sub-Andean Region Research Articles

Entering and exiting behaviour of the phlebotomine sand fly Lutzomyia longiflocosa (Diptera: Psychodidae) in rural houses of the sub-Andean region of Colombia.

The present study identified the entering and exiting sites for Lutzomyia longiflocosa in rural houses of the sub-Andean region in Colombia. Entering sites were identified with sticky traps set up outside the bedrooms, around the eave openings, and with cage traps enclosing the slits in the doors and windows inside the bedrooms. Exiting sites were identified by releasing groups of females indoors. These females were blood fed and marked with fluorescent powders. Females were recaptured with the trap placement described above but set up on the opposite sides of the openings. In the entering experiment, a significantly higher number of females were captured in the sticky traps at the zone nearest the eave openings (n = 142) than those captured in the other zones of the trap (n = 52); similarly, a higher number of females were captured on the front side of the house (n = 105) than at the rear side (n = 37). Only two females were collected in the cage trap. In the exiting experiment, at the ceiling, the highest percentage (86.2%) of females was recaptured with sticky traps nearest the eave openings and on the front side of the house (70.0%). Seven females were collected in the cage trap. Lu. longiflocosa entered and exited houses primarily through the eave openings in a non-random pattern in relation to the sides of the house.

Intraplate stress field in South America from earthquake focal mechanisms

We present an updated compilation of earthquake focal mechanisms in Brazil together with focal mechanisms from the sub-Andean region (mainly from global CMT catalogs). All earthquakes in the sub-Andean region show reverse (majority) or strike-slip faulting mechanisms. Focal mechanisms in Brazil show reverse, strike-slip and normal faulting. Focal mechanisms of nearby earthquakes in the same tectonic environment were grouped and inverted for the stress tensor. In the sub-Andean region, stresses are compressional, as expected, with the principal major compression (S1) roughly E-W, on average. A slight rotation of S1 can be observed and is controlled by the orientation of the Andean plateau. In the sub-Andean region, the intermediate principal stress (S2) is also compressional (i.e., larger than the lithostatic pressure, Sv), a feature that is not always reproduced in numerical models published in the literature. In mid-plate South America stresses seem to vary in nature and orientation. In SE Brazil and the Chaco-Pantanal basins, S1 tends to be oriented roughly E-W with S2 approximately equal to S3. This stress pattern changes to purely compressional (both SHmax and Shmin larger than Sv) in the São Francisco craton. A rotation of SHmax from E-W to SE-NW is suggested towards the Amazon region. Along the Atlantic margin, the regional stresses are very much affected by coastal effects (due to continent/ocean spreading stresses as well as flexural effects from sediment load at the continental margin). This coastal effect tends to make SHmax parallel to the coastline and Shmin (usually S3) perpendicular to the coastline. Few breakout data and in-situ measurements are available in Brazil and are generally consistent with the pattern derived from the earthquake focal mechanisms. Although numerical models of global lithospheric stresses tend to reproduce the main large-scale features in most mid-plate areas, the S1 rotation from ∼E-W in SE Brazil to SE-NW in the Amazon region are not well explained by the current numerical models. This means that the observed stress pattern in mid-plate South America should provide new insights into upper mantle dynamics, distinct from current global convection models.

Returning Home: Movement Strategies of Sub-Andean Birds in a Modified Landscape

We documented movement of a long-distant migrant (Swainson's Thrush Catharus ustulatus) and two understory resident species (Chestnut-capped Brush-finch Buarremon brunneinuchus and Streak-capped Treehunter Thripadectes virgaticeps) in a fragmented landscape dominated by a pasture matrix in a Sub-Andean region of central Colombia. Swainson's Thrush had no detectable difficulties traversing a pasture matrix and returning to the capture site. Chestnut-capped Brush-finch and Streak-capped Treehunter (understory resident species) avoided making lengthy flights and used stepping-stones and nearby corridors to ease their movement. Providing stepping stones such as live fences and isolated trees and maintaining corridors can enhance functional connectivity in regions with fragmented forests, aiding the conservation of bird species.

