Island Plant Research Articles

Chromosome Aberrations in a Group of People Exposed to Radioactive Releases from the Three Mile Island Nuclear Accident and Inferences for Radiation Effects.

Recently, it has been proposed that the doses received from 133Xe released during the accident in 1979 at the Three Mile Island (TMI) plant in Pennsylvania were much higher than has been conventionally assessed, due to a gross underestimation of the relative biological effectiveness of electrons from beta-particle-emitting radionuclides within the body. The central evidence cited in support of this proposal was the doses derived from cytogenetic analyses of blood sampled in the mid-1990s from people living near TMI at the time of the accident. However, the chromosome aberration data show a marked discrepancy in biodosimetric estimates evaluated from the frequencies of stable translocations and unstable dicentrics (corrected for temporal attenuation), strongly suggesting that exposures to clastogenic agents occurred long after the TMI accident. Few details have been reported on the people providing the blood samples and how they were selected for study. Crucially, this lack of information includes the distributions in the exposed and control groups of age at sampling, which is a critical factor in interpreting translocation data. Contrary to the recent claim, these cytogenetic data offer no support to the suggestion of a serious underestimation of internal doses from beta particles or from 133Xe discharged during the TMI accident.

Seaduck engineers in the Arctic Archipelago: nesting eiders deliver marine nutrients and transform the chemistry of island soils, plants, and ponds

Seabirds are thought to provide ecological services such as the movement of nutrients between marine and terrestrial ecosystems, which may be especially critical to productivity and diversity in nutrient-poor environments. Most Arctic ecosystems are unaffected by local human impacts and are naturally nutrient poor and especially sensitive to warming. Here, we assessed the effects of nesting common eider ducks (Somateria mollissima) on soil, vegetation, and pond sediments on island archipelagoes in Hudson Strait between Nunavut and Québec, Canada. Soil, moss, and pond sediments were significantly higher in nitrogen on islands with large numbers of nesting eiders compared to sites with no nesting birds. The highest concentrations of nitrogen in soils and moss occurred at the margins of ponds on eider islands, which correspond to the areas of highest eider use. δ15N and δ34S values in soils, moss, and sediments indicated substantial marine-derived organic matter inputs at the higher nutrient sites. We propose that by foraging on coastal marine benthic invertebrates and returning to islands to nest, eider ducks bio-transport and concentrate marine-derived nutrients to their colony islands, fertilizing Arctic island ecosystems in the process. As common eiders nest on thousands of low to mid-latitude islands throughout the circumpolar Arctic, these nutrient inputs likely dramatically affect biota and ecosystem functioning throughout the tundra biome.

Large frugivores matter more on an island: Insights from island-mainland comparison of plant-frugivore communities.

Endozoochory, a mutualistic interaction between plants and frugivores, is one of the key processes responsible for maintenance of tropical biodiversity. Islands, which have a smaller subset of plants and frugivores when compared with mainland communities, offer an interesting setting to understand the organization of plant–frugivore communities vis‐a‐vis the mainland sites. We examined the relative influence of functional traits and phylogenetic relationships on the plant–seed disperser interactions on an island and a mainland site. The island site allowed us to investigate the organization of the plant–seed disperser community in the natural absence of key frugivore groups (bulbuls and barbets) of Asian tropics. The endemic Narcondam Hornbill was the most abundant frugivore on the island and played a central role in the community. Species strength of frugivores (a measure of relevance of frugivores for plants) was positively associated with their abundance. Among plants, figs had the highest species strength and played a central role in the community. Island‐mainland comparison revealed that the island plant–seed disperser community was more asymmetric, connected, and nested as compared to the mainland community. Neither phylogenetic relationships nor functional traits (after controlling for phylogenetic relationships) were able to explain the patterns of interactions between plants and frugivores on the island or the mainland pointing toward the diffused nature of plant–frugivore interactions. The diffused nature is a likely consequence of plasticity in foraging behavior and trait convergence that contribute to governing the interactions between plants and frugivores. This is one of the few studies to compare the plant–seed disperser communities between a tropical island and mainland and demonstrates key role played by a point‐endemic frugivore in seed dispersal on island.

