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Khaya(Meliaceae) is a widespread genus of trees distributed from the tropical forests of Africa to Madagascar and the Comoros. Khayaspecies are very close morphologically and some contain considerable phenotypic and ecological diversity, raising the question of their delimitation: this is the case of Khaya anthothecas.l. (sensu lato, including K. nyasica), which is often lumped with K. grandifoliolaand K. ivorensis. We tested species delimitation within K. anthothecaby combining population‐genetic and morphological data. First, a visual inspection of over a thousand specimens suggested the existence of five morphogroups. Second, after genotyping 498 samples at 71 nuclear SNPs, Bayesian clustering analyses (STRUCTURE) first identified five genetic clusters (K1–K5), while further analyses subdivided K5 into two clusters. The six genetic clusters obtained are distributed in parapatry or allopatry from West Africa to East Africa, except for cluster K4, which is in sympatry with K3 in Central Africa. The partitioning of genetic clusters is also largely congruent with the morphogroups identified. The morphological differentiation of these clusters was confirmed by statistical analyses of 27 leaf characters. The clear‐cut genetic differentiation between clusters, with few admixed genotypes even in contact zones, argues for the recognition of distinct species following the biological species concept. Our analyses highlight that the current taxonomic treatment of Khayaunderestimates by one‐half the total number of species. We identify two new species, circumscribe K. anthothecaand support the rehabilitation at the rank of species of three taxa considered to be synonyms of K. anthotheca(K. agboensis, K. euryphylla, K. nyasica). These results illustrate the strength of combining population‐genetic and morphological data to delineate an African rainforest tree species complex.

Despite an attempt at intercontinental synthesis by Denevan and Turner (1974) almost 50 years ago, studies of agricultural raised fields (RF) in the Neotropics and in Africa and New Guinea are separate research traditions, with almost no communication between them. Neotropical studies refer to “raised-field agriculture” and almost exclusively concern archaeological systems in wetlands. Studies in Africa and New Guinea refer to “mound” or “ridge” cultivation and concern mostly present-day systems (in Africa) or both present-day and archaeological systems (in New Guinea) in both uplands and wetlands. Ethnographic studies of present-day systems provide insights into questions about past systems that are inaccessible using archaeological methods alone. Our review suggests that the Neotropical focus on RF agriculture as an exclusively wetland adaptation is misleading. We argue that the most widespread purpose of building RF, in both wetland and upland environments, is to concentrate topsoil and organic matter, enabling creation of fertile patches in infertile and low-biomass grassland environments. Avoiding flooding is an important function of RF built in wetlands and wetland margins. We further show that Old World RF are often not perennial, but are short-lived structures that rotate over the landscape, being torn down and rebuilt nearby in successive cycles. Short fallow periods are allowed (or even favored) by methods of managing fertility. Finally, we argue that the restriction—on all continents—of archaeological raised fields to wetland and wetland-margin environments is, in part, a result of their better preservation from erosion in wetland than in upland environments.

Semi-domesticated plants are good resources for agroecology, because they can survive without human intervention and can be managed together with non-domesticated plants. To explore the ecological know-how underlying farmer management of semi-domesticates at the landscape level, we compared how Yanacona Indigenous People in the southwestern Colombian Andes manage two semi-domesticated species ofPhaseolus beans, both locally namedcacha (Phaseolus coccineus andP. dumosus), and a full domesticate (the common beanPhaseolus vulgaris). We investigated what functional traits ofPhaseolus beans farmers identify and how farmers link these traits with the ability of beans to develop in different cultural-ecological niches within the landscape. In 60 semi-structured interviews conducted with Yanacona farmers, we found that (i) farmers compare functional traits of the different bean species, including perenniality, phenology, resistance to pests and diseases, and ability to compete with surrounding vegetation; (ii) farmers recognize and use the variation generated by hybridization between the twocacha species; (iii) farmers take advantage of the traits ofcacha to grow them under a wide array of niches at the landscape scale, including low-intervention spaces, such as hedges and swidden plots in fallow, and have detailed knowledge ofcacha beans' interactions with trees; and (iv)cacha traits contribute to the resilience of agroecosystems through the management practices and social relationships with which they are associated. Emic and etic perspectives must be combined to gain full understanding of the roles of functional traits of cultivated plants.

