Abiotic Dispersal Research Articles

Biotic and abiotic dispersal of a large-seeded keystone genus in Madagascar

In tropical forests, most plant species rely on frugivorous animals for seed dispersal services. Such mutualisms are imperiled by defaunation, which disproportionately affects large-bodied vertebrates and may impact the interactions of the large-seeded plants they disperse. However, frugivore-mediated seed dispersal (zoochory) may not be the only mechanism ensuring the dispersal of a given plant species. With a focus on large-seeded canopy trees in the genus Canarium in the rainforests of Madagascar, thought to be dispersed by large-bodied lemur species, we investigated the contribution of multiple dispersal mechanisms to the movement of large seeds. Specifically, we (1) examined the potential for dispersal by abiotic factors, such as winds and runoff associated with frequent cyclones, (2) documented the animal species that could effectively contribute to their primary and secondary seed dispersal, and (3) determined how non-lemur and abiotic dispersal compare to the imperiled function of extant, though threatened, lemur primary dispersers. Using field observations and experiments, we found that wind, water, and secondary dispersal can move seeds considerable distances away from the parent plants, though they were less effective at long-distance dispersal than primary dispersers (i.e., large-bodied lemurs). For secondary dispersal, we found that dispersal distance is positively correlated with predation, potentially reducing dispersal effectiveness. Future comparisons with predation of primary or abiotically dispersed seeds will be necessary. Our research highlights the role of understudied mechanisms in the dispersal of large-seeded plants in Madagascar. Understanding the existence and impact of non-lemur dispersers in these imperiled forests can help complete our understanding of the mechanisms that shaped their astounding biodiversity and may mediate their response to ongoing environmental change.

Dispersal‐related plant traits are associated with range size in the Atlantic Forest

AbstractAimThe efficiency of animal‐mediated seed dispersal is threatened by the decline of animal populations, especially in tropical forests. We hypothesise that large‐seeded plants with animal‐mediated dispersal tend to have limited geographic ranges and face an increased risk of extinction due to the potential decline in seed dispersal by large‐bodied fruit‐eating and seed‐dispersing animals (frugivores).LocationAtlantic Forest, Brazil, South America.TaxonAngiosperms.MethodsFirst, we collected dispersal‐related traits (dispersal syndrome, fruit size, and seed size), growth form (tree, climber, and other) and preferred vegetation type (open and closed) data for 1052 Atlantic Forest plant species. Next, we integrated these with occurrence records, extinction risk assessments, and phylogenetic trees. Finally, we performed phylogenetic generalised least squares regressions to test the direct and interactive effects of dispersal‐related traits and vegetation type on geographical range size.ResultsLarge‐seeded species had smaller range sizes than small‐seeded species, but only for species with animal‐mediated dispersal, not for those dispersed by abiotic mechanisms. However, plants with abiotic dispersal had overall smaller range sizes than plants with animal‐mediated dispersal. Furthermore, we found that species restricted to forests had smaller ranges than those occurring in open or mixed vegetation. Finally, at least 29% of the Atlantic Forest flora is threatened by extinction, but this was not related to plant dispersal syndromes.Main ConclusionsLarge‐seeded plants with animal‐mediated dispersal may be suffering from dispersal limitation, potentially due to past and ongoing defaunation of large‐bodied frugivores, leading to small range sizes. Other factors, such as deforestation and fragmentation, will probably modulate the effects of dispersal on range size, and ultimately extinction. Our study sheds light on the relationship between plant traits, mutualistic interactions, and distribution that are key to the functioning of tropical forests.

Host and nonhost bacteria support bacteriophage dissemination along mycelia and abiotic dispersal networks.