A review about the mechanisms associated with active deformation, regional uplift and subsidence in southern South America

A broad range of processes acted simultaneously during the Quaternary producing relief in the Andes and adjacent foreland, from the Chilean coast, where the Pacific Ocean floor is being subducted beneath South American, to the Brazilian and the Argentinean Atlantic platform area. This picture shows to be complex and responds to a variety of processes. The Geoid exemplifies this spectrum of uplift mechanisms, since it reflects an important change at 35°S along the Andes and the foreland that could be indicating the presence of dynamic forces modeling the topography with varying intensity through the subduction margin. On the other hand, mountains uplifted in the Atlantic margin, along a vast sector of the Brazilian Atlantic coast and inland regions seem to be created at the area where the passive margin has been hyper-extended and consequently mechanically debilitated and the forearc region shifts eastwardly at a similar rate than the westward advancing continent. Therefore the forearc at the Arica latitudes can be considered as relatively stationary and dynamically sustained by a perpendicular-to-the-margin asthenospheric flow that inhibits trench roll back, determining a highly active orogenic setting at the eastern Andes in the Subandean region. To the south, the Pampean flat subduction zone creates particular conditions for deformation and rapid propagation of the orogenic front producing a high-amplitude orogen. In the southern Central and Patagonian Andes, mountain (orogenic) building processes are attenuated, becoming dominant other mechanisms of exhumation such as the i) impact of mantle plumes originated in the 660 km mantle transition, ii) the ice-masse retreat from the Andes after the Pleistocene producing an isostatic rebound, iii) the dynamic topography associated with the opening of an asthenospheric window during the subduction of the Chile ridge and slab tearing processes, iv) the subduction of oceanic swells linked to transform zones and v) the accretion of oceanic materials beneath the forearc region. Additionally and after last geodetic studies, vi) exhumation due to co- and post-seismic lithospheric stretching associated with large earthquakes along the subduction zone, also shows to be a factor associated with regional uplift that needs to be further considered as an additional mechanism from the Chilean coast to the western retroarc area. Finally, this revision constitutes a general picture about the different mechanisms of uplift and active deformation along the Southern Andes, in which orogenic processes become dominant north of 35°S, while south of these latitudes dynamic forces seem to predominate all over the Patagonian platform.

Ecological Determinants of Forest to the Abundance ofLutzomyia longiflocosain Tello, Colombia

Lutzomyia longiflocosais considered the most likely vector of cutaneous leishmaniasis in the sub-Andean region of the upper valley of the Magdalena River between 1,000 and 2,000 meters in the Department of Huila, Colombia.L. longiflocosais anthropophilic, has endophagic behavior, and is especially important since its dominance in epidemics recorded in the last decade in the departments of Huila, Tolima, and the outbreak in Norte de Santander. The aim of our work is to identify ecological determinants in forest microhabitat level defining the abundance ofL. longiflocosa. We use sampling; this was performed in 56 microhabitats of 28 forests with CDC traps for two consecutive nights from 18:00 to 06:00 hours. Each microhabitat (favorable and unfavorable) was located 10 m from the ecotone, with an approximate area of 10 m2. Thirty-five variables were examined as potential explanatory variables which were recorded in each microhabitat. Regression models were used to identify ecological determinants. Our results confirm that there are favorable microhabitats in the forest with specific ecological determinants that define the aggregated distribution of the species and provide the conditions necessary for survival and abundance ofL. longiflocosa.

A REMARKABLE CLADONIACEAE FLORA AT SUBANDEAN REGION IN CHÁMEZA (CASANARE, COLOMBIA)

A remarkable Cladoniaceae flora was discovered in the subandean region of Chameza, ( Casanare, Colombia ) at 1200 meters above sea level. Four species of the genus Cladonia (Cladoniaceae, Lichenized Fungi) are new records for Colombia : Cladonia macilentoides, C. scabriuscula, C. sipmanii and C. subdelicatula. This shows the importance of increasing diversity studies at mid elevations where suitable habitats for species of Cladonia occur.

