Negative density dependence of seed dispersal and seedling recruitment in a neotropical palm

Interspecific interactions disrupted by roads

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

Developing evolutionary anthropology in local ecosystems

The traditional regional focus of evolutionary anthropology-typically defined as places where hominin fossils, nonhuman primates, and non-western populations reside-forms the basis of much evolutionary anthropological research. Using the highly biodiverse temperate region of Appalachia as an example, we suggest that evolutionary anthropologists have much to gain by stepping outside of this traditional geographic area. Being purposely provocative, we argue that evolutionary anthropologists might also benefit from conducting research in Appalachia and other temperate ecosystems. We briefly discuss multiple areas of study-including studies of seed dispersal, functional redundancy, convergent evolution, human behavioral ecology, and conservation-and how they can be considered within the purview of integrative and evolutionary anthropology. We also highlight broader impacts to higher education that evolutionary anthropologists can help promote by working in local ecosystems.

Interactive effects of two rodent species on the seed dispersal of Japanese walnut

The effects of seed dispersers on plant fitness (seed dispersal effectiveness, SDE) have been evaluated based on the number (quantity) and recruitment probability (quality) of dispersed seeds. Although seeds of most zoochorous species are dispersed by two or more animal species, which may interact with each other, SDE has often been studied assuming a one-plant and one-animal species system. We compared the SDE of Japanese walnut (Juglans ailanthifolia) between squirrel-only and squirrel-mouse sites in natural forests of Hokkaido, Japan, and found that the SDE from the red squirrel (Sciurus vulgaris), considered a primary seed disperser, was altered by an alternative seed disperser species, the Japanese wood mouse (Apodemus speciosus). Seed removal rates at the squirrel-mouse site were significantly higher than those at the squirrel-only site, and both dispersed seeds and seedlings were less aggregated, with a strongly repulsive relationship with adult conspecific trees at the squirrel-mouse site. Seedlings established themselves at a location with fewer medium-sized trees (< 10 cm DBH) at the squirrel-mouse site. These results suggest that the interactive effect of the rodent species affects the SDE of Japanese walnut.

Pinanga palms revisited 20 years on: what can changes in Pinanga species populations tell us about rainforest understory palm persistence?

Borneo is the centre of diversity of the palm genus Pinanga. At least 13 understory species have been recorded in the Ulu Temburong National Park in Brunei, but little is known of their persistence. Changes in populations of Pinanga understory palms may be indicative of more widespread changes due to climate change, such as changes in rainfall, which may be important for the palm diversity in the protected area. However, we know little about the population dynamics of these palms, how persistent their populations are or if they behave similarly over long time frames. In 1998, populations of five co-occurring species of Pinanga at several locations in the Ulu Temburong National Park were documented. This project aimed to undertake a comprehensive resurvey of the original five Pinanga palm species populations in order to assess if they showed similar population changes across sites and species after two decades. Overall, most species maintained their population size in the surveyed region but not consistently among sites, and one species significantly declined in abundance. There was considerable variation in population growth rate (R) within and among species and sites that was significantly correlated with density and the percentage of multi-stemmed plants. There was evidence of pulsed recruitment in some species and or sites rather than steady or exponential patterns of population growth.

Nondormant Acorns Show Higher Seed Dispersal Effectiveness Than Dormant Ones

Seed dormancy has been thought to be an important survival strategy to tune the seed dispersal timing. Although a theoretical trade-off between seed dormancy and dispersal is often proposed, empirical field evidence of the trade-off between seed dormancy, spatial dispersal, and seedling recruitment is still lacking. Here, we tracked seed dispersal of several Fagaceae species exhibiting different levels of dormancy both in artificial enclosures and in the field. We presented evidence that oak species with nondormant acorns rather than those bearing dormant species exhibit reduced spatial dispersal. Despite the empirical evidence that seed germination is negatively correlated with spatial dispersal, nondormancy rather than dormancy showed higher seed dispersal effectiveness, demonstrating a negative correlation between seed dormancy and dispersal fitness. Our study, using the oak-rodent system, may provide solid evidence of a dispersal–germination trade-off between spatial and temporal correlation, highlighting the ecological role of seed germination schedule in seed dispersal and life-history evolution.

Syagrus flexuosa (Mart.) Becc. (Arecaceae) seedling recruitment at the edge and interior of Cerrado remnants

The edge effect has impacts on seed and seedling survival due to modifications in biotic and abiotic factors. Often, large-seeded tree species lost seed vectors in the forest edge due to the rarity or absence of large frugivores at this habitat type. In this study, I compared the seedling abundance and distribution of the palm Syagrus flexuosa between edges and interiors of three large Cerrado remnants. In every remnant, the number of seedlings around parent palms in the edge was smaller than around palm individuals located in the Cerrado interior. Moreover, the distribution of seedlings around parent palms differed between edges and interiors. In the edges, most seedlings were found under parent crowns, while in the interiors, the contrary occurred. The high concentration of seedlings under parent palms suggests a decrease of seed dispersal at the edges. Because S. flexuosa is a widely distributed palm that serves as an important resource for several animals along Cerrado habitats, changes on the regeneration process of this palm due to edge effects can further impact frugivore populations. Therefore, the decline of seedling establishment along forest edges implies changes in the Cerrado regeneration dynamics, which may compromise the persistence of ecological processes and animal communities.

Rodent-mediated plant seed dispersal: What happens to the seeds after entering the gaps with different sizes?

