Pervasive effects of dispersal limitation on within- and among-community species richness in agricultural landscapes

Aim To determine whether the effect of habitat fragmentation and habitat heterogeneity on species richness at different spatial scales depends on the dispersal ability of the species assemblages and if this results in nested species assemblages. Location Agricultural landscapes distributed over seven temperate Europe countries covering a range from France to Estonia. Methods We sampled 16 local communities in each of 24 agricultural landscapes (16 km²) that differ in the amount and heterogeneity of semi‐natural habitat patches. Carabid beetles were used as model organisms as dispersal ability can easily be assessed on morphological traits. The proximity and heterogeneity of semi‐natural patches within the landscape were related to average local (alpha), between local (beta) and landscape (gamma) species richness and compared among four guilds that differ in dispersal ability. Results For species assemblages with low dispersal ability, local diversity increased as the proximity of semi‐natural habitat increased, while mobile species showed an opposite trend. Beta diversity decreased equally for all dispersal classes in relation to proximity, suggesting a homogenizing effect of increased patch isolation. In contrast, habitat diversity of the semi‐natural patches affected beta diversity positively only for less mobile species, probably due to the low dispersal ability of specialist species. Species with low mobility that persisted in highly fragmented landscapes were consistently present in less fragmented ones, resulting in nested assemblages for this mobility class only. Main conclusions The incorporation of dispersal ability reveals that only local species assemblages with low dispersal ability show a decrease of richness as a result of fragmentation. This local species loss is compensated at least in part by an increase in species with high dispersal ability, which obscures the effect of fragmentation when investigated across dispersal groups. Conversely, fragmentation homogenizes the landscape fauna for all dispersal groups, which indicates the invasion of non‐crop habitats by similar good dispersers across the whole landscape. Given that recolonization of low dispersers is unlikely, depletion of these species in modern agricultural landscapes appears temporally pervasive.     

Dispersal modes affect tropical forest assembly across trophic levels

We examined assemblages of trees and two major groups of vertebrate seed dispersers, birds and primates, in Ugandan protected areas to evaluate the roles of dispersal limitation and species sorting in community assembly. We conducted partial Mantel tests to investigate relationships between community similarity, environmental distance and geographic distance. Results showed that environmental factors, specifically temperature and rainfall, significantly and more strongly structured tree assemblages than geographic distance. Analysis of tree dispersal modes revealed wind‐dispersed tree guilds were significantly dispersal limited but trees dispersed by animals were not. For assemblages of vertebrate seed dispersers, dispersal limitation significantly and more strongly structured assemblages of primates than species sorting whereas environmental factors significantly and more strongly structured assemblages of birds than dispersal limitation. We therefore examined whether trees dispersed by primates were more dispersal limited than trees dispersed by birds. We found consistent trends that primate fruit trees were more dispersal limited than bird fruit trees using three definitions of dispersal syndromes based on fruit color. Our results suggest that the dispersal abilities of primary consumers may affect the distribution of primary producers at large spatial scales.     

Dispersal spectra,diaspore size and the importance of endozoochory in the equatorial Andean montane forests

The dispersal syndrome hypothesis states that plant diaspores show morphological features that are the results of adaptation for dispersal by a particular vector. This can enable to identify the relative importance of dispersal agents within plant communities. Nevertheless, there is still little information about seed dispersal spectra and diaspore traits related to different dispersal agents in the equatorial montane forests, despite their high biodiversity and important ecosystem services as watersheds for human communities. Due to an increase in environmental stress at high elevations a reduction in the prevalence of endozoochory, and a reduction in the size of endozoochorous diaspores in plant assemblages could be expected. We reviewed published data from 64 Andean cloud forest plots to assess the dispersal spectra, the incidence of different traits related to seed dispersal, and the distribution of dispersal syndromes within cloud forests of northern South America. We then evaluated two questions related to seed dispersal in these forests: (1) Does the number and percentage of endozoochorous species in woody plant assemblages decrease at higher elevation? and (2) Does the mean diaspore size of endozoochorously dispersed tree assemblages decrease with elevation?     

