Dispersal Traits Research Articles

Partitioning intraspecific variation in seed dispersal potential using a low‐cost method for rapid estimation of samara terminal velocity

Abstract Seed or samara terminal velocity is a key trait affecting the dispersal potential of wind‐dispersed plants. However, this trait is often represented in dispersal models by a single mean value per species. This is despite considerable variation in dispersal traits within species and individuals that may have implications for both phenotypic selection and rates of spread. Methodological constraints may have acted as a barrier for robust assessments of intraspecific variation in seed terminal velocity. To quantify intraspecific variation in wind dispersal traits, we develop a low‐cost, time‐efficient method to measure the terminal velocity of a large number of samaras. We made three separate terminal velocity measurements for each of 750 Pinus radiata samaras, allowing partitioning of variation among individual cones, trees and source populations. We use the mechanistic WALD model to assess the potential influence of observed variation in samara terminal velocity on predicted dispersal kernels under a variety of realistic conditions. We demonstrate a twofold range in samara terminal velocity within P. radiata, with the highest variation occurring within individual cones, and the lowest among cones within individual trees. We identify a potential influence of source population on terminal velocity. Our modelling results demonstrate that this within‐species variation is sufficient to affect the shape of the predicted dispersal kernels, particularly the kernel tails and therefore the likelihood of long‐distance dispersal events. The effect of samara terminal velocity on dispersal is especially pronounced under environmental conditions that enhance seed dispersal. Our findings illustrate the scale of within‐species variation in a key dispersal trait, and the likely effect of this variation on dispersal distance. We suggest that the high level of variation observed within individual cones of P. radiata is likely to reduce the potential for phenotypic selection, and may either be indicative of a “bet‐hedging” strategy, or simply the result of the constraints of cone morphology on samara development. To obtain accurate dispersal models for wind‐dispersed species we highlight the necessity of capturing this variation for inclusion in future modelling approaches, and describe a device that can achieve such measurements easily and at low cost.

Trait and phylogenetic patterns reveal deterministic community assembly mechanisms on Mount St. Helens

Primary plant succession provides an excellent natural experiment to test ecological questions about community assembly following major disturbances. Temporal phylogenetic and functional trait dispersion patterns can give insight into the relative importance of stochastic and deterministic processes, as well as the potential identity of deterministic (biotic vs. abiotic) drivers (e.g. dispersal, growth, nutrient acquisition, and herbivore resistance ability). We used 28 years of plant composition data across four primary succession sites at Mount St. Helens (collected since the 1980 volcanic eruption) to examine phylogenetic dispersion and trait patterns over time. We expected to find more evidence of clustering or random phylogenetic patterns early in succession (where environmental filtering and stochasticity are thought to dominate), with a switch to overdispersion via processes such as niche differentiation later in succession. Contrary to expectations, phylogenetic relatedness and trait dispersion patterns were idiosyncratic. We found evidence of deterministic community assembly even early in succession, suggesting that both local-scale abiotic filtering and biotic interactions start playing a role shortly after the initiating disturbance. Traits were less predictive of successional patterns, with few consistent changes in trait distribution across all sites, even though the traits we examined are linked to the processes thought to be important during succession. Together, these results suggest that the drivers of community assembly during succession may be less generalizable and more complex than previously thought. We suggest that combining experiments and these analytical tools with long-term monitoring could be a useful step forward.

