Guiana Shield Research Articles

Slow rate of secondary forest carbon accumulation in the Guianas compared with the rest of the Neotropics.

Secondary forests are a prominent component of tropical landscapes, and they constitute a major atmospheric carbon sink. Rates of carbon accumulation are usually inferred from chronosequence studies, but direct estimates of carbon accumulation based on long-term monitoring of stands are rarely reported. Recent compilations on secondary forest carbon accumulation in the Neotropics are heavily biased geographically as they do not include estimates from the Guiana Shield. We analysed the temporal trajectory of aboveground carbon accumulation and floristic composition at one 25-ha secondary forest site in French Guiana. The site was clear-cut in 1976, abandoned thereafter, and one large plot (6.25ha) has been monitored continuously since. We used Bayesian modeling to assimilate inventory data and simulate the long-term carbon accumulation trajectory. Canopy change was monitored using two aerial lidar surveys conducted in 2009 and 2017. We compared the dynamics of this site with that of a surrounding old-growth forest. Finally, we compared our results with that from secondary forests in Costa Rica, which is one of the rare long-term monitoring programs reaching a duration comparable to our study. Twenty years after abandonment, aboveground carbon stock was 64.2 (95% credibility interval 46.4, 89.0) Mg C/ha, and this stock increased to 101.3 (78.7, 128.5) Mg C/ha 20 yr later. The time to accumulate one-half of the mean aboveground carbon stored in the nearby old-growth forest (185.6 [155.9, 200.2] Mg C/ha) was estimated at 35.0 [20.9, 55.9] yr. During the first 40yr, the contribution of the long-lived pioneer species Xylopia nitida, Goupia glabra, and Laetia procera to the aboveground carbon stock increased continuously. Secondary forest mean-canopy height measured by lidar increased by 1.14m in 8 yr, a canopy-height increase consistent with an aboveground carbon accumulation of 7.1Mg C/ha (or 0.89Mg C·ha-1 ·yr-1 ) during this period. Long-term AGC accumulation rate in Costa Rica was almost twice as fast as at our site in French Guiana. This may reflect higher fertility of Central American forest communities or a better adaptation of the forest tree community to intense and frequent disturbances. This finding may have important consequences for scaling-up carbon uptake estimates to continental scales.

Checklist of the ichthyofauna of the Rio Negro basin in the Brazilian Amazon.

This study presents an extensive review of published and unpublished occurrence records of fish species in the Rio Negro drainage system within the Brazilian territory. The data was gathered from two main sources: 1) litterature compilations of species occurrence records, including original descriptions and revisionary studies; and 2) specimens verification at the INPA fish collection. The results reveal a rich and diversified ichthyofauna, with 1,165 species distributed in 17 orders (+ two incertae sedis), 56 families, and 389 genera. A large portion of the fish fauna (54.3% of the species) is composed of small-sized fishes < 10 cm in standard length. The main groups are Characiformes (454 species; 39.0%), Siluriformes (416; 35.7%), Gymnotiformes (105; 9.0%), and Cichliformes (102; 8.8%). The species composition differs between the main aquatic environments, such as: main channel (159 species), lakes (296), tributary rivers (596), small streams (234), seasonal beaches (186), and rapids (41). Part of the ichthyofauna is shared with adjacent basins, such as the Orinoco, rivers of the Guiana Shield, lower Solimões/Amazonas and upper Amazonas, which contributes to the remarkable ichthyofaunal diversity of the basin. A high rate of species endemism was observed in Characidae (24), Loricariidae (18), Cichlidae (18) and Callichthyidae (18), totalling 156 species (13.4%) endemic to the basin. An estimation of the species richness for the Rio Negro basin, considering 23 published references, resulted in 1,466 and 1,759 species (Jackknife 1 and 2, respectively), which seems reasonable when considering the large number of morphotypes left out of the present list and the low sampling effort in many areas of the basin. The results presented herein provide an additional tool for environmental managers and decision makers for conservation purposes of one of the richest and most well-preserved sub-basins of the Rio Amazonas system.