In general, it is accepted that gap formation significantly affects the placement of scatter-hoarded seeds by small rodents, but the effects of different forest gap sizes on the seed-eating and scatter-hoarding behaviors of small rodents remain unclear. Thus, we examined the effects of a closed-canopy forest, forest edge, and gaps with different sizes on the spatial dispersal of Quercus variabilis acorns and cache placement by small rodents using coded plastic tags in the Taihang Mountains, China. The seeds were removed rapidly, and there were significant differences in the seed-eating and caching strategies between the stand types. We found that Q. variabilis acorns were usually eaten after being removed from the closed-canopy forest and forest edges. By contrast, the Q. variabilis acorns in the forest gap stands were more likely to be scatter-hoarded. The dispersal distances of Q. variabilis acorns were significantly longer in the forest gap plots compared with the closed canopy and forest edge plots. However, the proportion of scatter-hoarded seeds did not increase significantly as the gap size increased. In small-scale oak reforestation projects or research, creating small gaps to promote rodent-mediated seed dispersal may effectively accelerate forest recovery and successional processes.

Human disturbance modifies the identity and interaction strength of mammals that consume Attalea butyracea fruit in a neotropical forest

Habitat loss and hunting are important drivers of mammal defaunation, affecting not only species presence but also their ecological roles. Frugivory is a key biotic interaction in the tropics due to its wide representation among mammals and its effects on forest dynamics. We assessed how human disturbance affects interactions between mammalian frugivores and Attalea butyracea fruit deposited on the forest floor by comparing visits to palms at two sites with contrasting levels of human disturbance (non–disturbed vs. disturbed sites) in the Lacandon rainforest in southern Mexico. Using camera traps, we recorded mammal species interacting with fruit and estimated their interaction strength. The frugivore ensemble was richer in the non–disturbed forest (nine species) than in the disturbed forest (four species), which lacked the largest body–sized mammals. Large–bodied mammals showed a stronger interaction with fruit in terms of the frequency and length of their visits. Our study highlights the need to undertake conservation actions not only to ensure that the species are maintained in disturbed forests but also to ensure that their biotic interactions remain unchanged.

The mutualism-antagonism continuum in Neotropical palm-frugivore interactions: from interaction outcomes to ecosystem dynamics

Frugivory, that is feeding on fruits, pulp or seeds by animals, is usually considered a mutualism when interactions involve seed dispersal, and an antagonism when it results in the predation and destruction of seeds. Nevertheless, most frugivory interactions involve both benefits and disadvantages for plants, and the net interaction outcomes thus tend to vary along a continuum from mutualism to antagonism. Quantifying outcome variation is challenging and the ecological contribution of frugivorous animals to plant demography thus remains little explored. This is particularly true for interactions in which animals do not ingest entire fruits, that is in seed‐eating and pulp‐eating. Here, we provide a comprehensive review of Neotropical palm–frugivore interactions, with a focus on how frugivore consumption behaviour (i.e. digestive processing, fruit‐handling ability and caching behaviour) and feeding types (fruit‐eating, pulp‐eating and seed‐eating) influence interaction outcomes at different demographic stages of palms. We compiled a total of 1043 species‐level palm–frugivore interaction records that explicitly captured information on which parts of palm fruits are eaten by animals. These records showed consumption of fruits of 106 Neotropical palm species by 273 vertebrate species, especially birds (50%) and mammals (45%), but also fish (3%) and reptiles (2%). Fruit‐eating involved all four taxonomic vertebrate classes whereas seed‐eating and pulp‐eating were only recorded among birds and mammals. Most fruit‐eating interactions (77%) resulted in positive interaction outcomes for plants (e.g. gut‐passed seeds are viable or seeds are successfully dispersed), regardless of the digestive processing type of vertebrate consumers (seed defecation versus regurgitation). The majority of pulp‐eating interactions (91%) also resulted in positive interaction outcomes, for instance via pulp removal that promoted seed germination or via dispersal of intact palm seeds by external transport, especially if animals have a good fruit‐handling ability (e.g. primates, and some parrots). By contrast, seed‐eating interactions mostly resulted in dual outcomes (60%), where interactions had both negative effects on seed survival and positive outcomes through seed caching and external (non‐digestive) seed dispersal. A detailed synthesis of available field studies with qualitative and quantitative information provided evidence that 12 families and 27 species of mammals and birds are predominantly on the mutualistic side of the continuum whereas five mammalian families, six mammal and one reptile species are on the antagonistic side. The synthesis also revealed that most species can act as partial mutualists, even if they are typically considered antagonists. Our review demonstrates how different consumption behaviours and feeding types of vertebrate fruit consumers can influence seed dispersal and regeneration of palms, and thus ultimately affect the structure and functioning of tropical ecosystems. Variation in feeding types of animal consumers will influence ecosystem dynamics via effects on plant population dynamics and differences in long‐distance seed dispersal, and may subsequently affect ecosystem functions such as carbon storage. The quantification of intra‐ and inter‐specific variation in outcomes of plant–frugivore interactions – and their positive and negative effects on the seed‐to‐seedling transition of animal‐dispersed plants – should be a key research focus to understand better the mutualism–antagonism continuum and its importance for ecosystem dynamics.

Cloning capacity helps seeds of Garcinia xanthochymus counter animal predation

Seed predators have the potential to act as agents of natural selection that influence seed traits and seed fates, which in turn affect the whole plant population dynamic. Accordingly, plants deploy a variety of mechanisms (e.g., resistance and tolerance strategies) to lessen the impact of predation on seed crop or on an individual seed. In this study, we described a novel mechanism, seed cloning strategy, in a tropical plant species in countering animal predation. By conducting field- and laboratory-based germination experiments, we found that both rodent damaged and artificially damaged seed fragments of a large-seeded tree Garcinia xanthochymus (Clusiaceae) could successfully germinate and establish as seedlings. Tissue culture experiments revealed that G. xanthochymus has no endosperm in seeds, and its seed fragments own strong capacity of differentiation and cloning. Seed damage negatively affected seedling growth and germination, but the seed germination rate was remarkably high. Our study suggests that, seed cloning capacity, adopted by the large-seeded tree G. xanthochymus may act as a novel strategy counteract for seed predation and would play a significant role in stabilizing the mutualism between plant and animals.

