Rodents mediate the relationship between seed rain, seed bank, and plant community with increased grazing disturbance

Seed rain and the soil seed bank represent the dispersal of seeds in space and time, respectively, and can be important sources of recruitment of new individuals during plant community regeneration. However, the temporal dynamics of seed rain and the mechanisms by which the seed rain and soil seed bank may play a role in plant community regeneration with increased grazing disturbance remain unclear. Seed rain, soil seed bank, aboveground vegetation, and rodent density were sampled along a grazing gradient in an alpine marsh on the eastern Tibetan Plateau. We described the temporal dynamics of seed dispersal using Bayesian generalized mixed models, and nonmetric multidimensional scaling and the structural equation model were used to examine the effects of grazing disturbance on the relative role of seed rain and soil seed bank on aboveground plant community regeneration. The temporal dynamics of seed rain changed from a unimodal to a bimodal pattern with increased grazing disturbance. Both species diversity and seed density of the seed rain and seed bank increased significantly with increased grazing disturbance. Increased grazing disturbance indirectly increased the similarity of composition between seed rain, seed bank, and aboveground plant community by directly increasing species diversity and abundance of aboveground plant community. However, increased grazing disturbance also indirectly decreased the similarity of seed rain, soil seed bank, and aboveground plant community by directly increasing rodent density. The similarity between seed rain and aboveground plant community was greater than that of the soil seed bank and aboveground plant community with increased grazing disturbance. Grazing disturbance spreads the risk of seed germination and seedling establishment by changing the temporal dynamics of seed dispersal. Plants (positive) and rodents (negative) mediated the role of seed rain and soil seed bank in plant community regeneration. The role of seed rain in plant community regeneration is higher than the seed bank in disturbed alpine marshes. Our findings increase our understanding of the regeneration process of the plant community, and they provide valuable information for the conservation and restoration of alpine marsh ecosystems.

Interspecific interactions disrupted by roads

Roads have pervasive impacts on wildlife, including habitat loss and fragmentation, road mortality, habitat pollution and increased human use of habitats surrounding them. However, the effects of roads on interspecific interactions are less understood. Here we provide a synthesis of the existing literature on how species interactions may be disrupted by roads, identify knowledge gaps, and suggest avenues for future research and conservation management. We conducted a systematic search using the Web of Science database for each species interaction (predation, competition, mutualism, parasitism, commensalism and amensalism). These searches yielded 2144 articles, of which 195 were relevant to our topic. Most of these studies focused on predation (50%) or competition (24%), and less frequently on mutualism (17%) or, parasitism (9%). We found no studies on commensalism or amensalism. Studies were biased towards mammals from high-income countries, with most conducted in the USA (34%) or Canada (18%). Our literature review identified several patterns. First, roads disrupt predator-prey relationships, usually with negative impacts on prey populations. Second, new disturbed habitats created in road corridors often benefit more competitive species, such as invasive species, although some native or endangered species can also thrive there. Third, roads degrade mutualistic interactions like seed dispersal and pollination. Fourth, roads can increase parasitism rates, although the intensity of the alteration is species specific. To reduce the negative impacts of roads on interspecific interactions, we suggest the following management actions: (i) verges should be as wide and heterogenous as possible, as this increases microhabitat diversity, thus enhancing ecosystem services like pollination and seed dispersal; (ii) combining different mowing regimes can increase the complexity of the habitat corridor, enabling it to act as a habitat for more species; (iii) the use of de-icing salts should be gradually reduced and replaced with less harmful products or maintenance practices; (iv) wildlife passes should be implemented in groups to reduce animal concentrations inside them; (v) periodic removal of carcasses from the road to reduce the use of this resource by wildlife; and (vi) implementation of traffic-calming schemes could enhance interspecific interactions like pollination and avoid disruption of predator-prey relationships.

Efficacy of Wolbachia-based mosquito control: Predictions of a spatially discrete mathematical model

Wolbachia is an endosymbiont bacterium present in many insect species. When Wolbachia-carrying male Aedes aegypti mosquitoes mate with non-carrier females, their embryos are not viable due to cytoplasmic incompatibility. This phenomenon has been exploited successfully for the purpose of controlling mosquito populations and the spread of mosquito-borne illnesses: Wolbachia carriers are bred and released into the environment. Because Wolbachia is not harmful to humans, this method of mosquito control is regarded as a safer alternative to pesticide spraying. In this article, we introduce a mathematical framework for exploring (i) whether a one-time release of Wolbachia carriers can elicit a sustained presence of carriers near the release site, and (ii) the extent to which spatial propagation of carriers may allow them to establish fixation in other territories. While some prior studies have formulated mosquito dispersal models using advection-reaction-diffusion PDEs, the predictive power of such models requires careful ecological mapping: advection and diffusion coefficients exhibit significant spatial dependence due to heterogeneity of resources and topography. Here, we adopt a courser-grained view, regarding the environment as a network of discrete, diffusively-coupled "habitats"-distinct zones of high mosquito density such as stagnant ponds. We extend two previously published single-habitat mosquito models to multiple habitats, and calculate rates of migration between pairs of habitats using dispersal kernels. Our primary results are quantitative estimates regarding how the success of carrier fixation in one or more habitats is determined by: the number of carriers released, sizes of habitats, distances between habitats, and the rate of migration between habitats. Besides yielding sensible and potentially useful predictions regarding the success of Wolbachia-based control, our framework applies to other approaches (e.g., gene drives) and contexts beyond the realm of insect pest control.