Soils are self-organized ecological systems within which organisms interact within a nested suite of discrete scales. Microorganisms form communities and physical structures at the smallest scale (microns), followed by the community of their predators organized in microfoodwebs (tens of microns), the functional domains built by ecosystem engineers (centimeters to meters), ecosystems, and landscapes. Ecosystem engineers, principally plant roots, earthworms, termites, and ants, play key roles in creating habitats for other organisms and controlling their activities through physical and biochemical processes. The biogenic, organic, and organomineral structures that they produce accumulate in the soil space to form three-dimensional mosaics of functional domains, inhabited by specific communities of smaller organisms (microfauna and mesofauna, microorganisms) that drive soil processes through specific pathways. Ecosystem engineers also produce signaling and energy-rich molecules that act as ecological mediators of biological engineering processes. Energy-rich ecological mediators may selectively activate microbial populations and trigger priming effects, resulting in the degradation, synthesis, and sequestration of specific organic substrates. Signaling molecules inform soil organisms of their producers’ respective presences and change physiologies by modifying gene expression and through eliciting hormonal responses. Protection of plants against pests and diseases is largely achieved via these processes. At the highest scales, the delivery of ecosystem services emerges through the functioning of self-organized systems nested within each other. The integrity of the different subsystems at each scale and the quality of their interconnections are a precondition for an optimum and sustainable delivery of ecosystem services. Lastly, we present seven general research questions whose resolution will provide a firmer base for the proposed conceptual framework while offering new insights for sustainable use of the soil resource.

Supplemental digital content is available in the text.The role of earthworms as one of the most important groups of ecosystem engineers in human-modified and natural environments has been increasingly recognized only during the last 30 years, yet earthworms and humans have been acting together in building landscapes for millennia. This relationship is well represented in the pre-Columbian raised fields, in flood-prone savannas around the rim of Amazonia, but also by the potentially significant role of earthworms in the formation and resilience of Amazonian Dark Earths. Through the bioturbating action of earthworms, soil is biologically, chemically, and physically altered; nutrients are translocated; organic matter is decomposed and transformed; and the surrounding biota interacts as a large orchestra where the soil musicians play together on the various instruments but where earthworms take a leading role, enhancing microbial activity and generally stimulating plant growth. In this article, we assess the remarkable role of earthworms at the center of soil pedogenetic processes within anthropogenic landscapes, dissecting their functions with a special focus on Amazonian Dark Earths.

AbstractPlacement of seeds in favourable microsites by inhumation in ant nests is considered a principal advantage of myrmecochory. However, nest chambers may be too deep to allow seedling emergence. In this case, successful germination requires secondary transport of seeds to shallower sites. Little is known about the architecture of nests of seed-dispersing ants and the locations within nests to which seeds are initially transported. These data are essential to assess the importance of secondary transport for germination success of seeds. We studied dispersal of Manihot esculentasubsp. flabellifoliaseeds by Ectatomma brunneumants in French Guianan savannas. We followed movements of seeds within nests by offering marked diaspores to foraging workers, observing transport into the nest, then excavating to determine locations of marked seeds. In 4 nests, chambers ranged from 2 to 40 cm deep. Because elaiosomes are fed to brood, Manihotdiaspores were initially transported to deep chambers, where brood was concentrated. Recovered diaspores had been carried to chambers 14–40 cm deep, all deeper than the maximum burial depth for emergence (= 13.8 cm) predicted from the mass (= 0.13 g) of Manihotseeds. Nest architecture thus makes secondary vertical transport of seeds crucial for dispersal success of this species. Failure of secondary transport may be an underestimated mortality factor in myrmecochorous plants.

•LiDAR topography sheds light on vestiges of mound-shaped pre-Columbian raised fields.•Humans built larger mounds in the lowest part of the topographic gradient.•Mounds are best preserved in the middle of the topographic gradient.•Mound size and vegetation state are correlated.•Raised fields may have covered a larger area when they were abandoned than today.