Concordance among stream assemblages and spatial autocorrelation along a fragmented gradient

Patterns of spatial autocorrelation of biota and distributional similarity (concordance) between assemblages of different organism groups have important implications in both theoretical ecology and biodiversity conservation. Here we report environmental gradients and spatial distribution patterns of taxonomic composition among stream fish, benthic macroinvertebrate, and diatom assemblages along a fragmented stream in south‐western France. We quantified spatial patterns of lotic assemblage structure along this stream, and we tested for concordance in distribution patterns among the three taxonomic groups. Our results showed that both environmental characteristics and stream assemblages were spatially autocorrelated. For stream fish and diatom assemblages, these patterns reflected assemblage changes along the longitudinal stream gradient, whereas environmental variables and benthic macroinvertebrates exhibited a more patchy spatial pattern. Cross‐taxa concordance was significant between stream fish and diatoms, and between stream fish and benthic macroinvertebrates. The assemblage concordance between stream fish and diatoms could be attributed to similar responses along the longitudinal gradient, whereas those between stream fish and benthic macroinvertebrates may result from biotic interactions. Based on potential dispersal capacities of taxa, our results validated the hypotheses that weakly dispersing taxa exhibit greater concordance than highly dispersing ones and that dispersal capacities affect how taxonomic groups respond to their local environment. Both diatoms and highly dispersing stream fish were affected by stream fragmentation (i.e. the number of dams between sites), while the effect of fragmentation was not significant for invertebrates that fly well in their adult stage, thus emphasizing the importance of the way of dispersal. These results suggest that addressing the effects of dispersal capacity on stream assemblage patterns is crucial to identifying mechanisms behind patterns and to better understanding the determinants of stream biodiversity.     

Spatial averaging and disturbance lead to high productivity in aquatic metacommunities

Dispersal in heterogeneous ecosystems, such as coastal metacommunities, is a major driver of diversity and productivity. According to theory, both species richness and spatial averaging shape a unimodal relationship of productivity with dispersal. We experimentally tested the hypothesis that disturbances acting on local patches would buffer the loss of productivity at high dispersal by preventing synchronized species oscillations. To simulate these disturbances, our experimental assemblages involved species that self‐organized in isolation under three inflow pulsing frequencies, where hydraulic displacement and nutrient loading affected assemblage diversity and composition. At steady‐state, the emerging isolated assemblages were connected at three levels of dispersal creating three metacommunities of different connectivity. Consistent with theory, as dispersal increased, species richness in the metacommunity declined; productivity however remained high. This occurred because the most productive species in our study (which dominated the isolated patch of intermediate inflow pulsing frequency) dominated all three patches (low, intermediate and high inflow pulsing frequencies) after dispersal commenced in our metacommunities. This experimental result provides empirical support for the mechanism of spatial averaging. Furthermore, disturbances, in the form of localized pulsed inflows, prevented population oscillation synchrony caused by homogenization. Overall, our observations suggest that localized environmental fluctuations and the identity of species seem to be more influential than dispersal in shaping the diversity and composition of phytoplankton assemblages and stabilizing productivity.     

Vertical stratification of rainforest collembolan (Collembola: Insecta) assemblages: description of ecological patterns and hypotheses concerning their generation

