Timber transported to Antarctica: a potential and undesirable carrier for alien fungi and insects

Antarctica’s severe climate and its geographical isolation are the factors that hinder the arrival of non-native species by natural means. However, the movement of people and cargo associated with national scientific programs and tourism render Antarctica much more accessible to exotic organisms. Both the transport routes and carriers are varied. The wide range of uses to which timber is put means that it is readily freighted to Antarctic stations. However, it can harbor numerous alien organisms. All the timber materials transported to the “Arctowski” station for the 32nd Polish Antarctic Expedition in the 2007/2008 season were scanned as a potential vector for alien species. This study focuses on the non-lichenized fungi and insects which were found on the timber. Four species of perithecia-forming Ascomycota, five species of corticioid and polyporoid Basidiomycota, four unidentified basidiomycetes taxa in form of sterile mycelia, and two insects belonging to Cerambycidae, were detected. Most of these ‘hitch-hikers’ were connected with the untreated parts of the timber. Their enduring survival in harsh Antarctic conditions is regarded as highly improbable. Nevertheless, some ascocarps frequently contained vital spores, and live insect larvae and imago were found in hibernation. The results also emphasize that such organisms can be accidentally transported to Antarctica and that the elementary rules for the eventual safe transport of non-infected goods should be obeyed and respected.     

Size and lipid content of nonmyrmecochorous diaspores: effects on the interaction with litter-foraging ants in the Atlantic rain forest of Brazil

Ants are often attracted to diaspores not adapted for dispersal by ants. These diaspores may occasionally benefit from this interaction. We selected six nonmyrmecochorous plant species (Virola oleifera, Eugenia stictosepala, Cabralea canjerana, Citharexylum myrianthum, Alchornea glandulosa and Hyeronima alchorneoides) whose diaspores differ in size and lipid content, and investigated how these features affect the outcome of ant-diaspore interactions on the floor of a lowland Atlantic forest of Southeast Brazil. A total of 23 ant species were seen interacting with diaspores on the forest floor. Ants were generally rapid at discovering and cleaning the diaspore pulp or aril. Recruitment rate and ant attendance were higher for lipid-rich diaspores than for lipid-poor ones. Removal rate and displacement distance were higher for small diaspores. The large ponerine ant Pachycondyla striata, one of the most frequent attendants to lipid-rich arillate diaspores, transported the latter into their nests and discarded clean intact seeds on refuse piles outside the nest. Germination tests with cleaned and uncleaned diaspores revealed that the removal of pulp or aril may increase germination success in Virola oleifera, Cabralea canjerana, Citharexylum myrianthum and Alchornea glandulosa. Gas chromatography analyses revealed a close similarity in the fatty acid composition of the arils of the lipid-rich diaspores and the elaiosome of a typical myrmecochorous seed (Ricinus communis), corroborating the suggestion that some arils and elaiosomes are chemically similar. Although ant-derived benefits to diaspores – secondary dispersal and/or increased germination – varied among the six plant species studied, the results enhanced the role of ant-diaspore interactions in the post-dispersal fates of nonmyrmecochorous seeds in tropical forests. The size and the lipid-content of the diaspores were shown to be major determinants of the outcome of such interactions.     

Alien lichens unintentionally transported to the “Arctowski” station (South Shetlands, Antarctica)

The recent climate changes combined with intensified human activity in Antarctica are promoting the synanthropization process and increasing the likelihood of alien species establishing in the native communities. Cargo items, expedition members’ equipment and food destined for the 32nd Polish Antarctic Expedition to the “Arctowski” station in the 2007/2008 season were inspected to determine their potential as vectors for alien lichen species. Within the cargo, packaging and foodstuffs scanned, a total of 45 lichen specimens (24 species) were identified. Most of them had been accidentally transported with various timbers. Cargo containers and fresh food were also found to harbour for single specimens. The majority of lichens detected are alien to the Antarctic biota and had never been observed in the region. This paper estimates the potential risk of these lichens establishing themselves in remote southern latitudes. The results emphasize the threat of accidental introduction of alien organisms into Antarctica and the need for taking every precaution to prevent the importation of non-native species to this unique environment.     

