43 research outputs found
Annual survival rate of tropical stingless bee colonies (Meliponini): variation among habitats at the landscape scale in the Brazilian Atlantic Forest
Stingless social bees live in perennial colonies whose longevity is influenced by various ecological factors. This study analyzed the influence of habitat anthropization and native forest regeneration stage on the longevity of natural colonies at the landscape scale. Random sampling of 25x25m plots, totaling 30ha per habitat type, located and monitored 118 nests of 14 species in the forest and 105 nests of six species in the anthropic habitat. Significant differences in colony longevity were observed between young and long-lived forests and between long-lived forests and anthropized habitat. Shorter longevities have generally been associated with a set of smaller-bodied species residing in anthropized habitats. The greatest longevities were associated with the three abundant and exclusive forest species, and was similar in the two forest regeneration stages: Melipona scutellaris, Scaptotrigona xanthotricha and Scaptotrigona bipunctata had high annual survival rates ranging from 87% to 93%. Another abundant species in the landscape was Tetragonisca angustula, a small habitat-generalist with short longevity (63%) that varied among habitats. Euclidean distance analysis based on this generalist placed young forest closest to anthropic habitat, and grouped the replicates of long-lived forest. Considering spatial variation in the life history traits, we infer that, among prospective landscape habitats, the Atlantic Forest favors stingless bees with high colonial longevity. On the other hand, generalists, such as T. angustula, with shorter colonial longevity and high reproduction rates are being favored by the expansion of anthropized habitats in place of deforested areas
Permeability of matrices of agricultural crops to Euglossina bees (Hymenoptera, Apidae) in the Atlantic Rain Forest
International audienceAbstractWe evaluate the permeability of three matrices of arboreal crops for the Euglossina bees that inhabit the Brazilian Atlantic rainforest hotspot. The comparisons of occurrences and abundances within three mosaics of forest and extensive arboreal crops (piassava palm, oil palm, and rubber tree) showed that all the matrices were permeable to most orchid bees. The piassava palm was the most permeable, where the spatial distribution of all species of Euglossina did not differ between forest fragments and matrix. The oil palm has shown some loss of permeability to Eulaema atleticana, while the rubber tree crop was not so permeable to El. atleticana and Euglossa imperialis. Euglossa iopoecila was sampled only in the forest fragments. At the present scale of forest cover in the three studied mosaics (10 to 40Â %), the arboreal matrices are contributing towards the functional connectivity in the Atlantic Rain Forest at both scales: the landscape mosaic and the Brazilian Atlantic Forest corridor
The Stellar Content of Obscured Galactic Giant HII Regions V: G333.1--0.4
We present high angular resolution near--infrared images of the obscured
Galactic Giant HII (GHII) region G333.1--0.4 in which we detect an OB star
cluster. For G333.1--0.4, we find OB stars and other massive objects in very
early evolutionary stages, possibly still accreting. We obtained --band
spectra of three stars; two show O type photospheric features, while the third
has no photospheric features but does show CO 2.3 m band--head emission.
This object is at least as hot as an early B type star based on its intrinsic
luminosity and is surrounded by a circumstellar disc/envelope which produces
near infrared excess emission. A number of other relatively bright cluster
members also display excess emission in the --band, indicative of
disks/envelopes around young massive stars. Based upon the O star photometry
and spectroscopy, the distance to the cluster is 2.6 0.4 kpc, similar to
a recently derived kinematic (near side) value. The slope of the --band
luminosity function is similar to those found in other young clusters. The mass
function slope is more uncertain, and we find - for stars with M M where the upper an lower limits are
calculated independently for different assumptions regarding the excess
emission of the individual massive stars. The number of Lyman continuum photons
derived from the contribution of all massive stars in the cluster is 0.2
. The
integrated cluster mass is 1.0
.Comment: 31 pages, including 12 figures and 3 tables. Accepted for publication
in the A
The Stellar Content of Obscured Galactic Giant HII Regions. VII. W3
Spectrophotometric distances in the K band have been reported by different
authors for a number of obscured Galactic HII regions. Almost 50% of them show
large discrepancies compared to the classical method using radial velocities
measured in the radio spectral region. In order to provide a crucial test of
both methods, we selected a target which does not present particular difficulty
for any method and which has been measured by as many techniques as possible.
The W3 star forming complex, located in the Perseus arm, offers a splendid
opportunity for such a task. We used the NIFS spectrograph on the Frederick C.
