The role of fleshy pericarp in seed germination and dispersal under flooded conditions in three wetland forest species

In flooded habitats, inundations affect important forest regeneration processes, such as seed dispersal and germination. The main seed dispersal mechanism used by species in Austral South American temperate swamp and riparian forests is endozoochory, which releases seeds from the fleshy pericarp. Endozoochory could be favorable or unfavorable in wetland habitats, since this mechanism exposes seeds directly to water and can, in some cases, be detrimental to germination. In this study, we studied whether or not the fleshy pericarp favors germination after the flooding period's end. Furthermore, we quantified if the number of days which the fruit was found to be floating related to its germination success. We used the seeds of three common fleshy fruit species of flooded habitats from southern Chile, the trees Luma apiculata and Rhaphithamnus spinosus, and the vine Luzuriaga radicans. We simulated flooding periods of 7, 15, 30 and 45 days submerging seeds, with and without pericarps, in water. We found that the pericarp's presence significantly increased Luma's germination success and significantly decreased that of Luzuriaga. The germination of Rhaphithamnus was low after periods of flooding in both seed treatments, with no significant differences found between them. The fruits could float for an average of one to four weeks, depending on the species, which did not relate to their germination success. These results show that germination was affected by the presence of fleshy pericarps in flooded conditions and furthermore, that flotation allows for hydrochory from one week to one month. We suggest that in swamp forests multiple seed dispersal mechanisms are advantageous, especially for fleshy-fruited species.     

From ratites to rats: the size of fleshy fruits shapes species' distributions and continental rainforest assembly

Seed dispersal is a key process in plant spatial dynamics. However, consistently applicable generalizations about dispersal across scales are mostly absent because of the constraints on measuring propagule dispersal distances for many species. Here, we focus on fleshy-fruited taxa, specifically taxa with large fleshy fruits and their dispersers across an entire continental rainforest biome. We compare species-level results of whole-chloroplast DNA analyses in sister taxa with large and small fruits, to regional plot-based samples (310 plots), and whole-continent patterns for the distribution of woody species with either large (more than 30 mm) or smaller fleshy fruits (1093 taxa). The pairwise genomic comparison found higher genetic distances between populations and between regions in the large-fruited species (Endiandra globosa), but higher overall diversity within the small-fruited species (Endiandra discolor). Floristic comparisons among plots confirmed lower numbers of large-fruited species in areas where more extreme rainforest contraction occurred, and re-colonization by small-fruited species readily dispersed by the available fauna. Species'' distribution patterns showed that larger-fruited species had smaller geographical ranges than smaller-fruited species and locations with stable refugia (and high endemism) aligned with concentrations of large fleshy-fruited taxa, making them a potentially valuable conservation-planning indicator.     

Peduncles elicit large-mammal endozoochory in a dry-fruited plant

Background and Aims

Plants have evolved a variety of seed dispersal mechanisms to overcome lack of mobility. Many species embed seeds in fleshy pulp to elicit endozoochory, i.e. disseminating seed through the animal gut. In contrast to well-studied fleshy fruited plants, dry-fruited plants may exploit this dispersal mutualism by producing fleshy appendages as a nutritional reward to entice animals to swallow their diaspores, but this has been little studied. In this study, it is hypothesized that these accessory fruits represent co-adaptations facilitating the syndrome of mammalian endozoochorous dispersal.

Methods

Field observations (focal tree watches, faecal surveys and fruiting phenology) with experimental manipulations (examination of seed germination and feeding trials) were conducted over 2 years in a native population of the raisin tree, Hovenia dulcis, which produces enlarged, twisted brown peduncles with external black seeds, in central China.

Key Results

Birds were not observed to swallow seeds or carry infructescences away during 190 h of focal tree watches. However, H. dulcis seeds were detected in 247 faecal samples, representative of two herbivore and four carnivore mammalian species. Feeding trials revealed that peduncles attracted mammals to consume the entire infructescence, thereby facilitating effective seed dispersal. The germination rate of egested seeds proved higher than that of unconsumed seeds. It was also noted that this mutualism was most vulnerable in degraded forest.