Sowing forests: a synthesis of seed dispersal and predation by agoutis and their influence on plant communities

Granivorous rodents have been traditionally regarded as antagonistic seed predators. Agoutis (Dasyprocta spp.), however, have also been recognized as mutualistic dispersers of plants because of their role as scatter-hoarders of seeds, especially for large-seeded species. A closer look shows that such definitions are too simplistic for these Neotropical animals because agoutis can influence plant communities not only through seed dispersal of large seeds but also through predation of small seeds and seedlings, evidencing their dual role. Herein, we summarize the literature on plant-agouti interactions, decompose agouti seed dispersal into its quantitative and qualitative components, and discuss how environmental factors and plant traits determine whether these interactions result in mutualisms or antagonisms. We also look at the role of agoutis in a community context, assessing their effectiveness as substitutes for extinct megafaunal frugivores and comparing their ecological functions to those of other extant dispersers of large seeds. We also discuss how our conclusions can be extended to the single other genus in the Dasyproctidae family (Myoprocta). Finally, we examine agoutis' contribution to carbon stocks and summarize current conservation threats and efforts. We recorded 164 interactions between agoutis and plants, which were widespread across the plant phylogeny, confirming that agoutis are generalist frugivores. Seed mass was a main factor determining seed hoarding probability of plant species and agoutis were found to disperse larger seeds than other large-bodied frugivores. Agoutis positively contributed to carbon storage by preying upon seeds of plants with lower carbon biomass and by dispersing species with higher biomass. This synthesis of plant-agouti interactions shows that ecological services provided by agoutis to plant populations and communities go beyond seed dispersal and predation, and we identify still unanswered questions. We hope to emphasise the importance of agoutis in Neotropical forests.

Seed dispersal as a search strategy: dynamic and fragmented landscapes select for multi-scale movement strategies in plants

BACKGROUND

Plant dispersal is a critical factor driving ecological responses to global changes. Knowledge on the mechanisms of dispersal is rapidly advancing, but selective pressures responsible for the evolution of dispersal strategies remain elusive. Recent advances in animal movement ecology identified general strategies that may optimize efficiency in animal searches for food or habitat. Here we explore the potential for evolution of similar general movement strategies for plants.

METHODS

We propose that seed dispersal in plants can be viewed as a strategic search for suitable habitat, where the probability of finding such locations has been optimized through evolution of appropriate dispersal kernels. Using model simulations, we demonstrate how dispersal strategies can optimize key dispersal trade-offs between finding habitat, avoiding kin competition, and colonizing new patches. These trade-offs depend strongly on the landscape, resulting in a tight link between optimal dispersal strategy and spatiotemporal habitat distribution.

RESULTS

Our findings reveal that multi-scale seed dispersal strategies that combine a broad range of dispersal scales, including Lévy-like dispersal, are optimal across a wide range of dynamic and patchy landscapes. At the extremes, static and patchy landscapes select for dispersal strategies dominated by short distances, while uniform and highly unpredictable landscapes both select for dispersal strategies dominated by long distances.

CONCLUSIONS

By viewing plant seed dispersal as a strategic search for suitable habitat, we provide a reference framework for the analysis of plant dispersal data. Consideration of the entire dispersal kernel, including distances across the full range of scales, is key. This reference framework helps identify plant species' dispersal strategies, the evolutionary forces determining these strategies and their ecological consequences, such as a potential mismatch between plant dispersal strategy and altered spatiotemporal habitat dynamics due to land use change. Our perspective opens up directions for future studies, including exploration of composite search behaviour and 'informed searches' in plant species with directed dispersal.

Landscape disturbance impacts on Attalea butyracea palm distribution in central Panama

BACKGROUND

Increased Attalea butyracea palm propagation, notable for its role as key habitat for the primary Chagas disease vector in Panama, has been linked to landscape disturbance in single-palm observations in this region. Close proximity of these palms to human dwellings is proposed to increase risk of Chagas disease transmission from sylvatic transmission cycles to domestic transmission involving human populations. This study examines the relationship between landscape disturbance and mature A. butyracea spatial distribution, density, and proximity to human populations and vector and reservoir species' movement corridors at a regional scale in a 300 km2 heterogeneous tropical landscape in central Panama.

METHODS

We remotely identified the locations of over 50,000 mature A. butyracea palms using high-resolution WorldView2 satellite imagery. A local Getis-Ord Gi* spatial analysis identified significant clusters of aggregated palms. Associations between palm and cluster abundance and a landscape disturbance gradient, derived from official Panama land cover data, were tested using Chi-square tests for Homogeneity and Z-test for proportions. Kruskall-Wallis non-parametric analysis of variance tests were run to assess whether palm cluster area varied by disturbance level, or whether disturbance was associated with proximity of palms and palm clusters to susceptible populations or vector movement corridors.

RESULTS

Our findings indicate a regional relationship between landscape disturbance and A. butyracea occurrence. We observe a significant increase in both individual and clustered A. butyracea in secondary forest, but a reduction of palms in agricultural settings. We do not detect evidence of any reduction in abundance of palms in residential settings. The majority of residential and commercial buildings in our study area are within vector flight distance of potential vector habitat in palm crowns.

CONCLUSIONS

We observe probable anthropogenic elimination of A. butyracea palms in agricultural, but not residential, settings. Even in heavily deforested regions, significant concentrations of mature palms remain in close proximity to human establishments.

