Efficiency of facultative frugivory in the nectar-feeding bat Glossophaga commissarisi: the quality of fruits as an alternative food source

The efficiency of food exploitation correlates positively with the extent of dietary specialization. Neotropical nectar-feeding bats (Glossophaginae) have one of the most specialized diets among mammals, as floral nectar constitutes a sugar-rich and highly digestible but protein and fiber depleted food source. However, dietary constraints, such as a temporary scarcity of nectar, or protein demands may sometimes require the uptake of alternative food items. We investigated the influence of a diet switch from nectar to fruit on intestinal morphology, body mass, and energy budget in the nectar-feeding bat Glossophaga commissarisi and quantified feeding efficiency. We hypothesized that these nectar specialists depend on a constant supply of nectar, if they were lacking the ability for morphological and physiological plasticity in response to a fiber-rich diet. Although capable of harvesting infructescences of Piper hispidum, G. commissarisi was less efficient in extracting energy from fruits (48% digestive efficiency of total fruit energy content) than from nectar (c. 99% digestive efficiency). The intestinal morphology and organ masses did not change after bats were switched from nectar to fruits. Captive bats exhibited lower daily energy expenditures and flight activity when feeding on fruits than during nectarivory. Possibly, this may have been a deliberate regulation to balance reduced feeding efficiency, or simply the consequence of extended digestive pauses. The low digestibility of Piper, in combination with slow digestion and the bats’ inability for morphological and physiological plasticity may cause nectar-feeders to reduce their maximum energy expenditure when feeding on fruits. We argue that although fruits may substitute for nectar, they may cause restricted maximum energy assimilation compared with nectar.     

Fruit Choice by Woolly Monkeys in Tinigua National Park,Colombia

I combined morphological fruit data, phenological, and demographic information for 128 plant species, with nutritional information for 78 species, to assess feeding preferences of woolly monkeys (Lagothrix lagothricha lugens) in Tinigua National Park, Colombia. I used multiple and simple regression analyses to predict fruit feeding time and one index of fruit preference from 20 independent variables presumed to affect fruit choice. The results of the independent regressions indicated a trend to spend more time consuming good tasting fruits from abundant plants that produce large quantities of fruits and produce large crops. Among these variables, abundant fruit production and the astringency index are the most important variables explaining feeding times when other variables are statistically controlled in a multiple regression analysis. Furthermore, the preference index showed that woolly monkeys prefer fruits from large trees that produce in periods of fruit scarcity, with high pulp/seed ratios, low lipid contents, and clumped spatial distributions. The results suggest that woolly monkeys are primarily generalized, opportunistic frugivores that avoid some fruits with secondary compounds. Their feeding behavior is determined by many factors, but the predictive power of each one is always low (<15%). No multiple regression model explained >69% of the variation in feeding time. I suggest that a detailed quantification of secondary compounds might increase the predictive power of the models to explain fruit choice by frugivorous primates.     

Seasonal patterns of diet and ranging in two species of tamarin monkeys: Stability versus variability

From June through December, data were collected on the diet and ranging patterns of moustached (Saguinus mystax) and saddle-back (Saguinus fuscicollis) tamarin monkeys in the Amazon Basin of northeastern Peru. During this 7-month period, insects and nonleguminous fruits accounted for 83% of tamarin feeding and foraging time. Despite marked seasonal variation in rainfall and forest productivity, patterns of habitat utilization, day range, dietary diversity, resource exploitation, and activity budget remained relatively stable throughout the year. Moustached and saddle-back tamarins appear to solve problems of food acquisition and exploit patchily distributed feeding sites using a relatively limited set of foraging patterns. In general, these primates concentrate their daily feeding efforts on several trees from a small number of target plant species. These feeding sites are uncommon, produce only a small amount of ripe fruit each day, and are characterized by a high degree of intraspecific fruiting and flowering synchrony. Trees of the same species are frequently visited in succession, and individual feeding sites are revisited several times over the course of 1–2 weeks. This type of foraging pattern occurred during both dry and wet seasons and when exploiting fruit, nectar, legume, and exudate resources. Seasonal variation in the percentage of feeding and foraging time devoted to insectivory was also limited. In this investigation, there was no consistent evidence that temporal changes in overall forest fruit production had a major impact on the feeding, foraging, or ranging behavior of either tamarin species.     