Bacteriophages play a crucial role in shaping bacterial communities, yet the mechanisms by which nonmotile bacteriophages interact with their hosts remain poorly understood. This knowledge gap is especially pronounced in structured environments like soil, where spatial constraints and air-filled zones hinder aqueous diffusion. In soil, hyphae of filamentous microorganisms form a network of 'fungal highways' (FHs) that facilitate the dispersal of other microorganisms. We propose that FHs also promote bacteriophage dissemination. Viral particles can diffuse in liquid films surrounding hyphae or be transported by infectable (host) or uninfectable (nonhost) bacterial carriers coexisting on FH networks. To test this, two bacteriophages that infect Pseudomonas putida DSM291 (host) but not KT2440 (nonhost) were used. In the absence of carriers, bacteriophages showed limited diffusion on 3D-printed abiotic networks, but diffusion was significantly improved in Pythium ultimum-formed FHs when the number of connecting hyphae exceeded 20. Transport by both host and nonhost carriers enhanced bacteriophage dissemination. Host carriers were five times more effective in transporting bacteriophages, particularly in FHs with over 30 connecting hyphae. This study enhances our understanding of bacteriophage dissemination in nonsaturated environments like soils, highlighting the importance of biotic networks and bacterial hosts in facilitating this process.

Negative impact of slash-and-burn agriculture on the seed rain in a tropical dry forest

Forest’s recovery potential in human-modified landscapes is increasingly threatened by agricultural activities that disrupt critical sources of forest regeneration, such as the seed rain. Slash-and-burn agriculture is a good example. By slashing and burning the vegetation, this farming method can promote seed source and seed dispersal limitation, but this hypothesis remains poorly tested. Here, we sampled the seed rain during a complete year in nine plots exposed to slash-and-burn agriculture (i.e., burned plots) and in forest stands (control plots) in the Caatinga biome – a species-rich tropical dry forest endemic to Brazil that is increasingly threatened by slash-and-burn agriculture. We compared seed density, seed species diversity, and the taxonomic and functional composition of seed assemblages between burned and control plots. As expected, seed density was 15 times lower in burned plots than in control plots. Species diversity was also lower in burned plots, but only when considering the number of rare species. However, burned plots showed a higher β-diversity of rare species than forest plots, mainly caused by species replacement (i.e. species turnover) from plot to plot. Burned plots also showed 30% more species with dry fruits and abiotic dispersal than control plots, but this difference was not statistically significant. Taken together, our findings highlight the low tolerance of the seed rain to this dominant agricultural practice in tropical dry forests. This is likely related to the lack of seed sources and seed dispersers in burned plots. Therefore, increasing the availability of seed sources and ecological connectivity in the surrounding landscape are critical management strategies for enhancing seed dispersal and forest recovery in forest areas exposed to this farming method.

Wind variability limits the potential influence of propagule morphology and descent rate on dispersal in the winged fruits of Carpinus (Betulaceae)

The dispersal of propagules is an important aspect of land plant life history that has the potential to impact diverse evolutionary and ecological processes. Identifying the relationship between form and function of extant propagules provides the opportunity to infer past dispersal processes using morphological information from fossils, especially for abiotic dispersal of winged propagules. Many studies under laboratory conditions have identified wing loading (propagule mass divided by wing area) as the character most important for descent rates of winged propagules, but its influence on dispersal distances in natural environments over entire dispersal seasons remains unclear. To clarify this relationship, morphological measurements and experimental drops were performed on dispersed propagules from two species of Carpinus collected along highly resolved transects radiating from individual source trees. A significant relationship was found between wing loading and descent rate in still air, but the relationship between wing loading and actual dispersal distance in the field was random in all directions. Results indicate that variable wind conditions over a dispersal season can erase any signal of form and descent rate on dispersal patterns. Consequently, this randomization should impact evolutionary patterns by hampering selective potential for details of form that might further slow descent rates once enough of a wing evolves for propagules to exhibit a consistent specialized aerodynamic behavior.

