Enhanced seed dispersal of Prunus africana in fragmented and disturbed forests?

Forest destruction and disturbance can have long-term consequences for species diversity and ecosystem processes such as seed dispersal. Understanding these consequences is a crucial component of conserving vulnerable ecosystems. In the heavily fragmented and disturbed Kakamega Forest, western Kenya, we studied seed dispersal of Prunus africana (Rosaceae). In the main forest, five forest fragments, and differently disturbed sites, we quantified the overall frugivore community as an indicator for species diversity. Furthermore, we determined the frugivores on 28 fruiting P. africana trees, estimated seed dispersal, crop size and the general fruit availability of surrounding trees. During the overall frugivore census we recorded 49 frugivorous species; 36 of them were observed visiting P. africana trees and feeding on their fruits. Although overall frugivore species richness was 1.1 times lower in fragments than in main forest sites and 1.02 times higher in highly disturbed than in less disturbed sites, P. africana experienced 1.1 times higher numbers of frugivores in fragments than in main forest sites and 1.5 times higher numbers of frugivores in highly disturbed than in less disturbed sites. Correspondingly, seed dispersal was 1.5 times higher in fragments than in main forest sites and 1.5 times higher in more disturbed than less disturbed sites. Fruit availability of surrounding trees and crop size influenced the number of visitors to some degree. Thus, the number of dispersed seeds seemed to be slightly higher in fragmented and highly disturbed sites. This indicates that loss of single species does not necessarily lead to a decrease of ecosystem services. However, loss of diversity could be a problem in the long term, as a multitude of species might act as buffer against future environmental change.     

Forest fragmentation and selective logging have inconsistent effects on multiple animal-mediated ecosystem processes in a tropical forest

Forest fragmentation and selective logging are two main drivers of global environmental change and modify biodiversity and environmental conditions in many tropical forests. The consequences of these changes for the functioning of tropical forest ecosystems have rarely been explored in a comprehensive approach. In a Kenyan rainforest, we studied six animal-mediated ecosystem processes and recorded species richness and community composition of all animal taxa involved in these processes. We used linear models and a formal meta-analysis to test whether forest fragmentation and selective logging affected ecosystem processes and biodiversity and used structural equation models to disentangle direct from biodiversity-related indirect effects of human disturbance on multiple ecosystem processes. Fragmentation increased decomposition and reduced antbird predation, while selective logging consistently increased pollination, seed dispersal and army-ant raiding. Fragmentation modified species richness or community composition of five taxa, whereas selective logging did not affect any component of biodiversity. Changes in the abundance of functionally important species were related to lower predation by antbirds and higher decomposition rates in small forest fragments. The positive effects of selective logging on bee pollination, bird seed dispersal and army-ant raiding were direct, i.e. not related to changes in biodiversity, and were probably due to behavioural changes of these highly mobile animal taxa. We conclude that animal-mediated ecosystem processes respond in distinct ways to different types of human disturbance in Kakamega Forest. Our findings suggest that forest fragmentation affects ecosystem processes indirectly by changes in biodiversity, whereas selective logging influences processes directly by modifying local environmental conditions and resource distributions. The positive to neutral effects of selective logging on ecosystem processes show that the functionality of tropical forests can be maintained in moderately disturbed forest fragments. Conservation concepts for tropical forests should thus include not only remaining pristine forests but also functionally viable forest remnants.     