Disentangling sources of maternal effects in the heterocarpic species Rumex bucephalophorus

Maternal effects are one of the most important influences on the offspring phenotype and their adaptive significance has been increasingly recognized. In this study we document the role of two sources of maternal effects, position and heterocarpy, on juvenile and adult traits of Rumex bucephalophorus, an annual plant that occurs in heterogeneous and unstable environments. Up to three different diaspore types can be found in populations of this species: buried diaspores (BD) at the plant base, and fixed diaspores (FD) and long dispersible diaspores (LD) both borne along aerial stems. The two sources of maternal effects affected most stages of the life cycle of R. bucephalophorus: seed size, dispersability, seedling size and survival, and adult plant fecundity. Maternal effects due to position affected mainly juvenile traits, while those due to heterocarpy were stronger and more persistent. In general, seedlings from FD showed higher survival and originated plants with higher fecundity but with lower dispersability than those derived from BD and LD. Dispersability was markedly affected by the two maternal effects at two different stages: first, there was a trend to place the slighter and more easily detachable diaspores (LD) at the optimal positions for dispersal, and second maternal effect due to heterocarpy surprisingly affected dispersability of the second generation progeny. Our study shows that maternal effects can play an important role in ecology, dynamic and evolution of populations and it adds to growing evidence about the important role of maternal effects.     

New mutualism for old: indirect disruption and direct facilitation of seed dispersal following Argentine ant invasion

The indirect effects of biological invasions on native communities are poorly understood. Disruption of native ant communities following invasion by the Argentine ant (Linepithema humile) is widely reported to lead indirectly to the near complete collapse of seed dispersal services. In coastal scrub in southeastern Australia, we examined seed dispersal and handling of two native and two invasive alien plant species at Argentine ant-invaded or -uninvaded sites. The Argentine ant virtually eliminates the native keystone disperser Rhytidoponera victoriae, but seed dispersal did not collapse following invasion. Indeed, Argentine ants directly accounted for 92% of all ant-seed interactions and sustained overall seed dispersal rates. Nevertheless, dispersal quantity and quality among seed species differed between Argentine ant-invaded and -uninvaded sites. Argentine ants removed significantly fewer native Acacia retinodes seeds, but significantly more small seeds of invasive Polygala myrtifolia than did native ants at uninvaded sites. They also handled significantly more large seeds of A. sophorae, but rarely moved them >5 cm, instead recruiting en masse, consuming elaiosomes piecemeal and burying seeds in situ. In contrast, Argentine ants transported and interred P. myrtifolia seeds in their shallow nests. Experiments with artificial diaspores that varied in diaspore and elaiosome masses, but kept seed morphology and elaiosome quality constant, showed that removal by L. humile depended on the interaction of seed size and percentage elaiosome reward. Small diaspores were frequently taken, independent of high or low elaiosome reward, but large artificial diaspores with high reward instead elicited mass recruitment by Argentine ants and were rarely moved. Thus, Argentine ants appear to favour some diaspore types and reject others based largely on diaspore size and percentage reward. Such variability in response indirectly reduces native seed dispersal and can directly facilitate the spread of an invasive alien shrub.     

