Barn owl pellet content was studied on seven occasions over a 2-y period during which terrestrial small-mammal populations were assessed via a capture-mark-recapture (CMR) programme in a Sahelian agro-ecosystem of the Inner Delta of Niger River in Mali. Rodents (especially Mastomys huberti representing 78.5% of the total number of prey) were the major prey of the barn owl on all but one occasion, when bats were dominant. This exception coincided with the period of lowest abundance of M. huberti at the study site. Distribution of M. huberti prey into four age classes was assessed through analysis of tooth wear in remains from the seasonal pellet samples. Comparisons with age structure of the CMR population indicate that the barn owl tended to prey on smaller-than-average (thus younger) individuals, especially when these are rare in the population (non-reproductive period between June and October). The spectrum of prey consumed is compared with data previously reported in Sahelian Africa, showing for the first time in this region a major shift in prey choice by the barn owl when its preferred prey becomes rare. At the rodent population level, the apparent choice of younger M. huberti prey at some periods is interpreted in the light of our knowledge on population dynamics of the species in this habitat.

In equatorial regions, where tree rings are less distinct or even absent, the response of forests to high-frequency climate variability is poorly understood. We measured stable carbon and oxygen isotopes in anatomically distinct, annual growth rings of four Pericopsis elata trees from a plantation in the Congo Basin, to assess their sensitivity to recorded changes in precipitation over the last 50 y. Our results suggest that oxygen isotopes have high common signal strength (EPS = 0.74), and respond to multi-annual precipitation variability at the regional scale, with low δ18O values (28–29‰) during wetter conditions (1960–1970). Conversely, δ13C are mostly related to growth variation, which in a light-demanding species are driven by competition for light. Differences in δ13C values between fast- and slow-growing trees (c. 2‰), result in low common signal strength (EPS = 0.37) and are driven by micro-site conditions rather than by climate. This study highlights the potential for understanding the causes of growth variation in P. elata as well as past hydroclimatic changes, in a climatically complex region characterized by a bimodal distribution in precipitation.

The relative effectiveness of arboreal or terrestrial birds at dispersing seeds of Ormosia macrocalyx and O. bopiensis (Fabaceae: Papilionoideae) were studied in south-eastern Peru. Seeds of both species were either scarified, to represent seed condition after dispersal by terrestrial birds, or left intact, to represent seed condition after dispersal by arboreal birds. Seeds were distributed along forest transects, and germination, seedling development and mortality were monitored to determine the successes of the two groups at producing seedlings. Scarified seeds germinated with the early rains of the dry-to-wet-season transition, when erratic rainfall was interspersed with long dry spells. Intact seeds germinated 30 d later when the rain was more plentiful and regular. Intact seeds of O. macrocalyx gave rise to significantly more seedlings (41.1% vs. 25.5%) than did scarified seeds, in part, because significantly more seedlings from scarified seeds (n = 20) than from intact seeds (n = 3) died from desiccation when their radicles failed to enter the dry ground present during the dry-to-wet-season transition. Also, seedlings from scarified seeds were neither larger nor more robust than those from intact seeds despite their longer growing period. Results are consistent with the hypothesis that dispersal effectiveness of arboreal birds, at least for O. macrocalyx, is greater than that of terrestrial birds. Screen-house experiments in which seedlings developed under different watering regimes supported this result. Numbers of seedlings developing from intact and scarified seeds of O. bopiensis did not differ significantly.

Young snakes are rarely seen in the field and little is known about their habits, mostly because they are too small for radio-telemetry (the primary method for studying snake spatial ecology). However, the offspring of some larger species can be fitted with transmitters and we investigated the spatial ecology and habitat use of ten hatchling water pythons (Liasis fuscus: Pythonidae) in the floodplain of the Adelaide River, tropical Australia. Patterns of habitat use in the late wet season and during the dry season were similar to those of adults tracked in the same vicinity in an earlier study. Soon after release the young snakes moved to the floodplain, avoiding pasture areas. Diurnal refuge sites were typically in the base of grass clumps or below the soil surface, especially in sites with thick vegetation and deep, wide soil cracks. Adult snakes are more sedentary but move longer absolute distances (mean ± SE = 252 ± 50 m wk−1) than hatchlings (66.3 ± 41 m wk−1). However, hatchling snakes moved longer distances relative to body size (84.4 ± 1.1 body lengths wk−1) than did the previously studied adults (66.0 ± 1.1 body lengths wk−1). Mean and minimum body temperatures of the hatchlings were correlated with mean and minimum air temperatures, respectively.

