Variation in wood density determines spatial patterns inAmazonian forest biomass

Uncertainty in biomass estimates is one of the greatest limitations to models of carbon flux in tropical forests. Previous comparisons of field‐based estimates of the aboveground biomass (AGB) of trees greater than 10 cm diameter within Amazonia have been limited by the paucity of data for western Amazon forests, and the use of site‐specific methods to estimate biomass from inventory data. In addition, the role of regional variation in stand‐level wood specific gravity has not previously been considered. Using data from 56 mature forest plots across Amazonia, we consider the relative roles of species composition (wood specific gravity) and forest structure (basal area) in determining variation in AGB. Mean stand‐level wood specific gravity, on a per stem basis, is 15.8% higher in forests in central and eastern, compared with northwestern Amazonia. This pattern is due to the higher diversity and abundance of taxa with high specific gravity values in central and eastern Amazonia, and the greater diversity and abundance of taxa with low specific gravity values in western Amazonia. For two estimates of AGB derived using different allometric equations, basal area explains 51.7% and 63.4%, and stand‐level specific gravity 45.4% and 29.7%, of the total variation in AGB. The variation in specific gravity is important because it determines the regional scale, spatial pattern of AGB. When weighting by specific gravity is included, central and eastern Amazon forests have significantly higher AGB than stands in northwest or southwest Amazonia. The regional‐scale pattern of species composition therefore defines a broad gradient of AGB across Amazonia.     

Tree species composition and diversity gradients in white-water forests across the Amazon Basin

Aim Attention has increasingly been focused on the floristic variation within forests of the Amazon Basin. Variations in species composition and diversity are poorly understood, especially in Amazonian floodplain forests. We investigated tree species composition, richness and α diversity in the Amazonian white‐water (várzea) forest, looking particularly at: (1) the flood‐level gradient, (2) the successional stage (stand age), and (3) the geographical location of the forests. Location Eastern Amazonia, central Amazonia, equatorial western Amazonia and the southern part of western Amazonia. Methods The data originate from 16 permanent várzea forest plots in the central and western Brazilian Amazon and in the northern Bolivian Amazon. In addition, revised species lists of 28 várzea forest inventories from across the Amazon Basin were used. Most important families and species were determined using importance values. Floristic similarity between plots was calculated to detect similarity variations between forest types and over geographical distances. To check for spatial diversity gradients, α diversity (Fisher) of the plots was correlated with stand age, longitudinal and latitudinal plot location, and flood‐level gradient. Results More than 900 flood‐tolerant tree species were recorded, which indicates that Amazonian várzea forests are the most species‐rich floodplain forests worldwide. The most important plant families recorded also dominate most Neotropical upland forests, and c. 31% of the tree species listed also occur in the uplands. Species distribution and diversity varied: (1) on the flood‐level gradient, with a distinct separation between low‐várzea forests and high‐várzea forests, (2) in relation to natural forest succession, with species‐poor forests in early stages of succession and species‐rich forests in later stages, and (3) as a function of geographical distance between sites, indicating an increasing α diversity from eastern to western Amazonia, and simultaneously from the southern part of western Amazonia to equatorial western Amazonia. Main conclusions The east‐to‐west gradient of increasing species diversity in várzea forests reflects the diversity patterns also described for Amazonian terra firme. Despite the fine‐scale geomorphological heterogeneity of the floodplains, and despite high disturbance of the different forest types by sedimentation and erosion, várzea forests are dominated by a high proportion of generalistic, widely distributed tree species. In contrast to high‐várzea forests, where floristic dissimilarity increases significantly with increasing distance between the sites, low‐várzea forests can exhibit high floristic similarity over large geographical distances. The high várzea may be an important transitional zone for lateral immigration of terra firme species to the floodplains, thus contributing to comparatively high species richness. However, long‐distance dispersal of many low‐várzea trees contributes to comparatively low species richness in highly flooded low várzea.     

