Competition for food between Neotropical vultures in forest

Carcasses were provided at a gallery forest site in Venezuela to compare the feeding methods of four vulture species. Turkey Vultures or Lesser Yellow-headed Vultures were always the first species to arrive. Black Vultures were most likely to arrive at large carcasses or those in open situations and were the only species to form large feeding groups. King Vultures were equally likely to arrive at small or large carcasses. There were marked differences in feeding technique, food selection, rate of feeding and bill morphology between Turkey, Black and King Vultures, and the level of aggression between species was low compared to intra-specific aggression.     

Competition for water for the food system

Although the global agricultural system will need to provide more food for a growing and wealthier population in decades to come, increasing demands for water and potential impacts of climate change pose threats to food systems. We review the primary threats to agricultural water availability, and model the potential effects of increases in municipal and industrial (M&I) water demands, environmental flow requirements (EFRs) and changing water supplies given climate change. Our models show that, together, these factors cause an 18 per cent reduction in the availability of worldwide water for agriculture by 2050. Meeting EFRs, which can necessitate more than 50 per cent of the mean annual run-off in a basin depending on its hydrograph, presents the single biggest threat to agricultural water availability. Next are increases in M&I demands, which are projected to increase upwards of 200 per cent by 2050 in developing countries with rapidly increasing populations and incomes. Climate change will affect the spatial and temporal distribution of run-off, and thus affect availability from the supply side. The combined effect of these factors can be dramatic in particular hotspots, which include northern Africa, India, China, parts of Europe, the western US and eastern Australia, among others.     

Competition between species of the aestivo-autumnal group of birch pests for food in Transuralia

The aestivo-autumnal group of birch pests includes 25 species belong to the Notodontidae, Geometridae, Noctuidae, and other families. The larvae of all its species hatch out in mid-July and feed until the end of August. On emerging from the eggs they spread from leaf to leaf, but as the food supply diminishes they crowd together and competition is intensified. The species structure of the group shows some variation over the territory, and only a few species dominate, different species in different places. It is suggested that improvement in the food supply leads to mass reproduction. Biochemical investigations confirmed this hypothesis: different species feeding on the same leaf assimilate different amino acids more completely, and their relative numbers on the leaves vary in different parts and at different times. The composition of secondary metabolites important for resistance of the plants also varies.     

Landscape variation of liana communities in a Neotropical rain forest

We studied local and landscape variation of liana communities across habitats differing in soil and topography in the Lacandon tropical rain forest, southeast Mexico. All liana stems 1 cm diameter breast height (DBH) were sampled within each one of eight 0.5 ha plots. Two plots were sampled in each of the following habitats: alluvial-terrace, flood plain, low-hill, and karst-range. In the whole sampled area, we recorded 2092 liana stems ha^–1 representing a total basal area of 1.95 m² ha^–1 and 90 species within 34 families. Lianas showed a strong clumped spatial pattern and a high taxonomic diversity at the scale of 50 m². On average (± s.e.), we found 10.4±0.6 stems, 4.4±0.2 species and 3.4±0.2 families per 50-m² quadrat. Bignonaceae (19 species), Malpighiaceae (9), and Fabaceae (8) comprised about 40% of total number of recorded species, and almost 50% of the total liana biomass, as expressed by an importance value index that combines species relative abundance, spatial frequency and basal area. Nineteen families (56%) were represented by just one species and Cydista (Bignoniaceae) and Machaerium (Fabaceae) were the most diverse genera with four species each. In the landscape, lianas showed a geometric diversity-dominance relationship with only three species (Combretum argenteum, Hiraea fagifolia and Machaerium floribundum) accounting for more than 50% of total biomass. More than 30% of the species were rare (<15 stems ha^–1) and showed low spatial frequency (recorded in just one of the eight plots). Liana communities differed in structure and composition among sites and habitats. Among sites, lianas exhibited four-fold variation both in stem density and basal area and two-fold variation in species richness. Liana density was significantly and positively correlated with treefall disturbance. Ordination analysis indicated a strong habitat differentiation of lianas at the family and species levels. Most species with non-random distribution among habitats (69% from 25 species) were significantly most abundant in low-hill or flood plain sites, and some (12%) were preferentially found at the karst-range sites. The karst-range habitat was well differentiated from the others in species composition and structure, and shared only 50% of common species with other habitats.Soil water availability, treefall dynamics, as well as tree host identity and abundance may play an important role in the organisation of the liana communities at the Lacandon forest.     

The effect of food quality on breeding strategy in Griffon vultures (Gyps spp.)