Different mechanisms underlie similar species-area relationships in two tropical archipelagoes

Despite much research in the field of island biogeography, mechanisms regulating insular diversity remain elusive. Here, we aim to explore mechanisms underlying plant species-area relationships in two tropical archipelagoes in the South China Sea. We found positive plant species-area relationships for both coral and continental archipelagoes. However, our results showed that different mechanisms contributed to similar plant species-area relationships between the two archipelagoes. For coral islands, soil nutrients and spatial distance among communities played major roles in shaping plant community structure and species diversity. By contrast, the direct effect of island area, and to a lesser extent, soil nutrients determined plant species richness on continental islands. Intriguingly, increasing soil nutrients availability (N, P, K) had opposite effects on plant diversity between the two archipelagoes. In summary, the habitat quality effect and dispersal limitation are important for regulating plant diversity on coral islands, whereas the passive sampling effect, and to a lesser extent, the habitat quality effect are important for regulating plant diversity on continental islands. More generally, our findings indicate that island plant species-area relationships are outcomes of the interplay of both niche and neutral processes, but the driving mechanisms behind these relationships depends on the type of islands.

Intraspecific variation in seed size is mediated by seed dispersal modes and animal dispersers - evidence from a global-scale dataset

Seed dispersal mechanisms play a crucial role in driving evolutionary changes in seed and fruit traits. While previous studies have primarily focussed on the mean or maximum values of these traits, there is also significant intraspecific variation in them. Therefore, it is pertinent to investigate whether dispersal mechanisms can explain intraspecific variations in these traits. Taking seed size as a case study, we compiled a global dataset comprising 3424 records of intraspecific variation in seed size (IVSS), belonging to 691 plant species and 131 families. We provided the first comprehensive quantification of dispersal mechanism effects on IVSS. Biotic-dispersed species exhibited a larger IVSS than abiotic-dispersed species. Synzoochory species had a larger IVSS than endozoochory, epizoochory, and myrmecochory species. Vertebrate-dispersed species exhibited a larger IVSS than invertebrate-dispersed species, and species dispersed by birds exhibited a larger IVSS than mammal-dispersed species. Additionally, a clear negative correlation was detected between IVSS and disperser body mass. Our results prove that the IVSS is associated with the seed dispersal mechanism. This study advances our understanding of the dispersal mechanisms' crucial role in seed size evolution, encompassing not only the mean value but also the variation.

The comparison of dispersal rate between invasive and native species varied by plant life form and functional traits

A long dispersal distance is widely used to indicate high invasiveness, but it ignores the temporal dimensions of plant invasion. Faster dispersal rates (= distance/time) of invasive species than native ones have been widely used in modeling species invasion and planning control management. However, the comparison of dispersal rate between invasive and native plants, particularly for dispersal on a local or landscape scale, has not been tested with a comprehensive dataset. Moreover, both the effects of plant functional traits on the dispersal rate and variation in the functional-trait effects between invasive and native plants remain elusive. Compiling studies from 30 countries globally, we compared seed dispersal rates (km/year) on a local or landscape scale between 64 observations of invasive and 78 observations of native plants given effects of plant life forms, disturbance levels, and measurement methods. Furthermore, we compared the effects of functional traits on dispersal rate between invasive and native species. We found that: (1) Trait values were similar between the invasive and native plants except for the greater height of woody native plants than woody invasive ones; (2) Compared within the same plant life form, the faster dispersal rates of invasive species were found in herbaceous plants, not in woody plants, and disturbance level and measurement methods did not affect the rate comparison; (3) Plant height and seed length had significant effects on dispersal rates of both invasive and native plants, but the effect of leaf dry matter content (LDMC) was only significant on herbaceous invasive plants. The comparison of dispersal rate between invasive and native plants varied by plant life form. The convergent values but divergent dispersal effects of plant traits between invasive and native species suggest that the trait effects on invasiveness could be better understood by trait association with key factors in invasiveness, e.g., dispersal rate, than the direct trait comparison between invasive and native plants.

Pervasive within-species spatial repulsion among adult tropical trees

For species to coexist, performance must decline as the density of conspecific individuals increases. Although evidence for such conspecific negative density dependence (CNDD) exists in forests, the within-species spatial repulsion it should produce has rarely been demonstrated in adults. In this study, we show that in comparison to a null model of stochastic birth, death, and limited dispersal, the adults of dozens of tropical forest tree species show strong spatial repulsion, some to surprising distances of approximately 100 meters. We used simulations to show that such strong repulsion can only occur if CNDD considerably exceeds heterospecific negative density dependence-an even stronger condition required for coexistence-and that large-scale repulsion can indeed result from small-scale CNDD. These results demonstrate substantial niche differences between species that may stabilize species diversity.

Effects of endozoochory and diploendozoochory by captive wild mammals on Juniperus deppeana seeds

Carnivorous mammals disperse seeds through endozoochory and diploendozoochory. The former consists of ingestion of the fruit, passage through the digestive tract, and expulsion of the seeds, a process that allows scarification and dispersal of the seeds over long or short distances. The latter is typical of predators that expel seeds that were contained in the prey and the effects of which may differ from those of endozoochory with respect to the retention time of the seeds in the tracts, as well as their scarification and viability. The objective of this study was to conduct an experimental evaluation comparing the capacity of each mammal species in terms of the dispersal of Juniperus deppeana seeds and, at the same time, to compare this capacity through the two dispersal systems: endozoochory and diploendozoochory. We measured dispersal capacity using indices of recovery, viability, changes in testas, and retention time of seeds in the digestive tract. Juniperus deppeana fruits were collected in the Sierra Fría Protected Natural Area in Aguascalientes, Mexico, and were administered in the diet of captive mammals: gray fox (Urocyon cinereoargenteus), coati (Nasua narica) and domestic rabbits (Oryctolagus cuniculus). These three mammals represented the endozoochoric dispersers. For the diploendozoochoric treatment, seeds excreted by rabbits were incorporated into the diets of captive mammals: bobcat (Lynx rufus) and cougar (Puma concolor), in a local zoo. Seeds present in the scats were then collected, and recovery rates and retention times were estimated. Viability was estimated by X-ray optical densitometry and testa thicknesses were measured and surfaces checked using scanning electron microscopy. The results showed a recovery of seeds greater than 70% in all the animals. The retention time was <24 h in the endozoochory but longer at 24-96 h in the diploendozoochory (p < .05). Seed viability (x ¯  ± SD) was decreased in rabbits (74.0 ± 11.5%), compared to fruits obtained directly from the canopy (89.7 ± 2.0%), while gray fox, coati, bobcat, and cougar did not affect seed viability (p < .05). An increase in the thickness of the testas was also observed in seeds excreted from all mammals (p < .05). Through evaluation, our results suggest that mammalian endozoochory and diploendozoochory contribute to the dispersal of J. deppeana by maintaining viable seeds with adaptive characteristics in the testa to promote forest regeneration and restoration. In particular, feline predators can provide an ecosystem service through scarification and seed dispersal.