Diet and Feeding Behavior of <Emphasis Type="Italic">Leontopithecus chrysomelas</Emphasis> (Callitrichidae) in Degraded Areas of the Atlantic Forest of South-Bahia,Brazil

Habitat disturbance alters plant diversity and food resource availability, affecting the ecology, and ultimately the survival and reproduction, of species depending on those plants. Studies in degraded areas serve to improve our understanding of the consequences of habitat modification for endangered species and to guide conservation actions. We studied diet composition, monthly variation in feeding behavior and fruit feeding time, and dietary diversity in two golden-headed lion tamarin (Leontopithecus chrysomelas) groups ranging in a degraded area of the Atlantic Forest in South-Bahia, Brazil, over a 12-mo period. We recorded feeding behavior and food items consumed through continuous observations and focal animal sampling, and performed dietary analyses on samples from consumed fruits. Substrate manipulation to search for animal prey was the feeding activity most frequently observed, followed by fruit consumption. We observed nectar drinking and exudate feeding at low frequencies from April through July. Bromeliads were the principal foraging substrate. We observed the use of 114 plant species, confirming the large dietary diversity reported for the species. Individual trees from the family Melastomataceae, common in degraded forests, accounted for the highest visiting frequencies (40%). Fruit availability was the main factor explaining variation in monthly fruit feeding time, despite the absence of climatic seasonality. Nutritional or energetic characteristics did not affect fruit choice. Differences in floristic composition appear to be a major determinant of the species’ diet in different study areas. Regional forest restoration programs should consider including advanced forest species, to improve both forest quality and animal mobility between fragments.     

Fruit size, crop mass, and plant height explain differential fruit choice of primates and birds

Seed dispersal by animals is an important ecological process shaping plant regeneration. In general, seed dispersers are highly variable and often opportunistic in their fruit choice. Despite much research, the factors that can explain patterns of fruit consumption among different animal groups remain contentious. Here, we analysed the interactions between 81 animal species feeding on the fruits of 30 plant species in Kakamega Forest, Kenya, during 840 h of observations. Our aim was to determine whether plant characteristics, fruit morphology, fruit colours and/or fruit compounds such as water, sugar, phenols and tannins explained the relative importance of fruit consumption by the two most important consumer groups, primates and birds. We found significant differences in fruit choice between both groups. Primates fed on larger fruits and on higher trees that had larger fruit crops, whereas birds were observed feeding on smaller fruits and on smaller plants producing fewer fruits. Fruit colours did not differ between fruits consumed by primates and those consumed by birds. However, differences in the fruit choice among frugivorous birds were associated with differences in fruit colours. Smaller plants with smaller fruits produced red fruits which contrasted strongly with the background; these fruits were dispersed by a distinct set of bird species. The contents of water, sugar, phenols and tannins did not differ between fruits eaten by primates and those eaten by birds. Some phylogenetic patterns were apparent; primates fed preferentially on a phylogenetically restricted subsample of large plants with large fruits of the subclass Rosidae. We discuss why the observed primate dispersal syndrome is most likely explained by a process of ecological fitting.     

Morphological-dietary relationships within two assemblages of marine demersal fishes

In this study we have used morphological characters related to feeding and prey capture and dietary data to investigate the trophic organization within two assemblages of marine demersal fishes. Morphological and dietary disparities within fish assemblages were estimated from species similarities based on Euclidean distances plus species projections on the principal axes from multivariate analyses. The analyses of the morphological variables indicated that species in each assemblage comprised morphologically distinct groups strongly influenced by trophically linked characters. Stomach content analyses revealed that fish species in each assemblage were classified into three basic feeding groups: polychaete-shrimp feeders, crab feeders and fish feeders. These results indicated that food resource partitioning was operating within each assemblage. However, when morphological and trophic data were compared no significant correlations were found. The results did not particularly support the ecomorphological hypothesis that dietary differences are due to morphological differences, since similar diets do not correspond to similar morphologies. The patterns of trophic organization within the fish assemblages examined, possibly reflect differences among species due not only to the effect of ecological demands on morphology but also by their evolutionary history and constructional constraints imposed by phylogeny. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dietary Differences Among Sympatric Callitrichinae in Northern Bolivia: Callimico goeldii,Saguinus fuscicollis and S. labiatus