Conclusions Hovenia dulcis

peduncle sets are confirmed to adapt primarily to mammalian endozoochory, a mutualistic association similar in function to fleshy pulp or foliage. This demonstrates that plant organ systems can be adapted to unique mutualisms that utilize animal dispersal agents. Such an ecological role has until now been attributed only to bird epizoochory. Future studies should consider more widely the putative role of peduncle sets and mammalian endozoochory as a dispersal mechanism, particularly for those plants that possess relatively large accessory fruits.     

Origin, adaptive radiation and diversification of the Hawaiian lobeliads (Asterales: Campanulaceae)

The endemic Hawaiian lobeliads are exceptionally species rich and exhibit striking diversity in habitat, growth form, pollination biology and seed dispersal, but their origins and pattern of diversification remain shrouded in mystery. Up to five independent colonizations have been proposed based on morphological differences among extant taxa. We present a molecular phylogeny showing that the Hawaiian lobeliads are the product of one immigration event; that they are the largest plant clade on any single oceanic island or archipelago; that their ancestor arrived roughly 13 Myr ago; and that this ancestor was most likely woody, wind-dispersed, bird-pollinated, and adapted to open habitats at mid-elevations. Invasion of closed tropical forests is associated with evolution of fleshy fruits. Limited dispersal of such fruits in wet-forest understoreys appears to have accelerated speciation and led to a series of parallel adaptive radiations in Cyanea, with most species restricted to single islands. Consistency of Cyanea diversity across all tall islands except Hawai ;i suggests that diversification of Cyanea saturates in less than 1.5 Myr. Lobeliad diversity appears to reflect a hierarchical adaptive radiation in habitat, then elevation and flower-tube length, and provides important insights into the pattern and tempo of diversification in a species-rich clade of tropical plants.     

Molecular analyses of MADS-box genes trace back to Gymnosperms the invention of fleshy fruits

Botanical fruits derive from ovaries and their most important function is to favor seed dispersal. Fleshy fruits do so by attracting frugivorous animals that disperse seeds together with their own excrements (endozoochory). Gymnosperms make seeds but have no ovaries to be transformed into fruits. Many species surround their seeds with fleshy structures and use endozoochory to disperse them. Such structures are functionally fruits and can derive from different anatomical parts. Ginkgo biloba and Taxus baccata fruit-like structures differ in their anatomical origin since the outer seed integument becomes fleshy in Ginkgo, whereas in Taxus, the fleshy aril is formed de novo. The ripening characteristics are different, with Ginkgo more rudimentary and Taxus more similar to angiosperm fruits. MADS-box genes are known to be necessary for the formation of flowers and fruits in Angiosperms but also for making both male and female reproductive structures in Gymnosperms. Here, a series of different MADS-box genes have been shown for the first time to be involved also in the formation of gymnosperm fruit-like structures. Apparently, the same gene types have been recruited in phylogenetically distant species to make fleshy structures that also have different anatomical origins. This finding indicates that the main molecular networks operating in the development of fleshy fruits have independently appeared in distantly related Gymnosperm taxa. Hence, the appearance of the seed habit and the accompanying necessity of seed dispersal has led to the invention of the fruit habit that thus seems to have appeared independently of the presence of flowers.     