Coupling of El Niño events and long-term warming leads to pervasive climate extremes in the terrestrial tropics

The El Niño Southern Oscillation (ENSO) is a major driver of seasonal and interannual climatic variability across the tropics. The 2015/16 El Niño event was one of the strongest El Niño events of the past century. Here we characterize the meteorological impacts of the 2015/16 El Niño event upon the terrestrial tropics, and place the severity of this event into context of previous strong events in 1982/83 and 1997/98. Strong drought-inducing meteorological anomalies (≥2 s.d.) occurred across vast regions (20%) of the terrestrial tropics, where the wet tropics (≥1200 mm yr−1) were more severely affected (33%) than the drier tropics (6%). Central and eastern Amazonia experienced the most sustained and spatially extensive drought inducing anomalies, while parts of the Congo basin and Insular Southeast Asia also experienced severe drought. Surprisingly, some regions of the tropics (e.g. the Guiana Shield) with well known ENSO teleconnections were only briefly affected by the 2015/16 El Niño event. 2015/16 El Niño soil water drought impacts affected 29% of the terrestrial tropics, compared to 16% and 18% in 1982/83 and 1997/98, respectively. Maximum temperatures were particularly exacerbated compared to previous strong El Niños because they were amplified by the warming trend due to anthropogenic climate change. This also intensified positive anomalies of atmospheric vapor pressure deficit (the atmospheric demand for moisture), which had strongly negative consequences for vegetation productivity in the tropics. Even if El Niño events do not increase in intensity over coming decades, the pervasive long-term warming trend means that the atmospheric drought impact of each strong El Niño is becoming more severe, and many parts of the tropics will experience novel climate (temperature and VPD) conditions with each new strong El Niño event.

First checklist of the ants (Hymenoptera: Formicidae) of French Guiana.

We provide here a checklist of the ants of French Guiana, an overseas department of France situated in northern South America, with a very low human population density and predominantly covered by old-growth tropical rainforests. Based on 165 scientific papers, specimens deposited in collections, and unpublished surveys, a total of 659 valid species and subspecies from 84 genera and 12 subfamilies is presented. Although far from complete, these numbers represent approximately 10% of the ant diversity known to occur in the Neotropical realm. Additionally, three ant genera and 119 species are reported for the first time for French Guiana. Finally, five species are recognized as erroneous records for the the department in the literature. This checklist significantly expands the basic knowledge of the ants in the Guiana Shield, one of the world's most important biodiversity hotspots.

Two New Species of the Armored Catfish Genus Baryancistrus Rapp Py-Daniel, 1989 (Siluriformes: Loricariidae) from Jari River, Amazon Basin, Brazil

Two new species of the suckermouth armored catfish genus Baryancistrus are described from the Jari River basin, at the border of Para and Amapa states, Brazil. The new species are the first representatives of the genus described from rivers draining the Guiana shield, and can be distinguished from their congeners by color pattern and a combination of nonexclusive characters. Baryancistrus micropunctatus, new species, has a color pattern similar to B. longipinnis from the Tocantins River, whereas Baryancistrus hadrostomus, new species, has a color pattern that is unique for the genus, with a gray to black body covered by small and widely spaced white points. The first exemplars of the two new species were collected in the late 1980s by INPA ichthyological staff, and in 2007 additional materials were collected by the Museu de Zoologia da Universidade de Sao Paulo (MZUSP), providing a foundation for this description of the new species.

The Amphibians of the Mitaraka massif, French Guiana

We undertook a 15-day survey of the amphibian fauna of the Mitaraka massif in southwestern French Guiana during the rainy season. We detected 56 species (12 species detected for the first time), including six only thanks to their calls. Thirteen additional species were previously detected from nearby sites. The total number of species occurring in the area is at least 69 but most of the species associated with temporary ponds remained undetected. Therefore, we assume the amphibian community of the Mitaraka massif could reach at least 75 species, which represents one of the richest amphibian faunas of the Guiana Shield. With at least six species not occurring further north in French Guiana, the amphibian fauna of the Mitaraka massif is notably distinct from the rest of the territory. Seven of the species discovered during the survey are highlighted here either because these new records represent range extensions or because they are putative new species.

A new species of Cetopsis from the Guiana Shield (Siluriformes: Cetopsidae: Cetopsinae).

A new species of Cetopsis is described from Guiana Shield drainages in Guyana and Suriname. The new species is found in the Konawaruk River and tributaries, Essequibo River basin, Guyana, and in the Mauritie Creek, tributary to the Tempati River, upper Commewijne River basin, Suriname. The new taxon can be distinguished from all congeners by a combination of features: dark spots on sides of the body eye-sized or larger, dark, bilobed patch at the base of the caudal fin, absence of a dark humeral spot, absence of dark pigmentation along the fin-membrane posterior to the first dorsal-fin ray, dark pigmentation at the base of the dorsal fin, dark spots extending ventrally to the bases of anal-fin rays, and 41 total vertebrae with 28 caudal vertebrae. Data on internal anatomy of the new species were incorporated into a previously-published phylogenetic analysis and resolves the position of the new species as the sister group of C. motatanensis, from Lago Maracaibo basin. The new Cetopsis is the first species of the genus known to occur exclusively in the Guiana Shield.

