Some aspects of the ecology of bagrid catfishes in River Ase, southern Nigeria were studied for a period of two years. Nine species of Bagridae were recorded and these accounted for 15.0% of the number and 24.4% of the weight of all fish captured. Chrysichthys nigrodigitatus and Chrysichthys auratus longifilis were the principal species. C. nigrodigitatus was a rainy season species, while C. auratus longifilis was abundant in both dry and rainy seasons. Both species showed a major peak in catches between 0600 and 0900 h. C. nigrodigitatus exhibited a minor peak in catches between 1500 and 2100h, while C. auratus longifilis showed a minor peak between 1500 and 1800h. The spatial distribution of C. nigrodigitatus and C. auratus longifilis populations was heterogeneous. Bagrid fishes were an important component in the fish yield of the study river and its species composition has been compared with those of other Nigerian waters. The distribution and abundance of C. nigrodigitatus and C. auratus longifilis are discussed in detail.

Species co-occurrence is an important ecological research area. Mark-and-recapture studies of mammals allow identification of coexisting species, a necessary step in determining mechanisms enabling habitat sharing. Using data from five 1-ha grids in January 2004 in tropical dry deciduous forest of coastal Colima, Mexico, we detected significantly more interspecific overlap than expected between seven species pairs. Oryzomys couesi shared more stations than expected with Sigmodon mascotensis, Baiomys musculus and Peromyscus perfulvus. Baiomys musculus was associated positively with S. mascotensis and Reithrodontomys fulvescens. Heteromys pictus shared fewer stations than expected with O. couesi and S. mascotensis. For species collectively, there was non-random community structuring, with two grids displaying more species aggregation than expected. While two grids had non-random co-occurrence patterns, three grids did not differ from random, which differs from that reported for mammalian taxa on average. Other small-mammal studies have documented species segregation, while this study detected more positive than negative associations. Similarities in preference and habitat use (or diet) are likely explanations for interspecific overlap patterns at stations and co-occurrence patterns among grids. Simultaneously evaluating associations of species pairs and all species on a grid collectively is novel methodology as applied to mammals, adding to understanding of species co-occurrence.

Most researchers assume litter decomposition to take place at the site where litterfall occurs, mostly by soil micro-organisms and microfauna of less than 1 mm in size. Accordingly, the litterbag method has become the standard technique for evaluating litter decomposition rates (Schlesinger 1985, Wedderburn & Carter 1999). However, there is evidence indicating that at least in tropical arid ecosystems litter can be removed from the site in substantial amounts by animals, including large vertebrates. For example, litter is removed for forage or as building material for nests by ants (particularly leaf-cutting ants) and termites (Bucher 1982, Scholes & Walker 1993). Moreover, ruminant species (including domestic cattle and goats) supplement their food intake by feeding on falling leaf litter during the dry season in African savannas (Owen-Smith & Cooper 1987) and in the Chaco savannas of Argentina (Morello & Saravia-Toledo 1959). These observations suggest that litter removal may be an important component of the decomposition process, particularly in tropical semi-arid environments where lack of soil moisture decreases microbial activity, increasing litter availability for herbivores.

A new technique for estimation of tree species richness in tropical forests was developed and tested in this study. The missing species extrapolation technique is based on the assumption that the rate of accumulation of new species with increasing area is the same within sampled and unsampled areas of similar habitat within a region. This new technique was tested on four 1-ha sites of subtropical moist forest in Rio Bravo, Belize for which complete species counts of trees ≥10cm dbh are available. Estimates given by the technique are 115, 98, 93 and 106% of the actual species counts within the four sites. The accuracy of these estimates was found to be equal to or better than most others obtained by using existing methods of extrapolation. The missing species extrapolation technique was also applied to a 21-ha riparian forest patch in the Mountain Pine Ridge, Belize, where it was used to obtain an estimate of the number of tree species ≥10cm dbh in the entire patch.

The fire regime is essential in creating a mosaic of plant structure and diversity in South American open savannas, especially favouring herbs. However, studies investigating diversity patterns in Neotropical savannas rarely focus on the herb–subshrub layer. This study investigated the variation of the herb–subshrub layer under contrasting fire regimes in the most conserved site within the Cerrado Domain, the Jalapão region, Brazil. We selected four sites of open savanna physiognomy with similar topographic, climatic and edaphic features: three burned every 2 years, while the fourth site has remained unburned for at least the last 10 years. We randomly distributed 15 plots of 4 m2 in each site and identified all herbs and subshrubs in each plot to estimate density, richness, alpha diversity and species composition. The unburned site had lower herb–subshrub density, richness and diversity than the frequently burned sites. Species composition varied between frequently burned and unburned sites, partially explained by the fire frequency across sites. Although other ecological factors may explain the patterns detected, we cannot rule out the importance of fire in structuring plant communities in the Jalapão region. As in other savannas, our study in the Cerrado Domain reinforces the essential role of the fire regimes in modifying and maintaining the diversity of herbaceous plants at the landscape scale.

