Lantana camara L. (Verbenaceae) is a shrub of Neotropical origin that has spread to at least 60 countries (Day et al. 2003), and its ability to rapidly occupy disturbed habitat has led to it being named one of the ten worst weeds on the planet (Cronk & Fuller 1995, Sharma et al. 2005). A number of traits may have contributed to its success as an invasive species. For example, L. camara increases the available soil nitrogen in otherwise nitrogen-poor ecosystems (Sharma & Raghubanshi 2009), it is extremely resilient to disturbance (Gentle & Guggin 1997a, Hiremath & Sundram 2005), it is allelopathic to native plants (Achhireddy & Singh 1984, Gentle & Duggin 1997b) and its fruits are dispersed by a variety of birds (Mandon-Dalger et al. 2004, Swarbrick et al. 1998). A potentially unappreciated aspect of L. camara biology that may also contribute to its invasiveness relates to pollination ecology.

During 5 y, we monitored reproductive activity and seed production of Carapa guianensis in two forest types to test the hypothesis that seed production is influenced by multiple factors across scales (regional climatic cues, local habitat heterogeneity and individual tree attributes). Variability in seed production was moderate at the population (CVp = 1.25) and individual level (xCVi = 1.24). A mixed model with a Poisson regression revealed that seed production was explained by variables at all scales. Total seed production was significantly higher in occasionally inundated forests. Diameter at breast height, dbh2, crown cross-sectional area, liana load, density, dry-season rainfall and mean maximum temperature were also significant in explaining seed production variation. Seed production increased with dbh until 40–50 cm, then decreased. Liana load demonstrated a negative relationship with seed production, but only in terra firme forests. Climatic cues (rainfall and temperature parameters) were central to setting overall patterns in reproductive activity and seemed to best explain why years with high seed production were consistent across the two forest types (habitats) examined. Dry-season rainfall was positively correlated with seed production.

Accurate measurements of seed rain are important for understanding tree reproduction (Greene & Johnson 1994), forest regeneration (Cole et al. 2010, Cubiña & Aide 2001, Howe et al. 2010, Zahawi & Augspurger 2006), forest ecology (Muller-Landau et al. 2008, Terborgh et al. 2011) and maintenance of community diversity (Harms et al. 2000). Seed traps generally consist of a bucket or net of a fixed area suspended 0.3–1 m above the ground, and seeds are typically collected once or twice per month. An implicit assumption of all seed-rain studies is that traps do not influence seed dispersal. Should birds perch on and defecate seeds into seed traps, seed abundance will be overestimated. This behaviour could produce a directional bias if birds perch on seed traps in one habitat more than others. To our knowledge, no study has considered this potential bias.

The landscape of the upper Rio Negro basin (North Amazon) exhibits distinctive habitats that are associated with differential soil characteristics and topographical conditions as well as species composition (Herrera et al. 1978). The mixed forests thrive on well-structured oxisols on slightly more elevated areas. The valleys with sandy podzols are occupied by the ‘Amazon caatinga’ complex with three distinct zones: the bottom valley and the gentle slopes, both of which have closed forests, and the sandy domes with open forests (‘bana’ or sclerophyllous forest; Breimer 1985). From the mixed forest towards the caatinga valley-slope-dome habitats, the leaf δ15N signatures become increasingly negative, suggesting a trend in N limitation in the same direction (Sobrado 2010). Thus, negative leaf δ15N signatures depleted in 15N compared with the soil indicate a very tight N cycle in all of the habitats. Water availability follows a similar pattern from the top of the oxisol towards the flooded valley bottom of the caatinga, with extreme water-table fluctuations in the sandy domes (Klinge 1978). Thus, parallel variation in nutrient and water availabilities exist in this area that are associated with soil characteristics and topography. Under such contrasting habitats, species-specific responses would be linked to particular conditions of the habitat at a local scale (Comita & Engelbrecht 2009, Engelbrecht et al. 2007). A number of studies in these habitats have shown that this is the case for soil fertility (Coomes 1997, Medina et al. 1990, Sobrado 2010, Sobrado & Medina 1980). Similarly, the hydraulic characteristics and long-term water use are species specific and related to particular conditions of the habitat at the local scale (Sobrado 2010). In this report, it was hypothesized that the leaf tissue water relations of species thriving in different habitats may reflect the water availability at the particular sites as well. The leaf tissue water relations of species thriving in the extreme nutrient and water-supply conditions of the sandy domes from the caatinga complex have been previously studied in detail (Sobrado 2009a). However, these data are currently not available for the species that thrive in the surrounding area of the closed forests, and importantly, such information would allow for a comparison across habitats. Therefore, the present study assessed the minimum leaf water potential (midday) under field conditions as well as the leaf tissue water relations by using pressure-volume analysis of dominant tree species in the top canopy of these high-stature forests.

