Modeling the Effect of Traffic Calming on Local Animal Population Persistence

A steady growth in traffic volumes in industrialized countries with dense human populations is expected, especially on minor roads. As a consequence, the fragmentation of wildlife populations will increase dramatically. In human-dominated landscapes, typically minor roads occur in high densities, and animals encounter them frequently. Traffic calming is a new approach to mitigate negative impacts by reducing traffic volumes and speeds on minor roads at a regional scale. This leads to a distinction between roads with low volumes as being part of the traffic-calmed area, whereas roads with bundled traffic are located around this area. Within the traffic-calmed area, volumes and speeds can be decreased substantially; this is predicted to decrease the disturbance and mortality risk for animals. Thus far, data on the effects of traffic calming on wildlife population persistence remain scarce. Using metapopulation theory, we derived a model to estimate thresholds in the size of traffic-calmed areas and traffic volumes that may allow persistent populations. Our model suggests that traffic calming largely increases the persistence of roe deer in a landscape with a dense road network. Our modeling results show trade-offs between traffic volume on roads within the traffic-calmed area and both the area of habitat available for this species in the traffic-calmed area and the size of the traffic-calmed area. These results suggest ways to mitigate the fragmentation of wildlife habitat by road networks and their expected traffic volume

Astrometry of circumstellar masers

The circumstellar masers around evolved stars offer an interesting possibility to measure stellar parameters through VLBI astrometry. In this paper the application of this technique is discussed, including the accuracy and the uncertainties of the method. The different maser species (OH, H_2O, SiO) have slightly different characteristics and applications. This paper does not concern astrometry of maser spots to study the kinematics of the envelope, but concentrates on attempting to measure the motion of the underlying star.Comment: 8 pages, 2 figures, to appear in "Mass-losing Stars and their Circumstellar Matter", eds Y. Nakada & M. Honma, Kluwer ASSL serie

Local positive feedback and the persistence and recovery of fringe Avicennia marina (Forssk.) Vierh. mangroves

While mangrove restoration efforts are reasonably successful, failure often occurs in high wave energy situations. Due to differences in wave energy, seedling mortality rates vary strongly with position on the intertidal flat between high water spring and high water neap elevations. However, a local positive feedback can be present between the pneumatophores of adult mangroves and the survival of mangrove seedlings to trigger recovery. In this study, a mangrove population of Avicennia marina is modelled to determine the effects of seedling mortality and local positive feedback on mangrove recovery. The model uses life history data and dispersal to simulate population dynamics. The mangrove range limits are determined by high water spring and high water neap levels. The results indicate that within these limits mangrove populations with life-history parameter values as derived from literature are indeed capable of fast growth under conditions with low seedling mortality. Local positive feedback has then a small positive influence on population recovery after mangrove loss. If, however, mortality rates increase, such as in high wave energy situations, the importance of a positive feedback increases. The model shows that a positive feedback may, given high seedling mortality rates, be an important factor for mangrove recovery. While a positive feedback may enable mangrove persistence in unfavourable conditions, destruction of adult mangroves can remove the positive feedback, which would render the system uninhabitable and practically prohibits reforestation of such areas. The model results and the presence of positive feedbacks and their importance for population dynamics in harsh conditions indicate that investigating and understanding possible feedbacks could be crucial for successful restoration effort

Not only the butterflies: managing ants on road verges to benefit Phengaris (Maculinea) butterflies

Obligate myrmecophilic butterfly species, such as Phengaris (Maculinea) teleius and P. nausithous, have narrow habitat requirements. Living as a caterpillar in the nests of the ant species Myrmica scabrinodis and M. rubra, respectively, they can only survive on sites with both host ants and the host plant Great Burnet Sanguisorba officinalis. After having been reintroduced into a nature reserve in the Netherlands in 1990, both butterfly species expanded their distribution to linear landscape elements such as road verges and ditch edges outside this reserve. As additional habitat of both butterfly species, vegetation management of these landscape elements became important. Our results show that a management beneficial for Phengaris butterflies should aim to increase the nest density of Myrmica species, at the same time reducing the density of nests of the competitor Lasius niger or at least keeping them at a low density. Unfavourable grassland management under which L. niger thrives, includes not mowing or flail-cutting the grass, or depositing dredgings along the side of the ditch. Management favourable for the two Myrmica species differs, demanding some flexibility if both species are to benefit. M. scabrinodis is best supported with early mowing of the road verge vegetation or late mowing in the nature reserve, both of which result in an open vegetation and warm microclimate. In contrast, the nest sites of M. rubra should be left undisturbed during the summer, and mown in late autumn. Mowing of butterfly habitat should be avoided between mid-June and mid-September as this would remove the flowerheads of the Sanguisorba plants, on which the butterflies lay their eggs

Contrasting timing of parturition of chital Axis axis and gaur Bos gaurus in tropical South India - the role of body mass and seasonal forage quality