Studies of sympatric species can provide important data to define how dietary and habitat requirements differ among them. I collected dietary data during a first yearlong comparative study of wild groups of Callimico goeldii, Saguinus labiatus and S. fuscicollis. Dietary overlap was highest between Saguinus fuscicollis and Saguinus labiatus throughout the year, and lowest between Saguinus labiatus and Callimico goeldii. All three species had high dietary overlap in February and March when a few abundant fruit species dominated their diets. Although all three species rely heavily on many of the same fruits and arthropods, there are several important distinctions among their diets. Surprisingly, Callimico goeldii consume large quantities of fungus throughout the year: 29% of annual feeding records. Mycophagy is more frequent in the dry season when fruits are scarce. In contrast, Saguinus labiatus rarely eat fungus during the period of fruit scarcity, and instead rely on nectar, a resource never exploited by Callimico goeldii. Saguinus fuscicollis also rely on nectar during periods of low fruit availability and increase their intake of arthropods and exudates. During April, a period of fruit scarcity, exudates comprise >50% of the feeding records of Saguinus fuscicollis. The use of different food resources during fruit scarcity, and differences in the heights at which each species feeds and forages appear to define a distinct ecological niche for each of them and allow them to maintain long-term associations throughout the year. Furthermore, I hypothesize that the limited distribution of Callimico goeldii may result from their restriction to forests that have high disturbance rates, where microhabitats appropriate for fungal growth are abundant, but which also contain abundant fruit and insects.     

Comparative functional analysis of skull morphology of tree-gouging primates

Many primates habitually feed on tree exudates such as gums and saps. Among these exudate feeders, Cebuella pygmaea, Callithrix spp., Phaner furcifer, and most likely Euoticus elegantulus elicit exudate flow by biting into trees with their anterior dentition. We define this behavior as gouging. Beyond the recent publication by Dumont ([1997] Am J Phys Anthropol 102:187-202), there have been few attempts to address whether any aspect of skull form in gouging primates relates to this specialized feeding behavior. However, many researchers have proposed that tree gouging results in larger bite force, larger internal skull loads, and larger jaw gapes in comparison to other chewing and biting behaviors. If true, then we might expect primate gougers to exhibit skull modifications that provide increased abilities to produce bite forces at the incisors, withstand loads in the skull, and/or generate large gapes for gouging.We develop 13 morphological predictions based on the expectation that gouging involves relatively large jaw forces and/or jaw gapes. We compare skull shapes for P. furcifer to five cheirogaleid taxa, E. elegantulus to six galagid species, and C. jacchus to two tamarin species, so as to assess whether gouging primates exhibit these predicted morphological shapes. Our results show little morphological evidence for increased force-production or load-resistance abilities in the skulls of these gouging primates. Conversely, these gougers tend to have skull shapes that are advantageous for creating large gapes. For example, all three gouging species have significantly lower condylar heights relative to the toothrow at a given mandibular length in comparison with closely related, nongouging taxa. Lowering the height of the condyle relative to the mandibular toothrow should reduce the stretching of the masseters and medial pterygoids during jaw opening, as well as position the mandibular incisors more anteriorly at wide jaw gapes. In other words, the lower incisors will follow a more vertical trajectory during both jaw opening and closing.We predict, based on these findings, that tree-gouging primates do not generate unusually large forces, but that they do use relatively large gapes during gouging. Of course, in vivo data on jaw forces and jaw gapes are required to reliably assess skull functions during gouging.     

