Effectiveness of Mistletoe Seed Dispersal by Tyrant Flycatchers in a Mixed Andean Landscape

The dependence of mistletoes on few dispersers and the directed dispersal they provide is well known, yet no recent work has quantified either the effectiveness of these ‘legitimate’ dispersers, or the extent of redundancy among them. Here, I use the seed dispersal effectiveness (SDE) framework to analyze how birds (Mionectes striaticollis and Zimmerius bolivianus) contribute to mistletoe (Struthanthus acuminatus and Phthirusa retroflexa) infection in traditional mixed plantations within a humid montane forest in Bolivia. I calculated SDE for each bird–mistletoe pair and for the disperser assemblage, by estimating both the quantity and the quality of dispersal. The quantity of dispersal was measured as: (1) disperser abundance; (2) frequency of visits; and (3) number of seeds dispersed per visit, and the quality of dispersal was measured as: (1) germination percentage and speed of germination of seeds regurgitated by birds; and (2) the concordance of deposited seeds and seedling distribution patterns with adult mistletoe distribution at three scales (habitat, host, and microhabitat). Dispersers were not redundant: the more generalist species M. striaticollis dispersed more seeds, but provided lower quality seed dispersal, whereas the mistletoe specialist Z. bolivianus provided low‐quantity and high‐quality seed dispersal. Whereas S. acuminatus benefited more from the SDE of Z. bolivianus, P. retroflexa benefited from the complementary seed dispersal provided by both birds. These results demonstrate how sympatric mistletoes that share the same disperser assemblage may develop different relationships with specific vectors, and describe how the services provided by two different dispersers (one that provides high‐quality and one that provides high‐quantity dispersal) interact to shape spatial patterns of plants.     

The Role of Arboreal Seed Dispersal Groups on the Seed Rain of a Lowland Tropical Forest1

Most tropical plants produce fleshy fruits that are dispersed primarily by vertebrate frugivores. Behavioral disparities among vertebrate seed dispersers could influence patterns of seed distribution and thus forest structure. This study investigated the relative importance of arboreal seed dispersers and seed predators on the initial stage of forest organization–seed deposition. We asked the following questions: (1) To what degree do arboreal seed dispersers influence the species richness and abundance of the seed rain? and (2) Based on the plant species and strata of the forest for which they provide dispersal services, do arboreal seed dispersers represent similar or distinct functional groups? To answer these questions, seed rain was sampled for 12 months in the Dja Reserve, Cameroon. Seed traps representing five percent of the crown area were erected below the canopies of 90 trees belonging to nine focal tree species: 3 dispersed by monkeys, 3 dispersed by large frugivorous birds, and 3 wind‐dispersed species. Seeds disseminated by arboreal seed dispersers accounted for ca 12 percent of the seeds and 68 percent of the seed species identified in seed traps. Monkeys dispersed more than twice the number of seed species than large frugivorous birds, but birds dispersed more individual seeds. We identified two distinct functional dispersal groups, one composed of large frugivorous birds and one composed of monkeys, drop dispersers, and seed predators. These groups dispersed plants found in different canopy strata and exhibited low overlap in the seed species they disseminated. We conclude it is unlikely that seed dispersal services provided by monkeys could be compensated for by frugivorous birds in the event of their extirpation from Afrotropical forests.     

The Spatial Distribution of Mistletoe in a Southern Indian Tropical Forest at Multiple Scales