Griffon vultures feed from the soft tissues of large mammal carcasses: a diet which contains very little calcium. Comparatively large amounts of calcium are required in order to breed, first for eggshell formation and then for bone mineralization of the chick. These requirements are estimated. Adults were not found to supply the chick with a mineral-rich crop secretion during rearing, but they must feed the young with calcium-rich food items, such as bone fragments. These are not abundant, and it is suggested that the mineral requirements for breeding have determined certain features of the breeding strategy in these birds—such as laying a single egg and having a prolonged rearing period.     

Contrasting above‐ground biomass balance in a Neotropical rain forest

Question: What are the relative roles of tree growth, mortality and recruitment in variations of above‐ground biomass in tropical forests? Location: Paracou, French Guiana. Methods: We quantified the contribution of growth, recruitment and mortality to total biomass of stands (trees DBH≥10 cm) in six 6.25‐ha permanent plots over 16 yr. Live biomass stocks and fluxes were computed for four separate size classes. Results: All plots showed increasing biomass stocks over the study period, with an average value of +0.9 Mg ha^?1 yr^?1. Plots aggrading biomass were characterized by either minor biomass losses due to mortality or substantial increases in the biomass of large trees (DBH≥60 cm). Conclusions: Within the study period, the rarity of mortality events could not counter‐balance the slow permanent increase in biomass, resulting in an apparent increase in biomass. Accounting for such rare events results in no net change in biomass balance.     

Spatial correlates of floristic and structural variation in a Neotropical wetland forest

Wetlands Ecology and Management - Despite the ecological importance of wetland forests, their classification is still unsatisfactory, partly due to insufficient knowledge about the environmental...     

Predictors of forest fragmentation sensitivity in Neotropical vertebrates: a quantitative review

Species' responses to tropical forest fragmentation are variable and not well understood. Species' functional traits might help to reveal patterns of fragmentation sensitivity and provide valuable guidance to conservation practice. On the basis of 30 reviewed studies published between 1997 and 2008, we present a quantitative analysis of 730 responses of Neotropical vertebrates to forest fragmentation and habitat loss in terms of Species' presence, abundance or fitness. Our intention was to identify possible ecological predictors of sensitivity to fragmentation, such as vertebrate group, feeding guild, forest dependency, and body size. We also controlled for methodology and study site characteristics, i.e. parameters studied, study design, study ID, and site ID. These ecological and methodological variables are frequently hypothesized to have an influence on reported fragmentation sensitivity. We conducted Linear Mixed Model analyses in order to relate the potential predictor variables to reported fragmentation effects. Model performance was assessed on the basis of AIC values. The best models included feeding guild, feeding guild+study design and feeding guild+forest dependency, respectively. We found that study ID and site ID significantly improved the models. Post‐hoc tests revealed that nectarivores, possibly herbivores, and species able to use open habitats were affected significantly less by forest fragmentation than others. We therefore conclude that Neotropical nectarivores that are able to use open habitats are less negatively affected by forest fragmentation. Furthermore, a study site's characteristics will always be crucial in explaining observed fragmentation effects.     

Competition for food between an introduced crayfish and two fishes endemic to the Colorado River basin

Synopsis Crayfish are not native to the Colorado River basin (CRB), however they are now established in portions of the mainstem and in many tributaries. I used density manipulation experiments in a laboratory setting to determine intra- and interspecific competition for food between Orconectes virilis, an aggressive polytrophic crayfish now common in the CRB, and two native fishes: Gila chub, Gila intermedia, and flannelmouth sucker, Catostomus latipinnis. I tested each fish species in separate trials. Growth of Gila chub decreased when animal densities increased, however they were more affected by intraspecific competition than by crayfish presence. In contrast, growth of flannelmouth suckers was more affected by crayfish than by intraspecific competition. Crayfish growth was not significantly altered by presence of either fish. Crayfish thus reduced fish growth by competition for food, but the effect differed markedly between the two species. An erratum to this article can be found at .     