Alternate successional pathway yields alternate pattern of functional diversity

AbstractQuestionIn Eastern Canada, wildfires turn Picea mariana forests into Kalmia angustifolia dominated heath or P. mariana forest depending on burn severity. These alternate end‐points of succession provide an opportunity to test assumptions concerning alternate successional trajectories dominated by distinct plant functional groups. Disturbance effects on functional diversity (FD) have been studied largely in single post‐disturbance communities, but rarely applied to alternate successional pathways. Do post‐fire Kalmia heaths have lower FD than forest communities, and does heath formation select for a narrow range of traits leading to biotic homogenization?LocationTerra Nova National Park, Newfoundland, Canada.MethodsBased on five functional traits (specific leaf area, leaf dry matter content, seed mass, height, specific root length), we measured functional trait dispersion within (alpha FD) and between sites (beta FD). We calculated overall FD metrics in nine heath and four forest sites as well as metrics for three functional groups (trees, shrubs, and herbs) in each site. We also performed a complementary taxonomic diversity (TD) analysis to establish links between FD and TD.ResultsWe could not detect a difference in overall alpha TD between the two successional communities but found significant loss of alpha and beta FD in heaths and within tree and herb groups. Overall beta FD was lower in heaths than forests. It was also lower for trees and herbs, indicating an increase in functional similarity (functional homogenization) of the majority of life forms.ConclusionsBetween the two successional pathways, trait space occupancy was lower in heaths than forests. Heath formation in post‐fire communities consistently restricts functional dispersion (low alpha FD) of tree and herb traits leading to functional homogenization (low beta FD). When a successional trajectory leads to heath formation, it is accompanied by a loss of functional diversity.

Pollination and dispersal trait spectra recover faster than the growth form spectrum during spontaneous succession in sandy old‐fields

AbstractQuestionSpontaneous succession is the most natural and cost‐effective solution for grassland restoration. However, little is known about the time required for the recovery of grassland functionality, i.e., for the recovery of reproductive and vegetative processes typical of pristine grasslands. Since these processes operate at different scales, we addressed the question: do reproductive and vegetative processes require different recovery times during spontaneous succession?LocationKiskunság sand region (Central Hungary).MethodsAs combinations of plant traits can be used to highlight general patterns in ecological processes, we compared reproductive (pollination‐ and dispersal‐related) and vegetative (growth form) traits between recovered grasslands of different age (<10 years old; 10–20 years old; 20–40 years old) and pristine grasslands.ResultsDuring spontaneous succession, the reproductive trait spectra became similar to those of pristine grasslands earlier than the vegetative ones. In arable land abandoned for 10 years, pollination‐ and dispersal‐related trait spectra did not show significant difference to those of pristine grasslands; anemophily and anemochory were the prevailing strategies. Contrarily, significant differences in the growth form spectrum could be observed even after 40 years of abandonment; in recovered grasslands erect leafy species prevailed, while the fraction of dwarf shrubs and tussock‐forming species was significantly lower than in pristine grasslands.ConclusionsThe recovery of the ecological processes of pristine grasslands might require different amounts of time, depending on the spatial scale at which they operate. The reproductive trait spectra recovered earlier than the vegetative one, since reproductive attributes first determine plant species sorting at the regional level towards their respective habitats. The recovery of the vegetative trait spectrum needs more time as vegetative‐based interactions operate on a smaller spatial scale. Thus, vegetative traits might be more effective in the long‐term assessment of restoration success than the reproductive ones.

Using Functional Trait Diversity Patterns to Disentangle the Processes Influencing the Recovery of Subalpine Grasslands Following Abandonment of Agricultural Use

