Primary Seed Dispersal by Red Howler Monkeys and the Effect of Defecation Patterns on the Fate of Dispersed Seeds1

The effectiveness of a seed disperser depends on the quantity and quality of dispersal. The quality of dispersal depends in large part on factors that affect the post–dispersal fate of seeds, and yet this aspect of dispersal quality is rarely assessed. In the particular case of seed dispersal through endozoochory, the defecation pattern produced has the potential of affecting the fate of dispersed seeds and consequently, dispersal quality and effectiveness. In this study, I assessed the effects of dung presence and dung/seed densities on seed predation by rodents and secondary dispersal by dung beetles. In particular, I compared seed fates in clumped defecation patterns, as those produced by howler monkeys, with seed fates in scattered defecation patterns, as those produced by other frugivores. I also determined the prevalence of red howler monkeys (Alouatta seniculus) as seed dispersers at the plant community level in Central Amazonia by determining the number of species they dispersed in a 25–month period. I found that dung presence and amount affected rodent and dung beetle behavior. Seed predation rates were higher when dung was present, and when it was in higher densities. The same number of seeds was buried by dung beedes, in dumped versus scattered defecation patterns, but more seeds were buried when they were inside large dung–piles versus small piles. Seed density had no effect on rodent or dung beetle behavior. Results indicate that caution should be taken when categorizing an animal as a high or low quality seed disperser before carefully examining the factors that affect the fate of dispersed seeds. Red howler monkeys dispersed the seeds of 137 species during the study period, which is the highest yet reported number for an Alouatta species, and should thus be considered highly prevalent seed dispersers at the plant community level in Central Amazonian terra firme rain forests.     

Persistence of the effect of frugivore identity on post‐dispersal seed fate: consequences for the assessment of functional redundancy

Large frugivores play an important role as seed dispersers and their extinction may affect plant regeneration. The consequences of such extinctions depend on the likelihood of other species being functionally redundant and on how post‐dispersal events are affected. We assess the functional redundancy of two seed dispersers of the Atlantic Forest, the muriqui (Brachyteles arachnoides) and the tapir (Tapirus terrestris) through the comparison of their seed dispersal quality, taking into account post‐dispersal events. We compare tapirs and muriquis for: (1) the dung beetle community associated with their feces; (2) the seed burial probability and burial depth by dung beetles; and (3) the seed mortality due to predators or other causes according to burial depth. We determine how seed burial affects seed dispersal effectiveness (SDE) and compare the dispersal quality of four plant species dispersed by these frugivores. Muriqui feces attract 16‐fold more dung beetles per gram of fecal matter and seeds experience 10.5‐fold more burial than seeds in tapir feces. In both feces types, seed mortality due to predation decreases with burial depth but seed mortality due to other causes increases. Total seed mortality differ within plant species according to the primary disperser. Therefore, the effect of seed burial on SDE varies according to the plant species, burial depth, and primary disperser. As tapirs and muriquis differently affect the seed fate, they are not functionally redundant. Since the effect of the primary disperser persists into the post‐dispersal events, we should consider the cascading effects of these processes when assessing functional redundancy.     

Avian frugivory and seed dispersal of a large fruited tree in an Indian moist deciduous forest

Seed dispersal systems in degraded areas can be compromised following the decline of large-bodied frugivore populations responsible for their dispersal. In this context we examined the seed dispersal ecology of a large fruited deciduous tree (Dillenia pentagyna) along a forest degradation gradient in India. We examined the effect of structural components of vegetation and frugivore foraging behavior on D. pentagyna seed dispersal. Depauperate mammalian community and declined large avian frugivores e.g. hornbills in our study site make this system a specialized one and currently dependent on only two large bodied avian frugivores. Seed dispersal followed an overall leptokurtic pattern and the seed dispersal kernels were best explained by an inverse power function. Seed dispersal kernels in dense forest indicated longer dispersal distances than moderately dense forest and degraded forest. In degraded areas, no dispersal away from the crown was recorded for D. pentagyna and it occurred at low density. Canopy foliage abundance of the surrounding vegetation of the focal trees was best explained by quantity of seed dispersal by large avian frugivores. The number of avian frugivore species those are effective disperser of D. pentagyna decreased along the degradation gradient. Avian frugivore behavior in terms of visitation and seed swallowed is a determining factor that controls quantity of seed dispersal. Our study underscores deleterious impact of forest degradation on avian disperser community which in turn would affect regeneration capacity of degraded forest.     