Molecular systematic analysis reveals cryptic tertiary diversification of a widespread tropical rain forest tree

The broad geographic range of many Neotropical rain forest tree species implies excellent dispersal abilities or range establishment that preceded the formation of current dispersal barriers. In order to initiate historical analyses of such widespread Neotropical trees, we sequenced the nuclear ribosomal spacer (ITS) region of Symphonia globulifera L. f. (Clusiaceae) from populations spanning the Neotropics and western Africa. This rain forest tree has left unmistakable Miocene fossils in Mesoamerica (15.5-18.2 Ma) and in South America ( approximately 15 Ma). Although marine dispersal of S. globulifera is considered improbable, our study establishes three marine dispersal events leading to the colonization of Mesoamerica, the Amazon basin, and the West Indies, thus supporting the paleontological data. Our phylogeographic analysis revealed the spatial extent of the three Neotropical S. globulifera clades, which represent trans-Andes (Mesoamerica+west Ecuador), cis-Andes (Amazonia+Guiana), and the West Indies. Strong phylogeographic structure found among trans-Andean populations of S. globulifera stands in contrast to an absence of ITS nucleotide variation across the Amazon basin and indicates profound regional differences in the demographic history of this rain forest tree. Drawing from these results, we provide a historical biogeographic hypothesis to account for differences in the patterns of beta diversity within Mesoamerican and Amazonian forests.     

Phylogeographic patterns of trans-Amazonian vicariants and Amazonian biogeography: the Neotropical rattlesnake (Crotalus durissus complex) as an example

Aim To investigate the phylogeography and execute a historical‐demographic analysis of the Neotropical rattlesnake, Crotalus durissus, thereby testing the hypothesis of a Pleistocene central Amazon corridor of dry forest or savanna that partitioned the Amazonian rain forest into western and eastern portions. Location South America. Methods Using sequences of three mitochondrial genes, we estimated the phylogeography, gene and nucleotide diversity across the South American range of C. durissus. Tree topology tests were used to test alternative biogeographical hypotheses, and tests of population genetic structure and statistical parsimony networks and nested clade phylogeographic analysis (NCPA) were used to infer connectivity and historical population processes on both sides of the Amazon basin. Results Tree topology tests rejected the hypothesis of a coastal dispersal in favour of a central corridor scenario. Gene diversity was similar on both sides of the Amazon basin. Nucleotide diversity indicated that the populations from north of the Amazon basin represented ancestral populations. Analysis of molecular variance (amova ) showed that intra‐population molecular variation was greater than between regions. Historical‐demographic statistics showed significant population expansion south of the Amazon, and little differentiation in the north, indicating moderate past gene flow between north and south of the Amazon. The parsimony network connected clades from the Roraima and Guyana populations with Mato Grosso, suggesting an Amazonian central corridor, and NCPA supported allopatric fragmentation between north and south of the Amazon. Main conclusions The distribution of C. durissus on both sides of the Amazon basin is evidence of changes in the distribution of rain forest vegetation during the Pleistocene. Our results suggest a formerly continuous distribution of this rattlesnake along a central Amazonian corridor during the middle Pleistocene. Allopatric fragmentation inferred from NCPA is consistent with vicariance resulting from a subsequent closure of this habitat corridor. This study emphasizes the potential of trans‐Amazonian open formation species to inform the debate on the past distribution of rain forests in the Amazon Basin.     

Comparative phylogeography of five widespread tree species: Insights into the history of western Amazonia

Various historical processes have been put forth as drivers of patterns in the spatial distribution of Amazonian trees and their population genetic variation. We tested whether five widespread tree species show congruent phylogeographic breaks and similar patterns of demographic expansion, which could be related to proposed Pleistocene refugia or the presence of geological arches in western Amazonia. We sampled Otoba parvifolia/glycycarpa (Myristicaceae), Clarisia biflora, Poulsenia armata, Ficus insipida (all Moraceae), and Jacaratia digitata (Caricaceae) across the western Amazon Basin. Plastid DNA (trnH–psbA; 674 individuals from 34 populations) and nuclear ribosomal internal transcribed spacers (ITS; 214 individuals from 30 populations) were sequenced to assess genetic diversity, genetic differentiation, population genetic structure, and demographic patterns. Overall genetic diversity for both markers varied among species, with higher values in populations of shade‐tolerant species than in pioneer species. Spatial analysis of molecular variance (SAMOVA) identified three genetically differentiated groups for the plastid marker for each species, but the areas of genetic differentiation were not concordant among species. Fewer SAMOVA groups were found for ITS, with no detectable genetic differentiation among populations in pioneers. The lack of spatially congruent phylogeographic breaks across species suggests no common biogeographic history of these Amazonian tree species. The idiosyncratic phylogeographic patterns of species could be due instead to species‐specific responses to geological and climatic changes. Population genetic patterns were similar among species with similar biological features, indicating that the ecological characteristics of species impact large‐scale phylogeography.     

