Ephemeral Pleistocene woodlands connect the dots for highland rattlesnakes of the Crotalus intermedius group

Aim To test how Pleistocene climatic changes affected diversification of the Crotalus intermedius species complex. Location Highlands of Mexico and the south‐western United States (Arizona). Methods We synthesize the matrilineal genealogy based on 2406 base pairs of mitochondrial DNA sequences, fossil‐calibrated molecular dating, reconstruction of ancestral geographic ranges, and climate‐based modelling of species distributions to evaluate the history of female dispersion. Results The presently fragmented distribution of the C. intermedius group is the result of both Neogene vicariance and Pleistocene pine–oak habitat fragmentation. Most lineages appear to have a Quaternary origin. The Sierra Madre del Sur and northern Sierra Madre Oriental are likely to have been colonized during this time. Species distribution models for the Last Glacial Maximum predict expansions of suitable habitat for taxa in the southern Sierra Madre Occidental and northern Sierra Madre Oriental. Main conclusions Lineage diversification in the C. intermedius group is a consequence of Pleistocene climate cycling. Distribution models for two sister taxa in the northern and southern Sierra Madre Occidental and northern Sierra Madre Oriental during the Last Glacial Maximum provide evidence for the expansion of pine–oak habitat across the Central Mexican Plateau. Downward displacement and subsequent expansions of highland vegetation across Mexico during cooler glacial cycles may have allowed dispersal between highlands, which resulted in contact between previously isolated taxa and the colonization of new habitats.     

Bird communities of dry forests and oak woodland of western Mexico

Bird species-richness and densities were studied in spring and autumn of 1991 and 1992 in dry forest and oak woodland in western Mexico. Classification of the vegetation resulted in the identification of six dry forest types: from thorn forests, dominated by Acacia , through broad-leaved tree forest (typical dry forest of western Mexico) and small-leaved tree forest to Ipomoea forest. Oak woodland and mixed woodland, which are a transition between dry forest and the more mesic oak woodland, formed two further forest types. In the study area as a whole, bird densities were higher in autumn, following the rainy season, than in spring, which is the dry season, and the beginning of the breeding season. Densities in the two autumns were very similar (mean 93 ± 7.8 birds per 2.8 ha) but differed significantly between spring 1991 (57 ± 2.2 per 2.8 ha) and spring 1992 (70 ± 3.2 per 2.8 ha), possibly due to unseasonal rain in 1992. In autumn, bird densities were highest in thorn forests and lowest in broad-leaved tree forests and oak woodland. In spring 1991, bird densities were highest in Prosopis thorn forest and mixed woodland, and lowest in oak woodland. Bird species-richness was low in oak woodland, in both seasons, and high in mixed woodland and Ipomoea forest in spring. Bird species composition between forest types was more similar in the spring than autumn. The spring similarity in species composition is explained by the presence of generalist species in times of food scarcity during the dry season, and by the homogeneity of the predominantly leafless vegetation. Comparison with the bird species composition of a dry forest in Venezuela and the Pacific coast of Mexico indicates that the sites in the present study have an intermediate number of species. Although the present study recorded a smaller number of bird species than on the Pacific coast, 16 were different, expanding the total for Mexican dry forest by 14% from 118 to 134.     

Vegetation associations of birds wintering in a California oak woodland

Conditions in wintering areas can have persistent effects throughout the year for bird populations. Most studies, however, are conducted during the breeding season and the non‐breeding ecology of many species remains poorly understood. We assessed vegetation associations of birds wintering in a diverse, well‐structured oak woodland in coastal‐central California. We calculated density estimates for 20 bird species and examined correlations between bird densities and vegetation characteristics as described by a principal components analysis. Ruby‐crowned Kinglets (Regulus calendula) and Hutton's Vireos (Vireo huttoni) were positively associated with vegetation characteristic of dense, floristically diverse woodland with abundant coast live oak (Quercus agrifolia) cover and a structurally complex understory. Conversely, White‐breasted Nuthatches (Sitta carolinensis) and Western Bluebirds (Sialia mexicana) were negatively correlated with dense woodland and occurred at the highest densities on plots with large widely spaced blue oaks (Q. douglasii) and a sparse understory. Thirteen of the remaining 16 species were more abundant in dense woodland patches, but these relationships were not statistically significant. Our results are in agreement with those of previous studies and suggest that evergreen oak trees and a dense understory provide key resources (e.g., cover and food) for some bird species during the winter. However, areas with large widely spaced deciduous oaks are important habitats for other species. We therefore suggest that dense patches of live oaks and shrubs should be retained, but a mosaic of dense and sparse woodland is necessary to accommodate the entire suite of oak‐woodland birds.     