Allometric allocation in fruit and seed packaging conditions the conflict among selective pressures on seed size

Selective pressures on seed size could vary among the different stages of plant life cycles, so no simple relation could explain a priori its evolution. Here, we determined the relationships between seed size and two fitness components—seed dispersal and survival from predation—in a bird-dispersed tree, Crataegus monogyna. We interpret these relationships in relation to the patterns of mass allocation to fruit and seed components. Selection patterns were assessed at two levels (1) selection pressures on the parent tree; comparing seed dispersal efficiency among individual plants and (2) selection pressures at the individual seed level; comparing seed size variation (i) before and after dispersal, and (ii) before and after postdispersal seed predation. Dispersal efficiency (percentage of seed crop dispersed) was positively correlated with fruit mass and fruit width. Differences in crop size did not offset this effect, and larger seeds were overrepresented in the seed rain relative to the seed pool before dispersal. However, the advantage of larger seeds during the dispersal stage was cancelled later by an opposite selection pressure exerted by seed predators. As a result, smaller seeds had a higher probability of surviving postdispersal seed predation, establishing an evolutionary conflict imposed by the need for dispersal and the danger of being predated. Birds and rodents preferentially selected highly profitable fruits and seeds in terms of the relative proportion of their components. Larger fruits had a higher pulp to seed proportion than smaller ones, and all seeds had the same proportion of coat relative to the embryo-plus-endosperm fraction. Hence, although predator pressures were stronger than disperser ones, larger seeds invested proportionally less in structural defense than in dispersal.     

Reliability of macaques as seed dispersers

Seed dispersal is an ecological process crucial for forest regeneration and recruitment. To date, most studies on frugivore seed dispersal have used the seed dispersal effectiveness framework and have documented seed-handling mechanisms, dispersal distances and the effect of seed handling on germination. In contrast, there has been no exploration of “disperser reliability” which is essential to determine if a frugivore is an effective disperser only in particular regions/years/seasons or across a range of spatio-temporal scales. In this paper, we propose a practical framework to assess the spatial reliability of frugivores as seed dispersers. We suggest that a frugivore genus would be a reliable disperser of certain plant families/genera if: (a) fruits of these plant families/genera are represented in the diets of most of the species of that frugivore, (b) these are consumed by the frugivore genus across different kinds of habitats, and (c) these fruits feature among the yearly staples and preferred fruits in the diets of the frugivore genus. Using this framework, we reviewed frugivory by the genus Macaca across Asia to assess its spatial reliability as seed dispersers. We found that the macaques dispersed the seeds of 11 plant families and five plant genera including at least 82 species across habitats. Differences in fruit consumption/preference between different groups of macaques were driven by variation in plant community composition across habitats. We posit that it is essential to maintain viable populations of macaques across their range and keep human interventions at a minimum to ensure that they continue to reliably disperse the seeds of a broad range of plant species in the Anthropocene. We further suggest that this framework be used for assessing the spatial reliability of other taxonomic groups as seed dispersers.     