A majority of Neotropical rain-forest trees have fruits evolved for animal consumption suggesting that seed-dispersal mutualisms are fundamental interactions structuring these ecosystems (Howe 1986, Howe & Smallwood 1982, van Roosmalen 1985). However, whether frugivores act as seed dispersers or predators of particular plant species is unknown for most tropical trees. Trees of the family Lecythidaceae are widespread in Neotropical rain forests forming an important component of the plant community (Aparecida Lopes 2007, Mori 1990, Mori et al. 2001, Sabatier & Prevost 1990), yet studies of plant–animal interactions are few (Jorge & Peres 2005, Silvius & Fragoso 2003, Trivedi et al. 2004). Results suggest that Lecythidaceae trees with zoochoric fruits are principally dispersed by bats, birds, rodents and primates (Prance & Mori 1983), although we know little about animal interactions with Eschweilera seeds.

Low germination and seedling survival probabilities are reported in various species of epiphytic bromeliad (Benzing 1978, Hietz et al. 2011, Toledo-Aceves & Wolf 2008, Winkler et al. 2005; but see Cascante-Marín et al. 2008). If germination and seedling survival are limiting factors in the life cycle, differential germination and seedling survival between species should be reflected in the relative abundance of established plants (Cascante-Marín et al. 2006, 2008) and in their presence or absence in secondary vegetation (Hietz et al. 2011), while differential germination within the tree would be expected to contribute to a heterogeneous distribution of established plants within the canopy (Hietz et al. 2011, Zotz & Vollrath 2002). Many factors influence the performance and distribution of epiphytes, including forest condition, disturbance type, distance from seed source, tree size and species, microclimate, epiphyte population dynamics and physiology (Cascante-Marín et al. 2009, Hietz et al. 2011, Valencia-Diaz et al. 2010, Zotz & Hietz 2001). In this study, we tested whether germination and seedling survival rates differ between the epiphytic bromeliads Tillandsia multicaulis Steud., T. punctulata Schldl. & Cham. and T. butzii Mez, and whether species abundance reflects the ability to germinate and survive as seedlings within the cloud-forest canopy. We also explore how morphological and physiological traits of the studied species can influence their early establishment.