We describe a complex vertical stratification of collembolan assemblages from rainforest leaf litter samples and identify distinct assemblages associated with forest floor, lower canopy and upper canopy samples. Leaf litter samples were collected from the forest floor and deposits of leaf litter suspended in epiphytes in the canopy of a subtropical rainforest site at Lamington National Park in southeast Queensland. The patterns of relationship among assemblages of Collembola extracted from these samples were examined using a variety of analyses of a matrix of similarities between samples. The results of ANOSIM analyses showed that forest floor, lower canopy and tipper canopy samples formed discrete groups. These results permit a discussion of these groups as three distinct collembolan assemblages. Analysis of the dissimilarities between these assemblages revealed a gradient of similarity from the forest floor through the lower to the upper canopy. This gradient represents a more complex vertical stratification than has previously been identified in rainforest canopy arthropods. We suggest that limitations on the dispersal of some forest floor species into the canopy may be responsible for this pattern. We also identify a second gradient of similarities among these assemblages. We show that dissimilarity among samples from forest floor is significantly lower than dissimilarity among samples from within the lower canopy, and that the level of dissimilarity between samples from within the upper canopy is significantly higher again. We suggest that dispersal barriers and higher probabilities of extinction in upper canopy collembolan colonies may be responsible for higher heterogeneity of species composition and abundance among samples from the upper canopy. We outline a number of testable hypotheses aimed at determining the importance of these processes in producing the patterns we have observed.     

Environmental and spatial controls of biotic assemblages in a discrete semi‐terrestrial habitat: comparison of organisms with different dispersal abilities sampled in the same plots

Aim The development of metacommunity theory inspired a series of studies exploring the importance of environmental and spatial effects on the composition of biotic assemblages. However, the comparison of different groups of organisms has been hampered by differences in sampling design, spatial scales or the environmental variables involved. Our aim was to test how dispersal ability affects metacommunity structure and associated species distributions by sampling different species groups in the same plots to avoid these problems. Location Western Carpathian Mountains (Europe). Methods In 191 fens we sampled the composition of diatom, bryophyte, vascular plant and mollusc assemblages, water chemistry, and macroclimatic data. We then generated spatial variables covering all relevant spatial scales using analysis of principal coordinates of neighbour matrices (PCNM). We applied the adjusted variation partitioning algorithm to quantify the effects of environment and space. Results Pure effects of water chemistry and space were highly significant for all groups of organisms. Spatial effects were stronger for groups with larger propagules (vascular plants, molluscs) than for those with smaller propagules (diatoms, bryophytes). Assemblages of macroscopic bryophytes were structured slightly less by geography and much more by environment than were those of microscopic diatoms. Vascular plant and mollusc assemblages turned out to be more spatially structured (as compared to diatom and bryophyte assemblages), with small differences between the two groups. Coarse‐scale spatial effects dominated in the bryophyte metacommunity, while in the other groups, including diatoms, finer‐scale effects were also important. Main conclusions Given that our analyses are based on a standardized sampling and analytical framework, our findings provide strong support for the hypothesis that both environmental and spatial variables structure metacommunities of organisms with very different dispersal abilities, including microscopic diatoms. In addition, we show for the first time that the strengths of these effects and their scale dependence may be predicted using important trait differences between organisms, for example differences in propagule size.     

Determining vulnerability of stream communities to climate change at the landscape scale

1. As the climate changes, species are expected to shift to higher latitudes and altitudes where suitable habitat is available if dispersal is not constrained by geographic barriers. We analyse patterns of turnover in freshwater macroinvertebrate assemblages to identify which communities are most likely to be at risk from climate change, and the location of geographic barriers that could impede such adaptive range shifts. 2. We analysed macroinvertebrate data from standard biological assessments at the family level, from surveys of all coastal basins of New South Wales, Australia, covering a latitudinal gradient of more than 1000 km. We used variance partitioning to separate the variation in composition explained by climate, among‐site distance, human disturbance and other stream factors. 3. Montane stream assemblages showed high turnover in response to climatic variation. Turnover in coastal‐fringe streams was least affected by climate, but strongly correlated with distance and stream variables. Significant shifts in assemblage composition occurred between habitats within catchments and across catchment boundaries. 4. Montane stream assemblages are most vulnerable to climate change because their distribution is most responsive to climatic factors, and elevated sites are isolated from one another, reducing the scope for altitudinal migration. Dispersal limitations in coastal‐fringe assemblages will also increase their vulnerability to habitat loss from sea‐level rise. For all stream classes, the separation of many neighbouring catchment assemblages, owing to either limited dispersal or the lack of suitable habitat, is likely to constrain adaptive range shifts. This would lead to an overall reduction in beta diversity among reaches and subsequently to a reduction in landscape‐level gamma diversity.     