Herbivorous mammals as seed dispersers in a Mediterranean dehesa

Endozoochrous seed dispersal by herbivorous mammals has been verified repeatedly and its possible influence on the structure and function of herbaceous communities has been suggested. Quantitative studies, however, are lacking in the field of seed dispersal via the dung of herbivore guilds in little-altered environments. The present paper analyses seed dispersal via rabbit, fallow deer, red deer and cow dung in a Mediterranean dehesa (open woodland used for hunting and ranching) during the seeding season. Dung seed content was determined by the glasshouse cultivation of eight dung samples from each herbivore, collected fortnightly between February and August. The four herbivores disperse many seeds (spring averages are 6–15 seeds per gram of dry dung and maxima of 25–70) from a large number of species (totals between 52 and 78). Dispersal seems to be mainly determined by seed production of the plant comminity. This is reflected in (i) the dissemination of a high percentage of the species present in the dehesa, (ii) great seasonal variability, related to seed production, in the amount of seeds and number of species dispersed, and (iii) a high semi-quantitative similarity of seed content in the four types of herbivore dung throughout the year. There is also important quantitative variation that depends on animal traits and feeding habits. These results and the characteristics of species found in dung suggest the adaptation of plant species to the dispersal of their seeds via herbivore gut. This process may well have profound implications for vegetation dynamics and the evolution of plant traits.     

The role of Orii’s flying-fox (Pteropus dasymallus inopinatus) as a pollinator and a seed disperser on Okinawa-jima Island, the Ryukyu Archipelago, Japan

The role of the Orii’s flying-fox (Pteropus dasymallus inopinatus) as a pollinator and a seed disperser on Okinawa-jima Island was investigated by direct observations and radio-tracking from October 2001 until January 2006. We found that Orii’s flying-fox potentially pollinated seven native plant species. Its feeding behavior and plant morphological traits suggested that this species is an important pollinator of Schima wallichii liukiuensis and Mucuna macrocarpa. The flying-fox also dispersed the seeds of 20 native plant species. The seeds of all plants eaten by the flying-fox were usually dropped beneath the parent tree, although large fruits of four plant species were occasionally brought to the feeding roosts in the mouth, with the maximum dispersal distance—for Terminalia catappa—estimated to be 126 m. Small seeds of 11 species (mostly Ficus species) were dispersed around other trees, during the subsequent feeding session, through the digestive tracts, with the mean dispersal distance for ingested seeds estimated at 150 ± 230.3 m (±SD); the maximum dispersal distance was 1833 m. A comparison of the seed dispersal of available fruits according to the size of flying-foxes and other frugivores suggested that the seed dispersal of eight plant species producing large fruits mostly depended on Orii’s flying-fox. On Okinawa-jima Island, the Orii’s flying-fox plays an important role as a pollinator of two native plants and as a long-distance seed disperser of Ficus species, and it functions as a limited agent of seed dispersal for plants producing large fruits on Okinawa-jima Island.     

Tree dispersal strategies in the littoral forest of Sainte Luce (SE-Madagascar)

Zoochory is the most common mode of seed dispersal for the majority of plant species in the tropics. Based on the assumption of tight plant-animal interactions several hypotheses have been developed to investigate the origin of life history traits of plant diaspores and their dispersers, such as species-specific co-evolution, the low/high investment model (low investment in single fruits but massive fruiting to attract many different frugivores versus high investment in single fruits and fruit production for extended periods to provide food for few frugivores), and the evolution of syndromes which represent plant adaptations to disperser groups (e.g. birds, mammals, mixed). To test these hypotheses the dispersal strategies of 34 tree species were determined in the littoral forest of Sainte Luce (SE-Madagascar) with the help of fruit traps and tree watches. The impact of fruit consumers on the seeds was determined based on detailed behavioral observations. Phenological, morphological and biochemical fruit traits from tree species were measured to look for co-variation with different types of dispersal. No indication for species-specific co-evolution could be found nor any support for the low/high investment model. However dispersal syndromes could be distinguished as diaspores dispersed by birds, mammals or both groups (mixed) differ in the size of their fruits and seeds, fruit shape, and seed number, but not in biochemical traits. Five large-seeded tree species seem to depend critically on the largest lemur, Eulemur fulvus collaris, for seed dispersal. However, this does not represent a case of tight species-specific co-evolution. Rather it seems to be the consequence of the extinction of the larger frugivorous birds and lemurs which might also have fed on these large fruits. Nevertheless these interactions are of crucial importance to conserve the integrity of the forest.     