Grasslands in the Qinghai-Tibetan Plateau, as in much of the world, are increasingly degrading due to agriculture exploitation. Restoring such grasslands or facilitating recolonization to create late-successional communities requires an understanding of how communities within grasslands are structured within a secondary succession series. Here we studied community assembly using species abundance, soil nutrient levels, three functional traits (photosynthesis rate, seed mass and seed germination rate) in two comparable chronosequences of sub-alpine grasslands in the Qinghai-Tibetan Plateau. These grasslands range from ‘natural grassland’ (without human managements), to those that have been excluded from agricultural exploitation for 4 to 13 years. We were interested in shifts in functional trait diversity (FD; the value and range of functional traits in a community) and trait dispersion represented by the differences between observed FD and the expectation under neutral assembly. We found that a series of abiotic and/or biotic filters significantly influenced the success of species in different successional states, leading to systematic shifts in plant life history strategies from traits that indicated high relative growth rate to traits that signified highly competitive ability. We also found comparable community assembly processes between 13-year and natural grasslands, where hierarchical competition led to the exclusion of forb species by graminoid species and facilitation induced by legume species. Our results have three implications for degraded subalpine grasslands caused by agriculture exploitation in Qinghai Tibetan plateau. First, in the course of the abandonment of agricultural use and the return from degraded to natural grasslands, deterministic processes induced a shift in plant strategies from rapid relative growth rate under low N competition to slow relative growth rate under high N competition. Second, active seeding of graminoid and legume species may reduce the hierarchical competition, which in turn speedup recovery from agriculture exploitation. Finally, monitoring FD and trait dispersion patterns may be a good way to evaluate the restoration efforts in degraded grasslands caused by agriculture exploitation in Qinghai Tibetan plateau, due to the close connection of functional attributes (e.g., growth, colonization, recruitment and resource competition) and natural state of this ecosystem.

Choices of sampling method bias functional components estimation and ability to discriminate assembly mechanisms

Abstract The understanding and prediction of species distributions have been advanced by the development of community assembly theories and functional trait‐based approaches. Coupled with null models, trait dispersion patterns are commonly used to gauge the relative importance of niche versus neutral‐based processes on shaping local communities. However, asymmetrical trait dispersion patterns of identical communities may artificially arise as a result of sampling methods choice. This non‐random filtering on traits is overlooked, and it may bias the estimation of functional components as well as the detection of underlying assembly mechanisms—especially for species‐rich arthropod communities. We sampled subtropical ground‐dwelling ant communities using a paired treatment design comprising pitfall traps and Winkler extractors (Winklers), two commonly used sampling techniques for terrestrial arthropods, in 17 shrublands and 33 secondary forest 400 m2 plots in Hong Kong to determine the effect of sampling filters on functional composition (community means of six morphological traits) and functional diversity (range and variance of individual traits; size and filling properties of multidimensional trait space) using a null model approach for each habitat. We found, as hypothesized, that sampling filters from different methods affected the trait composition and diversity of ant communities asymmetrically. In shrublands and forests, the trait compositions of communities sampled by pitfall traps were dominated by larger sized, slender‐shaped and long‐legged ants as compared to those sampled by Winklers. The latter method also underestimated the diversity of individual traits related to body size as well as the size and filling properties of multidimensional trait space. Our results highlight that the usage of particular sampling methods without prior knowledge on their potential filtering effects on traits can affect the detection of assembly processes, and interpretation of functional proxies, such as body size. Additional care should be taken when comparing trait components obtained from studies using different sampling methods, so as to distinguish the sampling artefacts from actual ecological phenomena. Hence, it is important to consider the potential biases that different sampling methods may introduce to functional trait‐based research.

Spatial reciprocity in the evolution of cooperation.

Cooperation is key to the survival of all biological systems. The spatial structure of a system constrains who interacts with whom (interaction partner) and who acquires new traits from whom (role model). Understanding when and to what degree a spatial structure affects the evolution of cooperation is an important and challenging topic. Here, we provide an analytical formula to predict when natural selection favours cooperation where the effects of a spatial structure are described by a single parameter. We find that a spatial structure promotes cooperation (spatial reciprocity) when interaction partners overlap role models. When they do not, spatial structure inhibits cooperation even without cooperation dilemmas. Furthermore, a spatial structure in which individuals interact with their role models more often shows stronger reciprocity. Thus, imitating individuals with frequent interactions facilitates cooperation. Our findings are applicable to both pairwise and group interactions and show that strong social ties might hinder, while asymmetric spatial structures for interaction and trait dispersal could promote cooperation.

Rapid changes in seed dispersal traits may modify plant responses to global change.

