Using a combination of spatially-explicit static and population dynamic data, we conducted multiple tests to examine hypotheses that falling palm fronds and/or peccaries are major structuring forces of lowland Neotropical rain forests [15, 36]. We found a restricted but significant direct effect of large arborescent mature fruiting palms on the spatial structure and species diversity of neighbouring sapling and seedling communities. There was also a strong and consistent larger-scale environmental effect of large palms being located in areas of lower neighbourhood density and diversity of saplings. Further, these patterns were corroborated by process in that we also found significant differences in the population dynamics of saplings (reduced growth and increased resprouting) and seedlings (lower survival) in the vicinity of mature palms. Evidence such as this was taken by previous authors to implicate falling palm fronds as major causal agents of mortality and selection in tropical forests . However, when we attempted to exclude the confounding effects of frugivores by analysing still-large but immature (ie. non-fruiting) palm trees, we found no significant spatial signature, although there is some evidence of reduced growth of neighbouring saplings. This would suggest that large frugivores such as peccaries, and not falling fronds, are the more important cause of physical damage and mortality of seedlings and saplings in the vicinity of mature palms as they root around for fruit , because we would expect falling fronds to have an equal effect around mature and immature palm trees.
We then tested these potential effects of peccaries by examining the spatial structure and population dynamics of seedlings and saplings around another important food source, the Myristicaceae. Most species of this family are large canopy trees  and produce abundant crops of fruit that are eaten by peccaries  among other frugivores [37, 38]. Unlike palms though, these trees do not have large heavy leaves that could damage seedlings and saplings beneath the canopy. Furthermore, the family is dioecious and so we could compare fruiting female trees with non-fruiting male trees. However, we found no convincing evidence that the seedling and sapling communities near female Myristicaceae were structured at all, and the significant population dynamic results we did find were in the opposite direction to that hypothesized.
Why did we find these conflicting results? One possibility is that peccaries are not large consumers of Myristicaceae fruit. It is known that peccaries consume a wide variety of species in tropical forests . However, the abundance of each species in peccary diets is less well known . Peccaries may focus largely on palms and eat other fruit as and when they happen upon it [32, 39]. Arboreal frugivores such as toucans and primates will also likely have a large effect on the availability of fruit on the ground. Further data on peccary and other frugivore diets are required. In addition, palm seeds likely remain attractive to peccaries (if not viable) long after abscission because of their hard seed coat. Myristicaceae seeds are not protected in this way and quickly decompose.
Alternatively, there may be a difference in the pattern of abscission of palm and Myrsticaceae fruit and the seed shadows these generate. Palm fruits are held in a single infructescence at the top of the tree. These fruit then fall in rapid succession, creating a very dense carpet of fruit around the tree with a short dispersal tail . Animals rooting around in this small area will likely have a big impact on the juvenile plants growing there . Myristicaceae trees, on the other hand, have a much larger canopy, the fruit carpet is thinner and more spread out. Animals foraging for fruit here will likely have a lower impact on juvenile plants.
A final possibility is our assumption that the fronds of mature and immature palms are equivalent does not hold, and that immature palm trees have lighter and/or smaller leaves that cause less damage to seedlings and saplings when they fall. We were not able to compare leaves from both types of palm trees to verify this, although Iriartea leaves do change morphology throughout their life cycle [23, 41]. Furthermore, leaves falling from shorter immature palms will have lower velocity and might do less damage than leaves falling from the greater height of mature palms. Finally, the size cut-offs determined by Iriartea for mature and immature individuals might be different for other species. However, these species are much less abundant than Iriartea and are unlikely to significantly influence our results.
Implications for forest diversity and community structure
Given the difficulties of reliably measuring seedling growth, it was not possible to repeat all three tests of dynamic data in both seedlings and saplings. Growth and resprouting were analysed solely in saplings. However, it seems that significant mortality of seedlings occurs in the vicinity of palm trees, but that saplings can generally withstand physical damage caused by peccaries and/or palm fronds, and rather suffer reduced growth and can potentially resprout. This difference in mortality implies that different mechanisms are at work at different life history stages and that if seedlings can grow large enough, their fate is more secure . The differences in spatial structure and sapling density around palms are therefore more likely to be formed at the seedling stage than the sapling stage. The small-scale repulsion of saplings (Figure 1B) may be a consequence of the immediate negative effect of large palms on seedlings (falling palm fronds cause increased mortality and stem breakage in neighboring saplings) and the large-scale effects (Figure 1A) could be a long-term cumulative population dynamics effect that results from many generations of palms having a negative impact on nearby seedlings.