Microsites of seed arrival: spatio–temporal variations in complex seed‐disperser networks

Microsites where seeds arrive during the dispersal process determine plant reproductive success, affecting the quality of dispersal. Despite their crucial role for plant recruitment, very few studies have addressed spatio–temporal variations in microsites of seed arrival in complex seed‐disperser networks. Using an endozoochorous dispersal system, we characterized the microsites of seed arrival of eight fleshy‐fruited plant species dispersed by five mammal species during two consecutive seasons across three sites in a Mediterranean environment (n = 383 feces with seeds; 261 453 seeds). We evaluated spatial and temporal variations in the probability of a seed to arrive at open microsites or at microsites with varying plant cover, considering selection by frugivores and assessing the extent to which seeds of particular species arrived under conspecifics or heterospecifics. We found strong spatio–temporal variations in the amounts of seeds of the eight target species arriving at different microsites. These variations were strongly driven by frugivores’ selection of different landscape elements (i.e. open areas and microsites dominated by different plant species), which differed from expectations based on their local availability. In general, more seeds than expected arrived at vacant (open) microsites. Using bipartite network graphs to connect seeds with their arrival microsites, we found that the proportion of seeds of fleshy‐fruited species arriving near conspecifics or heterospecifics, or at vacant microsites, varied depending on the target plant species, but also on the frugivore species dispersing it, on the study site and on the dispersal season. Our study revealed marked spatio–temporal variations in the microsites of seed arrival, which will potentially have implications for the quality of dispersal effectiveness, ultimately affecting plant population dynamics and community structure. Such a strong context‐dependence in the microsites of seed arrival is likely to confer resilience against unpredictable environmental conditions, like those typical of Mediterranean ecosystems.     

A herbivory-induced increase in the proportion of floating seeds in an invasive plant

It is important to determine the factors prompting seed dispersal because for plant species seed dispersal is the only opportunity to disperse into a new habitat. Previous studies showed that the maternal stress, such as high density and low nutrient levels, induces the adaptive plastic increase of the dispersal ability in seed heteromorphic plants. In this study, we examined whether herbivory can change the relative proportion of dispersal-related seed heteromorphism (floating or non floating seeds) in an invasive weed Ambrosia artemisiifolia. Because A. artemisiifolia often distributes in the riparian habitat, floating seeds might contribute to the long distance dispersal by hydrochory. Floating ability and seed weight were compared between plants damaged by a specialist herbivore Ophraella communa and undamaged plants. The damaged plants produced lighter and more likely floating seeds than the undamaged plants. However, multi-regression analysis revealed that the probability of floating was affected by seed weight but was not affected by herbivore treatment (damaged vs. undamaged plants). These results suggest that the increased proportion of floating seeds was not a direct response to the herbivore signal but an indirect response through the herbivore's effect on the reduction of seed weight. Plants damaged by herbivores might not only decrease seed production and quality but also increase the dispersal ability. These responses in dispersal ability against the herbivores might contribute to the spread of invasive plants.     

Incorporating dispersal distance into the disperser effectiveness framework: frugivorous birds provide complementary dispersal to plants in a patchy environment

Fleshy-fruited plants are usually dispersed by an array of frugivores, differing in the effectiveness of the dispersal service they provide to the plant. Body size differences among frugivores are hypothesized to affect seed dispersal distances and consequently their effectiveness as dispersers. We tested this hypothesis by comparing the effectiveness of two passerine birds, grackles ( Onychognathus tristramii ) and bulbuls ( Pycnonotus xanthopygos ), dispersing the desert shrub Ochradenus baccatus . Laboratory experiments, quantifying gut retention time and the effect on germination, were combined with field observations quantifying bird movements and fruit consumption rates. An empirically parameterized mechanistic model showed that the two dispersers switch roles as a function of spatial-scale: while most seeds within the local habitat were dispersed by bulbuls, the larger grackles were exclusively responsible for between-patches, long-distance dispersal. We suggest that distance-related differences are common and important to plant fitness, and thus should explicitly be considered in studies of disperser effectiveness.     

