We conducted a study in 30 plots distributed uniformly in an area of 25 km2 at Ducke Reserve, Manaus, to test the hypothesis that understorey herb richness and abundance are mediated by litter, manipulating experimentally the amount of litter in the field. Over 10 mo, we followed the emergence of herbaceous seedlings and sporophytes in control, litter-addition and litter-exclusion treatments, covering an area of 1.2 m2 per plot in each treatment. We also assessed the relationship between topography and litter depth and frequency of bare-soil patches; and the influence of density of reproductive individuals on the emergence of herbs. Litter depth decreased, and the frequency of bare-soil patches increased with terrain slope in the wet season, but were not related with the soil clay content. Neither was related to the topography in the dry season. Emergence of pteridophytes was four times higher in the litter-exclusion treatment (3.7 ± 1.1 individuals m−2) than in the litter-addition treatment (0.9 ± 0.28 indiv. m−2) and increased with soil clay content. Seedlings from monocot herbs emerged twice more frequently in the litter exclusion (0.71 ± 0.25 indiv. m−2) than in the litter-addition treatment (0.33 ± 0.11 indiv. m−2), and also more in sites with high density of fruiting plants. The results are consistent with the hypothesis that regeneration of herbs with very small propagules is strongly affected by the physical barrier imposed by litter. Given that litter is shallower on slopes during the wet season, this creates a pattern of higher density and richness of pteridophytes in these areas. Monocot herbs, although also limited by litter, were more highly limited by availability of propagules, and their distribution patterns are at least in part explained by dispersal limitation. We conclude that litter is an important causal factor behind the herb distribution patterns along topographical gradients.

The feeding traces in fossil ginger leaves and the conserved phylogenetic relationships seen today in certain clades of hispine beetles on their monocot hosts point towards a long and intimate plant–insect evolutionary relationship. Studies in the 1970s and 1980s documented the rich fauna of rolled-leaf hispine beetles and their association with the Neotropical monocot family Heliconiaceae in Central America. In this report, the taxonomic breadth of these early studies is expanded to include species in the families, Marantaceae, Poaceae, Arecaceae and Costaceae, all with species occurring sympatrically with the Heliconiaceae in lowland Panama. Additionally, the analysis is widened to include open-leaf scraping and internal leaf-mining clades of hispoid Cassidinae. The censuses add more than 5080 Cassidinae herbivore occurrence records on both open and unfurled new leaf rolls of 4600 individual plants. Cluster analysis reveals that while many Hispinae species tend to group with plant species in only one of the three monocot orders, 9 of 16 Hispinae species on Zingiberales hosts were recorded in substantial numbers on both the Heliconiaceae and the Marantaceae, indicating an underlying pattern of feeding flexibility at the host plant family level.