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Secondary removal of Myristica fatua (Myristicaceae) seeds by crabs in Myristica swamp forests in India
Abstract
Little is known about the role of crabs as seed dispersers and predators. Recently, there has been interest in understanding their influence on plant recruitment in coastal forests. Secondary seed removal by crabs in a swamp-specialist tree, Myristica fatua, was investigated in the rare and patchy freshwater Myristica swamps in the Western Ghats in India. Tethered-line experiments were used to determine the role of crabs as secondary seed-removal agents in two study sites. Crabs transported a large percentage (63.3%) of seeds (n = 60) placed on the forest floor compared with rodents (25%) and other unknown agents (13.3%). Simultaneous choice experiments suggested that the nutrient-rich arils covering seeds were consumed, but there was no evidence for seed predation by crabs. A small percentage (13.3%) of monitored seeds (n = 60) germinated from within crab burrows. The spatial scale of secondary removal by crabs was restricted to < 10 m. In these fragmented swamp forests, secondary removal by crabs retains seeds largely within the swamps, where conditions for their establishment and survival are optimal. Thus, secondary seed removal by crabs could provide temporal and spatial refugia from seed predators such as rodents in Myristica fatua.
... It is crucial to understand the pollination ecology of this species as it has been categorized as endangered (IUCN 2000) and recent studies have shown that climate change scenarios through modified hydrological regimes could result in population declines in this swamp specialist species (Priti et al. 2016). Moreover, M. fatua seeds are also dispersed by large frugivorous birds such as hornbills and threatened primates such as Macaca silenus and Trachypithecus johnii (Krishna and Somanathan 2016) and secondarily dispersed by freshwater crabs (Krishna and Somanathan 2014). Thus, insights into the reproductive biology of specialists such as M. fatua are considered critical. ...
... Generalized pollination systems are hypothesized to provide reproductive assurance by buffering plants from fluctuations in pollinator populations (Waser et al. 1996;Marten-Rodriguez and Fenster 2010). Such buffering is likely to be important in M. fatua since the fruit numbers are low and investment per seed is very high (mean seed weight = 20.9 ± 2.93 g; Krishna and Somanathan 2014), along with its restricted habitat requirements. ...
Myristica fatua is a dioecious specialist species restricted to the endangered, freshwater Myristica swamp forests in the Western Ghats, India. Earlier studies have alluded to pollination by deception in members of the Myristica genus, and thus we examined the pollination ecology comprising floral biology, flower production, flower visitors, and reproductive success in M. fatua and inferred the potential strategies that could permit such deception in this habitat specialist tree. Male flowers provide pollen rewards for an extended period of time while female flowers are rewardless and both sexes are visited by generalist insects, mainly by honeybees and stingless bees. Bee visits were significantly more frequent and longer on male than on female flowers as bees collected pollen from male flowers. We found that flower production patterns create a preponderance of males compared to females in the swamp populations. Using a model of honeybee color vision, we found the distance between the color loci of male and female flowers and based on minimum visual angle subtended by these flowers, we suggest that the two floral sexes cannot be discriminated by bees. Bees are likely deceived by the perceptual similarity of rewardless female flowers to pollen-offering male flowers and pollination is the consequence of foraging errors made by pollinators that encounter largely male–rarely female flower mosaics as they forage among clump-distributed M. fatua trees in the swamp habitat.
... In our previous study, we found that secondarily removed seeds met with mixed fates in which crabs secondarily removed more than 60% of M. fatua seeds (moved seeds into burrows which facilitated escape from predation), while 25% of the seeds were subjected to predation by rodents and squirrels or weevil infestation (1%) (Krishna and Somanathan 2014). ...
... However, in our study, secondary agents evenly removed seeds in all microsite types (>90% of total seeds in seed stations). The localized dispersal by crabs (mean distance = 1.89 m) into or close to burrows to consume the arils can preclude seed predation by other agents as well as retain seeds within the swamp habitat without substantially altering the initial spatial pattern of seed deposition (Krishna and Somanathan 2014). ...
Our understanding of processes underlying plant recruitment emerges from species and habitats that are widely distributed
at regional and global scales. However, the applicability of dispersal-recruitment models and the role of dispersal limitation
versus microsite limitation have not been examined for specialised habitats. In patchy, freshwater Myristica swamp forests (Western Ghats, India), we examine the roles of primary seed dispersal, secondary seed removal and microsite
suitability for the establishment of a swamp specialist tree, Myristica fatua. We estimated primary seed shadows, performed secondary removal experiments and enumerated recruits in swamp sites. Steady-state
fruiting was observed with the extended production (> 7 months) of small numbers of fruits. Frugivores dropped most of the
large and heavy seeds under parent crowns, while a few seeds were transported over short distances by hornbills. Seed placement
experiments indicated that removal, germination and establishment were similar within swamp microsites, while seeds failed
to survive in matrix habitats surrounding the swamp. Crabs, which were major secondary removers of M. fatua, did not alter the initial seed dispersal patterns substantially, which led to the retention of seeds within the swamp. Distribution
of saplings and adults from previous seasons also suggest that dispersal-recruitment dynamics in the swamp specialist M. fatua did not strictly follow predictions of Janzen-Connell model while abiotic effects were significant. Large seeds, steady-state
fruiting and small crop sizes may be significant selective forces facilitating escape from density and distance-dependent
effects in space and time in specialist plant species such as M. fatua.
... In our study system, flying foxes damaged the seeds of two species for which we could identify no functional seed disperser, and granivorous rats and crabs were often the only alternative consumer of some species. Rats can disperse very small seeds internally (Williams et al. 2000, Shiels and, but frequently carry largerseeded fruit to husking stations for processing, where some seeds may be Crabs were more likely than rats to disperse seeds (Lee 1985;Krishna and Somanathan 2014), but still destroyed seeds of three of the seven species we identified as crab-consumed. However, partial consumption of a seed's cotyledons does not always result in seed death. ...
... Even local dispersal events are dominated by flying foxes in our study system. Crabs move fruits away from the source to avoid competition with other crabs (Lee 1985); and, whereas distances are less than 10 m from parent crowns, they may leave seeds in burrows where the seed is protected from rodent predation (Lee 1985;Krishna and Somanathan 2014). ...