Paleoenvironment of Dryopithecus brancoi at Rudabánya, Hungary: evidence from dental meso- and micro-wear analyses of large vegetarian mammals

The environment of the hominoid Dryopithecus brancoi at Rudabánya (Late Miocene of Hungary) is reconstructed here using the dietary traits of fossil ruminants and equids. Two independent approaches, dental micro- and meso-wear analyses, are applied to a sample of 73 specimens representing three ruminants: Miotragocerus sp. (Bovidae), Lucentia aff. pierensis (Cervidae), Micromeryx flourensianus (Moschidae), and one equid, Hippotherium intrans (Equidae). The combination of meso- and micro-wear signatures provides both long- and short-term dietary signals, and through comparisons with extant species, the feeding styles of the fossil species are reconstructed. Both approaches categorize the cervid as an intermediate feeder engaged in both browsing and grazing. The bovid Miotragocerus sp. is depicted as a traditional browser. Although the dental meso-wear pattern of the moschid has affinities with intermediate feeders, its dental micro-wear pattern also indicates significant intake of fruits and seeds. Hippotherium intrans was not a grazer and its dental micro-wear pattern significantly differs from that of living browsers, which may suggest that the fossil equid was engaged both in grazing and browsing. However, the lack of extant equids which are pure browsers prevents any definitive judgment on the feeding habits of Hippotherium. Based on these dietary findings, the Rudabánya paleoenvironment is reconstructed as a dense forest. The presence of two intermediate feeders indicates some clearings within this forest; however the absence of grazers suggests that these clearings were most likely confined. To demonstrate the ecological diversity among the late Miocene hominoids in Europe, the diet and habitat of Dryopithecus brancoi and Ouranopithecus macedoniensis (Greece) are compared.     

PHYLOGENETIC,ECOLOGICAL, AND ALLOMETRIC CORRELATES OF CRANIAL SHAPE IN MALAGASY LEMURIFORMS

Adaptive radiations provide important insights into many aspects of evolution, including the relationship between ecology and morphological diversification as well as between ecology and speciation. Many such radiations include divergence along a dietary axis, although other ecological variables may also drive diversification, including differences in diel activity patterns. This study examines the role of two key ecological variables, diet and activity patterns, in shaping the radiation of a diverse clade of primates, the Malagasy lemurs. When phylogeny was ignored, activity pattern and several dietary variables predicted a significant proportion of cranial shape variation. However, when phylogeny was taken into account, only typical diet accounted for a significant proportion of shape variation. One possible explanation for this discrepancy is that this radiation was characterized by a relatively small number of dietary shifts (and possibly changes in body size) that occurred in conjunction with the divergence of major clades. This pattern may be difficult to detect with the phylogenetic comparative methods used here, but may characterize not just lemurs but other mammals.     

23种伞形科植物果实形态及其分类学意义

该实验采用徒手切片法对伞形科17属23种植物的果实进行了外部形态和解剖特征的观察,结果表明:伞形科果实有背腹压扁、两侧压扁和不压扁3种类型;侧棱有宽、有窄;油管的分布有棱槽单油管型和棱槽多油管型;花柱基多数为圆锥状,少数种的花柱基为扁平垫状;萼齿明显或不明显。通过进一步对属间和属内果实解剖特征的比较得出:(1)果实表面被钩刺或刚毛及果棱特征在属间差异明显,在属内表现出一致性,可作为伞形科属间分类的依据。(2)果实横切面的形状、胚乳腹面的凹凸以及萼齿的形态特征在属内种间的分类研究中有重要的意义。基于果实形态特征,编制了17属23种植物的分种检索表。     

Diets of Two Lemur Species in Different Microhabitats in Beza Mahafaly Special Reserve,Madagascar