Summary.: We examined the role of plant phenology in the evolution of anti-herbivore defence in symbiotic ant-plant protection mutualisms. Phenology of the host-plant affects traits of its herbivores, including size, growth rate, development time, and gregariousness. Traits of herbivores in turn determine what traits ants must have to protect their host. Diversity in plant phenological traits could thus help explain the great ecological diversity of coevolved ant-plant mutualisms. We explored the postulated causal chain linking phenology of the plant, herbivore adaptations to phenology, and ant adaptations for protection, by comparing two myrmecophytes presenting strong contrasts in phenology. In Leonardoxa africana, a slow-growing understory tree, growth at each twig terminal is intermittent, the rapid flushing of a single leaf-bearing internode being followed by a pause of several months. In contrast, axes of Barteria nigritana, a tree of open areas, grow continuously. Analysis of the phenology (kinetics of expansion) and chemistry of leaf development (contents of chlorophylls, lignin, and nitrogen during leaf growth) showed that these two species exhibit strongly contrasting strategies. Leonardoxa exhibited a delayed greening strategy, with rapid expansion of leaves during a short period, followed by synthesis of chlorophylls and lignins only after final leaf size has been reached. In contrast, leaves of Barteria expanded more slowly, with chlorophylls and lignin gradually synthesised throughout development. Differences in the phenology of leaf development are reflected in differences in the duration of larval development, and thereby in size, of the principal lepidopteran herbivores observed on these two plants. This difference may in turn have led to different requirements for effective defence by ants. The strategy of phenological defence may thus affect the evolution of biotic defence.

Contents of phenolic compounds in leaf extracts often serve as a measure of plant anti-herbivore defence. This method suffers from the multifunctionality of phenolics and from problems with their colorimetric quantification. Here we present further evidence for the pertinence of these problems. Contents of condensed tannins (CCT) were spectrophotometrically quantified in leaf extracts of 11 closely related mimosoid species, and Spodoptera littoralis caterpillars were reared on artificial diet containing these extracts. The relationship of CCT with caterpillar growth differed considerably among plant species, since both positive and negative correlations were detected. There was, however, a negative correlation of CCT with fungal spore germination, indicating a role of these compounds in resistance to fungi. Detailed knowledge on the structure and biological function of defensive compounds and on the overall composition of leaves is required to estimate a plant's defensive efficacy against a particular group of enemies.

AbstractDeveloping seeds of Sesbania drummondiiare attacked by nymphs and adults of the bug Hyalymenus tarsatus(Heteroptera: Alydidae), which kill some seeds and weaken others. Parasitism by this piercing-sucking insect reduced the resources for the future seedling and affected seed physiology, including dormancy and exudation of allelochemicals of imbibing seeds. Seeds attacked by H. tarsatushad reduced mass (20-80% reduction, depending on intensity of attack). Heavy attack led to irregular shape, changes in seed coat color, and disruption of dormancy. While intact seeds did not imbibe during a 48-hour test in water, a high proportion of bug-attacked seeds germinated, from 51 to 94%, depending on intensity of attack. Attack by H. tarsatusalso affected accumulation of allelochemicals and their exudation by imbibing seeds. There were no quantitative differences in proanthocyanidin content between exudates of attacked and unattacked seeds. In contrast, concentrations of total condensed tannins were higher in exudates of attacked seeds on the third day of imbibition. This change may reflect induction of chemical defenses by herbivore attack and/or a mechanism to restore seed coat impermeability. Although difficult to quantify, effects of sublethal attack by this sucking insect on the seed bank are likely to have important consequences for the demography of S. drummondii, a short-lived perennial in habitats where conditions for recruitment are variable and unpredictable among years.

Although observations suggest pairwise coevolution in specific ant–plant symbioses, coevolutionary processes have rarely been demonstrated. We report on, what is to the authors' knowledge, the strongest evidence yet for reciprocal adaptation of morphological characters in a species–specific ant–plant mutualism. The plant character is the prostoma, which is a small unlignified organ at the apex of the domatia in which symbiotic ants excavate an entrance hole. Each myrmecophyte in the genus Leonardoxahas evolved a prostoma with a different shape. By performing precise measurements on the prostomata of three related myrmecophytes, on their specific associated ants and on the entrance holes excavated by symbiotic ants at the prostomata, we showed that correspondence of the plant and ant traits forms a morphological and behavioural filter. We have strong evidence for coevolution between the dimensions and shape of the symbiotic ants and the prostoma in one of the three ant–Leonardoxaassociations.

