Abstract. Through seed dispersal and predation, terrestrial mammals should be an important component of the mechanisms that determine patterns of tree recruitment in tropical forests. Despite their great abundance and ubiquity in Neotropical forests, small rodents as seed predators and dispersers remain largely forgotten. To investigate the fates of seeds in a hunted primary forest in Belize, we tagged seeds of Astrocaryum mexicanum (Palmae), Ampelocera hottlei (Ulmaceae), and Pouteria sapota (Sapotaceae) and placed them into open plots, exclosures accessible only to small mammals, and exclosures accessible to medium‐sized and small mammals. The exclosure experiments and fates of the seeds show that the spiny pocket mouse, Heteromys desmarestianus (Heteromyidae), was the dominant handler of seeds of the first two species and also removed a significant proportion of the very large‐seeded Pouteria. Most of the seeds were killed immediately upon removal, but many of the seeds (3–18 %) of the first two species were scatterhoarded (dispersed and buried in the soil) by Heteromys. Some of the scatterhoarded seeds (29%) remain buried and therefore protected from predation by other animals. Agoutis (Dasyprocta punctata), a caviomorph rodent, buried 13 % of the seeds of Pouteria, and Heteromys consumed and dispersed but did not bury Pouteria seeds. Results of this study support predictions by some researchers that small rodents are dominant terrestrial granivores in Neotropical forests. The role of small rodents as seed dispersers, however, has never been fully appreciated.

Seed size may vary greatly among individuals within plant species. What effects the extremes of this variation have for seeds taken by small mammals are poorly understood. Not all seeds removed by small mammals are necessarily eaten. Small rodents are common seed predators, but they may disperse a significant proportion of seeds by scatter hoarding them via burial. Size‐dependent predation and dispersal of seeds has not been directly tested within a plant species for tropical rodents. This study tested whether or not large and small nuts of Astrocaryum mexicanum (Palmae) differed in their fates due to handling by the spiny pocket mouse Heteromys desmarestianus (Heteromyidae). Exclosures were used to give small rodents exclusive access to A. mexicanum nuts. H. desmarestianus preferentially consumed large over small A. mexicanum nuts, but cached (in burrows and by scatter hoarding) similar proportions of these nuts by size. Small nuts tended to be buried farther away from exclosures than large nuts. Although sample sizes of buried nuts were small, the rodents retrieved all buried large nuts, but 30% of the small nuts remained buried long enough to germinate. I also examined predispersal predation by insects and found that insects appear to have no size preference for A. mexicanum nuts, but insect predation appears to hinder nut development. Thus, nuts attacked by insects develop to be significantly smaller, with a low proportion of undamaged endosperm, than uninfested nuts. It is hypothesized that the preferential predation of large A. mexicanum nuts by H. desmarestianus is a response by these rodents to insect predation.

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Limestone tropical forests represent a meaningful fraction of the land area in Central America (25%) and Southeast Asia (40%). These ecosystems are marked by high biological diversity, CO uptake capacity, and high pH soils, the latter making them fundamentally different from the majority of lowland tropical forest areas in the Amazon and Congo basins. Here, we examine the role of bedrock geology in determining biological nitrogen fixation (BNF) rates in volcanic (low pH) vs. limestone (high pH) tropical forests located in the Maya Mountains of Belize. We experimentally test how BNF in the leaf-litter responds to nitrogen, phosphorus, molybdenum, and iron additions across different parent materials. We find evidence for iron limitation of BNF rates in limestone forests during the wet but not dry season (response ratio 3.2 ± 0.2; P = 0.03). In contrast, BNF in low pH volcanic forest soil was stimulated by the trace-metal molybdenum during the dry season. The parent-material induced patterns of limitation track changes in siderophore activity and iron bioavailability among parent materials. These findings point to a new role for iron in regulating BNF in karst tropical soils, consistent with observations for other high pH systems such as the open ocean and calcareous agricultural ecosystems.

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In addition to acting as seed predators, some terrestrial mammals bury seeds via scatter hoarding. This study system used two permanent plots in examining the interaction between small rodents and the seeds of the palm Astrocaryum mexicanum. We tested how experimental burial, and fruiting status of the parent, distance to the parent, seed size, and microsite characteristics affect the survival of these seeds. Up to 34% of the buried seeds that were exposed only to ignorant rodent foragers (individuals not responsible for burial) survived. In comparison, less than 1% of seeds buried by scatter hoarding rodents survived in previous studies, a percentage that is comparable to the low survival of unburied seeds in this study (<2%). Although unburied seeds had very low survival, increasing distance and/or seed density positively affected survival of unburied seeds. Distance to parent had no effect on buried seed survival. 
Buried seed survival was most strongly and significantly determined by the fruiting status of the trees under which they occurred. Seeds experienced significantly greater predation if buried under “parent” trees that fruited during the experiment. Buried seed survival was also negatively affected by germination, as germination may signal the presence of a seed to foraging rodents. There was some indication of a positive effect of tree density on seed survival between the two plots, whereas differences in rodent abundance appear to have no effect on seed survival. Seed size and microsite characteristics had no significant effect on buried seed survival, likely due to the greater proportional effects of other factors and the longevity of A. mexicanum seeds. The results of this study were used to generate a hypothetical causal network showing how comparatively low recovery of buried seeds by ignorant foragers – combined with processes determining the removal of scatter hoarding foragers from their scattered seed caches – may affect seedling recruitment in A. mexicanum.

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Aim  The flora of northern Mesoamerica conventionally has been thought to be derived from taxa that emigrated from South America, but this view has recently been challenged as too simple. The dominance of limestone substrata in much of northern Mesoamerica, and its rarity in the rest of the continental Neotropics, may be one cause of the complexity of northern Mesoamerican floristics. Furthermore, northern Mesoamerica experiences longer and more intense seasonal drought than the rest of the continental Neotropics. As edaphic drought is accentuated with elevation on limestone soils, it may be expected that different topographic features have different phytogeographical affinities for seasonally drought‐prone areas of the Neotropics. The objective of this study was to test for effects of different topographic positions on the composition, phytogeography and diversity of tree species in a limestone area of Belize. Location  Maya Mountains, Belize, Mesoamerica. Methods  The diversity and local, regional, and hemispheric distributions of tree species on limestone valley floors, lower and upper slopes, and ridges were compared in southern Belize using 2 × 500 m transects as sample plots. Results  Stem density increased, and percentage of large trees decreased, significantly with elevation above the valley floors. The proportions of species that had widespread distributions decreased significantly with increasing elevation above the valley floors. The proportions of species having northern Mesoamerican distributions increased significantly with elevation above the valley floors. All of the forests generally had the strongest phytogeographical affinities for the Petén (Guatemala) and Mexico, but greater affinities for the Yucatán were observed with increasing elevation above the valley floors. Species with distributions including the Greater Antilles made up an increasingly significant element, in terms of species and numbers of stems, with increasing elevation above the floors of valleys. Valley floors and ridges had the highest percentages of species unique to their topographic positions, 61% and 39% of their species, respectively, and were very similar in diversity. Slope forests had the highest diversity of trees ≥ 5 cm d.b.h. and were transitional in composition among the topographic positions. Main conclusions  Despite relatively small changes in elevation, the composition, diversity and physical structure of the limestone forests changed significantly with topography. Such changes were presumably due to the greater edaphic drought experienced by these forests, and possibly due to lower levels of disturbance and differences in forest age, with increasing elevation above the floors of valleys.