Seed dispersal of alien and native plants by vertebrate herbivores

Seed dispersal is crucial for the success and spread of alien plants. Herbivores often establish a dual relationship with plants: antagonist, through herbivory, and mutualist, through seed dispersal. By consuming plants, herbivores may disperse large amounts of seeds, and can facilitate the spread of alien plants. However, seed dispersal of alien plants by herbivores has been largely uninvestigated. I studied factors associated with dispersal of alien and native seeds by the three most important vertebrate herbivores in SW Australia: emus (Dromaius novaehollandia), western grey kangaroos (Macropus fuliginosus) and European rabbits (Oryctolagus cuniculus). Overall frequencies of alien and native seeds dispersed by these herbivores were determined by differences among them in (1) the plant groups they predominantly disperse, that differed in frequencies of aliens versus natives, and (2) the predominant dispersal of aliens or natives within those plant groups. Emus and kangaroos (natives) tended to disperse predominantly alien seeds within plant groups (defined by life forms, dispersal syndromes, and diaspore size), whereas rabbits (alien) tended to disperse predominantly natives. This agrees with the hypothesis that herbivores will use predominantly plants that have evolved in different areas, because of less effective defences against new enemies. Overall frequencies were consistent with this pattern in kangaroos and rabbits, but not in emus. Kangaroos dispersed mostly plant groups that were mainly aliens (herbaceous species and small and medium sized dispersal units and seeds), which together with their predominant use of aliens over natives within groups resulted in the highest overall frequency of alien seeds (73%). Rabbits were similar to kangaroos in the type of plants dispersed, but their predominant use of natives over aliens within groups contributed to an overall predominance of native seeds in their pellets (88%). Emus dispersed mostly plant groups that were mainly natives (e.g. woody species with big diaspores), resulting in low overall frequency of alien seeds (11%), despite their predominant use of aliens over natives within plant groups. Thus, the within-groups trend pointed to a facilitative role of native herbivores of plant invasions through seed dispersal, but was obscured by the different use by herbivores of plant groups with different frequency of aliens.     

Epizoochory in a hedgerow habitat: seasonal variation and selective diaspore adhesion

Epizoochory has been less studied than other seed dispersal mechanisms, such as endozoochory, and generally only a small percentage of plant species show adaptations to this strategy. Nevertheless, epizoochorous seed dispersal can affect an appreciable number of herb species in forests and man-made habitats. Also, few studies have dealt with temporal variation in epizoochory. In this paper, medium-long distance epizoochory is analyzed in a hedgerow habitat for the first time, using a domestic dog in an area in northwest Spain. Special attention is paid to seasonal variation and differential traits of plant taxa involved. Approximately 30 % of available herb taxa were found attached to hair. The intermonthly difference in the frequency of the taxa involved in epizoochory was significant, and the overall peak was reached in June–October linked with diaspore ripening phenology. Ninety-three percent of the plant taxa adhered to hair had diaspores with traits facilitating epizoochory (hooks, spines, awns, rigid hairs), in comparison with 17 % for available plant taxa not adhered to hair. The taxa involved in epizoochory had larger diaspores than the rest of the available taxa, but ranged considerably in size. Numerous hooks covered the largest, heaviest diaspores, and allowed them to attach to hair. There was no significant difference in mean plant height between taxa involved in epizoochory and the rest of the available taxa. The difference in life span between taxa involved in epizoochory and the rest of available taxa was not significant, most of them being perennials in both cases. Seventy-three percent of all the available plant taxa were potential forest plants typically found in edges and gaps, and 64 % of the plant taxa involved in epizoochory were these kinds of potential forest plants. High or medium involuntary positive selection by the dog of diaspores of Taraxacum gr. officinale, Galium aparine, Geum urbanum, and Agrimonia eupatoria was observed. In conclusion, epizoochorous dispersal can be quantitatively and functionally important in hedgerow habitats during summer-autumn, affecting mainly herb taxa with specialized diaspores.     

黄土丘陵沟壑区80种植物繁殖体形态特征及其物种分布

植物繁殖体的形态特征及其物种分布是植物长期适应环境的结果,对退化生态系统的更新与恢复具有重要的理论与实践指导意义。研究了80种植物的繁殖体形态特征及与其物种分布的关系,结果表明：1）繁殖体重量差别较大（0. 020—357.428 mg）,主要集中在1—9.999 mg（占52.5%）。2）繁殖体的形状指数FI变化范围较大（1.06—12.93）,61.3%的植物繁殖体的形状近圆球形。3）33种植物繁殖体具有明显的附属物,包括毛、翅、芒和刺等。4）87.5%的植物繁殖体表面具有各种纹饰（棱、被毛、纹和颗粒状等）;繁殖体颜色以褐色和黑色为主,少数繁殖体颜色鲜艳;6种植物繁殖体具有吸水分泌粘液的特性。5）黄土丘陵沟壑区繁殖体重量小或形状近圆球形的植物分布数量多、范围广。6）繁殖体具有毛、翅和芒附属物或吸湿分泌粘液的植物在黄土丘陵沟壑区较繁殖体无附属物的植物能够分布更多、更广。繁殖体这些有利于物种分布的形态特征对于植物适应该区干旱与土壤侵蚀干扰具有重要的生态学意义,而且可用于指导该区人工补播促进植被恢复的物种选择。     