Effects of microhabitat on rodent-mediated seed removal of endangered Kmeria septentrionalis in the karst habitat

Seed removal behaviors of rodents are largely influenced by microhabitat. Although the karst ecosystem is composed of a broad variety of microhabitats, we have no information on how they affect such behaviors. We investigated rodents’ seed removal behaviors in four karst microhabitats (stone cavern, stone groove, stone surface, and soil surface) using three types of Kmeria septentrionalis seeds: fresh, black (intact seeds with black aril that dehydrates and darkens), and exposed (clean seeds without the aril). We show that Rattus norvegicus, Leopoldamys edwardsi and Rattus flavipectus were the predominant seed predators. Even though all seed types experienced a high removal rate in all four microhabitats, but rodents preferentially removed seeds from the three stone microhabitats (stone caves: 69.71 ± 2.74%; stone surface: 60.53 ± 2.90%; stone groove: 56.94 ± 2.91%) compared to the soil surface (53.90 ± 2.92%). Seeds that had been altered by being exposed to the environment were more attractive to rodents than fresh seeds (76.25 ± 2.20% versus 36.18 ± 2.29%). The seed removal behavior of rodents was significantly affected by the microhabitat and seed type. Finally, seeds that had fallen on the soil surface microhabitat incurred a lower predation risk than seeds fallen on other microhabitats, which increased their probability to germinate. Our results indicate that the lower predation rate of seeds from the endangered K. septentrionalis dropped on the soil surface increases trees’ likelihood of survival.

Landscape Genetics of Plants: Challenges and Opportunities

Dispersal is one of the most important but least understood processes in plant ecology and evolutionary biology. Dispersal of seeds maintains and establishes populations, and pollen and seed dispersal are responsible for gene flow within and among populations. Traditional views of dispersal and gene flow assume models that are governed solely by geographic distance and do not account for variation in dispersal vector behavior in response to heterogenous landscapes. Landscape genetics integrates population genetics with Geographic Information Systems (GIS) to evaluate the effects of landscape features on gene flow patterns (effective dispersal). Surprisingly, relatively few landscape genetic studies have been conducted on plants. Plants present advantages because their populations are stationary, allowing more reliable estimates of the effects of landscape features on effective dispersal rates. On the other hand, plant dispersal is intrinsically complex because it depends on the habitat preferences of the plant and its pollen and seed dispersal vectors. We discuss strategies to assess the separate contributions of pollen and seed movement to effective dispersal and to delineate the effects of plant habitat quality from those of landscape features that affect vector behavior. Preliminary analyses of seed dispersal for three species indicate that isolation by landscape resistance is a better predictor of the rates and patterns of dispersal than geographic distance. Rates of effective dispersal are lower in areas of high plant habitat quality, which may be due to the effects of the shape of the dispersal kernel or to movement behaviors of biotic vectors. Landscape genetic studies in plants have the potential to provide novel insights into the process of gene flow among populations and to improve our understanding of the behavior of biotic and abiotic dispersal vectors in response to heterogeneous landscapes.

Is Variation in Conspecific Negative Density Dependence Driving Tree Diversity Patterns at Large Scales?

Half a century ago, Janzen and Connell hypothesized that the high tree species diversity in tropical forests is maintained by specialized natural enemies. Along with other mechanisms, these can cause conspecific negative density dependence (CNDD) and thus maintain species diversity. Numerous studies have measured proxies of CNDD worldwide, but doubt about its relative importance remains. We find ample evidence for CNDD in local populations, but methodological limitations make it difficult to assess if CNDD scales up to control community diversity and thereby local and global biodiversity patterns. A combination of more robust statistical methods, new study designs, and eco-evolutionary models are needed to provide a more definite evaluation of the importance of CNDD for geographic variation in plant species diversity.

Seed nutrient content rather than size influences seed dispersal by scatterhoarding rodents in a West African montane forest

Rodents can be important in seed dispersal through their scatterhoarding behaviour, yet, the seed traits that are most influential in seed removal by Afrotropical scatterhoarding rodents remains unclear. Here, we investigated the effect of seed size and nutrient content of four seed species on the scatterhoarding behaviour of rodents in an Afromontane forest, Ngel Nyaki forest, Nigeria. To do this we marked with thread-tags the seeds of Santiria trimera, Beilschmedia mannii, Carapa oreophila and Anthonotha noldeae and observed their fate. We predicted that (1) caching frequency would be higher for larger than smaller seed species; (2) caching frequency would be higher for nutrient-rich than nutrient-poor seeds; (3) larger seeds would be taken across farther distances; and (4) survival of cached seeds would be higher for nutrient-rich seeds. In contrast to studies elsewhere we found no difference in caching probabilities based on seed size, although nutrient-rich (high fat content) seeds had a higher probability of being predated than seeds with lower fat content. Larger and smaller seeds were dispersed over the same distances and nutrient-poor (high fibre content) seeds survived longer in seed caches. Overall, our findings suggest that large, nutrient-rich seed species are less likely to be dispersed by rodents.

Friend or foe? A parasitic wasp shifts the cost/benefit ratio in a nursery pollination system impacting plant fitness

Nursery pollination systems are species interactions where pollinators also act as fruit/seed herbivores of the plant partner. While the plants depend on associated insects for pollination, the insects depend on the plants' reproductive structures for larval development. The outcome of these interactions is thus placed on a gradient between mutualism and antagonism. Less specialized interactions may fluctuate along this gradient with the ecological context, where natural enemies can play an important role. We studied whether a natural enemy may impact the level of seed consumption of a nursery pollinator and how this in turn may influence individual plant fitness. We used the plant Silene latifolia, its herbivore Hadena bicruris, and its ectoparasitoid Bracon variator as a model plant-herbivore-natural enemy system. We investigated seed output, germination, survival, and flower production as proxies for individual plant fitness. We show that B. variator decreases the level of seed consumption by H. bicruris larvae which in turn increased seed output in S. latifolia plants, suggesting that parasitism by B. variator may act as a regulator in the system. However, our results also show that plant survival and flower production decrease with higher seed densities, and therefore, an increase in seed output may be less beneficial for plant fitness than estimated from seed output alone. Our study should add another layer to the complex discussion of whether parasitoids contribute to plant fitness, as we show that taking simple proxies such as seed output is insufficient to determine the net effect of multitrophic interactions.

