Diaspore Dispersal Research Articles

High potential of sub-Mediterranean dry grasslands for sheep epizoochory

AbstractThere is a general decline of grasslands across Europe due to habitat loss and degradation. Ensuring plant dispersal thus becomes a key process for preserving grassland patches in all scales. We examined diaspore dispersal by sheep epizoochory in the pastures of the North Adriatic Karst (NW Slovenia) and determined the qualitative and quantitative features of diaspores in fur. We recorded 25,650 diaspores of 141 plant taxa (with 107 taxa and 23,350 diaspores determined to species level), using three different methods: (i) the “whole-coat method”, (ii) the “part-of-thecoat method” and (iii) a “seedling emergence method”. A comparison of these techniques revealed that the “wholecoat method” provided the highest number of diaspores and plant species. All diaspores were clustered into five emergent groups based on seven functional traits (diaspore weight, length, width, height, volume, specific weight and the diaspore surface structure). Our research revealed that sheep represent an important dispersal vector, since about half of the plant species recorded in the pastures were found as diaspores in fur. This study contributes to knowledge about the modes of seed dispersal in seminatural grasslands. Taking into account that livestock play a key role in vegetation dynamics, understanding their effects on seed dispersal is essential for conservation and restoration of these species-rich grassland communities.

Post-release fates of seeds in dehiscent and indehiscent siliques of the diaspore heteromorphic species Diptychocarpus strictus (Brassicaceae)

Abstract Fruit/seed heteromorphic plants have been studied most extensively for differences in dispersal and germination of the morphs. However, fates of the heteromorphic diaspores beginning with seed release and ending with germination/seed death have been documented for relatively few species. Our primary aim was to follow the fates of the two dispersal unit morphs of Diptychocarpus strictus over a several-year period or until they germinated or died. Our hypothesis was that the winged, mucilaginous seeds (dispersal unit) from the dehiscent upper siliques form a short-lived seed bank and the nearly-wingless, nonmucilaginous seeds inside the indehiscent lower siliques (dispersal unit) a long-lived seed bank. Thus, for the two morphs we monitored phenology of seed release in 2010, germination phenology from 2010 to 2014 and germination and survival during burial in soil from 2010 to 2012. All lower siliques had been released from mother plants by late July, whereas seed release of the winged seeds of upper siliques was not completed until late October, after the main stem had become detached (near the base). Most seeds (18%) from upper siliques that did so (c. 20%) germinated in spring 2011, whereas no seeds in lower siliques germinated until autumn 2011 (0.2%). All seeds from upper siliques had germinated or lost viability by the end of the autumn 2012 germination season, whereas 11% of seeds inside lower siliques germinated in autumn 2014 and a high proportion of the nongerminated seeds was still viable, thus supporting our hypothesis. Buried seeds of both morphs exhibited a 6-mo dormancy cycle in which the nondormant phase coincided with the two germination seasons. Dehiscence of the upper siliques and indehiscence of the lower siliques are required for D. strictus to have a high risk-low risk strategy (H/H-L/L) for diaspore dispersal and dormancy.

AreDeschampsia caespitosa(L.) Beauv. Tussocks Safe Sites for Seedling Recruitment in the Succession of Wet Meadows?

In stressful and harsh environments, safe sites for seedling recruitment may be created by nurse plants, which accumulate propagules and subsequently facilitate the establishment of individuals. The main goal of the presented studies focused on observations of seedling recruitment in small and large tussocks of Deschampsia caespitosa derived from patches of unmanaged Molinietum caeruleae meadows situated along the successional gradient and dominated by small meadow species (Patch I), by macroforbs (Patch II), or overgrown by trees and shrubs (Patch III).The studies showed that, irrespective of patch character, Serratula tinctoria, Selinum carvifolia, Lysimachia vulgaris and Filipendula ulmaria are among the best colonizers of Deschampsia caespitosa tussocks. The gradual decrease in number of species and offspring abundance along the successional gradient may be connected with a prolonged period of water stagnation accelerating the development of fungal pathogens, a major cause of mortality for buried diaspores. The growing frequency of species present in standing vegetation and the gradually rising contribution of swamp and forest taxa in consecutive patches may be due to the production of non-persistent diaspores by early successional species, as well as reduced seed immigration from neighboring sites.The obtained results included evidence that, regardless of patch character, the percentage of seedlings representing species present in and absent from existing vegetation as well as taxa with various vegetation types is similar in small and large tussocks. Furthermore, in small tussocks, regardless of patch character, anemochorous and hydrochorous taxa dominated, the frequency of endo- and epizoochorous taxa was much lower, while the percentage of species characterized by other modes of diaspore dispersal attained the lowest rates. In large tussocks, anemochorous and epizoochorous species prevailed, the share of endozoochorous and hydrochorous taxa was lower, and the contribution of species characterized by other modes of dissemination was very scarce.On the basis of these studies it might be concluded that, despite the successive decrease of species and seedling abundance, and along with the increase in the recruitment of taxa resident in standing vegetation, especially woody species, the tussocks of Deschampsia caespitosa are reservoirs of meadow species even in advanced successional stages and may play a significant role in the process of long-term species turnover.