Taxonomic Revision of Cyathea, Clade Hymenophyllopsis (Cyatheaceae)

We present a taxonomic revision of Cyathea, clade Hymenophyllopsis, a monophyletic group restricted to the tepuis of the Guiana Shield, a region in northern South America. We recognize fifteen species, including four newly described here: C. indefinita, C. minima, C. pseudoctenitoides, and C. tatei. The main diagnostic characters for the species are: rhizome (symmetry and scales), lamina division (pinnatisect to 5-pinnate), pinnae (congested or sparse, recurverd to ascending), scales and/or hairs of the rachis (shape, size, margins), as well as the shape and margin of the indusium (bivalvate or cyatheoid, entire to deeply lacerate). An identification key, descriptions, taxonomic comments, illustrations, and geographical distribution maps for all recognized taxa are provided.

(2703) Proposal to conserve the name Tontelea attenuata against Maytenus amygdalina (Celastraceae)

(2703) Proposal to conserve the name <i>Tontelea attenuata</i> against <i>Maytenus amygdalina</i> (<i>Celastraceae</i>)

Multi-Decadal to Short-Term Beach and Shoreline Mobility in a Complex River-Mouth Environment Affected by Mud From the Amazon

On the 1500 km-long mud-dominated Guianas coast of South America, between the mouths of the two mega-rivers, the Amazon and the Orinoco, debouch numerous small rivers draining the humid tropical/equatorial Guiana Shield. The geomorphic development of the mouths of these rivers reflects interactions among water discharge, fluvial sediment load, and the alongshore migration of Amazon-derived mud banks alternating with inter-bank areas. The mouth of the Maroni River, astride the French Guiana-Suriname border, shows advanced estuarine infill and geomorphic development characterized by a western (downdrift) side comprising numerous recent cheniers and an eastern (updrift) side bound by an old (> 2000 years B.P.) chenier. A multi-decadal analysis of the beach bounding this chenier shows little net overall mobility notwithstanding significant decadal to sub-decadal variation. The overall stability reflects the diversion of sand supply from the Maroni River towards the downdrift coast and limited sand supply by the smaller Mana River further east, and the south bank of which was contiguous with this beach. The variability in beach multi-decadal mobility reflects the influence, on waves, of alongshore-migrating banks (strong wave dissipation, limited beach mobility) and inter-bank areas (limited wave dissipation, larger beach mobility), highlighted by a comparison, in the current bank phase, of offshore and inshore waves. Erosion of the beach between 2011 and 2017 coincides with the sealing of the mouth of the Mana by muddy progradation in 2011 and mouth relocation several kilometers eastward. The morphodynamics of the beach and shorter-term fluctuations in budget are related to: (1) interaction with estuarine sand dunes mobilized by strong tidal currents on the adjacent shallow shoreface, (2) the influence of the Maroni channel, and (3) rapid encroachment of the leading edge of the shore-attached mud bank on the eastern part of the beach. The beach morphodynamics and evolution highlight, thus, embedded levels of influence: the Maroni at the local scale, and the net westward sediment-transport system and bank and inter-bank alternations that affect the Guianas coast at a regional scale. The recent erosion poses a threat to the local communities by reducing beach space available for recreation and turtle-nesting.

Long-term influence of early human occupations on current forests of the Guiana Shield.