Habitat specifity,endemism and the neotropical distribution of Amazonian white‐water floodplain trees

.The Amazon basin is covered by the most species‐rich forests in the world and is considered to house many endemic tree species. Yet, most Amazonian ecosystems lack reliable estimates of their degree of endemism, and causes of tree diversity and endemism are intense matters of debate. We reviewed the spatial distribution of 658 of the most important flood‐tolerant Amazonian white‐water (várzea) tree species across the entire Neotropics by using data from herbaria, floras, inventories and checklists. Our results show that 90% of the várzea tree species are partially or widely distributed across neotropical macro‐regions and biomes. Chi‐square analyses indicated that várzea species richness in non‐várzea macro‐regions was dependent on the flooding gradient and the longitudinal position. Cluster analysis combined with association tests indicated four significant patterns of várzea species distributions depending on species flood‐tolerance (low vs high) and spatial distribution (restricted vs widespread). We predict that the predominance of Andean substrates is the most important factor that determines the distribution of várzea tree species within and beyond the Amazon basin and explains the high floristic similarity to the Orinoco floodplains. Distribution patterns in other extra‐Amazonian macro‐regions are more likely linked to climatic factors, with rainforest climates housing more várzea species than savanna climates. 130 tree species were restricted to South‐American freshwater floodplains, and 68 (> 10%) were endemic to Amazonian várzea. We detected two centers of endemism, one in the western Amazon characterized by low and brief floods, and one in the central Amazon, characterized by high and prolonged floods. Differences in taxonomic composition of endemic centers in the western and central Amazon are the result of different abiotic factors (i.e. flood regimes), as well as the regional species pools from where the species are recruited from. We hypothesize that numerous morphological, physiological and biochemical adaptations permit survival of trees in flooded environments. Furthermore, these adaptations are independently derived across many taxa and result in a highly specialized flora. We attribute higher than expected levels of endemism to the great spatial extent and age of floodplain ecosystems in the Amazon basin, and highlight the role of Amazonian várzea as an potential driver in speciation and diversification processes.     

Molecular systematics and phylogeography of Amazonian poison frogs of the genus Dendrobates

The study of Amazonian biodiversity requires detailed knowledge of the phylogenetic relationships of closely related taxa distributed across Amazonia. The Amazonian poison frogs of the genus Dendrobates have undergone many taxonomic revisions, but the phylogenetic relationships within this group remain poorly understood. Most previous classifications were based on morphology and skin toxin analyses, with limited use of DNA sequence data. Using mtDNA sequence data from four gene regions (cytochrome b, cytochrome oxidase I, 16S rRNA, and 12S rRNA), we present a molecular phylogenetic analysis of the evolutionary relationships within a representative group of Amazonian Dendrobates. We use the resulting phylogenetic hypothesis to investigate different biogeographic hypotheses concerning genetic divergence and species diversity in Amazonia. The results of the analysis support the presence of ancient paleogeographic barriers to gene flow between eastern and western Amazonia, and indicate substantial genetic divergence between species found in the northern and southern regions of western Amazonia.     

Cebus phylogenetic relationships: a preliminary reassessment of the diversity of the untufted capuchin monkeys