Limited seed dispersal distance in endemic species from tropical mountaintop grasslands may restrict upward migration in response to climate change

Understanding dispersal systems is a key step towards improving our ability to predict species migration trajectories in response to climate change. However, the abiotic seed dispersal systems of tropical plants remain largely overlooked, with studies inferring seed dispersal from fruit morphology than conducting empirical tests. Here, we determined seed dispersal season experimentally tested the seed dispersal mode, and estimated dispersal distance kernels for five edaphic specialists, mountaintop endemics from campo rupestre, a tropical, megadiverse and nutrient-impoverished grassland. We monitored fruiting phenology for 12 months and established field and laboratory experiments to assess the role of abiotic factors in releasing seeds from dry capsules and to measure seed dispersal distance. Contrary to previous studies that suggested abiotic dispersal, we found no evidence of water- or wind-operated primary seed dispersal mechanisms for all species. We show that fruiting peaks coincided with optimum conditions for seedling establishment, and that short seed dispersal distances are consistent with the idea of reduced dispersibility in edaphic specialists. Seed buoyancy experiments show a large potential for secondary seed dispersal by water run-off. Our data suggest that abiotic dispersal in the study species plays a limited role in displacing seeds away from parental plants, a pattern that markedly contrasts with that found in other vegetation types. Short-distance dispersal in campo rupestre is consistent with theory explaining the evolution of phylomatry, but it also represents reason for concern of species migration in face of global climate changes. The combination of edaphic endemism and limited dispersal in mountaintops species provides limited opportunity for migration and poses a significant threat to their long-term survival.

Landscape‐scale range filling and dispersal limitation of woody plants

AbstractAimThe extent to which species fill their predicted current ranges and the underlying process of dispersal limitation have implications for species' abilities to track climate change. Range filling is intimately related to spatial scale, yet range filling estimates at high resolutions are largely lacking. In this study, we aim to estimate range filling and dispersal limitation at a high resolution for woody plants with different dispersal systems and habitat affinities.LocationSweden.TaxonAll genera of woody plants (trees and shrubs).MethodsWe estimated landscape‐scale range filling for 64 species. Two main dispersal systems, vertebrate dispersal and abiotic dispersal, occurred among these species. Range filling was estimated as the realized range divided by the potential range, that is, the occupied proportion of a species' modelled range, at a 1 km2 resolution. We estimated potential ranges using species distribution models and realized ranges from presence records. To increase the likelihood that absences represented true absences the estimations were restricted to areas with high sampling effort. We tested the effects of dispersal system on range filling, controlling for species' habitat affinities.ResultsVertebrate‐dispersed woody species had significantly lower landscape‐scale range filling than species with abiotic dispersal. Range filling was also linked to habitat affinity. Species associated with intermediate levels of light and moisture had the highest range filling estimates.Main conclusionsLandscape‐scale range filling of woody species is linked to their dispersal traits. When controlling for habitat affinity, our result suggests that dispersal limitation partly explains the lower occupancy in suitable habitat found for vertebrate‐dispersed plants. Given that vertebrate‐dispersed species fail to reach suitable habitats at this scale, they are less likely to track changes in climate than woody plants with abiotic dispersal.

Cross‐scale drivers of woody plant species commonness and rarity in the Brazilian drylands