The ecological impact of oceanic island colonization – a palaeoecological perspective from the Azores

Aim In many cases, human colonization drastically modified the ecosystems of remote oceanic islands before scientists arrived to document the changes. Palaeoecological records before and after human colonization provide insights into the original ecosystems and an assessment of subsequent human impact. We used pollen analysis to compare the impact of 15th century colonization of the Azores with that of natural disturbances such as volcanic eruptions and climate changes. Location Azores archipelago, Atlantic Ocean. Methods Sediment records from three highland sites in the Azores (on the islands of Pico and Flores) were dated radiometrically and analysed palynologically. Pollen taxa were classified as native, endemic or introduced based on comparison with flora lists. Data were statistically zoned and temporal trends identified using detrended correspondence analysis. Results Human colonization of the Azores resulted in rapid, widespread, persistent vegetation changes on a scale unprecedented in the last 2700 years, detectable through the decline of dominant trees, the spread of grasses and fire‐tolerant species, the introduction of exotic plants, evidence for grazing and fire, and changes to soils and moisture availability. During the same period, volcanic eruptions appear to have had more localized impacts on the vegetation, lasting 500–1000 years and favouring endemic taxa. The effect of late Holocene climatic changes on the highland vegetation of the Azores seems to have been minor. Palaeoecological data indicate that at least two plant species went extinct on Pico after human colonization and that some plants regarded as introduced were almost certainly part of the original flora of the islands. Despite a consistent signal of human impact, compositional differences between Juniperus brevifolia communities on Pico and Flores remained after colonization. Main conclusions Human colonization had a greater impact on the pristine vegetation of Pico and Flores than climatic changes and volcanic activity during recent millennia. The similarity between post‐colonization changes on the Azores and other oceanic islands suggests a consistent pattern and scale to historical‐era human impact on otherwise pristine ecosystems. These characteristics could be used to further elaborate biogeographical theory and direct conservation efforts towards species that appear most susceptible to human activity.     

Cryptic speciation between Juniperus deltoides and Juniperus oxycedrus (Cupressaceae) in the Mediterranean

Analyses of individuals classically treated as Juniperus oxycedrus L. var. oxycedrus from Morocco, Portugal, Spain, France, Italy, Greece and Turkey, using DNA sequencing of nrDNA (ITS 1, 5.8S, ITS 2) plus RAPDs, leaf terpenoids and morphology revealed that two cryptic, genetically distinct but morphologically almost identical species are present. These species, J. oxycedrus L. var. oxycedrus and Juniperus deltoides R.P. Adams, are about as different from each other as Juniperus navicularis and Juniperus macrocarpa are from J. oxycedrus var. oxycedrus. Examination of herbarium specimens revealed that the two species are largely allopatric with J. deltoides occurring from Italy eastward through Turkey into the Caucasus Mts. and Iran. J. oxycedrus var. oxycedrus appears to be largely concentrated west of Italy (France, Spain, Portugal, Morocco). Cryptic speciation is discussed.     

Dispersal ability of island endemic plants: What can we learn using multiple dispersal traits?

Island endemic species are expected to have lower dispersal ability than their non-endemic congeners. Several studies have demonstrated differences in diaspore morphology between endemic species and their non-endemic congeners. It is, however, relatively difficult to translate the differences in morphology of the diaspores into differences in dispersal ability. To avoid this problem, we measured directly dispersal values (anemo-, hydro-, exozoo- and endozoo-chory) of 27 pairs of closely related endemic and non-endemic species from Canary Islands. We did not explicitly support the hypothesis about the loss of dispersal ability of island species. The comparison of pairs of endemic and non-endemic species showed the reduction in dispersal potential only for endozoochory. In many cases, endemic species had, in fact, the same or better dispersal ability than their non-endemic congeners. Higher dispersal ability of endemic species could have been evolved as a consequence of species subsequent dispersal to neighboring islands. As a support for this we found that the endemic species dispersing better than their non-endemic congeners also occupy more islands within the archipelago. We conclude that reduction of dispersal ability of species on islands may not be as general as previously expected and we need to take into account multiple species traits to understand the possible evolution of species dispersal potential.     