To decipher the long-term influences of pre-Columbian land occupations on contemporary forest structure, diversity, and functioning in Amazonia, most of the previous research focused on the alluvial plains of the major rivers of the Amazon basin. Terra firme, that is, nonflooded forests, particularly from the Guiana Shield, are yet to be explored. In this study, we aim to give new insights into the subtle traces of pre-Columbian influences on present-day forests given the archaeological context of terra firme forests of the Guiana Shield. Following archaeological prospects on 13 sites in French Guiana, we carried out forest inventories inside and outside archaeological sites and assessed the potential pre-Columbian use of the sampled tree species using an original ethnobotanical database of the Guiana Shield region. Aboveground biomass (320 and 380 T/ha, respectively), basal area (25-30 and 30-35m2 /ha, respectively), and tree density (550 and 700 stem/ha, respectively) were all significantly lower on anthropized plots (As) than on nonanthropized plots (NAs). Ancient human presence shaped the species composition of the sampled forests with Arecaceae, Burseraceae, and Lauraceae significantly more frequent in As and Annonaceae and Lecythidaceae more frequent in NAs. Although alpha diversity was not different between As and NAs, the presence of pre-Columbian sites enhances significantly the forest beta diversity at the landscape level. Finally, trees with edible fruits are positively associated with pre-Columbian sites, whereas trees used for construction or for their bark are negatively associated with pre-Columbian sites. Half a millennium after their abandonment, former occupied places from the inner Guiana Shield still bear noticeable differences with nonanthropized places. Considering the lack of data concerning archaeology of terra firme Amazonian forests, our results suggest that pre-Columbian influences on the structure (lower current biomass), diversity (higher beta diversity), and composition (linked to the past human tree uses) of current Amazonian forests might be more important than previously thought.

Gold in weathering mantle of the Guiana shield (South America)

The article describes mineral composition of laterite weathering mantle overlapping the Amamuri and Kontakt gold deposits in the greenstone rocks, located 20 km southeast of the Aurora deposit (reserves of 185 tons Au, Republic of Guyana). The major minerals of the weathering mantle include disordered kaolinite (35–90 wt. %), relict quartz and hydromica (up to 20 wt. % illite). The heavy concentrate is represented by limonite (up to 8 wt. % goethite), magnetite, hematite, ilmen-ite, anatase, ferrous rutile, psilomelane, pyrite, chalcopyrite, galena, sphalerite, covellite, zircon, tourmaline, epidote and amphibole. Native gold composes signifcant amount of heavy concentrates (up to 9 wt. %) and includes the following types: 1) lode gold in relict quartz veins and stockwork, 2) relict gold in laterite and 3) supergene gold. According to mineralogical studies, moderate late-ritization and monosialitization processes are probably due to erosion of ancient areal weathering mantle and the presence of immature laterites over the Amamuri and Kontakt deposits. Most amount of gold is relic. The processes of its redeposition and supergene alterations are weak. The dominant size of gold grains of &lt;100 µm makes gravitational concentration of laterites more difcult, whereas weakly ordered kaolinite prevents agglomeration during cyanidation and heap leaching. Alluvial placers are probably more promising for exploration, since they provide natural fractionation of gold particles by size favorable for gravity extraction.

Temperature rising would slow down tropical forest dynamic in the Guiana Shield

Increasing evidence shows that the functioning of the tropical forest biome is intimately related to the climate variability with some variables such as annual precipitation, temperature or seasonal water stress identified as key drivers of ecosystem dynamics. How tropical tree communities will respond to the future climate change is hard to predict primarily because several demographic processes act together to shape the forest ecosystem general behavior. To overcome this limitation, we used a joint individual-based model to simulate, over the next century, a tropical forest community experiencing the climate change expected in the Guiana Shield. The model is climate dependent: temperature, precipitation and water stress are used as predictors of the joint growth and mortality rates. We ran simulations for the next century using predictions of the IPCC 5AR, building three different climate scenarios (optimistic RCP2.6, intermediate, pessimistic RCP8.5) and a control (current climate). The basal area, above-ground fresh biomass, quadratic diameter, tree growth and mortality rates were then computed as summary statistics to characterize the resulting forest ecosystem. Whatever the scenario, all ecosystem process and structure variables exhibited decreasing values as compared to the control. A sensitivity analysis identified the temperature as the strongest climate driver of this behavior, highlighting a possible temperature-driven drop of 40% in average forest growth. This conclusion is alarming, as temperature rises have been consensually predicted by all climate scenarios of the IPCC 5AR. Our study highlights the potential slow-down danger that tropical forests will face in the Guiana Shield during the next century.

Composición florística y formas de vida de las macrófitas acuáticas de la serranía de La Lindosa (Guaviare), Guayana colombiana

La serranía de La Lindosa hace parte de los afloramientos rocosos del escudo Guayanés colombiano. Aunque la vegetación de este ecosistema ha sido estudiada, en esta región y en Colombia la diversidad de plantas acuáticas ha sido pobremente investigada. En este trabajo se caracterizó la flora acuática de La Lindosa mediante recolecciones generales en cuerpos de agua lóticos y lénticos. Se encontraron 110 especies en 70 géneros y 46 familias. Las familias más importantes fueron Cyperaceae (seis géneros/17 especies), Poaceae (diez/catorce) y Lentibulariaceae (una/catorce). Se reporta a Eleocharis alveolatoides como nuevo registro para la flora de Colombia y 38 para el Guaviare. La mayoría de las especies se localizaban en la ribera de los caños y la forma de vida arraigada emergente fue predominante. La cantidad de nuevos registros exponen la escasez de muestreos de macrófitas en la región, se muestra la gran riqueza de plantas acuáticas albergada en este macizo rocoso, y se destaca la presencia de elementos de distribución restringida. Lo anterior puede tener importantes implicaciones para la generación de mejores estrategias de conservación de esta zona.