Evidence of endozoochory in upland geese Chloephaga picta and white‐bellied seedsnipes Attagis malouinus in sub‐Antarctic Chile

Birds are known to act as potential vectors for the exogenous dispersal of bryophyte diaspores. Given the totipotency of vegetative tissue of many bryophytes, birds could also contribute to endozoochorous bryophyte dispersal. Research has shown that fecal samples of the upland goose (Chloephaga picta) and white‐bellied seedsnipe (Attagis malouinus) contain bryophyte fragments. Although few fragments from bird feces have been known to regenerate, the evidence for the viability of diaspores following passage through the bird intestinal tract remains ambiguous. We evaluated the role of endozoochory in these same herbivorous and sympatric bird species in sub‐Antarctic Chile. We hypothesized that fragments of bryophyte gametophytes retrieved from their feces are viable and capable of regenerating new plant tissue. Eleven feces disk samples containing undetermined moss fragments from C. picta (N = 6) and A. malouinus (N = 5) and six moss fragment samples from wild‐collected mosses (Conostomum tetragonum, Syntrichia robusta, and Polytrichum strictum) were grown ex situ in peat soil and in vitro using a agar Gamborg medium. After 91 days, 20% of fragments from A. malouinus feces, 50% of fragments from C. picta feces, and 67% of propagules from wild mosses produced new growth. The fact that moss diaspores remained viable and can regenerate under experimental conditions following the passage through the intestinal tracts of these robust fliers and altitudinal and latitudinal migrants suggests that sub‐Antarctic birds might play a role in bryophyte dispersal. This relationship may have important implications in the way bryophytes disperse and colonize habitats facing climate change.     

Soluble carbohydrates in developing and mature diaspores of polar Caryophyllaceae and Poaceae

The accumulation of soluble carbohydrates in maturing diaspores of flowering plants comprising Arctic populations of Cerastium alpinum, indigenous Antarctic species Colobanthus quitensis and Deschampsia antarctica, and cosmopolitan Poa annua from the Antarctic was investigated. For comparative purposes, the diaspores of two species of flowering plants growing in the area of Olsztyn (Poland), Poa annua (Poaceae) and Cerastium arvense (Caryophyllaceae) were used. A qualitative and quantitative analysis of soluble carbohydrates conducted by means of high-resolution gas chromatography showed that monosaccharides (glucose and fructose), maltose and sucrose, raffinose, myo-inositol and galactinol are ubiquitous in developing and mature diaspores among investigated species. Moreover, D. antarctica and P. annua caryopses additionally contained stachyose and 1-kestose; the seeds of Caryophyllaceae studied were found to contain d-pinitol and d-ononitol. The development and maturation of the seeds of polar Caryophyllaceae and Poaceae were accompanied by the changes in the concentration of their soluble carbohydrates. During maturation, seeds accumulated galactinol and raffinose family of oligosaccharides (RFOs), except C. quitensis. Although seeds of the studied Caryophyllaceae contained d-pinitol and lower amounts of d-ononitol, they did not accumulate α-d-galactoside derivatives of mentioned cyclitols. P. annua caryopses, occurring in the Antarctic, were found to accumulate considerably higher amounts of sucrose and 1-kestose than those developed in Olsztyn.     