The untufted, or gracile, capuchin monkeys are currently classified in four species, Cebus albifrons, C. capucinus, C. olivaceus, and C. kaapori, with all but C. kaapori having numerous described subspecies. The taxonomy is controversial and their geographic distributions are poorly known. Cebus albifrons is unusual in its disjunct distribution, with a western and central Amazonian range, a separate range in the northern Andes in Colombia, and isolated populations in Trinidad and west of the Andes in Ecuador and northern Peru. Here we examine previous morphological and molecular hypotheses of the taxonomy and phylogeny of Cebus. We construct a time-calibrated phylogeny based upon mitochondrial DNA sequences from 50 Cebus samples from across their range. Our data indicate that untufted capuchins underwent a radiation at about 2 Ma, and quickly diversified in both the Andes and the Amazon. We provide a provisional reassessment for the taxonomy of untufted capuchins in the Amazon, the Llanos, the Andes, Trinidad, and Central America, splitting currently paraphyletic taxa into several species, including: at least two Amazonian species (C. yuracus and C. unicolor); a species from the Guiana Shield (most likely the same as Humboldt's C. albifrons); two northern Andean species, C. versicolor, C. cesarae; C. brunneus (with trinitatis a junior synonym) on the Venezuelan coast, and C. adustus in the region of Lake Maracaibo; C. capucinus in northwestern Ecuador and Colombia, and Panama; C. imitator in Central America; C. olivaceus and C. castaneus occupying a large part of the Guiana Shield; and C. kaapori in the eastern Amazon, south of the Rio Amazonas. More intensive and extensive geographic sampling is needed, including that for some subspecies not represented here. Taxa from the southwestern Amazon (yuracus, cuscinus, and unicolor) and the phylogenetic position of Humboldt's Simia albifrons from the Orinoco remain particularly poorly defined.     

The Evolutionary History and Genetic Diversity of Kinkajous, <Emphasis Type="Italic">Potos flavus</Emphasis> (Carnivora,Procyonidae)

The genus Potos (Procyonidae) is currently recognized as a monotypic genus comprising the single species Potos flavus, the kinkajou. Kinkajous are widely distributed throughout forested habitats of tropical Central and South America, extending from eastern Brazil across central Bolivia, eastern Peru, northern Ecuador, Guianas, Suriname, Venezuela, Colombia, and then through Central America and into western Mexico. The taxonomic history of the species is complex, with seven or eight subspecies historically recognized to acknowledge the phenotypic variation among populations. In this study, the systematics and the evolutionary history of Potos flavus were investigated based on the mitochondrial gene cytochrome b, including specimens from a large range of localities, covering most of the distribution of the species, from central Middle America (Costa Rica and Panama) through South America (Ecuador, Peru, Bolivia, Brazil, Guyana, and French Guiana). Analyses of 30 Potos flavus sequences showed 27 haplotypes that were grouped in five main clades in all phylogenetic analyses. These clades suggested a high geographic structure with specimens from (1) Costa Rica, (2) Guianas and North Brazil, (3) North Peru, (4) Ecuador and Panama, (5a) interfluves Branco-Negro rivers in the Brazilian Amazon, (5b) Eastern Atlantic Forest, (5c) Amazonian lowlands east Negro river including Bolivia, Peru, and West Brazil. Each of these clades differs from 4.5 % to 9.3 % in their genetic distance estimates, which suggests that the specific status of some of these lineages should be reconsidered. Divergence dating and biogeographic analysis suggested that crown Potos diversified in the Miocene-Pliocene in South America, and geographic barriers, such as savannas and rivers, may have played a significant role in the kinkajou diversification.     

Survival,fidelity, and recovery rates of white-winged doves in Texas

Management of migratory birds at the national level has historically relied on regulatory boundaries for definition of harvest restrictions and estimation of demographic parameters. Most species of migratory game birds are not expanding their ranges, so migratory corridors are approximately fixed. White-winged doves (Zenaida asiatica), however, have undergone significant variation in population structure with marked range expansion occurring in Texas, and range contraction in Arizona, during the last 30 years. Because >85% of white-winged dove harvest in the United States (approx. 1.3 million annually) now occurs in Texas, information on vital rates of expanding white-winged dove populations is necessary for informed management. We used band recovery and mark–recapture data to investigate variation in survival and harvest across 3 geographic strata for white-winged doves banded in the pre-hunting season in Texas during 2007–2010. We banded 60,742 white-winged doves, recovered 2,458 bands via harvest reporting, and recaptured 455 known-age birds between 2007 and 2010. The best supporting model found some evidence for geographic differences in survival rates among strata (A–C) in both hatch-year (juvenile; A = 0.205 [SE = 0.0476], B = 0.213 [SE = 0.0278], C = 0.364 [SE = 0.0254]) and after-hatch year (adult; A = 0.483 [SE = 0.0775], B = 0.465 [SE = 0.0366], C = 0.538 [SE = 0.251]) birds. White-winged doves had a low probability of moving among strata (0.009) or being recaptured (0.002) across all strata. Harvest recovery rates were concordant with estimates for other dove species, but were variable across geographic strata. Based on our results, harvest management strategies for white-winged doves in Texas and elsewhere should consider differences in population vital rates among geographic strata. © 2012 The Wildlife Society.     