The low species diversity that often characterizes island ecosystems could result in low functional redundancy within communities. Flying foxes (large fruit bats) are important seed dispersers of large-seeded species, but their redundancy within island communities has never been explicitly tested. In a Pacific archipelago, we found that flying foxes were the sole effective disperser of 57% of the plant species whose fruits they consume. They were essential for the dispersal of these species either because they handled more than 90% of consumed fruit, or were the only animal depositing seeds away from the parent canopy, or both. Flying foxes were especially important for larger-seeded fruit (>13 mm wide), with 76% of consumed species dependent on them for dispersal, compared to 31% of small seeded-species. As flying foxes decrease in abundance, they cease to function as dispersers long before they become rare. We compared the seed dispersal effectiveness (measured as the proportion of diaspores dispersed beyond parent crowns) of all frugivores for four plant species in sites where flying foxes were, and were not, functionally extinct. At both low and high abundance, flying foxes consumed most available fruit of these species, but the proportion of handled diaspores dispersed away from parent crowns ("quality") was significantly reduced at low abundance. Since alternative consumers (birds, rodents, and land crabs) were unable to compensate as dispersers when flying foxes were functionally extinct, we conclude that there is almost no redundancy in the seed dispersal function of flying foxes in this island system, and potentially on other islands where they occur. Given that oceanic island communities are often simpler than continental communities, evaluating the extent of redundancy across different ecological functions on islands is extremely important.
Published by Oxford University Press on behalf of the Annals of Botany Company.
... Large frugivorous birds such as the Oriental Pied Hornbill (Anthracoceros albirostris), Malabar Pied Hornbill (Anthracoceros coronatus), Malabar Grey Hornbill (Ocyceros griseus), and Mountain Imperial Pigeon (Ducula badia), as well as arboreal mammals including the Malabar giant squirrel, lion-tailed macaque and Nilgiri langur (Semnopithecus johnii), are known to disperse seeds of Myristicaceae (Tambat 2007;Krishna and Somanathan 2018). Freshwater crabs (Barytelphusa guerini and Travancoriana schirnerae) feed on lipid-rich arils and act as secondary seed dispersers of swampspecialist tree species, including M. fatua (Krishna and Somanathan 2014). Increased habitat fragmentation and decreased tree cover connecting swamps may have long-standing effects on between-swamp seed dispersion by these facilitators, many of which are endangered. ...
Myristica swamps are tree-covered wetlands within the evergreen forests of the Western Ghats, India. Even with their little-known biota, the swamps are virtually a live museum that is of great interest to biologists. The swamps harbour several rare-relic floristic and faunal taxa, comprising many endemic and threatened species. Most of the plant species in the swamp are highly restricted in their distribution and have several structural and physiological modifications. These swamps are one of the most unique and primeval ecosystems of the Western Ghats. They once formed a large hydrological network all along the Western Ghats, but due to increased human pressure, these now exist as small, isolated pockets and are one of the most threatened ecosystems in India. The presumed widespread loss of Myristica swamps and other perennial freshwater swamps calls for intensive research on the ecosystem services provided by these swamps, their landscape value and the function they play in watershed dynamics. Swamps are primarily drained for areca gardens and paddy fields. The swamps of the Western Ghats are threatened with extinction, yet scientists know little about them. Studies on flora and faunal diversity of these swamps exist, but the research gaps are notable when it comes to the hydrology, soil studies, and ecosystem services provided by these swamps. Further research is needed on these three topics in order to provide a comprehensive understanding of the abiotic factors governing swamps and to formulate a rationale for their preservation. There is also a lack of research on the potential impacts of climate change and population growth on these swamps. This review highlights the importance of these freshwater swamps, their ecology and prior research on them, and focuses on the need for conservation initiatives to save the last few swamps.
... Secondary seed dispersal agents include rodents, dung beetles, ants, and crabs. While the former two are generalists, ant-and crabdispersed seeds have elaiosomes or arils, the nutritive part they are interested in (Krishna and Somanathan 2014;Lengyel et al. 2009). ...
Seed dispersal is crucial for plants to maintain structure, diversity, population, and community. Although wind and water can disperse seeds, 75% of total terrestrial plants require animals to move their seeds to microsites that favor recruitment. Animals move seeds externally (epizoochory) and internally (endozoochory). While epizoochory is promising for plants, not many plants have evolved fruit/seed traits to favor it or evolved as a major dispersal mechanism in grasslands, scrub forests, and dry deciduous forests. Frugivorous animals perform endozoochory and long-distance dispersal of seeds, particularly in tropical rainforests. The quantity and quality of endozoochory are predicted by the abundance and fruit-handling behavior of animals. Birds, mammals, fishes, and ants are major biotic dispersal agents of tropics; but, crabs, wasps, and dung beetles are also often reported as seed dispersal agents of tropical plants.
... These swamps are dominated by trees of the Myristicaceae family which is placed along with other 'living fossil' families of primitive dicots like Magnoliaceae, Annonaceae and Chloranthaceae 19 . These swamps are also a site for unique plant-animal interactions such as pollination 20,21 and secondary seed removal 22 . The swamps are characterized by high endemism 23 of up to 61.11% (ref. ...
The vegetation of Myristica swamp forests in Kulathupuzha, southern Kerala, India, was examined with reference to floristic composition, structure and diversity. Quadrates of 100 X 10 m were laid inside (17) and outside the swamps (14), and trees >10 cm girth at breast height were enumerated. A total of 2246 individual trees belonging to 58 species were recorded inside the swamps as against 1203 trees belonging to 89 species from outside the swamps. A total of 1775 shrubs belonging to 46 species and 26 species of herbs with 1082 individuals were recorded from inside the swamps. A total of 3535 shrubs belonging to 83 species and 491 herbs belonging to 30 species were recorded from outside the swamps. The Myristica swamp forests showed less diversity when compared to other forest types and was dominated by two Myristicaceae species, Myristica fatua var. magnifica and Gymnacranthera farquhariana. Comparison with Myristica swamps in other regions indicates that the Kulathupuzha region has the largest populations of the endangered M. fatua var. magnifica. Immediate steps for conservation are suggested.