Dispersal ability and niche breadth influence interspecific variation in spider abundance and occupancy

The relationship between species local abundance and their regional distribution (occupancy) is one of the most extensively recognized and investigated patterns in ecology. While exceptions exist, the generally held model is that locally abundant species also tend to be more widespread geographically. However, there is only a limited understanding of both the mechanisms driving this relationship, and their scale dependency. Here we use occupancy and abundance data for 123 species of spider from across the Canary Islands to understand how both dispersal ability and niche breadth might mediate variation among species for local abundance and occupancy. We test the predictions that (i) dispersal ability explains variation among species for both abundance and occupancy, and (ii) species with a higher degree of habitat specialization, reflecting more limited niche breadth, will have both higher occupancy and abundance. We find no evidence within habitat patches for an effect of dispersal ability on either local abundance or site occupancy, while across all patches species with higher dispersal ability tend to occupy more sites. Species largely restricted to laurel forests have higher abundance than species with broader niche breadth, but similar occupancy. The study revealed that dispersal ability and niche breadth were significant predictors of the abundance-occupancy relationship, highlighting the importance of both factors for understanding patterns of abundance and occupancy among spider species.

Seed Size, Not Dispersal Syndrome, Determines Potential for Spread of Ricefield Weeds by Gulls

Recent field data suggest that migratory gulls disperse many rice field weeds by gut passage (endozoochory), most of which are dry fruited and widely assumed to have no long-distance dispersal mechanisms, except via human activity. We investigated this mechanism with a feeding experiment, in which seeds of five common rice field weeds (in order of increasing seed size: Juncus bufonius, Cyperus difformis, Polypogon monspeliensis, Amaranthus retroflexus, and the fleshy-fruited Solanum nigrum) were fed to seven individuals of lesser black-backed gulls Larus fuscus held in captivity. We quantified seed survival after collecting faeces at intervals for 33 h after ingestion, then extracting intact seeds and running germination tests, which were also conducted for control seeds. All five species showed high seed survival after gut passage, of >70%. Gut retention times averaged 2-4 h, but maxima exceeded 23 h for all species. Germinability after gut passage was 16-54%, and gut passage accelerated germination in J. bufonius and S. nigrum, but slowed it down in the other species. All species had lower germinability after gut passage compared to control seeds (likely due to stratification prior to the experiment), but the loss of germinability was higher in smaller seeds. There was no evidence that the different dispersal syndromes assigned to the five species (endozoochory, epizoochory or barochory) had any influence on our results. In contrast, mean gut retention time was strongly and positively related to seed size, likely because small seeds pass more quickly from the gizzard into the intestines. Non-classical endozoochory of dry-fruited seeds by waterbirds is a major but overlooked mechanism for potential long-distance dispersal, and more research into this process is likely essential for effective weed management.

The genome size, chromosome number and the seed adaption to long-distance dispersal of Ipomoea pes-caprae (L.)

Ipomoeapes-caprae (L.) (IPC) is a common species in tropical and subtropical coastal areas and one of the world's most widely distributed plants. It has attracted researchers for its outstanding biological, ecological and medicinal values. It has been reported that the genetic diversity of IPCs located on different continents is very low because of their frequent gene flow. During the long journey of evolution, every aspect of the plant morphologies has evolved to the best adaptivity to the environment, seeking their survival and progeny expansion. However, the fundamental genetic characteristics of IPC and how their seed adapted to the success of population expansion remain unknown. In this study, the fundamental genetic characteristics, including the genome size and the chromosome number of IPC, were investigated. The results showed that IPC's genome size is approximately 0.98-1.08 GB, and the chromosome number is 2n=30, providing the basic information for further genome analysis. In order to decipher the long-distance dispersal secret of this species, the fruit and seed developments, seed morphology, and seed germination were extensively investigated and described. The results showed an exquisite adaptive mechanism of IPC seeds to fulfil the population expansion via ocean currents. The large cavity inside the seeds and the dense tomenta on the surface provide the buoyancy force for the seeds to float on the seawater. The hard seed coats significantly obstructed the water absorption, thus preventing the seed from germination during the dispersal. Meanwhile, the fully developed embryos of IPC also have physiological dormancy. The physical and physiological characteristics of IPC seeds provide insight into the mechanism of their long-distance dispersal across the oceans. Moreover, based on morphological observation and semi-section microscopy, the development pattern of IPC glander trichomes was described, and their physiological functions were also discussed.

The morphological and ecological variation of Arctostaphylos (Ericaceae) fruit: A link between plant ecology and animal foraging behavior

Persistent soil seed banks are characteristic of Arctostaphylos (Ericaceae) species in the Mediterranean-climate California Floristic Province. While most species are obligate seeders, regeneration of stands of all Arctostaphylos species ultimately depends on post-fire seedling recruitment. Arctostaphylos seed banks are created, in large part, by scatter-hoarding rodents. Variation in fruit morphology, therefore, is expected to impact the Arctostaphylos-rodent interaction. Seeds produce sufficient rewards (nutritious mature embryo) to entice rodents to disperse and ultimately bury seeds in the soil. Hard seed coats increase the time required to extract the embryo, encouraging rodents to choose storage over immediate predation, and nutlets are frequently empty. We assessed the variation of fruit nutlet fusion and seed viability among 38 Arctostaphylos taxa. Factors such as latitude, elevation, life history, ploidy, and phylogenetic position were also analyzed. Generalized mixed-effects models were used to determine the factors contributing to variation in fruit nutlet fusion and seed viability. Our results indicate that fruit volume and shape are the most important variables affecting nutlet fusion and seed viability. Additionally, other potential influences only show a weak correlation and are not predicted to significantly impact nutlet fusion or seed viability. These findings provide insights into evolved strategies used by plants to increase reproductive success via scatter-hoarding rodents. Our study benefits the conservation and restoration of Arctostaphylos stands by emphasizing the importance of animal-mediated dispersal and providing estimates of seed viability for different species. With the anticipated effects of climate change, such as departures from historic fire regimes, the preservation of the relationship between plants and animal foragers is crucial for the continued survival of Arctostaphylos and California's evergreen chaparral.