Fragmentation of tropical forests influences abiotic and biotic processes that affect the genetic structure of plant populations. In forest fragments, edge effects, i.e. changes of abiotic and biotic factors at forest edges, may be prevalent. In two forest fragments (c. 200 ha at c. 2450 m asl) of tropical montane forest in Bolivia, sympatric populations of the dioecious tree species Clusia sphaerocarpa and C. lechleri were used as case study species to compare genetic diversity and small-scale genetic structure (SGS) between edge and interior habitats. Eight microsatellite markers were employed to genotype 343 individuals including adults, juveniles and seedlings of C. sphaerocarpa and 196 of C. lechleri. Genetic differentiation was found between habitats in both species (ΦRT = 0.071 for C. sphaerocarpa and ΦRT = 0.028 for C. lechleri) and among ages in C. sphaerocarpa (ΦRT = 0.016). Overall, SGS was weak but significant with more pronounced SGS in C. lechleri (Sp = 0.0128) than in C. sphaerocarpa (Sp = 0.0073). However, positive spatial genetic autocorrelation extended only up to 10 m. For C. sphaerocarpa, SGS was stronger in seedling and juvenile stages than in adults and in the forest interior than at forest edges. Our results show that edge effects can extend to the genetic level by breaking-up local genetic structures, probably due to increased gene flow and enhanced pollination and seed-dispersal interactions at forest edges.

Uncertainty about the H+ buffering capacity in tropical rain forest limits our ability to predict the future effect of anthropogenic deposition on the streamwater chemistry. Export of major ions to the stream and the ion-fluxes via rainfall, throughfall, litter-leachate and soil-water pathways were observed to examine the source of streamwater nutrients in a small catchment in Sabah, Malaysia. The streamwater and the ion-fluxes were measured for 3.75 and 2 y, respectively, by collecting water twice a month and setting ion-exchange-resin columns. Streamwater pH ranged from 6.5 to 7.6 and was not sensitive to water discharge controlling base cations. The NO3−-N, Ca2+ and Mg2+ fluxes were low in atmospheric depositions (0.6, 0.5 and 0.3 kg ha−1 y−1, respectively) and markedly increased in the litter layer. The NO3−-N flux decreased drastically from subsoil (70 kg ha−1 y−1) to the stream (1.4 kg ha−1 y−1) whereas the Ca2+ and Mg2+ fluxes were not different between subsoil (38 and 18 kg ha−1 y−1) and stream (30 and 15 kg ha−1 y−1). Neutral pH in tropical streams was mainly due to the base cation leaching with deep chemical weathering in deeper strata, and a rapid decrease in NO3− leaching from the subsoil to the stream.

The habitat distribution and relative abundance of 113 species of Gramineae were documented by releves in 82 stands near Conception, Santa Cruz, Bolivia. A factor analysis was used to compare the floristic similarity of stands situated in semideciduous forest, cerradao, cerrado, campo rupestre, valley-side campo, pantanal complex or on granite outcrops. Individual grass species usually had a preferred habitat and occurred with decreasing abundance in stands judged to be transitional by physiognomic, edaphic, and floristic criteria. Stands situated in cerrado vegetation were most similar to one another in grass species composition. Cerradao was transitional to semideciduous forest and cerrado but certain grasses were characteristic of this vegetation type. The floristic composition of the single campo rupestre locality was somewhat similar to cerrado; however, several of the more abundant grass species of this vegetation type did not occur in any nearby cerrado stand. Granite outcrops had a distinct grass flora and showed little similarity to other vegetation types. In savanna wetland communities, grass species distribution was influenced by water regime. Differences between stands on valley-side campo corresponded to topographic position on a gradient of increasing water surplus. Seasonally humid/dry stands on valley-side campo and pantanal complexes had a high degree of similarity. Stands lower on the catenary sequence of pantanal complexes and valley-side campos were increasingly dissimilar, a result of the different edaphic conditions of the seasonally flooded soils of pantanal complexes when compared with the permanently saturated (but never flooded) soils of valley-side campos. Pantanal complexes had the richest grass flora of all vegetation types because their microtopographic variability creates numerous micro-habitats with distinct water regimes, each supporting different grass species.