The importance of dispersal in determining seed versus safe site limitation of plant populations

The traditional dichotomy of seed versus safe site limitation of plant populations is an oversimplification. While most plant models implicitly assume that the number of safe sites colonized will increase directly with increased seed production by each plant, the number of sites colonized may also strongly depend on patterns of seed dispersal relative to the parent plant, since the majority of a plant’s seeds are deposited very close to it and so not all safe sites are equally accessible. I created a series of spatially explicit individual based plant population models exploring how seed versus safe site limitation is jointly affected by the number of seeds produced per plant and mean dispersal distances. While increased dispersal distance led to reduced seed limitation (more saturation of available safe sites) when a parent plant’s site was temporarily unsuitable following its death, increased dispersal distances could increase seed limitation, especially at low per-plant fecundities, if safe sites did not turn over through time. Models comparing localized to global seed dispersal indicated substantially different degrees of seed limitation for constant per-plant fecundities. Thus seed addition experiments need to be designed to add seeds in realistic spatial patterns to yield meaningful results.     

Effects of habitat alteration on the effectiveness of plant-avian seed dispersal mutualisms: Consequences for plant regeneration

Anthropogenic habitat alteration may affect the dispersal service provided by avian seed dispersers, ultimately causing regeneration collapse, through a decay in both the quantitative (seed removal) and qualitative (seed arrival to safe sites) components of seed dispersal effectiveness. However, despite its implications for management in real-world landscapes, few studies have investigated the shifts in components of seed dispersal effectiveness resulting from habitat alteration. We advocate the use of stage-specific transition probabilities, combined with data on seed shadows and bird abundance and mobility, for a mechanistic inference of the consequences for recruitment of the disruption of plant-frugivore mutualism in altered habitats. Such an approach allows the identification of regeneration bottlenecks, evaluates the differential contribution to recruitment of quantitative and qualitative components of seed dispersal, and provides the means to compare seed dispersal limitation. We exemplify our conceptual approach with studies of seed dispersal and recruitment in the wild olive tree in unaltered and severely altered adjacent sites. We show that simplification of the habitat substantially affected bird abundance, diversity and mobility, which caused a reduction in fruit removal and a concomitant simplification of the seed shadows compared to the unaltered site. Linked to these shifts, postdispersal seed survival and seedling emergence and survival were affected. The final outcome of habitat alteration was the collapse of the regeneration dynamics with very few seeds escaping the influence of maternal plants and reaching the safest sites for recruitment (dispersal limitation). As predicted, the collapse in the regeneration dynamics resulted from severe decays in the quantitative but especially in the qualitative components of seed dispersal effectiveness. Management of fleshy-fruited plant populations in altered habitats should thus pay attention to landscape elements that promote frugivore abundance, diversity and mobility and that alleviate the dispersal limitation.     

Seed rain into upland plant communities in Hong Kong, China

Hong Kong is an extreme example of tropical landscape degradation, with no substantial remnants of the original forest cover and a highly impoverished disperser fauna. Seed availability is a potential limiting factor in vegetation recovery in such landscapes. To assess the quantity and quality of the seed rain of woody taxa, seed traps were placed in the major upland vegetation types: fire-maintained grassland, shrubland, and secondary forest. Within the grassland site, traps were placed under isolated trees, isolated male and female shrubs of Eurya chinensis, and in the open. Seeds were collected every 2 weeks for 2 years. The seed rain was highest under female shrubs in grassland (6455 seeds m⁻² year⁻¹), where it was almost entirely confined to their fruiting period. Next highest were isolated trees (890 seeds), followed by male isolated shrubs (611 seeds), shrubland (558 seeds), forest (129 seeds) and open grassland (47 seeds). The number of seed taxa was highest in shrubland (59), followed by isolated trees (42), forest (42), female isolated shrubs (28), male isolated shrubs (15), and open grassland (9). The seed rain differed in species composition between the forest, shrubland, and grassland sites, while the differences within the grassland site were largely in terms of quantity. Birds (particularly bulbuls, Pycnonotus spp.) are known or inferred to be the major dispersal agents for 85% of the seed taxa trapped, 99% of the total number of seeds trapped, and 99.8% of the seeds trapped in the grassland site. Few taxa and of the total seeds were dispersed by wind and no seed taxa were definitely dispersed by fruit bats. The results suggest that even in the most degraded landscape the seed rain is adequate for the development of woody vegetation cover, but that human intervention will be needed for the restoration of plant diversity.     