Phytochemical investigation of the methanol extract of the fruit rind of Myristica malabarica led to the isolation of eight known compounds that were identified as malabaricones A‐D, promalabaricones B and C, 1‐(2,6‐dihydroxyphenyl) tetradecane‐1‐one, and ericanone by comparison with literature spectroscopic data. The structures of malabaricones A‐D, promalabaricone B, and 1‐(2,6‐dihydroxyphenyl) tetradecane‐1‐one were confirmed by X‐ray crystallography. In vitro assay of the isolated phenols indicated that they exhibited moderate anti‐proliferative activity against the A2780 human ovarian cancer cell line.
Synzoochory is the dispersal of seeds by seed‐caching animals. The animal partner in this interaction plays a dual role, acting both as seed disperser and seed predator. We propose that this duality gives to synzoochory two distinctive features that have crucial ecological and evolutionary consequences. First, because plants attract animals that have not only positive (seed dispersal) but also negative (seed predation) impacts on their fitness, the evolution of adaptations to synzoochory is strongly constrained. Consequently, it is not easy to identify traits that define a synzoochorous dispersal syndrome. The absence of clear adaptations entails the extra difficulty of identifying synzoochorous plants by relying on dispersal traits, limiting our ability to explore the full geographic, taxonomic and phylogenetic extent of synzoochory. Second, the positive and negative outcomes of interactions with synzoochorous animals are expressed simultaneously. Consequently, synzoochorous interactions are not exclusively mutualistic or antagonistic, but are located at some point along a mutualism–antagonism continuum. What makes synzoochory interesting and unique is that the position of each partner along the continuum can be evaluated for every plant–animal interaction, and thus the continuum can be precisely described by assessing the relative frequency of positive and negative interaction events in each pairwise interaction. Herein we explore these two main features of synzoochory with a comprehensive quantitative survey of published studies on synzoochory. Synzoochory has been recorded for at least 1339 plant species differing in life forms, from annual and short‐lived herbs to long‐lived trees, belonging to 641 genera and 157 families widely distributed across the globe and across the seed plant phylogeny. Over 30 animal families belonging to five disparate taxonomic groups (rodents, marsupials, birds, insects, and land crabs) potentially act as synzoochorous dispersers. Although synzoochory appears to be fundamentally a secondary dispersal mode, many abundant and dominant trees are primarily synzoochorous. In addition, we found evidence of the existence of diplosynzoochory (caching animals acting both as primary and secondary dispersers of the same individual seed), mostly in nut‐bearing trees. Finally, we found that synzoochorous interactions are widely spread across the mutualism–antagonism continuum. Nevertheless, there were some differences among disperser species and functional groups. Corvids and some rodents (cricetids, nesomyids, sciurids) were located in the positive‐effects region of the continuum and presumably behave mostly as dispersers, whereas land crabs and insects were located in the negative‐effects extreme and behave mostly as seed predators. Our review demonstrates that synzoochory is not an anecdotal ecological interaction. Rather, it is pivotal to the functioning of many ecosystems where the natural regeneration of keystone plant species depends on the activity of granivorous animals that play a dual role. This distinctive interaction should not be ignored if we wish to have an accurate understanding of the functioning of natural systems.
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 birddispersed, 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 observed birds and mammals visiting individual plants in a Panamanian population of the rainforest tree Virola surinamensis ("Wild Nutmeg") to determine (1) relative importance of different dispersal agents, and (2) the relationships between crop size, crop quality, and seed removal. Arils of this tree are exceptionally nutritious (63% fat, 9% nonstructural carbohydrate, 3% protein), but draw remarkably few species of fruit-eating animals. Six birds take 77% of the seeds handled by animals. One toucan (Ramphastos@?swainsonii) accounts for 35% of the seeds handled; other birds (Penelope purpurascens, Trogon massena, Baryphthengus martii, Pteroglossus torquatus, Ramphastos sulfuratus) play lesser roles. The smallest visitor, a cotinga (Tityra semifasciata) eats arils but does not disperse seeds. One monkey (Ateles geoffroyi) removes 3% of the seeds handled by frugivores, but smells and rejects or otherwise wastes 9%. Such a small assemblage is anomalous in a forest with at least 78 species of fruit-eating animals; other trees with arillate seeds of similar size draw as many as 23 frugivores. We hypothesize that the size of the assemblage is limited by seed size, small crop size, and perhaps by defensive compounds in the arils. Despite the small assemblage, an average of 62% (range: 13-91%) of the fruits available to animals are taken. Fruits are so nutritious that trees with both small and large crops are depleted; no variance in the percentage of seeds removed can be attributed to crop size. Fruits of different individual trees do vary in size; 59% of the variation in the percentage of seeds taken can be attributed to mean seed size. Fruit-eating animals preferentially deplete trees with small seeds, and coincidentally favor trees with high aril-to-seed ratios. No significant portion of the variance in "dispersal success" can be explained by aril mass alone. We hypothesize that consistent differences in seed size could result in dramatic differences in dispersal, and hence reproduction, over the lifetime of individual trees. On the other hand, selection may alternatively favor small seed size and high dispersability in years when frugivores are abundant, and large seed size and enhanced seedling vigor in the parental stand when fruit-eating birds are scarce. Small-seeded plants are likely to colonize new sites; large-seeded individuals are likely to produce offspring that fare well in competition with other seedlings near parent trees.
We studied predation upon the fruits of four common terrestrial plant species of atolls by excluding: 1) all predators; 2) large predators only; and 3) no predators. Each of these treatments was located within the vegetation at three distances from the shore: beach edge of fringing thicket; middle of the thicket; and inner forest. The plants were Terminalia catappa, Messerschmidia argentea, Scaevola taccada, and Guettarda speciosa. Predation loss over the year was significant (P < 0.01) for all four species. Location contributed significantly only for S. taccada. Amount of loss and predominant type of seed predator for a plant species were related to size and conspicuousness. The largest fruits, those of the widespread tree T. catappa, were destroyed completely at all sites; the damage was done by both insects and terrestrial crabs. The large fruits of G. speciosa were destroyed by insects inland and by crabs at the beach edge. The small fruits of M. argentea, a plant which is common along the beach, tended to have greater losses away from the beach edge; those losses were caused primarily by insects. For S. taccada, which occurred at the beach edge, fruit survival was highest in the middle of the fringe thicket; average damage and disappearance were high and caused primarily by large predators. In sum, the experiment demonstrated that predation by widespread, omnivorous large animals and insects on an atoll island was important in survival of fruits and enclosed seeds. We conclude that this interaction could have a significant influence on the dynamics of plants on atolls.