The dynamics of early life-history stages are important for understanding regional diversity patterns in tropical trees. In this study, patterns of seed removal, seedling survival and ectomycorrhizal (ECM) colonization in monodominant and mixed tropical rain forests in Guyana were investigated during a masting event of an ECM monodominant tree, Dicymbe corymbosa. Two seed densities (1 m−2 and 6 m−2) were tested in two forest types (monodominant versus mixed) with 10 plots per treatment (40 plots total). Germination success, seed and seedling survival after 1 y were measured for the monodominant tree, and four non-dominant canopy tree species found in both forest types (Eschweilera sagotiana, Licania laxiflora, Chrysophyllum sanguinolentum and Carapa guianensis). A significant effect of forest type was detected for seed removal and seedling survival. In the mixed forest, seed removal was higher for all species, with 27% average removal compared with 7% average seed removal in the monodominant forest. Germination success was significantly lower for all but one species in the mixed forest, with average germination of 41% compared with 78% germination in the monodominant forest. Seed and seedling survival of the monodominant tree was greatest within the monodominant forest with 93% of seeds germinating and 85% of seedlings surviving after 1 y compared with 65% germination and 15% seedling survival in the mixed forest. Per cent ectomycorrhizal colonization of Dicymbe corymbosa was near 100% in the monodominant forest, but significantly lower (14%) in the mixed forest. These results suggest that seedling survival patterns, rather than seed survival, are more important for recruitment success in this system and that ectomycorrhizal inoculum may limit establishment of Dicymbe corymbosa in the mixed forest.

The main interest in studying monodominant forests in the tropics (i.e. single-dominant forest sensu Richards 1996 and Connell & Lowman 1989) is that processes leading to monodominance may highlight mechanisms controlling species diversity (Hart et al. 1989). Among the various cases of monodominant forest (Hart 1990), the most intriguing are the rare ones that stand in contact with a considerably more diverse forest, without apparent environmental boundaries, and for many generations (i.e. type I sensu Connell & Lowman 1989). Rather than a single mechanism, it is likely that this type of monodominance results from a suite of interacting traits (Torti et al. 2001). This has been well illustrated for the neotropical tree Dicymbe corymbosa whose monodominance relies on: (1) ectomycorrhizal symbiosis (Henkel et al. 2002) linked to (2) mast fruiting (Henkel et al. 2005), (3) high seedling survival rate (Henkel et al. 2005, McGuire 2007a, 2007b) and, potentially, (4) slow litter decomposition (Mayor & Henkel 2006, McGuire et al. 2010), moreover, (5) the reiterative habit of D. corymbosa slows the gap dynamics, and reduces species richness (Woolley et al. 2008). Thus, a comprehensive understanding of monodominance may only emerge from the comparison of many case studies to point out shared mechanisms. Here, we report a new case of a monodominant species: Spirotropis longifolia (DC.) Baill.