Gillett Gemini North telescope to classify candidate "naked photosphere" OB
stars based on 2MASS photometry. Two of the targets are revealed to be mid
O-type main sequence stars leading to a distance of d = 2.20 kpc. This is in
excellent agreement with the spectrophotometric distance derived in the optical
band (d = 2.18 kpc, Humphreys 1978) and with a measurement of the W3
trigonometric parallax (d = 1.95 kpc, Xu et al. 2006). Such results confirm
that the spectrophotometric distances in the K band are reliable. The radio
derived kinematic distance, on the contrary, gives a distance twice as large (d
= 4.2 kpc, Russeil 2003). This indicates that this region of Perseus arm does
not follow the Galactic rotation curve, and this may be the case also for other
HII regions for which discrepancies have been found
Disks in the Arches cluster -- survival in a starburst environment
Deep Keck/NIRC2 HK'L' observations of the Arches cluster near the Galactic
center reveal a significant population of near-infrared excess sources. We
combine the L'-band excess observations with K'-band proper motions, to confirm
cluster membership of excess sources in a starburst cluster for the first time.
The robust removal of field contamination provides a reliable disk fraction
down to our completeness limit of H=19 mag, or about 5 Msun at the distance of
the Arches. Of the 24 identified sources with K'-L' > 2.0 mag, 21 have reliable
proper motion measurements, all of which are proper motion members of the
Arches cluster. VLT/SINFONI K'-band spectroscopy of three excess sources
reveals strong CO bandhead emission, which we interpret as the signature of
dense circumstellar disks. The detection of strong disk emission from the
Arches stars is surprising in view of the high mass of the B-type main sequence
host stars of the disks and the intense starburst environment. We find a disk
fraction of 6 +/- 2% among B-type stars in the Arches cluster. A radial
increase in the disk fraction from 3 to 10% suggests rapid disk destruction in
the immediate vicinity of numerous O-type stars in the cluster core. A
comparison between the Arches and other high- and low-mass star-forming regions
provides strong indication that disk depletion is significantly more rapid in
compact starburst clusters than in moderate star-forming environments.Comment: 51 pages preprint2 style, 22 figures, accepted by Ap
Spectrophotometric Distances to Galactic H\,{\sc{ii}} Regions
We present a near infrared study of the stellar content of 35 H\,{\sc{ii}}
regions in the Galactic plane. In this work, we have used the near infrared
domain , and band color images to visually inspect the
sample. Also, color-color and color-magnitude diagrams were used to indicate
ionizing star candidates, as well as, the presence of young stellar objects
such as classical TTauri Stars (CTTS) and massive young stellar objects
(MYSOs). We have obtained {\it Spitzer} IRAC images for each region to help
further characterize them. {\it Spitzer} and near infrared morphology to place
each cluster in an evolutionary phase of development. {\it Spitzer} photometry
was also used to classify the MYSOs. Comparison of the main sequence in
color-magnitude diagrams to each observed cluster was used to infer whether or
not the cluster kinematic distance is consistent with brightnesses of the
stellar sources. We find qualitative agreement for a dozen of the regions, but
about half the regions have near infrared photometry that suggests they may be
closer than the kinematic distance. A significant fraction of these already
have spectrophotometric parallaxes which support smaller distances. These
discrepancies between kinematic and spectrophotometric distances are not due to
the spectrophotometric methodologies, since independent non-kinematic
measurements are in agreement with the spectrophotometric results. For
instance, trigonometric parallaxes of star-forming regions were collected from
the literature and show the same effect of smaller distances when compared to
the kinematic results. In our sample of H\,{\sc{ii}} regions, most of the
clusters are evident in the near infrared images. Finally, it is possible to
distinguish among qualitative evolutionary stages for these objects.Comment: 59 pages, 146 figures and 4 tables. MNRAS accepte
The Stellar Content of Obscured Galactic Giant H II Regions IV.: NGC3576
We present deep, high angular resolution near-infrared images of the obscured
Galactic Giant H II region NGC3576. Our images reach objects to ~3M_sun. We
collected high signal-to-noise K-band spectra of eight of the brightest
objects, some of which are affected by excess emission and some which follow a
normal interstellar reddening law. None of them displayed photospheric features
typical of massive OB type stars. This indicates that they are still enshrouded
in their natal cocoons. The K-band brightest source (NGC3576 #48) shows CO 2.3
micron bandhead emission, and three others have the same CO feature in
absorption. Three sources display spatially unresolved H_2 emission, suggesting
dense shocked regions close to the stars. We conclude that the remarkable
object NGC3576 #48 is an early-B/late-O star surrounded by a thick
circumstellar disk. A number of other relatively bright cluster members also
display excess emission in the K-band, indicative of reprocessing disks around
massive stars (YSOs). Such emission appears common in other Galactic Giant H II
regions we have surveyed. The IMF slope of the cluster, Gamma = -1.51, is
consistent with Salpeter's distribution and similar to what has been observed
in the Magellanic Cloud clusters and in the periphery of our Galaxy.Comment: 14 pages, 11 figures, accepted for publication in A