Taxillus tomentosus is a mistletoe of significant management concern in southern India. This mistletoe affects the productivity of several nontimber forest products, most significantly Amla (Phyllanthus emblica and Phyllanthus indofischeri), whose fruits provide an important source of income for indigenous forest communities. Management interventions are required to secure the continued viability of Amla and thereby its role in livelihoods. To enhance the scientific basis for management, we characterized the distribution of T. tomentosus at three scales, examined potential mechanisms underlying this distribution, and compared both with those documented in other habitats. Mistletoes were aggregated at all three scales: on individual trees, within forest plots of 500 m², and at scales of 3–4 km. Seed deposition patterns provide an initial distribution ‘template’ that largely determines patterns at tree and plot scales. This initial pattern is subsequently altered as variation in host suitability and mistletoe mortality from forest fires influence establishment success and postestablishment survival. Local prevalence of infection contributed most to infection spread, and areas of high infection prevalence are highlighted as appropriate foci for management intervention. Although novel underlying mechanisms and variation in the scale of aggregation have been identified, mistletoe distribution in a tropical forest appears to be shaped by similar forces as those documented previously in temperate systems.     

Frugivory and Seed Dispersal by Four Species of Primates in Madagascar's Eastern Rain Forest1

In the unique faunal assemblage of the Malagasy rain forest, lemurs appear to play particularly important roles as seed-dispersing frugivores. A three-month study of feeding ecology and seed dispersal by four species of lemurs in Madagascar's eastern rain forest found that three species, Eulemur rubriventer, Eulemur fulvus, and Varecia variegata were seed dispersers, and the fourth, Propithecus diadema, was a seed predator. In germination trials, seeds passed by lemurs sprouted significantly faster and in greater numbers than those not passed by lemurs. Analysis of fruit morphologies of 69 local plant taxa producing fleshy fruits during the study period found that these fruits fell into two well-defined color categories that correlated significantly with fruit size. Seventy seven percent of fleshy fruits greater than 10 mm in diameter were colored green, brown, tan, purplish, or black, while all fruits less than 10 mm in diameter were colored red, yellow, orange, pink, blue, or white. Three introduced exotic plant species provided exceptions to this pattern, producing fruits which were larger than 10 mm and pink or orange. Fruits chosen by the primates in this study were usually larger than 10 mm in diameter and were in nearly all cases colored green, brown, tan, purplish, red, or some combination of these colors. Morphological traits shared by fruits of multiple plant taxa in the diets of seed-dispersing lemurs suggest possible coevolved relationships between Malagasy rain forest plants and lemurs.     

Seed Dispersal by Monkeys and the Fate of Dispersed Seeds in a Peruvian Rain Forest1

Primary seed dispersal by two species of monkeys and the effects of rodents and dung beetles on the fate of dispersed seeds are described for a rain forest in southeastern Perú. During the six-month study period (June–November 1992) spider monkeys (Ateles paniscus) dispersed the seeds of 71 plant species, whereas howler monkeys (Alouatta seniculus) dispersed seeds of 14 species. Spider and howler monkeys also differed greatly in their ranging behavior and defecation patterns, and as a consequence, produced different seed rain patterns. Monkey defecations were visited by 27 species of dung beetles (Scarabaeidae). Dung beetles buried 41 percent of the seeds in the dung, but the number of seeds buried varied greatly, according to seed size. Removal rates of unburied seeds by rodents varied between 63–97 percent after 30 d for 8 plant species. The presence of fecal material increased the percentage of seeds removed by seed predators, but this effect became insignificant with time. Although seed predators found some seeds buried in dung balls (mimicking burial by dung beetles), depth of burial significantly affected the fate of these seeds. Less than 35 percent of Brosimum lactescens seeds buried inside dung balls at a depth of 1 cm remained undiscovered by rodents, whereas at least 75 percent of the seeds escaped rodent detection at a depth of 3 cm and 96 percent escaped at 5 cm. Both dung beetles and rodents greatly affected the fate of seeds dispersed by monkeys. It is thus important to consider postdispersal factors affecting the fate of seeds when assessing the effectiveness of frugivores as seed dispersers.     