The multiethnic ancestry of Bolivians as revealed by the analysis of Y-chromosome markers.

We have analyzed the specific male genetic component of 226 Bolivians recruited in five different regions ("departments"), La Paz, Cochabamba, Pando, Beni, and Santa Cruz. To evaluate the effect of geography on the distribution of genetic variability, the samples were also grouped into three main eco-geographical regions, namely, Andean, Sub-Andean, and Llanos. All the individuals were genotyped for 17 Y-STR and 32 Y-SNP markers. The average Y-chromosome Native American component in Bolivians is 28%, and it is mainly represented by haplogroup Q1a3a, while the average Y-chromosome European ancestry is 65%, and it is mainly represented by haplogroup R1b1-P25. The data indicate that there exists significant population sub-division in the country in terms of continental ancestry. Thus, the partition of ancestries in Llanos, Sub-Andean, and Andean regions is as follows (respectively): (i) Native American ancestry: 47%, 7%, and 19%, (ii) European ancestry: 46%, 86%, and 75%, and (iii) African ancestry: 7%, 7%, and 6%. The population sub-structure in the country is also well mirrored when inferred from an AMOVA analysis, indicating that among-population variance in the country reaches 9.74-11.15%. This suggests the convenience of using regional datasets for forensic applications in Bolivia, instead of using a global and single country database. By comparing the Y-chromosome patterns with those previously reported on the same individuals on autosomal SNPs and mitochondrial DNA (mtDNA), it becomes clear that Bolivians show a strong gender-bias.

Ancestry analysis reveals a predominant Native American component with moderate European admixture in Bolivians

We have genotyped 46 Ancestry Informative Markers (AIMs) in two of the most populated areas in Bolivia, namely, La Paz (Andean region; n=105), and Chuquisaca (Sub-Andean region; n=73). Using different analytical tools, we inferred admixture proportions of these two American communities by comparing the genetic profiles with those publicly available from the CEPH (Centre d'Etude du Polymorphisme Humain) panel representing three main continental groups (Africa, Europe, and America). By way of simulations, we first evaluated the minimum sample size needed in order to obtain accurate estimates of ancestry proportions. The results indicated that sample sizes above 30 individuals could be large enough to estimate main continental ancestry proportions using the 46 AIMs panel. With the exception of a few individuals, the results also indicated that Bolivians showed a predominantly Native American ancestry with variable levels of European admixture. The proportions of ancestry were statistically different in La Paz and Chuquisaca: the Native American component was 86% and 77% (Mann-Whitney U-test: un-adjusted P-value=2.1×10(-5)), while the European ancestry was 13% and 21% (Mann-Whitney U-test: un-adjusted P-value=3.6×10(-5)), respectively. The African ancestry in Bolivians captured by the AIMs analyzed in the present study was below 2%. The inferred ancestry of Bolivians fits well with previous studies undertaken on haplotype data, indicating a major proportion of Native American lineages. The genetic differences observed in these two groups suggest that forensic genetic analysis should be better performed based on local databases built in the main Bolivian areas.