Proposal to determine the carbon and ecological footprint of seawater reverse osmosis desalination in the Canary Islands plants considering the energy mix

Proposal to determine the carbon and ecological footprint of seawater reverse osmosis desalination in the Canary Islands plants considering the energy mix

A meta‐analysis of insularity effects on herbivory and plant defences

AbstractAimPlants on islands are often subjected to lower levels of herbivory relative to those found at mainland sites. As a consequence, island plants are predicted to exhibit lower levels of physical or chemical defences, which renders them more susceptible to introduced herbivores. Yet, instances of high pressure by superabundant herbivores native to islands have been reported in many insular systems, which presumably would result in heightened plant defences. To date, no quantitative review has been conducted to determine how common these contrasting patterns are and their implications for the evolution of plant‐herbivore interactions.LocationIslands worldwide.TaxonPlants, insects, molluscs, mammals.MethodsWe conducted a meta‐analysis of insularity effects on herbivory and plant defences by including studies that involved island‐mainland comparisons of the same plant species in both environments (90% of cases), or insular endemics versus mainland congeners (10% of cases). We tested for differences between mammalian and invertebrate (mollusc or insect) herbivory as well as between plant chemical and physical defences by specifying comparisons based on the type of herbivore (vertebrate or invertebrate) or plant trait included in the study.ResultsMammalian herbivory was significantly higher on islands than on mainlands. In contrast, no significant effect was observed on invertebrate herbivory. In addition, we found no significant difference in either plant physical or chemical defences between insular and mainland plants, though physical defences tended to be higher for plants on islands.Main conclusionsAll analysed mammal studies focused on species introduced to islands, suggesting greater susceptibility of insular plants to exotic mammals, whereas the lack of effects in the case of invertebrate herbivory suggests no difference in susceptibility to molluscs or insects between insular and mainland plants. Interestingly, plant trait patterns suggest a trend for increased physical defences by insular plants, possibly due to heightened pressure by exotic mammalian herbivores on islands, whereas chemical defences appear uncorrelated to differences in herbivory. These findings call for further experimental and observational studies measuring defences and herbivory for multiple sympatric plant species occurring at both mainland and island sites within a system, or comparing insular endemics to congeneric mainland species.

Collections‐based systematics and biogeography in the 21st century: A tribute to Dr. Vicki Funk

Collections‐based systematics and biogeography in the 21st century: A tribute to Dr. Vicki Funk

Similar mechanisms underlie beta diversity of bryophytes in two archipelagos with different isolation time

AbstractCommunity assembly of island plants is a central topic in island biogeography. Most previous studies have focused on seed plants, while our understanding of bryophytes is limited. Specifically, how dispersal limitation and habitat heterogeneity shape beta diversity of bryophyte communities on islands remains unknown. We used two datasets of bryophyte communities from an artificial (~60 yr of isolation) and natural archipelago (~8500 yr of isolation) to understand their beta diversity patterns. The null model, in which species could disperse randomly and colonize successfully between islands, but the number of species on each island and the frequency of each species occurrence across all islands remain unchanged, was used to calculate expected beta diversity. Although we found significant differences in species composition between the two archipelagos, the difference in observed beta diversity was negligible. Further, there was no significant difference between observed and expected beta diversity in each archipelago. The difference in island area, rather than isolation, was significantly correlated with the beta diversity of bryophytes in both archipelagos. Our results suggest that the dispersal limitation is not the major ecological process driving the assembly of bryophyte communities in both archipelagos, but the habitat heterogeneity related to island area determines the beta diversity of bryophytes.

Floral fungal-bacterial community structure and co-occurrence patterns in four sympatric island plant species

Flowers’ fungal and bacterial communities can exert great impacts on host plant wellness and reproductive success—both directly and indirectly through species interactions. However, information about community structure and co-occurrence patterns in floral microbiome remains scarce. Here, using culture-independent methods, we investigated fungal and bacterial communities associated with stamens and pistils of four plant species (Scaevola taccada, Ipomoea cairica, Ipomoea pes-caprae, and Mussaenda kwangtungensis) growing together under the same environment conditions in an island located in South China. Plant species identity significantly influenced community composition of floral fungi but not bacteria. Stamen and pistil microbiomes did not differ in community composition, but differed in co-occurrence network topological features. Compared with the stamen network, pistil counterpart had fewer links between bacteria and fungi and showed more modular but less concentrated and connected structure. In addition, degree distribution of microbial network in each host species and each microhabitat (stamen or pistil) followed a significant power-law pattern. These results enhance our understanding in the assembly principles and ecological interactions of floral microbial communities.

