodents gather and scatter hoard seeds, and some of these may be overlooked, germinate, and establish plants. We show that these two disparate modes of seed dispersal are linked in some plants. Rodents removed large (>25 mg) seeds from simulated bird feces (pseudofeces) at rates of 8–50%/day and scatter hoarded them in soil. Ants (Formica sibylla) also harvested some seeds and carried them to their nests. Rodents carried seeds 2.5±3.2 m to cache sites (maximum 12 m) and buried seeds at 8±7 mm depth. Enclosure studies suggest that yellow pine chipmunks (Tamias amoenus) and deer mice (Peromyscus maniculatus) made the caches. In spring, some seeds germinated from rodent caches and established seedlings, but no seedlings established directly from pseudofeces. This form of two-phase seed dispersal is important because each phase offers different benefits to plants. Frugivory by birds permits relatively long-range dispersal and potential colonization of new sites, whereas rodent caching moves seeds from exposed, low-quality sites (bird feces on the ground surface) to a soil environment that may help maintain seed viability and promote successful seedling establishment.     

Asian Tapirs Are No Elephants When It Comes To Seed Dispersal

The elimination of the largest herbivores (elephants and rhinoceroses) from many forests in tropical East Asia may have severe consequences for plant species that depend on them for seed dispersal. We assessed the capacity of Malayan tapirs Tapirus indicus—the next largest nonruminant herbivore in the region—as a substitute for the lost megafauna in this role by studying their ability to disperse the seeds of nine fleshy‐fruited plants with seeds 5–97 mm in length. We combined information from feeding trials, germination tests, and field telemetry to assess the effect of tapir consumption on seed viability and to estimate how far the seeds would be dispersed. The tapirs (N=8) ingested few seeds. Seed survival through gut passage was moderately high for small‐seeded plants (e.g., 36.9% for Dillenia indica) but very low for medium‐ (e.g., 7.6% for Tamarindus indica) and large‐seeded (e.g., 2.8% for Artocarpus integer) plants. Mean seed gut passage times were long (63–236 h) and only the smallest seeds germinated afterwards. Using movement data from four wild tapirs in Peninsular Malaysia we estimated mean dispersal distances of 917–1287 m (range=22–3289 m) for small‐seeded plants. Malayan tapirs effectively dispersed small‐seeded plants but acted as seed predators for the large‐seeded plants included in our study, suggesting that they cannot replace larger herbivores in seed dispersal. With the absence of elephants and rhinos many megafaunal‐syndrome plants in tropical East Asia are expected to face severe dispersal limitation problems.     

Fragmentation modifies seed trait effects on scatter-hoarders’ foraging decisions

Scatter-hoarding animals are crucial in seed dispersal of nut-bearing plants. We used the holm oak Quercus ilex—wood mouse Apodemus sylvaticus mutualism as a model system to evaluate the relative importance of seed size and fat content on scatter-hoarders’ foraging decisions influencing oak dispersal and potential recruitment. We performed a field experiment in which we offered holm oak acorns with contrasting seed size (2 vs 5 g) and fat content (3 vs 11%). Moreover, to test if the strength of these seed trait effects was context-dependent, experimental acorns were placed in small fragments, where natural regeneration is scarce or absent, and forest habitats. In small fragments, rodents had to face increased intraspecific competition for acorns and reduced anti-predator cover during transportation. As a result, they became more selective to ensure rapid acquisition of most valuable food items but, in turn, transported seeds closer to avoid unaffordable predation risks. During harvesting and caching, larger acorns were prioritized and preferentially cached. Fat content only had a minor effect in harvesting preferences. In contrast, in forest sites, where rodent abundance was four times lower and understory cover was well-developed, rodents were not selective but provided enhanced dispersal services to oaks (caching rates were 75% higher). From the plants’ perspective, our results imply that the benefits of producing costly seeds are context-dependent. Seed traits modified harvesting and caching rates only when rodents were forced to forage more efficiently in response to increased intraspecific competition. However, when landscape traits limited cache protection strategies, a more selective foraging behavior by scatter-hoarders did not result in enhanced dispersal services. Overall, our result shows that successful dispersal of acorns depends on how specific traits modulate their value and how landscape properties affect rodents’ ability to safeguard them for later consumption.     

Seed dispersal by wind decreases when plants are water‐stressed,potentially counteracting species coexistence and niche evolution

Hydrology is a major environmental factor determining plant fitness, and hydrological niche segregation (HNS) has been widely used to explain species coexistence. Nevertheless, the distribution of plant species along hydrological gradients does not only depend on their hydrological niches but also depend on their seed dispersal, with dispersal either weakening or reinforcing the effects of HNS on coexistence. However, it is poorly understood how seed dispersal responds to hydrological conditions. To close this gap, we conducted a common‐garden experiment exposing five wind‐dispersed plant species (Bellis perennis, Chenopodium album, Crepis sancta, Hypochaeris glabra, and Hypochaeris radicata) to different hydrological conditions. We quantified the effects of hydrological conditions on seed production and dispersal traits, and simulated seed dispersal distances with a mechanistic dispersal model. We found species‐specific responses of seed production, seed dispersal traits, and predicted dispersal distances to hydrological conditions. Despite these species‐specific responses, there was a general positive relationship between seed production and dispersal distance: Plants growing in favorable hydrological conditions not only produce more seeds but also disperse them over longer distances. This arises mostly because plants growing in favorable environments grow taller and thus disperse their seeds over longer distances. We postulate that the positive relationship between seed production and dispersal may reduce the concentration of each species to the environments favorable for it, thus counteracting species coexistence. Moreover, the resulting asymmetrical gene flow from favorable to stressful habitats may slow down the microevolution of hydrological niches, causing evolutionary niche conservatism. Accounting for context‐dependent seed dispersal should thus improve ecological and evolutionary models for the spatial dynamics of plant populations and communities.     

Seed preferences by rodents in the agri‐environment and implications for biological weed control

Post‐dispersal seed predation and endozoochorous seed dispersal are two antagonistic processes in relation to plant recruitment, but rely on similar preconditions such as feeding behavior of seed consumers and seed traits. In agricultural landscapes, rodents are considered important seed predators, thereby potentially providing regulating ecosystem services in terms of biological weed control. However, their potential to disperse seeds endozoochorously is largely unknown. We exposed seeds of arable plant species with different seed traits (seed weight, nutrient content) and different Red List status in an experimental rye field and assessed seed removal by rodents. In a complementary laboratory experiment, consumption rates, feeding preferences, and potential endozoochory by two vole species (Microtus arvalis and Myodes glareolus) were tested. Seed consumption by rodents after 24 h was 35% in the field and 90% in the laboratory. Both vole species preferred nutrient‐rich over nutrient‐poor seeds and M. glareolus further preferred light over heavy seeds and seeds of common over those of endangered plants. Endozoochory by voles could be neglected for all tested plant species as no seeds germinated, and only few intact seeds could be retrieved from feces. Synthesis and applications. Our results suggest that voles can provide regulating services in agricultural landscapes by depleting the seed shadow of weeds, rather than facilitating plant recruitment by endozoochory. In the laboratory, endangered arable plants were less preferred by voles than noxious weeds, and thus, our results provide implications for seed choice in restoration approaches. However, other factors such as seed and predator densities need to be taken into account to reliably predict the impact of rodents on the seed fate of arable plants.