AbstractAimLocally abundant species are typically widespread, while locally scarce species are geographically restricted—the so‐called abundance‐occupancy relationships (AORs). AORs help explain the drivers of species rarity and community assembly, but little is known about how variation around such relationship is driven by species traits and niche‐based processes, particularly in tropical woody plants. We tested the hypothesis that AORs in tropical dryland woody plants are positive and mediated by niche and functional traits along environmental gradients.LocationThe Caatinga dry forest and Cerrado savannah, Brazil.MethodsWe aggregated abundance and occurrence data into grid‐cells representing local (10‐km) to landscape scales (50‐km). We calculated species mean relative abundance at occupied grid‐cells (local abundance) and the proportion of grid‐cells occupied (occupancy), and estimated their niche breadth and marginality along multivariate environmental gradients.ResultsAORs were positive but weak at different scales in both regions due to some locally abundant but geographically restricted species, with most species being both locally and geographically rare. Cross‐species variation in local abundance was largely unpredictable, but occupancy was strongly driven by niche and functional traits, with a prominent negative effect of niche marginality. Geographically restricted species were associated with rare habitats, such as wetter and less intensively used habitats. Large seeds and abiotic dispersal favoured occupancy in Caatinga at small and large spatial scales, respectively, whereas species with conservative leaves were more widespread across scales in Cerrado.Main conclusionsWoody plants in dry tropical biotas exhibit weak AORs, a pattern likely related to low habitat availability and dispersal limitation. Caatinga and Cerrado biotas emerge as environmentally structured at multiple spatial scales, with several habitat‐specialist rare species bearing specific regenerative and resource‐use traits and relying on conditions threatened by climate change and land‐use intensification. Examining AORs through the lens of niche, functional traits and spatial scales enables mapping patterns and drivers of species commonness and rarity, enhancing understanding of species assembly and providing tools for biodiversity conservation.

The distribution of dioecious plant pollination, sex ratio and seed dispersal research by climate type in Australia

Dioecious-plant life-history characteristics and reproduction vary greatly among species, and have been linked to certain climate and habitat types, particularly tropical and island habitats. Australia is a large, predominantly arid continent, although it also contains mediterranean, temperate and tropical climates. Dioecious plants occupy each of these climate types, with their respective habitats and evolutionary pressures. As a result, dioecious species demonstrate great variation in key reproductive characteristics (pollination mechanism, sex ratio, and seed dispersal), which require understanding so as to conserve dioecious species effectively among climate types. Therefore, to understand dioecious-plant ecology across Australia, research must include all climate types, and investigate reproductive traits in each to better focus conservation strategies. An external factor which could prevent equal study effort across climate types would be geoclimatic preference of study location or biases in researcher interest, causing gaps in practical understanding and less effective dioecious-plant conservation management in understudied systems. To assess the prevalence and nature of dioecious plant research in Australia, we conducted a systematic mapping and scoping review to answer the following questions: (1) what climate zones have been captured by dioecious-plant research in Australia, focusing on pollination, sex ratio and seed dispersal; and (2) what is the distribution of dioecious-plant pollination, sex ratio and seed dispersal research by climate type; of the 43 studies that met the inclusion criteria, 27 (62.8%) studies were conducted in temperate climates, 8 (18.6%) in dry climates, 6 (13.9%) in tropical climates, and 5 (11.6%) in continental climates. Of the three focal areas, pollination studies (n = 24, 75% studies of entomophily) were most common, whereas sex ratio (n = 17, 41% studies of sex ratio over more than one population) and seed dispersal studies (n = 13, 54% of studies investigated abiotic dispersal) were less frequently researched. Considering the climate classification distribution in Australia, studies of dioecious species in dry climates are less prevalent than those in temperate climates. Of the focal areas of research, particularly under-investigated areas were anemophily, biotic seed dispersal, and study of female-biased species. Further studies addressing these gaps would be beneficial to inform conservation initiatives for Australian dioecious plant species. Additionally, it would be informative to investigate whether similar patterns are found in dioecious plant research in other countries with diverse climate types.

Inferring trait‐based mechanisms and variance consequences of abiotic secondary dispersal from the spatio‐temporal distribution of a desert soil seed bank