Studies of primate diets usually focus on differences that distinguish species or populations. However, variation in diet can occur at a more local level of groups within a population, especially in a non-homogeneous habitat. I compared dietary variation in food composition and toughness across groups of 2 lemur species in Beza Mahafaly special reserve, Madagascar. Beza Mahafaly contains an 80-ha reserve (Parcel 1) that, while small, hosts a dense population of Lemur catta (ring-tailed lemurs) and Propithecus verreauxi verreauxi (sifakas). Microhabitats in the eastern vs. western sides of the parcel are structurally and floristically distinct. Sifakas in this parcel have small, discrete home ranges and are morphological folivores. For these reasons, I expected that the 6 groups studied would eat a different menu of food plants but with similar toughness values. Ring-tailed lemurs have comparatively large, overlapping home ranges, and I expected that the 5 study groups would eat similar foods. Despite living in different microhabitats across the parcel, sifakas exhibit high dietary uniformity both in dietary plant species composition and the toughness of the foods. Food selection in sifakas operates on two distinct levels. Sifaka groups share many key food species that appear independent of local abundances, but the ranking of the foods within each group appears related to availability. Ring-tailed lemur groups are more heterogeneous in the composition of their diets relative to sifakas, though the time spent feeding on individual foods reveals a marked preference for the fruits of Tamarindus indica by all groups. Food toughness is consistent across the parcel with the exception of the most western group. Ring-tailed lemurs are highly specific feeders, but indiscriminate nibblers. Sifakas are targeted, balanced feeders. There does not appear to be a consistent microhabitat effect operating across species. Differences within sifaka and ring-tailed lemur populations in food composition and toughness, however, correspond to an east-west microhabitat gradient. Measures of dietary flexibility must take into account not only the plant species consumed and the different parts eaten but also their associated food properties and proportion of time spent feeding on them.     

The relationship between cranial morphology,bite performance,diet and habitat in a radiation of dwarf chameleon (Bradypodion)

Many animals show unique morphological and behavioural adaptations to specific habitats. In particular, variation in cranial morphology is known to influence feeding performance, which in turn influences dietary habits and, ultimately, fitness. Dietary separation is an important means of partitioning ecological niches and avoiding inter‐ and intraspecific competition. Consequently, differences in dietary resources may help explain phenotypic divergence in closely‐related species occupying different habitats, as well as sexual dimorphism. We test this hypothesis on five phenotypic forms of a recent radiation of dwarf chameleons (Bradypodion) that vary extensively in habitat use and cranial morphology. By examining stomach contents, the dietary composition of each phenotypic form is compared to investigate potential differences in feeding strategies. Overall, chameleons in the present study exhibit considerable dietary overlap (at both inter‐ and intraspecific levels), indicating that diet is not a major driver of variation in cranial morphology within this radiation. However, the stomachs of closed‐canopy females were found to contain more prey items than male stomachs, possibly indicating that females require a greater caloric intake than their male counterparts.     

Social implications of gummivory in marmosets

Gummivory or exudate feeding is a major dietary specialization which has received relatively little attention in the literature. While plant exudates contribute to the diet of many primate species, we suggest that the callitrichid species Cebuella pygmaea and Callithrix jacchus are obligate exudate feeders under free-ranging conditions. Callithrix jacchus provides an excellent model for examining the effects of exudate feeding and foraging upon social behavior, since other callitrichid species of similar body size do not share this dietary specialization. We review the effects of exudate foraging on specific social behaviors observed both in field and laboratory populations of C. jacchus. By comparing this species to closely related species, exudate foraging is seen to (1) be retained under laboratory conditions, (2) increase the frequency of territorial marking behavior while decreasing the frequency of overt aggression in males, (3) decrease the duration of infant care, and (4) increase the number of nonadults in social groups but not affect group size. The evidence presented supports the hypothesis that the consequences of exudate foraging in C. jacchus are fundamental and socially complex. © 1994 Wiley-Liss, Inc.     

Comparing ungulate dietary proxies using discriminant function analysis

A variety of tooth‐wear and morphological dietary proxies have been proposed for ungulates. In turn, they have been applied to fossil specimens with the purpose of reconstructing the diets of extinct taxa. Although these dietary proxies have been used in isolation and in combination, a consistent set of statistical analyses has never been applied to all of the available datasets. The purpose of this study is to determine how well the most commonly used dietary proxies classify ungulates as browsers, grazers, and mixed feeders individually and in combination. Discriminant function analysis is applied to individual dietary proxies (hypsodonty, mesowear, microwear, and several cranial dietary proxies) and to combinations thereof to compare rates of successful dietary classification. In general, the tooth‐wear dietary proxies (mesowear and microwear) perform better than morphological dietary proxies, though none are strong proxies in isolation. The success rates of the cranial dietary proxies are not increased substantially when ruminants and bovids are analyzed separately, and significance among the three dietary guilds is reduced when controlling for phylogenetic relatedness. The combination of hypsodonty, mesowear, and microwear is found to have a high rate of successful dietary classification, but a combination of all commonly used proxies increases the success rate to 100%. In most cases, mixed feeders bear the greatest resemblance to browsers suggesting that a morphology intermediate to browsers and grazers may represent a fitness valley resulting from the inability to exploit both browse and graze efficiently. These results are important for future paleoecological studies and should be used as a guide for determining which dietary proxies are appropriate to the research question. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Diet of chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda, 2. Temporal variation and fallback foods