In a range of systems, studies on mistletoe distribution on the host plant have documented a number of factors that affect their occurrence and spread (Aukema & Martinez del Rio 2002a, Bowie & Ward 2004, Overton 1996, Reid et al. 1995). These patterns can be determined by host specificity, environmental conditions, host plant characteristics (Martinez del Rio et al. 1995) and the movement patterns of dispersal agents (Aukema & Martinez del Rio 2002a, 2002b). In mistletoe plants, host choice can be considerably influenced by the advantages of interacting with relatively abundant hosts (Norton & Carpenter 1998, Norton & De Lange 1999). Besides the relative abundance of host species, characteristics such as branch size, age and height can have a strong effect on mistletoe attachment resulting in size-related mistletoe infection patterns (Overton 1994). Generally positive relationships between mistletoe infection and host size have been demonstrated worldwide (Donohue 1995, Martinez del Rio et al. 1996, Norton et al. 1997, Reid & Stafford Smith 2000) and they have been interpreted in terms of the preferences by dispersing birds to perch and feed in taller trees (Aukema & Martinez del Rio 2002a) and trees accumulating infections as they age (Overton 1994). Aukema & Martinez del Rio (2002a) reported more frequent perching in taller-than-average trees by the phainopepla (Phainopepla nitens), which is the principal disperser of the desert mistletoe Phoradendron californicum. Thus, visits by mistletoe-seed-dispersing birds, and therefore mistletoe seeds received, tend to increase with tree height (Aukema & Martinez del Rio 2002a). Using a simple metapopulation model, Overton (1994) predicted the frequency of parasitized trees to increase with host age. Therefore, assuming that size is a good proxy for age, large trees are likely to be more infected than smaller trees. Reid & Stafford Smith (2000), using experimentally disinfected trees, found that larger trees were disproportionately re-infected with mistletoes. This size–intensity relationship may be used to describe mistletoe infection patterns. However, several previous studies have shown size–intensity relationships to be weak (Aukema & Martinez del Rio 2002a, Donohue 1995, Overton 1994, Reid & Stafford Smith 2000). This indicates that other factors may be important in determining mistletoe infection intensity, including that already parasitized hosts of a specific height are more likely to receive seeds than non-parasitized hosts of the same height or dispersers are likely to be attracted to trees for reasons other than size (Aukema & Martinez del Rio 2002a).

Even though the full process of seed dispersal is the combination of movement mode and distance, deposition, successful germination and survival (Nathan 2006, Westcott et al. 2005), relatively few studies have documented the role of mammals as facilitators of germination and survival (Paine & Harms 2009). In particular, the effectiveness of large terrestrial mammals (>50 kg) as effective dispersers of large seeds is poorly known, but has been linked to the treatment of the seeds in their digestive system, the deposition of viable seeds in nutrient-rich environments (faeces) and favourable sites. Other aspects related to long-distance movements, defecation patterns and home-range size are frequently cited as factors that favour the deposition of seeds far from parent trees, which is expected to reduce predation and intraspecific competition, and enhance fitness (Schupp et al. 2002). We addressed these issues through a large-scale field experiment.

The marula (Sclerocarya birrea (A.Rich.) Hochst., Anacardiaceae) has a strongly lignified endocarp or stone which contains several seeds, each of which is within its own locule that is sealed by an individual operculum (Figure 1). The strong casing prevents germination, not by preventing the passage of water to the seeds, but by preventing oxygen from reaching the seeds (von Teichman et al. 1985). It is well known that marula fruits taken from the dung of the African elephant (Loxodonta africana Blumenbach) have more rapid germination than those that have not been eaten by elephants (Dudley 2000, Lewis 1987). This positive impact of elephants on marula germination continues to be considered to be through acid treatment in the digestion system of the elephant (Helm et al. 2011). We hypothesize that the primary mechanism which favours germination is mastication by elephants which physically loosens the opercula, rather than digestive dissolution of the stone. If true, the relevance of this is that only elephants would be the legitimate dispersers of marula seeds, because none of the many other species that are attracted to marula fruits would have jaws powerful enough to loosen the opercula.

Habitat fragmentation may affect essential ecosystem processes, such as pollination, causing negative effects on plants and pollinators (Aizen & Feinsinger 1994, Jennersten 1988, Lennartsson 2002, Liow et al. 2001, Murcia 1996). Effects of fragmentation on plant–pollinator interaction were evaluated in several studies (Aguirre & Dirzo 2008, Dauber et al. 2010, Dick 2001, Donaldson et al. 2002, Dunley et al. 2009, Fuchs et al. 2003, Ghazoul & McLeish 2001, Lopes & Buzato 2007). The Brazilian savanna, called cerrado, has been fragmented due in large part to extensive agricultural activity (Carvalho et al. 2009). Studies with the main objective of evaluating the influence of fragment size on ecosystem processes and on plant reproductive output has not been determined in cerrado. The plants of this type of vegetation seem to produce generally low number of fruits per flower (Gribel & Hay 1993, Munin et al. 2008, Ortiz et al. 2003). This may be due to the low soil fertility (Franco 2002, Haridasan 2000). But the recent fragmentation of this biome may reduce even more their plant reproductive success because it can increase the effect of pollination limitation and inbreeding caused by the habitat isolation and degradation.