Phylogenetic and functional diversity area relationships in two temperate forests

Phylogenetic diversity (PD, the diversity of lineages) and functional diversity (FD, the diversity of functional traits or groups in a biological community) reflect important yet poorly understood attributes of species assemblages. Until recently, few studies have examined the spatial variation of PD and FD in natural communities. Yet the relationships between PD and FD and area (termed PDAR and FDAR), like the analogous species–area relationship (SAR), have received less attention and may provide insights into the mechanisms that shape the composition and dynamics of ecological communities. In this study, we used four spatial point process models to evaluate the likely roles of the random placement of species, habitat filtering, dispersal limitation, and the combined effects of habitat filtering and dispersal limitation in producing observed PDARs and FDARs in two large, fully mapped temperate forest research plots in northeast China and in north‐central USA. We found that the dispersal limitation hypothesis provided a good approximation of the accumulation of PD and FD with increasing area, as it did for the species area curves. PDAR and FDAR patterns were highly correlated with the SAR. We interpret this as evidence that species interactions, which are often influenced by phylogenetic and functional similarity, may be relatively unimportant in structuring temperate forest tree assemblages at this scale. However, the scale‐dependent departures of the PDAR and FDAR that emerged for the dispersal limitation hypothesis agree with operation of competitive exclusion at small scales and habitat filtering at larger scales. Our analysis illustrates how emergent community patterns in fully mapped temperate forest plots can be influenced by multiple underlying processes at different spatial scales.     

Factors influencing macroinvertebrate assemblages in artificial subtropical ponds of Taiwan

Macroinvertebrate assemblages and its association with environmental factors at the 11 artificial subtropical ponds of Taiwan were examined using the multivariate analysis software STATICO. The aims of the study were to determine whether spatial and seasonal variation of macroinvertebrate assemblages changed seasonally, to examine which environmental factors determined the spatial and temporal structure of maroinvertebrate assemblages, and to compare between-pond variations in the taxon composition of macroinvertebrates. Macroinvertebrates were collected seasonally by a corer and a sweep net in 2007, and 13 physical and chemical factors were measured at the same time. A total of 31 macroinvertebrate taxa were collected during the sampling period, and the most dominant taxa were Chironomidae (31.7% of total animal abundance) and Tubificidae (22.4%). STATICO identified pond size, pond depth, sediment depth, and altitude as the major abiotic factors and Bufo melanostictus (Amphibia) as the major biotic factor to influence macroinvertebrate assemblages at these ponds. These factors changed with seasonality. For example, the abundance of B. melanostictus was the most important factor during the spring but became much less important in other seasons. According to the spatial distribution patterns of macroinvertebrate assemblages, macroinvertebrates could be split into two groups based on their dispersal. The active dispersers, such as insect taxa, were strongly associated with pond size and the passive dispersers, such as non-insect taxa, were strongly associated with the pond depth and/or sediment depth. The results of this study suggested that pond size might influence macroinvertebrate assemblages through their dispersal mechanisms and that the environmental factors which influenced the macroinvertebrate assemblages most changed with seasons in this study area.     