Dynamics of juvenile woody plant communities on termite mounds in a West African savanna landscape

Termites are keystone species in savanna ecology, and their mounds are thought to be an important source of habitat heterogeneity and structural complexity of the savanna. Macrotermes termitaria have been shown to allow woody plant colonisation of landscapes otherwise dominated by C4 grasses. In this study, we assess how resource-rich Macrotermes mounds affect juvenile woody plant and non-woody plant species diversity, community composition, biomass and population dynamics. We repeatedly sampled paired termite mound and savanna plots in Pendjari National Park (Sudanian vegetation zone, North Benin, West Africa) over the course of two years. Despite considerable overlap in their species pools, plant communities of mound and savanna plots were clearly separated in ordinations. Species richness and diversity of juvenile woody plants was consistently higher on termite mounds, while no differences could be detected for non-woody plants. Evenness of juvenile woody plants was generally lower on mounds, whereas density and basal area were higher on mounds. In contrast, we did not detect any influence of the mound microhabitat on colonisation, mortality and turnover of woody juveniles. Therefore, we suggest that differences in the communities on and off mounds should be strongly influenced by directed diaspore dispersal through zoochory.

Spatio‐temporal pattern of specific gravity of mangrove diaspore: implications for upstream dispersal

Mangrove plants, which develop highly productive forests on tropical–subtropical coastlines and river estuaries, rely mainly on river and sea water currents for their diaspore dispersal. Mangrove diaspores are basically dispersed in brackish to sea waters; thus whether they sink or float during the dispersal period could be changed dynamically, both spatially and temporally, depending on the salinity to which they are exposed, as well as on their specific gravity (SG). We found that the SG of diaspores of two mangrove species, Rhizophora stylosa and Bruguiera gymnorrhiza, which are dominant species and form a typical zonation (B. gymnorrhiza in inland areas and R. stylosa in more seaward areas) in the study area, changed spatially and temporally. Bruguiera gymnorrhiza gradually lost its SG in accordance with elapsed time, while R. stylosa lost its SG in the first 6 h and gained gradually according to elapsed time. Hydrodynamic simulation of dispersal patterns, in combination with observed specific gravity changes of both diaspores and river water, demonstrated that the spatio‐temporal pattern of specific gravity change was closely related to the difference in dispersal behaviors between the species. The diaspore of B. gymnorrhiza generally disperses upstream, and covers wider ranges than that of R. stylosa, at least in the early phase of dispersal. These dispersal behaviors agreed well with the distribution pattern of the species across estuaries in the study site. To date, hydrochory has been considered to be a mostly passive process governed by the dynamics of water current and subsequent sediment movement, with fixed diaspore characteristics such as shape and buoyancy. The present study shed new light on an active and dynamic process in hydrochory and found that the buoyancy of diaspores may be controlled by changes in their spatial and temporal SG.

Understorey vegetation gradient in a Eucalyptus grandis plantation between a savanna and a semideciduous forest