Seedling growth under three shade levels was studied at Varanasi, India, for five tree species of tropical dry forest, which differed in life-history traits. Three of these were small-seeded pioneer (Albizia procera, Acacia nilotica and Phyllanthus emblica) and the other two were large-seeded non-pioneer (Terminalia arjuna and Terminalia chebula) species. Seedlings of all the species were subjected to three light levels (80–100%, 20–30% and 3–7% of full sunlight) comparable to sunlit gaps and shaded microsites in the dry forest. After 4 mo of shade treatment, height, basal area, biomass and other growth traits, viz. RGR (relative growth rate), NAR (net assimilation rate), and SLA (specific leaf area) were determined. Etiolation and plasticity indices were calculated. Reduction in seedling height, biomass and relative growth rates and enhancement in SLA due to shade was greater for small-seeded pioneer species. Seedlings from large-seeded non-pioneer species exhibited a stronger etiolation response to shade than seedlings from small-seeded species. Phenotypic plasticity indices for basal area, plant biomass and relative growth rate were greater for the three small-seeded early successional species (A. procera, A. nilotica and P. emblica), indicating their specialization in a more favourable light environment such as large gaps and forest peripheries. The non-pioneer and pioneer species differed only in the degree of shade tolerance, and we suggest that dry forest species cannot be strictly categorized into two distinct groups (shade tolerant vs. intolerant), rather shade preference and gap preference would be the more expressive terms. Marked environmental heterogeneity in terms of irradiance and the phenology of dry tropical trees permits coexistence of species of varying ecological traits, contributing to the maintenance of diversity in the dry forest.

To prevent seed losses from predation, plants have developed protective strategies. Seeds may utilize chemical or structural defences to deter predators. Mucuna holtonii (Fabaceae) has large seeds containing a toxic amino acid, L-dopa, and covered with a hard seed coat. Our study assessed the effectiveness of chemical and mechanical seed defences against vertebrate and invertebrate seed predators within Estación Biológica La Selva, Costa Rica. Pre-dispersal insect and fungus attack of M. holtonii seeds was low (95.7% of 1493 seeds were undamaged). Camera traps monitoring 90 marked M. holtonii seeds showed that the collared peccary (Pecari tajacu) consumed 98.6% of 69 removed seeds over 16 d. Field experiments involving 100 seeds with intact and 100 with opened seed coats found that only opened seeds had endosperm removed by Sericomyrmex amabilis ants (0.5–100% of endosperm removed). Shade-house experiments showed that seeds with high amounts of endosperm removed by ants resulted in low germination success and low seedling biomass production. Although M. holtonii seeds are rich in L-dopa, this compound is not an effective chemical defence against mammals that possess foregut fermentation. The seed coat of M. holtonii is an effective structural defence against invertebrate seed predators, preventing endosperm removal and enhancing seedling survival.

The factors that influence food choice have implications for animal survival, reproduction and population growth. We conducted a 1-y study of food choice by four mountain gorilla groups that consumed herbs and fruit at two locations differing spatially and temporally in food availability in Bwindi Impenetrable National Park, Uganda. We collected data on 45 important foods consumed by the gorillas, the availability of those foods in each gorilla group's home range and their corresponding nutrient and phenolic concentrations. Employing a linear multiple regression, we tested three hypotheses regarding the influence of food availability and the nutritional and phenolic concentrations of food on food choice. Regardless of changes in herb availability, the choice of herbs was positively influenced by their abundance and sugar concentrations and negatively influenced by their fibre, condensed tannin and protein concentrations. Furthermore, regardless of changes in fruit availability, the choice of fruit was positively influenced by its abundance and negatively influenced by its condensed tannin concentrations. During periods of low fruit availability, the gorillas did not increase the consumption of herbs high in fibre and sugar. The choice of herbs low in fibre had less of an influence on food choice at the location with lower fruit availability than the other location. Our results underscore the importance of incorporating both availability and nutrient concentrations into studies of food choice; by doing so we found Bwindi gorillas were able to choose abundant, relatively high-quality foods year round.

The land crab Cardisoma guanhumi populations have been on the decline in Puerto Rico for the last three decades. While some studies suggest overexploitation and pesticides as causing the observed population declines, the effect of land-use/land-cover (LULC) changes have not been investigated. In this study we compared the abundance and size of Cardisoma guanhumi in five different LULC types (mangroves, grasslands, forest, urban and industrial), and investigated the relationship between differences in physical microhabitat conditions among the LULC types with crab abundance and size. Although no significant differences in size were found among the different LULC types, crabs were significantly less abundant in grassland sites. Surface soil temperature, depth to groundwater and air temperature were found to vary significantly among the LULC types. Of these, only surface soil temperatures had a significant negative relationship with crab abundance. It appears that high variation in soil temperature and a high groundwater table observed in the grasslands is most detrimental to crabs. Interestingly, during the time when land crab populations declined there was corresponding change of LULC from agriculture to grasslands. Cardisoma guanhumi is resilient to changes in LULC, however, changes that alter their access to groundwater and escape from high soil temperature reduce their habitat.