The Avifauna of the Rio Branco, an Amazonian evolutionary and ecological hotspot in peril

SummaryThe Rio Branco is a river with unique biogeographic and ecological features, threatened by the Brazilian Government’s plan to build a major hydroelectric dam and associated hydroway along its course. The river crosses one of Amazonia’s largest rainfall gradients and a major geomorphological boundary along a savanna/forest ecotone, marked by the Bem Querer rapids. Above the rapids, the upper Rio Branco runs through the Boa Vista sedimentary formation and crosses the crystalline rocks of the Guiana Shield, and its margins are flanked by gallery forests. Downriver, it runs through a low-lying sedimentary basin, with Amazonian floodplain forests along its margins. Here, we present the results of ∼ 15 years of ornithological research on the Branco and its major tributaries, providing baseline data and evaluating potential threats to the riverine avifauna. Our surveys included opportunistic observations and standardized surveys along the entire length of the river in 16 systematically distributed localities. We catalogued 439 bird species, 87% of which are documented by physical evidence (specimens, recordings, photographs). Forty-six percent are restricted to single habitats, suggesting a high degree of habitat specialisation. A third of the species are widely distributed along the river, whereas 45% are restricted to either the upper or the lower Rio Branco, including 40 and 30 Indicator Species, respectively. Twenty-five species are threatened at global or national levels, including two ‘Critically Endangered’, nine ‘Vulnerable’, and 14 ‘Near Threatened’. We present a list of 50 bird species that are candidates for monitoring studies. Threats to the avifauna from dam construction include permanent flooding above the dam, eliminating gallery forests, river islands, and sandy beaches, and the disruption of the flood pulse along the river, affecting river island and floodplain forest specialists, many of which are globally threatened with extinction. If built, the Bem Querer dam will wipe out the ecotone region and affect dramatically the river’s avifauna.

Botanical novelties from the Sierra de Maigualida, southern Venezuela III: revision and two new species of the genus &lt;em&gt;Ilex (Aquifoliaceae)&lt;/em&gt;

The Sierra de Maigualida is a poorly explored mountain range in the central Guayana Shield with high levels of endemism. In the present installment, this area is further delimited and mapped, toponymy is reviewed, and the genus Ilex L. is locally reviewed, with two species, namely I. huberi J.R.Grande sp. nov. and I. maigualidensis J.R.Grande sp. nov., described as new to science. Ilex huberi sp. nov. can be distinguished by its leaf blades strongly revolute, mucronate, and with obscure secondary venation, simple dichasia, and depressed-lunate sepals; I. maigualidensis sp. nov. by its dull leaves, flowers with undeveloped styles, and capitate-subcoronate stigmata. Stem buds and cataphylls are proposed as useful characters in species delimitation within the genus, while I. magnifructa Edwin is illustrated for the first time. A key is presented to differentiate all the species of Ilex of the Sierra de Maigualida.

Three additional new genera of acidocerine water scavenger beetles from the Guiana and Brazilian Shield regions of South America (Coleoptera, Hydrophilidae, Acidocerinae).