How human disturbance of tropical rainforest can influence avian fruit removal

Fruit consumption by birds is an important ecological interaction that contributes to seed dispersal in tropical rainforests. In this field experiment, we asked whether moderate human disturbance alters patterns of avian frugivory: we measured fruit removal by birds in the lower montane rainforest of Tobago, West Indies, using artificial infructescences made with natural fruits from two common woody plants of the forest understory (Psychotria spp., Rubiaceae). Displays were mounted simultaneously in three forest habitats chosen to represent a gradient of increasing habitat disturbance (primary, intermediate and disturbed), caused by subsistence land use adjacent to a protected forest reserve. We measured the numbers of fruits removed and the effect of fruit position on the likelihood of removal, along with the abundances of all fruits and fruit‐eating birds at the study sites. Fruit removal was highly variable and there was not a significant difference in removal rate among forest habitats; however, the trend was for higher rates of removal from displays in primary forest. Canopy cover, natural fruit availability, and frugivore abundance were not good predictors of fruit removal. Birds preferred more accessible fruits (those proximal to the perch) in all habitats, but in disturbed forest, there was a tendency for distal fruits to be chosen more frequently than in the other forest types. One possible explanation for this pattern is that birds in disturbed forests were larger than those in other habitats, and hence were better able to reach the distal fruits. Coupled with differences in bird community composition among the forest types, this suggests that different suites of birds were removing fruit in primary versus disturbed forest. As frugivore species have different effectiveness as seed dispersers, the among‐habitat differences in fruit removal patterns that we observed could have important implications for plant species experiencing disturbance; these possible implications include altered amounts of seed deposition and seedling recruitment in Tobago's tropical rainforest.     

Diversity and ecology of lianas in tropical dry evergreen forests on the Coromandel Coast of India under various disturbance regimes

In this study we attempted to explore patterns of diversity, abundance, climbing and dispersal mode of lianas in relation to disturbance in 40 Indian subtropical dry forests. The sites were selected to represent four disturbance categories: relatively undisturbed, moderately disturbed, much disturbed and heavily disturbed. All lianas ≥1 cm dbh were counted, which resulted in a total amount of 5689 individuals of lianas, representing 77 species in 62 genera and 32 families. Liana species richness and abundance increased with forest disturbance, but the liana basal area values showed an opposite trend, with high scores in undisturbed sites. Twining was the main climbing mechanism (61.3%) and zoochory (59.6%) was the main dispersal mode in all the four forest categories. Application of Bray–Curtis cluster analysis produced three distinct clusters in which the much disturbed category was more distant from the others. High abundance of large lianas in undisturbed sites and that of the invasive Lantana camara in heavily disturbed site signals the conservation significance of the less disturbed study sites. The predominance of zoochorous dispersal indicates the faunal dependence of lianas, besides of host trees, thus underlining the need for a holistic approach in biodiversity conservation of this and similar tropical forests.     

Can remnant frugivore species effectively disperse tree seeds in secondary tropical rain forests?

Seed dispersal by frugivores in tropical rain forests is important for maintaining viable tree populations. Over the years, vertebrate assemblages in tropical forests have been altered by anthropogenic disturbances, leading to concerns about the ability of remnant vertebrates to substitute for the lost or declining vertebrate populations. We compared vertebrate composition and frugivore visitation rates as an indirect measure of rate of seed dispersal in three tropical rain forests in Uganda, namely Mabira, Budongo and Kibale Forests. Mabira is highly disturbed, Kibale is little and Budongo is intermediate. The aim was to determine whether vertebrate assemblages in differentially disturbed forests had comparable abilities to disperse seeds and whether tree species were equally vulnerable to loss of seed dispersers. Assemblages of forest generalist species were similar in all forests, but specialists were less abundant in the heavily disturbed forest. Remnant frugivores in the heavily disturbed forest were mainly small-bodied species that spat seeds beneath fruiting trees compared to large-bodied species observed in the less disturbed forests that ingested and carried away the seeds. We postulate that the quantity of seeds dispersed in heavily disturbed forests is much reduced due to low visitation rates of frugivores and the absence of large frugivores that consume large quantities of fruit. The quality of seed dispersal is affected as well by the distance over which seeds are moved. Assessment of vulnerability of trees shows no evidence for disperser substitution for trees producing large fruits. Fruit trees with low nutritional contents and digestibility were least visited in frugivore-impoverished forests. The loss of large specialist frugivores is likely to affect recruitment of many trees, especially of species that cannot establish beneath adult conspecifics.     