Conserving the Diversity of Ecological Interactions: The Role of Two Threatened Macaw Species as Legitimate Dispersers of “Megafaunal” Fruits

The extinction of ecological functions is increasingly considered a major component of biodiversity loss, given its pervasive effects on ecosystems, and it may precede the disappearance of the species engaged. Dispersal of many large-fruited (>4 cm diameter) plants is thought to have been handicapped after the extinction of megafauna in the Late Pleistocene and the recent defaunation of large mammals. We recorded the seed dispersal behavior of two macaws (Anodorhynchus hyacinthinus and Anodorhynchus leari) in three Neotropical biomes, totaling >1700 dispersal events from 18 plant species, 98% corresponding to six large-fruited palm species. Dispersal rates varied among palm species (5%–100%). Fruits were moved to perches at varying distances (means: 17–450 m, maximum 1620 m). Macaws also moved nuts after regurgitation by livestock, in an unusual case of tertiary dispersal, to distant perches. A high proportion (11%–75%) of dispersed nuts was found undamaged under perches, and palm recruitment was confirmed under 6%–73% of the perches. Our results showed that these macaws were legitimate, long-distance dispersers, and challenge the prevailing view that dispersal of large-fruited plants was compromised after megafauna extinction. The large range contraction of these threatened macaws, however, meant that these mutualistic interactions are functionally extinct over large areas at a continental scale.

Intrinsic and extrinsic drivers of intraspecific variation in seed dispersal are diverse and pervasive

There is growing realization that intraspecific variation in seed dispersal can have important ecological and evolutionary consequences. However, we do not have a good understanding of the drivers or causes of intraspecific variation in dispersal, how strong an effect these drivers have, and how widespread they are across dispersal modes. As a first step to developing a better understanding, we present a broad, but not exhaustive, review of what is known about the drivers of intraspecific variation in seed dispersal, and what remains uncertain. We start by decomposing 'drivers of intraspecific variation in seed dispersal' into intrinsic drivers (i.e. variation in traits of individual plants) and extrinsic drivers (i.e. variation in ecological context). For intrinsic traits, we further decompose intraspecific variation into variation among individuals and variation of trait values within individuals. We then review our understanding of the major intrinsic and extrinsic drivers of intraspecific variation in seed dispersal, with an emphasis on variation among individuals. Crop size is the best-supported and best-understood intrinsic driver of variation across dispersal modes; overall, more seeds are dispersed as more seeds are produced, even in cases where per seed dispersal rates decline. Fruit/seed size is the second most widely studied intrinsic driver, and is also relevant to a broad range of seed dispersal modes. Remaining intrinsic drivers are poorly understood, and range from effects that are probably widespread, such as plant height, to drivers that are most likely sporadic, such as fruit or seed colour polymorphism. Primary extrinsic drivers of variation in seed dispersal include local environmental conditions and habitat structure. Finally, we present a selection of outstanding questions as a starting point to advance our understanding of individual variation in seed dispersal.

The total dispersal kernel: a review and future directions

The distribution and abundance of plants across the world depends in part on their ability to move, which is commonly characterized by a dispersal kernel. For seeds, the total dispersal kernel (TDK) describes the combined influence of all primary, secondary and higher-order dispersal vectors on the overall dispersal kernel for a plant individual, population, species or community. Understanding the role of each vector within the TDK, and their combined influence on the TDK, is critically important for being able to predict plant responses to a changing biotic or abiotic environment. In addition, fully characterizing the TDK by including all vectors may affect predictions of population spread. Here, we review existing research on the TDK and discuss advances in empirical, conceptual modelling and statistical approaches that will facilitate broader application. The concept is simple, but few examples of well-characterized TDKs exist. We find that significant empirical challenges exist, as many studies do not account for all dispersal vectors (e.g. gravity, higher-order dispersal vectors), inadequately measure or estimate long-distance dispersal resulting from multiple vectors and/or neglect spatial heterogeneity and context dependence. Existing mathematical and conceptual modelling approaches and statistical methods allow fitting individual dispersal kernels and combining them to form a TDK; these will perform best if robust prior information is available. We recommend a modelling cycle to parameterize TDKs, where empirical data inform models, which in turn inform additional data collection. Finally, we recommend that the TDK concept be extended to account for not only where seeds land, but also how that location affects the likelihood of establishing and producing a reproductive adult, i.e. the total effective dispersal kernel.

Land-use change and the ecological consequences of personality in small mammals

Many plants rely on animals for seed dispersal, but are all individuals equally effective at dispersing seeds? If not, then the loss of certain individual dispersers from populations could have cascade effects on ecosystems. Despite the importance of seed dispersal for forest ecosystems, variation among individual dispersers and whether land-use change interferes with this process remains untested. Through a large-scale field experiment conducted on small mammal seed dispersers, we show that an individual's personality affects its choice of seeds, as well as how distant and where seeds are cached. We also show that anthropogenic habitat modifications shift the distribution of personalities within a population, by increasing the proportion of bold, active, and anxious individuals and in-turn affecting the potential survival and dispersal of seeds. We demonstrate that preserving diverse personality types within a population is critical for maintaining the key ecosystem function of seed dispersal.