AbstractQuestionsQuantifying the combined effects of seed traits, microsite types, and abiotic dispersal agents on the mean and variance of seed bank density and composition will help understand vegetation dynamics in deserts. In a site with NE slope and mainly southerly winds, we asked whether large and oblong seeds were more likely to be transported and deposited in water obstructions and underneath the northern part of shrub understories. We also asked whether seed standing crop was less variable in water obstructions than in other microsites less affected by seed deposition.LocationA sand field in San Juan province, Argentina.MethodsWe sampled the soil seed banks of four microsite types: water obstructions where debris/litter accumulates, southern and northern shrub understories, and open spaces among shrubs. Sampling was carried out in 11 plots and replicated at six moments between 2010 and 2012.ResultsDebris microsites showed the highest levels of seed density, species richness and standing crop; seed density and standing crop were also least variable in these microsites. Debris microsites also contained high seed abundance of stress‐intolerant, shrub‐dependent species. Seed density, species richness, seed standing crop, and the proportions of both large and oblong seeds were all higher in northern than in southern understories. The relationship between seed mass and the proportion of seeds that were apparently retained (i.e., not washed away and deposited in water obstructions) was more strongly negative in southern than in northern understories.ConclusionsNorthern and southern understories appeared to act as water run‐on (i.e., seed recipients) and run‐off zones (i.e., seed donors), respectively. Seed accumulation under the shelter provided by shrubs may promote seed predation in these microsites. Abiotic dispersal would therefore contribute to the maintenance of vegetation patches when seed arrival underneath shrub canopies saturates granivore consumption.

Effects of local characteristics and landscape patterns on plant richness: A multi-scale investigation of multiple dispersal traits

Abstract Plant species distributions are determined by various factors (including the dispersal modes and the complex physical environment) across multiple spatial scales, in which the dispersal distance of different dispersal modes and the external environment (including local characteristics and landscape patterns) are closely related. Therefore, understanding the response mechanism of plant species with different dispersal abilities to environmental factors is critical for developing effective landscape management strategies and prioritizing biodiversity conservation efforts at the appropriate scale. In this study, we aimed to explore: (1) the spatial distribution of plant species richness; (2) the spatial scale at which plant species have the strongest response to environment variables (scale of effect); and (3) to identify the key factors that affect the plant species at local and six landscape scales (a 0.5 km, 1 km, 1.5 km, 2 km, 3 km and 4 km-radius circle) considering multiple dispersal traits. We conducted vegetation surveys at 53 sites and classified plant species into three dispersal modes, including biotic dispersal (BD), abiotic dispersal (AD) and autochorous (AT), based on the respective dispersal vector of the seed. We classified land use types into 15 categories and clipped 6 specified radii around each sampling site using ENVI 5.1 and ArcGIS 10.3 software. We applied linear mixed effects models (LMM) to analyze the local and the surrounding landscape variables in predicting plant species richness in Qingshui town of Beijing, China. Our results revealed that the response traits of species to environment factors varied across different scales, proving the existence of scale effect in our study area. The biotically-dispersed (BD) and abiotically-dispersed (AD) species favored structurally complex habitats with greater tree height and cover of herb at the local scale. The area-weighted mean of shape metric (SHAPE_MN) of shrubbery and the euclidean nearest neighbor distance distribution (ENN_AM) of bare land play a major role in determining BD and AD species at large spatial extents, which suggest that the patterns and ecological attributes of patches of these two land use types hinder the migration and colonization ability of species and thus affect the species richness. These results suggest that a multi-scale approach should be encouraged to help guide effective landscape managements in conserving biodiversity for different response traits.

Is dispersal mode a driver of diversification and geographical distribution in the tropical plant family Melastomataceae?