Highly frugivorous primates like chimpanzees (Pan trogolodytes) must contend with temporal variation in food abundance and quality by tracking fruit crops and relying more on alternative foods, some of them fallbacks, when fruit is scarce. We used behavioral data from 122 months between 1995 and 2009 plus 12 years of phenology records to investigate temporal dietary variation and use of fallback foods by chimpanzees at Ngogo, Kibale National Park, Uganda. Fruit, including figs, comprised most of the diet. Fruit and fig availability varied seasonally, but the exact timing of fruit production and the amount of fruit produced varied extensively from year to year, both overall and within and among species. Feeding time devoted to all major fruit and fig species was positively associated with availability, reinforcing the argument that chimpanzees are ripe fruit specialists. Feeding time devoted to figs-particularly Ficus mucuso (the top food)--varied inversely with the abundance of nonfig fruits and with foraging effort devoted to such fruit. However, figs contributed much of the diet for most of the year and are best seen as staples available most of the time and eaten in proportion to availability. Leaves also contributed much of the diet and served as fallbacks when nonfig fruits were scarce. In contrast to the nearby Kanywara study site in Kibale, pith and stems contributed little of the diet and were not fallbacks. Fruit seasons (periods of at least 2 months when nonfig fruits account for at least 40% of feeding time; Gilby & Wrangham., Behavioral Ecology and Sociobiology 61:1771-1779, 2007) were more common at Ngogo than Kanyawara, consistent with an earlier report that fruit availability varies less at Ngogo [Chapman et al., African Journal of Ecology 35:287-302, 1997]. F. mucuso is absent at Kanyawara; its high density at Ngogo, combined with lower variation in fruit availability, probably helps to explain why chimpanzee population density is much higher at Ngogo.     

Influence of Fruit Availability on Fruit Consumption in a Generalist Primate,the Rhesus Macaque <Emphasis Type="Italic">Macaca mulatta</Emphasis>

Fluctuations in resource availability occur in all ecosystems. To survive, species must alter their foraging strategies according to the quantity, quality, and distribution of available food. The rhesus macaque (Macaca mulatta), a commensal primate, is considered a generalist omnivore and very few studies have addressed how its feeding strategies change with respect to resource availability. We examined dietary diversity and frugivory levels in a group of rhesus macaques at the Buxa Tiger Reserve in northern India across one year. Using behavioural observations of diet and phenological monitoring, we found that although rhesus macaques fed on 107 food items including leaves, flowers, fruits, seeds, and insects, fruits made up ca. 74% of their diet. Fruit consumption correlated positively with fruit availability, but fruit preference appeared to play an important role; 16% of all the fruit species they fed on accounted for >50% of all fruit feeding observations. We suggest that afforestation programs involving preferred fruit species at the agricultural land–forest interface would prevent forest groups of rhesus macaques from gravitating toward human habitations and reduce conflict over anthropogenic resources. We further propose that the movement of certain primates in the direction of human habitations may be contingent on resource availability and food preference rather than an inherent propensity to gravitate to anthropogenic areas.     

Sugar Composition of Nectars and Fruits Consumed by Birds and Bats in the Tropics and Subtropics1