In this paper we present original data on morphological and genetic diversity of cassava managed by the Makushi Amerindians from Guyana. Although they propagate cassava exclusively vegetatively by means of stem cuttings, many Amerindian farmers also use and multiply volunteer plants grown from seeds produced by sexual reproduction. Morphological characters were recorded for 29 varieties cultivated by the Makushi and two populations of plants originating from volunteer cassava seedlings. Genetic characterisation with AFLP markers was available for 21 of the examined varieties. The morphological and agronomic characters were highly variable among varieties. Every variety could be differentiated from any other one, except for one pair of varieties. However, high intra-varietal variability existed, which might lead to confusions between phenotypically similar varieties by the Makushi. Seedlings were on average different from the pool of the varieties studied, but 67% were found to resemble closely enough one of the varieties to be liable to be assigned to it. Confusion between very similar varieties, as well as assignment of seedlings to a variety, should generate genetic variability within varieties, which was detected with AFLP markers. As in other sites in Amazonia, there was only a weak correlation between inter-varietal distances assessed with molecular and with morphological markers, suggesting that diversification of morphological characters has taken place repeatedly and independently across the Amazonian range of the crop. Diversifying selection, exchanges of varieties between farmers, and incorporation of sexually produced volunteer plants are key mechanisms responsible for the high diversity observed. Strategies of conservation of genetic resources should take these dynamic processes into account.

Many ant plants possess caulinary domatia, hollow and usually swollen stems. What are the evolutionary origins of this key trait of ant–plant symbioses? In a single lineage, myrmecophytes often differ in the timing of the first appearance of domatia. What processes have led to diversification in the timing of expression of domatia in ontogeny? We suggest that an approach based on the analysis of leaf–stem size correlations, that appear general in trees, can supply answers to both these questions. Traits associated with increased primary diameter of twigs may have facilitated the evolution of domatia. Among lineages, differences in stem diameter may help to explain why domatia appeared in some, and not in others. Within species, because twig primary diameter increases over plant ontogeny, initially ants may have colonized only plants at later stages of development, whose twigs had reached a minimum size. We thus postulate that expression of domatia later in development is the primitive condition in lineages with domatia, and that increasing specialization of ants and plants enhanced both the probability of establishment and ant protection, favouring precocity of onset of domatia and other myrmecophytic characters. In the language of heterochrony, these characters are affected by pre-displacement.

While observations suggest that plant chemicals could be important in maintaining the specificity and permitting the functioning of ant-plant symbioses, they have been little studied. We report here the strongest evidence yet for chemical signalling between ants and plants in a specific ant-plant protection symbiosis. In the mutualism between Leonardoxa africana subsp. africana and Petalomyrmex phylax , ants continuously patrol young leaves, which are vulnerable to attacks by phytophagous insects. We provide experimental evidence for chemical mediation of ant attraction to young leaves in this system. By a comparative analysis of the related non-myrmecophytic tree L. africana subsp. gracilicaulis , we identify likely candidates for attractant molecules, and suggest they may function not only as signals but also as resources. We also propose hypotheses on the evolutionary origin of these plant volatiles, and of the responses to them by mutualistic ants.

Summary. We determined the localization of phenolic compounds in dormant seeds of two American species of Sesbania (Fabaceae) by a combination of histochemical and biochemical methods. Phenolics are located in different layers of the seed coat and in the subhilar parenchyma. We then investigated the release of these compounds by imbibing seeds of both species. The annual S. vesicaria releases the flavonoid luteolin, with minor amounts of proanthocyanidins, whereas the perennial S. drummondii releases mostly proanthocyanidins. Types and amount of allelochemicals exuded seem related to ecology and life history traits of each species. We then showed mobilisation of these allelochemicals by histochemical sections in imbibing seeds of both species. Histological structure is similar in both species. A number of characters (lens, subhilar parenchyma, tracheid bar) appear to function together to facilitate the exudation of compounds that protect young seedlings. Furthermore, the spatial organization of these organs with interlocking function allows retrieval of defensive substances stored in the seed, and their redeployment is beneficial for seedling survival. We hypothesize that optimisation of the chemical defences allocated to the seed by the maternal parent confers a significant advantage to the seedling, whose energy is mainly committed to growth.