Hydrological connectivity structures concordant plant and animal assemblages according to niche rather than dispersal processes

1. Understanding the processes that structure community assembly across landscapes is fundamental to ecology and for predicting and managing the consequences of anthropogenically induced changes to ecosystems. 2. We assessed the community similarity of fish, macroinvertebrate and vegetation communities against geographic distances ranging from 4 to 480 km (i.e. distance–decay relationships) to determine the balance between local environmental factors and regional dispersal processes, and thus whether species‐sorting (niche processes) or dispersal limitation (neutral processes) was more important in structuring these assemblages in Australia’s wet‐dry tropics. We investigated whether the balance between niche and dispersal processes depended on the degree of hydrological connectivity, predicting that dispersal processes would be more important at connected sites, and also whether there was spatial concordance among these three assemblage types. 3. There was significant but weak spatial concordance among the study communities, suggesting limited potential for surrogacy among them. Distance–decay in community similarity was not observed for any study assemblage at perennial sites, suggesting dispersal was not limiting and assemblages were structured more strongly by local niche processes at these connected sites. At intermittent sites, weak distance–decay relationships for each assemblage type were confounded by significant relationships with environmental dissimilarity, suggesting that dispersal limitation contributed, albeit weakly, to niche processes in structuring our three study assemblages at disconnected sites. 4. Two environmental factors, flow regime and channel width, explained significant proportions of variation in all three assemblages, potentially contributing to the observed spatial concordance between them and representing local environmental gradients along which these communities re‐assemble after the wet season, according to niche rather than dispersal processes.     

Modern pollen and vegetation relationships in northeastern Patagonia (Golfo San Matías,Río Negro)

The understanding of modern pollen is a critical component of palaeoecological research. The pollen assemblages reflect general patterns in vegetation distribution; however, pollen representation is biased by several factors such as differences in pollen production, dispersal and preservation. Therefore, this relationship cannot be applied directly in pollen records of the past. The aim is to study the relationship between modern pollen and vegetation and to apply this new information on the interpretation of Holocene pollen records. Classification of the vegetation into groups corresponding to different geomorphological units was carried out by cluster analysis. Discriminant analysis was applied on the surface samples to test if different vegetation types could be distinguished by their pollen assemblages. To evaluate the relationship between pollen assemblages and vegetation types, association (A), under-representation (U) and over-representation (O) indexes were calculated for all present taxa in both plant and pollen dataset. The main vegetation types are reflected in pollen assemblages but with greater differences in the proportions of Poaceae, Hyalis argentea, Chenopodiaceae, Asteraceae subf. Asteroideae and Larrea divaricata. Association and representation indexes provided information related to the production rate and pollen dispersal. This study helps to interpret Holocene vegetation and environmental changes from fossil pollen records of the study area.     

Animal Colonization of Restored Peatlands: Inoculation of Plant Material as a Source of Insects

Ecological restoration of mined peatlands in North America involves active reintroduction of bog plant species. Animals are not actively reintroduced, thus the re‐establishment of peatland fauna must occur either by inoculation along with introduced plant material or by dispersal. We examined the extent to which insects are reintroduced to restored sites with plant material by rearing insects from shredded vegetation collected in three donor sites. We assessed differences in abundance, diversity, and composition of taxonomic and trophic groups among seasons and sites. Abundance and species richness did not differ by season, but species assemblages did. The three sites were significantly different in abundance, but not in species richness and assemblages. Few insects emerged from the vegetation, suggesting that shredded plant material may not be the primary source of insect colonists. Insects likely recolonize by active or passive dispersal from the surrounding area. The species pool was similar among donor sites; consequently a mined site could be inoculated with vegetation from another peatland in the same region and this would not affect the insect assemblages at the initial stage of establishment. Diapause may be a major factor for emergence success among seasons of collection. Knowledge of how restoration techniques influence establishment of insect communities will help predict longer‐term outcomes of restoration on biotic communities in peatlands.     