When climatic or environmental conditions change, plant populations must either adapt to these new conditions, or track their niche via seed dispersal. Adaptation of plants to different abiotic environments has mostly been discussed with respect to physiological and demographic parameters that allow local persistence. However, rapid modifications in response to changing environmental conditions can also affect seed dispersal, both via plant traits and via their dispersal agents. Studying such changes empirically is challenging, due to the high variability in dispersal success, resulting from environmental heterogeneity, and substantial phenotypic variability of dispersal-related traits of seeds and their dispersers. The exact mechanisms that drive rapid changes are often not well understood, but the ecological implications of these processes are essential determinants of dispersal success, and deserve more attention from ecologists, especially in the context of adaptation to global change. We outline the evidence for rapid changes in seed dispersal traits by discussing variability due to plasticity or genetics broadly, and describe the specific traits and biological systems in which variability in dispersal is being studied, before discussing some of the potential underlying mechanisms. We then address future research needs and propose a simulation model that incorporates phenotypic plasticity in seed dispersal. We close with a call to action and encourage ecologists and biologist to embrace the challenge of better understanding rapid changes in seed dispersal and their consequences for the reaction of plant populations to global change.

Cross‐scale effects of structural and functional connectivity in pond networks on amphibian distribution in agricultural landscapes

Abstract Connectivity in pond ecosystems is essential for amphibian population persistence. To test the role of connectivity, a diversity of scales accounting for the different processes underlying species distribution needs to be considered. Several approaches exist for accounting for the potential connectivity, mainly based on structural versus functional methods. Based on occupancy data, our aim was to assess the relative power of connectivity metrics in explaining amphibian distribution when accounting for cross‐scale effects from pond to network scales, and to identify network features relevant to amphibian conservation in agricultural landscapes in the Seine‐et‐Marne department (east of Paris, France). We propose an original analytical framework that allows examining different spatial scales of influence, with a focus on connectivity. We analyse the distribution of three amphibian species (Bufo bufo, Rana dalmatina, and Lissotriton vulgaris) in relation to various pond conditions (fish presence, water quality, and nearby woodland habitat) as well as connectivity using three connectivity approaches: (1) structural, (2) area‐functional based on potential migration areas, and (3) path‐functional based on the least accumulated cost paths. Values of landscape resistance were assigned according to a biological risk‐based approach that is proposed as an enhanced, transparent expert‐based approach. We further investigated cross‐scale effects in amphibian responses to the environment by assessing the relative importance of pond and network characteristics as well as their interactions. Despite some species‐specific characteristics, the area‐functional approach of connectivity was generally the most effective in explaining species distribution by emphasising the relevance of potential migration areas as conservation units. Although pond conditions usually had a greater influence than network connectivity, we highlighted important cross‐scale and threshold effects in species’ response to local conditions, to pond connectivity, and to the availability of potentially suitable terrestrial habitats in the networks. Our cross‐scale approach accounts for scale‐dependent processes that potentially underlie amphibian distribution such as habitat selection and metapopulation dynamics. Both structural and functional connectivity should be considered as complementary features of pond connectivity when dispersal traits are likely to be less limiting. From a management perspective, our results encourage conservation plans to combine functional network‐centred strategies with the preservation of local conditions. We give guidelines as to the features of such networks to help maintain amphibian populations in agricultural landscapes.

Landscape context mediates the relationship between plant functional traits and decomposition

It has been well demonstrated that several interacting endogenous and exogenous factors influence decomposition. However, teasing apart the direct and indirect effects of these factors to predict decomposition patterns in heterogenous landscapes remains a key challenge. At 157 locations in a temperate forest, we measured decomposition of a standard substrate (filter paper) over two years, the landscape context in which decomposition took place, and the functional composition of the woody species that contributed leaf litter to the forest floor where litter bags were placed. We tested for direct and indirect effects of landscape context and direct effects of forest functional composition on decay using structural equation modelling. We found that landscape context had direct effects on decay and indirect effects on decay via its influence on the functional composition of the surrounding forest. Forest functional composition also had direct effects on decay, but these effects decreased or disappeared completely over time. Moreover, community weighted mean trait values were better predictors of decay than functional dispersion of leaf traits, and leaf nitrogen content and carbon content were better predictors of decay than leaf dry matter content or leaf toughness. Our results highlight the importance of an integrative approach that examines the direct and indirect effects of multiple factors for understanding and predicting decomposition patterns across heterogenous landscapes.