Many studies of postdispersal seed fate use seed removal as an index of seed predation. However, following primary seed dispersal, some seeds are transported intact by ants, dung beetles, scatter-hoarding animals, or abiotic processes to new microsites (secondary dispersal) where germination is possible. Despite a growing realization that secondary seed dispersal can play an important role in plant recruitment, many researchers continue to use seed removal as a proxy for seed predation and are focused too intently on only the initial step of seed fate. We describe, using examples from the recent literature, how the results of some seed removal studies may have been misinterpreted, present plausible, alternative explanations for the fate of seeds in those studies, and discuss the importance of detailed studies of seed fates. Following the fates of seeds can be difficult, but such studies contribute much more to our understanding of seed dynamics and plant fitness.
Dispersal-viewed as the departure of a diaspore (eg. seed or fruit) from the parent plant-is examined in terms of mechanisms, advantages (eg. in connection with escape from parental influence, and colonization), and patterns of production (eg. geographical aspects, seasonality, and intraspecific variation).-P.J.Jarvis
A high number of tree species, low density of adults of each species, and long distances between conspecific adults are characteristic of many low-land tropical forest habitats. I propose that these three traits, in large part, are the result of the action of predators on seeds and seedlings. A model is presented that allows detailed examination of the effect of different predators, dispersal agents, seed-crop sizes, etc. on these three traits. In short, any event that increases the efficiency of the predators at eating seeds and seedlings of a given tree species may lead to a reduction in population density of the adults of that species and/or to increased distance between new adults and their parents. Either event will lead to more space in the habitat for other species of trees, and therefore higher total number of tree species, provided seed sources are available over evolutionary time. As one moves from the wet lowland tropics to the dry tropics or temperate zones, the seed and seedling predators in a habitat are hypothesized to be progressively less efficient at keeping one or a few tree species from monopolizing the habitat through competitive superiority. This lowered efficiency of the predators is brought about by the increased severity and unpredictability of the physical environment, which in turn leads to regular or erratic escape of large seed or seedling cohorts from the predators.
The land crab, Gecarcinus
quadratus (Gecarcinidae), affects plant diversity in a mainland, neotropical rain forest through selective seedling consumption. In Costa Rica's Corcovado National Park, G.
quadratus lives in fossorial populations with up to six crabs m−2 in coastal forest extending c. 600 m inland from the Pacific Ocean. A narrow transition zone (c. 30 m) separates the crab zone from the crabless zone that comprises the remainder of the 55 000-ha park. The composition of dicotyledonous plants from the adjacent zones were distinct: crabless zone transects (240 m2) contained 97 species representing 76 genera and 41 families; crab zone transects contained 46 species representing 38 genera and 25 families. Despite the narrow zonal separation, the crabless zone shared only 27.4, 29.9 and 52.8% of its species, genera and families, respectively, with the crab zone; in contrast, crab zone transects shared 56.5, 60.5 and 88% of their species, genera and families with the crabless zone. This abrupt diversity gradient suggests a powerful selection pressure in the crab zone preventing the establishment of certain dicotyledonous species. Two years of experimental crab exclusion suggested that G.
quadratus reduces seedling density and diversity. Densities of seedlings (3–25 cm tall) within exclosures increased 144% over baseline values while control densities decreased. In contrast, seedlings at the cotyledon stage and taller (26–50 cm) were unaffected by crab exclusion. Preference tests conducted in the crab zone revealed a five-fold ratio of mortality rates for seedlings transplanted from the crabless zone and crab zone respectively. However, when protected from crabs, transplanted crabless and crab zone seedlings survived similarly well over 6 mo (83 and 70% respectively). Together, data from transects and experiments suggest that G.
quadratus influences plant community composition.
Averaged over all species and forests, 75.7 + or - 28.7% of the seeds used in the experiments were consumed by predators (small crabs belonging to the family Grapsidae). Avicennia marina was most heavily preyed upon, followed in decreasing order by Bruguiera exaristata, Ceriops tagal, B. gymnorrhiza and Rhizophora stylosa. Differences in chemical composition of the propagules accounted for = or >97% of the differences in amounts of predation among the 5 species. Nutritive quality of the propagules, expressed as a function of protein, simple sugar, fiber, and tannin content, was more important in explaining the differences than was propagule size. Significant differences also existed among 3 forest types, which differed in species dominance. Lowest amounts of predation for C. tagal were in the forest where adults of this species were absent, and highest in the forest where the species was most dominant. For A. marina, the 2 Bruguieras, and R. stylosa, however, amounts of predation were significantly higher in forests where conspecifics were rare or absent and lowest where conspecifics were dominant. For these last 4 species, conspecific dominance in the canopy explained = or >63% of the variation in predation among forest types. Seed predators may play a significant role in determining the intertidal distribution of the mangrove species studied.-from Author
The recruitment of Phillyrea latifolia L. (Oleaceae), a bird-dispersed tree of Mediterranean forest, is described. Fruit removal by birds, seed rain, post-dispersal seed predation, seed germination, and seedling emergence, survival, and establishment were studied. The main objective was testing whether seed dispersal by birds produced a pre- dictable seedling shadow as a result of coupled patterns of seed rain, seedling emergence, and seedling establishment. P. latlfolia is a mast-fruiting species and large fruit crops were produced in only 2 (1 98 1 and 1989) out of 15 yr (1 978-1 992). We report here on the 1989 fruiting event at one scrubland and one forest site. Ripe fruits were available from mid-September to early June. Extensive removal by birds started after fruit crops of other species were depleted. Seed dispersers were more abundant, and fruit predators more scarce, in scrubland than in forest. P. latifolia fruits were a major component in the diet of principal seed dispersers (Sylvia atricapilla and Erithacus rubecula) that depended almost exclusively on them for food late in the season. Fruit removal levels were higher, crops were depleted earlier, and individual plants dis- persed more seeds in scrubland than in forest. Crop size was the best predictor of number of seeds dispersed by individual plants in scrubland, while fruit characteristics were more influential in forest. Seed dispersal was largely a within-population phenomenon, as no seed fall occurred in traps set beyond the distributional limits of P. latifolia in the study region. Frugivores produced a spatially predictable seed rain at the two sites. Seed rain was greatest beneath fleshy fruit-producing species (under female individuals in dioecious species) in scrubland and at forest-gap interfaces in forest. Post-dispersal seed predation was low at the two sites (39 and 54% after 1-yr exposure). In forest, seed survival was lower in gaps than in forest interior or forest edges. In scrubland, seed survival differed widely among microhabitats (defined by overlying plant species), ranging from 19% (open ground) to 6 1% (beneath Rosmarinus oficinalis). In forest, density of emerging seedlings was unrelated to location in the habitat mosaic (gap, forest edge, interior). Seedling density did differ among microhabitats in scrubland, where emergence was greatest under fleshy fruit-producing species. Seedling survival was higher in forest than in scrubland, where seedlings incurred greater mortality due to desiccation. In both sites, seedling survival depended significantly on microhabitat and was depressed under adult conspecifics. The activity of frugivores directly impacted seedling distribution in scrubland, as spatial patterns of seed deposition were not overshadowed by later-acting factors, such as rodent seed predation or variation in germination. In forest, there was spatial discordance between seed rain and seedling distribution, as a consequence of uncoupled seed rain and seedling emergence. Spatial patterns of seed deposition by birds may thus have a lasting impact on the population dynamics of P. latlfolia, but this will vary among populations depending on the extent of coupling of the different stages in the recruitment process (dispersal-seed rain-germination and seedling establishment).
