We investigated the presumption that wind-wave exposure is a major regulator of vegetation distribution within lakes. Along a 675-km stretch of shore in northern Lake Victoria (Uganda), the pattern of vegetation distribution in relation to shoreline features, and the variation of shoreline swamp area along a gradient of wave exposure were examined. The ability of wave exposure, when combined with bay morphometric characteristics, to predict the lakeward limit of vegetation distribution was assessed. Data were collected through a shoreline survey and from maps. Maximum effective fetch, computed from topographic maps, was used as a surrogate for wave exposure. Our results reinforce and amplify the notion that wave exposure is an important regulator of the within-lake distribution of vegetation. We found shoreline plants to either occupy stretches of shore shielded by coastal islands or hidden by convolutions of the lake margin. The area of shoreline swamps declined exponentially with increasing wave exposure. Of the coastal characteristics examined, bay area had the strongest influence on the lakeward expansion of vegetation. Wave exposure acting together with bay area, accounted for 64.4% of the variance in the limit of lakeward vegetation advancement.

In the Neotropics, crops that are grown in agroforestry systems with shade trees support high levels of bird diversity compared with crops grown without shade (Estrada & Coates-Estrada 2005, Faria et al. 2006). Several experiments in shaded coffee farms have explored how insectivorous birds reduce herbivore numbers and their damage to plants and have simultaneously approached ecological questions that are applied (e.g. biological control) and basic (e.g. tri-trophic interactions) (Borkhataria et al. 2006, Greenberg et al., Perfecto et al. 2004). Here we used exclosures to test whether birds lower the densities of herbivorous insects and reduce insect damage to cocoa (Theobroma cacao L., Sterculiaceae) foliage in shaded farms of western Panama. Although bird predation has been shown to reduce insect damage to crops in other systems (Mols & Visser 2002), we provide the first test for shade-grown cocoa.

The genus Piper is an important component of tropical forests worldwide. Many Piper species have been reported as self-compatible (Figueiredo & Sazima 2000), and many have the ability to reproduce asexually, forming clonal aggregations (Grieg 1993). Furthermore, the main dispersers of Piper (bats) transport whole infructescences to feeding roosts (Fleming & Heithaus 1981), tending to disperse closely related seeds in clumps. These characteristics of Piper biology are likely to result in populations with strongly marked spatial genetic structure, and raise the potential for inbreeding depression through self-fertilization. A few studies using allozymes to evaluate spatial genetic structure in Piper spp. support this view. These studies indicate that populations separated by more than 1 km are genetically distinct (high FST values; Wright 1943) and that for some species inbreeding could be substantial (high values of FIS and FIT; Heywood & Fleming 1986, Mariot et al. 2002). However, the contributions of limited pollen and seed dispersal to generating spatial genetic structure remain unknown. Estimates of seed dispersal probabilities by Carollia perspicillata (Phyllostomidae) bats on Barro Colorado Island (BCI), Panama, and at Santa Rosa, Costa Rica, indicate that Piper dispersers move most seeds 50–300 m from the parent plant, with occasional long-distance events of > 1 km (Fleming 1981, Thies 1998). However, no studies have assessed how far Piper flower visitors move pollen. If seed dispersal is limited, and clonal reproduction is common, then long-distance pollen transfer may play a critical role in preventing inbreeding depression in Piper populations.

The tree Lysiloma microphyllum (Fabaceae) dominates in the seasonally tropical dry forests of central Mexico. In this study foliar N and P concentrations (on leaf mass basis), foliar N and P resorption efficiency and proficiency, as well as the decomposition of senescent leaves of L. microphyllum were studied in primary and in regenerating, secondary seasonally tropical dry forests. Our study included an area of early successional forest (10 y old), with phosphorus-poor soils and comparatively abundant nitrogen, an area of late-successional forest (∼60 y old), in which soil P and N were comparatively abundant, and an area of primary forest, in which soil P was comparatively abundant and N was less abundant than in the secondary counterparts. N and P concentrations in mature leaves varied across forests, reflecting soil nutrient availability. Nitrogen concentration in senescent leaves did not change among sites, which led to very different patterns of N resorption. In contrast, P concentration in senescent leaves was lower in the early than in late-successional and primary forests, which resulted in similar patterns of resorption. Leaf decomposition increased from 70% mass loss in the first year in the early successional to ∼80% in the same period in late-successional and primary forests. The element loss during decomposition change across forests in the following order: for N, early successional = late-successional > primary forest, and for P, primary forest > late-successional > early successional forest. Overall, the pattern of variation in leaf chemistry and nutrient release on the forest floor among sites is consistent with soil nutrient availability along this sequence, while decomposition rate may be related with the P concentration in senescent leaves.