What happens to glass eels after restocking in upland rivers? A long‐term study on their dispersal and behavioural traits

Abstract The European eel Anguilla anguilla is a critically endangered fish species as a result of human activities and climate change in river and oceanic ecosystems. Restocking using glass eels in continental freshwater areas is a potential conservation measure for enhancing local eel stocks and for conserving the species in aquatic habitats, where it may otherwise disappear. However, little is known about the fate of these restocked individuals and the early ecological behaviour of the young eels translocated in rivers. A portable radio‐frequency identification (RFID) telemetry system and 12‐mm tags were used to track restocked eels for a duration of 4 years. The aim was to understand the early movement, behavioural traits, dispersal, and habitat use of elvers after restocking performed in 2013 with glass eels in a shallow riverine environment. From the 241 tagged eels (total length, Q50 = 152 mm), 85% were detected in 1968 positions during a period of 4 years, beginning in 2014. Clear seasonality in eel activity was observed, with higher mobility in summer when the water temperature was high (above 12°C). Dispersal was slowed by numerous artificial obstacles and the high carrying capacity of habitats. There was a negative relationship between the body size of eels at tagging and their mobility. Five behavioural categories of mobility patterns were identified: ascending, descending, oscillating with an upstream trend, oscillating with a downstream trend, and stationary. The first four categories depleted with time, in favour of stationary individuals that displayed a highly sedentary lifestyle. This study provides new knowledge of the long‐term dispersal behaviour of restocked eels and the influence of seasons, barriers, and habitats on their colonization strategy changing with time. The results contribute to a better understanding of the issue of uncommon restocking practices in upland rivers.

Spatial patterns and determinants of trait dispersion in freshwater fish assemblages across Europe

AbstractAimUnderstanding how species assemble into assemblages and identifying the determinants of assembly processes remains a key challenge in ecology. Within assemblages, functional trait dispersion can be used to infer assembly processes, but this inference could depend on the trait considered. Here, using both single and multiple trait‐based approaches, we analysed dispersion patterns for alpha (i.e., related to niche partitioning) and beta (i.e., related to environmental tolerance) traits in freshwater fish assemblages and characterized how trait dispersion patterns vary along environmental gradients at large spatial scale.LocationWestern Palaearctic, 290 river catchments.Time periodContemporary.Major taxa studiedFreshwater fish.MethodsBased on freshwater fish occurrence records in 290 European river catchments, we computed dispersion indices (mean pairwise distance) using standardized effect sizes for each single trait and multiple traits. We then used linear models including climatic, geo‐morphological, biotic and human‐related factors to determine the key drivers shaping freshwater fish dispersion patterns across Europe.ResultsWe highlighted spatial variation in trait dispersion, with both underdispersion and overdispersion simultaneously observed for a given trait, but also distinct patterns of trait dispersion, even within beta and alpha traits. We provided evidence that elevation range and current and past climatic conditions mainly structured trait dispersion patterns. Finally, our results revealed that spatial patterns in trait dispersion based on multiple traits were less pronounced than those based on individual traits.Main conclusionsOur results highlighted that traits showed different spatial and environmental patterns, reflecting different ecological patterns. This could lead to potential problems when using functional indices computed on multiple traits and challenges their relevance to describe diversity patterns and to infer the assembly processes shaping community structure.

Factors influencing aquatic and terrestrial bacterial community assembly.