Nested species subsets of amphibians and reptiles on Neotropical forest islands

Nested species subsets are a common pattern of community assembly characteristic of many types of fragmented landscapes and insular systems. Here we describe nested subset patterns of amphibian and reptile occupancy on 23 forest islands in north-eastern Bolivia. We used observed occupancy patterns to differentiate five distributional guilds: widespread species, rare species, poor colonizers, area-sensitive species and supertramps. Amphibian occurrences were nested along a forest island isolation gradient, and when species from each of the distribution classes were removed from subsequent analyses of nestedness, we found that dispersal-limited poor colonizers were responsible for the association between nestedness and isolation. Amphibians associated with the grassland matrix at the study site showed a nested pattern linked with area, although this pattern did not scale up to all amphibians and could not be unequivocally attributed to any of the distributional guilds we recognized. There were no strong associations between two biological characteristics, body size and relative abundance in the matrix, and the likelihood of occupancy along either forest island area or isolation gradients. The relative importance of isolation in shaping nested patterns of amphibians on these forest islands may be a result of either (1) the greater range in isolation values included in this study compared with many others; (2) the long time since isolation in this landscape, manifesting a footprint of isolation not apparent in more recently fragmented patches; (3) the relatively homogeneous grassland matrix surrounding forest islands that likely provides little refuge for animals moving among forest islands.     

Tree species composition and environmental relationships in a Neotropical swamp forest in Southeastern Brazil

We examined the relationships between topography, soil properties and tree species composition in a Neotropical swamp forest in southeastern Brazil. Plots were sampled in the forest, encompassing three different soil ground water regimes along the topographical declivity. All non-climbing plant individuals with trunk height >1.3 m were sampled. A canonical correspondence analysis—CCA—of the species–environmental relationships grouped tree species according to drainage and chemical soil conditions. A total of 86 species were found, being 77 species in the inferior, 40 species in the intermediate and 35 species in the superior topographic section. Some species were among the 10 most abundant ones, both in the overall sampled area and in each topographical section, with alternation events occurring only with their abundance position. However, substantial differences in floristic composition between sections were detected in a fine spatial scale, due to higher number of species, diversity index (H′) and species unique (exclusives) in the inferior topographic section. These higher values can be attributed to its higher spatial heterogeneity that included better drained and seasonally waterlogged soils, higher soil fertility and lower acidity. The increase of the soil water saturation and the uniform conditions derived from the superficial water layer has led to a lower number of species and an increase on the palm trees abundance in the intermediate and superior sections. Our results showed that at a small spatial scale niche differentiation must be an important factor related to the increase of the local diversity. The wide distribution of the most abundant species in the studied area and the increase of local diversity corroborate the pattern of distribution of species in larger scales of swamp forests, in which the most abundant species repeat themselves in high densities in different remnants. However, the floristic composition of each remnant is strongly variable, contributing to the increase of regional diversity.     

Feeding group responses of a Neotropical termite assemblage to rain forest fragmentation

Biomass collapse and its associated microclimatic stresses within recently isolated rain forest fragments may negatively affect species diversity of most resident taxa. However, for some decomposer organisms, increased resource availability via accompanying tree die-off may effect positive responses, at least for a time, with implications for rates of nutrient cycling and greenhouse gas release. This study investigates the early effects of forest fragmentation on a Neotropical termite assemblage. Numbers of encounters (surrogate for relative abundance) and species richness of wood and leaf-litter feeders, soil feeders, and the whole assemblage, were studied across true forest islands and mainland sites at a hydroelectric reservoir in French Guiana. Results showed no overall effect of fragmentation on either total termite encounters or species richness. However, numbers of encounters and species richness of wood and leaf-litter feeders showed positive responses to forest fragmentation. By contrast, soil feeders showed a negative response for numbers of encounters and no significant effect for species richness. Environmental data suggest that increased tree die-off, and other edge effects associated with biomass collapse, were underway at the time of sampling. Resulting increase in resource availability may therefore explain the positive influence on wood and leaf-litter feeders. A possible decrease in predation pressure from ants with decrease in island size was not tested for, but was a likely effect of the flooded matrix habitat. Fragmentation effects on soil feeder encounters may be due to the energetic and microclimatic constraints of feeding lower down the humification gradient of termite food substrates, but were not sufficient to affect species richness. The patterns revealed suggest that rates of wood decomposition following tree die-off, and of soil nutrient cycling, under different rain forest fragmentation scenarios, merit further study.     

Phylogenetic community structure during succession: Evidence from three Neotropical forest sites

The phylogenetic structure of communities can reveal forces shaping community assembly, but the vast majority of work on phylogenetic community structure has been conducted in mature ecosystems. Here, we present an analysis of the phylogenetic structure of three Neotropical rain forest communities undergoing succession. In each site, the net relatedness of the community is initially high and consistently declines during succession. This pattern is evident both when comparing plots of different age classes and when comparing stem size classes within each plot: the oldest plots and the youngest stem cohorts, representing the most advanced stages of succession, have the lowest relatedness. Our results suggest that succession leaves a distinct signature in the phylogenetic structure of communities, which may reflect an increasing role of biotic interactions in community assembly during succession. We discuss theoretical explanations for the decline in community phylogenetic relatedness during succession, and suggest directions for future study.     