The seasonality of both rainfall and solar irradiance might influence the evolution of flowering and fruiting in tropical forests. In seasonally dry forests, to the degree that soil moisture limits plant productivity, community-wide peaks in reproduction are expected during the rainy season, with seedfall and germination timed to allow seedlings to become well established while soil moisture is available. Where soil moisture is never seasonally limiting, seasonal changes in light availability caused by periods of cloudiness or seasonally low zenithal sun angles should favour reproduction during seasons when irradiance levels are high. To evaluate these predictions, we documented the timing of flower and fruit fall for 10 and 15 y at El Verde, Puerto Rico, and Barro Colorado Island (BCI), Panama. At El Verde, rainfall is abundant year-round and solar declination largely determines seasonal variation in irradiance. At BCI, rainfall is abundant throughout the 8-mo wet season while drought develops and average solar irradiance increases by 40–50% over the 4-mo dry season. Seasonal variation in the number of species flowering and fruiting at both sites was generally consistent with the hypothesis that seasonal variation in irradiance limits the evolution of reproductive phenologies. Community-level metrics provided no evidence for a similar role for moisture availability at BCI. Seasonal variation in irradiance also strongly influenced seed development times at both sites. Thus, community-wide phenologies reveal a strong signature of seasonal changes in irradiance, even in those forests that exhibit some degree of seasonality in rainfall.

The regeneration processes and the spatial distribution of the shade-intolerant Weinmannia tinctoria seedlings in the south of Réunion were investigated, with a special focus on the role of tree-ferns in seedling establishment. Mature individuals and seedling patches of Weinmannia tinctoria, and also tree-ferns, were mapped on two 1-ha rain-forest plots. Weinmannia tinctoria has hemi-epiphytic behaviour since seedlings were generally located on plant supports (99.6%). Regeneration was better on a support than on the ground, and germination tests showed that seeds were light-stimulated. Tall tree-ferns (Cyathea spp.) were suitable supports. Cyathea glauca and C. excelsa were more suitable supports than C. borbonica. Weinmannia tinctoria establishment complies with the facilitation model of succession and is dependent on tree-ferns.

La régénération et la distribution spatiale des semis de Weinmannia tinctoria, espèce intolérante à l'ombre, ont été étudiées dans le sud de La Réunion. Nous nous sommes intéressés au rôle des fougères arborescentes sur l'émergence de plantules. Les adultes matures et les taches de semis (ensembles de plusieurs plantules) de Weinmannia tinctoria, de même que les fougères arborescentes, ont été cartographiés sur deux parcelles de 1 ha en forêt humide. Weinmannia tinctoria a un comportement hémi-épiphyte car les semis se situaient principalement sur des supports (99,6%). La régénération se révélait meilleure sur les supports qu'au sol, et les tests de germination ont montré que les semences germaient mieux à la lumière. Les grandes fougères arborescentes (Cyathea spp.) constituaient des supports privilégiés. Cyathea glauca et Cyathea excelsa représentaient des supports plus favorables que Cyathea borbonica. W. tinctoria apparaît donc comme une espèce qui s'installe principalement en utilisant le modèle de facilitation et qui dépend de la présence de fougères arborescentes.