During recent years, many studies have shown that different processes including drift, environmental selection and dispersal can be important for the assembly of bacterial communities in aquatic and terrestrial ecosystems. However, we lack a conceptual overview about the ecological context and factors that influence the relative importance of the different assembly mechanisms and determine their dynamics in time and space. Focusing on free-living, i.e., nonhost associated, bacterial communities, this minireview, therefore, summarizes and conceptualizes findings from empirical studies about how (i) environmental factors, such as environmental heterogeneity, disturbances, productivity and trophic interactions; (ii) connectivity and dispersal rates (iii) spatial scale, (iv) community properties and traits and (v) the use of taxonomic/phylogenetic or functional metrics influence the relative importance of different community assembly processes. We find that there is to-date little consistency among studies and suggest that future studies should now address how (i)-(v) differ between habitats and organisms and how this, in turn, influences the temporal and spatial-scale dependency of community assembly processes in microorganisms.

The evolution of dispersal traits based on diaspore features in South American populations of Senecio madagascariensis (Asteraceae)

Plant invasion success is influenced by several driving factors such as the dispersal, environmental conditions and the species characteristics. In wind dispersed plants, the dispersal traits and the altitude are key for predicting dispersal ability. In this work, we estimated this feature in Senecio madagascariensis invasive populations from Argentina and Brazil using diaspore traits to understand its dynamics. Our results show that dispersal is strongly affected by the geographic conditions. We observed that in Argentinian populations growing at higher altitudes, selection favours larger seeds, which might favour seedling establishment over of longer dispersal distance. Conversely, populations grouped in lower altitudes show higher dispersal ability, probably due to the adaptation to environment and assortment of the better dispersal genotypes. In contrast, the Brazilian populations display rapid dispersal ability due to recent colonisation and multiple introductions. The variability in the gene pool could facilitate the occurrence of genotypes with greater dispersal, which could explain why these populations display greater dispersal ability than the Argentine ones. In conclusion, the phenotypic response to geographic conditions and the population density play an important role in the dispersion strategies in S. madagascariensis.

Relative effects of elevational and habitat constraints on alpine spring biodiversity

Global climatic changes and local disturbances may alter composition and distribution of spring invertebrates in mountains. In this study, we compared the effects of elevation, landscape and local characteristics on spring biodiversity. At 16 springs (from 570 to 1650 m a.s.l.) in The Chartreuse Range (French Alps) benthic, vegetation, and interstitial habitats were sampled in summer for aquatic invertebrate assemblage structure (abundances, richness, reproduction and dispersal traits, functional feeding groups). Assemblages were related to geographic location (elevation), landscape characteristics and local variables. Elevation was the major driver of the fauna: taxonomic richness and the percentage of scrapers decreased with elevation, while the proportion of predators and species with an asexual reproduction increased with elevation. The landscape characteristics around the spring had a weak influence on the benthic taxonomic richness which increased with the percentage of forest and decreased with the proportion of grassland. Finally, the habitat characteristics had no effect on taxonomic richness, but partially control the abundances of benthic assemblages and sediment-feeder organisms that both decreased with increasing sediment grain size. Current and future changes in the temperature patterns would affect alpine spring fauna, but disturbance of the local characteristics of springs must not be neglected.

Effects of mis-alignment between dispersal traits and landscape structure on dispersal success in fragmented landscapes.

Dispersal is fundamental to population dynamics and hence extinction risk. The dispersal success of animals depends on the biophysical structure of their environments and their biological traits; however, comparatively little is known about how evolutionary trade-offs among suites of biological traits affect dispersal potential. We developed a spatially explicit agent-based simulation model to evaluate the influence of trade-offs among a suite of biological traits on the dispersal success of vagile animals in fragmented landscapes. We specifically chose traits known to influence dispersal success: speed of movement, perceptual range, risk of predation, need to forage during dispersal, and amount of suitable habitat required for successful settlement in a patch. Using the metric of relative dispersal success rate, we assessed how the costs and benefits of evolutionary investment in these biological traits varied with landscape structure. In heterogeneous environments with low habitat availability and scattered habitat patches, individuals with more equal allocation across the trait spectrum dispersed most successfully. Our analyses suggest that the dispersal success of animals in heterogeneous environments is highly dependent on hierarchical interactions between trait trade-offs and the geometric configurations of the habitat patches in the landscapes through which they disperse. In an applied sense, our results indicate potential for ecological mis-alignment between species' evolved suites of dispersal-related traits and altered environmental conditions as a result of rapid global change. In many cases identifying the processes that shape patterns of animal dispersal, and the consequences of abiotic changes for these processes, will require consideration of complex relationships among a range of organism-specific and environmental factors.