The dry matter digestibility of 94 species of leaf was assayed by a simple method involving sequential treatment with pepsin and fungal cellulase enzymes. It was demonstrated that for foliage from rainforest trees of a wide range of dicotyledonous plant families the assay showed high positive correlation with estimates of dry matter digestibility obtained using rumenliquor from a fistulated steer. Both assays were found to reflect negative correlates of digestibility, notably fibre and condensed tannin, rather than the nutritional value of an item. The higher dry matter digestibility of immature leaves relative to mature leaves appeared to be accounted for by their lower fibre content. It is suggested that the pepsin/cellulase assay offers a cheap, quick, routine method of gaining information on the effects of some types of plant secondary compounds (digestibility reducers) on the ‘food potential’ of different kinds of foliage to herbivores. Its use in studies of herbivory in rainforest areas in relation to analyses for plant secondary compounds and food selection by herbivores is discussed.

By estimating relative costs and benefits, we explored the role of the homopteran partner in the protection mutualism between the myrmecophyte Leonardoxa africanaT3, the ant Aphomomyrmex afer, and sap–sucking homopterans tended by ants in the tree's swollen hollow twigs. The ants obtain nest sites and food from their host–plant (food is obtained either directly by extrafloral nectar or indirectly via homopterans). Aphomomyrmexworkers patrol the young leaves of L. africanaT3 and protect them against phytophagous insects. Because ants tended, either solely or primarily, coccids in some trees and pseudococcids in others, we were able to study whether the nature of the interaction was dependent on the identity of the third partner. First, the type of homopteran affects the benefits to the tree of maintaining a large ant colony. Larger colony size (relative to tree size) confers greater protection against herbivory; this relationship is more pronounced for trees whose ants tend pseudococcids than for those in which ants tend coccids. Second, for trees (and associated ant colonies) of comparable size, homopteran biomass was much larger in trees harbouring coccids than in trees with pseudococcids. Thus, the cost to the tree of maintaining ants may be greater when ants are associated with coccids. The net benefits to the plant of maintaining ants appear to be much greater with pseudococcids as the third partner. To explore how the type of homopteran affects functioning of the system, we attempted to determine which of the resources (nest sites, extrafloral nectar, and homopterans) is likely to limit ant colony size. In trees where ants tended coccids, ant–colony biomass was strongly dependent on the number of extrafloral nectaries. In contrast, in trees whose ants tended only pseudococcids, colony biomass was not related to the number of nectaries and was most strongly determined by the volume of available nest sites. We present hypotheses to explain how the type of homopteran affects functioning of this symbiosis, and discuss the implications of our study for the evolutionary ecology of ant–plant–homopteran relationships.

Abstract: Ficus species (figs) and their species-specific pollinator wasps are involved in an intimate mutualism in which wasps lay eggs in some ovaries of the closed inflorescences (syconia), and mature, inseminated offspring carry pollen from mature syconia to fertilize receptive inflorescences. In monoecious species, each syconium produces seeds and wasps. In functionally dioecious fig species, making up approximately half the figs worldwide, male and female functions are separated; hermaphrodite (functionally male) trees produce wasps and pollen only, while female trees produce seeds only. This sexual separation allows selection to act independently on the reproductive biology of each sex. Examining sexual specialization in a tight mutualism allows us to determine aspects of the mutualism that are flexible and those that are canalized. In this study, we quantified the phenology of two species of dioecious figs, F. exasperata and F. hispida, for 2 years by following the fates of several thousand syconia over time. In studying each of these species in a dry and a wet site in south India, we tested specific predictions of how dioecious figs might optimize sexual function. On female trees of both species, more inflorescences matured during the wet (monsoon) season than in any other season; this fruiting period enabled seeds to be produced during the season most suitable for germination. In F. exasperata, functionally male trees released most wasps from mature syconia in the dry season, during peak production of receptive female syconia, and thus maximized successful pollination. In F. hispida, “male” trees produced more syconia in the dry and monsoon seasons than in the post-monsoon season. In both species, male and female trees abscised more unpollinated, young inflorescences than pollinated inflorescences, but abscission appeared to be more likely due to resource- rather than pollinator- limitation. The phenology of F. exasperata requires that male inflorescences wait in receptive phase for scarce pollinators to arrive. As expected, male inflorescences of this species had a longer receptive phase than female inflorescences. In F. hispida, where pollinators are rarely scarce, duration of receptive phase was the same for both sexes. Duration of developing phase was longer in female syconia of both species than in male syconia, most likely because they need a longer period of investment in a fleshy fruit. Variation in developing phase of female syconia in one species (F. exasperata) was also greater than that in male syconia, and enabled female trees to sample a variety of germination environments in time. The strong sexual differences in both fig species support the hypothesis that selection for sexual specialization has strongly influenced the reproductive biology of these species.

