Field studies of several species of Myristica (Myristicaceae) have produced a more detailed understanding of the pollination and reproduction of nutmeg, which had long been wanting. Nutmegs are dioecious tropical forest trees within the order Magnoliales. Nutmegs conform to the general pattern of dioecious tropical trees; they have small, inconspicuous flowers with a pollen reward system, and interact with a guild of small, generalist insects, predominately beetles, thrips and flies. Pollen is the only obvious reward, so pollination operates by deception and foraging errors. Fluctuations in floral displays may encourage foraging errors, and beetles have been found to be sensitive and responsive to such changes in floral displays. Natural populations of nutmegs are generally male-biased, although irregular flowering can shift sex ratios from season to season. Intersexual differences in microhabitat preference were found in some, but not all nutmeg species studied. Compared to their importance and prevalence in tropical forests, the nutmeg family remains both under-studied and difficult to study. Future work should focus on aspects of nutmeg reproduction such as pollen flow and fruiting success (or seed set) that may offer conservation insights.

In tropical forests, large frugivores are assumed to be important seed dispersers for many large-seeded trees such as the Myristicaceae, a widespread and common family. However, not all frugivores are effective seed dispersers, and understanding which frugivores are effective is vital for conservation biology. Here, we summarize the available data on fruit characteristics and frugivores for a large number of Myristicaceae species in the Asia-Pacific region and suggest future directions for evaluating the effects of disperser loss for these trees. Studies of fruit characteristics of Myristicaceae were highly biased toward morphological information, and few studies examined reproductive phenology or fruit chemistry. We identified 338 instances of nutmeg-frugivore interactions that included 129 species of Myristicaceae and 109 species of frugivores, including 40 bird, 68 mammal, and one reptile species. Large birds were major seed dispersers for this tree family. These bird species, such as hornbills and pigeons, consumed a variety of nutmeg species, remained briefly at fruiting trees, and dispersed intact seeds far from the parent trees in the forest. Although most seeds dispersed by birds subsequently suffered high seed predation by rodents, some germinated and established as seedlings, indicating the qualitative effectiveness of large birds as seed dispersers for Myristicaceae. Mammals were also major consumers of Myristicaceae. Gibbons, macaques, and civets potentially acted as long-distance dispersers for some nutmeg species. Orangutans, leaf monkeys, squirrels, and rodents consumed a variety of nutmeg species, but their roles as seed dispersers for Myristicaceae remain unclear. Studies of nutmeg-vertebrate interactions have typically focused on frugivory, whereas few studies have specifically quantified the effectiveness of frugivores as seed dispersers; thus, it remains difficult to evaluate the effect of frugivore loss on the populations of most nutmeg species in this region. Further studies of nutmeg-frugivore interactions are of great ecological importance, and the results of such studies will contribute to a general understanding of which evolutionary forces may have shaped current nutmeg-frugivore interactions in tropical forests worldwide.

Sexual dimorphism in dioecious plants is a common phenomenon that has received widespread attention, yet the implications for reproductive function and fitness remain poorly understood. Using data from a long-term study of a population of 839 dioecious Iryanthera hostmannii (Myristicaceae ‘nutmeg’) trees in a large permanent plot in a lowland tropical rain forest, we examined the effects of greater investment in reproduction by females compared to males for various aspects of life history. Although male trees often produced more inflorescences than females, total dry mass of flowers was roughly equal in two out of three years for both sexes, implying that any investment differential lies in fruit production. There was no difference in the 12-year relative growth rate of males and females, suggesting that females can compensate somehow for their greater reproductive investment, although there were weak suggestions that mortality might have been greater in females. Male flowers opened slightly earlier in the day than female flowers and were short-lived, lasting at most two nights compared to up to four nights in females. Understanding the interacting effects of resource availability (studied here) and pollen movement (currently unknown in Iryanthera) on reproduction is essential in terms of life history theory. Knowledge of reproductive biology is key in considering the ecology and conservation of tropical forest communities.