Tropical montane rain forest is widely considered to be a highly threatened hotspot of global diversity (Brummitt & Nic Lughadha 2003), and one of the least understood humid tropical forest ecosystems in terms of nutrient cycling (Bruijnzeel & Proctor 1995). There is, therefore, an urgent need to improve our understanding of nutrient cycling processes in this ecosystem, including the absorption of nutrients (mainly N and P) from senescing leaves, which may be a key component of adaptive mechanisms that conserve limiting nutrients (Killingbeck 1996). Nutrients which are not resorbed, however, will be circulated through litterfall in the longer term (Aerts 1996). The degree of nutrient resorption affects litter quality, which consequently affects decomposition rates and soil nutrient availability (Aerts & Chapin 2000). The importance of resorption in nutrient conservation has led to general hypotheses that species adapted to nutrient-poor environments have high resorption efficiencies (Richardson et al. 2005), and that low leaf nutrient concentrations are associated with high resorption efficiencies within species (Aerts 1996, Kobe et al. 2005). Nutrient resorption has also been shown not to differ greatly between growth forms (e.g. shrubs, grasses, forbs and trees) (Aerts 1996). However, its relative importance among plant functional groups is still highly controversial (Richardson et al. 2005).

Interactions between sympatric species are of particular interest for understanding the mechanisms that allow animal coexistence in the ecological community. The mantled howler monkey (Alouatta palliata Gray) and the white-nosed coati (Nasua narica Linnaeus) are similar-sized mammals with a sympatric distribution in the Neotropics (Nowak 1999). Since these two species are partly frugivorous (howler, Crockett & Eisenberg 1987; coati, Gompper 1997), and fruit is often limited (Laurance et al. 2003), howlers and coatis might be observed foraging from the same fruiting tree, but there is no information regarding this possibility. We studied the feeding encounters between these two species in a small forest fragment, and discuss the conditions under which these episodes occur.

Bird's nest ferns (Asplenium nidus complex) (Yatabe & Murakami 2003) are common epiphytes of the Old World tropics and house a high abundance of arthropods (Ellwood & Foster 2004). Through interception and retention of leaf litter (Paoletti et al. 1991, Piggott 1996, Richardson 1999), epiphytes interrupt litterfall dynamics (Clark et al. 1998, Nadkarni & Matelson 1991) and delay the return of nutrients to the forest floor (Nadkarni 1984). Precipitation percolating through the canopy as throughfall is enriched as nutrients are leached from plant surfaces (Levia & Frost 2006). Water flowing down the trunk of trees as stemflow is further enriched from prolonged contact and accumulated nutrient deposits on the trunk (Levia & Frost 2003, Liu et al. 2002). Epiphytes can alter stemflow nutrient concentrations by slowing water percolation and by nutrient uptake and release (Awasthi et al. 1995, Strigel et al. 1994).

Data on pollination ecology of Araceae are still scarce and most concern species belonging to the subfamily Aroideae (García-Robledo et al. 2004, Gibernau 2003, Ivancic et al. 2004, 2005; Maia & Schlindwein 2006). In this subfamily, inflorescences consist of unisexual flowers: female flowers are located in the lower portion and the male flowers are in the upper portion of the inflorescence (Mayo et al. 1997). In the documented neotropical Aroideae, pollinators are nocturnal beetles and pollination mechanisms take place within a floral chamber during a short flowering cycle (generally 24–48 h) with floral rewards (sterile flowers rich in proteins and/or lipids) for the beetle pollinators, the secretion of resin to secure pollen on the pollinator, and the production of heat and odours (Chouteau et al. 2007, García-Robledo et al. 2004, Gibernau & Barabé 2002, Gibernau et al. 1999, 2000, 2003; Maia & Schlindwein 2006, Young 1986).

Heterogeneous agroforestry systems play an important role in maintaining animal pollinator diversity (Klein et al. 2003, Perfecto et al. 1996), most likely by extending floral resources in lean periods. An understanding of the mutualistic relationship between flower-visiting insects and crop species in such agroforestry systems (Kearns et al. 1998), particularly on the diversity of pollinator species, their spatio-temporal variations, foraging behaviour (Cunningham 2000, Greenleaf & Kremen 2006, Klein et al. 2003) and their pollination efficiency (Motten et al. 1981), is important as they are some of the crucial biological predictors of pollination success.