Habitat disturbance reduces seed dispersal of a forest interior tree in a fragmented African cloud forest

Habitat fragmentation and disturbance are known to impact animals and plants in different ways, depending on species' characteristics and the type and scale of habitat modification involved. In contrast, direct or indirect ramifications on mutualistic relationships between plants and animals are less clear, possibly because general patterns are confounded by the diffuse nature of many of these interactions. Here, we examine how fragment size and/or severe disturbance of a Kenyan mountain cloud forest affects the frugivore community and seed removal of a large-seeded, bird-dispersed tree of the forest interior, for three consecutive years. Forest deterioration reduced avian visitation and seed removal rates independent of fragment size, consistently so despite strong temporal variation in fruit production over the three-year study. In disturbed forest fragments, seed removal rates were on average 3.5 times lower than in more intact ones. Strong differences in both visitation and seed removal rates were largely attributable to shifts in frugivore assemblages, characterized by loss or reduced abundance of the most effective seed dispersers, most of which were forest specialists. Although some disturbed fragments benefited from visits of non-forest dependent seed dispersers, such 'resilience' was not predictable or reliable in time or space. We conclude that disruption of seed disperser-seed interactions in highly fragmented and disturbed tropical forests may be persistent in time when resiliency is inadequate, possibly posing long-term effects on tree communities.     

Cordia millenii: on the risk of local extinction?

Selective logging of valuable tropical timber trees is a conservation concern because it threatens the long-term sustainability of forests. However, there is insufficient information regarding the postlogging recovery of harvested species. Here, I assessed the seed dispersal patterns, recruitment and abundance of Cordia millenii , a valuable timber tree in two Ugandan tropical rain forests that have been subjected to varying disturbance regimes. The aim was to determine the vulnerability of Cordia in these forests. The rate of seed dispersal was lower in the heavily disturbed Mabira Forest compared with the less disturbed Budongo Forest. Frugivores in Mabira were small-bodied individuals that spat seeds beneath fruiting trees, whereas 90% of the fruit in Budongo was consumed by large-bodied chimpanzees that disperse seeds over long distances. Juveniles of Cordia were not found in the closed forest, although they were found in forest gaps in Budongo but not Mabira. Mature tree density was higher in Budongo compared with Mabira. Lack of effective seed dispersal coupled with the inability of seedlings of Cordia to establish under closed canopy account for the arrested recruitment in Mabira. Enrichment planting in felling gaps is necessary to avoid local extinction of Cordia in forests without large vertebrates.     

Lowland tapirs facilitate seed dispersal in degraded Amazonian forests

The forests of southeastern Amazonia are highly threatened by disturbances such as fragmentation, understory fires, and extreme climatic events. Large‐bodied frugivores such as the lowland tapir (Tapirus terrestris) have the potential to offset this process, supporting natural forest regeneration by dispersing a variety of seeds over long distances to disturbed forests. However, we know little about their effectiveness as seed dispersers in degraded forest landscapes. Here, we investigate the seed dispersal function of lowland tapirs in Amazonian forests subject to a range of human (fire and fragmentation) and natural (extreme droughts and windstorms) disturbances, using a combination of field observations, camera traps, and light detection and ranging (LiDAR) data. Tapirs travel and defecate more often in degraded forests, dispersing much more seeds in these areas [9,822 seeds per ha/year (CI_95% = 9,106; 11,838)] than in undisturbed forests [2,950 seeds per ha/year (CI_95% = 2,961; 3,771)]. By effectively dispersing seeds across disturbed forests, tapirs may contribute to natural forest regeneration—the cheapest and usually the most feasible way to achieve large‐scale restoration of tropical forests. Through the dispersal of large‐seeded species that eventually become large trees, such frugivores also contribute indirectly to maintaining forest carbon stocks. These functions may be critical in helping tropical countries to achieve their goals to maintain and restore biodiversity and its ecosystem services. Ultimately, preserving these animals along with their habitats may help in the process of natural recovery of degraded forests throughout the tropics. Abstract in Portuguese is available with online material.     

Dispersal limits natural recruitment of African mahoganies

The abundance of forest tree species may be locally limited by the inability of species to disperse to all sites suitable for germination and establishment. This phenomenon of "dispersal limitation" has been suggested to promote the maintenance of high species diversity in tropical forests by slowing down competitive exclusion. We present the first direct experimental evaluation of dispersal limitation in tropical forests, and of its importance relative to other factors affecting recruitment. Seed addition, litter removal and light availability effects on seedling establishment were evaluated in a full factorial experiment on two African mahogany species, Entandrophragma utile and Khaya anthotheca . Seedling recruitment after 18 months, was ∼22 times greater in seed addition treatments (with addition rates corresponding to the tail of seed shadows of large reproductive trees) compared to controls. This seed addition effect was an order of magnitude greater than either gap or litter removal effects, with similar results observed in both logged and primary forest locations. We conclude that dispersal limitation strongly limits seedling establishment for the two species studied. An important "applied corollary" of this result is that seed supplementation may substantially increase local abundance of valuable or rare species in disturbed or managed tropical forests.     