The impacts of palms on the forest structure are of smaller spatial scale than that hypthesized by Peters et al. , who suggested that the effect of palms extended out to 7 m and that at least a quarter of lowland forest could be impacted by falling palms fronds per year. We found significant negative effects of palm trees out to only 3 m (in terms of over-dispersion of saplings [spatial pattern]) and 5 m (in terms of species repelled [ISAR]). Given the spatial pattern and density of palm trees in our plot, the area of forest predicted to be directly affected by this process is therefore reduced to 17%, although we noted above that these effects could multiply over generations leading to large areas of lower sapling density.
The negative impacts identified above appear limited to large palms and do not involve other fruiting trees such as the Myristicaceae. We would conclude therefore that this process is not a disturbance that affects large swathes of forest (or everywhere there is a tree that produces large peccary-consumed fruit). If the effect is limited to the environment of palms, this creates heterogeneity in the forest, which may lead to a wide variety of regeneration niches for species that can withstand the effects of falling leaves, fruit and rooting frugivores . Once established, however, these individuals may have better access to light and soil resources, given the diffuse nature of palm canopies and the large amounts of decaying fruit and animal faeces that likely accumulate around the base of palm trees. The stilt-roots of many arborescent palms probably increase nutrient availability by trapping leaves and organic matter.
This kind of widespread small-scale disturbance creates heterogeneity in regeneration niches in both space and time. Fruiting and frugivory by peccaries is episodic, and palms generally mature one infructescence at a time. Furthermore, in the aseasonal forest of Yasuní, Iriartea fruit production is not confined to a few months of the year (Nancy Garwood, unpublished data). Confoundingly, palm fronds are also produced regularly throughout the year. Beck et al.  found no difference in leaf-fall rates between two widely separated forests in Peru. In seasonal sites such as Yasuní, therefore, where seedling germination takes place throughout the year, some individuals may escape damage simply by growing enough before the next frond or infructescence falls. In more seasonal forests where germination is often restricted to short periods, individuals are of similar ages and/or vulnerabilities and so may suffer greater impact. A further test of our hypotheses could take place in seasonal forest and examine if seedlings and saplings suffer greater mortality during the fruiting season (therefore more likely caused by peccaries) or during the non-fruiting season (more likely leaf-fall).
The ubiquitous nature of the palm family in Neotropical forests implies that given some effect, palm trees could be a powerful force structuring these forests . Several species of tree dominate large areas of lowland forests in western Amazonia, and arborescent palms such as Iriartea are among this 'oligarch' group [24, 26, 28]. Widespread small-scale mosaics created by these palms may affect the composition of advanced regeneration for when a larger canopy gap does open. However, we note that peccaries are among the first large mammals to be hunted out of forest near to human habitation. Hunting will likely have dramatic effects on forest structure .
If reduced survival and growth around palms is predictable and selective, what can we hypothesize about species that occur in the neighbourhood of palms? Species that are better able to survive damage by falling fronds or rooting peccaries would be more likely to survive in areas close to palm trees. From our community-level analyses we cannot identify traits of individual species. However, species with underground storage organs or cotyledons might find an advantage in germinating near to a large palm because of their increased resource availability allowing resprouting following damage . We identified a number of species that had significantly higher or lower abundance around palms - identification of key functional traits of these species implicated by this pattern would be useful. An advantage might even apply to the seedlings of arborescent palm trees themselves, if they can survive predation and falling fronds. Iriartea is one of the most widespread and abundant tree species in western Amazonia. If Iriartea seedlings can survive better in the adult zone of influence than the majority of non-palm species, this may go some way to explaining how such abundant populations can be maintained. Future work should therefore look for more evidence of selection potential of the process that Peters et al. , Beck et al.  and we have identified. What species are selected for? Does species diversity change predictably from seedlings to saplings? Are there species that appear more frequently together in proximity to palms than in other parts of the forest? Furthermore, a broader-scale comparison with other forests may be helpful. For example, the forests of SE Asia are not dominated by palms as are Neotropical ones, and yet peccaries have a significant impact on seedling and sapling communities .
Palms themselves are not immune to the effects of branch falls  and suffer negative density dependence , caused by falling fronds [22, 46–48], peccaries [32, 34], and pathogenic fungi . Although palm trees significantly impact non-palms, the combination of falling fronds and peccary seed predation and fungal attack inhibit population growth such that palms may currently be at maximum density in the forest.