An Ant-Plant Mesocosm Experiment Reveals Dispersal Patterns of Myrmecochorous Plants

For Central European herbs, ants are one common dispersal vector acting at relatively small spatial scales. Though extensively studied concerning the different benefits to plants, specific dispersal patterns mediated by ants have been reportedly very sparsely and without any validation. Thus, we studied the seed dispersal pattern of a set of myrmecochorous plant species in a novel mesocosm experiment. We examined the seed dispersal distances of four forest herbs (Hollow Root-Corydalis cava (L.) Schweigg. & Korte, Alpine Squill-Scilla bifolia L., and Common Dog-violet-Viola riviniana Rchb. and the annual Ivy-leaved Speedwell-Veronica hederifolia L.) by the red ant Myrmica ruginodis Nylander in 8.25 m2 large plots under natural conditions with and without ants. In the presence of Myrmica ants, the bulb geophytes C. cava and S. bifolia showed a significantly higher fraction of dispersed seedlings and a maximum dispersal distance of 322 cm. Estimated by nearest neighbor analyses, distances between single C. cava seedlings were significantly higher in ant plots than in exclosures without ants. The annual species Veronica hederifolia showed a few dispersed seedlings in ant plots only, while the diplochorous hemicryptophyte Viola riviniana germinated in a widely scattered manner with distances up to 241 cm due to ballochorous dispersal in both ant and exclosure plots, but with a maximum of 324 cm only by means of ants. Our results indicate the escape from the mother plant and dispersal for distance as an important benefit for myrmecochorous species, potentially accompanied by benefits through reduced competition

Plant community persistence strategy is elevation‐specific

Aims Persistence plays a key role in both plant population and community dynamics as it allows withstanding temporarily habitat conditions unsuitable for growth and reproduction. Plants can exploit three different strategies to persist in situ (building soil seed banks, increasing adult longevity and/or clonal reproduction), the dominance of which in a community might vary along environmental gradients. Yet, their relative role in plant persistence has never been investigated. Location The Bavarian Alps, Germany. Methods We collected data on seed soil persistence, adult longevity and clonality for 290 species occurring in 18 grasslands located along an elevational gradient of 1,000 metres and examined their contribution to persistence in a community. Linear models were used to estimate the relationship between elevation and these persistence strategies. Results We found that dominance of a certain persistence strategy varied depending on environmental variability. Specifically, persistence in lowlands was mainly achieved by persistent and dense soil seed banks along with extended clonal growth (larger spread distances and higher number of offspring). Contrastingly, the main persistence strategy in the alpine communities was increased adult longevity. Conclusions The changes in relative contribution of each strategy to community persistence along the elevational gradient are interrelated suggesting a trade-off among them. We conclude that this trade-off plays an important role in species co-existence and community assembly, and might be useful to understand vegetation dynamics under ongoing climate change and improve restoration efforts of upland ecosystems

Hydrology regime and hydrology recruitment niche predict changes in plant community composition across a pond habitat

Questions Niche differentiation is widely accepted as a key mechanism important for species coexistence. Seed germination and seedling survival were recognized as important contributors to niche segregation and could be a crucial filter for determining species' distributions and community composition. Only a little is known about the direct relationship between hydrology recruitment niche, hydrology regimes, and community composition. Therefore, the main aim of this study is to identify the changes in the composition of a pond community with respect to the hydrological regime and predict them by the recruitment niche of species. Location The Gloggere pond in the Altdorfer forest (47.848 N, 9.698 E, Ravensburg vicinity, Upper Swabia, Baden-Wuerttemberg, Germany). Methods A transect with 46 permanent plots was established throughout the Gloggere pond, and species percentage cover was recorded in September 1992–1995, 2006, and 2017. Pond drawdown was implemented in 1993. Sediment samples were collected in March 1995 across the transect, and a pot germination experiment with six hydrological treatments was performed. The hydrology recruitment niche from the seed bank germination experiment was compared with the field hydrology niche to show the importance of the hydrology regime for community composition. Results The hydrological regime determined the community composition in both the germination experiment and the field. Species-specific hydrology niche from the field correlated with species-specific recruitment niche measured in the germination experiment. Conclusions Our results support the importance of recruitment niche as a driver of community composition for pond areas. For understanding and predicting changes in plant community composition, it is necessary to combine knowledge about the recruitment niche and the ability of seeds’ survival in the sediment along a hydrological gradient with knowledge about abiotic filters, biotic interactions, and species-specific traits. Recognizing the recruitment niche is useful for better predicting the effect of future environmental changes, especially in the context of climate change and conservation management

Ready for change: seed traits contribute to the high adaptability of mudflat species to their unpredictable habitat