Edge disturbance drives liana abundance increase and alteration of liana–host tree interactions in tropical forest fragments

Closed‐canopy forests are being rapidly fragmented across much of the tropical world. Determining the impacts of fragmentation on ecological processes enables better forest management and improves species‐conservation outcomes. Lianas are an integral part of tropical forests but can have detrimental and potentially complex interactions with their host trees. These effects can include reduced tree growth and fecundity, elevated tree mortality, alterations in tree‐species composition, degradation of forest succession, and a substantial decline in forest carbon storage. We examined the individual impacts of fragmentation and edge effects (0–100‐m transect from edge to forest interior) on the liana community and liana–host tree interactions in rainforests of the Atherton Tableland in north Queensland, Australia. We compared the liana and tree community, the traits of liana‐infested trees, and determinants of the rates of tree infestation within five forest fragments (23–58 ha in area) and five nearby intact‐forest sites. Fragmented forests experienced considerable disturbance‐induced degradation at their edges, resulting in a significant increase in liana abundance. This effect penetrated to significantly greater depths in forest fragments than in intact forests. The composition of the liana community in terms of climbing guilds was significantly different between fragmented and intact forests, likely because forest edges had more small‐sized trees favoring particular liana guilds which preferentially use these for climbing trellises. Sites that had higher liana abundances also exhibited higher infestation rates of trees, as did sites with the largest lianas. However, large lianas were associated with low‐disturbance forest sites. Our study shows that edge disturbance of forest fragments significantly altered the abundance and community composition of lianas and their ecological relationships with trees, with liana impacts on trees being elevated in fragments relative to intact forests. Consequently, effective control of lianas in forest fragments requires management practices which directly focus on minimizing forest edge disturbance.     

Effects of site and fruit size on the composition of avian frugivore assemblages in a fragmented Afrotropical forest

Factors influencing the interaction between fruiting trees and their frugivorous seed dispersers in fragmented Afrotropical landscapes are poorly known. With the use of Mantel statistics we analysed assemblages of frugivorous birds on 58 individual trees belonging to 11 species growing in seven Kenyan cloud forest fragments. Overall, frugivores showed little specialization on particular trees. Fruit size explained a substantial amount of the variation in frugivore assemblages among different tree species at the same site. In addition, frugivore assemblages on conspecific trees were significantly more similar when the trees occurred at the same site. This location effect was attributable to the different sites and forest fragments (of different sizes and disturbance levels) varying in the densities and composition of their avian frugivores, vegetation composition and tree fruiting phenologies. It was consolidated further by the low mobility of most of these avian frugivores, particularly their reluctance to cross between forest fragments. Habitat disturbance and fragmentation may therefore have affected fruit selection, with implications for both seed dispersal and regeneration.     

Impact of habitat structure and fruit abundance on avian seed dispersal and fruit predation

So far, it is poorly understood how differential responses of avian seed dispersers and fruit predators to changes in habitat structure and fruit abundance along land-use gradients may translate into consequences for the seed dispersal of associated plants. We selected a gradient of habitat modification (forest, semi-natural, and rural habitat) characterized by decreasing tree cover and a high variation in local fruit availability. Along this gradient we quantified fruit removal by avian seed dispersers and fruit predators from 18 Sorbus aucuparia trees. We analyzed the relative importance of tree cover and fruit abundance in explaining species richness, abundance and fruit removal rates of both guilds from S. aucuparia trees. Species richness and abundance of seed dispersers decreased with decreasing tree cover, whereas fruit removal by seed dispersers decreased with decreasing fruit abundance independent of tree cover. Both variables had no effect on species richness, abundance and fruit removal by fruit predators. Consequently, seed dispersers dominated relative fruit removal in fruit-rich sites but the dispersal/predation ratio shifted in favor of predation in fruit-poor habitat patches. Our study demonstrates that variation in local habitat structure and fruit abundance can cause guild-specific responses. Such responses may result in a shift in fruit removal regimes and might affect the dispersal ability of dependent fruiting plants. Future studies should aim at possible consequences for plant recruitment and guild-specific responses of frugivores to disturbance gradients on the level of entire plant–frugivore associations.     