Apparent survival of tropical birds in a wet,premontane forest in Costa Rica

Despite the importance of tropical birds in the development of life history theory, we lack information about demographic rates and drivers of population dynamics for most species. We used a 7‐year (2007–2013) capture‐mark‐recapture dataset from an exceptionally wet premontane forest at mid‐elevation in Costa Rica to estimate apparent survival for seven species of tropical passerines. For four of these species, we provide the first published demographic parameters. Recapture probabilities ranged from 0.21 to 0.53, and annual estimates of apparent survival varied from 0.23 to 1.00. We also assessed the consequences of inter‐annual variation in rainfall on demographic rates. Our results are consistent with inter‐annual rainfall increasing estimates of apparent survival for two species and decreasing estimates for three species. For the three species where we could compare our estimates of apparent survival to estimates from drier regions, our estimates were not consistently higher or lower than those published previously. The temporal and spatial variability in demographic rates we document within and among species highlights the difficulties of generalizing life history characteristics across broad biogeographic gradients. Most importantly, this work emphasizes the context‐specific role of precipitation in shaping tropical avian demographic rates and underscores the need for mechanistic studies of environmental drivers of tropical life histories.     

Factors Affecting Nest Survival of Greater Sage-Grouse in Northcentral Montana

Abstract: We studied greater sage-grouse (Centrocercus urophasianus) in northcentral Montana, USA, to examine the relationship between nest success and habitat conditions, environmental variables, and female sage-grouse characteristics. During 2001-2003, we radiomarked 243 female greater sage-grouse, monitored 287 nests, and measured 426 vegetation plots at 4 sites in a 3,200-km² landscape. Nest survival varied with year, grass canopy cover, daily precipitation with a 1-day lag effect, and nesting attempt. In all years, daily survival rate increased on the day of a rain event and decreased the next day. There was temporal variation in nest success both within and among years: success of early (first 28 d of nesting season) nests ranged from 0.238 (SE = 0.080) in 2001 to 0.316 (SE = 0.055) in 2003, whereas survival of late (last 28 d of nesting season) nests ranged from 0.276 (SE = 0.090) in 2001 to 0.418 (SE = 0.055) in 2003. Renests experienced higher survival than first nests. Grass cover was the only important model term that could be managed, but direction and magnitude of the grass effect varied. Site, shrub and forb canopy cover, and Robel pole reading were less useful predictors of nest success; however, temporal and spatial variation in these habitat covariates was low during our study. We note a marked difference between both values and interpretations of apparent nest success, which have been used almost exclusively in the past, and maximum-likelihood estimates used in our study. Annual apparent nest success (0.46) was, on average, 53% higher than maximum-likelihood estimates that incorporate individual, environmental, and habitat covariates. The difference between estimates was variable (range = +8% to +91%). Management of habitats for nesting sage-grouse should focus on increasing grass cover to increase survival of first nests and contribute to favorable conditions for renesting, which should be less likely if survival of first nests increases.     

Reinforcing and expanding the predictions of the disturbance vicariance hypothesis in Amazonian harlequin frogs: a molecular phylogenetic and climate envelope modelling approach