Behavioral and Social Structure Effects on Seed Dispersal Curves of a Forest‐Interior Bulbul (Pycnonotidae) in a Tropical Evergreen Forest

Movement patterns of animals can vary dramatically as a function of their reproductive cycle or social structure; however, little is known about how changes in the social structure of dispersers affect patterns of seed dispersal. We examined the movement patterns of the forest‐dwelling and cooperatively breeding Puff‐throated Bulbul (Alophoixus pallidus) in relation to different stages of their reproductive cycle, time of day, and group size, to determine potential impacts on the shape and scale of dispersal curves generated using a combination of gut passage time and displacement distance data. There were significant differences in dispersal distances depending on group size, season (breeding, non‐breeding), incubation (vs. other times of the year), and time of the day. The estimated median seed dispersal distance was 28 m. The median dispersal distances produced by birds in larger groups were longer than those of smaller groups (29 m vs. 25 m). During the breeding season, median dispersal distances were longer than during the non ‐ breeding season (31 m vs. 25 m), but the median dispersal distances were significantly shorter during incubation than during outside incubation (24 m vs. 28 m). The median dispersal distance produced in the early morning (30 m) was also longer than that of other times of the day (23 m late morning, 28 m early afternoon, and 26 m late afternoon). This study suggests that various aspects of an animal's behavior are likely to have significant effects on seed shadows and that this may vary significantly even among individuals of the same species.     

Spatial and Temporal Patterns of Frugivorous Hornbill Movements in Central Africa and their Implications for Rain Forest Conservation

Tropical forest conservation and restoration require an understanding of the movements and habitat preferences of important seed dispersers. With forests now being altered at an unprecedented rate, avian frugivores are becoming increasingly vital for forest regeneration. Seed movement, however, is highly dependent on the behavioral characteristics of their dispersers. Here, we examined the movements, habitat preferences, and range sizes of two African frugivores: the Black‐casqued (Ceratogymna atrata) and the White‐thighed (Bycanistes albotibialis) Hornbill, in the lowland rain forests of southern Cameroon. Using satellite transmitters, we tracked eight hornbills for 3 yr to characterize their movements and relate them to environmental landscape features. Hornbill movements differed significantly, with B. albotibialis ranging over larger areas (mean = 20,274 ha) than C. atrata (mean = 5604 ha), and females of both species covering over 15 times the area of males. Evidence suggests that movements are irruptive during particular periods, perhaps driven by low resource availability. In addition, hornbills often returned to the same localities within a year, although movements were not characterized as migratory. Both species displayed significant differences in habitat preference, with B. albotibialis utilizing disturbed habitat more frequently than C. atrata (t = ?22.04, P = 2.2 × 10^?16). Major roads were found to act as barriers for C. atrata, but not for B. albotibialis. The ability of both hornbill species to move large distances suggests hornbills will play a vital role in the maintenance and regeneration of rain forests in Central Africa as forest fragmentation increases and terrestrial vertebrates decline in numbers.     

Genetic evidence of frequent long-distance recruitment in a vertebrate-dispersed tree

The importance of dispersal for the maintenance of biodiversity, while long-recognized, has remained unresolved. We used molecular markers to measure effective dispersal in a natural population of the vertebrate-dispersed Neotropical tree, Simarouba amara (Simaroubaceae) by comparing the distances between maternal parents and their offspring and comparing gene movement via seed and pollen in the 50 ha plot of the Barro Colorado Island forest, Central Panama. In all cases (parent-pair, mother-offspring, father-offspring, sib-sib) distances between related pairs were significantly greater than distances to nearest possible neighbours within each category. Long-distance seedling establishment was frequent: 74% of assigned seedlings established > 100 m from the maternal parent [mean = 392 +/- 234.6 m (SD), range = 9.3-1000.5 m] and pollen-mediated gene flow was comparable to that of seed [mean = 345.0 +/- 157.7 m (SD), range 57.6-739.7 m]. For S. amara we found approximately a 10-fold difference between distances estimated by inverse modelling and mean seedling recruitment distances (39 m vs. 392 m). Our findings have important implications for future studies in forest demography and regeneration, with most seedlings establishing at distances far exceeding those demonstrated by negative density-dependent effects.     