Reproductive ecology of tropical forest trees in logged and fragmented habitats in Thailand and Costa Rica

Invertebrates mediate several important ecological processes, including pollination and seed predation, and events that affect invertebrate diversity or behaviour can potentially disrupt forest regeneration processes. This study investigates the impact of logging in Thailand and forest fragmentation in Costa Rica on the pollination and seed production of two self-incompatible forest trees. Logging in a dry deciduous dipterocarp forest in Thailand resulted in reduced densities of the common dipterocarp treeShorea siamensis and variably isolated individual trees. The number of flower visits to S. siamensis by pollinating Trigona bees was not affected by logging disturbance. However, pollinators did spend longer periods of time foraging in the canopies of isolated trees which were more prevalent in logged areas where tree density had been reduced. Consequently, at the logged site few cross-pollinations were effected and fruit set of S. siamensis was considerably lower than at nearby unlogged sites where distances between flowering conspecifics were smaller. Reduced fruit set has long-term implications for the recovery of S. siamensis populations in disturbed areas, and local population genetic structure is likely to be affected as reduced outcrossing rates among trees in disturbed regions results in relatively inbred seed. In Costa Rica forest fragmentation has restricted the once widespread tree Anacardium excelsum to forest patches located in an agriculturally-dominated landscape. As with S. siamensis, the abundance of pollinators, also Trigona bees, in the canopies of A. excelsum was largely unaffected by fragment size. Nevertheless, pollination success and seed production was positively correlated with fragment size. We propose that small bees rarely move between forest fragments and gene exchange through pollination occurs predominantly among trees within fragments and, together with likely low genetic variability in small fragments, that this contributes to the observed reduced fertilisation and seed set of A. excelsum. Thus increased tree isolation tree through selective logging or habitat fragmentation by forest clearance can result in reduced seed set due to changes in the foraging patterns of poorly mobile pollinators. Even if population sizes of the pollinators are maintained following environmental perturbation, this study shows that disturbance may disrupt pollination processes through changes in pollinator foraging behaviour. More attention needs to be focussed on changes in the behaviour of species involved in key ecological interactions following disturbance events in tropical forests.     

Loss of animal seed dispersal increases extinction risk in a tropical tree species due to pervasive negative density dependence across life stages

Overhunting in tropical forests reduces populations of vertebrate seed dispersers. If reduced seed dispersal has a negative impact on tree population viability, overhunting could lead to altered forest structure and dynamics, including decreased biodiversity. However, empirical data showing decreased animal-dispersed tree abundance in overhunted forests contradict demographic models which predict minimal sensitivity of tree population growth rate to early life stages. One resolution to this discrepancy is that seed dispersal determines spatial aggregation, which could have demographic consequences for all life stages. We tested the impact of dispersal loss on population viability of a tropical tree species, Miliusa horsfieldii, currently dispersed by an intact community of large mammals in a Thai forest. We evaluated the effect of spatial aggregation for all tree life stages, from seeds to adult trees, and constructed simulation models to compare population viability with and without animal-mediated seed dispersal. In simulated populations, disperser loss increased spatial aggregation by fourfold, leading to increased negative density dependence across the life cycle and a 10-fold increase in the probability of extinction. Given that the majority of tree species in tropical forests are animal-dispersed, overhunting will potentially result in forests that are fundamentally different from those existing now.     