Niche theory for positive plant-soil feedbacks

Interactions between plants and the soil are an important ecological process in terrestrial ecosystems as they affect plant community structure: when and where we find different plant species. Those interactions are typically thought of as one-directional: local soil conditions filter through dispersing species to produce a community of locally adapted plants. However, plants can modify local physicochemical soil conditions via their roots and associations with soil microbes. These may in turn affect the local fitness of other plants, making plant-soil interactions bidirectional. In order to understand how they differ from other ecological processes that structure plant communities, we need a theory connecting these individual-level plant-soil feedbacks to community-level patterns. Here, we build this theory with a mathematical model of plant community dynamics in which soil conditioning is explicitly modeled over time and depends on the density of the plants. We analyze this model to describe the long-term composition and spatial distribution of the plant community. Our main result is that positive plant-soil feedbacks will create clustering of species with similar soil preferences. The composition of these clusters is further influenced by niche width and conditioning strength. In contrast with competitive dynamics driven by niche overlap, only species belonging to the same cluster can maintain high relative abundance in the community. Spatial heterogeneity in the form of an environmental gradient generates patches, each representing a single cluster. However, such patchiness is disfavored when species differ in dispersal ability. We show that stronger dispersers cannot take over the habitat as long as an exogenous driver favors soil conditions that benefit the other species. If exogenous drivers supersede soil conditioning by plants, we retrieve classic habitat filtering, where species are selected based on their suitability to the local environment. Overall, we provide a novel mathematical model for positive plant-soil feedback that we use to describe the spatial patterns of plant abundance and traits related to soil preference and conditioning ability.

The effects of dispersal, herbivory, and competition on plant community assembly

Dispersal is a key process in community assembly but is often considered separately from downstream assembly processes (e.g., competition, herbivory). However, dispersal varies by species and can interact with other assembly processes through establishment as species enter communities. Here, we sought to distinguish the role of dispersal in community assembly and its interaction with two biotic assembly processes: competition and herbivory. We used a tallgrass prairie restoration experiment that manipulated the competitive and herbivore environments while allowing for natural dispersal and establishment from a diverse regional species pool into areas of low diversity. Dispersal, competition, and herbivory all influenced local communities. By tracking the spread of four target species across the plots, we found interspecific and intraspecific differences in establishment patterns, with herbivores influencing the number of individuals present and the distances species moved. At the community level, only dispersal and competition significantly influenced alpha diversity, but all three processes additively influenced community composition. There was also evidence of herbivore-competition and herbivore-colonization trade-offs in our experiment. Some species that could tolerate herbivory were less likely to establish in competitive environments, while others that could tolerate herbivory were more likely to disperse greater distances. More work is needed to understand the contexts under which dispersal variation affects community assembly and its synergy with other processes.

Effects of seed size and toucan regurgitation on the germination of the tropical tree Eugenia uniflora

Understanding the quality of seed dispersal effectiveness of frugivorous species can elucidate how endozoochory structures tropical forests. Large seeds, containing more resources for growth, and gut passage by frugivores, which remove seed pulp, both typically enhance the speed and probability of germination of tropical seeds. However, the interaction of seed size and gut passage has not been well studied. We assessed the role of two species of toucans (Ramphastos spp.) in seed germination of the tropical tree Eugenia uniflora, which produces seeds that vary considerably in size (3.7–14.3 mm), using 151 control and 137 regurgitated seeds in germination trials. We found that toucan regurgitation did not increase germination success, although 93.4% germinated compared to 76.8% of control seeds; however, larger seeds germinated more often at faster rates. Although only marginally significant, germination rates were 3.6× faster when seeds were both large and regurgitated by toucans, demonstrating that toucan regurgitation can disproportionally benefit larger E. uniflora seeds. As tropical forests are increasingly disturbed and fragmented by human activities, the ability of toucans to continue providing seed dispersal services to degraded habitats may be vital to the persistence of many tropical plants that contain larger seeds and depend on larger dispersers.

Unmasking the perching effect of the pioneer Mediterranean dwarf palm Chamaerops humilis L

Although farmlands are the most extensive terrestrial biomes, the abandonment of traditional agriculture in many parts of the world has brought opportunities and challenges for the restoration of such human-disturbed habitats. Seed arrival is a crucial necessary ecological process during plant recolonization that can be enhanced by the use of the so-called “perch plants”. Little is known, however, about whether the seed arrival via frugivorous birds is affected by the spatial distribution of the perch plants in disturbed habitats. To evaluate several spatial aspects of “perching” effect, we used a spatially explicit approach in two disturbed plots within the Doñana National Park (SW Spain). Specifically, we chose as study system the pioneer Mediterranean dwarf palm Chamaerops humilis L., which is often used as a perch by a variety of frugivorous bird species. A total of 289 C. humilis individuals were sampled in search of bird feces (N = 2998) and dispersed seeds (N = 529). Recorded seeds belonged to six different woody species from five different families. Nine bird species from six different families were recorded using C. humilis as perches. GLMs analyses indicated that taller C. humilis males with higher numbers of spatially associated woody species received more dispersed seeds. We detected a random spatial structure of bird feces and dispersed seeds in one study plot, while a nonrandom spatial structure was found in the other one, where isolated C. humilis received a higher number of bird feces and dispersed seeds than expected under spatial null models. The difference in spatial patterns between both study plots could relate, among other factors, to their different state of development in the ecological succession. Most of dispersed seeds were concentrated in a small number of C. humilis individuals, usually male and large ones, that acted as “hotspots” of seed arrival. The fact that frugivorous birds in one study site visited most often isolated C. humilis questions the aggregated spatial structure of revegetation designs typically used in restoration projects. This study reveals novel spatial aspects of the “perching” effect which could be helpful in the restoration of human-disturbed habitats worldwide.