Plant community assemblage is influenced by many factors, including soil characteristics and the arrival of diaspores from surrounding areas. These factors may be especially important in transition areas, leading to spatial gradients in the plant community. This study was performed in the understorey of an abandoned Eucalyptus grandis W. Hill ex Maiden plantation between a savanna and a forest, 490 m apart, in south-eastern Brazil. This study assessed whether the spatial variation in several variables related to the understorey’s structure and composition is best described by linear or non-linear (quadratic) models. The linear model would indicate a gradient between the two vegetation types, whereas the quadratic model would indicate a stronger effect of the plantation’s edges. There was a gradient in species composition between the two edges of the plantation. Mean vegetation height was greatest at the savanna edge and lowest in the centre of the plantation. The total number of individuals per plot and the phylogenetic diversity decreased with distance from the savanna edge. Different patterns were observed for different dispersal syndromes, with animal dispersal being more common at the savanna edge, wind dispersal in the centre of the plantation and self dispersal at the forest edge. The greater number of individuals at the savanna edge may indicate that dispersal and arrival of diaspores are the most important factors influencing community structure and composition of the understorey of this abandoned E. grandis plantation, with most propagules coming from the savanna area. The smaller vegetation height in the centre of the fragment may also indicate older colonisation at the edges. Therefore, in addition to highlighting the recovery potential of undergrowth beneath abandoned Eucalyptus spp. plantations, these results show that this recovery is spatially heterogeneous and that dispersal plays a large role in it. This should be taken into account in restoration projects. The authors recommend careful consideration before removing regenerating Eucalyptus spp. trees as part of the site restoration. Instead the focus should be on the recovery potential of the undergrowth, with gradual removal of Eucalyptus trees, if necessary.

Critical transitions in disturbance‐driven ecosystems: identifying Windows of Opportunity for recovery

Summary Vegetation recovery in disturbance‐driven ecosystems is difficult to predict. We demonstrate a concept to analyse time series for short‐term variability in external forcing that can identify potential events for sudden vegetation recovery in biogeomorphic ecosystems such as saltmarshes, mangroves, dunes or floodplains. Time series of external forcing (i.e. water level and wind speed) were analysed for ‘Windows of Opportunity’ (WoO), defined as disturbance‐free periods of a critical minimal duration directly following potential diaspore dispersal, which allow seedling establishment and can induce a sudden shift to a new persistent vegetation cover. Across different ecosystems, the minimal required WoO duration determines how many WoO events are available for seedling establishment. The distribution of WoO along an elevation gradient on riverbanks and in tidal systems, for example, is defined by the combination of the overall disturbance regime (e.g. seasonal vs. tidal flooding cycles) and the stochastic deviations from that regime (e.g. changes in weather conditions). Standardizing the WoO for the frequency of the regular disturbance regime shows that tidal and river systems have a similar relation between the required WoO length and the elevation suitable for establishment. WoO analysis correctly predicted a sudden vegetation recovery event in a saltmarsh case study. Synthesis. Time‐series analysis for ‘WoO’ offers an important tool towards predicting the establishment of vegetation cover in disturbance‐driven ecosystems and may have broader implications for understanding critical transitions in general. Quantifying the effects of stochastic external forcing on critical transitions in ecosystems is crucial for restoration efforts and to assess the effects of anthropogenic and global change.

Pericarp ontogenesis with emphasis on the dispersal apparatus of three weed species of Faboideae (Fabaceae)

It is known that the efficient dispersal is one among other features that amplify the invasion potential of a plant. Knowledge of the ontogeny, morphology and fruit dispersal of species is indispensable for weed control in crops. To identify the pericarp structures involved in the fragmentation and dehiscence processes and other features related to dispersal, we studied the pericarp development of Aeschynomene evenia Wright, Desmodium incanum (Sw.) DC. and Vigna luteola (Jacq.) Benth. (Fabaceae-Faboideae), all of which are considered weeds in certain situations. For light and scanning electron microscopy studies, we fixed and processed buds, flowers and fruits, according to usual methods, at different stages of development. We observed that the sclerenchymatous endocarp is essential for dehiscence in legumes, as well as for fragmentation in loments. We also found that the presence of hook-shaped trichomes, sclereid nests in the mesocarp, septum, hypodermis and the formation of false septa are essential to the diaspore dispersal of the species studied.

Trade-offs between seed dispersal and dormancy in an amphi-basicarpic cold desert annual.