The genetic diversity of Myrciaria floribunda, a common Atlantic Forest tree, was investigated in six populations located in two small fragments (10 and 18 ha), two medium-sized fragments (36 and 44 ha) and one large fragment (3003 ha). Two populations occur in the large fragment. It is expected that smaller fragments should have lower genetic diversity and higher inbreeding. Distances between fragments varied from 0.66 to 10 km. On average 32 young trees smaller than 20 cm basal girth were sampled in each population. Allozyme electrophoresis was carried out, and six loci were scored. The effective number of alleles was lower for populations of the two small fragments (1.46 and 1.51) and higher for populations of the large (1.62 and 1.71) and medium ones (1.69 and 1.84). Small fragments showed lower values of expected and observed heterozygosities than large and medium fragments. Most of the genetic variability occurs within populations, and there was a moderate genetic variation among them ($\hat{\theta}_p$ = 0.097). Our findings show a tendency of lower genetic diversity within small and isolated fragments and higher genetic differentiation among them. But, few correlations between genetic diversity indices and fragment features (size and isolation) were significant.

African elephants Loxodonta africana (Blumenbach) may profoundly affect vegetation and associated animal bio-diversity in savannas (Conybeare 2004, Skarpe et al. 2004). Understanding the patterns of habitat use by elephants is crucial to predict their impacts on ecosystems (Ben-Shahar 1993, Nelleman et al. 2002), particularly now that many populations are recovering from past culling events or poaching outbreaks (Blanc et al. 2007). Surface water is one of the major constraints on elephant distribution (Chamaillé-Jammes et al. 2007, Stokke & du Toit 2002), and accordingly, elephant impacts are higher in the vicinity of water (Ben-Shahar 1993, de Beer et al. 2006). However, waterhole selection by elephant remains poorly understood. Weir (1972) showed in Hwange National Park (hereafter Hwange NP), Zimbabwe, that elephant numbers at waterholes over 24 h increased with the sodium concentration of water on nutrient-poor Kalahari sands. His work has become widely cited in elephant studies as it remains the only one, to the best of our knowledge, to have studied elephant use of waterholes in relation to the mineral concentration of water. Weir's work, however, took place when elephant densities in Hwange NP were low, likely below 0.5 elephants km−2 as estimated by aerial censuses (Williamson 1975). Since then, the elephant population has increased dramatically, particularly since the halt to culling operations in 1986 (Chamaillé-Jammes 2006, Cumming 1981). The present elephant density is much higher, estimated to be over 2 elephants km−2 (Chamaillé-Jammes et al. 2007, in press), and is one of the highest in the world (Blanc et al. 2007). Increased density may modify ecological constraints and affect the hierarchy of habitat selection processes (Morris 2003), and the extent to which water-nutrient selection still constrains elephant distribution at high population density – when their impact on savanna vegetation is the highest – remains unknown.

Rainfall and soil moisture availability vary greatly both spatially and temporally. They are prime factors influencing species distribution patterns, diversity and habitat associations in a range of biomes, and limit primary productivity in many natural ecosystems, as well as in forestry and agricultural systems (Hawkins et al. 2003, Kozlowski & Pallardy 1997, Lieth 1975). Projections of drying trends, and increased frequency and intensity of drought events with climate and land-use changes (Hulme & Viner 1998, IPCC 2001) have fuelled an increased interest in the role of drought in determining the structure and function of natural and managed forest systems (Allen & Breshears 1998, Miles et al. 2004). Such projections accentuate the need to assess, understand and predict plant reactions to drought, as well as soil moisture variation at different scales.

Bates' theory of mimicry (Bates 1862) postulates that vertebrate predators avoid attacks on chemically defended butterflies, and a profitable species, usually referred to as the mimic, can obtain protection by resembling one or more unpalatable models. The evolution of Batesian mimicry requires that predators meet, taste and learn to avoid the models before meeting the mimics. For this reason, some authors have adopted the assumption that mimic population sizes must be smaller than the models' populations (Fisher 1930, Huheey 1980, Lindström et al. 1997).