Seasonal variation in forage availability and quality is understood to affect the annual timing of parturition in large herbivores. In India-where seasonal monsoonal rains define variation in forage availability and quality-chital Axis axis exhibit stronger seasonality in parturition than the larger gaur Bos gaurus. We hypothesized that this difference can be explained by forage requirements determined by body mass. We developed a model to simulate changes in leaf biomass and nitrogen content based on plant available moisture and nutrients, and calibrated our model with field data. Our results show that the minimum forage nitrogen content required by lactating gaur was available throughout the year, but that required by lactating chital was available for less than 40% of the year, i.e. during the early wet season, which coincides with the annual peak period of chital births. The three to four month spread of chital births, which begins in the dry season, implies that the period of highest quality is also important for females to replenish maternal reserves for future reproduction and help maximize the growth rate of neonates. This spread also indicates low synchrony of chital births and suggests that predator swamping was less important in influencing their timing of parturition. As monsoonal rain exhibits annual temporal variation, we analyzed our model under different rainfall patterns while keeping the total annual rainfall constant. We found that the difference between the durations of how long forage quality is available to satisfy the minimum requirements of lactating gaur and lactating chital is similar for all simulated patterns. This insensitivity to variable rainfall patterns lends support to our hypothesis that forage requirements determined by body mass is one plausible explanation for the variation in parturition strategies among large herbivores species

Molecular outflows and 1000 AU structure of low mass YSO envelopes

We present the results of an observational study into the molecular outflows and small scale ( ~ 1000 AU) envelope structure of a sample of nine low mass young stellar objects (YSOs) in Taurus. The characteristics of the outflows are derived from ^(12)CO J = 3 - 2 mapping with the James Clerk Maxwell Telescope, while the envelopes are imaged in the HCO^+ 1-0, ^(13)CO 1- 0 and C^(18)O 1-0 emission lines with the Owens Valley Millimeter Array. Using dust envelope continuum fluxes at 1 mm as the basis for an evolutionary ordering, a picture emerges in which the mass, extent, and collimation of outflows decreases over time as the envelopes become less massive, the opening angle of the outflow cavity increases, and mass accretion through the disk slows down. On 1000 AU scales the HCO+ and ^(13)CO/C^(18)O emission in the envelope is closely related to the outflow cavity, often outlining the cavity walls. In addition, the envelopes are clumpy, and two sources appear surrounded by an incomplete ring or torus, 1500-3000 AU in radius. The role of the outflow in shaping the small scale molecular emission may be passive (creating a low-opacity pathway for heating radiation) rather than, or in addition to, active (compressing and shock-heating the material)

The spatial distribution of excited H_2 in T Tau: a molecular outflow in a young binary system

Strong extended emission from molecular hydrogen in the v = 1 → 0 S(l) transition is mapped around T Tau. In addition, the v = 2 → 1 S(l) line is detected close to the star. The ratio of the two transitions is consistent with an excitation process in which both fluorescence by stellar ultraviolet radiation and collisions in a warm, dense medium play a role. The morphology is interpreted as emission from a molecular outflow which appears to wiggle as a result of the fact that T Tau is a binary system seen almost pole-on. It is shown that an outflow with a small opening angle can reproduce the observed extended emission. From comparison with previous studies it is argued that the molecular outflow originates from T Tau S, the infrared component. The presented model constrains the orientation and geometry of the system

Habitat connectivity and fragmented nuthatch populations in agricultural landscapes