The disturbance vicariance hypothesis (DV) has been proposed to explain speciation in Amazonia, especially its edge regions, e.g. in eastern Guiana Shield harlequin frogs (Atelopus) which are suggested to have derived from a cool-adapted Andean ancestor. In concordance with DV predictions we studied that (i) these amphibians display a natural distribution gap in central Amazonia; (ii) east of this gap they constitute a monophyletic lineage which is nested within a pre-Andean/western clade; (iii) climate envelopes of Atelopus west and east of the distribution gap show some macroclimatic divergence due to a regional climate envelope shift; (iv) geographic distributions of climate envelopes of western and eastern Atelopus range into central Amazonia but with limited spatial overlap. We tested if presence and apparent absence data points of Atelopus were homogenously distributed with Ripley’s K function. A molecular phylogeny (mitochondrial 16S rRNA gene) was reconstructed using Maximum Likelihood and Bayesian Inference to study if Guianan Atelopus constitute a clade nested within a larger genus phylogeny. We focused on climate envelope divergence and geographic distribution by computing climatic envelope models with MaxEnt based on macroscale bioclimatic parameters and testing them by using Schoener’s index and modified Hellinger distance. We corroborated existing DV predictions and, for the first time, formulated new DV predictions aiming on species’ climate envelope change. Our results suggest that cool-adapted Andean Atelopus ancestors had dispersed into the Amazon basin and further onto the eastern Guiana Shield where, under warm conditions, they were forced to change climate envelopes.     

Multilocus data of a manakin species reveal cryptic diversification moulded by vicariance

We used molecular tools and a multilocus approach to investigate the phylogeography of Lepidothrix coronata across most of its ample range. We sequenced six DNA fragments to produce phylogenies, molecular dating estimates, analyses of the dynamics of the demographic history of the species and a biogeographic analysis to estimate the events and changes in the ancestral distribution of the species. The results indicated the presence of four well-established lineages, with high levels of divergence. These lineages are delineated by well-defined geographic barriers, with one lineage, restricted to the west of the Andes, being the first to diverge from the complex. The other three lineages are exclusive to the Amazonian distribution of the species, with two being found north of the Amazon River, and the third, south of the Amazon. Some of the relationships found between these lineages were distinct from those described in previous studies. Important disagreements were found between the mtDNA phylogeny and that of the multilocus analysis, in relation to the lineages located to the west of the Andes. We propose that past introgression events may have influenced shifts in the relationships between lineages, despite the fact that the groups were well defined in both the phylogenies. The biogeographic analysis indicates that the lineages arose through successive vicariance events, which had a primary role in the diversification of the group. Two or three genetically structured subclades were also found within each Amazonian lineage, although these subclades are not isolated by an obvious geographic barrier.     

Historical diversification of a terra-firme forest bird superspecies: a phylogeographic perspective on the role of different hypotheses of Amazonian diversification

Among those few hypotheses of Amazonian diversification amenable to falsification by phylogenetic and population genetics methods, three can be singled out because of their general application to vertebrates: the riverine barrier, the refuge, and the Miocene marine incursion hypotheses. I used phylogenetic and population genetics methods to reconstruct the diversification history of the upland (terra-firme) forest superspecies Xiphorhynchus spixii/elegans (Aves: Dendrocolaptidae) in Amazonia, and to evaluate predictions of the riverine barrier, refuge, and Miocene marine incursion hypotheses. Phylogeographic and population genetics analyses of the X. spixiilelegans superspecies indicated that the main prediction of the riverine barrier hypothesis (that sister lineages occur across major rivers) hold only for populations separated by "clear-water" rivers located on the Brazilian shield, in central and eastern Amazonia; in contrast, "white-water" rivers located in western Amazonia did not represent areas of primary divergence for populations of this superspecies. The main prediction derived from the refuge hypothesis (that populations of the X. spixii/elegans superspecies would show signs of past population bottlenecks and recent demographic expansions) was supported only for populations found in western Amazonia, where paleoecological data have failed to support past rainforest fragmentation and expansion of open vegetation types; conversely, populations from the eastern and central parts of Amazonia, where paleoecological data are consistent with an historical interplay between rainforest and open vegetation types, did not show population genetics attributes expected under the refuge hypothesis. Phylogeographic and population genetics data were consistent with the prediction made by the Miocene marine incursion hypothesis that populations of the X. spixii/elegans superspecies found on the Brazilian shield were older than populations from other parts of Amazonia. In contrast, the phylogeny obtained for lineages of this superspecies falsified the predicted monophyly of Brazilian shield populations, as postulated by the Miocene marine incursion hypothesis. In general, important predictions of both riverine barrier and Miocene marine incursion hypotheses were supported, indicating that they are not mutually exclusive; in fact, the data presented herein suggest that an interaction among geology, sea level changes, and hydrography created opportunities for cladogenesis in the X. spixii/elegans superspecies at different temporal and geographical scales.     