Dispersal and population structure of a New World predator, the army ant Eciton burchellii

The army ant Eciton burchellii is probably the most important arthropod predator in the Neotropics, and many animal species depend upon it. Sex-biased dispersal with winged males and permanently wingless queens may render this species especially sensitive to habitat fragmentation and natural barriers, which might have severe impacts on population structure and lead to population decline. Using nuclear microsatellite markers and mitochondrial sequences, we investigated genetic differentiation in a fragmented population in the Panama Canal area. While nuclear markers showed little differentiation between subpopulations (F(ST) = 0.017), mitochondrial differentiation was maximal in some cases (Phi(ST) = 1). This suggests that, while females are not capable of crossing barriers such as large rivers, flying males are able to promote nuclear gene flow between the studied forest patches. Consistent with this interpretation, we did not find any evidence for inbreeding or genetic deterioration on Barro Colorado Island over the last 90 years since its formation.     

The Stability of Invertebrate Communities in Bromeliad Phytotelmata in a Rain Forest Subject to Hurricanes

Communities of invertebrate animals in lower canopy and saxicolous tank bromeliads, originally studied in 1993–1997, were resampled along an elevational gradient in tabonuco, palo colorado, and dwarf or cloud forest in Puerto Rico in 2010. These Puerto Rican montane rain forests were impacted strongly by hurricanes in 1989 and 1998, so the surveys in the 1990s represented 4–8 yr of post‐hurricane recovery, whereas our recent survey represents 12 yr of post‐hurricane recovery. At most elevations, species diversity, both within individual bromeliads and at the forest scale, declined between the 1990s and 2010. This decline in diversity between decades is associated with reductions in bromeliad density as the canopy progressively closed during recovery from hurricane damage. The observed decline in alpha and gamma diversity appears to have involved the loss of rarer species, as might be expected from standard metapopulation theory. By contrast, the most common species were remarkably stable in abundance, composition, and frequency of occurrence over the two decades. In the lowermost tabonuco forest, two endemic bromeliad specialists, restricted to bromeliads for their entire life cycle, were not found on resampling. This study also demonstrates that, at least in Puerto Rico, sets of ten plants from each forest were sufficient to monitor bromeliad invertebrate populations and their diversity over time.     

The Use of Seeds by a Twig-Dwelling Ant on the Floor of a Tropical Rain Forest

The role of Pheidole praeses , a twig-nesting ant inhabiting the floor of the Brazilian Atlantic forest, as potential secondary seed disperser was investigated. A total of 901 seeds (20 morphospecies) were retrieved from 50 nests, most of them intact and able to germinate. Considering the abundance of Pheidole species and the evidence pointing to their potential as seed dispersers, these ants may be important determinants of the recruitment of small-seeded plants in tropical forests.
Abstract in Portugese is available at http://www.blackwell-synergy.com/loi/btp .     

Spatial scale and sampling resolution affect measures of gap disturbance in a lowland tropical forest: implications for understanding forest regeneration and carbon storage

Treefall gaps play an important role in tropical forest dynamics and in determining above-ground biomass (AGB). However, our understanding of gap disturbance regimes is largely based either on surveys of forest plots that are small relative to spatial variation in gap disturbance, or on satellite imagery, which cannot accurately detect small gaps. We used high-resolution light detection and ranging data from a 1500 ha forest in Panama to: (i) determine how gap disturbance parameters are influenced by study area size, and the criteria used to define gaps; and (ii) to evaluate how accurately previous ground-based canopy height sampling can determine the size and location of gaps. We found that plot-scale disturbance parameters frequently differed significantly from those measured at the landscape-level, and that canopy height thresholds used to define gaps strongly influenced the gap-size distribution, an important metric influencing AGB. Furthermore, simulated ground surveys of canopy height frequently misrepresented the true location of gaps, which may affect conclusions about how relatively small canopy gaps affect successional processes and contribute to the maintenance of diversity. Across site comparisons need to consider how gap definition, scale and spatial resolution affect characterizations of gap disturbance, and its inferred importance for carbon storage and community composition.     