Species of plants with different life history strategies may differ in their seed dispersal mechanisms, impacting their distribution and diversification patterns. Shorter or longer distance dispersal is favored by different dispersal modes, facilitating (or constraining) population isolation, which can, in turn, impact speciation and species range sizes. While these associations are intuitive, few studies have explicitly tested these hypotheses for large clades of angiosperms. The plant family Melastomataceae is found on disparate habitats with different dispersal modes, representing a good model to address these questions. In this study, we reconstruct the phylogeny of Melastomataceae and gather data on their dispersal mode and range size to test the impact of dispersal mode on diversification and range size evolution. We found that abiotic dispersal is ancestral in the family, while biotic dispersal evolved multiple times. Species richness distribution is very similar across dispersal modes, although abiotically dispersed species tend to be relatively more diverse in seasonal environments. Range sizes across dispersal modes are not significantly different, although biotically dispersed species have slightly wider distributions. Model comparisons indicate that factors other than dispersal mode might have driven diversification heterogeneity. We did not find evidence for the role of dispersal mode driving diversification rates or range size in the Melastomataceae, suggesting a complex macroevolutionary scenario for this diverse angiosperm family. The bulk of changes to biotic dispersal coinciding with an increase in passerine diversification suggests a possible “past” key innovation in Melastomataceae. Future studies should investigate the role of other diversification drivers in the family and the relatively higher diversity of abiotically dispersed species in open habitats.

Continents as Units for the Study of Floristic Assembly and Biodiversity: Focus on North America

Continents as Units for the Study of Floristic Assembly and Biodiversity: Focus on North America

Distance and environmental difference in alpine plant communities

Differences in plant communities are a response to the abiotic environment, species interactions, and dispersal. The role of geographic distance relative to the abiotic environment is explored for alpine tundra vegetation from 319 plots of four regions along the Rocky Mountain cordillera in the USA. The site by species data were ordinated using nonmetric multidimensional scaling to produce dependent variables for use in best-subsets regression. For independent variables, observations of local topography and microtopography were used as environmental indicators. Two methods of including distance in studies of vegetation and environment are used and contrasted. The relative importance of geographic distance in accounting for the pattern of alpine tundra similarity indicates that location is a factor in plant community composition. Mantel tests provide direct correlations between difference and distance but have known weaknesses. Moran spatial eigenvectors used in regression based approaches have greater geographic specificity, but require another step, ordination, in creating a vegetation variable. While the spatial eigenvectors are generally preferable, where species–environment relations are weak, as seems to be the case for the alpine sites studied here, the fewer abstractions of the Mantel test may be useful.

Comparison of forest regeneration in two sites with different primate abundances in Northwestern Ecuador

There is increasing evidence that large-bodied primates play important roles as seed dispersers and in the maintenance of tree diversity in forest ecosystems. In this study we compared forest regeneration at two sites with differing primate abundances in the Ecuadorian Chocoan rainforest. We predicted: (1) significant differences in primate abundance between the two sites; (2) higher understory tree species richness and density at the site with greater primate abundance; (3) the site with lower primate abundance characterized by tree species dispersed by non-primate biotic agents and/or abiotic factors. We compared two sites, Tesoro Escondido (TE) a campesino cooperative, and the El Pambilar (EP) wildlife refuge that both maintain populations of mantled howler monkey (Alouatta palliata), the brown-headed spider monkey (Ateles fusciceps fusciceps) and the capuchin monkey (Cebus capucinus). We characterized canopy structure by point-quadrant sampling, determined primate abundance and sampled seedlings/saplings in 1 m2 plots, classifying tree species based on three dispersal syndromes: adapted for primate dispersal, dispersed by other biological agents, and abiotic dispersal. We compared sites in terms of primate abundance (groups and individuals observed per day) and regeneration characteristics (overall density, species richness, and dispersal syndrome). We carried out within site comparisons and constructed understory tree species accumulation curves. Overall the forests were structurally similar - with significantly higher densities of A. f. fusciceps at TE. Encounter rates for the other two primate species were similar at both sites. Understory tree density and species richness was significantly higher in TE with no stabilization of tree species accumulation curves. The species accumulation curve for understory trees at EP stabilized. Higher densities and species richness of primate dispersed tree species were observed at TE, with non-primate biotically dispersed tree species the dominant dispersal syndrome at both sites. Our observations are consistent with those from other studies investigating the role of large-bodied frugivorous primates in forest regeneration, and point to a general pattern: future lowland tropical forest tree diversity depends on maintaining robust populations of large primate species in these systems. It is highly probable that the maintenance of high levels of tree diversity in Chocoan rainforests is dependent on the conservation of its largest resident primate, the critically endangered brown-headed spider monkey (A. f. fusciceps).