Rodent-Mediated Seed Dispersal Shapes Species Composition and Recruitment Dynamics in Ecotones

Ecotones are considered unique environments, and the concepts of edge effects and ecotonal species have been applied widely. Our understanding of the mechanisms that underlie population and community responses to edge effects has been advanced by recent studies. However, little evidence exists to support an increased density and species richness in ecotones regarding rodent-mediated seed dispersal in response to edge plots between communities. Pinus armandii and Quercus variabilis communities are typical of the Qinling Mountains, China. To elucidate what shapes tree species composition and recruitment dynamics in ecotones, we compared the differences in secondary and tertiary seed dispersal as well as predation in pine and oak by scatter-hoarding rodents as well as the regeneration characteristics of both species in their ecotones with different plots (i.e., 5-8, 15-18, and 27-30 m widths) in the eastern Qinling Mountains. We found that the seeds of pine and oak were removed rapidly, with no differences in the seed removal rates in their ecotones with different plots. Moreover, 13.0 and 36.0% of the scatter hoards of pine and oak, respectively, were established by small rodents in ecotones with a width of 5-8 m, and 3.67 and 7.33% in ecotones with a width of 27-30 m. The seedling densities of pine and oak were significantly higher in ecotones at widths of 5-8 m compared with widths of 15-18 and 27-30 m. According to the seed dispersal and seedling recruitment patterns of pine and oak, the disproportionate abundance of seedlings in ecotones may be due at least partly to patterns of seed caching by rodents.

Weaker plant-enemy interactions decrease tree seedling diversity with edge-effects in a fragmented tropical forest

In fragmented forests, tree diversity declines near edges but the ecological processes underlying this loss of diversity remain poorly understood. Theory predicts that top-down regulation of seedling recruitment by insect herbivores and fungal pathogens contributes to maintaining tree diversity in forests, but it is unknown whether proximity to forest edges compromises these diversity-enhancing biotic interactions. Here we experimentally demonstrate that weakened activity of fungal pathogens and insect herbivores reduced seedling diversity, despite similar diversity of seed rain, during recruitment near forest edges in a human-modified tropical landscape. Only at sites farthest from forest edges (90-100 m) did the application of pesticides lower seedling diversity relative to control plots. Notably, lower seedling diversity corresponded with weaker density-dependent mortality attributable to insects and fungi during the seed-to-seedling transition. We provide mechanistic evidence that edge-effects can manifest as cryptic losses of crucial biotic interactions that maintain diversity.

Density-dependent seed predation in Attalea geraensis Barb. Rodr. (Arecaceae) caused by bruchid beetles in the Brazilian Cerrado

Palms are an important component of Neotropical communities as they are often diverse and abundant. In some areas, palms occur in high density and act as limiting factor in tree recruitment by limiting tree seedling and sapling abundance. In this study, I evaluated the intensity of seed mortality caused by insects in Attalea geraensis, in a large area of preserved Cerrado (Serra do Cabral, MG, Brazil) during wet season when both A. geraensis fruits and bruchid beetles were abundant. I collected a total of 63 infructescences which had from 3 fruits and 7 seeds to 82 fruits and 251 seeds. Endocarps had from 1 to 6 seeds. Seed mortality per infructescence due to beetles (Pachymerus cardo) was intense, and increases positively and disproportionally according to seed number per infructescence. Besides that, average proportions of seeds preyed upon by insects were consistently high (> 0.83), irrespective of seed number per endocarp. Positive density-dependent seed mortality caused by specialized natural enemies has been assumed to promote species rarity, an important feature of species coexistence in Neotropical forests. Then, the intense seed mortality documented in this study suggests that seed predators may contribute to the richness and diversity of plant species in the Cerrado, the richest and most endangered savanna in the world.

The effect of size and density on nut removal in Syagrus loefgrenii Glassman (Arecaceae) in the Brazilian Cerrado

In this study I tested the effect of Syagrus loefgrenii nut size and number on the intensity of removal by rodents across seasons. Trials were performed in which piles of either small or large endocarps (1, 3, 6, 12, and 25) were subjected to removal by rodents in the Cerrado (Brazilian savanna). Despite of variations in the intensity of removal, always this process decrease conform endocarp number. Also, mean proportion of endocarp removal was unrelated to year period, initial number, and size of endocarps. Hence, endocarp removal was consistently negative density-dependent. As, in principle, the observed patterns of nut removal point out similar survival chances for both nut sizes, the pervasive negative density-dependent response emerges as a strategy in S. loefgrenii to swamp rodents all year round irrespective of seed size.

Effects of fragmentation on the seed predation and dispersal by rodents differ among species with different seed size

Fragmentation influences the population dynamics and community composition of vertebrate animals. Fragmentation effects on rodent species in forests may, in turn, affect seed predation and dispersal of many plant species. Previous studies have usually addressed this question by monitoring a single species, and their results are contradictory. Very few studies have discussed the fragmentation effect on rodent-seed interaction among tree species with different seed sizes, which can significantly influence rodent foraging preference and seed fate. Given that fruiting periods for many coexisting plant species overlap, the changing foraging preference of rodents may substantially alter plant communities. In this study, we monitored the dispersal and predation by rodents of 9600 seeds, belonging to 4 Fagaceae species with great variation in seed size, in both the edge and interior areas of 12 tropical forest fragments ranging in area from 6.3 to 13872.9 ha in Southwest China. The results showed that forest fragmentation altered the seed fates of all the species, but the intensity and even the direction of fragmentation effect differed between species with large versus small seeds. For the seeds harvested, fragment size showed negative effects in forest interiors but positive effects at edges for the 2 large-seeded species, but showed little effect for the 2 small-seeded species. For the seeds removed, negative effects of fragment size only existed among the small-seeded species. The different fragmentation effect on seed dispersal and predation among plant species may, in turn, translate into the composition differences of the regeneration of the whole fragmented forest.