Species distribution models (SDM): applications, benefits and challenges in invasive species management.

Abstract The use of species distribution models (SDM) is of increasing popularity when studying biological invasions, e.g. to assess the impact of climate change on invasive species, to prioritize conservation measures, or to study invasive evolutionary biology. SDM correlate known occurrences of species with environmental variables and predict a species' potential distribution on other geographies over space and time. Today, SDM are widely used to produce invasion risk maps by delineating probable risk areas based on climatic suitability for a species. These maps can guide early detection and rapid response measures. While recent developments in modelling approaches and wider availability of environment datasets have helped to create better and more accurate SDM, in many cases the used models ignore the associated underlying ecological processes for e.g. dispersal and biotic interactions and thus provide only an incomplete picture of invasion risks. In this paper, we present a review of the most common applications of SDM in invasive species management and provide an overview of possible solutions to various challenges like uncertainty and transferability associated with them. Based on our review we conclude that ways towards more accurate model outputs include fitting models with existing ecological knowledge (hybrid models), address uncertainty and biotic interactions and link species dispersal traits with projections of species distributions. In the future, work is required on developing more hybrid approaches and models that addresses both local diffusion and long distance movement of alien species.

Landscape permeability and individual variation in a dispersal-linked gene jointly determine genetic structure in the Glanville fritillary butterfly.

There is now clear evidence that species across a broad range of taxa harbor extensive heritable variation in dispersal. While studies suggest that this variation can facilitate demographic outcomes such as range expansion and invasions, few have considered the consequences of intraspecific variation in dispersal for the maintenance and distribution of genetic variation across fragmented landscapes. Here, we examine how landscape characteristics and individual variation in dispersal combine to predict genetic structure using genomic and spatial data from the Glanville fritillary butterfly. We used linear and latent factor mixed models to identify the landscape features that best predict spatial sorting of alleles in the dispersal‐related gene phosphoglucose isomerase (Pgi). We next used structural equation modeling to test if variation in Pgi mediated gene flow as measured by Fst at putatively neutral loci. In a year when the population was recovering following a large decline, individuals with a genotype associated with greater dispersal ability were found at significantly higher frequencies in populations isolated by water and forest, and these populations showed lower levels of genetic differentiation at neutral loci. These relationships disappeared in the next year when metapopulation density was high, suggesting that the effects of individual variation are context dependent. Together our results highlight that (1) more complex aspects of landscape structure beyond just the configuration of habitat can be important for maintaining spatial variation in dispersal traits and (2) that individual variation in dispersal plays a key role in maintaining genetic variation across fragmented landscapes.

The double role of pigmentation and convolute leaves in community assemblage of Amazonian epiphytic Lejeuneaceae