Human-Assisted Invasions of Pacific Islands by Litoria Frogs: A Case Study of the Bleating Tree Frog on Lord Howe Island

There are substantial differences among taxonomic groups in their capacity to reach remote oceanic islands via long-distance overwater dispersal from mainland regions. Due to their permeable skin and intolerance of saltwater, amphibians generally require human-assisted dispersal to reach oceanic islands. Several Litoria frog species have been introduced to remote islands throughout the Pacific Ocean region. Lord Howe Island (LHI) is an oceanic island that lies approximately 600 km east of the Australian mainland and has a diverse, endemic biota. The bleating tree frog (Litoria dentata) is native to mainland eastern Australia, but was accidentally introduced to LHI in the 1990s, yet its ecology and potential impact on LHI has remained unstudied. We used a mitochondrial phylogeographical approach to determine that L. dentata was introduced from the Ballina region in northeastern New South Wales. The founding population was likely accidentally introduced with cargo shipped from the mainland. We also completed the first detailed investigation of the distribution, ecology and habitat use of L. dentata on LHI. The species is widespread on LHI and is prevalent in human habitat, cattle pasture and undisturbed forest. We discuss the potential impact of introduced Litoria species on Pacific islands and outline what biosecurity protocols could be implemented to prevent the introduction of further amphibian species to the ecologically sensitive oceanic area.     

Differential seed dispersal systems of endemic junipers in two oceanic Macaronesian archipelagos: the influence of biogeographic and biological characteristics

This article evaluates the seed dispersal systems of two congeneric and endemic fleshy-fruited plants in the context of two relatively close oceanic archipelagos. For this purpose, representative populations of the endangered junipers Juniperus cedrus in the Canary Islands and Madeira, and Juniperus brevifolia in the Azores were studied. Despite both species sharing the same biogeographic region, we set out to test whether different conditions of the islands and biological characteristics of each juniper species determine the distinctive guilds of seed dispersers involved. We assessed the quantitative and qualitative role of the potential frugivores, showing that the wintering Turdus torquatus and the native Turdus merula were the main seed dispersers for J. cedrus and J. brevifolia, respectively (Frequency of occurrence: 74.9%, 80.2%; germination increase with respect to controls: 11.6%, 15.5%; for J. cedrus and J. brevifolia, respectively). The endemic lizard Gallotia galloti was quantitatively outstanding as seed disperser of J. cedrus, although its qualitative effect does not appear to be beneficial. The introduced rabbit Oryctolagus cuniculus acts as a disruptor in both natural seed dispersal systems, as inferred from the high percentage of damaged seeds found in their droppings. Our results indicate that J. cedrus and J. brevifolia are primarily adapted to ornithochory processes, T. torquatus and T. merula being their respective legitimate long-distance dispersers. Although these birds should be playing a key role in the connectivity of fragmented populations, the dependence of J. cedrus on a migrant bird involves a notable fragility of the system.     

Long‐distance dispersal syndromes matter: diaspore–trait effect on shaping plant distribution across the Canary Islands

Oceanic islands emerge lifeless from the seafloor and are separated from continents by long stretches of sea. Consequently, all their species had to overcome this stringent dispersal filter, making these islands ideal systems to study the biogeographic implications of long‐distance dispersal (LDD). It has long been established that the capacity of plants to reach new islands is determined by specific traits of their diaspores, historically called dispersal syndromes. However, recent work has questioned to what extent such dispersal‐related traits effectively influence plant distribution between islands. Here we evaluated whether plants bearing dispersal syndromes related to LDD – i.e. anemochorous (structures that favour wind dispersal), thalassochorous (sea dispersal), endozoochorous (internal animal dispersal) and epizoochorous (external animal dispersal) syndromes – occupy a greater number of islands than those with unspecialized diaspores by virtue of their increased dispersal ability. We focused on the native flora of the lowland xeric communities of the Canary Islands (531 species) and on the archipelago distribution of the species. We controlled for several key factors likely to affect the role of LDD syndromes in inter‐island colonization, namely: island geodynamic history, colonization time and phylogenetic relationships among species. Our results clearly show that species bearing LDD syndromes have a wider distribution than species with unspecialized diaspores. In particular, species with endozoochorous, epizoochorous and thalassochorous diaspore traits have significantly wider distributions across the Canary archipelago than species with unspecialized and anemochorous diaspores. All these findings offer strong support for a greater importance of LDD syndromes on shaping inter‐island plant distribution in the Canary Islands than in some other archipelagos, such as Galápagos and Azores.     