Assessing occupancy and habitat connectivity for Baird’s tapir to establish conservation priorities in the Sierra Madre de Chiapas,Mexico

Baird’s tapir (Tapirus bairdii) is the largest native mammal that inhabits the Neotropics, and it is enlisted as Endangered by the IUCN Red List. The historic distribution of this species included the area from southern Mexico to northern Colombia. However, its distribution and populations have been reduced drastically during the past 30 years. The main threats for Baird’s tapir are the direct persecution for subsistence hunting, habitat destruction, and habitat fragmentation. In this study, we used camera traps and occupancy models to identify the landscape characteristics that were associated with the occurrence of tapirs in the Sierra Madre de Chiapas, which is one of the most important populations of the species in Mexico, with the aim to identify areas with habitat suitability for the species. We used our best occupancy model to generate a resistance matrix to develop a model of habitat connectivity using Circuit Theory. According to the best occupancy model, the most suitable areas for this species were the forested areas located at the highest elevations of the mountain ranges that provided rugged terrain. We identified three critical corridors to allow for the connectivity of tapir populations in the Sierra Madre de Chiapas, and one of these corridors provides connectivity between this population and the population in the Ocote Biosphere Reserve. With this approach, we propose a conservation strategy for the species that incorporates a more realistic and detailed scheme of Baird’s tapir occurrence in the Sierra Madre de Chiapas region. Priority actions to conserve tapirs in the Sierra Madre de Chiapas over the long term include ensuring the complete protection of prime habitat for the species, improved connectivity by protecting forest cover, implementation mitigation measures in areas where paved roads interrupt connectivity of populations, and eradicating poaching of the species in the region completely.     

Prioritizing conservation areas and vulnerability analyses of the genus Pinus L. (Pinaceae) in Mexico

Mexico hosts the highest species richness of pines (Pinus, Pinaceae) worldwide; however, the priority areas for their conservation in the country are unknown. In this study, the ecological niche of the 50 native pine species was modeled. Then, through a multi-criteria analysis, the priority areas for the conservation of the genus Pinus were identified according to the spatial patterns of richness, geographic rareness, irreplaceability, the level of vulnerability of their habitat and the status of legal protection. The results revealed that the regions with high species richness differed from those with high endemism. Also, most pine species have undergone processes of habitat degradation, having been the endemic species the most affected. The priority areas covered regions with high species richness, high endemism, and highly degraded forests, located at mountainous portions of the Baja California Peninsula, the Sierra Madre Occidental, the Sierra Madre Oriental, the Trans-Mexican Volcanic Belt, and the Sierra Madre del Sur. A low proportion of priority areas overlapped with protected areas or terrestrial regions considered priorities for biological conservation. These results suggest that conservation efforts for this genus should be focused beyond regions with high species richness and current protected areas. Besides, the priority areas identified in this study can be the basis to create biological corridors and new protected areas, which could contribute significantly to the conservation of this genus in Mexico.     

Evaluating the benefits of CAP reforms: Can afforestations restore bird diversity in Mediterranean Spain?