Determinants of plant species invasions in an arid island: evidence from Socotra Island (Yemen)

Understanding the factors which affect the distribution of alien plants in arid islands is complicated by the complex and stochastic nature of the invasion process per se, the harsh environmental conditions, and the low number of researchers and sampling effort. We present the results of the most comprehensive inventory to date of alien vascular plant species occurring in Socotra Island, a global biodiversity hotspot just beginning to be developed. A floristic survey was conducted between 2006 and 2008 in 36 grid cells of 10?×?10?km. We integrated this data from this survey with those from scientific literature. We recorded 88 alien plant species. Tree and herbaceous species were the most common growth forms. Species from Asia and edible species were prevalent. We identified 80 species considered weeds worldwide with >50?% adapted to arid conditions. We used a two-part model to analyze the spatial distribution of naturalized and alien plant species in relation to environmental and anthropogenic factors. Altitude and human-related factors play a significant role in the distribution of both naturalized and invasive species. Notably, the latter can potentially spread mainly in the alluvial basal areas. This study underpins the knowledge about alien species and their spatial distribution in Socotra Island. It provides a baseline for plant invasion management and contributes data for the analyses of invasion processes on islands worldwide.     

Spatial structure of the soil seed bank of Poa annua L.—alien species in the Antarctica

Poa annua L. (annual bluegrass) is the only non–native flowering plant species that has successfully established a breeding population in the maritime Antarctic and has been shown to maintain a soil seed bank. The characteristic of the spatial structure of the Antarctic population of this species is the formation of distinct dense clumps—tussocks. In the temperate zone the species is only loosely tufted. We focused on the characteristics of seed deposition associated with the tussocks and some aspects of the spatial heterogeneity of the soil seed bank of P. annua in the Antarctic. We wanted to assess the microspatial structure of the soil seed bank of annual bluegrass at Arctowski Station. Therefore we compared the number of seeds deposited underneath and in the vicinity of P. annua clumps. Our results indicate that P. annua in the Antarctic maintains a soil seed bank comparable to species typical for the polar tundra. The microspatial structure of P. annua soil seed bank in the Antarctic is highly associated with the presence of tussocks. Seeds are deposited underneath the tussock rather than in the vicinity of the clump. Our results also indicate that seeds are able to survive the Antarctic winter and readily germinate under optimal conditions.     

Impact of anthropogenic transportation to Antarctica on alien seed viability

Antarctic ecosystems are at risk from the introduction of invasive species. The first step in the process of invasion is the transportation of alien species to Antarctic in a viable state. However, the effect of long-distance human-mediated dispersal, over different timescales, on propagule viability is not well known. We assessed the viability of Poa trivialis seeds transported to Antarctica from the UK, South Africa and Australia by ship or by ship and aircraft. Following transportation to the Antarctic Treaty area, no reduction in seed viability was found, despite journey times lasting up to 284 days and seeds experiencing temperatures as low as −1.5°C. This work confirms that human-mediated transport may overcome the dispersal barrier for some propagules, and highlights the need for effective pre-departure biosecurity measures.     

潮虫消耗木本植物凋落物的可选择性试验

近年来,越来越多的学者关注外来植物入侵对土壤生态功能的影响效应及其相应反馈机制的探索与研究,然而本地原生土壤生物群落对不同入侵程度下的外来植物种以及本地原生植物种之间是否存在消耗差异却尚不明了.通过等足目潮虫的选择性喂养试验来测试10个本地种、5个非入侵性外来种和5个强入侵性外来种之间的适口性差异,试图求证外来植物的入侵性是否与植物落叶被消耗率呈现必然联系.数据分析结果显示潮虫对本地种、非入侵性外来种和入侵性外来种的消耗并无显著差异;而潮虫对不同生活型下木本植物的取食却存在显著差异,即灌木消耗率显著高于乔木.其次,通过植物初始性状指标(包括木质素、纤维素、半纤维素、碳、氮含量)与相应消耗率的相关比较,消耗量总体上与植物凋落物的氮含量呈正相关关系(R2 =0.358).由此,研究结论强调植物落叶的降解速率并不一定与植物入侵性或入侵阶段呈绝对相互关连,但是氮含量,抑或各种形式的植物氮元素成分都可能在一定程度上参与并影响着外来植物的入侵进程.     