Levels of total phenolics, condensed tannins, acid detergent fiber, pepsin/cellulase digestibility, and nitrogen in mature leaves of 26 individuals of the ant-plant,Barteria fistulosa, have been determined. Analysis of the results in terms of the presence or absence of ants and the position of the branch from which the leaves were collected showed no relationship with concentrations of phenolics or fiber and only a weak relationship with digestibility and nitrogen. By contrast, light intensity strongly influenced levels of phenolics, notably condensed tannins, so that mature leaves of individuals growing in direct sunlight were less digestible and appeared to be of lower quality as food for herbivores than did mature leaves of individuals in shaded positions. Possible reasons for the variation in condensed tannin levels are discussed.

Figs (Ficusspp., Moraceae) are considered a classic example of plants with fleshy fruits adapted for seed dispersal by vertebrates, usually mammals or birds. Partially covering the endocarp of each individual drupelet of F. microcarpais a fleshy, discrete lipid‐containing exocarp that suggests adaptation for seed dispersal by ants. This structure is highly attractive to ants. F. microcarpadrupelets from which the fleshy exocarp was experimentally removed were much less likely to be transported by ants than those with this structure intact. The exocarps retained their attractiveness to ants and were not visibly altered following passage of the entire fruit through the gut of a frugivorous bird, the Indian Hill Mynah (Gracula religiosa). Germination percentage was not significantly affected by gut passage or exocarp removal. These results suggest that F. microcarpahas a two‐stage seed dispersal system, in which primary dispersal by vertebrates is followed by secondary dispersal by ants. Dispersal aided by ants may be of significance in the biology of this exotic hemiepiphyte in southern Florida, where it is naturalized and appears to be spreading.

TheLeonardoxa africana(Leguminosae: Caesalpinioideae) complex is a group of four closely related taxa (L1 to L4) exhibiting various grades of specificity and specialization in mutualistic associations with ants. Each of the two most specialized species,Leonardoxataxon 3 (L3) andL. africanasensu stricto (L4), interacts with a specific species of formicine ant, respectivelyAphomomyrmex aferandPetalomyrmex phylax,which nests in specialized swollen twigs. These two monotypic genera are the sole African members of the tribe Myrmelachistini, and their occurrence in closely related plants suggested the hypothesis that the two associations L4/Petalomyrmexand L3/Aphomomyrmexare derived by cospeciation from an ancestral association. Phylogenies based on DNA sequences were reconstructed for the ants and compared with phylogenies available for the plants in order to test for this hypothesis of cospeciation. The resulting topologies suggest either that the association with myrmelachistine ants arose several times or that a plant species (L2) and an ant population split off from an ancestral association. Furthermore, dates of speciation events appear to differ between ants and corresponding plants. An estimate of at least 4 million years was obtained for the separation ofAphomomyrmexandPetalomyrmex,whereas biological, biogeographic, and molecular–genetic data suggest a much more recent divergence for the plants. Thus, we reject the hypothesis of cospeciation and conclude thatAphomomyrmexandPetalomyrmexindependently colonized different taxa ofLeonardoxa.This striking instance of parallel evolution supports the notion that specific ant–plant associations originated by ecological fitting of preadapted partners. We discuss alternative evolutionary scenarios that are consistent with molecular data.

Abstract: In this study, we demonstrate that an important benefit provided by the small host-specific ant Petalomyrmex phylax to its host plant Leonardoxa africana is efficient protection against herbivores. We estimate that in the absence of ants, insect herbivory would reduce the leaf area by about one-third. This contributes considerably to the fitness of the plant. Our estimates take into account not only direct damage, such as removal of leaf surface by chewing insects, but also the effects of sucking insects on leaf growth and expansion. Sucking insects are numerically predominant in this system, and the hitherto cryptic effects of ant protection against the growth-reducing effects of sucking insects accounted for half of the total estimated benefit of ant protection. We propose that the small size of workers confers a distinct advantage in this system. Assuming that resource limitation implies a trade off between size and number of ants, and given the small size of phytophagous insects that attack Leonardoxa, we conclude that fine-grained patrolling by a large number of small workers maximises protection of young leaves of this plant. Since herbivores are small and must complete their development on the young leaves of Leonardoxa, and since a high patrolling density is required for a fine-grained search for these enemies, numerous small ants should provide the most effective protection of young leaves of Leonardoxa. We also discuss other factors that may have influenced worker size in this ant.