Estimating seed dispersal distance: A comparison of methods using animal movement and plant genetic data on two primate‐dispersed Neotropical plant species

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Tropical Montane Forest Restoration in Costa Rica: Overcoming Barriers to Dispersal and Establishment

Tropical forests are being cleared at an alarming rate although our understanding of their ecology is limited. It is therefore essential to design restoration experiments that both further our basic knowledge of tropical ecology and inform management strategies to facilitate recovery of these ecosystems. Here we synthesize the results of research on tropical montane forest recovery in abandoned pasture in Costa Rica to address the following questions: (1) What factors limit tropical forest recovery in abandoned pasture? and (2) How can we use this information to design strategies to facilitate ecosystem recovery? Our results indicate that a number of factors impede tropical forest recovery in abandoned pasture land. The most important barriers are lack of dispersal of forest seeds and seedling competition with pasture grasses. High seed predation, low seed germination, lack of nutrients, high light intensity, and rabbit herbivory also affect recovery. Successful strategies to facilitate recovery in abandoned pastures must simultaneously overcome numerous obstacles. Our research shows that establishment of woody species, either native tree seedlings or early‐successional shrubs, can be successful in facilitating recovery, by enhancing seed dispersal and shading out pasture grasses. On the contrary, bird perching structures alone are not an effective strategy, because they only serve to enhance seed dispersal but do not reduce grass cover. Remnant pasture trees can serve as foci of natural recovery and may enhance growth of planted seedlings. Our results highlight the importance of: (1) understanding the basic biology of an ecosystem to design effective restoration strategies; (2) comparing results across a range of sites to determine which restoration strategies are most generally useful; and (3) considering where best to allocate efforts in large‐scale restoration projects.     

The cost of defeat: Capuchin groups travel further,faster and later after losing conflicts with neighbors

Although competition between social groups is central to hypotheses about the evolution of human social organization, competitive interactions among group‐mates are thought to play a more dominant role in shaping the behavior and ecology of other primate species. However, few studies have directly tested the impact of intergroup conflicts in non‐human primates. What is the cost of defeat? To address this question, the movements of six neighboring white‐faced capuchin (Cebus capucinus) social groups living on Barro Colorado Island, Panama were tracked simultaneously using an Automated Radio Telemetry System (ARTS), for a period of six months. Groups moved 13% (441 m) further on days they lost interactions compared with days they won interactions. To cover these larger distances, they traveled faster, stopped less frequently, and remained active later in the evening. Defeat also caused groups to alter their patterns of space use. Losing groups had straighter travel paths than winning groups, larger net displacements and were more likely to change their sleeping site. These results demonstrate that losing groups pay increased travel costs and suggest that they forage in low‐quality areas. They provide some of the first direct evidence that intergroup conflicts have important energetic consequences for members of competitively unsuccessful primate social groups. A better understanding of how intergroup competition impacts patterns of individual fitness is thus needed to clarify the role that this group‐level process plays in shaping the evolution of human‐ and non‐human primate behavior. Am J Phys Anthropol 152:79–85, 2013. © 2013 Wiley Periodicals, Inc.     

