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Tropical Conservation Science
Special Issue November 2013 | Vol. 6 | Issue 5 | pages 592-704

Guest Editors: Simon A. Queenborough, Pierre Michel Forget and Sabrina Russo

© Pierre Michel Forget
Review Articles
    Pollination of Myristica and other nutmegs in natural populations | pages 595-607
    Sharma, M.V. and Armstrong, J.E.
    Wild nutmegs are important and prevalent in evergreen forests of the Old and New World tropics, but their inconspicuous nocturnal flowers high up in forest canopies and their small pollinators has made their floral biology and pollination a difficult subject for research. This paper reviews what is known so far from studies across the tropics on aspects of flowering and pollination in the nutmeg family, Myristicaceae. Male flowers offer pollen as reward while females do not produce nectar. The stigmas are wet, and although there are no prominent exudates that might function as a food reward, insects such as beetles may feed on the stigmatic secretion. In what seemed to be a system of classical ‘mistake pollination’, beetles specializing on nutmeg flowers are deceived into visiting non-rewarding female flowers. More studies on wild nutmeg species revealed that the flowers interacted with a diversity of insects such as thrips, bees and flies as potential pollinators. The review also brings together data on the way male and female trees are spaced in natural forests: many of the studied populations were male-biased. Our knowledge of nutmeg reproduction remains quite limited, thus rendering many conservation strategies futile.

    Nutmeg-vertebrate interactions in the Asia-Pacific region: importance of frugivores for seed dispersal in Myristicaceae | pages 608- 636
    Kitamura, S. and Poonswad, P.
    Who disperses nutmeg seeds in the Asia-Pacific region? Summarizing the current knowledge of frugivory and seed dispersal of nutmegs by animals in the Asia-Pacific region. Seed dispersal consists of the removal and deposition of seeds away from parent plants. Because seeds are not mobile, their movements must be facilitated by dispersal agents such as gravity, wind, water or animals. Without thousands of animal species acting as seed dispersers, many plants including nutmegs in tropical forests, would fail to reproduce successfully. Therefore understanding which animals are important seed dispersers for nutmegs is vital for their conservation. Results summarized from the available data on fruit characteristics and fruit consumers of nutmegs in the Asia-Pacific region shows that 338 instances of nutmeg-frugivore interactions including 129 nutmeg and 109 frugivore species and that large birds such as hornbills and pigeons are the major seed dispersers. Both 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. This could mean that they provide excellent seed dispersal services to the nutmegs. However, there is still insufficient data on nutmeg-frugivore interactions in this region and evaluating the effect of disperser loss for nutmeg trees remains challenging. Nutmeg trees are abundant, and most species are easily recognized in the field. Further studies on nutmeg-frugivore interactions will be of great ecological importance in the Asia-Pacific region, and the results of future studies will contribute to a general understanding of which evolutionary forces might have shaped current nutmeg-frugivore interactions in tropical forests worldwide.

Research Articles
    Sex-specific flowering patterns and demography of the understorey rain forest tree Iryanthera hostmannii (Myristicaceae) | pages 637-652
    Queenborough, S.A., Humphreys, A.M., and Valencia, R.
    Long-term studies of individual plants are extremely rare, especially in isolated tropical forests. Our study highlights the results of 12 years following the same 839 trees in a large lowland rain forest in Amazonian Ecuador, visiting them every year to count the number of flowers each one produced, as well as documenting growth and survival. These data can be used to understand some intriguing aspects of the life history of this species. For example, it is dioecious, meaning it has separate male and female trees, much like humans and unlike the majority of plants in the world. As in humans, females invest more resources than males - female trees produce fruit and male trees contribute pollen. This difference in investment leads to outcomes such as male trees becoming reproductive at smaller sizes than females and flowering more frequently than females. We also produce the first data on when Neotropical Myristicaceae trees open their flowers - at night; and the life cycle of these flowers. Most flowers do not last very long, only a few days, and again females invest more, producing larger longer-lived flowers. Our results suggest that flowering and fruiting behaviour of individual trees is highly variable and to adequately conserve populations, large areas of forest are required.