Effect of Seed Traits and Waterbird Species on the Dispersal Effectiveness of Wetland Plants

Seed dispersal is an important ecological process in wetland ecosystems and helps maintain community structure and ecosystem biodiversity. Waterbird-mediated endozoochory is an effective and feasible dispersal mechanism for wetland plants; however, the influence of vectors and seed traits on this mechanism remains unclear. To investigate the effects of vector species and seed traits (length and lignin) on retention time, retrieval and germination of gut-surviving seeds, we fed Baikal teals (Anas formosa) and green-winged teals (Anas crecca) eight common plant seeds (Polygonum aviculare, Rumex dentatus, Polygonum orientale, Vallisneria natans, Ranunculus polii, Polygonum hydropiper, Carex cinerascen and Euphrasia pectinata) in the Shengjin Lake wetland (a Ramsar site). We collected fecal samples at intervals of 2-6 h for 36 h, and found that the percentage of recovered seeds differed significantly among teal and plant species (3%~30%); 94% of viable seeds were recovered within 12 h after feeding. Moreover, the germination rate of the recovered seeds (25%~56%) was higher than that of the control. The seed retention time was affected by seed lignin and disperser species; higher lignin made digestion difficult with higher retrieval. Smaller seeds passed through the guts but had no significant effect on recovered seeds. Seed length and disperser species showed no significant correlation with germination. These findings suggested endozoochory by dabbling ducks as an effective wetland seed dispersal mechanism.

Frugivory and Seed Dispersal by Carnivorans

Seed dispersal is critical to the ecological performance of sexually reproducing plant species and the communities that they form. The Mammalian order Carnivora provide valuable and effective seed dispersal services but tend to be overlooked in much of the seed dispersal literature. Here we review the literature on the role of Carnivorans in seed dispersal, with a literature search in the Scopus reference database. Overall, we found that Carnivorans are prolific seed dispersers. Carnivorans’ diverse and plastic diets allow them to consume large volumes of over a hundred families of fruit and disperse large quantities of seeds across landscapes. Gut passage by these taxa generally has a neutral effect on seed viability. While the overall effect of Carnivorans on seed dispersal quality is complex, Carnivorans likely increase long-distance dispersal services that may aid the ability of some plant species to persist in the face of climate change.

Functional Traits Drive Dispersal Interactions Between European Waterfowl and Seeds

Endozoochory by waterfowl is important for a broad range of angiosperms, most of which lack a fleshy fruit. This dispersal function contributes to the formation and maintenance of plant communities and may allow range shifts for plant species under global change. However, our current understanding of what seed or plant traits are important for this dispersal mechanism, and how they relate to variation in waterbird traits, is extremely limited. We addressed this question using a unique dataset identifying the plant species whose seeds are ingested by 31 different waterfowl species in Europe. We used RLQ and fourth-corner analyses to explore relationships between (1) bird morphological and foraging strategy traits, and (2) plant traits related to seed morphology, environmental preferences, and growth form. We then used Generalized Additive Models to identify relationships between plant/seed traits and the number of waterfowl species that disperse them. Although many waterfowl feed intentionally on seeds, available seed trait data provided little explanation for patterns compared to plant traits such as Ellenberg indicators of habitat preference and life form. Geese were associated with terrestrial plants, ingesting seeds as they graze on land. Diving ducks were associated with strictly aquatic plants, ingesting seeds as they feed at greater depths. Dabbling ducks ingest seeds from plants with high light and temperature requirements, especially shoreline and ruderal species growing in or around the dynamic and shallow microhabitats favored by these birds. Overall, the number of waterfowl vector species (up to 13 per plant species) increases for plants with greater soil moisture requirements and salinity tolerance, reflecting the inclination of most waterfowl species to feed in coastal wetlands. Our findings underline the importance of waterfowl dispersal for plants that are not strictly aquatic, as well as for plants associated with high salinities. Furthermore, our results reveal a soil moisture gradient that drives seed-bird interactions, in line with differences between waterfowl groups in their microhabitat preferences along the land-water continuum. This study provides an important advance in our understanding of the interactions that define plant dispersal in wetlands and their surroundings, and of what plants might be affected by ongoing changes in the distributions of waterfowl species.

Interactions with soil fungi alter density dependence and neighborhood effects in a locally abundant dipterocarp species

Seedling recruitment can be strongly affected by the composition of nearby plant species. At the neighborhood scale (on the order of tens of meters), adult conspecifics can modify soil chemistry and the presence of host microbes (pathogens and mutualists) across their combined canopy area or rooting zones. At local or small spatial scales (on the order of one to few meters), conspecific seed or seedling density can influence the strength of intraspecific light and resource competition and also modify the density-dependent spread of natural enemies such as pathogens or invertebrate predators. Intrinsic correlation between proximity to adult conspecifics (i.e., recruitment neighborhood) and local seedling density, arising from dispersal, makes it difficult to separate the independent and interactive factors that contribute to recruitment success. Here, we present a field experiment in which we manipulated both the recruitment neighborhood and seedling density to explore how they interact to influence the growth and survival of Dryobalanops aromatica, a dominant ectomycorrhizal tree species in a Bornean tropical rainforest. First, we found that both local seedling density and recruitment neighborhood had effects on performance of D. aromatica seedlings, though the nature of these impacts varied between growth and survival. Second, we did not find strong evidence that the effect of density on seedling survival is dependent on the presence of conspecific adult trees. However, accumulation of mutualistic fungi beneath conspecifics adults does facilitate establishment of D. aromatica seedlings. In total, our results suggest that recruitment near adult conspecifics was not associated with a performance cost and may have weakly benefitted recruiting seedlings. Positive effects of conspecifics may be a factor facilitating the regional hyperabundance of this species. Synthesis: Our results provide support for the idea that dominant species in diverse forests may escape the localized recruitment suppression that limits abundance in rarer species.