Geological control of floristic composition in Amazonian forests

AIM: Conservation and land-use planning require accurate maps of patterns in species composition and an understanding of the factors that control them. Substantial doubt exists, however, about the existence and determinants of large-area floristic divisions in Amazonia. Here we ask whether Amazonian forests are partitioned into broad-scale floristic units on the basis of geological formations and their edaphic properties. LOCATION: Western and central Amazonia. METHODS: We used Landsat imagery and Shuttle Radar Topography Mission (SRTM) digital elevation data to identify a possible floristic and geological discontinuity of over 300 km in northern Peru. We then used plant inventories and soil sampling to document changes in species composition and soil properties across this boundary. Data were obtained from 138 sites distributed along more than 450 km of road and river. On the basis of our findings, we used broad-scale Landsat and SRTM mosaics to identify similar patterns across western and central Amazonia. RESULTS: The discontinuity identified in Landsat and SRTM data corresponded to a 15-fold change in soil cation concentrations and an almost total change in plant species composition. This discontinuity appears to be caused by the widespread removal of cation-poor surface sediments by river incision to expose cation-rich sediments beneath. Examination of broad-scale Landsat and SRTM mosaics indicated that equivalent processes have generated a north-south discontinuity of over 1500 km in western Brazil. Due to similarities with our study area, we suggest that this discontinuity represents a chemical and ecological limit between western and central Amazonia. MAIN CONCLUSIONS: Our findings suggest that Amazonian forests are partitioned into large-area units on the basis of geological formations and their edaphic properties. The evolution of these units through geological time may provide a general mechanism for biotic diversification in Amazonia. These compositional units, moreover, may correspond to broad-scale functional units. The existence of large-area compositional and functional units would suggest that protected-area, carbon sequestration, and other land-use strategies in Amazonia be implemented on a region-by-region basis. The methods described here can be used to map these patterns, and thus enable effective conservation and management of Amazonian forests.     

Life history patterns,individual heterogeneity,and density dependence in breeding common goldeneyes of the northern boreal forest

Life history patterns and their associated tradeoffs influence population dynamics, as they determine how individuals allocate resources among competing demographic traits. Here we examined life history strategies in common goldeneyes Bucephala clangula (hereafter goldeneye), a cavity‐nesting sea duck, in the northern boreal forest of interior Alaska, USA. We used multistate capture–mark–recapture models to estimate adult survival, breeding probability, first‐year survival, and recruitment probability using a long‐term nest box study (1997–2010). We detected annual variation in adult survival, which varied from 0.74 ± 0.12 (SE) to 0.93 ± 0.06. In contrast, breeding probability remained relatively high and invariant (0.84 ± 0.11) and was positively related to individual nest success the year prior. Nonbreeding individuals in one year were more likely to remain a nonbreeder, than attempt to breed the following year. First‐year survival decreased with smaller residual duckling mass and larger brood sizes. Probability of recruitment into the breeding population conditioned on survival was constant during the study (0.96 ± 0.06), and did not vary among ages 2–5 yr‐old. Overall, goldeneyes exhibited high, but somewhat variable, adult survival, and high breeding and recruitment probabilities, which is consistent with observed patterns in bet‐hedging species that breed annually in high quality breeding environments, but whose reproductive output is often influenced by stochastic events. Demographic estimates from this study are among the first for goldeneyes within Alaska. Life history patterns are known to vary geographically, therefore, we recommend further examination of life history patterns within the distribution of goldeneyes.     