The Radiation of Darwin’s Giant Daisies in the Galápagos Islands

Evolutionary radiations on oceanic islands have fascinated biologists since Darwin's exploration of the Galápagos archipelago [1, 2]. Island radiations can provide key insights for understanding rapid speciation, including evolutionary patterns and the processes behind them. However, lack of resolution of species relationships has historically hindered their investigation, particularly in the plant kingdom [3-5]. Here, we report a time-calibrated phylogenomic analysis based on genotyping-by-sequencing data [6] of the 15 species of Scalesia (Darwin's giant daisies), an iconic and understudied plant radiation endemic to the Galápagos Islands and considered the plant counterpart to Darwin's finches [1, 7-9]. Results support a Pliocene to early Pleistocene divergence between Scalesia and the closest South American relatives, and rapid diversification of extant Scalesia species from a common ancestor dated to the Middle Pleistocene. Major evolutionary patterns in Scalesia include the following: (1) lack of compliance with the "progression rule" hypothesis, in which earlier diverging lineages are expected to occupy older islands; (2) a predominance of within-island speciation over between-island speciation; and (3) repeated convergent evolution of potentially adaptive traits and habitat preferences on different islands during the course of diversification. Massive sequencing provided the essential framework for investigating evolutionary and ecological processes in the complex natural laboratory of the Galápagos, thereby advancing our understanding of island plant radiations.

The importance of historical ecology for interpreting evolutionary processes in plants of oceanic islands

AbstractOceanic islands and archipelagos are natural laboratories for investigating patterns and processes of evolution. Islands change with the course of time, resulting in a dynamic ontogeny over millions of years. The combined forces of tectonic plate subsidence and erosion from waves, wind, and rainwater bring about substantial geomorphological change over millions of years, until islands eventually disappear under the sea. Added to these long‐term natural changes to the environment of the islands are the changes caused by human activities in recent centuries. After humans reach a previously unpopulated island, they utilize the natural resources for their own survival, cutting forests for making houses, boats, and firewood. The size of the human population and the length of time on the island determine the degree of environmental impact. Evolutionary processes in plants of oceanic islands take place during ontogeny of the islands, resulting in population divergence, speciation, and hybridization. Due to the dramatic alterations suffered by many islands over millions of years, the present patterns of distribution and ecology of species within endemic groups may have little to do with the patterns when the species originated. Understanding these environmental changes is fundamental to infer a founder effect, reasons for levels of genetic variation within and among populations, and modes of speciation. Special caution must be exercised while making comparisons between groups located on islands of different geological ages and that have endured differing environmental modifications from humans. Examples are provided from the Juan Fernández Archipelago and Lord Howe Island.

Genome-wide genotyping estimates mating system parameters and paternity in the island species Tolpis succulenta.

The mating system has profound consequences, not only for ecology and evolution, but also for the conservation of threatened or endangered species. Unfortunately, small populations are difficult to study owing to limits on sample size and genetic marker diversity. Here, we estimated mating system parameters in three small populations of an island plant using genomic genotyping. Although self-incompatible (SI) species are known to often set some self-seed, little is known about how "leaky SI" affects selfing rates in nature or the role that multiple paternity plays in small populations. We generalized the BORICE mating system program to determine the siring pattern within maternal families. We applied this algorithm to maternal families from three populations of Tolpis succulenta from Madeira Island and genotyped the progeny using RADseq. We applied BORICE to estimate each individual offspring as outcrossed or selfed, the paternity of each outcrossed offspring, and the level of inbreeding of each maternal plant. Despite a functional self-incompatibility system, these data establish T. succulenta as a pseudo-self-compatible (PSC) species. Two of 75 offspring were strongly indicated as products of self-fertilization. Despite selfing, all adult maternal plants were fully outbred. There was high differentiation among and low variation within populations, consistent with a history of genetic isolation of these small populations. There were generally multiple sires per maternal family. Twenty-two percent of sib contrasts (between outcrossed offspring within maternal families) shared the same sire. Genome-wide genotyping, combined with appropriate analytical methods, enables estimation of mating system and multiple paternity in small populations. These data address questions about the evolution of reproductive traits and the conservation of threatened populations.

Pollination effectiveness of specialist and opportunistic nectar feeders influenced by invasive alien ants in the Seychelles.