Habitat loss and fragmentation are major threats to biodiversity worldwide, and little is known about their effects on bats in Africa. We investigated effects of forest fragmentation on bat assemblages at Kakamega Forest, western Kenya, examining captures at edge and interior locations in three forest fragments (Buyangu, 3950 ha; Kisere, 400 ha; and Malava, 100 ha) varying in forest area and human-use regimes. Basal area, canopy cover, tree density and intensity of human use were used as predictors of bat abundance and species richness. A total of 3456 mist-net hours and 3168 harp-trap hours resulted in the capture of 4983 bats representing 26 species, eight families and four foraging ensembles (frugivores, forest-interior insectivores, forest-edge insectivores and open-space insectivores). Frugivores were frequently captured at the edges of the larger, better-protected forests, but also in the interior of the smaller, more open fragment. Forest-interior insectivores and narrow-space foragers predominated in the interiors of larger fragments but avoided the smallest one. Forest specialists showed positive associations with forest variables (canopy cover, basal area and tree density), whereas frugivores responded positively to the human-use indicators. On these bases, specialist species appear to be especially vulnerable to forest fragmentation.

Biological N fixation by symbiotic micro-organisms plays a key role in making atmospheric N largely available to other organisms and nodule formation by rhizobia in roots of many legume species represents a very important pathway (Postgate 1998). Estimates of the contribution of symbiotic fixation to total N content in soils range from 44 to 200 Tg y−1 (Bøckman 1997).

The effects of precipitation regime on the size of soil carbon (C) pools were compared in mature tropical dry forests of the Yucatan Peninsula. Our study included three forest stands in each, a dry site (potential evapotranspiration ratio = 3.2 mm mm−1; mean annual precipitation = 537 mm), a wetter site (2.0 mm mm−1; 993 mm) and a site in which water was comparatively less limiting (1.3 mm mm−1; 1086 mm). At each site, soil C pools in dead fallen phytomass (includes leaves, flowers, fruits, small twigs and deadwood debris) deposited on the litter layer and in roots and organic matter of the mineral soil (from the upper 10 cm) were measured in samples collected during the dry season. A high proportion of the total C pool (93–95%) was in the top 10 cm of soil in all forest sites. The smallest C pool was in roots (1.8–2.4% of the total C), meanwhile the C in the litter layer represented 3–5% of the total pool. These patterns were observed irrespective of study site. However, distribution of C (i.e. wood debris vs. fine litter) varied across sites; the proportion of the forest-floor C pool in wood debris decreased from 80% in the driest site, to 51% and 42% in 993-mm and 1086-mm sites, respectively. Overall, we observed that three pools (wood debris, roots and soil organic C) provide evidence for the significant decrease in soil C storage with increase in mean annual precipitation in Yucatan Peninsula. A potential explanation for this unexpected pattern includes an increasing C turnover time with decreasing mean annual precipitation, resulting in higher C accumulation per unit of C input in the driest site.

To understand the population dynamics of a species, it is necessary to document the way in which its demographic behaviour varies through space and time. Anthropogenic disturbance, such as shifting cultivation, is an important factor causing demographic variation in many tropical non-timber forest products. The leaves of the palm Sabal yapa are an important non-timber forest product used for thatching by Mayan peoples. The demography of Sabal yapa was studied in three habitats (mature forest, successional forest and crop fields), representing successional phases along the slash-and-burn agricultural cycle in the Yucatan Peninsula. Matrix population models, along with elasticity analyses and life-table-response experiments were employed. Population growth rate differed between patches (MF: λ = 1.043; SF: λ = 1.027; CF: λ = 0.959). Only the λ value of the mature forest was significantly higher than unity. Fecundity and seedling survival were lowest in the crop fields and highest in the mature forest. The elasticity analyses and life-table-response experiments showed that entries with a high positive contribution to λ also showed high elasticity values, while those with a negative contribution to λ showed low elasticity. Thus, both analyses are crucial to understand the demography of a species and to aid in conservation and management practices.