Are Weeds Hitchhiking a Ride on Your Car? A Systematic Review of Seed Dispersal on Cars

When traveling in cars, we can unintentionally carry and disperse weed seed; but which species, and where are they a problem? To answer these questions, we systematically searched the scientific literature to identify all original research studies that assess seed transported by cars and listed the species with seed on/in cars. From the 13 studies that fit these criteria, we found 626 species from 75 families that have seed that can be dispersed by cars. Of these, 599 are listed as weeds in some part of the world, with 439 listed as invasive or naturalized alien species in one or more European countries, 248 are invasive/noxious weeds in North America, 370 are naturalized alien species in Australia, 167 are alien species in India, 77 are invasive species in China and 23 are declared weeds/invaders in South Africa. One hundred and one are classified as internationally important environmental weeds. Although most (487) were only recorded once, some species such as Chenopodium album, Poa pratensis and Trifolium repens were common among studies. Perennial graminoids seem to be favoured over annual graminoids while annual forbs are favoured over perennial forbs. Species characteristics including seed size and morphology and where the plants grew affected the probability that their seed was transported by cars. Seeds can be found in many different places on cars including under the chassis, front and rear bumpers, wheel wells and rims, front and back mudguards, wheel arches, tyres and on interior floor mats. With increasing numbers of cars and expanding road networks in many regions, these results highlight the importance of cars as a dispersal mechanism, and how it may favour invasions by some species over others. Strategies to reduce the risk of seed dispersal by cars include reducing seed on cars by mowing road verges and cleaning cars.     

Pathways of alien invertebrate transfer to the Antarctic region

Alien species pose an increasing threat to the biodiversity of the Antarctic region. Several alien species have established in Antarctic terrestrial communities, some representing novel functional groups such as pollinators and predators, with unknown impacts on ecosystem processes. We quantified the unintentional introduction of alien invertebrates to the Antarctic region over a 14-year period (2000–2013). To do this, probable pathways (Australian Antarctic cargo operations) and endpoints (research stations) for invertebrate introductions were searched. In addition, we undertook a stratified trapping programme targeting invertebrates on supply vessels in transit to the Antarctic region and also at cargo facilities in Australia during the 2012–2013 austral summer field season. Our results show that a diverse suite of invertebrate taxa were being introduced to the Antarctic region, with 1,376 individuals from at least 98 families observed or trapped during the sampling period. Many individuals were found alive. Diptera, Coleoptera and Lepidoptera were the most common taxa, comprising 74 % of the collection. At the family level, Phoridae (small flies) and Noctuidae (moths) were most commonly observed. Individuals from 38 different families were repeatedly introduced over the study period, sometimes in high numbers. Food and large cargo containers harboured the most individuals. These findings can assist in improving biosecurity protocols for logistic activities to Antarctica, thereby reducing the risk of invasions to the Antarctic region.     

Invasion of the cosmopolitan species Echinochloa colona into herbaceous vegetation of a tropical wetland system

The negative effects of alien plant species on ecosystem structure and functions are increasingly recognised, and efforts to control these species are vital to restore degraded ecosystems and preserve biodiversity. However, we lack a full understanding of factors that determine alien species invasions along spatial gradients in herbaceous vegetation of tropical systems. We therefore examined the effects of community properties, environmental variables and human-related disturbance factors on the invasion of the alien grass Echinochloa colona (L.) Link at small- and large scales in the Kilombero Valley wetland, Tanzania. Generalized additive mixed models showed that E. colona abundance on a small scale was negatively related to above-ground biomass and evenness of resident species, whereas E. colona abundance was positively related to grazing intensity. On a large scale, biomass (negatively related to E. colona abundance) and distance to river (positive) were important in explaining E. colona abundance. These findings support the assertion that different factors may contribute to the invasion of alien plant species at different spatial scales, as also reported in many temperate systems. Overall, our results show that successful invasion of alien species is a function of plant community properties, human-related disturbance and favourable environmental conditions. Effective management strategies should consider mitigations that can increase the biomass and evenness of native species and a reduction of grazing pressure to restore the wetland and conserve biodiversity.     