We examined the importance of seed dispersal in predicting the pioneer seedling composition in recent gaps in a forest plot on Barro Colorado Island (BCI), Panama. We characterize seed dispersal for 13 taxa from seed rain data collected over 13 years in 200 mesh traps, and for an additional species from germination from soil samples collected in one year. We describe seedling distribution patterns from a complete census of all seedlings of these 14 taxa present in 36 treefall gaps.
A maximum likelihood model, incorporating both distance to adult trees and tree size, fitted observed seed rain to traps quite well for all taxa.
The ability to predict seedling recruit number per gap varied greatly among taxa. For 8 of 14 taxa, regression models incorporating predicted seed rain were significantly better predictors of seedling recruitment than models in which recruitment probability was assumed constant in all sites.
To see if variation in local dispersal patterns determined the community composition of gaps, we examined the relative abundances of these 14 pioneer taxa in the 36 gaps. We found that taxon abundances were significantly positively correlated with abundances predicted from seed dispersal models and seed–seedling regressions for 27 out of 36 gaps.
Overall, we find evidence that limited seed dispersal is an important factor contributing, together with factors affecting post‐dispersal recruitment success, to seedling distribution patterns in gaps.
Amounts of seed predation by grapsid crabs (Brachyura: Grapsidae) on two species of mangroves (Aegiceras corniculatum and Avicennia marina) were compared among different habitats in an Australian mangrove forest. For Avicennia, comparisons were between canopy gaps and the adjacent forest understory for six, mid intertidal, gaps of different sizes. For Aegiceras the comparisons were among canopy gaps in the high intertidal; open, accreting mud/sand banks where mangroves were colonizing in the low intertidal; and in the forest understory in both the high and low intertidal zones. These were repeated in the high salinity (35\%) downstream portion and the low salinity (0–5\%) upstream portion of a tidal river.
Predation on Avicennia was significantly higher in the understory than in adjacent canopy gaps. Within a canopy opening, predation was greatest in the smallest gaps and lowest in the largest gaps. Predation on Aegiceras was greater in the high intertidal compared to the low intertidal, but no differences were found between river mouth and upstream locations. In the high intertidal zone of the forest, there were no differences in predation between canopy gap or forest understory sites for Aegiceras. In the low intertidal zone, however, significant differences in amount of predation were found between habitats. More Aegiceras propagules were consumed in the understory than on adjacent accreting sandbanks.
Frequency of tidal inundation, which in turn affects the amount of time available to forage, is hypothesized to account for differences in predation between low and high intertidal forests and between small and large canopy gaps. Our results also suggest that ‘shade intolerance’ in these two species may actually reflect an escape from predators, successful when the seeds are dispersed into open areas such as canopy gaps or mud banks.
Spatial and temporal patterns of predation on seeds of the seagrass Phyllospadix torreyi S. Watson were quantified at four sites near Santa Barbara, California, USA. Over a period of four flowering seasons during
1995 to 1998, monthly patterns of seed fall and intensity of seed predation were similar among sites, but were temporally
quite variable. Abundance of dispersed seeds varied greatly both among seasons and years. Within any one year, seeds were
present in the environment every month, but they peaked in abundance during the fall months following the annual flowering
period. Seeds were more abundant during the earlier years of the study. The intensity of predation steadily increased throughout
the study period, from a low of ≤10% seeds consumed during 1995 to ∼50% consumption by 1997, and it was not correlated with
abundance of seeds in the environment. Pre-dispersal seed loss also was estimated in two flowering seasons by counting the
numbers of seeds consumed prior to release from the plant, and was relatively low (<15%). No differences were detected among
the four study sites in patterns of pre-dispersal loss. Field surveys were done at two sites to identify potential seed predators.
Three of the most abundant species identified in these surveys were tested in the laboratory to determine size-specific patterns
of feeding activity and to assess which early life stages of P. torreyi (fruits within spadices, dehisced fruits, seedlings) were most vulnerable to predation. All three of the early life stages
were consumed. The crabs Pugettiaproducta (Randall) and Pachygrapsus crassipes Randall were much more voracious predators than the isopod Idotea resecata Stimpson.