Several studies have demonstrated trade-offs between depth of seed dormancy and dispersal ability for diaspore-dimorphic species. However, relatively little is known about trade-offs between these two life history traits for a species that produces more than two diaspore morphs. The aim of this study was to investigate the relationship between seed dormancy and dispersal in Ceratocarpus arenarius, an amphi-basicarpic cold desert annual that produces a continuum of dispersal unit morphs. A comparison was made of dispersal and dormancy breaking/germination responses of dispersal units from ground level (a), the middle of the plant canopy (c) and the top of the plant canopy (f). Various features of the morphology and mass of dispersal units and fruits (utricles) were measured. The role of bracteoles in diaspore dispersal by wind, settlement onto the soil surface and dormancy/germination was determined by comparing responses of intact dispersal units and fruits. Movement of dispersal units by wind and animals, seed after-ripening, germination phenology and the presence of water-soluble germination inhibitors in bracteoles were tested using standard procedures. Dispersal units a, c and f differed in morphology and mass; in the majority of cases, extremes were exhibited by a and f, with c being intermediate. Overall, relative dispersal ability was f > c > a, whereas relative intensity of dormancy was a > c > f. Bracteoles increased dispersal distance by wind, enhanced settlement of diaspores onto the soil surface and mechanically inhibited germination. The results provide evidence for a model in which there is a continuous inverse-linear relationship between diaspore dispersal ability and depth of dormancy. Thus, dispersal unit heteromorphism of C. arenarius results in a continuum, from no dispersal ability/high dormancy (dispersal unit a) to high dispersal ability/low dormancy (unit f), which may be a bet-hedging strategy in the cold desert environment.

Dispersal and predation of diaspores of Coula edulis Baill. in an evergreen forest of Gabon

AbstractThe African walnut (Coula edulis) is a tree species of African evergreen forests, the seeds of which are collected and traded by African people. Many animal species consume African walnut diaspores; however, their roles as dispersers or predators have yet to be clarified. In this study, we present observations conducted in two different habitats of a Gabonese region over a 3‐year period. The originality of this research resides in the combination of three complementary approaches: (i) the use of camera‐traps (ii) the exploration of land rodent burrows and (iii) the examination of elephant dung. In total, 408 camera‐trap photographs have shown seven animal species involved in the dispersal/predation of C. edulis. Among these seven frugivorous species, the bush pig was found to be the main consumer and predator of seeds. Land rodents (Muridae) are potential predators, as they damaged the seeds and buried them deep in the soil. They may also play a role in the regeneration process as a result of the loss of seeds during transportation. Finally, no seeds appeared to emerge intact from elephant faeces. These results indicate that the natural regeneration rate of this tree species is low, unless other complex mechanisms are involved.

Quantification of plant dispersal ability within and beyond a calcareous grassland

AbstractQuestionMany calcareous grasslands in Europe have declined in species richness in recent decades. This loss of species could be partly due to habitat loss and fragmentation, leading to increased distances and reduced connectivity through seed flow between calcareous grassland patches resulting in increased local extinction risk related to small population size, and partly due to abandonment of traditional management practices that fostered dispersal within and between patches. Here, we quantify short‐ and intermediate‐distance dispersal ability of dry calcareous grassland species and relate these to dispersal traits.LocationSchaffhauser Randen, Switzerland.MethodsWe studied wind dispersal of diaspores under natural conditions within and beyond two replicate calcareous grassland patches. Funnel traps (n = 230) were set up at heights of 0.2 m and 0.7 m along ten transects traversing the calcareous grassland and extending 40 m into the surrounding landscape. We developed a new method for quantifying short ‐ (0–1 m) and intermediate‐distance (1–40 m) dispersal ability, related these to species traits, and tested whether they were able to explain dispersal rates into the adjacent landscape.ResultsWhile grasses could be categorized as good dispersers over short or intermediate distances, or both, forbs were generally poor dispersers over both distance classes. Only small numbers of diaspores were found in the adjacent landscape, and these were predominantly grasses. Diaspore traits, such as terminal velocity or diaspore mass, contributed little to explaining dispersal ability, whereas release height was an important predictor, especially for intermediate‐distance dispersal.ConclusionsUnder natural field conditions, dispersal into the adjacent landscape depends on release height rather than terminal velocity, and is heavily biased towards grasses, so that seed rain does not reflect the species composition of the calcareous grassland community. Thus natural regeneration of species richness of degenerated calcareous grassland communities even over short distances should not rely on wind dispersal alone.