Crustal thickness map of Brazil: Data compilation and main features

We present a crustal thickness map of Brazil and adjacent areas based on a compilation of data published in the literature as well as new measurements. We used crustal thicknesses mainly derived from seismic datasets such as deep seismic refraction experiments, receiver function analyses, and surface-wave dispersion velocities. Crustal thicknesses derived from modelling gravity anomalies commonly depend on assumptions, such as constant density contrast across the Moho interface, which are not always easily verifiable and were considered only along the continental shelf to fill large gaps in the seismic data. Our compilation shows that the crust in the stable continental area onshore has an average thickness of 39 ± 5 km (1-σ deviation) and that no clear difference can be observed between low altitude, intracratonic sedimentary basins, NeoProterozoic foldbelts (except for the Borborema Province), and cratonic areas. The thinnest crust is found in the Borborema Province of NE Brazil (30–35 km) and along a narrow belt within Tocantins Province (∼35 km), roughly parallel to the Eastern border of the Amazon craton, while the thickest crust is found in the Amazon and São Francisco cratons (41 ± 4 km), and the Paraná Basin (42 ± 4 km). Both the Ponta Grossa and the Rio Grande Arches are areas of thinned crust, and the western border of the Brazilian platform, near the sub-Andean region, seems to be characterized by a crustal thickness of less than 40 km. Although sparse in data coverage, we expect the resulting crustal thickness map to be useful for future studies of isostasy, dynamic topography, and crustal evolution of the country.

Models of crustal thickness for South America from seismic refraction, receiver functions and surface wave tomography

Abstract An extensive compilation of crustal thicknesses is used to develop crustal models in continental South America. We consider point crustal thicknesses from seismic refraction experiments, receiver function analyses, and surface-wave dispersion. Estimates of crustal thickness derived from gravity anomalies were only included along the continental shelf and in some areas of the Andes to fill large gaps in seismic coverage. Two crustal models were developed: A) by simple interpolation of the point estimates, and B) our preferred model, based on the same point estimates, interpolated with surface-wave tomography. Despite gaps in continental coverage, both models reveal interesting crustal thickness variations. In the Andean range, the crust reaches 75 km in Southern Peru and the Bolivian Altiplano, while crustal thicknesses seem to be close to the global continental average (~ 40 km) in Ecuador and southern Colombia (despite high elevations), and along the southern Andes of Chile–Argentina (elevation lower than 2000 m). In the stable continental platform the average thickness is 38 ± 5 km (1-st. deviation) and no systematic differences are observed among Archean–Paleoproterozoic cratons, NeoProterozoic fold belts, and low-altitude intracratonic sedimentary basins. An exception is the Borborema Province (NE Brazil) with crust ~ 30–35 km thick. Narrow belts surrounding the cratons are suggested in central Brazil, parallel to the eastern and southern border of the Amazon craton, and possibly along the TransBrasiliano Lineament continuing into the Chaco basin, where crust thinner than 35 km is observed. In the sub-Andean region, between the mid-plate cratons and the Andean cordillera, the crust tends to be thinner (~ 35 km) than the average crust in the stable platform, a feature possibly inherited from the old pre-Cambrian history of the continent. We expect that these crustal models will be useful for studies of isostasy, dynamic topography, and crustal evolution of the continent.

Land-use change versus natural controls on stream water chemistry in the Subandean Amazon, Peru

Abstract This study evaluates the effects of deforestation and land-use change, as compared to natural controls, on stream water chemistry in the Subandean Amazon. Dissolved major and trace elements were determined near the stream outlet of 48 independent watersheds with varying morphology, bed rock composition and intactness of forest cover (pristine to highly exploited). Geomorphological characteristics were derived from a digital elevation model, geological formations from digitalized maps and forest cover from digital classification of SPOT satellite images. Partial least square regression and multiple linear regression showed that watershed average elevation, which ranged between 396 and 1649 m, was the strongest control on stream water chemistry, explaining >70% of the variation in K and a considerable part also for Mn, U, Mg and HCO 3 with near exponential concentration increases down the altitude gradient. Forest cover, which ranged between 7% and 99%, correlated strongly with average elevation (Spearman correlation coefficient, r s = 0.8), but had no statistically significant impact on stream solute concentrations. Thus, in the studied Subandean region, watershed scale deforestation has not resulted in measurable impacts on stream water chemistry which is dominated by the spatial variation in natural controls.