Plants have an inherent flexibility to respond to different environmental conditions. One axis of plant ecophysiological strategy is seen in the spectrum of leaf functional traits. Flexibility in these traits would be suggestive of plants’ phenotypic plasticity in response to environmental changes. This research seeks to identify differences between leaves of sprout and non-sprout shoots of a broad ecological range of neotropical tree species. Using a functional-trait approach, this study assesses a large pool of species for within-species physiological flexibility. Leaf mass per area (LMA) and leaf area were measured for plants of sprout and non-sprout origin for 26 tree species grown in a reforestation plantation in Panama. Sprouts had a consistently lower LMA than non-sprouts, but there was no consistent pattern for leaf area. These trends show that sprouts are more like pioneer species than conspecific saplings, a finding in general agreement with fast sprout growth seen in previous studies. Further, later-successional (high LMA) species showed a greater reduction of LMA in sprouts. These results show that tropical tree species adjust physiologically to changing ecological roles and suggest that certain species may be more resilient than realized to changing climate and disturbance patterns.

Several species of non-venomous snake are known to flatten their heads when disturbed, and this behaviour has been suggested to be a mimicry of vipers (Arnold & Ovenden 2002, Hailey & Davies 1986, Young et al. 1999). Using plasticine models, Guimarães & Sawaya (2011) tested the antipredatory function of a triangular head shape in snakes. Their article presents the first published empirical experiment testing the adaptive significance of vipers' triangular head shape. Guimarães & Sawaya (2011) found no support for the viper mimicry hypothesis. Accordingly, they concluded that ‘the shape of [the] head seemed not to confer advantage itself’. Although the use of plasticine models is a generally accepted method of testing predation pressure on snakes, we argue that the experiment may have failed to find the antipredatory function of triangulation due to the pooling of attacks by mammalian and avian predators. Mammals generally rely on olfactory cues during foraging. Plasticine has a strong odour which does not resemble the odour of any prey species. It is thus unlikely that mammals would treat snake replicas as true snakes.

Palms are important components of tropical forest plant communities, due both to their abundance (Henderson et al. 2000) and to the network of interactions with their pollinators and dispersers (Henderson 2002, Zona & Henderson 1989). Forest fragmentation alters the biotic and abiotic conditions of habitats (Ewers & Didham 2006, Fahrig 2003) and it has been observed that Attalea palms increase their densities in disturbed sites (Aguiar & Tabarelli 2009, Andreazzi et al. 2012, Lorenzi et al. 2004). Increased light availability (Salm 2005, Souza & Martins 2004), changes in seed dispersal and predation patterns (Andreazzi et al. 2012, Pimentel & Tabarelli 2004, Wright et al. 2000), and ability to recover after disturbance (Souza & Martins 2004) are among the main mechanisms that have been proposed to explain enhanced palm densities. However, how altered conditions following disturbances influence the dynamics of flower and fruit production is still little understood.

The impact of hurricanes on tropical forests has been well documented in recent decades, with hurricane disturbance hypothesized to be a leading contributor to maintenance of the high diversity of trees in lowland tropical rain forests (Frangi & Lugo 1991, Vandermeer et al. 2000). Hurricanes have a heterogeneous impact both on landscapes and tree species (Liu & Fearn 2000, Walker et al. 1996). Damage to trees can take many forms, from leaf loss to stem snapping to uprooting, and is variable across the landscape due to topography, wind speed, direction and tree density (Walker 1995).

It has already been suggested that snake head triangulation might be related to mimicry of the head shape of vipers (Greene & McDiarmid 2005, and references therein). Until very recently, this hypothesis has never been experimentally tested. We first tested the hypothesis of snakes’ head shape as a dangerous signal to predators by use of plasticine models (Guimarães & Sawaya 2011). We suggested in that study that shape of the head does not confer advantage itself but may work in synergy with a set of traits including colour and behavioural displays that warn and discourage predator attacks.