Habitat fragmentation alters the distance of abiotic seed dispersal through edge effects and direction of dispersal

Habitat loss and fragmentation are leading causes of species declines, driven in part by reduced dispersal. Isolating the effects of fragmentation on dispersal, however, is daunting because the consequences of fragmentation are typically intertwined, such as reduced connectivity and increased prevalence of edge effects. We used a large-scale landscape experiment to separate consequences of fragmentation on seed dispersal, considering both distance and direction of local dispersal. We evaluated seed dispersal for five wind- or gravity-dispersed, herbaceous plant species that were planted at different distances from habitat edges, within fragments that varied in their connectivity and shape (edge-to-area ratio). Dispersal distance was affected by proximity and direction relative to the nearest edge. For four of five species, dispersal distances were greater further from habitat edges and when seeds dispersed in the direction of the nearest edge. Connectivity and patch edge-to-area ratio had minimal effects on local dispersal. Our findings illustrate how some, but not all, landscape changes associated with fragmentation can affect the key population process of seed dispersal.

Cascading Impacts of Seed Disperser Loss on Plant Communities and Ecosystems

Seed dispersal is key to the persistence and spread of plant populations. Because the majority of plant species rely on animals to disperse their seeds, global change drivers that directly affect animals can cause cascading impacts on plant communities. In this review, we synthesize studies assessing how disperser loss alters plant populations, community patterns, multitrophic interactions, and ecosystem functioning. We argue that the magnitude of risk to plants from disperser loss is shaped by the combination of a plant species’ inherent dependence on seed dispersal and the severity of the hazards faced by their dispersers. Because the factors determining a plant species’ risk of decline due to disperser loss can be related to traits of the plants and dispersers, our framework enables a trait-based understanding of change in plant community composition and ecosystem functioning. We discuss how interactions among plants, among dispersers, and across other trophic levels also mediate plant community responses, and we identify areas for future research to understand and mitigate the consequences of disperser loss on plants globally.

Seed dispersal by wind decreases when plants are water-stressed, potentially counteracting species coexistence and niche evolution

Hydrology is a major environmental factor determining plant fitness, and hydrological niche segregation (HNS) has been widely used to explain species coexistence. Nevertheless, the distribution of plant species along hydrological gradients does not only depend on their hydrological niches but also depend on their seed dispersal, with dispersal either weakening or reinforcing the effects of HNS on coexistence. However, it is poorly understood how seed dispersal responds to hydrological conditions. To close this gap, we conducted a common-garden experiment exposing five wind-dispersed plant species (Bellis perennis, Chenopodium album, Crepis sancta, Hypochaeris glabra, and Hypochaeris radicata) to different hydrological conditions. We quantified the effects of hydrological conditions on seed production and dispersal traits, and simulated seed dispersal distances with a mechanistic dispersal model. We found species-specific responses of seed production, seed dispersal traits, and predicted dispersal distances to hydrological conditions. Despite these species-specific responses, there was a general positive relationship between seed production and dispersal distance: Plants growing in favorable hydrological conditions not only produce more seeds but also disperse them over longer distances. This arises mostly because plants growing in favorable environments grow taller and thus disperse their seeds over longer distances. We postulate that the positive relationship between seed production and dispersal may reduce the concentration of each species to the environments favorable for it, thus counteracting species coexistence. Moreover, the resulting asymmetrical gene flow from favorable to stressful habitats may slow down the microevolution of hydrological niches, causing evolutionary niche conservatism. Accounting for context-dependent seed dispersal should thus improve ecological and evolutionary models for the spatial dynamics of plant populations and communities.

Discovering the role of Patagonian birds in the dispersal of truffles and other mycorrhizal fungi

Dispersal is a key process that impacts population dynamics and structures biotic communities. Dispersal limitation influences the assembly of plant and microbial communities, including mycorrhizal fungi and their plant hosts. Mycorrhizal fungi play key ecological roles in forests by feeding nutrients to plants in exchange for sugars, so the dispersal of mycorrhizal fungi spores actively shapes plant communities. Although many fungi rely on wind for spore dispersal, some fungi have lost the ability to shoot their spores into the air and instead produce enclosed belowground fruiting bodies (truffles) that rely on animals for dispersal. The role of mammals in fungal spore dispersal is well documented, but the relevance of birds as dispersal agents of fungi has been understudied, despite the prominence of birds as seed dispersal vectors. Here, we use metagenomics and epifluorescence microscopy to demonstrate that two common, widespread, and endemic Patagonian birds, chucao tapaculos (Scelorchilus rubecula) and black-throated huet-huets (Pteroptochos tarnii), regularly consume mycorrhizal fungi and disperse viable spores via mycophagy. Our metagenomic analysis indicates that these birds routinely consume diverse mycorrhizal fungi, including many truffles, that are symbiotically associated with Nothofagaceae trees that dominate Patagonian forests. Epifluorescence microscopy of fecal samples confirmed that the birds dispersed copious viable spores from truffles and other mycorrhizal fungi. We show that fungi are a common food for both bird species and that this animal-fungi symbiosis is widespread and ecologically important in Patagonia. Our findings indicate that birds may also act as cryptic but critical fungal dispersal agents in other ecosystems.

Emergent spatial patterns of coexistence in species-rich plant communities

Statistical physics has proved essential to analyze multiagent environments. Motivated by the empirical observation of various nonequilibrium features in Barro Colorado and other ecological systems, we analyze a plant-species abundance model of neutral competition, presenting analytical evidence of scale-invariant plant clusters and nontrivial emergent modular correlations. Such first theoretical confirmation of a scale-invariant region, based on percolation processes, reproduces the key features in natural rainforest ecosystems and can confer the most stable equilibrium for ecosystems with vast biodiversity.