    Insect functional guilds in the flowering canopy of Myristica fatua in a lowland swamp, central Western Ghats, India | pages 653-662
    Sinu, P.A. and Sharma, M.V.
    Forest canopies not only guide several ecosystem processes but are the heart of an exceptionally high diversity of organisms that are woven in a complex web of functions and interactions. We sampled insects in the canopy of Myristica fatua, an endangered tree inhabiting the rare and vanishing lowland swamps of the Western Ghats of India. Yellow Sticky Traps were hung in tree canopies to record insect diversity. The insect visitors encountered during the flowering period of the tree were categorized using their feeding habit and based on their functional role in the tree canopy. This included pollinators such as bees, beetles and flies, gall makers such as mites, predators such as spiders, parasites such as mites and fleas, and parasitoids such as microscopic wasps and some flies. These functional guilds are important in keeping large populations of plant eating insects (herbivores) in check. Since sticky traps were the only capturing technique in the study, small wingless insects appeared to have been left out, including some beetles, field crickets and ants. Some beetles in the study initially thought to be strict fungivores, herbivores or predators were found to be potential pollinators based on observations on foraging and pollen load on insect bodies. Such an overlap of functional guilds is only natural in tropical systems and it is useful to be warned that a change in faunal assemblage could have a cascading effect on pollination processes.

    Reconciling natural history and species ecology: Myristica beddomei (Myristicaceae) in the Western Ghats, India | pages 663-673
    Chetana, H.C. and Ganesh, T.
    Good natural history is essential for doing ecological and conservation work. This is because species that appear very similar to each other and are closely related may differ from each other in subtle ways that are critical for each other survival but are not very obvious. These subtle differences are often ignored inadvertently or due to other necessities and observations on one species is extrapolated to the other which does not help in understanding the species ecology or helpful in its conservation. In this study, we document some natural history observations of fruit-frugivore interactions on the nutmeg (Myristica beddomei) found in the evergreen forests of the Western Ghats, India and compare with other nutmeg species. Seeds of the tree family Myristicaceae to which the nutmeg belongs are usually dispersed by large fruit eating birds such as pigeons and hornbills in Asia and by primates and other birds in Central America. Our observations of M. beddomei over several years did not indicate birds eating the fruit even though some fruit traits were common to other nutmegs eaten by birds. Instead M.beddomei was eaten by monkeys and squirrels that consume the seed coat called aril that covers the seed and discard the seed itself thereby allowing the seed from being eaten. We discuss these observations in the context of other nutmegs and explore why M. beddomei could have evolved such strategies in the region.

    Phenology, seed dispersal and regeneration patterns of Horsfieldia kingii, a wild nutmeg | pages 674-689
    Datta, A. and Rane, A.
    We studied the flowering and fruiting patterns, seed dispersal and regeneration of a wild tropical nutmeg tree Horsfieldia kingii (Myristicaceae). The tree species is rare and scattered, and did not flower and fruit every year. Flowering was observed from April to July, while fruiting was from February to March. There was no fruiting in several years, while 33% of trees bore fruit in other years. The ripe fruits of this species are available when hornbills start breeding. All hornbill nests are not active every year varying from 50 to 100% of nests and it appears that there is a relationship between amount of Horsfieldia eaten by hornbills and number of active hornbill nests. However, because of low fruiting in most years, Horsfieldia does not form a major part of hornbill diet and there is limited dispersal of seeds at hornbill nests. Regeneration of the species under parent trees and hornbill nest trees was low, although seedlings seem to survive somewhat better below nest trees suggesting that dispersal by hornbills is important, even in clumped conditions where seeds are eaten by rodent predators. However, current regeneration under 21 nest trees is much lower than at nest trees. The abundance of this species may be mainly limited by seed availability, while inadequate dispersal may play a secondary role.

    The role of frugivores in determining seed removal and dispersal in the Neotropical nutmeg | pages 690-704
    Ratiarison S. and Forget, P.M.
    In French Guiana, we studied the degree of interaction between two nutmeg tree species that differ in seed size, and the animal species eating their fruits and thus potentially swallowing and removing their seeds away from parent trees. For numerous tropical tree species, this mechanism is considered to increase success of tree regeneration by allowing seeds to escape from the competition for seedling establishment assumed to be higher under fruiting trees. In that purpose, we identified the animal species eating the focal fruit species; concurrently, we evaluated for each fruit species if seed features influenced fruit selection by animal species and ultimately seed removal rate. A limited number of animal species – all of relatively large body sizes – ate the large-seeded nutmeg species: the spider monkey and three large species of toucans. The small-seeded nutmeg species was eaten by these same animal species and three other smaller bird species. Only the large-seeded species showed a significant relationship between seed size and seed removal rate. Our results suggest that the seed size of the large-seeded nutmeg species might have evolved under the influence of large-bodied disperser animal species, more efficient at removing and dispersing seeds away from parent trees. They also suggest that the extinction of spider monkeys, more severely hunted given their large body size, could decrease the seed dispersal rate of the large-seeded nutmeg species, and ultimately its capacities for regeneration.

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   Tropical Conservation Science is an open-access e-journal that publishes research relating to conservation of tropical forests and other tropical ecosystems.

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