Little is known of canopy insects and pollinators of the nutmeg family (Myristicaceae), despite its being a common pantropical tree family and a commercially-grown spice. To address this lack of knowledge, an assessment was made of the insect fauna associated with the canopy of Myristica fatua (Myristicaceae), an endemic tree species inhabiting the rare and endangered lowland ‘Myristica’ swamps of the south and central Western Ghats of India. Yellow Sticky Traps were hung in tree canopies to record insect diversity. Insect visitors encountered during the flowering period of Myristica fatua were classified based on their functional role. The captured arthropod fauna was characterised by an abundance of parasitic, predatory, herbivorous and gall-making insects of Chalcidoidea, Platygastroidea, Bethyloidea, Ceraphronoidea, Dolichopodidae, Empididae and Cicadellidae, and a scarcity of beetles. The exclusive gall-making hymenopterans of Cynipidae formed one of the largest insect families in the canopy of M. fatua. The faunal assemblage appeared to be a subset of the entire insect fauna associated with the tree species, as sticky traps leave out the apterygote, sedentary and large insects, and a higher turnover in the insects at the family level could be expected during the fruiting season of the tree. The study highlights the importance of canopy arthropods and their functional roles in community structure.

Natural history is an important component of any ecological or conservation research. Very often this is not given adequate attention, and observations on the genera or species are often generalized to other, supposedly similar, congeneric species. In this study, we document the natural history of fruit-frugivore interactions of Myristica beddomei (Myristicaceae) found in the mid-elevation evergreen forests of the Western Ghats, India, and determine how different these interactions are compared to other Myristicaceae species. M. beddomei has a single hard seed covered by an orange-yellow aril. Species of Myristicaceae are usually dispersed by large frugivorous birds, and also by primates in the Neotropics. In South Asia, Myristicaceae dispersal is usually by large birds such as hornbills, but our observations over several years indicate that M. beddomei is not bird-dispersed, even though some fruit traits suggest bird dispersal. Our observations suggest that obligate seed predators like macaques and squirrels can facilitate dispersal of the species. We discuss these observations and explore why such outliers might have evolved in the region

We present observational data on the flowering and fruiting patterns, seed dispersal, seedling recruitment and survival of a dioecious Myristicaceae species, Horsfieldia kingii, that occurs in the tropical forests of Arunachal Pradesh. Horsfieldia is rare (1 tree ha¹) with a scattered distribution; Horsfieldia trees did not flower every year, and flowering was staggered from April to July. Peak ripe fruit availability of Horsfieldia is from February to March. Failure of fruiting occurred in most years, and only 0-33% of sampled trees bore ripe fruits. Initiation of hornbill breeding coincides with the ripe fruit availability of this species. The percentage of hornbill nests in which nesting is initiated each year varies from 50 to 100% of nests, and our results show a significant positive relationship between the percentage of hornbill nests that are active in a given year and the contribution of the species to hornbill diet (n = 6 years). However, the overall contribution to the breeding season diet of hornbills is very low because of poor fruit availability in most years, resulting in limited seed dispersal at nests. Recruitment and survival of Horsfieldia seedlings below parent trees and hornbill nest trees were low; however, seedling survival was marginally higher at nest trees, suggesting that dispersal by hornbills even in a spatially contagious manner may be critical for this species. However, current recruitment of Horsfieldia at hornbill nests (2010) is significantly lower than at parent trees. This species appears to be seed-limited, while dispersal limitation may play a secondary role in determining its abundance.

At the Nouragues field station (French Guiana), we studied the seed dispersal system of two sympatric tropical tree species that differ in seed size, Virola kwatae and V. michelii (Myristicaceae), to evaluate the degree of interaction between Virola species and their dispersers, and consistency in the fruit traits affecting seed removal rate. Only the spider monkey (Ateles paniscus) and three species of ramphastid toucan dispersed the large (4.8g) V. kwatae seeds. These four animal species, as well as three smaller-bodied bird species, also dispersed the small V. michelii seeds (2.1g). Annual fecundity of both Virola species did not affect seed removal rate. However, variation in V. kwatae seed size within tree populations, and increased seed removal rate due to fruit selection on seed size, suggest a potential for an evolutionary response of seed size to selection by large-bodied frugivores in this species. In contrast, seed size did not affect V. michelii seed removal rate, and the interactions between V. michelii and its dispersers are interpreted to be too diffuse to result in strong selection on plant traits affecting seed removal rate. Because hunting pressure is greater on larger than on smaller frugivores, extinction of A. paniscus (the main large-bodied seed disperser of the study Virola) is likely to affect the long tail of dispersal kernel, thus decreasing recruitment away from fruiting adult trees.