Neogene magmatism and its possible causal relationship with hydrocarbon generation in SW Colombia

The Cretaceous oil-bearing source and reservoir sedimentary succession in the Putumayo Basin, SW Colombia, was intruded by gabbroic dykes and sills. The petrological and geochemical character of the magmatic rocks shows calc-alkaline tendency, pointing to a subduction-related magmatic event. K/Ar dating of amphibole indicates a Late Miocene to Pliocene age (6.1 ± 0.7 Ma) for the igneous episode in the basin. Therefore, we assume the intrusions to be part of the Andean magmatism of the Northern Volcanic Zone (NVZ). The age of the intrusions has significant tectonic and economic implications because it coincides with two regional events: (1) the late Miocene/Pliocene Andean orogenic uplift of most of the sub-Andean regions in Peru, Ecuador and Colombia and (2) a pulse of hydrocarbon generation and expulsion that has reached the gas window. High La/Yb, K/Nb and La/Nb ratios, and the obtained Sr–Nd–Pb isotopic compositions suggest the involvement of subducted sediments and/or the assimilation of oceanic crust of the subducting slab. We discuss the possibility that magma chamber(s) west of the basin, below the Cordillera, did increase the heat flow in the basin causing generation and expulsion of hydrocarbons and CO2.

More constraints to determine the seismic structure beneath the Central Andes at 21°S using teleseismic tomography analysis

A set of seismological stations was deployed in the Central Andes region along a ∼600 km long profile at 21°S between Chile and Bolivia and operated for a period of almost two years, from March 2002 to January 2004. Here we present the results of the tomographic inversion for P-wave velocity anomalies, based on teleseismic data recorded at the stations. The reliability of the results has been checked by a series of synthetic tests. The tomographic images show high-velocities on the west of the profile that are indicative of cold material from the fore-arc. A low-velocity anomaly is detected at the border between the fore- and the volcanic arc where the Quebrada Blanca seismic anomaly was previously described. This anomaly might be related to the presence of fluids that originate at the cluster of earthquakes at a depth of ∼100 km in the subducted plate. A strong low-velocity anomaly is detected beneath the entire Altiplano plateau and part of the Eastern Cordillera, in agreement with previous receiver function results. The Brazilian Shield is thought to be responsible for the strong high-velocity anomaly underneath the Interandean and Subandean regions.

Remote sensing of floodplain geomorphology as a surrogate for biodiversity in a tropical river system (Madre de Dios, Peru)

The complex floodplains of large rivers offer a striking example of how geomorphology, by dictating patterns in the frequency and duration of soil saturation and surface flooding, influences ecosystem structure and function. This study draws on multiple sources of data from remote sensing, together with ground observations and water sampling, to distinguish floodplain ecosystems in the Madre de Dios River, a tributary of the Amazon River in Perú. This remote tropical river meanders across sub-Andean alluvial deposits in a tectonically active region and creates floodplain surfaces of varying ages, including terraces that are above the reach of present-day river floods. Data from Landsat ETM+ (optical multispectral), JERS-1 (L-band radar), and the Shuttle Radar Topography Mission (C-band interferometric Digital Elevation Models) were integrated in an object-oriented image analysis approach to distinguish five classes of floodplain vegetation. Vegetation classes generally correspond with successional age and reflect the activity of the riverine meander belt. Stage data for the river show erratic fluctuations and an annual range exceeding 8 m, but the maximum depth of floodplain inundation varied from > 1 m close to the river to approximately 0.1 m on more elevated terraces. The major ion composition of standing waters on the floodplain during the dry season indicated the importance of emergence of local groundwater in maintaining saturated soils, particularly further from the river, where backswamp vegetation is distinct and includes palm swamps. Thus, a hydrological continuum exists from deep but sporadic river inundation near the river to constant soil saturation by groundwater emergence in distal backswamps, reflecting the geomorphological origin and age of the floodplain deposits. This hydrogeomorphic continuum results in fundamental ecological differences. The exceptionally rich biodiversity of the sub-Andean region may be ascribed in part to the enhanced biodiversity associated with fluvial geomorphological features, and, thus, conservation planning must account for the diverse landforms created by fluvial dynamics.