The energy budget of all fish populations was estimated in two small tributaries of the Paraná River (Paraná, Brazil). Total energy consumed by fish in the Caracu and the Agua do Rancho Rivers was 4.1 and 1.8 MJ m−2 y−1, and food items consumed were 2284 and 994.5 g wet weight m−2 y−1, respectively. The gross (K1) and net (K2) ecological efficiency coefficients were very low, but 43.2 and 59.6% of the total fish diet in these two streams, respectively, consisted of plant detritus. In both fish communities, omnivorous (opportunist) species dominated and specialists were rare. Although the Caracu River was more affected by human activity than was the Agua do Rancho, ecological efficiency coefficients calculated for the dominant fish populations were not significantly different.

Dioecious plant populations have generally been considered to maintain sex ratios of 1:1 (Allen & Antos 1993, Carroll & Mulcahy 1993, Charnov 1982). The sex ratio does, however, change if the plants are growing in a stressful environment, often being male-biased under these conditions (Ortiz et al. 1998, 2002). This pattern has been explained by differences in how the sexes resolve their respective energy requirements (Obeso et al. 1998). Females generally assign more resources to reproduction in comparison to growth and maintenance than do males, and they are smaller and longer-lived (Allen & Antos 1993, Nicotra 1999, Obeso et al. 1998, Willson 1983). Thus their higher reproductive costs take a toll on females, modifying the population sex ratio in favour of males (Allen & Antos 1993, Lovett-Doust & Lovett-Doust 1988). However, in order to determine the reproductive cost it is necessary to consider the compensatory mechanisms (Obeso 2002). These reduce the reproductive cost and include plastic response in terms of plant architecture and plant physiology. For example, nutrient resorption is a process that may help decrease dependence on nutrient intake, thereby constituting an important nutrient economy mechanism that can also reduce the reproductive cost if a significant proportion of the nutrients had been reassigned to reproduction (Killingbeck 1986, Obeso 2002).

Phosphorus uptake by grass species from natural South American grasslands can change depending on root and leaf attributes capable of determining higher, or lower, relative growth rate. The aim of the current study is to investigate whether leaf and root attributes capable of determining leaf and root area production in native C4 grass species Axonopus affinis and Andropogon lateralis are related to higher relative growth rate (RGR), P uptake capacity (maximum P influx; Imax) and concentration. Species grown in 2-litre pots with added nutrition solution were subjected to two treatments, namely 5 μM P l−1 and 30 μM P l−1. Solution aliquots (10 ml) were collected for 30 hours at the end of the study to determine P concentrations. RGR was 3.6 and 2.8 times higher in A. affinis than in A. lateralis in treatments with 5 μM P and 30 μM P. Axonopus affinis recorded the highest P concentration in leaf tissue. This outcome was associated with Imax 85% higher in A. affinis. High RGR was associated with larger leaf and root surface area per dry mass unit, as well as with high P influx capacity and with higher affinity transporters. These species often prevail in areas accounting for greater natural fertility and are more responsive to phosphate fertilization.

Animals must eat, necessitating their encounter with food. At least one of the two, predator or prey, must move for the two to meet. Many predators forage for prey by one of two strategies, or foraging modes. They forage either actively, in which case their prey may be mobile or sessile, or passively by waiting in ambush, depending on prey motility. These two foraging modes have been studied extensively in lizards as a model organism (Cooper 1995, Huey & Pianka 1981, Pianka 1966, Pietruzska 1986). Many aspects of a species' biology are correlated with its foraging mode. For example, active foragers employ their chemosensory apparatus for following the prey's trail. Sit-and-wait foragers rely on their eyes to identify approaching prey (Cooper 1995). Other differences are briefly referenced elsewhere (Werner et al. 1997, 2004).