Revisiting Darwin's naturalization conundrum: explaining invasion success of non‐native trees and shrubs in southern Africa

Summary Invasive species are detrimental ecologically and economically. Their negative impacts in Africa are extensive and call for a renewed commitment to better understand the correlates of invasion success. Here, we explored several putative drivers of species invasion among woody non‐native trees and shrubs in southern Africa, a region of high floristic diversity. We tested for differences in functional traits between plant categories using a combination of phylogenetic independent contrasts and a simulation‐based phylogenetic anova. We found that non‐native species generally have longer flowering duration compared with native species and are generally hermaphroditic, and their dispersal is mostly abiotically mediated. We also revealed that non‐native trees and shrubs that have become invasive are less closely related to native trees and shrubs than their non‐invasive non‐native counterparts. Non‐natives that are more closely related to the native species pool may be more likely to possess traits suited to the new environment in which they find themselves and thus have greater chance of establishment. However, successful invaders are less closely related to the native pool, indicating evidence for competitive release or support for the vacant niche theory. Synthesis. Non‐native trees and shrubs in southern Africa are characterized by a suite of traits, including long flowering times, a hermaphroditic sexual system and abiotic dispersal, which may represent important adaptations promoting establishment. We suggest that differences in the evolutionary distances separating the native species pool from invasive and non‐invasive species might help resolve Darwin's naturalization conundrum.

Life History Traits of Lianas During Tropical Forest Succession

Tropical secondary forests form an important part of the landscape. Understanding functional traits of species that colonize at different points in succession can provide insight into community assembly. Although studies on functional traits during forest succession have focused on trees, lianas (woody vines) also contribute strongly to forest biomass, species richness, and dynamics. We examined life history traits of lianas in a forest chronosequence in Costa Rica to determine which traits vary consistently over succession. We conducted 0.1 ha vegetation inventories in 30 sites. To examine the establishment of young individuals, we only included small lianas (0.5–1.5 cm diameter at 1.3 m height). For each species, we identified seed size, dispersal mode, climbing mode, and whether or not the seedling is self-supporting. We found a strong axis of variation determined by seed size and seedling growth habit, with early successional communities dominated by small-seeded species with abiotic dispersal and climbing seedlings, while large-seeded, animal-dispersed species with free-standing seedlings increased in abundance with stand age. Contrary to previous research and theory, we found a decrease in the abundance of stem twiners and no decrease in the abundance of tendril-climbers during succession. Seed size appears to be a better indicator of liana successional stage than climbing mode. Liana life history traits change predictably over succession, particularly traits related to seedling establishment. Identifying whether these trait differences persist into the growth strategies of mature lianas is an important research goal, with potential ramifications for understanding the impact of lianas during tropical forest succession.

Frugivoria por aves em um mosaico de Floresta Estacional Semidecidual e reflorestamento misto em Rio Claro, São Paulo, Brasil

Visando subsidiar futuros projetos de recuperação florestal com base nas interações animal-planta, foram avaliadas as espécies ornitocóricas e o consumo de frutos por aves em um mosaico de Floresta Estacional Semidecidual e um reflorestamento misto, em Rio Claro, São Paulo. Através do monitoramento da frutificação e avaliação dos eventos de frugivoria em sessões focais e ad libitum, foram registradas 31 espécies ornitocóricas fornecendo frutos para 38 espécies de aves consumidoras. No reflorestamento misto foram observadas 90,3% (n=28) das espécies ornitocóricas frutificando ao longo de todo ano, enquanto no fragmento florestal, somente 51,6% (n=16) delas foram registradas, com maiores variações temporais na oferta de frutos; 65,2% (n=1027) dos frutos foram consumidos no reflorestamento misto e 34,8% (n=547) no fragmento florestal. Tais resultados podem estar relacionados ao menor tamanho do fragmento de vegetação nativa, o que, proporcionalmente, poderia determinar uma menor riqueza de espécies vegetais no mesmo e/ou ao fato de a dispersão abiótica tender a predominar nos locais fragmentados e perturbados. O reflorestamento misto, embora apresente algumas espécies vegetais exóticas, está sendo ecologicamente mais funcional para a avifauna e, devido à proximidade com o fragmento, parece estar contribuindo para a manutenção das comunidades de aves residentes e visitantes deste último através dos recursos alimentares oferecidos.