Anatomy of myxospermic diaspores of selected species in the Succulent Karoo, Namaqualand, South Africa

Environmental conditions encountered in arid ecosystems differ vastly from those in more mesic ecosystems. Dispersal strategies in arid environments reflect these differences and many mechanisms have evolved that restrict or hinder dispersal. Myxospermy is a trait developed by plant species from arid regions to restrict diaspore dispersal by means of an anchorage mechanism. Several of the abundant plant species in Namaqualand, within the arid Succulent Karoo Biome, display myxospermy. Diaspores of these species produce copious amounts of mucilage when they are moistened and are anchored to the soil once the mucilage dries out again. This study investigated the origin of the mucilaginous layer of 12 species anatomically, using both light and scanning electron microscopy. The mucilage production of the species investigated could best be grouped into three types: 1, epidermal and sub-epidermal cells of seeds and achenes; 2, specialized tissue in wings or the pappus of achenes; and 3, mucilage excreting hairs. Previous systems for classifying the different types of mucilage production did not recognize the mucilaginous nature of wings or a pappus. A short note on the composition of the mucilage is included.

Diaspore Trait Preferences of Dispersing Ants

Elaiosomes of myrmecochorous plant seeds are known to enhance the attraction of diaspore-dispersing ants by serving as a nutritional reward. However, it remained unclear which (nutritional) compounds affect diaspore preferences of ants. We hypothesized that apart from elaiosome/seed-size ratio, volume, and physical surface of diaspores, the quantity and the composition of fatty acids, amino acids, and sugars strongly influence the diaspore preferences of different species. Chemical (nutritional) profiles as well as structural properties of seeds with and without elaiosomes were analyzed and correlated with observed seed choice behavior of ants. Cafeteria experiments in the field confirmed the enhanced attractiveness of elaiosome-bearing seeds for all three ant species tested (Lasius fuliginosus, Myrmica ruginodis, and Temnothorax nylanderi), although seeds lacking elaiosomes also were transported. In multiple-choice cafeteria experiments with simultaneously offered diaspores of 16 plant species with and without elaiosome and with highly varying structural and chemical properties, all three ant species showed distinct preferences for certain diaspore species. Correlation analyses confirmed that the presence of an elaiosome represents the crucial factor that favors ant diaspore dispersal. In addition, the composition and the content of free amino acids, and to varying degrees fatty acids, were found to significantly affect preferences of each ant species, whereas the effect of single fatty acids acting as chemical triggers for diaspore transport by ants, as supposed by several studies, was not confirmed. In conclusion, although at least some diaspore species lacking elaiosomes attract ants for diaspore removal services by presenting nutritional seed coats, the production of elaiosomes seems to provide a worthwhile investment. Elaiosomes ensure rapid diaspore detection and removal due to chemical cue compounds and by offering a highly nutritional food supply, probably fitting the nutritional demands of ants.

Pioneers and Perches—Promising Restoration Methods for Degraded Renosterveld Habitats?

Areas of abandoned agricultural fields are globally increasing and are also common features in the Cape Lowlands of South Africa. Previous restoration attempts in degraded West Coast renosterveld, a Mediterranean‐climate shrubland, have attained limited success and therefore novel approaches are needed for this area. The study reports on two restoration experiments, designed to re‐introduce key plant functional types back into this critically endangered habitat. The first experiment concentrated on a common pioneer species in renosterveld vegetation, Otholobium hirtum. Although in vitro experiments showed a significantly elevated germination response after scarification, in vivo experiments failed to produce establishment in an abandoned field. The second restoration experiment focused on bush clumps, a sub‐type of renosterveld vegetation that is characterized by broad‐leaved shrubs with fleshy bird‐dispersed diaspores. The effect of artificial bird perches and their potential to enhance diaspore dispersal by frugivorous birds in two abandoned field communities was tested. Results showed a significant increase in seed dispersal at artificial perch sites. However, in the next fruiting season, and after perch removal, seed germination and establishment in abandoned fields was not successful. The experiments revealed that restoration using early‐succession species and natural dispersal vectors appear not to produce demonstrable benefits, despite their promising potential and pre‐testing of effectiveness. Before launching large‐scale restoration programs in abandoned fields of renosterveld, preliminary studies in‐field are strongly recommended.