We develop a model that outlines the movements and fates of seeds after they leave the parent plant, and then we examine the relative influences of abiotic and biotic factors on those movements and fates. Phase I dispersal is movement of a seed from the parent to a surface, while Phase II dispersal includes subsequent horizontal or vertical movements. Although less studied, Phase Il dispersal is more likely to account for the patterning of plants in communities and ecosystems and is the focus of this review. Abiotic factors influence Phase II dispersal-the distance and type of movement depend on seed morphology, surface attributes, and the nature of the physical forces. Biotic factors (animals) move seeds to new sites passively either on body surfaces or by ingestion, or actively by consuming fruits or hoarding seeds. Animals also influence the movements of seeds through digging and burrowing activities. Arrival at microsites suitable for germination and establishment is critical and is affected not only by abiotic and biotic factors but also by seed morphology and germination responses. We emphasize that seed banks are much more dynamic than they are usually portrayed. Although often poorly quantified, seed mortality can occur at any point in the model. Sufficient differences exist among biomes that certain generalizations can be made regarding seed dynamics. Knowledge of seed movements and fates is essential for ecosystem restoration and conservation efforts and for the control of alien species in all biomes.
Experiments were performed to investigate monthly variations in seed fate of Carapa procera (Meliaceae), a rodent-dispersed subcanopy tree species in French Guiana. A total of 600 thread-marked seeds were placed on the ground in mature forest under 20 adult trees during different months (March, April and May 1991) of the species' fruiting season. In 1991 the seed crop reached 1536 seeds in the study area, with a majority of seeds being produced in March and May. On average, seed removal rate steadily increased from March (23%) to May (96%). Of the seeds removed, the proportion cached almost doubled between March (28%)-April (25%) and May (48%), whereas the proportion eaten (gnawed) steadily declined between March (43%) and May (9%). Approximately 75-100% seed removal was therefore associated with intense scatterhoarding and low seed predation, especially in May. Greater seed dispersal rates occurred during the late wet season when fruit diversity decreased but when overall fruit biomass peaked because of fruiting occurrence of large-seeded species. The seasonal hoarding behaviour of rodents is discussed.
The spatial distribution of two rain forest tree species, Carapa procera (Meliaceae) and Vouacapoua americana (Caesalpiniaceae) was analysed within and between plots of different sizes (6.25 and 25 ha) at Paracou, French Guiana. The L(d) function was used to characterize spatial patterns, and the L-ij(d) intertype to study independancy between young and adult trees. Although both species are known to be dispersed by caviomorph rodents within short distances (c. 10-20 m and up to 50 m) of parent tree crowns, the analysis of tree positions led to different spatial patterns between species depending on soil drainage characteristics. Overall, while V. americana showed a strongly aggregated spatial distribution, C. procera had a weaker propensity to depart from complete spatial randomness (CSR). A complex distribution, sometimes clustered in areas with hydromorphic soils (swamps and around streams) and sometimes very near CSR outside these areas characterized the C. procera population. When C. procera tree aggregation occurred, there was a slight attraction between juveniles and adults. The aggregation of V. americana trees was evidenced at different levels depending on the scale of investigation. Within small plots (6.25 ha), a first level of aggregation with short distance radii of c. 10-25 m giving small clusters, and a second level which is composed of small clusters aggregated at c. 40-50 m distance radius, were observed. A third level of aggregation was suggested by analysing the tree population at the larger scale (25 ha) whose boundaries outside the plot were not delimited. Aggregation of V. americana trees at all levels was enhanced by a strong attraction between juveniles and adults. These results were discussed in light of seed and seedling ecology, especially with regard to seedling and sapling gap-dependence and soil drainage, which likely affected the recruitment of juvenile trees, and henceforth final tree spatial pattern.
Protected areas in India have historically been established on an ad hoc basis with little attention to the conservation value of an area. This study focuses on a set of protected areas in the Agastyamalai region of the Western Ghats (WG), India. We examine forest loss and land-use changes in the study area from the early 1900s to 1960 and from 1960 to 1990. We use GIS to perform a biodiversity gap analysis of the protected areas in the study site. We produce a detailed map of existing floristic types and use it to generate layers corresponding to floristic species richness, zones of floristic endemism, floristically unique areas, and habitat distribution of representative endemic faunal species. These layers are combined with a map of the protected area network to highlight areas of high conservation value excluded from adequate protection. Deforestation rates are high in the study region and several areas of high biodiversity value are excluded from the highest levels of protection. We offer this method as a step toward developing a utilitarian conservation value index for assigning conservation and management priorities.
Plant populations are regulated by a diverse assortment of abiotic and biotic factors that influence seed dispersal and viability, and seedling establishment and growth at the microsite. Rarely does one animal guild exert as significant an influence on different plant assemblages as land crabs. We review three tropical coastal ecosystems-mangroves, island maritime forests, and mainland coastal terrestrial forests-where land crabs directly influence forest composition by limiting tree establishment and recruitment. Land crabs differentially prey on seeds, propagules and seedlings along nutrient, chemical and physical environmental gradients. In all of these ecosystems, but especially mangroves, abiotic gradients are well studied, strong and influence plant species distributions. However, we suggest that crab predation has primacy over many of these environmental factors by acting as the first limiting factor of tropical tree recruitment to drive the potential structural and compositional organisation of coastal forests. We show that the influence of crabs varies relative to tidal gradient, shoreline distance, canopy position, time, season, tree species and fruiting periodicity. Crabs also facilitate forest growth and development through such activities as excavation of burrows, creation of soil mounds, aeration of soils, removal of leaf litter into burrows and creation of carbon-rich soil microhabitats. For all three systems, land crabs influence the distribution, density and size-class structure of tree populations. Indeed, crabs are among the major drivers of tree recruitment in tropical coastal forest ecosystems, and their conservation should be included in management plans of these forests.
A fundamental goal of plant population ecology is to understand the consequences for plant fitness of seed dispersal by animals. Theories of seed dispersal and tropical forest regeneration suggest that the advantages of seed dispersal for most plants are escape from seed predation near the parent tree and colonization of vacant sites, the locations of which are unpredictable in space and time. Some plants may gain in fitness as a fortuitous consequence of disperser behavior if certain species of dispersers nonrandomly place seeds in sites predictably favorable for seedling establishment. Such patterns of directed dispersal by vertebrates long have been suggested but never demonstrated for tropical forest trees. Here we report the pattern of seed distribution and 1-year seedling survival generated by five species of birds for a neotropical, shade-tolerant tree. Four of the species dispersed seeds to sites near the parent trees with microhabitat characteristics similar to those at random locations, whereas the fifth species, a bellbird, predictably dispersed seeds under song perches in canopy gaps. The pattern of seedling recruitment was bimodal, with a peak near parent trees and a second peak, corresponding to bellbird song perches, far (>40 m) from parent trees. Seedling survival was higher for seeds dispersed by bellbirds than by the other species, because of a reduction in seedling mortality by fungal pathogens in gaps. Thus, bellbirds play a significant role in seed dispersal by providing directed dispersal to favorable sites and therefore may influence plant recruitment patterns and species diversity in Neotropical forests.