Several characteristics of flowers and fruits have been suggested as comprising syndromes of characters that indicate particular classes of pollinators and fruit dispersers. Common phylogenetic history among species, however, may also significantly influence these characters and obscure or enhance perceived patterns of plant syndromes. We analyzed the proportions of glucose, fructose, and sucrose by paper chromatography in the nectar and fruit juice of 525 tropical and subtropical plant species to test whether sugar chemistry was correlated with volant vertebrate pollinator or fruit disperser classes. Samples were taken from Old World and New World species and the calculations kept separate. Kruskal-Wallis tests of family means showed significant deviations in the percent sucrose content among pollinatorl disperser classes. Mann-Whitney U-tests showed significant differences among nectars of all pollinator classes but fruit juices differed only due to the high sucrose content of megachiropteran dispersed fruits. In addition, sign tests of samples occurring within families showed significant correlations between percentage sucrose content and pollinator/disperser classes. Passerine nectars had low sucrose content. In striking contrast, the nectar of hummingbird flowers had very high sucrose content. The Microchiroptera nectars showed hexose richness with a sucrose content somewhat greater than that of passerine flowers. Megachiroptera flowers showed sucrose-rich nectars. The results for fruits were comparable to those for nectars. Passerine fruits were hexose dominated, microchiropteran fruits had a sucrose content similar to passerine fruits, and megachiropteran fruits were sucrose-rich. We speculate on the evolutionary sequence of changes in nectar and fruit juice sugar composition and suggest that future investigations consider the chemistry of other food sources such as pollen and leaves. Only with these additions and other ecological studies can the full interplay of such plant-animal interactions be anticipated.     

Fruit set, nectar reward, and rarity in the Orchidaceae

A review of comparative levels of reproductive success among nectariferous and nectarless orchids worldwide was compiled from a comprehensive survey of fruit set from 117 orchid species in the literature and from our own field studies. It confirms the hypothesis that nectariferous orchids are more successful in setting fruit than are nectarless species. Overall fruit set figures for nectarless and nectariferous orchids were 19.5 and 49.3% for North America, 27.7 and 63.1% for Europe, 41.4 and 74.4% for the temperate southern hemisphere, and 11.5 and 24.9% for the tropics, demonstrating that the dichotomy is consistent across all geographical areas. On average, the provision of nectar doubles the probability of fruit set in both temperate and tropical areas, but tropical orchids are remarkable in that all (whether nectarless or nectariferous, or terrestrial or epiphytic) display low fruit productivity (<50%). Fruiting failure in the tropics may be balanced by higher productivity per capsule, since tropical orchid fruits contain on average 150 times more seeds than temperate ones. Hybridization occurs more frequently among nectarless orchids in Britain and Europe than among nectariferous ones, and there is a significant positive association between orchid rarity and lack of nectar reward in the British Isles. Sexual reproduction in the Orchidaceae is predominantly pollinator dependent, but this can sometimes be successfully circumvented by asexual seed production (agamospermy) or, more frequently, by automatic self-pollination (autogamy). The proportion of highly successful nectarless orchids from all geographic areas is very low and comparable with that of orchids offering rewards other than nectar (～14% of species in each case) emphasizing that high reproductive success is only associated with nectar reward (53% of species). It is suggested that the evolution of nectar production within the family has been the most frequent means of escaping the reproductive limitations of low pollinator visitation frequencies.     

Seasonal variation in the feeding ecology of the grey-cheeked mangabey (Lophocebus albigena) in Cameroon

Seasonal fluctuations in resource abundance often cause primates to change their feeding behavior and ecology. The objective of this study was to examine the response of a largely frugivorous monkey, the grey-cheeked mangabey (Lophocebus albigena), to seasonal variations in fruit abundance. We used 15-min scan sampling to quantify feeding, activity, and habitat use by monkeys between February and December 1998 in the Dja Reserve, Cameroon. L. albigena were found to have omnivorous feeding habits, consuming the fruits, seeds, leaves, and flowers of 132 plant species. Although monkeys fed from many plant species, only five plant species accounted for 45% of all feeding records. The number of feeding observations on a plant species was significantly correlated with its fruit production. L. albigena responded to fruit-lean periods by shifting from a diet dominated by fruit to one dominated by seeds, flowers, and young leaves. This diet shift coincided with greater use of swamp habitat and higher dietary diversity. L. albigena spent the greatest percentage of scan samples feeding and traveling, but activities varied significantly over the day. Individuals spent a significantly higher percentage of scan samples feeding during the fruit-rich season than in the fruit-lean season. Comparing our results to those of studies in Gabon and Uganda, we found that L. albigena differ across regions in the number of plant species they consume and time spent feeding. These differences may be a result of variations in tree diversity or the strength of seasonal fluctuations in resource abundance among sites.