Post‐Dispersal Seed Removal and Germination Selected Tree Species Dispersed by Cebus capucinus on Barro Colorado Island,Panama1

Dispersal quality, an important component of seed disperser effectiveness, may strongly affect the rate of plant recruitment. Here we evaluated the quality of Cebus monkey dispersal by comparing the secondary removal fate and germination of fresh and Cebus‐ingested seeds of nine tree species on Barro Colorado Island, Panama. Overall, rates of secondary seed removal by vertebrates were low, with most Cebus defecations remaining undisturbed for extended periods on the forest floor. Only four of 30 feces were completely buried by dung beetles, and we found significantly higher vertebrate removal of defecated seeds than control seeds for only one species, Cordia bicolor. Seed germination varied greatly between plant taxa. Seeds of 3 out of 9 species showed significantly higher percent germination after monkey gut passage than control fresh seeds. Germination times tended to be shorter for defecated than for control seeds but were significantly different only for one of nine species, Cecropia insignis. Low rates of seed removal from Cebus feces, coupled with high germination probabilities, suggest high dispersal effectiveness for Cebus and contrasts strongly with patterns of post‐dispersal seed fate recorded for other primate species.     

Wind dispersal in freshwater wetlands: Knowledge for conservation and restoration

Questions: For wetland plants, dispersal by wind is often overlooked because dispersal by water is generally assumed to be the key dispersal process. This literature review addresses the role of seed dispersal by wind in wetlands. Why is wind dispersal relevant in wetlands? Which seeds are dispersed by wind and how far? And how can our understanding of wind dispersal be applied to wetland conservation and restoration? Methods: Literature review. Results and conclusions: Wind is a widely available seed dispersal vector in wetlands and can transport many seeds over long distances. Unlike water, wind can transport seeds in all directions and is therefore important for dispersal to upstream wetlands and to wetlands not connected by surface water flows. Wind dispersal transports seeds to a wider range of sites than water, and therefore reaches more sites but with lower seed densities. Many wetland plant species have adaptations to facilitate wind dispersal. Dispersal distances increase with decreasing falling velocity of seeds, increasing seed release height and selective release mechanisms. Depending on the adaptations, seeds may be dispersed by wind over many km or only a few m. The frequency of long‐distance wind dispersal events depends on these adaptations, the number of produced seeds, the structure of the surrounding vegetation, and the frequency of occurrence of suitable weather conditions. Humans reduce the frequency of successful long‐distance wind dispersal events in wetlands through wetland loss and fragmentation (which reduce the number and quality of seeds) and eutrophication (which changes the structure of the vegetation so that seed release into the wind flow becomes more difficult). This is yet another reason to focus on wetland conservation and restoration measures at increased population sizes, prevention of eutrophication, and the restoration of sites at short distances from seed sources.     

Detecting plant spatial pattern change after disperser loss: A simulation and a case study

Disruption of seed dispersal processes may affect plant population spatial structure. We used a spatial simulation model and an empirical case study to assess the conditions under which the loss of seed dispersers has a detectable effect on a species' spatial pattern. Our simulation experiments suggested that detecting spatial change following disperser loss will be difficult, except when rates of fruit removal are initially high and then completely disappear. To contextualize the simulation modeling, we used spatial point pattern analyses to characterize the spatial pattern of two large-seeded species (Leucopogon nutans, a fire-killed seeder shrub and Macrozamia riedlei, a long-lived, resprouting cycad) in the jarrah (Eucalyptus marginata) forests of southwestern Australia. The plant species' primary disperser, the emu (Dromaius novaehollandiae), was absent from one of the sites we considered, but present at the other two. There was no detectable difference for either plant species in the strength of aggregation between sites with and without emu. However, even if disperser loss may not greatly affect local spatial structure for most plant species, it is likely to be important for long distance dispersal and genetic structuring of populations, so accurate characterization of the dispersal kernel is critical, especially in terms of plant emigration.     