Current Common Agricultural Policy (CAP) subsidies in the Mediterranean region tend to prioritize afforestation on former arable land with oaks rather than pines because pine plantations would maintain lower biological diversities than native forests. Nevertheless, no thorough evaluations of the conservation values of pine plantations as compared to oak remnants have been carried out to date. We analyze the diversity and conservation value of bird assemblages breeding in 200 remnants of Holm oak Quercus ilex woodlands and 82 mature (>50-year-old) pine plantations in central Spain, a Mediterranean region mostly devoted to arable farming. Species–area relationships were compared between forest types. The conservation value of bird assemblages was assessed using the “Species of European Conservation Concern” (SPEC) classification of Burfield and van Bommel [(2004). Birds in Europe: Populations estimates, trends and conservation status. Cambridge: BirdLife International]. Overall numbers of bird species maintained by oak and pine archipelagoes were rather similar, but species–area relationships differed between forest types. Intercepts were higher in oak fragments, whereas slopes were steeper in pine plantations. Small oak fragments held more species (mainly Mediterranean Sylvia warblers) than plantations, whereas large plantations held more species than large oak remnants. Differences in species–area relationships seemed to be due to differences in vegetation structure, especially understorey shrub cover and tree height and cover. We recorded nine SPECs, all exclusive (6) or near-exclusive (3) to oak woodlands, although such woodlands do not appear to be critical for their conservation. Hence, we conclude that pine afforestations have played a role for maintaining and restoring forest bird communities in the farming landscapes of central Spain. Promoting large and shrubby plantations would enhance their conservation value for breeding birds, together with promoting growth, regeneration and expansion of Holm oak remnants by means of set-aside measures previous or alternative to oak reafforestation. The increasing importance of non-commercial as compared to commercial values of Mediterranean forests would justify subsidizing the proposed policy.     

Holocene altitudinal shifts in vegetation belts and environmental changes in the Sierra Madre Occidental, Northwestern Mexico, based on modern and fossil pollen data

A modern pollen rain study was performed in a 300 km-long altitudinal transect (~ 28° N latitude) from 300 to 2300 m elevation. The higher elevation modern communities: epithermal oak–pines, pine–oak forest, pine forest, and mixed conifer forest were easy to distinguish from their pollen content. In contrast, lower elevation subtropical communities: thornscrub and tropical deciduous forest were difficult to separate, because they share many pollen taxa. Nevertheless we identify high frequencies of Bursera laxiflora as an important component of the tropical deciduous forest.Additionally, fossil pollen was analyzed at three sites located between 1700 and 1950 m altitude at ~ 28° latitude north in the Sierra Madre Occidental of northwestern Mexico. The sites were in pine–oak (Pinus–Quercus), pine, and mixed-conifer forests respectively. Shifts in the altitudinal distribution of vegetation belts were recorded for the last 12,849 cal yr BP, and climate changes were inferred. The lowest site (pine–oak forest) was surrounded by pine forest between 12,849 and 11,900 cal yr BP, suggesting a cold and relatively dry Younger Dryas period. The early Holocene was also cold but wetter, with mixed conifer forest with Abies (fir) growing at the same site, at 1700 m elevation, 300 m lower than today. After 9200 cal yr BP, a change to warmer/drier conditions caused fir migration to higher elevations and the expansion of Quercus at 1700 m. At 5600 cal yr BP Abies was growing above 1800 m and Picea (spruce) that is absent today, was recorded at 1950 m elevation. Fir and spruce disappeared from the 1950 m site and reached their present distribution (scattered, above 2000 m) after 1000 cal yr BP; we infer an episodic Holocene migration rate to higher elevations for Abies of 23.8 m/1000 cal yr and for Picea of 39.2 m/1000 cal yr. The late Holocene reflects frequent climate oscillations, with variations in the representation of forest trees. A tendency towards an openness of the forest is recorded for the last 2000 yrs, possibly reflecting human activities along with short-term climate change.     