Drought strongly influences plant phenology, growth and mortality in tropical forests, thereby shaping plant performance, population dynamics and community structure (Bunker & Carson 2005, Condit et al. 1995). Microbial symbionts of plants profoundly influence host water relations (Lösch & Gansert 2002), but are rarely considered in studies of tropical plant physiology. In particular, plant–fungus associations, which are ubiquitous in plant communities and especially common in tropical forests, play important and varied roles in plant water status. Fungal pathogens associated with roots, vascular tissue and foliage may interfere with water uptake and transport, increase rates of foliar transpiration, and induce xylem embolism and tissue death (Agrios 1997). In contrast, rhizosphere mutualists such as ecto- and arbuscular mycorrhizal fungi may benefit hosts by increasing surface area for water uptake, enhancing stomatal regulation of water loss, and increasing root hydraulic conductivity (Auge 2001, Lösch & Gansert 2002).

Leaf-cutting ants (genera Atta and Acromyrmex) have been denoted key species of American rain-forest ecosystems (Fowler et al. 1989) because of their multifarious effects on the vegetation. Being dominant herbivores, cutting up to 13% of the standing leaf crop in a colony's territory per year, they affect directly and significantly individual plants, plant communities and ecosystems (Wirth et al. 2003). The considerable ecological impact of these ants is paralleled by the well-known fact that some species strongly benefit from human-driven habitat alterations and represent prime pests throughout Latin America (Cherrett 1986). Numerous studies have documented populations of leaf-cutting ant to increase with increasing agricultural land use, deforestation and/or disturbance (Fowler et al. 1986, Jaffe & Vilela 1989, Jonkman 1979). Specifically, elevated colony densities have been recorded in (1) transformed vegetation such as pastures (Fowler 1983) and plantations (Jaffe 1986, Oliveira et al. 1998), (2) early successional forests (Vasconcelos & Cherrett 1995), and recently (3) isolated forest remnants (Terborgh et al. 2001).

The Asian elephant Elephas maximus is the only living species of the genus Elephas (Elephantidae) that evolved in Africa c. 5–6 million y ago and migrated into Eurasia (Sukumar 2003). The Asian elephant is one of the few remaining extant megafauna (Owen-Smith 1988) and has disappeared from c. 95% of its historical range (Sukumar 2006). Asian elephants eat fruit when it is available, defecating intact seeds, of which some later germinate in the dung (Lekagul & McNeely 1977, Ridley 1930). However, to date there has been no detailed study of frugivory and seed dispersal by Asian elephants (Corlett 1998). The only common feature of the fruit reported to be eaten by Asian elephants is their relatively large size, but there is no evidence that they are exclusive dispersers of any plant species (Corlett 1998), in contrast to the more frugivorous African forest elephants, Loxodonta africana cyclotis (Babweteera et al. 2007, Chapman et al. 1992, Cochrane 2003, Feer 1995).

Frugivorous bats are important seed dispersers for many plant species (Cox et al. 1991, Fleming & Heithaus 1981, Hodgkison et al. 2003a, McConkey & Drake 2006, Nyhagen et al. 2005, Utzurrum 1995). They regularly consume figs in the wild (Fujita & Tuttle 1991, Kalko et al. 1996, Shilton et al. 1999). Various species of pteropodid bats have been reported foraging on the fruits of more than 30 fig species in tropical and subtropical Asia, Africa and Australia (Bhat 1994, Fujita & Tuttle 1991, Marshall & McWilliam 1982, Thomas 1984). Food transit times in frugivorous bats are relatively rapid; generally less than 30 min (Laska 1990, Tedman & Hall 1985). Several studies have demonstrated that seed germination was either enhanced or unaffected after passage through the digestive tract of bats (Figueiredo & Perin 1995, Fleming & Heithaus 1981, Lieberman & Lieberman 1986).

Disperser effectiveness is the contribution that a disperser makes to the future reproduction of a plant (Schupp 1993), and it has two components: quality and quantity of dispersal. Quantity of dispersal is a function of the number of visits that a disperser makes to a fruiting plant and the number of seeds that are dispersed during each visit. Quality of dispersal is a function of the treatment that a seed receives from its disperser and the site that the seed is finally deposited in. The quality of seed dispersal of the mistletoe Phragmanthera dschallensis (Engl.) M.G. Gilbert (Loranthaceae) by frugivorous birds was examined in this study.