Effects of local biotic neighbors and habitat heterogeneity on seedling survival in a spruce-fir valley forest, northeastern China

Seedlings are vulnerable to many biotic and abiotic agents, and studying seedling dynamics helps understand mechanisms of species coexistence. In this study, the relative importance of biotic neighbors and habitat heterogeneity to seedling survival was examined by generalized linear mixed models for 33 species in a spruce‐fir valley forest in northeastern China. The results showed that the relative importance of these factors varied with species and functional groups. Conspecific negative density dependence (CNDD) was important to the survival of Abies nephrolepis and Picea koraiensis seedling, whereas phylogenetic negative density dependence (PNDD) was critical to Pinus koraiensis and Betula platyphylla, as well as functional groups of tree, deciduous, and shade‐intolerant seedlings. For shrubs and Acer ukurunduense, habitat heterogeneity was significant. Despite of the significance of CNDD, PNDD, and habitat heterogeneity on seedling survival, large proportions of the total variance were not accounted for by the studied variables, suggesting the needs to examine the influences of other factors such as pests, diseases, herbivores, forest structure, species functional traits, and microclimatic conditions on seedling survival in the future.

Seed removal of Dipteryx alata Vog. (Leguminosae: Faboidae) in the edge and interior of Cerrado

Abstract Post-dispersal seed agents of mortality include pathogens, invertebrates, and vertebrates, which may shape tropical tree populations and communities. In this study I experimentally evaluated Dipteryx alata endocarp removal both in the interior and edge of Cerrado vegetation. Specifically, I simulated primary dispersion of endocarps by bats and evaluated secondary removal intensity according to habitat, season, and endocarp number. This study was developed in the Pombo Natural Municipal Park, a large Cerrado remnant with an area of 9,000 ha, located in the Western Brazil. In each of the two habitat types, I set down 45 points in which D. alata piles of 1, 3, 7, 15, and 40 endocarps were positioned. On average, endocarp removal in the interior was higher than in the edge, so that the intensity of removal varied from positive density-dependent (interior: rains), to negative density-dependent (edge: both seasons). Also, at both habitat types and seasons non removed endocarps were intensely attacked by fungus. Indeed, seed mortality by fungus infestation was positive density-dependent. The results indicate high propensity of endocarps to escape from removal in the edge, in principle, a defaunated area. As Dipteryx species strongly rely on caviomorph rodents for their dispersal, the scarcity of these vectors might reduce recruitment chances of D. alata in remnants of Cerrado. This imply in future changes in the vegetation structure from the edge to the interior towards low tree diversity.

Natural persistence of the coastal plant Glehnia littoralis along temperate sandy coasts

We studied germination behaviors and persistence mechanism of wild Glehnia littoralis, a typical coastal species at temperate sandy coasts of the North Pacific Ocean, and tested the hypothesis that the coastal plants may have evolved special seeds adapting to the coasts, by which they recruit and persist easily, occupying the coasts as ideal habitats. In the Shandong Peninsula, China, we investigated temperature and moisture conditions of coast sand in relation to germination and evaluated effects of sand burial, seawater immersion and sowing time on germination. When germination began, daily dawn temperatures of sand were about 10 °C and daily noon temperatures were about 25 °C; the temperatures were not different in the sand <8 cm deep. The sand at these depths showed a significant difference in moisture contents. The seeds exhibited large germination rates if sand burial was at depths >= 3 cm and winter freezing was kept longer than 2.5 months. Seeds experiencing seawater immersion were able to germinate well. These evidences suggest that G. littoralis has evolved special seeds adapting to seawater dispersal and specific season rhythm. By the seeds, G. littoralis occupies temperate sandy coasts as ideal habitats to persist.

Adult trees cause density-dependent mortality in conspecific seedlings by regulating the frequency of pathogenic soil fungi

Negative density-dependent seedling mortality has been widely detected in tropical, subtropical and temperate forests, with soil pathogens as a major driver. Here we investigated how host density affects the composition of soil pathogen communities and consequently influences the strength of plant-soil feedbacks. In field censuses of six 1-ha permanent plots, we found that survival was much lower for newly germinated seedlings that were surrounded by more conspecific adults. The relative abundance of pathogenic fungi in soil increased with increasing conspecific tree density for five of nine tree species; more soil pathogens accumulated around roots where adult tree density was higher, and this greater pathogen frequency was associated with lower seedling survival. Our findings show how tree density influences populations of soil pathogens, which creates plant-soil feedbacks that contribute to community-level and population-level compensatory trends in seedling survival.

Cascading effects of defaunation on the coexistence of two specialized insect seed predators

Identification of the mechanisms enabling stable coexistence of species with similar resource requirements is a central challenge in ecology. Such coexistence can be facilitated by species at higher trophic levels through complex multi-trophic interactions, a mechanism that could be compromised by ongoing defaunation. We investigated cascading effects of defaunation on Pachymerus cardo and Speciomerus giganteus, the specialized insect seed predators of the Neotropical palm Attalea butyracea, testing the hypothesis that vertebrate frugivores and granivores facilitate their coexistence. Laboratory experiments showed that the two seed parasitoid species differed strongly in their reproductive ecology. Pachymerus produced many small eggs that it deposited exclusively on the fruit exocarp (exterior). Speciomerus produced few large eggs that it deposited exclusively on the endocarp, which is normally exposed only after a vertebrate handles the fruit. When eggs of the two species were deposited on the same fruit, Pachymerus triumphed only when it had a long head start, and the loser always succumbed to intraguild predation. We collected field data on the fates of 6569 Attalea seeds across sites in central Panama with contrasting degrees of defaunation and wide variation in the abundance of vertebrate frugivores and granivores. Speciomerus dominated where vertebrate communities were intact, whereas Pachymerus dominated in defaunated sites. Variation in the relative abundance of Speciomerus across all 84 sampling sites was strongly positively related to the proportion of seeds attacked by rodents, an indicator of local vertebrate abundance.