Maternal Environmental Light Conditions Affect the Morphological Allometry and Dispersal Potential of Acer palmatum Samaras

Seed dispersal plays critical roles in determining species survival and community structures. Since the dispersal is biologically under maternal control, it is hypothesized that intraspecific variation of dispersal potential and associated traits of seeds (diaspores) should be influenced by maternal habitat quality. We tested this hypothesis by examining the effects of maternal environmental light condition on morphological traits and descending performance of nearly 1800 wind-dispersed samaras collected from maple species Acer palmatum. Results showed that samaras produced by trees from shaded microhabitats had greater dispersal potential, in terms of slower terminal velocity of descent, than those produced in open microhabitats. This advantage was largely attributed to morphological plasticity. On average, samaras produced in shaded microhabitats, as compared to those produced in open habitats, had lower wing loading by only reducing weight but not area. In allometric details, in the large size range, samaras from shaded microhabitats had larger areas than those from open microhabitats; in the small size range, samaras from shaded microhabitats had wider wings. These findings suggest that greater dispersal potential of samaras in response to stressful maternal light environment reflected an active maternal control through the morphological allometry of samaras.

Tracking Animal-Dispersed Seedlings Using 15N Xylem Injection Method

Although various seed-marking methods have been developed for seed dispersal, it remains difficult to track the actual patterns of seed dispersal and seedling recruitment. Thus, new labeling methods that accurately track seedling establishment along with seed movement would help us better understand seed dispersal. Here, we developed a new nondestructive method using ¹⁵N xylem injection to track seed dispersal and seedling recruitment based on the enriched isotopic signals in the mature seeds. Our results first showed that xylem injection of ¹⁵N successfully enriched ¹⁵N both in the acorns and seedlings of Quercus variabilis. By marking acorns and seedlings with ¹⁵N stable isotopes, we successfully tracked seedlings established from acorns dispersed by seed-eating animals in the field. Our xylem ¹⁵N injection caused little alteration to seeds and showed no significant effects on seed selection by seed-eating animals as well as seed germination and seedling establishment, verifying the validity of the ¹⁵N xylem injection method to track seedling establishment. Our xylem ¹⁵N injection method is expected to be a powerful tool for tracking seed dispersal and seedling recruitment mediated by seed-eating animals in seed dispersal ecology.

Biogeomorphological processes and structures facilitate seedling establishment and distribution of annual plants: Implications for coastal restoration

Biogeomorphological processes and structures (BPS) can affect plant growth and community structure and promote landscape complexity in ecosystems. However, there is a lack of understanding of how BPS facilitates seedling establishment and distribution of annual plants and promotes the success of coastal restoration. We studied the relationships between seedling establishment of a native annual plant species (Suaeda salsa) and BPS resulting from crabs and plants in a middle elevation salt marsh with moderate tides (where inhabited generally high density of plants and crabs) in the Yellow River Delta of China. While there were many crabs but fewer plants in lower elevation areas with more frequent and stronger tides; and in higher elevation areas with weaker tides there were both fewer crabs and plants. Investigations and field manipulation experiments of microtopography, crabs and plants were conducted to determine if and how these BPS influenced seedling establishment and distribution under tidal influence in the middle elevation salt marshes. Results demonstrated that biogeomorphological structures, mainly concave hollows generated by crab burrowing and concave hollows around plant roots and stems under tidal influence, were associated with the trapping of seeds and influenced the establishment and distribution of seedlings. Additionally, upon senescence, maternal plants with unreleased seeds lodged on the ground and influenced seed retention and seedling establishment. The artificial concave hollows that were created experimentally also trapped many seeds and facilitated seedling establishment. Experimental plantings and creation of artificial hollow microtopography attracted crabs that created burrows, resulting in a positive feedback on seedling establishment. We used information obtained from the experimental component of the study to conduct a hollow microtopography manipulation to successfully restore degraded salt marshes. Understanding the associations between seedling establishment and biogeomorphological processes provides important insights for the utilization of natural or human ecosystem engineering to restore coastal vegetation ecosystems.

Emigrating Together but Not Establishing Together: A Cockroach Rides Ants and Leaves

AbstractSymbionts of ant colonies can hitchhike on winged ant reproductives (alates) during colony nuptial flights. Attaphila fungicola Wheeler, a miniature cockroach that lives in the nests of Texas leaf-cutter ants (Atta texana Buckley), hitchhikes on female alates (winged queens). Hitchhiking roaches are presumably vertically transmitted from leaf-cutter parent colonies to daughter colonies, remaining with female alates as they transition into foundresses (workerless queens); however, foundresses have limited resources and high mortality rates. Rather than remaining with foundresses likely to die (vertical transmission), roaches might abandon them during dispersal to infect higher-quality later stages of colony development (female alate-vectored transmission). In field experiments, I find evidence for female alate-vectored transmission and discover that roaches use a second hitchhiking step (riding foraged plant material) to infect established colonies. This work reveals a novel relationship between host dispersal and symbiont transmission and shows that colony development can be an important selection pressure on transmission.

Resistance Genes Affect How Pathogens Maintain Plant Abundance and Diversity

AbstractSpecialized pathogens are thought to maintain plant community diversity; however, most ecological studies treat pathogens as a black box. Here we develop a theoretical model to test how the impact of specialized pathogens changes when plant resistance genes (R-genes) mediate susceptibility. This work synthesizes two major hypotheses: the gene-for-gene model of pathogen resistance and the Janzen-Connell hypothesis of pathogen-mediated coexistence. We examine three scenarios. First, R-genes do not affect seedling survival; in this case, pathogens promote diversity. Second, seedlings are protected from pathogens when their R-gene alleles and susceptibility differ from those of nearby conspecific adults, thereby reducing transmission. If resistance is not costly, pathogens are less able to promote diversity because populations with low R-gene diversity suffer higher mortality, putting those populations at a disadvantage and potentially causing their exclusion. R-gene diversity may also be reduced during population bottlenecks, creating a priority effect. Third, when R-genes affect survival but resistance is costly, populations can avoid extinction by losing resistance alleles, as they cease paying a cost that is unneeded. Thus, the impact pathogens can have on tree diversity depends on the mechanism of plant-pathogen interactions. Future empirical studies should examine which of these scenarios most closely reflects the real world.