The contribution of edaphic heterogeneity to the evolution and diversity of Burseraceae trees in the western Amazon

Environmental heterogeneity in the tropics is thought to lead to specialization in plants and thereby contribute to the diversity of the tropical flora. We examine this idea with data on the habitat specificity of 35 western Amazonian species from the genera Protium, Crepidospermum, and Tetragastris in the monophyletic tribe Protieae (Burseraceae) mapped on a molecular-based phylogeny. We surveyed three edaphic habitats that occur throughout terra firme Amazonia: white-sand, clay, and terrace soils in eight forests across more than 2000 km in the western Amazon. Twenty-six of the 35 species were found to be associated with only one of three soil types, and no species was associated with all three habitats; this pattern of edaphic specialization was consistent across the entire region. Habitat association mapped onto the phylogenetic tree shows association with terrace soils to be the probable ancestral state in the group, with subsequent speciation events onto clay and white-sand soils. The repeated gain of clay association within the clade likely coincides with the emergence of large areas of clay soils in the Miocene deposited during the Andean uplift. Character optimizations revealed that soil association was not phylogenetically clustered for white-sand and clay specialists, suggesting repeated independent evolution of soil specificity is common within the Protieae. This phylogenetic analysis also showed that multiple cases of putative sister taxa with parapatric distributions differ in their edaphic associations, suggesting that edaphic heterogeneity was an important driver of speciation in the Protieae in the Amazon basin.     

Pattern and process in Amazon tree turnover, 1976-2001

Previous work has shown that tree turnover, tree biomass and large liana densities have increased in mature tropical forest plots in the late twentieth century. These results point to a concerted shift in forest ecological processes that may already be having significant impacts on terrestrial carbon stocks, fluxes and biodiversity. However, the findings have proved controversial, partly because a rather limited number of permanent plots have been monitored for rather short periods. The aim of this paper is to characterize regional-scale patterns of 'tree turnover' (the rate with which trees die and recruit into a population) by using improved datasets now available for Amazonia that span the past 25 years. Specifically, we assess whether concerted changes in turnover are occurring, and if so whether they are general throughout the Amazon or restricted to one region or environmental zone. In addition, we ask whether they are driven by changes in recruitment, mortality or both. We find that: (i) trees 10 cm or more in diameter recruit and die twice as fast on the richer soils of southern and western Amazonia than on the poorer soils of eastern and central Amazonia; (ii) turnover rates have increased throughout Amazonia over the past two decades; (iii) mortality and recruitment rates have both increased significantly in every region and environmental zone, with the exception of mortality in eastern Amazonia; (iv) recruitment rates have consistently exceeded mortality rates; (v) absolute increases in recruitment and mortality rates are greatest in western Amazonian sites; and (vi) mortality appears to be lagging recruitment at regional scales. These spatial patterns and temporal trends are not caused by obvious artefacts in the data or the analyses. The trends cannot be directly driven by a mortality driver (such as increased drought or fragmentation-related death) because the biomass in these forests has simultaneously increased. Our findings therefore indicate that long-acting and widespread environmental changes are stimulating the growth and productivity of Amazon forests.     

Estimates of Apparent Survival Rates for Forest Birds in Eastern Ecuador

Knowledge of survival rates of Neotropical landbirds remains limited, with estimates of apparent survival available from relatively few sites and species. We used capture–mark–recapture models to estimate apparent survival of 31 species from eastern Ecuador based on data collected from 2001 to 2006. Models assuming constant survival had highest support for 27 species; models incorporating effects of transients were highest for four. Average apparent survival across 30 species of passerines was 0.58 (± 0.02 SE); apparent survival was lower during the first interval after initial capture (φ₁: mean = 0.49 ± 0.03) than during subsequent intervals (φ₂: mean = 0.60 ± 0.02). Apparent survival was similar among three families represented by at least four species (Thamnophilidae: 0.57 ± 0.03, N = 10; Furnariidae: 0.59 ± 0.03, N = 5; Pipridae: 0.56 ± 0.02, N = 4). There was no indication that species that occur in flocks had higher survival than nonflocking species (obligate flock members: 0.57 ± 0.03, N = 10; facultative flock members: 0.56 ± 0.04, N = 5; nonflocking: 0.59 ± 0.03, N = 15). Comparisons of published estimates of apparent survival of tropical species demonstrated substantial differences among species and, in some cases, within species across different sites in the Neotropics. Our results support previous studies that concluded that early estimates of high (> 85%) survival in tropical birds may not be representative of all tropical species. Future studies should focus on understanding factors ( e.g. , life-history traits) that promote differences in survival among species within tropical forests.