Invasive plant integration into native plant–pollinator networks across Europe

The structure of plant–pollinator networks has been claimed to be resilient to changes in species composition due to the weak degree of dependence among mutualistic partners. However, detailed empirical investigations of the consequences of introducing an alien plant species into mutualistic networks are lacking. We present the first cross-European analysis by using a standardized protocol to assess the degree to which a particular alien plant species (i.e. Carpobrotus affine acinaciformis, Impatiens glandulifera, Opuntia stricta, Rhododendron ponticum and Solanum elaeagnifolium) becomes integrated into existing native plant–pollinator networks, and how this translates to changes in network structure.Alien species were visited by almost half of the pollinator species present, accounting on average for 42 per cent of the visits and 24 per cent of the network interactions. Furthermore, in general, pollinators depended upon alien plants more than on native plants. However, despite the fact that invaded communities received more visits than uninvaded communities, the dominant role of alien species over natives did not translate into overall changes in network connectance, plant linkage level and nestedness. Our results imply that although supergeneralist alien plants can play a central role in the networks, the structure of the networks appears to be very permeable and robust to the introduction of invasive alien species into the network.     

Signals Can Trump Rewards in Attracting Seed-Dispersing Ants

Both rewards and signals are important in mutualisms. In myrmecochory, or seed dispersal by ants, the benefits to plants are relatively well studied, but less is known about why ants pick up and move seeds. We examined seed dispersal by the ant Aphaenogaster rudis of four co-occurring species of plants, and tested whether morphology, chemical signaling, or the nutritional quality of fatty seed appendages called elaiosomes influenced dispersal rates. In removal trials, ants quickly collected diaspores (seeds plus elaiosomes) of Asarum canadense, Trillium grandiflorum, and Sanguinaria canadensis, but largely neglected those of T. erectum. This discrepancy was not explained by differences in the bulk cost-benefit ratio, as assessed by the ratio of seed to elaiosome mass. We also provisioned colonies with diaspores from one of these four plant species or no diaspores as a control. Colonies performed best when fed S. canadensis diaspores, worst when fed T. grandiflorum, and intermediately when fed A. canadense, T. erectum, or no diaspores. Thus, the nutritional rewards in elaiosomes affected colony performance, but did not completely predict seed removal. Instead, high levels of oleic acid in T. grandiflorum elaiosomes may explain why ants disperse these diaspores even though they reduce ant colony performance. We show for the first time that different elaiosome-bearing plants provide rewards of different quality to ant colonies, but also that ants appear unable to accurately assess reward quality when encountering seeds. Instead, we suggest that signals can trump rewards as attractants of ants to seeds.     

Species,Diaspore Volume and Body Mass Matter in Gastropod Seed Feeding Behavior

Background

Seed dispersal of ant-dispersed plants (myrmecochores) is a well studied ecosystem function. Recently, slugs have been found to act as seed dispersers of myrmecochores. The aim of our study was to (1) further generalize the finding that gastropods feed on seeds of myrmecochores and hence may act as seed dispersers, (2) to test whether gastropod body mass and the volume of diaspores have an influence on the seed dispersal potential.

Methodology and Principal Findings

We assessed the seed dispersal potential of four slug and snail species with a set of seven myrmecochorous plant species from seven different plant families common to Central European beech forests. Diaspores differed in shape and size. Gastropods differed in their readiness to feed on diaspores and in the proportion of seeds that were swallowed as a whole, and this readiness generally decreased with increasing diaspore size. Smaller Arionid slugs (58 mm body length; mean) mostly fed on the elaiosome but also swallowed small diaspores and therefore not only act as elaiosome consumers, a nutrient rich appendage on myrmecochorous diaspores, but may also disperse seeds. Large Arionid slugs (>100 mm body length) swallowed diaspores of all sizes. Diaspores swallowed by gastropods were defecated without damage. Within-species variability in body size also affect seed dispersal potential, as larger individuals of the red slug (Arion rufus) swallowed more diaspores of wood anemone (Anemone nemorosa) than smaller ones.

Conclusions and Significance

Our results help to generalize the finding that gastropods consume and potentially disperse seeds of myrmecochores. The dispersal potential of gastropods is strongly influenced by diaspore size in relation to gastropod size.