Mimosa luisana is functionally important in the Tehuacán-Cuicatlán Valley, Mexico, since it is able to create favourable microsites for the establishment of other plant species. The endozoochory of M. luisana seeds by goats was evaluated in terms of excrement deposition pattern, seed survival and germination. The excrement deposition pattern was evaluated by collecting pellets in four plots of 25 × 2 m randomly placed in a grazing area and recording the microhabitat where pellets were found. Seed survival and germination were evaluated by feeding the goats with seeds and collecting dung pellets at 8-h intervals for 80 h. Seeds from goat pellets (treatment) and seeds collected from pods (control) were placed in a germination chamber for 24 d. Goats mainly deposited M. luisana seeds in viable sites (open areas) for growth. Mimosa luisana seeds survived the goat digestive treatment (5.91% ± 2.86%) and most of them (67% ± 25.9%) were recovered 8–32 h after ingestion. Goat gut treatment increased M. luisana final germination (47.5% ingested, 5.83% control) and shortened initial and mean time of germination. Our results indicate that goats may be an efficient disperser of M. luisana seeds.

Flowers of Aphelandra sinclairiana have features of flowers pollinated by hermit humming-birds (long corollas) and of those pollinated by territorial humming-birds (dilute nectar, clustered distribution). Flowers in large clumps at the peak of the blooming season were pollinated by two territorial humming-birds, but at the end of the season or in isolated plants the main avian pollinator was the non-territorial hermit Phaethornis superciliosus. Visits by avian nectar thieves were more frequent at high flower densities. The reproductive output of inflorescences was similar at different levels of flower aggregation. Aphelandra flowers in large clumps could exchange pollen with extraterritorial plants because territorial humming-birds did not completely exclude pollinating hermits. The commonest nectar thief at high flower aggregations was the passerine Vermivora peregrina, the second most common nectar thief was the hermit Phaethornis longuemareus.

Necrophagous Diptera were sampled in a seasonal tropical mixed forest in Hong Kong from February 1985 to May 1986 using carrion-baited traps. Six families of flies were caught but only Calliphoridae, Muscidae and Sarcophagidae were considered. They made up a total of 14,669 flies of 21 species in the sample. Total species abundance followed Fisher's log-series distribution. The commonest five species were calliphorids, constituting 79.44% of the total combined catch. Temperature was apparently the main factor affecting seasonality of necrophagous Diptera in Hong Kong. Fluctuations in total abundance, species richness and H' followed seasonal changes in weekly mean air temperatures.

Analysing phenological diversity of tropical trees provides a potential tool to detect climate change effects and devise forest management options. In this study, the leaf phenological activity of 28 dominant tree species in a moist sub-tropical hill forest of north-eastern India was examined for a period of 2 years and related to functional traits (i.e. leaf mass per area (LMA) and wood density (WD)). The peak phase of leaf fall occurred in the cool dry period (November to January) with leaf flush peaking in the pre-monsoon period (February to March), but variation was found between species as influenced by their phenological strategy, i.e. evergreen, leaf-exchanging or deciduous (<4 months leafless). Photoperiod and minimum temperature were the environmental factors most strongly correlated with phenological activity, and the synchrony index within species for both phenophases was 0.81. LMA was less in the deciduous species compared with the evergreen species, whereas WD did not differ. LMA was negatively correlated with the length of deciduousness as well as timing of leaf flush and fall indicating that LMA may be more important than WD in influencing phenological patterns in this forest. The study revealed that the phenological diversity of tropical trees is related to changes in environmental variables and has implication for forest management under changing climate. Further study will help in understanding the phenological response of trees to climatic factors and their potential future changes.

Southern pine beetles (Dendroctonus frontalis Zimmermann) and symbiotic fungi are associated with mass mortality in stands of Caribbean pine (Pinus caribaea Morelet). This study provides a 12.7-year assessment of semiochemical mediation between southern pine beetle and Caribbean pine in relation to concentrations of 4-allylanisole (estragole, methyl chavicol) and monoterpenes measured by gas chromatography–mass spectrometry in different seasons in premontane and coastal pine stands of Belize and Guatemala. Individual trees and stands with >2.5% (relative mass %) of 4-allylanisole in the xylem oleoresin exhibited significantly less beetle-induced mortality than those with <2.5%. Changes in relative levels of 4-allylanisole and monoterpenes during this study are consistent with seasonal temperature and cumulative water deficit effects and suggest bark beetle attack of P. caribaea may intensify in the future.

The importance of deterministic and stochastic processes in structuring ecological communities is an enduring debate. Although this debate is nearly a century old, the extent to which communities are structured by species interactions or chance events is a central issue in ecology. We examined the assemblages of plants living inside 119 birds’ nest ferns (Asplenium goudeyi), which are endemic to Lord Howe Island. Specifically, we investigated whether patterns of species richness and community composition were influenced by fern size, fern isolation and plant dispersal abilities. Fern size and fern isolation significantly predicted plant community richness. At the community level, plant composition patterns did not deviate from randomized expectations. Individual species occurrences increased with increasing community richness, and no species exclusions were observed. Wind-dispersed taxa, which accounted for 29% of all species, were well represented in isolated ferns. Comparatively, poorer dispersers were confined to ferns nearest the forest at the base of the cliffs. We suggest that dispersal plays a key role in structuring plant communities living within birds’ nest ferns, and that species interactions are less important. Our study emphasizes the importance of epiphytes with a nest-like growth form as habitat for plants in a harsh environment.