Crop size,plant aggregation,and microhabitat type affect fruit removal by birds from individual melastome plants in the Upper Amazon

We studied the efficiency (proportion of the crop removed) and quantitative effectiveness (number of fruits removed) of dispersal of Miconia fosteri and M. serrulata (Melastomataceae) seeds by birds in lowland tropical wet forest of Ecuador. Specifically, we examined variation in fruit removal in order to reveal the spatial scale at which crop size influences seed dispersal outcome of individual plants, and to evaluate how the effect of crop size on plant dispersal success may be affected by conspecific fruit abundance and by the spatial distribution of frugivore abundance. We established two 9-ha plots in undisturbed terra-firme understory, where six manakin species (Pipridae) disperse most seeds of these two plant species. Mean levels of fruit removal were low for both species, with high variability among plants. In general, plants with larger crop sizes experienced greater efficiency and effectiveness of fruit removal than plants with smaller crops. Fruit removal, however, was also influenced by microhabitat, such as local topography and local neighborhood. Fruit-rich and disperser-rich patches overlapped spatially for M. fosteri but not M. serrulata, nonetheless fruit removal of M. serrulata was still much greater in fruit-rich patches. Fruit removal from individual plants did not decrease in patches with many fruiting conspecifics and, in fact, removal effectiveness was enhanced for M. fosteri with small crop sizes when such plants were in patches with more conspecifics. These results suggest that benefits of attracting dispersers to a patch balanced or outweighed the costs of competition for dispersers. Spatial pattern of fruit removal, a measure of plant fitness, depended on a complex interaction among plant traits, spatial patterns of plant distribution, and disperser behavior.     

Seed dispersal in Erythronium grandiflorum (Liliaceae)

Primary and secondary seed dispersal was investigated for the glacier lily Erythronium grandiflorum in the Colorado Rocky Mountains. These heavy seeds have no obvious adaptations for biotic or abiotic dispersal, but can be thrown short distances when the dehiscent fruits are shaken by wind. We used sticky traps to measure primary transport of seeds up to 1 m away from individual plants. A seed cafeteria experiment examined the role of ants and rodents in secondary seed transport. Primary dispersal by wind was positively skewed and median transport distances were influenced by variation in plant height. Secondary dispersal was negligible compared to Viola nuttallii, an elaiosome-bearing species. Thus, seed dispersal was highly restricted in E. grandiflorum, and a 1 m radius encompassed the modal section of the seed dispersal curve. The seed dispersal component of gene flow was quantified and combined with previous measurements of pollen flow to yield a more complete estimate of Wright's neighborhood size, N _e, for E. grandiflorum. The lack of a special seed dispersal mechanism in E. grandiflorum is discussed in terms of a source-sink model for seedling establishment with respect to distance from the parental plants.     

Herb endozoochory by cockatoos: Is ‘foliage the fruit’?

Establishing whether herb seed endozoochory is accidental or has evolved independently or in combination with other dispersal mechanisms may be valuable in the study of plant–animal interactions, but it remains unexplored for birds. We tested whether an Australian cockatoo, the galah (Eolophus roseicapilla), swallows entire seeds when feeding on other tissues without subsequent seed digestion, thus enhancing seed dispersal (the ‘foliage is the fruit’ hypothesis). Our preliminary sampling provides strong evidence supporting that this seed predator also acts as a legitimate endozoochorous disperser. A large proportion of droppings contained numerous seeds of six herb species of three plant families, surviving gut passage to be dispersed as viable propagules. The wide range in the number of seeds found in combinations with up to five species in particular droppings suggests both simultaneous and sequential passive ingestion without seed digestion and/or focused seed predation and digestion. As expected for inadvertent ingestion and inefficient digestion, our findings suggest that seed number and richness of dispersed plants are associated traits in this particular mutualistic interaction. This relationship can have important implications in community‐wide processes, favouring herbs whose seeds are disseminated in a viable state over those predated or negatively affected by gut transit.