Opportunistic nectar-feeders may act as effective pollinators; nonetheless, we still lack information on whether these opportunistic species differ in their pollination effectiveness from specialized nectarivorous vertebrates and insects. Many nectar specialists have coevolved with the plants on which they feed; therefore, we would expect higher pollination effectiveness in specialists than in opportunistic feeders. Here, we assessed quantity and quality components of pollination effectiveness in specialist and opportunistic vertebrate nectarivores and insects, focusing on three plants from the Seychelles: Thespesia populnea, Polyscias crassa, and Syzygium wrightii. We determined the quantity component (QNC) of pollination effectiveness with pollinator observations, and the quality component (QLC) by measuring fruit and seed set resulting from single visits by each pollinator. To detect potential negative effects of invasive ants on native plant-pollinator interactions, we classified pollinator visits (quantity component) as disturbed (>6 ants/30 min) vs. undisturbed. All focal plants were visited by insects, and vertebrate specialist and opportunist nectarivores, yet their pollination effectiveness differed. Flying insects were the most effective pollinators of T. populnea. The other two plants were most effectively pollinated by vertebrates; i.e., sunbirds (nectar specialists) in S. wrightii and Phelsuma geckos (nectar opportunists) in P. crassa, despite marked variation in QNC and QLC. Ant presence was associated with lower pollinator visitation rate in P. crassa and S. wrightii. Our study highlights the importance of all pollinator guilds, including opportunist nectarivorous vertebrates as pollinators of island plants, and the vulnerability of such interactions to disruption by nonnative species.

Distribution of n-alkanes and their δ2H and δ13C values in typical plants along a terrestrial-coastal-oceanic gradient

Reconstructing past responses of coastal wetlands to climate change contextualizes ongoing and future developments in these globally important ecosystems. The molecular distributions and stable isotope ratios (δ2H and δ13C) of sedimentary plant wax n-alkanes are frequently used to infer past vegetation and hydroclimate changes in wetland systems. However, there is limited modern information available about these compounds in subtropical wetlands. Here we analyzed mature leaves from 30 typical plant species and roots from 6 plant species collected in the Florida Everglades, including tree island plants, freshwater wetland plants, mangroves, and seagrass. The n-alkane abundance (2 to 884 µg/g dry weight), percent of aquatic plants ratio (Paq, 0 to 1), average chain length (ACL23-33, 24.0–30.7), concentration weighted average (CWA) δ2H (−231 to −78‰) and δ13C values (−38.9 to −14.4‰) spanned wide ranges with plant growth habit. Significant differences in n-alkane abundances, Paq, ACL23-33, CWA δ2H and δ13C values were found to exist between the leaves and roots of some emergent aquatic plants. Simple mass balance calculations of wetland aquatic plants suggest that long chain n-alkanes (e.g., C29n-alkanes) are predominantly derived from leaves rather than roots in wetland surface sediments/soils. However, the contribution from mid-chain n-alkanes (e.g., C23n-alkane) from roots may be equal to or greater than those from leaves. This implies that the differences in the isotopic compositions between root and leaf derived material need to be taken into account when interpreting down core changes in mid-chain n-alkane δ2H and δ13C values, which may be derived from variable contributions from leaves and roots rather than a change in hydroclimate or vegetation. Considering the large variation in both n-alkane distribution proxies and isotopic composition, no single molecular index or stable isotope ratio can capture multivariate changes of wetland ecosystems in the past. Nevertheless, principal component analysis shows promising potential to resolve different plant functional types. Paleo-reconstruction of subtropical aquatic ecosystems using n-alkanes will be most useful if the full molecular and isotopic distribution information of plant waxes are used.

Iconic, threatened, but largely unknown: Biogeography of the Macaronesian dragon trees (Dracaena spp.) as inferred from plastid DNA markers

AbstractThe genus Dracaena in Macaronesia comprises two threatened species of arborescent monocots that are often associated with one of the most intriguing biogeographic disjunctions: the Rand Flora pattern. Molecular information is, however, largely missing for the Macaronesian Dracaena taxa (“MDT”, hereafter), and the biogeographic or population genetic patterns of this lineage have not yet been thoroughly assessed. To fill this gap, we generated plastid DNA sequence data of 14 Dracaena populations representing the entire natural distribution of MDT (including mainland Morocco and all recognized subspecies), 9 additional populations of subspontaneous origin, and a set of related species of the genus. We performed phylogenetic, biogeographic, and population genetic analyses at different spatial scales and conducted a comparative review on plant haplotype diversity in Macaronesian plants. The results of our phylogenetic analyses indicated the monophyly of the MDT and an origin separate from a clade of geographically distant species that so far were postulated as their closest living relatives (D. cinnabari, D. ombet, D. schizantha, D. serrulata). The results of our phylogeographic analyses indicated that diversification within D. draco occurred throughout the Pleistocene and that wild peripheral populations (Madeira, mainland Morocco) may have a recent origin from Canarian source populations. Recent dispersals, coupled with remarkably low levels of haplotype diversity, probably account for the weak phylogeographic signal observed across wild populations. However, our results suggested that human‐assisted expansion of Dracaena inflates the extant phylogeographic signal by non‐random translocation of a specific subset of haplotypes. Our study demonstrates that many of the previous biogeographic scenarios on MDT are not supported by molecular data. Instead, our results highlight (i) the impact that human activity may have on the phylogeographic pattern of island plants, and (ii) the need of a deeper taxonomic sampling in future investigations on MDT and close relatives.