Potential distribution of Ursus americanus in Mexico and its persistence: Implications for conservation

The black bear Ursus americanus is an endangered species in Mexico. Its historical distribution has decreased by approximately 80% although its current distribution is not known with precision; it is only reported to be present in the mountains of Northern Mexico. This study proposes two ensemble models: Mexicós black bear (a) potential distribution compared with Natural Protected Areas (NPAs); and, (b) persistence areas for 2024. The current distribution variables are coniferous forest, elevation and dry forest. Suitable habitat for black bear (354,047 km², 18.07% of the country) was found mainly in the north of the Sonoran biogeographical zone, along the Sierra Madre Occidental, the center and south of the Sierra Madre Oriental and some northern regions of the Altiplano Norte. Comparing these areas with NPAs documented that only 12.41% of potential distribution coincided with current suitable habitat. There are unprotected areas in Sierra Madre Occidental center and central and southern of Sierra Madre Oriental. The model for 2024 indicates a reduction of suitable habitat of 64.5%, mainly in the northern Sonoran zone and the center Sierra Madre Occidental. On the other hand, areas that will persist (125,673 km²) are located along the two main mountain ranges of Mexico. Identification of these sites will allow strengthening of long-term conservation strategies.     

Using Endemic Plant Species to Establish Critical Habitats in the Sierra de La Laguna Biosphere Reserve, Baja California Sur, Mexico

The Sierra de La Laguna, in the southern part of the state of Baja California Sur, Mexico, was decreed a biosphere reserve in 1994. It harbors relict plant communities with a high level of endemism. Floristic research has established that the two main communities, the oak–pine woodland (OPW) and the dry tropical forest (TDF), harbor 43 and 33 endemic species, respectively. We segregate the reserve surface into seven major habitats and each endemic species were assigned a hierarchic value into an abundance-distribution scale, useful as dominance ranking. Using such scale, we found that almost half of the species are in the lowest rank (low abundance and aggregate distribution). Using GIS, we obtain the surface for each habitat, where mountainsides represent the largest in the reserve area. We obtained an index of importance from the proportion of endemic species by habitat and its surface occupied, founding that, in spite of the small and fragmented nature of the upland riparian habitats, they have the greatest index value. Consequently, for future conservation plans in the reserve, these habitats should be considered remarkable sites, meriting better attention to ensure endemic plant preservation. Also, since 86% of the endemic species appear in one, two or three habitats, a high dependency on particular environmental conditions is suggested for them.     

Impacts of anthropogenic disturbances on forest succession in the mid-montane forests of Central Himalaya

We studied the influence of anthropogenic drivers on the distribution and regeneration of tree species in vegetation at different stages of succession from grasslands to oak forests in mid-montane Central Himalaya. We found fire, grazing, and lopping as the main factors hindering a progressive successional regime towards a late-successional oak community. Succession was studied in five vegetation formations (grasslands, pine, pine–oak, open oak, and dense oak), with similar site conditions, representing a theoretical successional sequence from early- to late-successional stages. A structured survey with uniform distribution of sampling plots in the five selected vegetation formations was conducted to gather information abut the vegetation communities. Early-successional grasslands and pine forests were found to harbour high densities of pine and oak seedling and sapling regeneration. However, recurring fires and chronic unsustainable levels of grazing in these vegetation formations obstructed progressive succession by eliminating regenerating seedling and saplings from the forest understorey. Similarly, in intermediate- and late-successional stages (including pine–oak, open oak, and dense oak), overexploitation of existing oaks trees via lopping and grazing of regenerating oak seedlings and saplings hampered oak regeneration and development. The possibility to convert pine forests into oak as well as the conservation of existing oak forests through controlled grazing and lopping are management options that can contribute to an enhanced functioning of forest ecosystems in the study area. We conclude that with strategic management that restricts the current anthropogenic disturbances, the extent of oak forest in the study area can be increased.     

Response of Grassland Birds in Sand Shinnery Oak Communities Restored Using Tebuthiuron and Grazing in Eastern New Mexico