Functional diversity in fruit‐frugivore interactions: a field experiment with Mediterranean mammals

Using field seed sowings, we assessed how four mammal species (Meles meles, Vulpes vulpes, Sus scrofa, and Oryctolagus cuniculus) influenced seed germination in three fleshy‐fruited Mediterranean shrubs (Corema album, Pyrus bourgaeana, and Rubus ulmifolius). We predicted that gut passage and removal away from mother plants would enhance the quantity, speed, and asynchrony of seed germination. Results showed that percent germination was altered by gut passage, but that the magnitude and even the direction of such effects varied according to plant and disperser species. Likewise, dispersal away from mother plants affected the percentage and germination speed in some species but not others. Gut passage increased asynchrony of germination in Rubus and Pyrus, and removal from the mother plant increased asynchrony in Rubus, which likely enhances plant fitness in unpredictable environments. Gut passage generally had a stronger effect on germination than removal away from mother plants, but for some species both factors were similarly influential. Therefore, the combined effects of both seed dispersal services varied individually among fruit and frugivore species, leading to unusually high functional diversity in this seed dispersal mutualism.     

Early diversification dynamics in a highly successful insular plant taxon are consistent with the general dynamic model of oceanic island biogeography

The general dynamic model (GDM) of oceanic island biogeography views oceanic islands predominantly as sinks rather than sources of dispersing lineages. To test this, we conducted a biogeographic analysis of a highly successful insular plant taxon, Cyrtandra, and inferred the directionality of dispersal and founder events throughout the four biogeographical units of the Indo-Australian Archipelago (IAA), namely Sunda, Wallacea,  Philippines, and Sahul. Sunda was recovered as the major source area, followed by Wallacea, a system of oceanic islands. The relatively high number of events originating from Wallacea is attributed to its central location in the IAA and its complex geological history selecting for increased dispersibility. We also tested if diversification dynamics in Cyrtandra follow predictions of adaptive radiation, which is the dominant process as per the GDM. Diversification dynamics of dispersing lineages of Cyrtandra in the Southeast Asian grade showed early bursts followed by a plateau, which is consistent with adaptive radiation. We did not detect signals of diversity-dependent diversification, and this is attributed to Southeast Asian cyrtandras occupying various niche spaces, evident by their wide morphological range in habit and floral characters. The Pacific clade, which arrived at the immaturity phase of the Pacific Islands, showed diversification dynamics predicted by the island immaturity speciation pulse model (IISP), wherein rates increase exponentially, and their morphological range is controlled by the least action effect favoring woodiness and fleshy fruits. Our study provides a first step toward a framework for investigating diversification dynamics as predicted by the GDM in highly successful insular taxa.     

Effects of rabbit gut passage on seed retrieval and germination of three shrub species

It has been known for a few decades that European rabbits consume seeds and fleshy fruits of native woody plants, but relevant factors in the endozoochory processes such as seed predation (chewing and digestion), sexual differentiation, or the temporal pattern of seed recovery have been little evaluated until now. In this study, we examined seed dispersal of three Mediterranean shrub species by wild rabbits through monitoring of seed retrieval and germination after gut passage. Twelve adult wild rabbits (Oryctolagus cuniculus; six males and six females) of similar size and age were fed seeds of three shrub species with fleshy fruits (Crataegus monogyna, Myrtus communis and Pistacia lentiscus). After ingestion of fruits, seeds were retrieved from dung every 12 h for a day and a half. The viability and germination of retrieved seeds were tested along with that of uneaten seeds. Between 5% and 76% of ingested seeds were retrieved from dung, with significant differences between species and sex. Most M. communis seeds were retrieved with 12–24 h after ingestion; almost all C. monogyna seeds were recovered with 0–12 h after ingestion; no seeds of P. lentiscus were recovered. Only in the case of M. communis seed was the recovery rate greater in female than in male. Passage through the rabbit gut significantly increased seed germination in M. communis, and decreased it in C. monogyna. In conclusion, wild rabbits acted in this study as predators of C. monogyna and P. lentiscus seeds and potential dispersers of M. communis seeds.     