Question A better understanding of species distribution and establishment requires in-depth information on their seed ecology. We hypothesised that seed traits of mudflat species may indicate a strong environmental adaptation in their highly specialised habitat. Furthermore, we asked the question, do seeds of mudflat species have a specific trait value to contribute high adaptability to small-scale variation in their unpredictable habitat? Location Central Europe. Methods Seeds of 30 typical mudflat species were used to measure 15 traits that govern seed dispersal (buoyancy and production), persistence (seed desiccation, mass and persistence in soil), and germination and establishment (germination response to different light, temperature and oxygen conditions). Cluster analysis and phylogenetic principal components analysis (pPCA) were conducted to define potential mudflat species functional groups as per their ecological optima. Results Seed production and seed mass displayed extremely high variation while seed buoyancy, desiccation and persistence in soil showed almost no variation. All study species produced buoyant, desiccation-tolerant and long-term persistent seeds. Germination and establishment traits also displayed similarity in their responses to different germination treatments as the majority (73%) of species has a moderate seed germination niche width. They germinated well under light/aerobic conditions irrespective to temperature fluctuations. The cluster analysis and pPCA separated species into three potential plant functional groups as 'true', 'flood-resistant' and 'facultative', mudflat species. Conclusion Moderate variation in the seed traits of mudflat plants suggests they employ different ecological strategies that seem highly predictive to the peculiarity of their specific micro-habitats, which are largely controlled by the hydroperiod gradient. It implies that seed trait information, which further needs to be tested for their adaptability, can advance our understanding of how community composition at the micro-habitat level depends on trait values of participating species

Soil Seed Bank Persistence Across Time and Burial Depth in Calcareous Grassland Habitats

Seed persistence in the soil is crucial for population dynamics. Interspecific differences in soil seed mortality could be a mechanism that may stimulate species coexistence in herbaceous plant communities. Therefore, understanding the levels and causes of seed persistence is vital for understanding community composition and population dynamics. In this study, we evaluated the burial depth as a significant predictor of the temporal dynamics of soil seed persistence. We suppose that species differ in this temporal dynamics of soil seed persistence according to burial depth. Furthermore, we expected that burial depth would affect soil seed persistence differently concerning the species-specific type of dormancy, light, and fluctuating temperature requirements for germination. Seeds of 28 herbaceous species of calcareous grasslands were buried in the field into depths of 1, 5, and 10 cm under the soil surface. Seed viability was tested by germination and tetrazolium tests several times for three years. Species-specific seed traits—a type of dormancy, light requirements and alternating temperature requirements for germination, and longevity index—were used for disentangling the links behind species-specific differences in soil seed persistence. Our study showed differences in soil seed persistence according to the burial depth at the interspecific level. Generally, the deeper the buried seeds, the longer they stayed viable, but huge differences were found between individual species. Species-specific seed traits seem to be an essential determinant of seed persistence in the soil. Seeds of dormant species survived less and only dormant seeds stayed viable in the soil. Similarly, seeds of species without light or alternating temperature requirements for germination generally remained viable in the soil in smaller numbers. Moreover, seeds of species that require light for germination stayed viable longer in the deeper soil layers. Our results help understand the ecosystem dynamics caused by seed reproduction and highlight the importance of a detailed long-term investigation of soil seed persistence. That is essential for understanding the fundamental ecological processes and could help restore valuable calcareous grassland habitats

Restoration of calcareous grasslands by natural recolonization after forest clearing and its impact on the genetic variation of three common herb species

Species-rich calcareous grasslands in Europe strongly declined during the twentieth century due to drastic land use changes. Many grasslands were converted into more productive pastures or are covered by shrubs or forests today, since they were overgrown after abandonment or afforested. Restoration of calcareous grasslands by shrub or forest clearing and subsequent recolonization of grassland species from adjacent grasslands is, therefore, an important conservation approach. Restored populations of calcareous grassland species may, however, differ from their source populations in genetic diversity and differentiation due to potential founder and bottleneck effects. In our study we analyzed, therefore, the impact of restoration by forest clearing and natural recolonization on the genetic variation of three common calcareous grassland species (Agrimonia eupatoria, Campanula rotundifolia, and Knautia arvensis) without a contribution of persistent seed bank, in South Western Germany. We used molecular markers AFLPs (Amplified fragment length polymorphisms) to compare genetic diversity within and differentiation between spontaneously recovered subpopulations with adjacent historically old, natural subpopulations at eight study sites. Restored parts of the grasslands have been re-established during the 1990s. Molecular markers revealed broadly similar levels of genetic diversity in source and restored subpopulations of the study species. Only A. eupatoria exhibited slightly higher diversity in restored subpopulations, which may be explained by higher dispersal potential due to the hooky fruits of the species. Genetic differentiation between source and restored subpopulations was not significant, indicating strong gene flow between the subpopulations. Our study underlines, therefore, that restoration of calcareous grasslands by natural recolonization after forest clearing is an efficient method to re-establish genetically variable subpopulations comparable to their sources