Coppicing is an important regeneration mechanism in tropical dry forest after disturbance, but little is known about the long-term dynamics and the rate of recovery of the coppice shoots following clearance. This study reports on the growth and dynamics of coppice shoots following experimental cutting in a tropical dry forest in Jamaica. The fate of coppice shoots was tracked on a total of 481 stumps, representing 51 species over 10 y. The number of coppice shoots and the height and dbh of the leading shoots were measured on the tree stumps 14 mo and 10 y after cutting. Coppicing was vigorous for most tree species, but the average number of shoots per stump decreased significantly over the 9 y period, from 25 to 8 shoots per stump. The average height and diameter of the leading shoots after 10 y were 4.5 m and 3.8 cm, respectively, and the average percentage diameter recovered by the shoots varied between 36% and 95% among the species. Coppicing facilitates the long-term persistence of this dry forest, and the rapid growth of coppice shoots contributed to the resilience of most species after cutting.

Capture–mark–recapture methods were used to study the influence of density-dependent and density-independent factors on population dynamics of the spiny pocket mouse Heteromys desmarestianus in a lowland forest in Belize. Fourteen trapping sessions were conducted in six 0.5-ha grids at irregular intervals from July 2000 to March 2005. Responses by H. desmarestianus to four disturbance events depended on the type and magnitude of the events. Although fluctuations in density were strongly related to fruit availability, the disturbances tended to magnify direct and delayed density-dependent effects on reproduction and juvenile survival. A catastrophic flood in July 2000 eliminated the entire population, but by September 2001 population density had increased from 34.4 individuals ha−1 immediately pre-flood to 42.5 individuals ha−1. Indirect effects from a hurricane in October 2001 had greater and longer lasting influences on demographic rates than direct effects from less severe floods in August 2002 and September 2003. Fruiting ceased for almost 2.5 y after the hurricane, resulting in extremely low juvenile survival and a decline in density from 46.8 individuals ha−1 in January 2002 to 23.0 individuals ha−1 in January 2004. Fruiting began again in January 2004, and after several subsequent pulses of reproduction and generally higher rates of juvenile survival the population reached a maximum of 77.3 individuals ha−1 in March 2005. Inferences from the study, especially on the duration of delayed-density-dependent effects, must be made cautiously because of the irregular trapping intervals resulting from the unplanned disturbances. However, the results indicate that population dynamics of many tropical small-mammal populations will be driven by direct and indirect effects from density-independent events that amplify density-dependent influences on demographic rates.

Understanding how wood decomposition varies spatially at the mesoscale (between 1-ha plots) may improve carbon flux estimates in Amazonian forests. An experiment was carried out to test the influence of soil, slope, above-ground tree live biomass (biomass), fine-litter mass and characteristics of neighbouring trees on the variation of wood decomposition between 1-ha plots in four species of tropical trees that vary in wood density (Manilkara huberi – 0.86 g cm−3, Couratari guianensis – 0.54 g cm−3, Hura crepitans – 0.32 g cm−3 and Parkia pendula – 0.29 g cm−3). A wood sample from each species (30 × 5 × 2.5 cm) was placed in each of 71 plots within 64 km2 of terra firme tropical moist forest in Reserva Florestal Adolpho Ducke. One year later, samples were collected and weighed. The effects of specificity of decomposers was measured by the association of decomposition with the wood density and with the taxonomic group of the nearest tree with dbh ≥30 cm. Wood decomposition was independent of soil (texture and nutrients), slope, biomass and fine-litter mass at the mesoscale, except for C. guianensis, which showed greater decomposition in locations with greater biomass. Decomposition was also independent of wood density and taxonomic group of nearby large trees. In general, none of the variables was useful as a predictor of wood decomposition at the scale larger than 1 ha. Thus, the use of models that include soil and topography to improve estimates of carbon flux are limited because wood decomposition does not follow similar mesoscale patterns to that of biomass and fine-litter decomposition. Also, the results indicate that wood decomposition is more likely to be associated with generalist decomposers than with specialists associated with neighbouring trees.