Global patterns of population genetic differentiation in seed plants

Evaluating the factors that drive patterns of population differentiation in plants is critical for understanding several biological processes such as local adaptation and incipient speciation. Previous studies have given conflicting results regarding the significance of pollination mode, seed dispersal mode, mating system, growth form and latitudinal region in shaping patterns of genetic structure, as estimated by F_ST values, and no study to date has tested their relative importance together across a broad scale. Here, we assembled a 337-species data set for seed plants from publications with data on F_ST from nuclear markers and species traits, including variables pertaining to the sampling scheme of each study. We used species traits, while accounting for sampling variables, to perform phylogenetic multiple regressions. Results demonstrated that F_ST values were higher for tropical, mixed-mating, non-woody species pollinated by small insects, indicating greater population differentiation, and lower for temperate, outcrossing trees pollinated by wind. Among the factors we tested, latitudinal region explained the largest portion of variance, followed by pollination mode, mating system and growth form, while seed dispersal mode did not significantly relate to F_ST . Our analyses provide the most robust and comprehensive evaluation to date of the main ecological factors predicted to drive population differentiation in seed plants, with important implications for understanding the basis of their genetic divergence. Our study supports previous findings showing greater population differentiation in tropical regions and is the first that we are aware of to robustly demonstrate greater population differentiation in species pollinated by small insects.

Advancing an interdisciplinary framework to study seed dispersal ecology

Although dispersal is generally viewed as a crucial determinant for the fitness of any organism, our understanding of its role in the persistence and spread of plant populations remains incomplete. Generalizing and predicting dispersal processes are challenging due to context dependence of seed dispersal, environmental heterogeneity and interdependent processes occurring over multiple spatial and temporal scales. Current population models often use simple phenomenological descriptions of dispersal processes, limiting their ability to examine the role of population persistence and spread, especially under global change. To move seed dispersal ecology forward, we need to evaluate the impact of any single seed dispersal event within the full spatial and temporal context of a plant's life history and environmental variability that ultimately influences a population's ability to persist and spread. In this perspective, we provide guidance on integrating empirical and theoretical approaches that account for the context dependency of seed dispersal to improve our ability to generalize and predict the consequences of dispersal, and its anthropogenic alteration, across systems. We synthesize suitable theoretical frameworks for this work and discuss concepts, approaches and available data from diverse subdisciplines to help operationalize concepts, highlight recent breakthroughs across research areas and discuss ongoing challenges and open questions. We address knowledge gaps in the movement ecology of seeds and the integration of dispersal and demography that could benefit from such a synthesis. With an interdisciplinary perspective, we will be able to better understand how global change will impact seed dispersal processes, and potential cascading effects on plant population persistence, spread and biodiversity.

Soil nutrients, forest structure and species traits drive aboveground carbon dynamics in an old-growth temperate forest

Forests store a substantial amount of terrestrial carbon (C), but the drivers of forest C dynamics remain poorly understood, especially in old-growth forests. Here, we evaluate how aboveground C dynamics (i.e., net C change and its demographic processes: C gain from the growth of surviving trees (∆C-surv), C gain from the growth of recruited trees (∆C-recr) and C loss by tree mortality (∆C-mort)) are driven by vegetation attributes (diversity, trait composition and forest structure) and habitat conditions (soil properties and light environment), as well as how ∆C-surv, ∆C-recr and ∆C-mort contribute to net C change. Using 10-year interval demographic data from a 9-ha permanent plot in an old-growth temperate forest in northeastern China, we performed structural equation model to relate the C dynamics to the vegetation attributes and habitat conditions. The net C change is most strongly determined by ∆C-mort. High soil phosphorus concentrations increased ∆C-surv, soil moisture increased ∆C-recr, and leaf area index increased both ∆C-surv and ∆C-recr. Diversity (i.e., structural diversity) had a positive relationship with ∆C-surv but was not related to ∆C-recr or ∆C-mort. Trait composition was significantly related to all three demographic processes. Forest structure was the best predictor of ∆C-surv and ∆C-recr. The net C change increased with higher soil phosphorus concentrations and basal area and in communities dominated by conservative traits (i.e., high wood density). This study highlights that soil nutrients, forest structure and trait composition are important drivers of net C change in old-growth temperate forests. Better insights into C storage and productivity can be gained by simultaneously evaluating the vegetation attributes and habitat conditions of C dynamics in natural ecosystems.

Animal movement drives variation in seed dispersal distance in a plant-animal network

Frugivores play differing roles in shaping dispersal patterns yet seed dispersal distance is rarely quantified across entire communities. We model seed dispersal distance using gut passage times and bird movement for the majority (39 interactions) of known bird-tree interactions on the island of Saipan to highlight differences in seed dispersal distances provided by the five avian frugivores. One bird species was found to be a seed predator rather than a disperser. The remaining four avian species dispersed seeds but differences in seed dispersal distance were largely driven by interspecific variation in bird movement rather than intraspecific variation in gut passage times. The median dispersal distance was at least 56 m for all species-specific combinations, indicating all species play a role in reducing high seed mortality under the parent tree. However, one species-the Micronesian Starling-performed 94% of dispersal events greater than 500 m, suggesting this species could be a key driver of long-distance dispersal services (e.g. linking populations, colonizing new areas). Assessing variation in dispersal patterns across this network highlights key sources of variation in seed dispersal distances and suggests which empirical approaches are sufficient for modelling how seed dispersal mutualisms affect populations and communities.