Polymorphism is common in nature, but few Heliconius species are polymorphic for wing colour patterns. Eastern Brazil H. erato phyllis populations are polymorphic for hindwing elements (red raylets) and studies suggest that trait distribution varies seasonally. We carried a 3-y sampling to evaluate the hypothesis that season, wing length and pollen foraging were associated with morph diversity. Individual phenotypes were scored with regards to number of red elements in the dry and in the wet seasons. Co-mimic H. melpomene nanna was also analysed. We scored 432 H. erato and 513 H. melpomene. Our results confirm polymorphism in H. erato, with individuals showing from one to eight elements, with a mode between five and six. We found that H. melpomene is polymorphic for red dots, varying from two to five (mode = 2). Red basal dots were mostly invariant in H. erato. Even though we found a seasonal change in pollen loads, we found no association between individual phenotypes and season, pollen load scores, or wing length. We reject the hypothesis of ecological correlates of morph frequency, and suggest that trait colour variation in the two species is linked to and constrained by effects on mate recognition.

To investigate the influence of forests and agroforestry systems on fruit consumption by birds, we studied two landscapes, one covered predominantly with forests and the other dominated by traditional shade cocoa plantations. In each landscape, we sampled three forest fragments and three shade cocoa plantations. We placed 15 artificial fruits in 25, 1–2-m-tall shrubs spaced every 50 m and evaluated the detection and consumption of fruits after 72 h. We used hemispherical photographs positioned above each fruit station to evaluate canopy openness. We found a statistically significant difference in fruit consumption between landscapes, which means that more fruits were detected and consumed in the forest-dominated landscape. However, forests and shade cocoa plantations within each landscape exhibited similar fruit consumption. Canopy openness was similar between the landscapes, however, the cocoa plantations exhibited greater canopy openness than forests. The results of this study reinforce the importance of the presence of forests in the agricultural landscape. Thus, to evaluate the capacity of agroforest to protect species and maintain ecological interactions it is also necessary to consider the landscape context.

Staminodes are sterile stamens that produce no pollen, exhibit diverse structures and perform various functions. Flowers of Phanera yunnanensis possess three fertile stamens with large anthers and long filaments, and seven staminodes with tiny anthers and short filaments. To investigate the adaptive significance of staminodes in this species, we studied effects of staminode removal on pollen removal and deposition, flower visitation rate and fruit set in Xishuangbanna, south-western China. Four species of nectar-foraging pollinators visited flowers, mostly Amegilla zonata and Apis cerana (2.80 ± 0.15 and 1.76 ± 0.41 visits h−1 per flower, respectively). Staminode removal did not affect fruit set, but increased visitation by A. cerana by 2.6-fold, reduced visitation by A. zonata by 68% and increased the pollen removal rate for both pollinators (all effects were significant). Staminode removal significantly reduced pollen deposition rate for A. zonata, but not for A. cerana. These results suggest that the staminodes of P. yunnanensis filter which insects act as pollinators and affect pollen removal and deposition rates. By reducing pollen removal rates, staminodes may implement a pollen-dispensing schedule that spreads pollen dispersal from individual flowers over multiple pollinators. By altering pollen deposition rates, staminodes may influence reproductive fitness in other ways.

Ants (Hymenoptera: Formicidae) are important predators of herbivorous insects on plants (Rosumek et al. 2009). Ant removal or absence may result in negative indirect effects on plants, as herbivore abundance and herbivory increase and plant growth and reproduction decline (Rosumek et al. 2009, Schmitz et al. 2000). Ant presence on plants often results from a mutualistic interaction. For example, strong highly coevolved ant–plant mutualisms are found on myrmecophytic plants that house ants in domatia (specialized nesting sites). Weaker mutualistic associations are found with myrmecophilic plants that only offer extra-floral nectaries (EFNs) or food bodies to attract ants, or on other plants hosting honeydew-producing hemipterans (indirect ant–plant interactions) that mediate ant abundance (Hölldobler & Wilson 1990). However, in most cases, plants and arboreal ants form more passive associations, where ants nest in the natural cavities of branches or bark, or construct carton nests on plant substrates (Hölldobler & Wilson 1990) and the only reward plants offer these ants is the use of their substrates. In these situations the indirect effect of ants on plants is merely by chance, a byproduct of ant presence (byproduct association).