We examine the relative importance of processes that underlie plant population abundance and distribution. Two opposing views dominate the field. One posits that the ability to establish at a site is determined by the availability of suitable microsites (establishment limitation), while the second asserts that recruitment is limited by the availability of seeds (seed limitation). An underlying problem is that establishment and seed limitation are typically viewed as mutually exclusive. We conducted a meta-analysis of seed addition experiments to assess the relative strength of establishment and seed limitation to seedling recruitment. We asked (1) To what degree are populations seed and establishment limited? (2) Under what conditions (e.g., habitats and life-history traits) are species more or less limited by each? (3) How can seed addition studies be better designed to enhance our understanding of plant recruitment? We found that, in keeping with previous studies, most species are seed limited. However, the effects of seed addition are typically small, and most added seeds fail to recruit to the seedling stage. As a result, establishment limitation is stronger than seed limitation. Seed limitation was greater for large-seeded species, species in disturbed microsites, and species with relatively short-lived seed banks. Most seed addition experiments cannot assess the relationship between number of seeds added and number of subsequent recruits. This shortcoming can be overcome by increasing the number and range of seed addition treatments.
Interest in land crabs has burgeoned as biologists have increasingly focused on the evolution of terrestriality. Before the publication of this volume in 1988, there had been no single comprehensive source of information to serve biologists interested in the diverse aspects of terrestrial decapod crustacean. Biology of the Land Crabs was the first synthesis of recent and long-established findings on brachyuran and anomuran crustaceans that have evolved varying degrees of adaptation for life on land. Chapters by leading researchers take a coordinated evolutionary and comparative approach to systematics and evolution, ecology, behaviour, reproduction, growth and molting, ion and water balance, respiration and circulation, and energetics and locomotion. Each discusses how terrestrial species have become adapted from ancestral freshwater or marine forms. With its extensive bibliography and comprehensive index, including the natural history of nearly eighty species of brachyuran and anomuran crabs, Biology of the Land Crabs will continue to be an invaluable reference for researchers and advanced students.
The importance of local dispersal to Pandanus tectorius Park. ex Z. (Pandanaceae) is assessed by analyzing the spatial distribution of juveniles. Juveniles are, on average, further away from adults than undispersed seeds; and older juveniles are at a greater distance than seedlings. These results indicate the importance of local dispersal to successful reproduction. The agent of this dispersal is a land crab, Cardisoma carnifex (Herbst.). C. carnifex readily locates and eats the fruit of Pandanus tectorius. Crabs transport the fruit before consuming it, and discard the woody portion which contains the seeds, thus serving as dispersal agents. Experiments show the distance crabs may carry the fruit varies widely and averages 7.3 m in this study. /// Значение локальной дисперсии для Pandanus tectorius Park ex Z. (Pandanaceae) оценивали методоманализа пространственного распределения ювенильных особей. Молодые растения в среднем удалены от взрослых на большее расстояние, чем нерассеянные семена, а ювенильные растения более старшего возраста находились на большем удалении, чем всхобы. Эти результаты показывают значение локальной дисперсии для репродуктивного успеха. Агентом зтой дисперсии оказывается наземный краб Cardisoma carnifex (Herbst). C. carnifex локализуется поблизости и питается плодами Pandanus tectorius. Крабы перемещают плоды перед тем, как их сьесть, и выбрасывают одревесневшие части, содержащие семена, действуя таким образом, как агенты расселения. Опыты показали, что дистанция переноса плодов крабами может широко варьировать; в среднем она составляет в данном исследовании 7,3 м.
The red land crab (Gecarcoidea nalalis) is the major collector of fruits and seeds from the rain forest Moor on Christmas Island, Indian Ocean. At three sites, they rapidly removed fruits and seeds of 17 species tested (usually within 12 h after placement) and most were taken to crab burrows. Direct observations of seed predation, and application of estimated chelar forces of red crabs indicated that seeds of many species, especially those with thin seed coats, are likely to be killed through handling. However, removal of some resistant seeds to burrows may be favourable for seedling establishment when canopy gaps occur. Fruit removal rates by crabs were positively related to nitrogen concentration in fruit tissues but negatively correlated with condensed tannins. These observations suggest that seed predation by land crabs may affect the success of colonization and the relative abundance of plants on oceanic islands.
Abstract Although pigeons from the genus Ducula are considered among the best avian dispersers of large seeds in Asia and the Pacific, little has been documented on their role. The early fate of dispersed and undispersed seeds of the large-seeded tree Myristica hypargyraea A. Gray was studied in order to understand the advantage of seed dispersal by the Pacific Pigeon, Ducula pacifica Gmelin in Tonga. Frequency of visits by frugivores to fruiting trees and dispersal distance of seeds were measured. Pre-dispersal vertebrate seed predation was assessed, then post-dispersal predation was measured over 160 days. Overall, pre-dispersal seed predation by parrots was low but variable among trees sampled. Most seeds (54.7%) in the study area were estimated to be dispersed by D. pacifica; 79.7% of those ingested were expelled directly beneath conspecific fruiting crowns, 20% were dispersed locally and < 0.3% were dispersed more than 300 m into a different forest type. Flying foxes (Pteropus tonganus Quoy and Gaimard) dispersed very few seeds (0.7%) and all were dropped below fruiting crowns. Between 4% and 39% of dispersed and undispersed seeds were still viable, or had established seedlings after 160 days. Most seeds had been removed or killed by rats, and seed survival was highest for locally dispersed seeds (approx. 20 m from source trees and within the M. hypargyraea forest). Although D. pacifica was the only frugivore observed to disperse seeds into this higher zone of survival, overall they did not confer a great advantage to seed survival since significant numbers of seeds/seedlings also persisted under fruiting crowns (27% under crowns compared with 39% locally dispersed). Nevertheless, D. pacifica was the only vector by which seeds were regularly moved within the M. hypargyraea forest and over longer distances, and hence, D. pacifica still plays a significant role in the regeneration of M. hypargyraea.