Recent study of the water scavenger beetle subfamily Acidocerinae in the Neotropical region has uncovered numerous undescribed species that are not able to be placed in existing genera. Here, we describe three new genera to accommodate 17 of these new species from South America: Aulonocharesgen. nov. for Aulonochareslingulatussp. nov. (French Guiana, Suriname), Aulonocharesnovoairensissp. nov. (Brazil), and Aulonocharestubulussp. nov. (Brazil, Guyana, Suriname, Venezuela); Ephydrolithusgen. nov. for Ephydrolithushamadaesp. nov. (Brazil), Ephydrolithusminorsp. nov. (Brazil), Ephydrolithusogmossp. nov. (Brazil), Ephydrolithusspiculatussp. nov. (Brazil), and Ephydrolithustelisp. nov. (Brazil); and Primocerusgen. nov. for Primoceruscuspidissp. nov. (Venezuela), Primocerusgigassp. nov. (Venezuela), Primocerusneutrumsp. nov. (Guyana, Suriname, Venezuela), Primocerusocellatussp. nov. (Venezuela), Primoceruspetilussp. nov. (Brazil), Primoceruspijiguaensesp. nov. (Venezuela), Primocerusmaipuresp. nov. (Venezuela), Primocerussemipubescenssp. nov. (Guyana), and Primocerusstriatolatussp. nov. (Suriname). The genus Ephydrolithusgen. nov. is currently known to be restricted to seepages in the mountainous regions of the Brazilian Shield. Aulonocharesgen. nov. and Primocerusgen. nov. are both currently only known from the Guiana Shield, though widespread in that region where they are associated with streams and seeps. We present differential diagnoses, maps, habitat details, and illustrations of all new genera and species here described.

Can timber provision from Amazonian production forests be sustainable?

Around 30 Mm3 of sawlogs are extracted annually by selective logging of natural production forests in Amazonia, Earth’s most extensive tropical forest. Decisions concerning the management of these production forests will be of major importance for Amazonian forests’ fate. To date, no regional assessment of selective logging sustainability supports decision-making. Based on data from 3500 ha of forest inventory plots, our modelling results show that the average periodic harvests of 20 m3 ha−1 will not recover by the end of a standard 30 year cutting cycle. Timber recovery within a cutting cycle is enhanced by commercial acceptance of more species and with the adoption of longer cutting cycles and lower logging intensities. Recovery rates are faster in Western Amazonia than on the Guiana Shield. Our simulations suggest that regardless of cutting cycle duration and logging intensities, selectively logged forests are unlikely to meet timber demands over the long term as timber stocks are predicted to steadily decline. There is thus an urgent need to develop an integrated forest resource management policy that combines active management of production forests with the restoration of degraded and secondary forests for timber production. Without better management, reduced timber harvests and continued timber production declines are unavoidable.

A new species of Microlicia (Melastomataceae): first record of the genus for Colombia.

Microlicia (Melastomataceae) is a Neotropical genus nearly restricted to southeastern Brazil, and the Guiana Shield in Venezuela, with a few species in some places in the Andes of Bolivia and Peru. A new species of Microlicia endemic to the mountains of eastern Andes of Colombia is described and illustrated. Its affinities with other morphologically similar species from Venezuela are also documented. This novelty is the first record of the genus for Colombia and the northern Andes. It is argued that this disjunct distribution of the genus is attributable to the phenomenon of long-distance seed dispersal by wind.

Contrasting genetic, acoustic, and morphological differentiation in two closely related gladiator frogs (Hylidae: Boana) across a common Neotropical landscape.

Mountain chains and rivers are often found to represent barriers promoting vicariant differentiation in terrestrial vertebrates. Previous studies have supported the idea that the Cordillera de Mérida (CM), the easternmost branch of the Northern Andes, represents a geographic barrier for vertebrates, including frogs. Previous studies have also suggested that the Orinoco River (OR), the biggest river in Venezuela, also represents a geographic barrier for terrestrial vertebrates. Boana pugnax and B. xerophylla are two Neotropical hylids, members of the B. faber species group, that are distributed on either side of the CM, and whose ranges extend up to 605 and 2450 m in elevation, respectively. In addition, B. xerophylla occurs on either side of the OR. Herein, we assess the genetic, acoustic, and morphological differentiation within B. pugnax and within B. xerophylla across the CM and within B. xerophylla across the OR, and test if genetic differentiation is correlated with geographic distance. We also evaluated the acoustic differentiation between the recently recognized B. xerophylla and its sister species, B. crepitans, and found marked differences between advertisement calls, corroborating their status as distinct species. Genetic and morphometric analyses of populations from opposite sides of the CM revealed differentiation in B. pugnax but not in B. xerophylla. Within the latter species, we found molecular, acoustic, and morphometric differentiation among samples of B. xerophylla from western Venezuela versus the Guiana Shield. Genetic variation within B. pugnax and within B. xerophylla was not explained by geographic distance. Thus, our data show conspecific population structure across the CM in B. pugnax, plus the possible existence of two species within what today is considered B. xerophylla, yet the CM apparently is not involved in this divergence. These results suggest that even for closely related species with shared ecology and distribution, genetic and phenotypic differentiation respond differently to common ecological or historical factors.