SYNTHESIS

We show that two species of insect seed predators relying on the same host plant species are niche differentiated in their reproductive strategies such that one species has the advantage when fruits are handled promptly by vertebrates and the other when they are not. Defaunation disrupts this mediating influence of vertebrates and strongly favours one species at the expense of the other, providing a case study of the cascading effects of defaunation and its potential to disrupt coexistence of non-target species, including the hyperdiverse phytophagous insects of tropical forests.

Nut density and removal in Syagrus loefgrenii Glassman (Arecaceae) in the Brazilian Cerrado

Abstract In this study, I tested the effect of Syagrus loefgrenii nut number on the removal intensity by rodents across seasons. Also, I assessed both S. loefgrenii fruit production, and dispersion pattern to analyze the relationship between these parameters and nut removal. Trials were performed (autumn, winter, spring, and summer), in which endocarps were placed inside trays (5, 15, and 40 endocarps) in the Cerrado (Brazilian savanna). Syagrus loefgrenii exhibited clumped distribution, although its local density had no correlation with endocarp removal rate. Despite of variations, S. loefgrenii fruit production had no seasonal difference, although, high proportions of endocarps were year round removed. This mostly results from nearly complete endocarp loss in depots of 5 and 15, while the opposite occurred in those of 40. Hence, the intensity of removal consistently decreases with endocarp number, so that endocarp removal conformed to negative distance-dependence. As this palm exhibit clumped distribution and, in principle, fruit asynchronously, if, at least, a group of neighboring stems bore fruits simultaneously, an enhanced number of nuts might be available at a given site. Therefore, seeds within a dense S. loefgrenii fruit patch might experience high survival rates due to satiation of post dispersal seed predators.

The contribution of seed dispersers to tree species diversity in tropical rainforests

Tropical rainforests are known for their extreme biodiversity, posing a challenging problem in tropical ecology. Many hypotheses have been proposed to explain the diversity of tree species, yet our understanding of this phenomenon remains incomplete. Here, we consider the contribution of animal seed dispersers to the species diversity of trees. We built a multi-layer lattice model of trees whose animal seed dispersers are allowed to move only in restricted areas to disperse the tree seeds. We incorporated the effects of seed dispersers in the traditional theory of allopatric speciation on a geological time scale. We modified the lattice model to explicitly examine the coexistence of new tree species and the resulting high biodiversity. The results indicate that both the coexistence and diversified evolution of tree species can be explained by the introduction of animal seed dispersers.

Drivers of seedling survival in a temperate forest and their relative importance at three stages of succession

Negative density dependence (NDD) and niche partitioning have been perceived as important mechanisms for the maintenance of species diversity. However, little is known about their relative contributions to seedling survival. We examined the effects of biotic and abiotic neighborhoods and the variations of biotic neighborhoods among species using survival data for 7503 seedlings belonging to 22 woody species over a period of 2 years in three different forest types, a half-mature forest (HF), a mature forest (MF), and an old-growth forest (OGF), each of these representing a specific successional stage in a temperate forest ecosystem in northeastern China. We found a convincing evidence for the existence of NDD in temperate forest ecosystems. The biotic and abiotic variables affecting seedlings survival change with successional stage, seedling size, and age. The strength of NDD for the smaller (<20 cm in height) and younger seedlings (1-2 years) as well as all seedlings combined varies significantly among species. We found no evidence that a community compensatory trend (CCT) existed in our study area. The results of this study demonstrate that the relative importance of NDD and habitat niche partitioning in driving seedling survival varies with seedling size and age and that the biotic and abiotic factors affecting seedlings survival change with successional stage.

The critical role of ants in the extensive dispersal of Acacia seeds revealed by genetic parentage assignment

Ants are prominent seed dispersal agents in many ecosystems, and dispersal distances are small in comparison with vertebrate dispersal agents. However, the distance and distribution of ant-mediated dispersal in arid/semi-arid environments remains poorly explored. We used microsatellite markers and parentage assignment to quantify the distance and distribution of dispersed seeds of Acacia karina, retrieved from the middens of Iridomyrmex agilis and Melophorus turneri perthensis. From parentage assignment, we could not distinguish the maternal from each parent pair assigned to each seed, so we applied two approaches to estimate dispersal distances, one conservative (CONS), where the parent closest to the ant midden was considered to be maternal, and the second where both parents were deemed equally likely (EL) to be maternal, and used both distances. Parentage was assigned to 124 seeds from eight middens. Maximum seed dispersal distances detected were 417 m (CONS) and 423 m (EL), more than double the estimated global maximum. Mean seed dispersal distances of 40 m (±5.8 SE) (CONS) and 79 m (±6.4 SE) (EL) exceeded the published global average of 2.24 m (±7.19 SD) by at least one order of magnitude. For both approaches and both ant species, seed dispersal was predominantly (44-84% of all seeds) within 50 m from the maternal source, with fewer dispersal events at longer distances. Ants in this semi-arid environment have demonstrated a greater capacity to disperse seeds than estimated elsewhere, which highlights their important role in this system, and suggests significant novel ecological and evolutionary consequences for myrmecochorous species in arid/semi-arid Australia.