Diets of Frugivorous Bats in Montane Rain Forest and Coffee Plantations in Southeastern Chiapas, Mexico

ABSTRACTFrugivorous are one of the main diaspore dispersers in tropical ecosystems, particularly in open areas and sites in the early stages of ecological succession. Frugivorous bat species respond differentially to habitat modification, and in the context of their diaspore dispersal functions it is important to understand species' ecological requirements. We compared the diversity of diaspores, obtained from fecal samples and from fruits carried by frugivorous bats, among five shaded coffee plantations under different management regimes and a montane rain forest in southeastern Chiapas, Mexico. At each site, bats were captured every 2 mo from March 2004 to July 2005, using six mist‐nets, during two consecutive nights. We captured 2589 individuals from 18 frugivorous species, from which we collected 969 fecal samples, containing 42 diaspore species associated with early and late successional plants. Although, we captured more frugivorous bat species in montane rain forest, the number of diaspore species in this site (N=14) was not significantly different from the coffee plantations under different management regimes (16–24). In montane rain forest, Sturnira ludovici fed mainly on Piper auritum, but in coffee plantations ate Peperomia sp., Saurauia madrensis, Solanum chrysotrichum and Solanum diphyllum. Artibeus jamaicensis and Artibeus intermedius feed mostly Cecropia obtusifolia and Ficus cookii in all coffee plantations. We suggest that the presence of frugivorous bats in shaded coffee plantations is favored by trees and shrubs associated with secondary and introduced vegetation that farmers have allowed to grow within or around the plantations.

Floristic composition and dispersal syndromes at an urban remnant from the Atlantic forest in Brazilian Northeast

Floristic composition and dispersal syndromes were determined along one year in an open ombrophilous forest fragment in the Municipal Park of Maceió, Alagoas State, Brazil. A total of 178 species belonging to 61 families were examined. Fabaceae was the most species-rich family, with 24 species. Among sampled species, 123 had their syndromes of diaspore dispersal determined, and most of them (69%) were zoochoric. Anemochoric and autochoric plants represent 11 and 20% from the total, respectively. The data about reproductive phases indicate coincident peaks of flowering and fruiting in August, at the end of the rainy season. The results are in accordance to those expected for ombrophilous forest with poorly defined seasonality.

Bryophyte dispersal by sheep on dry grassland

Many bryophytes may depend on epizoochorous dispersal by large mammals for maintaining their populations and colonizing new habitats. On dry grassland we investigated the transport of bryophyte diaspores by sheep, which are known to be effective epizoochorous dispersal vectors of seed plants. Twelve sheep of two breeds were examined by collecting gametophyte fragments from their fleece and hooves. Furthermore, microscopic diaspores from the soil adhering to the hooves were grown in a greenhouse. Species frequency and composition were compared to bryophyte vegetation on the pasture. Considerable amounts of unspecialized gametophyte fragments from 16 moss species, 40% of the species growing on the pasture, were transported by sheep, especially on the belly and the tail. Additionally, we provide first evidence of epizoochorous dispersal of thallus fragments from fruticose lichens. Sheep breeds differed in species spectrum and frequency, i.e. sheep with dense, curly fleece carried more fragments and larger species than those with smooth and fine hair. Among the dispersed bryophytes pleurocarps, certain taxa, sizes (small species) and life forms (mats) were overrepresented compared to the vegetation of the pasture, while large species, acrocarps, wefts and turfs were underrepresented, reflecting fragmentation and adhesion features of the species. In the hooves mostly acrocarpous colonist species were transported. We conclude that sheep are important dispersal vectors with the potential of long-range dispersal for bryophytes, especially for species without sexual reproduction, and that epizoochorous dispersal of microscopic diaspores might be underestimated in its importance so far.

Chuva de sementes de espécies lenhosas florestais em mosaicos de floresta com Araucária e campos no Sul do Brasil

Mecanismos de dispersão de diásporos e recrutamento de plântulas evitam a competição intra-específica e possibilitam a colonização de novos ambientes. Em áreas de transição entre florestas e vegetação campestre esses processos não são aleatórios, e sim associados muitas vezes a indivíduos lenhosos isolados em tais áreas de campo ou a formações arbustivas. No sul do Brasil, as Florestas com Araucária formam mosaicos com áreas campestres e observa-se o avanço da floresta sobre os campos. O estudo teve como objetivo avaliar a chuva de sementes de espécies lenhosas florestais associadas a áreas de ecótonos de Floresta com Araucária e campos e a indivíduos lenhosos isolados na matriz campestre. Os estudos foram realizados no Centro de Pesquisas e Conservação da Natureza Pró-Mata PUCRS, em São Francisco de Paula, RS, em vegetação campestre excluída de fogo e de pastejo há 16 anos, circundada por florestas. A chuva de sementes foi avaliada mensalmente por um período de oito meses com o uso de coletores que foram posicionados em ecótonos de floresta e campos com diferentes fisionomias e sob indivíduos lenhosos isolados na matriz campestre. Tais ambientes foram comparados através de análise de variância univariada e multivariada para verificar padrões de chuva de sementes. Os resultados indicaram que a dispersão de sementes em áreas campestres ocorre preferencialmente associada a indivíduos isolados de Araucaria angustifolia e a formações arbustivas de Baccharis uncinella e que tais ambientes funcionariam como extensões de condições mais semelhantes à floresta na matriz campestre.