What are the consequences of ant–seed interactions on the abundance of two dry-fruited shrubs in a Mediterranean scrub?

Strong interactions between dry-fruited shrubs and seed-harvesting ants are expected in early successional scrubs, where both groups have a major presence. We have analysed the implications of the seed characteristics of two dry-fruited shrub species (Coronilla minima and Dorycnium pentaphyllum) on seed predation and dispersal mediated by harvester ants and the consequences of these processes on spatio-temporal patterns of plant abundance in a heterogeneous environment. We found that large C. minima seeds were collected much more (39%) than small D. pentaphyllum seeds (2%). However, not all of the removed seeds of these plant species were consumed, and 12.8% of the seeds were lost along the trails, which increased dispersal distances compared with abiotic dispersal alone. Seed dropping occurred among all microhabitats of the two plant species, but especially in open microhabitats, which are the most suitable ones for plant establishment. The two plant species increased their presence in the study area during the study period: C. minima in open microhabitats and D. pentaphyllum in high vegetation. The large size of C. minima seeds probably limited the primary seed dispersal of this species, but may have allowed strong interaction with ants. Thus, seed dispersal by ants resulted in C. minima seeds reaching more suitable microhabitats by means of increasing dispersal distance and redistribution among microhabitats. In contrast, the smaller size of D. pentaphyllum seeds arguably allows abiotic seed dispersal over longer distances and colonization of all types of microhabitats, although it probably also limits their interaction with ants and, consequently, their redistribution in suitable microhabitats. We suggest that dyszoochory could contribute to the success of plant species with different seed characteristics in scrub habitats where seeds are abundantly collected by seed-harvesting ants.

Dispersal abilities and spatial patterns in fragmented landscapes

Recent theoretical studies suggest that the distribution of species in space has important implications for the conservation of communities in fragmented landscapes. Facilitation and dispersal are the primary mechanisms responsible for the formation of spatial patterns. Furthermore, disruptions in the formation of patterns arise after degradation, which can serve as an early indicator of stress in plant communities. Spatial dispersal ability and pattern formation were evaluated in 53 linear transects of 500 m in length within 14 fragments of natural vegetation within a matrix of abandoned crop fields in Cabo de Gata National Park, Almeria, Spain. Fragments were classified into three size classes ( 900 ha). Fragment connectivity was quantified using the distances between fragments. Spatial dispersal ability was quantified for the 187 species recorded in the study. Species with restricted dispersal had the highest degree of long-range spatial autocorrelation and, species that disperse by biotic vectors (e.g. vertebrates), the lowest. In addition, species most susceptible to fragmentation are vertebrate-dispersed shrubs, which declined in abundance and was associated with loss of spatial organization in the smallest fragments. It is postulated that the positive feedback between abundance of recruitment and vertebrate visits influences the colonization and persistence of vertebrate-dispersed shrubs, explaining its abundance in large fragments. Indeed, fragments lower than a certain threshold reduced spatial organization not only in shrubs with biotic dispersal, but also in species with abiotic dispersal (mainly wind) and with restricted dispersal. Fragments lower than a certain threshold may be vulnerable to a cascade of species loss because of reduced recruitment, establishment and patch biomass as a result of natural senescence, finally breaking up facilitative plant interactions.