西双版纳片段化石灰岩森林附生兰科植物多样性研究

西双版纳石灰岩地区拥有丰富的兰科植物资源,但近年来随着橡胶树的大面积种植,使得该地区很多石灰岩森林呈片段化。为了解片段化石灰岩森林中附生兰科植物多样性状况以及片段化对附生兰科植物的影响,该研究选取了生境片段化的青岩寨和曼纳览,以及连续生境的绿石林和巴卡新寨等4个样地的29个样方进行多样性调查和对比研究。结果表明:4个石灰岩森林样共记录到附生兰科植物34属76种1 528株(丛)。通过对坡向、坡度、海拔、地形、郁闭度和森林类型等6个环境因子与附生兰科植物丰富度进行CCA分析,发现石灰岩地区附生兰科植物的分布主要受海拔和森林类型2个因素的影响,在海拔较高的青岩寨和巴卡新寨附生兰科植物物种丰富度高于低海拔的绿石林和曼纳览,而片段化对附生兰科植物的物种多样性和多度均无显著影响,这可能与片段化的历史较短有关。虽然目前来看生境片段化对石灰岩地区的附生兰科植物多样性无显著影响,但生境脆弱的石灰岩森林植被的保护对于兰科植物多样性保护则更具重要性。     

Disturbance regime changes the trait distribution,phylogenetic structure and community assembly of tropical rain forests

A rapidly increasing effort to merge functional community ecology and phylogenetic biology has increased our understanding of community assembly. However, studies using both phylogenetic‐ and trait‐based methods have been mainly conducted in old‐growth forests, with fewer studies in human‐disturbed communities, which play an increasingly important role in providing ecosystem services as primary forests are degraded. We used data from 18 1‐ha plots in tropical old‐growth forests and secondary forests with different disturbance histories (logging and shifting cultivation) and vegetation types (tropical lowland and montane forests) on Hainan Island, southern China. The distributions of 11 functional traits were compared among these six forest types. We used a null model approach to assess the effects of disturbance regimes on variation in response and effect traits and community phylogenetic structure across different stem sizes (saplings, treelets, and adult trees) and spatial scales (10–50 m). We found significant differences in the distribution of functional traits in highly disturbed lowland sites versus other forest types. Many individuals in highly disturbed lowland sites were deciduous, spiny, with non‐fleshy fruits and seeds dispersed passively or by wind, and low SLA. The response traits of coexisting species were clustered in all sites except for highly disturbed lowland sites where evenness was evident. There were different distributions of effect traits for saplings and treelets among different forest types but adult trees showed stronger clustering of trait values with increasing spatial scale among all forest types. Phylogenetic clustering predominated across all size classes and spatial scales in the highly disturbed lowland sites, and evenness in other forest types. High disturbance can lead to abiotic filtering, generating a community dominated by closely related species with disturbance‐adapted traits, where biotic interactions play a relatively minor role. In lightly disturbed and old growth forests, multiple processes simultaneously drive the community assembly, but biotic processes dominate at the fine scale.     

Forest disturbance and seasonal food availability influence a conditional seed dispersal mutualism

The interaction between granivorous scatterhoarding mammals and plants is a conditional mutualism: scatterhoarders consume seeds (acting as predators), but the movement of seed by scatterhoarders may contribute to dispersal (acting as mutualists). Understanding the ecological factors that shape this relationship is highly relevant in anthropogenically disturbed tropical forests where large‐bodied frugivores are extirpated. In such forests, large‐seeded trees that once depended on these frugivores for dispersal may now only have scatterhoarders as prospective dispersers. We studied Carapa oreophila (Meliaceae) in an Afromontane forest, to test the hypotheses that the proportion of seeds immediately consumed or hoarded (dispersed) would vary over a disturbance gradient. Temporal replication also afforded exploration of how habitat effects might vary with food availability. Using a Bayesian framework, we demonstrate that seeds were more likely to be hoarded in less disturbed forest, irrespective of temporal variation in food abundance. In contrast, forest disturbance only appeared to increase seed predation in temporal replicates that coincided with sustained food availability. These results highlight the potential variability in the dynamics between plants and scatterhoarders over fine temporal scales, elucidating possible ecological scenarios where scatterhoarders might act as mutualists (contributing positively to plant recruitment). Our study also fills important knowledge gaps about the importance of scatterhoarders as dispersers in tropical forests depleted of large‐bodied frugivores, particularly in Africa where scatterhoarding mutualisms have not been extensively studied.     