Tertiary tectonics of the sub-Andean region of the North Patagonian Andes, southern central Andes of Argentina (41–42°30′S)

The sub-Andean region of the North Patagonian Andes is located between the north Patagonian foreland and the highest elevations of the Andean Cordillera. Its Tertiary contractional structure, active since the upper Late Oligocene and through the upper Late Miocene, corresponds to the external sector of the North Patagonian Andes fold-and-thrust belt, which is characterized by east-vergent thrusts that affect stratified Cenozoic rocks. The units involved in the deformation correspond to El Maitén Oligocene volcanic belt, deformed between east-vergent thrusts and backthrusts, and Oligocene–Miocene sedimentary rocks of the Ñirihuau–Collón Curá Basin. The northern sector of the basin was structured as a thin-skinned fold belt that comprises the Ñirihuau fold belt and a frontal sedimentary wedge. To the south, sedimentary depocenters are confined between medium- to high-angle reverse faults with evidence of basement structural control. In both cases, the general tectonosedimentary framework shows the youngest units toward the east, in agreement with the advance of the orogenic wedge. Most of the Ñirihuau–Collón Curá Basin infill fits a foreland basin system model. Some sectors of the basin show evidence of structural control by normal faults in the initial sedimentation stages. This early extensional regime might be associated with late phases of Oligocene volcanism. Extensional structures probably were partially reactivated during the upper Late Oligocene, as suggested by seismic data.

Morphometrical evidence for speciation within Bolivian Lutzomyia aragaoi (Diptera: Psychodidae)

For Bolivian specimens of Lutzomyia aragaoi (Costa Lima, A., 1932. Sobre os phlebotomos americanos (Diptera, Psychodidae). Mem. Inst. Oswaldo Cruz 26, 15–69), collected in the same light-traps, we show the existence of two distinct morphotypes distinguished by male parameres. These sympatric forms were observed in the Alto Beni, Subandean region of Bolivia, and in the North Beni, Amazonian region of Bolivia, two areas separated by large, sparsely forested, “llanos”. Univariate morphometric comparisons between these two forms showed non-overlapping variation of size for external structures of the genitalia (lateral lobe, style and coxite), allowing separation of them on the basis of a single measurement. Multivariate discriminant analysis of head and wing dimensions—excluding genitalia structures—grouped the insects according to their morphotype instead of their geographic origins. The two forms also showed different patterns in number and distribution of low mesepisternal setae. The existence of these two separate forms in close sympatry suggests reproductive isolation, hence a speciation process.

The influence of intraplate structural accommodation zones on delineating petroleum provinces of the Sub-Andean foreland basins

The Sub-Andean foreland region is summarized in a series of palaeogeographical maps. Various time-slices show important basin-forming processes and the extent and evolution of principal depositional elements. Based on spatial and temporal changes in palaeodepositional setting, the Sub-Andean region can be subdivided longitudinally into a number of tectonostratigraphic domains. The differential amount of subsidence between two adjacent tectonostratigraphic provinces or sub-provinces has been taken up across, complex, broad, transverse, transcontinental accommodation zones, which probably represent the multiphase reactivation of pre-existing fault systems in the underlying basement. Two predominant sets of basement lineaments are recognized: ENE–WSW and NW–SE. Both sets of lineaments occur as major structural anisotropies throughout the basement rocks of South America, providing zones of weakness, which were repeatedly reactivated and, at least in part, controlled: (a) the geometry of inter- and intra-cratonic rifting; (b) rates of subsidence and uplift along the Andean depositional axis; (c) the position of basin-bounding and intra-basinal highs/arches; (d) the structural geometry of the Andean Deformation Zone, correlating with changes in deformational style and major deflections; and (e) the location of magmatism. Based primarily on source rock age, it is suggested that these transverse, structural accommodation zones had a profound effect on source rock distribution and hydrocarbon occurrence; subdividing the Sub-Andean region into five petroleum provinces/megasystems: a ‘Northern’ Late Cretaceous (La Luna Formation and equivalents); a ‘Western’ Late Palaeozoic–Early Mesozoic (Permian and Upper Triassic to Lower Jurassic source rocks); a ‘Central’ Palaeozoic (Late Devonian and Silurian); an ‘Eastern’ Tertiary; and a ‘Southern’ Mesozoic.