The Robustness of Plant-Pollinator Assemblages: Linking Plant Interaction Patterns and Sensitivity to Pollinator Loss

Most flowering plants depend on pollinators to reproduce. Thus, evaluating the robustness of plant-pollinator assemblages to species loss is a major concern. How species interaction patterns are related to species sensitivity to partner loss may influence the robustness of plant-pollinator assemblages. In plants, both reproductive dependence on pollinators (breeding system) and dispersal ability may modulate plant sensitivity to pollinator loss. For instance, species with strong dependence (e.g. dioecious species) and low dispersal (e.g. seeds dispersed by gravity) may be the most sensitive to pollinator loss. We compared the interaction patterns of plants differing in dependence on pollinators and dispersal ability in a meta-dataset comprising 192 plant species from 13 plant-pollinator networks. In addition, network robustness was compared under different scenarios representing sequences of plant extinctions associated with plant sensitivity to pollinator loss. Species with different dependence on pollinators and dispersal ability showed similar levels of generalization. Although plants with low dispersal ability interacted with more generalized pollinators, low-dispersal plants with strong dependence on pollinators (i.e. the most sensitive to pollinator loss) interacted with more particular sets of pollinators (i.e. shared a low proportion of pollinators with other plants). Only two assemblages showed lower robustness under the scenario considering plant generalization, dependence on pollinators and dispersal ability than under the scenario where extinction sequences only depended on plant generalization (i.e. where higher generalization level was associated with lower probability of extinction). Overall, our results support the idea that species generalization and network topology may be good predictors of assemblage robustness to species loss, independently of plant dispersal ability and breeding system. In contrast, since ecological specialization among partners may increase the probability of disruption of interactions, the fact that the plants most sensitive to pollinator loss interacted with more particular pollinator assemblages suggest that the persistence of these plants and their pollinators might be highly compromised.     

Dispersal as a regional process affecting the local dynamics of marine and stream benthic invertebrates

Recent work has shown that benthic invertebrate assemblages may be influenced in an ongoing fashion by dispersal. Water-column movements of meiofauna, juvenile insects and marine postlarvae are common and can act to alter greatly local dynamics such as predator-prey and competitive interactions in marine and stream ecosystems. These findings are important because past research on the role of dispersal in invertebrate dynamics has focused almost exclusively on how planktonic larval supply influences the establishment and maintenance of local assemblages, on the colonization of newly opened sites, or on the settlement success of new recruits. The emerging framework is that dispersal needs to be viewed as a regional process that may routinely influence local benthic dynamics, because fauna can move to and from water-column dispersal 'pools' and may do so at frequent intervals.     

Spatial structure, rock type, and local environmental conditions drive moss and lichen distribution on calcareous boulders

Although mosses and lichens are a relevant component of the biota of rock habitats targeted for biodiversity conservation in Europe, the ecological factors driving their distribution are still poorly known. In this work, we examined the epilithic moss and lichen assemblages colonizing boulders of different types of calcareous rocks co-occurring in the same area in the Italian Alps. The goals were: (1) to evaluate if and to what extent different calcareous rocks host different assemblages; (2) to identify species associated to each rock type; (3) to quantify the relative importance of rock type, local environmental factors, and habitat spatial structure in explaining species distribution. Our results demonstrated that different calcareous rocks host different moss and lichen assemblages with some typical species, indicating that each rock type contributes to the total diversity of both mosses and lichens. Local environmental conditions influenced mosses and not lichens whose distribution is mainly associated to rock type. The patterns of both organism groups were also significantly related to habitat spatial structure, species assemblages tending to have a patchy distribution, which may reflect dispersal dynamics. Our results have implications for conservation: (1) each rock type may play a relevant role in maintaining the overall diversity contributing with unique assemblages and typical species; (2) the patchy distribution of both moss and lichen assemblages should warn from considering rock patches as a monotonous repetition of the same habitat across space.     