Differentiation between Neotropical rainforest,dry forest,and savannah ecosystems by their modern pollen spectra and implications for the fossil pollen record

Accurate differentiation between tropical forest and savannah ecosystems in the fossil pollen record is hampered by the combination of: i) poor taxonomic resolution in pollen identification, and ii) the high species diversity of many lowland tropical families, i.e. with many different growth forms living in numerous environmental settings. These barriers to interpreting the fossil record hinder our understanding of the past distributions of different Neotropical ecosystems and consequently cloud our knowledge of past climatic, biodiversity and carbon storage patterns. Modern pollen studies facilitate an improved understanding of how ecosystems are represented by the pollen their plants produce and therefore aid interpretation of fossil pollen records. To understand how to differentiate ecosystems palynologically, it is essential that a consistent sampling method is used across ecosystems. However, to date, modern pollen studies from tropical South America have employed a variety of methodologies (e.g. pollen traps, moss polsters, soil samples). In this paper, we present the first modern pollen study from the Neotropics to examine the modern pollen rain from moist evergreen tropical forest (METF), semi-deciduous dry tropical forest (SDTF) and wooded savannah (cerradão) using a consistent sampling methodology (pollen traps). Pollen rain was sampled annually in September for the years 1999–2001 from within permanent vegetation study plots in, or near, the Noel Kempff Mercado National Park (NKMNP), Bolivia. Comparison of the modern pollen rain within these plots with detailed floristic inventories allowed estimates of the relative pollen productivity and dispersal for individual taxa to be made (% pollen/% vegetation or ‘p/v’). The applicability of these data to interpreting fossil records from lake sediments was then explored by comparison with pollen assemblages obtained from five lake surface samples.Pollen productivity is demonstrated to vary inter-annually and conforms to a consistent hierarchy for any given year: METF > SDTF > cerradão. This suggests an association between pollen productivity and basic structural characteristics of the ecosystem, i.e. closed canopy vs. open canopy vs. savannah. Comparison of modern pollen and vegetation revealed that some important floristic elements were completely absent from the pollen: Qualea and Erisma (METF), Bauhinia, Simira and Guazuma (SDTF), and Pouteria and Caryocar (cerradão). Anadenanthera was found to be abundant in both the pollen and flora of SDTF (p/v = 3.6), while Poaceae was relatively poorly represented in cerradão (0.2). Moraceae, Cecropia and Schefflera were found to be over-represented palynologically in all ecosystems. Overall, the data demonstrated that no one taxon could be used as a definitive indicator of any of the ecosystems. Instead, associations of taxa were found to be important: METF = Moraceae (> 40%), Cecropia, Hyeronima, Celtis; SDTF = Anadenanthera, Apuleia, Ferdinandusa and non-arboreal Asteraceae, Bromeliaceae, Piper and fern spores; cerradão = Poaceae, Myrtaceae, Borreria, Solanum plus Asteraceae and fern spores. Interpretation of Poaceae pollen was highlighted as problematic, with relatively low abundance in the cerradão (< 20%) in comparison to high abundance in lake environments (c. 30–50%). Re-examination of fossil pollen records from NKMNP revealed that modern vegetation associations were only established in the last few thousand years.     

Population structure and mitochondrial DNA variation in sedentary Neotropical birds isolated by forest fragmentation

The current worldwide concern about tropical deforestation raises questions about the sustainability of avian populations in isolated forest fragments. One of the most important issues concerns the sizes of forest fragments necessary to maintain populations and the genetic variation within them. We address this by: (1) using mtDNA sequence variation to infer aspects of the population structure of four species of understory birds from four sites in southern Costa Rican rainforest; and (2) determining whether forest fragmentation that has occurred in the last 50 years has had an effect on the amount of within-population variation for the species in question. High levels of between-population differentiation (D_xy) were found over a relatively small geographic scale (<130 km) for white-breasted wood-wren (Henicorhina leucosticta), bicolored antbird (Gymnopithys leucaspis), and gray-headed tanager (Eucometis penicillata), suggesting that these species are highly sedentary and exhibit strong female philopatry. No mtDNA variation was found in Plain Antvireo (Dysithamnus mentalis). In all three of the polymorphic species there was a significant decrease in mtDNA nucleotide diversity in populations isolated by forest fragmentation as compared to populations in contiguous primary forest. Even in relatively large (250–1000 ha) forest reserves, sedentary avian species have lost roughly half (range 43–85) of the nucleotide diversity in mtDNA over a relatively short period of time. Our results indicate that sedentary avian species in forest fragments isolated by clearing have undergone severe reductions in effective population size due to population bottlenecks perpetuated by prolonged isolation and potential edge effects.     