In the coastal semideciduous forest of La Mancha, Veracruz (Mexico), we evaluated the removal of fallen fruits and seeds of different species by the land crab Gecarcinus lateralis under different environmental conditions (age soil of forest stand, topography, and cover). Crabs removed 67 percent of the propagules in the experiments (3106 of a total of 4608), and seeds were removed in greater quantities (61.1%) than fruits (38.9%). Fruits of Maclura tinctoria (Moraceae) and Ehretia tinifolia (Boraginacea) and seeds of E. tinifolia were the most affected species. Crabs removed higher quantities of fruits in old-soil forest and in the understory than in young-soil forest and gaps. In experiments with seeds, only for the older forest, the crabs removed more seeds in slopes and peaks than in valleys and in the understory than gaps, whereas in the young-soil forest, the differences were not significant. Our results suggest that G. lateralis, like Gecarcoidea natalis and Gecarcinus quadratus, is an efficient propagule predator and can exert pressure in the establishment of plant species, but in La Mancha, this also depends on site conditions and identity of the species. © 2005 by The Association for Tropical Biology and Conservation.
Predator effects on Zostera marina L. seed abundance were studied in the York River, VA, USA, using enclosure and exclosure caging experiments. Seeds were placed in cages in two concurrent experiments. The first experiment was a predator exclosure experiment to test the effects of excluding predators, using a full predator exclosure cage, a partial exclosure top-only cage, a partial exclosure side-only cage and uncaged plots. The second experiment was a predator enclosure experiment, using two highly abundant macro-benthic predators in the Chesapeake Bay: the decapod crustacean Callinectes sapidus Rathbun and the sciaenid fish Micropogonias undulatus L. Additionally, two-week long trials of sequentially protected and exposed seeds were also performed. Replicate treatment plots were sampled by removing the top 5–10 cm of the sediment surface with a suction sampler and still viable seeds in each plot were counted. Full exclosure cages contained significantly higher numbers of seeds than the uncaged or partial caged treatments. Seed abundances in the C. sapidus enclosure cages were significantly less than the full exclusion cage, but not significantly different than the uncaged treatments. Seed abundances in the M. undulatus cages were not significantly different than the full exclusion cage. The least number of seeds were found in the uncaged and partial cage treatments. Results of the sequentially protected and exposed trials were similar to results from the one-week uncaged treatments. These experiments suggest that seed predation can affect the abundance of Z. marina seeds, possibly causing up to 65% of the seed losses observed in these experiments. Results suggest that seed predation has the potential to be an important force governing the sexual reproductive success and propagation of eelgrass beds and that the degree of seed loss via predation may be related to predator and primary food abundances.
Growing interest in spatial ecology is promoting new approaches to the study of seed dispersal, one of the key processes determining the spatial structure of plant populations. Seed-dispersion patterns vary among plant species, populations and individuals, at different distances from parents, different microsites and different times. Recent field studies have made progress in elucidating the mechanisms behind these patterns and the implications of these patterns for recruitment success. Together with the development and refinement of mathematical models, this promises a deeper, more mechanistic understanding of dispersal processes and their consequences.
A revised survey of the forest types of India
- H G Seth
CHAMPION, H. G. & SETH, S. K. 1968. A revised survey of the forest types
of India. Manager of Publications, New Delhi. 404 pp.
On the conservation of the Myristica swamps of the Western Ghats. Pp. 1–19 in Uma Shaanker Forest genetic resources: status, threats, and conservation strategies Myristica swamps of Uttara Kannada District
- M D S Mesta
- D K Naik
CHANDRAN, M. D. S. & MESTA, D. K. 2001. On the conservation of the
Myristica swamps of the Western Ghats. Pp. 1–19 in Uma Shaanker,
R., Ganeshaiah, K. N. & Bawa, K. S. (eds.). Forest genetic resources:
status, threats, and conservation strategies. Oxford & IBH, New Delhi.
CHANDRAN, M. D. S, MESTA, D. K. & NAIK, M. B. 1999. Myristica
swamps of Uttara Kannada District. My Forest 35:217–222.
Herbivores and the number of tree species in tropical forests
JANZEN, D. H. 1970. Herbivores and the number of tree species in
tropical forests. American Naturalist 104:501–552.
Seed predators and plant population dynamics Seeds: the ecology of regeneration in plant communities
CRAWLEY, M. J. 2000. Seed predators and plant population dynamics.
Pp. 167–182 in Feener, M. (ed.). Seeds: the ecology of regeneration in
plant communities. CAB International, Wallingford.
A revised survey of the forest types of India
- H G Champion
- S K Seth
CHAMPION, H. G. & SETH, S. K. 1968. A revised survey of the forest types
of India. Manager of Publications, New Delhi. 404 pp.
Forest genetic resources: status, threats, and conservation strategies
- M D S Chandran
- D K Mesta
CHANDRAN, M. D. S. & MESTA, D. K. 2001. On the conservation of the
Myristica swamps of the Western Ghats. Pp. 1-19 in Uma Shaanker,
R., Ganeshaiah, K. N. & Bawa, K. S. (eds.). Forest genetic resources:
status, threats, and conservation strategies. Oxford & IBH, New Delhi.
Myristica swamps of Uttara Kannada District
- M D. S Chandran
- D K Mesta
- M B Naik
CHANDRAN, M. D. S, MESTA, D. K. & NAIK, M. B. 1999. Myristica
swamps of Uttara Kannada District. My Forest 35:217-222.
Seeds: the ecology of regeneration in plant communities
- M J Crawley
CRAWLEY, M. J. 2000. Seed predators and plant population dynamics.
Pp. 167-182 in Feener, M. (ed.). Seeds: the ecology of regeneration in
plant communities. CAB International, Wallingford.
The 2000 IUCN red list of threatened species
- Iucn
IUCN. 2000. The 2000 IUCN red list of threatened species. IUCN, Gland.
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Myristica swamps of Uttara Kannada District
- CHANDRAN