A Multi-Forest Comparison of Dietary Preferences and Seed Dispersal by <Emphasis Type="BoldItalic">Ateles</Emphasis> spp

Investigations of coevolutionary relationships between plants and the animals that disperse their seeds suggest that disperser-plant interactions are likely shaped by diffuse, rather than species-to-species, coevolution. We studied the role of dietary plasticity in shaping the potential for diffuse coevolution by comparing dietary fruit preferences and seed dispersal by 3 species of spider monkeys (Ateles spp.) in 4 moist forests in Colombia, Ecuador, Panama, and Surinam. In all forests, spider monkeys were highly frugivorous and preyed upon seeds of few species. We estimated dietary use of fruiting taxa based on absolute consumption and preference, which accounts for resource availability. Of the 59 genera that comprised the 20 most frequently consumed genera summed in each forest, only 3—Brosimum (Moraceae), Cecropia (Cecropiaceae) and Virola (Myristicaceae)—ranked within the top 20 at every forest. Most genera were within the 20 most frequently consumed at only 1 or 2 forests. Based on preferences, only 4 genera ranked in the 20 most-preferred in all 4 forests: Brosimum, Cecropia, Ficus (Moracae), and Virola. Patterns in fruit consumption and preference at the familial level were similar in that only 2 families—Myristicaceae and Moraceae—were in the 10 most-consumed or most-preferred in all 4 forests. Interforest variation in plant specific composition and abundances and supra-annual fruiting phenologies, combined with dietary flexibility of Ateles spp., may partly explain these patterns. Our results suggest that variation in plant community structure strongly influences dietary preferences, and hence, seed dispersal by spider monkeys. Thus, diffuse coevolution in spider monkey-plant relationships may be limited to few taxa at the generic and familial levels.     

Teasing apart crypsis and aposematism – evidence that disruptive coloration reduces predation on a noxious toad

Both cryptic and aposematic colour patterns can reduce predation risk to prey. These distinct strategies may not be mutually exclusive, because the impact of prey coloration depends on a predator's sensory system and cognition and on the environmental background. Determining whether prey signals are cryptic or aposematic is a prerequisite for understanding the ecological and evolutionary implications of predator–prey interactions. This study investigates whether coloration and pattern in an exceptionally polymorphic toad, Rhinella alata, from Barro Colorado Island, Panama reduces predation via background matching, disruptive coloration, and/or aposematic signaling. When clay model replicas of R. alata were placed on leaf litter, the model's dorsal pattern – but not its colour – affected attack rates by birds. When models were placed on white paper, patterned and un‐patterned replicas had similar attack rates by birds. These results indicate that dorsal patterns in R. alata are functionally cryptic and emphasize the potential effectiveness of disruptive coloration in a vertebrate taxon.     

Spread pathways of the invasive weed Parthenium hysterophorus L.: The potential for water dispersal

Parthenium hysterophorus L. (Asteraceae) utilises multiple mechanisms to facilitate its dispersal. It has been speculated that the cypsela, the propagule of this species, can be dispersed by water under varying environmental conditions. Four experiments were conducted to test this hypothesis, using simulated shaking and immersion to test floating ability and viability of the propagule in water. The influence of the acidity of the immersion medium on cypsela viability was also examined. Our results revealed that the freshly harvested cypselae could float on river water for at least 20 days, although around 80% sank within a week if moderate or severe turbulence was applied. Sinkage was observed to be more rapid in naked seeds (within a day) than in cypsela (within a week). On still water surfaces, germination occurred within a week but extended to 1.5 weeks under turbulent conditions due to sinkage. In river water, initial germination of floating cypselae was greater (70%) under illuminated conditions as compared to dark conditions (20%). The viability of immersed cypselae was found to remain high in distilled water for 45 days, when immersion was in cool conditions (10 or 15°C). However, in moderate (20 and 24°C) or warm (25 and 30°C) conditions, the rate of viability loss increased, and at 34°C, around 50% of the cypselae died after 20 days of immersion. Similar trends for cypselae longevity were observed in studies using river and pond water; viability loss was faster, especially in pond water. In summary, a proportion of cypselae will float in turbulent water and could be carried significant distances in river systems. Immersed cypselae can remain viable for weeks and can germinate on contact with soil. Water bodies or floods are therefore considered as important pathways in parthenium weed dispersal; hence, post‐flood monitoring is strongly recommended to minimise its spread.