Variability in Colletotrichum infecting chilli plants of Andaman and Nicobar Islands, India

Variability in Colletotrichum infecting chilli plants of Andaman and Nicobar Islands, India

Linking Plant Functional Ecology to Island Biogeography.

The study of insular systems has a long history in ecology and biogeography. Island plants often differ remarkably from their noninsular counterparts, constituting excellent models for exploring eco-evolutionary processes. Trait-based approaches can help to answer important questions in island biogeography, yet plant trait patterns on islands remain understudied. We discuss three key hypotheses linking functional ecology to island biogeography: (i) plants in insular systems are characterized by distinct functional trait syndromes (compared with noninsular environments); (ii) these syndromes differ between true islands and terrestrial habitat islands; and (iii) island characteristics influence trait syndromes in a predictable manner. We are convinced that implementing trait-based comparative approaches would considerably further our understanding of plant ecology and evolution in insular systems.

Plant hydraulic traits reveal islands as refugia from worsening drought.

Relatively mesic environments within arid regions may be important conservation targets as ‘climate change refugia’ for species persistence in the face of worsening drought conditions. Semi-arid southern California and the relatively mesic environments of California’s Channel Islands provide a model system for examining drought responses of plants in potential climate change refugia. Most methods for detecting refugia are focused on ‘exposure’ of organisms to certain abiotic conditions, which fail to assess how local adaptation or acclimation of plant traits (i.e. ‘sensitivity’) contribute to or offset the benefits of reduced exposure. Here, we use a comparative plant hydraulics approach to characterize the vulnerability of plants to drought, providing a framework for identifying the locations and trait patterns that underlie functioning climate change refugia. Seasonal water relations, xylem hydraulic traits and remotely sensed vegetation indices of matched island and mainland field sites were used to compare the response of native plants from contrasting island and mainland sites to hotter droughts in the early 21st century. Island plants experienced more favorable water relations and resilience to recent drought. However, island plants displayed low plasticity/adaptation of hydraulic traits to local conditions, which indicates that relatively conserved traits of island plants underlie greater hydraulic safety and localized buffering from regional drought conditions. Our results provide an explanation for how California’s Channel Islands function as a regional climate refugia during past and current climate change and demonstrate a physiology-based approach for detecting potential climate change refugia in other systems.

Evaluation of wild edible plants of Andaman and Nicobar Islands for food and nutritional security

Evaluation of wild edible plants of Andaman and Nicobar Islands for food and nutritional security

Entosthodon productus (Bryophyta, Funariaceae), an addition to the moss flora of the subantarctic Îles Crozet

Bednarek-Ochyra, H. & Plasek, V. 2019. Entosthodon productus (Bryophyta, Funariaceae), an addition to the moss flora of the subantarctic Iles Crozet. - Herzogia 32: 326 -337.Entosthodon productus, an Australasian species, is recorded for the second time from the Subantarctic. In contrast to Marion Island in the Prince Edward Islands archipelago where the species is relatively frequent, only a single specimen of E. productus was found on Ile de la Possession in the conterminous Iles Crozet archipelago. The island's plants are characterised and illustrated and the geographical distribution of E. productus is reviewed. The present diversity of the moss flora of Iles Crozet is briefly summarised.

The effect of small-scale topography on patterns of endemism within islands

Topography influences evolutionary and ecological processes by isolating populations and enhancing habitat diversity. While the effects of large-scale topography on patterns of species richness and endemism are increasingly well documented, the direct effect of local topography on endemism is less understood. This study compares different aspects of topographic isolation, namely the isolating effect of deep barrancos (ravines) and the effect of increasing isolation with elevation in influencing patterns of plant endemism within a topographically diverse oceanic island (La Palma, Canary Islands, Spain). We collected plant presence–absence data from 75 plots in 8 barrancos on the northern coast of La Palma, spanning an elevation gradient from 95 to 674m a.s.l. Using mixed-effects models, we assessed the effect of barranco depth and elevation on the percentage of single-island endemics, multi-island endemics, and archipelago endemics. We found that percent endemism was not significantly correlated with barranco depth and correlated negatively with elevation within barrancos (rather than the expected positive relationship). The topographic barriers associated with the deep island barrancos thus appear insufficient to drive speciation through isolation in oceanic island plants. The decrease in endemism with elevation contradicts findings by previous broader-scale studies and it may reflect local influences, such as high habitat heterogeneity at low elevations.