The influence of scale and geography on relationships between stream community composition and landscape variables: description and prediction

SUMMARY 1. We analysed an existing database of macroinvertebrates and fish in the context of a newly established geographical information system (GIS) of physical features to determine the relationships between stream community composition and physical factors measured at three landscape scales – catchment, reach and bedform. Both an exploratory (concordance analysis) and a predictive ( ausrivas ) approach were used.
2. The environmental variables that most successfully accounted for variation in macroinvertebrate assemblages were mainly 'natural' and at the catchment-scale (relief ratio, basin diameter, etc.) but the human-induced physical setting of percentage of pasture in the riparian zone was also influential. For fish, 'natural' variables were also dominant, but these were mostly at the bedform or reach scales and land use featured strongly.
3. Geographic location accounted for some of the variation in invertebrate assemblages, partly because geography and influential conditions/resources are correlated but also because different species may have evolved in different places and have not colonised every 'ecologically appropriate' location. Geographic location was not influential in accounting for variation in assemblages of strongly flying invertebrates, supporting the hypothesis that organisms having high dispersal potential can be expected to break down geographic barriers more readily than those with poor dispersal powers. In accord with what is known about the local evolution and restricted distributions of native and exotic species, history (reflected in geography) appeared to account for some variation in fish assemblages.
4. Given their different mathematical bases, the fact that exploratory and predictive analyses yielded similar results provides added confidence to our conclusions.     

Linking seed dispersal and genetic structure of trees: a biogeographical approach

Aim Natural and human‐induced differences in frugivore assemblages can influence the seed dispersal distances of trees. An important issue in seed dispersal systems is to understand whether differences in seed dispersal distances also affect the genetic structure of mature trees. One possible approach to test for a relationship between seed dispersal and the genetic structure of mature trees is to compare the genetic structure of two closely related tree species between two biogeographical regions that differ in frugivore assemblages and seed dispersal distances. Previous studies on two Commiphora species revealed that Commiphora guillauminii in Madagascar has a much lower seed dispersal distance than Commiphora harveyi in South Africa. We tested whether the lower seed dispersal distance might have caused decreased gene flow, resulting in a stronger genetic structure in Madagascar than in South Africa. Location Madagascar and South Africa. Methods Using amplified fragment length polymorphism markers we investigated the genetic structure of 134 trees in Madagascar and 158 trees in South Africa at a local and a regional spatial scale. Results In concordance with our hypothesis, kinship analysis suggests that gene flow was restricted mostly to 3 km in Madagascar and to 30 km in South Africa. At the local spatial scale, the genetic differentiation among groups of trees within sample sites was marginally significantly higher in Madagascar (F_ST = 0.069) than in South Africa (F_ST = 0.021). However, at a regional spatial scale genetic differentiation was lower in Madagascar (F_ST = 0.053) than in South Africa (F_ST = 0.163). Main conclusions Our results show that lower seed dispersal distances of trees were linked to higher genetic differentiation of trees only at a local spatial scale. This suggests that seed dispersal affects the genetic population structure of trees at a local, but not at a regional, spatial scale.     

Age and Date for Early Arrival of the Acheulian in Europe (Barranc de la Boella,la Canonja,Spain)

The first arrivals of hominin populations into Eurasia during the Early Pleistocene are currently considered to have occurred as short and poorly dated biological dispersions. Questions as to the tempo and mode of these early prehistoric settlements have given rise to debates concerning the taxonomic significance of the lithic assemblages, as trace fossils, and the geographical distribution of the technological traditions found in the Lower Palaeolithic record. Here, we report on the Barranc de la Boella site which has yielded a lithic assemblage dating to ∼1 million years ago that includes large cutting tools (LCT). We argue that distinct technological traditions coexisted in the Iberian archaeological repertoires of the late Early Pleistocene age in a similar way to the earliest sub-Saharan African artefact assemblages. These differences between stone tool assemblages may be attributed to the different chronologies of hominin dispersal events. The archaeological record of Barranc de la Boella completes the geographical distribution of LCT assemblages across southern Eurasia during the EMPT (Early-Middle Pleistocene Transition, circa 942 to 641 kyr). Up to now, chronology of the earliest European LCT assemblages is based on the abundant Palaeolithic record found in terrace river sequences which have been dated to the end of the EMPT and later. However, the findings at Barranc de la Boella suggest that early LCT lithic assemblages appeared in the SW of Europe during earlier hominin dispersal episodes before the definitive colonization of temperate Eurasia took place.