BackgroundEpiphytic bryophyte communities in the Amazon forest show a vertical gradient in species composition along the trunk of the host trees. The investigation of species traits related to this pattern has focused on the physiology of selected taxa with a clear preference for one of the extremes of the gradient. Although some species are indeed only found on the tree base or in the outer canopy, the vertical gradient is composed mainly by the variation in the abundances of species with a broader occurrence along the height zones. Therefore, this study approaches the differences among community assemblages, rather than among species, to test the role of morphological and dispersal traits on the establishment of the vertical gradient in species composition.MethodsA character state matrix was built for 104 species of the family Lejeuneaceae recorded as epiphytes in the Amazonian terra firme forests, and six binary traits supposed to influence species occurrence: dark pigmentation on leaves; ability to convolute leaves when drying; possession of thickened cell walls; reproduction mode (monoicous or dioicous); occurrence of asexual reproduction; and facultative epiphyllous habit. Based on a previous dataset on community composition along the vertical gradient, trait occurrences in random draws of the metacommunity was compared to trait occurrences in field data, in order to detect significant deviations in the different height zones.ResultsFour out of the six traits tested showed significantly higher or lower occurrence in the species composition of canopy and/or understory communities. Traits related to high dispersal ability did not vary much along the vertical gradient; although facultative epiphylls were overrepresented on tree base. Dark pigmentation and convolute leaves were significantly more frequent in the canopy communities, but also significantly less frequent in communities at the base of the tree.DiscussionDark pigmentation and convolute leaves seem to be advantageous for the establishment in the canopy zones. They may, respectively, prevent light damage and allow longer periods of photosynthesis. Interestingly, these traits occur randomly along the trunk, but are wiped out of communities on the tree base. In the relatively deep shade of the first meters of the understory, they possibly hamper net carbon gain, the first by darkening the leaf surface and the second by delaying desiccation—which can be damaging under high temperatures and low light. The fact that production of asexual propagules is not overrepresented in the most dynamic microenvironment along the gradient, the canopy, challenges current views of bryophyte life strategy theory.

Synzoochory: the ecological and evolutionary relevance of a dual interaction.

ABSTRACTSynzoochory is the dispersal of seeds by seed‐caching animals. The animal partner in this interaction plays a dual role, acting both as seed disperser and seed predator. We propose that this duality gives to synzoochory two distinctive features that have crucial ecological and evolutionary consequences. First, because plants attract animals that have not only positive (seed dispersal) but also negative (seed predation) impacts on their fitness, the evolution of adaptations to synzoochory is strongly constrained. Consequently, it is not easy to identify traits that define a synzoochorous dispersal syndrome. The absence of clear adaptations entails the extra difficulty of identifying synzoochorous plants by relying on dispersal traits, limiting our ability to explore the full geographic, taxonomic and phylogenetic extent of synzoochory. Second, the positive and negative outcomes of interactions with synzoochorous animals are expressed simultaneously. Consequently, synzoochorous interactions are not exclusively mutualistic or antagonistic, but are located at some point along a mutualism–antagonism continuum. What makes synzoochory interesting and unique is that the position of each partner along the continuum can be evaluated for every plant–animal interaction, and thus the continuum can be precisely described by assessing the relative frequency of positive and negative interaction events in each pairwise interaction. Herein we explore these two main features of synzoochory with a comprehensive quantitative survey of published studies on synzoochory. Synzoochory has been recorded for at least 1339 plant species differing in life forms, from annual and short‐lived herbs to long‐lived trees, belonging to 641 genera and 157 families widely distributed across the globe and across the seed plant phylogeny. Over 30 animal families belonging to five disparate taxonomic groups (rodents, marsupials, birds, insects, and land crabs) potentially act as synzoochorous dispersers. Although synzoochory appears to be fundamentally a secondary dispersal mode, many abundant and dominant trees are primarily synzoochorous. In addition, we found evidence of the existence of diplosynzoochory (caching animals acting both as primary and secondary dispersers of the same individual seed), mostly in nut‐bearing trees. Finally, we found that synzoochorous interactions are widely spread across the mutualism–antagonism continuum. Nevertheless, there were some differences among disperser species and functional groups. Corvids and some rodents (cricetids, nesomyids, sciurids) were located in the positive‐effects region of the continuum and presumably behave mostly as dispersers, whereas land crabs and insects were located in the negative‐effects extreme and behave mostly as seed predators. Our review demonstrates that synzoochory is not an anecdotal ecological interaction. Rather, it is pivotal to the functioning of many ecosystems where the natural regeneration of keystone plant species depends on the activity of granivorous animals that play a dual role. This distinctive interaction should not be ignored if we wish to have an accurate understanding of the functioning of natural systems.