Forest cover,hunting pressure,and fruit availability influence seed dispersal in a forest‐savanna mosaic in the Congo Basin

Forest fragmentation, reduced forest cover, and hunting pressure are the main threats affecting animal‐mediated seed dispersal. However, their combined effects on seed dispersal rates have been simultaneously investigated only rarely, and never in Africa. We aimed to disentangle the effects of forest cover, hunting pressure, frugivore abundance, and fruit availability at the local and landscape scales on the seed dispersal rates of Staudtia kamerunensis (Myristicaceae). To estimate the percentages of seed dispersal failure (undispersed seeds), we quantitated fruit remains below fruiting trees distributed across five contrasting sites in a semi‐natural forest‐savanna mosaic in the Democratic Republic of Congo. We used statistical analyses accounting for spatial autocorrelation and found that forest cover in the surrounding landscape, hunting level, the associated abundance of dispersers, and fruit availability all had significant effects on the percentage of seed dispersal failure. The combination of high fruit availability and reduced abundance of seed dispersers could accelerate seed disperser satiation, causing the seed dispersal system to be saturated. Our study highlights how two major factors associated with anthropogenic activities, forest cover and hunting, affect seed dispersal by animals. These findings could have far‐reaching implications for our understanding of tree‐frugivore interactions and the conservation of tropical communities.     

Sleeping Sites and Latrines of Spider Monkeys in Continuous and Fragmented Rainforests: Implications for Seed Dispersal and Forest Regeneration

Spider monkeys (Ateles geoffroyi) use sites composed of one or more trees for sleeping (sleeping sites and sleeping trees, respectively). Beneath these sites/trees they deposit copious amounts of dung in latrines. This behavior results in a clumped deposition pattern of seeds and nutrients that directly impacts the regeneration of tropical forests. Therefore, information on the density and spatial distribution of sleeping sites and latrines, and the characteristics (i.e., composition and structure) of sleeping trees are needed to improve our understanding of the ecological significance of spider monkeys in influencing forest composition. Moreover, since primate populations are increasingly forced to inhabit fragmented landscapes, it is important to assess if these characteristics differ between continuous and fragmented forests. We assessed this novel information from eight independent spider monkey communities in the Lacandona rainforest, Mexico: four continuous forest sites and four forest fragments. Both the density of sleeping sites and latrines did not differ between forest conditions. Latrines were uniformly distributed across sleeping sites, but the spatial distribution of sleeping sites within the areas was highly variable, being particularly clumped in forest fragments. In fact, the average inter-latrine distances were almost double in continuous forest than in fragments. Latrines were located beneath only a few tree species, and these trees were larger in diameter in continuous than fragmented forests. Because latrines may represent hotspots of seedling recruitment, our results have important ecological and conservation implications. The variation in the spatial distribution of sleeping sites across the forest indicates that spider monkeys likely create a complex seed deposition pattern in space and time. However, the use of a very few tree species for sleeping could contribute to the establishment of specific vegetation associations typical of the southeastern Mexican rainforest, such as Terminalia-Dialium, and Brosimum-Dialium.     

Frugivory and Seed Fate in Bursera inversa (Burseraceae) at Tinigua Park,Colombia: Implications for Primate Conservation1

The large ateline primates are efficient seed dispersers in Neotropical forests and hunting is driving their populations to extinction, but we do not know whether other frugivores could substitute primates in their ecological role as seed dispersers. In this study we test this possibility using a potential keystone species (Bursera inversa) at Tinigua Park, Colombia. This plant species allows us to compare seed removal rates between emergent, isolated trees, without primate visitors and trees with connected crowns. We used traps to estimate fruit production and seed removal rates in six different trees, and fruiting trees were observed during 2 yr to quantify the number of seeds manipulated by different animal species. We carried out seed predation experiments to test if seed removal by predators was affected by distance or density effects. We found that the most productive trees attracted more visiting species and seed removal rates differed among trees, the lowest corresponding to trees without primate access. Seed removal rates from the ground by predators were not higher below parental trees than away from them, but the distribution of saplings in the forest suggests that seed dispersal is advantageous. Although it is likely that the effect of primate extinctions will vary depending on tree species traits, conserving the populations of primate seed dispersers is critical to maintain the ecological processes in this forest.