Non-redundancy in seed dispersal and germination by native and introduced frugivorous birds: implications of invasive bird impact on native plant communities

Seed dispersal by vertebrate animals is important for the establishment of many fleshy-fruited plant species. Different frugivorous species can provide different seed dispersal services according to their specific dietary preferences as well as behaviour and body traits (e.g. body size and beak size of birds). Our aim was to study redundancies and complementarities in seed dispersal and germination between the two main native seed disperser birds and the introduced silver pheasant Lophura nycthemera in the temperate Patagonian forests. For this, we collected fresh droppings from the studied species and analyzed seed content. We conducted germination trials for four plant species common in bird droppings; two native species (Aristotelia chilensis and Rhaphithamnus spinosus) and two invasive non-native species (Rubus ulmifolius and Rosa rubiginosa). Both native frugivorous birds and the silver pheasant dispersed fruits of non- native fleshy-fruited plants, but their roles were non-redundant in terms of species dispersed and effect on seed germination. The silver pheasant dispersed a proportionally high number of non-native seeds, while native birds dispersed a high number of native seeds. In addition, the effect of gut treatment in seed germination differed between seed dispersers. Native birds promoted the germination for the two native plant species studied, while the silver pheasant promoted the germination of one non-native plant. This suggests that seed dispersal by the silver pheasant may contribute to the spread of some invasive fleshy-fruited plants in the ecosystems that otherwise would not be dispersed by any other bird. The understanding of redundancies and complementarities on seed dispersal and germination between native and introduced birds will allow improving the management of fleshy-fruited non-native plants.     

Investment in seed dispersal structures is linked to invasiveness in exotic plant species of south-eastern Australia

Naturalized plant species disperse their populations over considerable distances to become invasive. We tested the hypothesis that this shift from naturalization to invasion is facilitated by increased investment of resources in seed dispersal appendages, using an assemblage of naturalized plants of south-eastern Australia. Compared with non-invasive species, we found in both cross-species and independent-contrasts analyses that invasive species invested more heavily in seed dispersal appendages, regardless of the structure present on the seed associated with the mode of dispersal (e.g., wings versus fleshy fruits). Invasive species such as Lonicera japonica, Hedera Helix and Acetosa sagittata were found to invest as much as 60–70% of total diaspore mass in dispersal appendages. The positive relationship between dispersal investment and invasion success was still prevalent after controlling for the effects of plant growth form, seed mass and capacity for vegetative growth. Our findings demonstrate that a plant’s investment in dispersal appendages helps to overcome the dispersal barrier in the shift from naturalization to invasion.     

Exploitation of Fallen Diaspores by Ants: Are there Ant–Plant Partner Choices?

Ants frequently interact with fleshy fallen diaspores (fruits or seeds) not adapted for ant‐dispersal. Such interactions are usually considered as opportunistic, but recent evidence has indicated that these ants may differ in their effects on diaspore survival and plant recruitment. We investigated if partner choices are recognizable among genera of ants and plants, and if ant and plant traits may influence such preferences in cerrado (savanna‐like vegetation) from southeast Brazil. During a 2‐yr period, 521 ant–diaspore interactions were recorded through various methods, yielding 71 ant species and 38 plant species. Exploitation of fallen diaspores was common among several ant genera, and included carnivorous, omnivorous, and fungivorous ants. Contrary to others areas around the world, where true myrmecochory (seed dispersal by ants) is common among shrubs, ants also exploited diaspores from several cerrado trees. Plant life form, diaspore size, and ant body size did not seem to explain the pattern of interactions observed. Two subsets of preferential interactions, however, segregated fungivorous ants from another group composed of carnivorous and omnivorous ants, probably influenced by the chemical composition of the plant diaspores. Omnivorous ants usually remove the fleshy portion of diaspores on spot and probably provide limited benefits to plants. Carnivorous and fungivorous ants usually remove the whole diaspore to the nest. As each of these ant groups may influence the fitness of diaspores in different ways, there are possible subtle pathways for the evolution of partner choices between ants and these non‐myrmecochorous diaspores.     