In agricultural landscapes, the habitat of many species is subject to fragmentation. When the habitat of a species is fragmented and the distances between patches of habitat are large relative to the movement distances of the species, it can be expected that the degree of habitat connectivity affects processes at population and individual level. In this thesis, I report on a study of effects of habitat fragmentation and opportunities to mitigate these effects by planning ecological networks. The objective of the study is to contribute to an improved knowledge about the effects of fragmentation and defragmentation of habitat on populations, in particular effects of differences in the degree of habitat connectivity on colonization and habitat selection. The main question of the research was: do networks of patches contribute to population sustainability of species in fragmented habitat?The development of planning for nature in the Netherlands is sketched in the second chapter. It is illustrated with the spatial concepts for the rural areas that landscape planning became landscape ecological based. After this chapter, I addressed three questions that were derived from the main question.The first question was: what variables can measure the degree of connectivity of habitat patches and are the differences in the degree of connectivity related to the colonization probability of patches? Therefore, habitat patches and the distances between these patches were modelled as networks. In landscapes with fragmented habitat for a certain species, these networks appear as so-called nonconnected networks consisting of disjointed subsets of patches. Between these subsets, exchange of individuals happens seldom of never.We derived parameters that measure the degree of connectivity of the patches in those networks. The parameters can deal with the size (the number of elements) and the spatial configuration of these subsets. One of the parameters was used to investigate the relationship between the degree of connectivity measured at different spatial scales and colonization of unoccupied patches by the nuthatch Sitta europaea in three regions in the Netherlands.To vary the spatial scale, I used threshold distances as maximum dispersal distances for which the degree of habitat connectivity was calculated. Habitat patches are assumed to be connected when the distances between the patches are less than this threshold distance. The degree of habitat connectivity measured for threshold distances of approximately 2.4 to 3 km best explains the differences in the colonization probability of unoccupied patches. These threshold distances give an indication of the distances covered by dispersing nuthatches that led to successful colonizations. Moreover, I could give an indication of the range of threshold distances where effects of constrained dispersal can be expected in the three regions.The second question was: is habitat selection limited in landscapes with fragmented habitat? Therefore, effects of the degree of habitat connectivity on the selection of territories were investigated. Based on a spatially explicit individual-based model, it could be hypothesized that habitat selection is limited when the degree of connectivity is low. This hypothesis was tested with empirical data of nuthatches in four regions in the Netherlands. One of the regions can be considered as the reference region with contiguous habitat where dispersal is not constrained. The habitat quality for nuthatches could be measured by the mean trunk diameter of oaks and beeches.We concluded that selection of territories is limited in fragmented habitat compared to selection in contiguous habitat. The quality of the occupied territories in fragmented habitat is lower than in contiguous habitat. This is especially the case when the population level is low. We showed that a lower average breeding success can be found in territories with low degree of connectivity. The results indicate the absence of a negative feedback between population level and the average breeding success in fragmented habitat, which contributes to the increased extinction probability of populations. Among other factors, limited habitat selection in fragmented habitat may thus result in a lower population density than in contiguous habitat.The degree of habitat connectivity can increase due to the allocation of new habitat. This may mitigate the effects of fragmentation. The third question was: how can networks of patches be optimally allocated in agricultural landscapes that both meets the requirements for population sustainability and takes into consideration the suitability of the land for competing land uses? We developed two spatial allocation models that plan new habitat considering ecological guidelines of minimum patch sizes and maximum threshold distances and the suitability of the land for competing land uses. The model MENTOR adds new patches that may act as "stepping stones" between reserve sites. The model ENLARGE enlarges existing sites. We showed that both the allocation of stepping stones and the enlargement of existing sites provide a higher percentage of occupied habitat. An interesting question for further research is under which conditions either the allocation of stepping stones or the enlargement of existing sites is preferred as strategy for conservation planning in human-dominated landscapes.The results of the research provide evidence that the degree of habitat connectivity determines both the colonization probability of unoccupied patches and the selection of habitat. They also give an indication at what spatial scale the degree of habitat connectivity affects these processes as observed for nuthatches. When through networks of patches the degree of habitat connectivity can be enhanced, positive effects on population sustainability can be expected. This thesis contributes to an improved problem detection of effects of habitat fragmentation and explores opportunities for defragmentation of habitat and optimization of land use allocation in human-dominated landscapes. With the knowledge about the effects of fragmentation and defragmentation, this study may be a step forward to enhance and preserve biodiversity.</p

Subarcsecond Imaging at 267 GHz of a Young Binary System: Detection of a Dust Disk of Radius Less than 70 AU around T Tauri N

The young binary system T Tauri was observed with the Owens Valley Millimeter Array in the 267 GHz continuum and HCO^+ J = 3-2 emission at 0".8 resolution, with the single-baseline interferometer of the James Clerk Maxwell Telescope-Caltech Submillimeter Observatory in the 357 GHz continuum and with the W. M. Keck Telescope at λ = 4 μm. The 267 GHz emission is unresolved, with a flux of 397±35 mJy, located close to the position of the optical star T Tau N. An upper limit of 100 mJy is obtained toward the infrared companion T Tau S. The 357 GHz continuum emission is unresolved, with a flux of 1.35±0.68 Jy. HCO^+ J = 3-2 was detected from a 2" diameter core surrounding T Tau N and S. Both stars are detected at 4 μm, but there is no evidence of the radio source T Tau R. We propose a model in which T Tau S is intrinsically similar to T Tau N but is obscured by the outer parts of T Tau N's disk. A fit to the spectral energy distribution (SED) between 21 cm and 1.22 μm is constructed on this basis. Adopting an r^(−1) surface density distribution and an exponentially truncated edge, disk masses of 0.04±0.01 and 6×10^(−5) to 3×10^(−3) M_☉ are inferred for T Tau N and T Tau S, respectively. A 0.005-0.03 M_☉ circumbinary envelope is also required to fit the millimeter to mid-infrared SED

Lifetime of OH masers at the tip of the asymptotic giant branch

Context: A large fraction of otherwise similar asymptotic giant branch stars (AGB) do not show OH maser emission. As shown recently, a restricted lifetime may give a natural explanation as to why only part of any sample emits maser emission at a given epoch. Aims: We wish to probe the lifetime of 1612 MHz OH masers in circumstellar shells of AGB stars. Methods: We reobserved a sample of OH/IR stars discovered more than 28 years ago to determine the number of stars that may have since lost their masers. Results: We redetected all 114 OH masers. The minimum lifetime inferred is 2800 years (1 sigma). This maser lifetime applies to AGB stars with strong mass loss leading to very red infrared colors. The velocities and mean flux density levels have not changed since their discovery. As the minimum lifetime is of the same order as the wind crossing time, strong variations in the mass-loss process affecting the excitation conditions on timescales of ~3000 years or less are unlikely. Keywords: OH masers -- Stars: AGB and post-AGB -- circumstellar matterComment: 8 pages, 5 figures, accepted for publication in Astronomy & Astrophysic