In order to refine hypotheses concerning food selection by generalist herbivores with ruminant-like digestive systems the chemical correlates of digestibility in such a system have been studied. Samples of seeds and leaves from tree species growing in two African rainforests (Douala-Edea Forest Reserve, Cameroon, and Kibale Forest, Uganda) were assayed for phenolic content and nutrient content, and in-vitro dry matter digestibility was analysed utilizing rumen inoculum from a fistulated steer. Both forests studied carry populations of colobine monkeys with ruminant like digestive tracts. Content of condensed tannins and, to a lesser extent of total phenolics, was found to be negatively correlated with digestibility; a result that may be attributable to the inctivation of microbial enzymes by tannins. The negative association of tannin content and digestibility was stronger in material from the Cameroon site, the vegetation of which contains considerably higher concentrations of tannins and is generally less digestible than that from the Ugandan site. Gross energy content of leaves was also found to be persistently negatively correlated with digestibility. The interpretation of this result is uncertain; however, gross energy yield may well reflect variation in content of cell wall polymers, especially lignin. For the complete set of data, tannins presented the strongest observed correlation with digestibility, but when only mature leaves were considered the relationship with gross energy appeared stronger. No strong association was noted between high nutrient content and high digestibility. This was attributed to the fact that the assay measured the extent of digestion under standardised and very favourable conditions of nutrient supply. The results obtained are discussed in relation to observations of leaf and seed selection preferences of Colobus spp. in these two forests.

A model is proposed for the population dynamics of an annual plant (Sesbania vesicaria) with a seed bank (i.e. in which a proportion of seeds remain dormant for at least one year). A simple linear matrix model is deduced from the life cycle graph. The dominant eigenvalue of the projection matrix is estimated from demographic parameters derived from field studies. The estimated values for population growth rate (?) indicates that the study population should be experiencing a rapid exponential increase, but this was not the case in our population.

Data are presented from an 11-month study of the ranging movements of a group of Colobus satanasin a rain forest on the coast of Cameroon. Discussion centers on correlations between seasonal variation in ranging behaviour and seasonal variation in food availability, diet composition and diversity, and weather conditions. The data support the hypothesis that the scarcity of nutrient-rich, highly digestible leaves in this site has led to a feeding strategy based on seeds, which are characterised by high nutritive quality and occurrence in large clumps, allowing monotonous feeding and low expenditure of energy in ranging movements.

- Le manioc constitue la base de l’alimentation de la très grande majorité des populations amazoniennes et leur principale culture. Selon les régions et les populations (amérindiennes, métissées ou d’immigration récente) cette culture s’accompagne d’une plus ou moins ample diversité variétale, de deux à trois variétés cultivées par parcelle à une trentaine. Les stratégies de conservation des ressources phytogénétiques doivent s’appuyer tant sur une meilleure compréhension des bases génétiques de cette diversité que sur les conditions de production ou de maintien de celle-ci. La recherche comparative menée associe des approches génétique, écologique, ethnobiologique et socio-anthropologique et s’attache à expliciter les liens entre diversité variétale, pratiques agricoles et représentations associées, et environnement socio-économique. Les analyses génétiques soulignent un important polymorphisme inter et intravariétal. Les résultats montrent aussi la spécificité de chaque groupe culturel quant à la valeur accordée aux variétés, aux modalités de circulation des boutures et à la place donnée aux maniocs issus de graines. Des dynamiques plus globales jouent aussi sur la diversité variétale (commercialisation croissante de farine, changements d’habitudes alimentaires, politiques agricoles). Elles tendent à réduire le nombre de variétés cultivées et à modifier la structure de cette diversité. Les résultats plaident en faveur de la constitution de pôles régionaux de conservation, qui pourraient prendre le relais des structures centralisées actuelles ou les compléter.