A multi-scale test for dispersal filters in an island plant community

Constraints on plant distributions resulting from seed limitation (i.e. dispersal filters) were evaluated on two scales of ecological organization on islands off the coast of British Columbia, Canada. First, island plant communities were separated into groups based on fruit morphology, and patterns in species diversity were compared between fruit‐type groups. Second, abundance patterns in several common fleshy‐fruited, woody angiosperm species were compared to species‐specific patterns in seed dispersal by birds. Results from community‐level analyses showed evidence for dispersal filters. Dry‐fruited species were rare on islands, despite being common on the mainland. Island plant communities were instead dominated by fleshy‐fruited species. Patterns in seed dispersal were consistent with differences in diversity, as birds dispersed thousands of fleshy‐fruited seeds out to islands, while dry fruited species showed no evidence of mainland‐island dispersal. Results from population‐level analyses showed no evidence for dispersal filters. Population sizes of common fleshy‐fruited species were unrelated to island isolation, as were rates of seed dispersal. Therefore, island isolation distances were not large enough to impose constraints on species’ distributions resulting from seed limitation. Rates of seed dispersal were also unrelated to island area. However, several species increased in abundance with island area, indicating post‐dispersal processes also help to shape species distributions. Overall results suggest that seed dispersal processes play an important role in determining the diversity and distribution of plants on islands. At the community‐level, dry‐fruited species were seed limited and island communities were instead dominated by fleshy‐fruited species. At the population‐level, common fleshy‐fruited species were not seed limited and showed few differences in distribution among islands. Therefore, although evidence for dispersal filters was observed, their effects on plant distributions were scale‐dependent.     

Colonization of the Galápagos Islands by plants with no specific syndromes for long‐distance dispersal: a new perspective

Since nobody has witnessed the arrival of early plant colonists on isolated islands, the actual long‐distance dispersal (hereafter LDD) has historically been a matter of speculation. In the present study, we offer a new approach that evaluates whether particular syndromes for LDD (i.e. the set of traits related to diaspore dispersal by animals, wind and sea currents) have been favourable in the natural colonization of the Galápagos Islands by plants. Dispersal syndromes of the 251 native genera (509 angiosperm species) presently acknowledged as native were carefully studied, combining data from floristic lists of the Galápagos Islands, diaspore traits, characteristics of continental relatives and our own observations. We used these genera (and occasionally infrageneric groups) as the working units to infer the number of introductions and colonists. A final number of native plants was inferred and analysed after correcting by pollen records of six species from six genera previously considered exotic (palaeobotanical correction). The number of early colonists was also corrected by incorporating information from the few (n= 12) phylogenetic studies of genera from both the Galápagos Islands and the Americas (phylogenetic correction). A total of 372 colonization events were inferred for the native flora using the latest check‐list. The proportions of native colonists grouped into five categories were: endozoochory 16.4%, epizoochory 15.7%, hydrochory 18.6%, anemochory 13.3%, and unassisted diaspores 36.0%. These figures did not vary significantly on analysing only the 99 genera that include endemic species in order to rule out any human‐mediated introductions. Irrespective of the roles of the different agents involved in LDD, diaspores with no special syndrome for LDD (unassisted diapores), such as many dry fruits, have been successful in reaching and colonizing the Galápagos archipelago. This finding leads us to suggest that unpredictable and so far unknown LDD mechanisms should be further considered in the theory of island biogeography.