Does sex make a difference? Genetic diversity and spatial genetic structure in two co-occurring species of Gagea (Liliaceae) with contrasting reproductive strategies

Gagea lutea and G. spathacea are spring geophytes naturally co-occurring in woodlands, characterised by contrasting reproductive strategies probably caused by divergent ploidy levels. The hexaploid G. lutea relies on vegetative reproduction by subterranean bulbils in young stages but completely switches to sexual reproduction once a certain bulb size is attained. The nonaploid G. spathacea seems to be sterile and reproduces only vegetatively; the plants continue to form bulbils even in the rare event of flowering. This study used AFLP genotyping to investigate the consequences of these reproductive strategies for genetic diversity. For 150 and 100 samples from three Western Pomeranian populations of G. lutea and G. spathacea, respectively, AFLP fingerprints were analysed for three different spatial scales, the patch, the transect, and the region. Applying a threshold for genotypic identity of <0.05 simple matching distance, 22–30 genets were detected in the three G. lutea populations, with all genets confined to single populations. Clonal genets consisted of 2–9 samples and extended over up to 28 m, but never occupied the whole length of a transect; 67–75% of all patches had different genets. Genetic distances between genets within populations were similar to those recorded between populations. Genotyping of G. spathacea revealed a single clonal genet for all three populations sampled within a distance of 30 km. The absent genetic diversity confirms the suspected sexual sterility. Gagea spathacea seems to be one of the few non-apomictic, fully clonal vascular plants able to occupy a significant range solely by dispersal of vegetative diaspores.

Myrmecochorous plants use chemical mimicry to cheat seed‐dispersing ants

Summary 1. Deceptive species are a characteristic trait of insect–plant mutualisms. Deception of pollinators is essential for reproduction in diverse plant species; however, mimicry in seed dispersal is almost unknown. Myrmecochory, the dispersal of diaspores by ants, is a mutualism in which the elaiosome, a lipid‐rich seed appendage, works as an ant reward. This coevolved interaction may be exploited by cheating, non‐rewarding diaspores that mimic elaiosomes. 2. Our study assesses the impact of the morphology and fatty acid composition of diaspores on ant dispersal in rewarding and cheating myrmecochores and non‐myrmecochorous species. Four elaiosome types (defined by Sernander 1906) were included in our research: the ‘Viola odorata type’, with a clearly defined elaiosome, the similar but diplochorous ‘Euphorbia type’ with an additional ballistic dispersal of diaspores, and the ‘Puschkinia’ and ‘Hepatica’ types, which we classify as ‘cheaters’ as they mimic ant rewards by chemical cues. 3. We tested the influence of morphology, chemical composition of diaspores and presence of rewards on removal rates of diaspores, dummies impregnated with seed extracts and pure fatty acids and scent‐standardized diaspores in a population of Formica polyctena ants with 10 European spring ephemerals, mostly Ranunculaceae. The main free fatty acids of diaspores were identified by gas chromatography and mass spectrometric analysis. 4. Removal rates of diaspores and dummies treated with seed extracts were significantly influenced by their fatty acid composition. Discriminant function analysis confirmed oleic acid as the main trigger substance eliciting seed‐removal behaviour by ants in most species. Oleic acid content and removal rates differed among elaiosome types and were highest in rewarding myrmecochores, lower in cheaters and smallest in non‐myrmecochorous seeds. Removal rates of scent‐standardized diaspores did not differ among mutualists and cheaters suggesting a selective pressure for morphological adaptation and were lowest in non‐myrmecochorous species, thus corroborating an influence of diaspore morphology on ant‐removal patterns. 5. For the first time, we demonstrate chemical mimicry in myrmecochory as a means of seed dispersal. Evolutionary stability of the ant–seed mutualism is maintained by the ability of ants to discriminate between certain types of rewards and to respond with differential diaspore distribution rates.