A tectonostratigraphic synthesis of the Sub-Andean basins: implications for the geotectonic segmentation of the Andean Belt

The tectonic, structural and depositional history of 19 Sub-Andean foreland and eight southern Caribbean basins has been synthesized and is summarized by regional geohistory charts. These charts recapitulate the subsidence regimes recognized and have been used to evaluate correlations between genetically related stratigraphic sequences. Based on spatial and temporal changes in palaeo-depositional setting, the Sub-Andean region can be subdivided longitudinally into several tectonostratigraphic domains. The differential amount of subsidence between two adjacent tectonostratigraphic provinces or sub-provinces relies on the presence of a transverse zone of structural accommodation. The location of these transfer zones correlates with a number of known and several newly identified zones of intracontinental deformation. Combined with changes in the structural geometry of the Andean Fold and Thrust Belt and the relative dominance of basement fault systems along the length of the Andean foreland, it is suggested that the Andean Belt can be separated into five tectonic domains (which are themselves bounded by transverse, structural accommodation zones). Representing the multiphase reactivation of pre-existing basement fault systems, the influence of these broad zones of transcontinental deformation is most apparent during the Triassic–Jurassic period, suggesting that they were intimately associated with accommodating intraplate stresses during the breakup of the Gondwana Supercontinent.

Co-infection by Leishmania amazonensis and L. infantum/ L. chagasi in a case of diffuse cutaneous leishmaniasis in Bolivia

We present the first report of a co-infection by Leishmania amazonensis and L. infantum/L. chagasi isolated in 1993 from a patient with diffuse cutaneous leishmaniasis (DCL), living in the sub-Andean region of Bolivia. This is the third reported case of DCL in Bolivia, but the first one with isoenzymatic identification of the aetiological agents involved and the first one giving evidence for a mixed infection by 2 Leishmania parasites in the same lesion.

EFFECT OF NATURAL AND ANTHROPOGENIC LANDSCAPE MATRICES ON THE ABUNDANCE OF SUBANDEAN BIRD SPECIES

The nature of the landscape matrix can control the capacity of forest organisms to move among forest patches. Some matrices may constitute foraging or breeding habitat and, as a result, could influence the local abundance of forest organisms and their persistence in fragmented landscapes. This study represents a first approach to examining the effect of natural vs. anthropogenic landscape matrices on the abundance of neotropical birds in forest sites. The influence of three contrasting matrices on the relative abundance of 113 bird species in a subandean region was evaluated. Species were grouped into categories showing the same response to the matrix, and these groups were then examined to determine whether ecological characteristics or taxonomic affinities were associated with responses to surrounding matrices. The abundance of individual species in forest plots within a continuous forest matrix was compared with their abundance in forest fragments embedded in pastures or exotic-tree plantations. The matrix surrounding forest areas was a major factor influencing bird abundance: 65.5% of the species showed significant differences in abundance among sites surrounded by different matrices. The most important explanatory factors in the variation in abundance within fragments were: abundance within continuous forest, presence in the anthropogenic matrices, migratory strategy, and habitat association. Species with small geographic ranges and species of terrestrial insectivores had low tolerance to fragmentation. Responses were highly species specific and largely independent of foraging strata, trophic group, and taxonomic affinities. Several lines of evidence indicate an increased connectivity among forest remnants surrounded by exotic-tree plantations compared to pastures. Landscape supplementation by the exotic-tree plantation matrix was observed for a hummingbird species. These results suggest that structurally complex anthropogenic matrices have potential as management tools for bird conservation by complementing habitat protection and restoration.