Complex evolutionary history of a Neotropical lowland forest bird (Lepidothrix coronata) and its implications for historical hypotheses of the origin of Neotropical avian diversity

Here we apply a combination of phylogeographic and historical demographic analyses to the study of mtDNA sequence variation within the Blue-crowned Manakin (Lepidothrix coronata), a widespread Neotropical bird. A high degree of phylogeographic structure allowed us to demonstrate that several vicariant events, including Andean uplift, the formation of riverine barriers, and climatically induced vegetational shifts, as well as a non-vicariant process, range expansion, have all acted, at varying spatial and temporal scales, to influence genetic structure within L. coronata, suggesting that current historical hypotheses of the origin of Neotropical avian diversity that focus on single vicariant mechanisms may be overly simplistic. Our data also support an origin (>2 mybp) that is substantially older than the late Pleistocene for the genetic structure within this species and indicate that phylogeographic patterns within the species are not concordant with plumage-based subspecific taxonomy. These data add to a growing body of evidence suggesting that the origin of several Neotropical avian species may have occurred in the mid-Pliocene, thus, geological arguments surrounding putative Pleistocene vicariant events, while interesting in their own right, may have little relevance to Neotropical avian diversification at the species level.     

Hydrogeomorphology and river impoundment affect food-chain length of diverse Neotropical food webs

Food-chain length is a central characteristic of ecological communities that affects community structure and ecosystem function. What determines the length of food chains is not well resolved for most ecosystems. Herein, we examine environmental correlates of food-chain length based on the productivity hypothesis, compare food-chain lengths among aquatic ecosystem types and identify bi-directional effects of river impoundment on food-chain length in the Paraná River Basin of South America. Both temperature regime, a surrogate of productivity, and ecosystem type significantly affected food-chain length in independent analyses. However, when analyzed together, only ecosystem type explained significant variation in food-chain length. Food chains were longest in reservoirs, and shortest in high-gradient rivers. The proximate mechanism driving this pattern appears to be body-size ratios of primary consumers to apex predators, which differ among trophic pathways. Food chains based on phytoplankton production may have an additional size-structured link not present in food chains based on other basal sources such as detritus and algae. Hydrogeomorphology is the ultimate mechanism influencing food-chain length because it affects the relative importance of basal carbon sources supporting higher trophic levels, which through differences in the number of trophic links along the different size-structured pathways, appears to drive the observed patterns in food-chain length. We discuss a hypothesis of food-chain length that integrates energy flow and size-structure, facilitates inclusion of temporal dynamics and which is readily testable in both 'closed' and 'open' ecosystems.     

Competition between phenotypes

Summary We present two models for phenotypic-dependent interspecific competition. In both cases the survivorship of individuals of one population depends on the entire phenotypic distribution of the other species. The first model considers a continuously varying metric trait, with assortative or random mating; the second model examines a character controlled by two alleles at a single locus. Pursuing the notion that each population maximizes its mean fitness we define a vector-optimum strategy using the concepts of cooperative and competitive optima. It is found that the dynamical constraints placed on the equations of motion by Mendelian genetics often prevent a population from evolving to a strategic optimum. However, for the single locus case with complete dominance, the competitive optimum always coincides with some dynamical equilibrium on the Hardy-Weinberg manifold.     

Balancing food production and nature conservation in the Neotropical dry forests of northern Argentina

The growing human population and the increase in per capita food consumption are driving agriculture expansion and affecting natural ecosystems around the world. To balance increasing agriculture production and nature conservation, we must assess the efficiency of land‐use strategies. Soybean production, mainly exported to China and Europe, has become the major driver of deforestation in dry forest/savanna ecosystems of South America. In this article we compared land cover patterns (based on satellite imagery) and land‐use and human population trends (based on government statistics) in regions with two contrasting development pathways in the Chaco dry forests of northern Argentina, since the early 1970s. The area (ca. 13 million hectares) includes one of the largest continuous patches of tropical dry forests and has experienced rapid land‐use change. In the region where land use has been driven by government‐sponsored colonization programs, the expansion of extensive grazing has led to a growing rural population, low food production, and widespread environmental degradation. In contrast, in the region dominated by market‐driven soybean expansion, the rural population has decreased, food production is between 300% and 800% greater, and low‐density extensive cattle production has declined over extensive remaining forested areas, resulting in a land‐use trend that appears to better balance food production and nature conservation.