Sand shinnery oak (Quercus havardii) communities are a unique component of grassland bird habitat in eastern New Mexico and have been impacted by human activities for decades. These communities are frequently managed with livestock grazing and herbicide application for shrub control, strategies that potentially can be used to restore the historical shrub–grass composition of this plant community. During spring migration and the breeding seasons of 2004 and 2005, we compared density and community structure of grassland bird species among four combinations of tebuthiuron application and grazing treatments that were being evaluated for restoration of shinnery oak communities. We performed biweekly point transects on sixteen 65‐ha study plots in these communities. Density of all avian species combined did not differ between grazed and ungrazed plots. Tebuthiuron‐treated plots had a 40% higher average density for combined species than untreated plots. There was a 41% higher average density of all species during spring 2005 than 2004, but density was similar during the breeding season of both years. These trends were predominantly influenced by densities of migratory Cassin’s Sparrow (Aimophila cassinii), which were greater in tebuthiuron‐treated plots in both years. Densities of resident Meadowlarks (Sturnella spp.) exhibited little response to tebuthiuron or grazing treatments. Avian species richness, evenness, and diversity were only minimally affected by the tebuthiuron and grazing treatments. This study occurred over a period of highly variable precipitation, so future assessments, spanning longer wet–dry cycles and maturing plant communities, may be necessary to completely determine avian response to these restoration efforts.     

Forecasting cloud forest in eastern and southern Mexico: conservation insights under future climate change scenarios

Assuming that co-distributed species are exposed to similar environmental conditions, ecological niche models (ENMs) of cloud forest species were developed to study how climate change could affect the distribution of cloud forest in eastern and southern Mexico for the year 2050. Using ENM-based predictions and climatic data for IPCC climate change A2 and B2 scenarios, we observed 54–76% reduction of the cloud forest, mainly in the northern region of its current range (Sierra Madre Oriental) and the Pacific slope of Chiapas. With predicted 2050 climate change, cloud forest in the Los Tuxtlas region and El Cielo Biosphere Reserve may face a serious threat of extinction due to the observed upward migration to higher elevations. Our results add to recent studies detecting negative impacts of climate change in montane forests, but the negative impacts of climate change might be exacerbated by current environmental changes in the region. The integration of ecological-niche characteristics of cloud forest in conjunction with projections of extreme climate scenarios constitute a suitable tool to define appropriate areas in which proactive conservation and management strategies should be focused.     

Habitat selection of European pine marten in Central Italy: from a tree dependent to a generalist species

Studies at small spatial scale are often fundamental to highlight the behavioural plasticity of a species and thus have important implications for conservation planning, in particular for species usually considered as habitat specialists. We investigated second-order habitat selection of the European pine marten in an area dominated by deciduous oak forest and open fields in central Italy, by radio-tracking 16 pine martens (eight males, eight females). Pine martens placed home ranges in areas with more open field than in the study area, whereas woodland (oak and conifer forests) comprised a smaller portion of the home range than predominant forest character of the studied area. Although the presence of the species in the open habitats has been documented, to our knowledge, our results provide the first evidence of home range establishment in this cover type by pine marten at population level. The combination of low predation risk and high availability of resources could allow pine martens to occupy open fields in our study area. We highlighted different individual strategies of habitat selection, with some individuals placing home ranges in areas with high forest coverage while others occupying open areas. We found no effects of sex and body condition on habitat selection, and this could indicate that in the study area, both forested and non-forested cover types, such as open fields, shrub and anthropic areas, can provide adequate food, overhead cover and resting sites for all individuals. Pine marten ability to occupy open fields seems thus more related to the behavioural flexibility of the species, rather than to the need to supplement dens and forage from complementary lower quality habitat. The high quality of the Mediterranean continental area studied could also explain the selection of open areas by the pine marten. Our results offer useful information on pine marten ecology and may be helpful for conservation management of this species in southern Europe.     

Postfledging habitat selection of juvenile middle spotted woodpeckers: a multi-scale approach

Despite its relevance for the persistence of populations, the ecological mechanisms underlying habitat use decisions of juvenile birds are poorly understood. We examined postfledging habitat selection of radio-tracked juvenile middle spotted woodpeckers Dendrocopos medius at multiple hierarchically-nested spatial scales in NW Spain. At the landscape and home range scales, old oak forest was the most used and selected habitat, young oak forests and pine plantations were avoided, and riverside forests were used as available. At a lower scale, birds selected larger diameter trees for foraging. Home ranges had higher densities of large deciduous trees (mainly oaks Quercus spp., but also poplars Populus spp. and willows Salix spp. >22  cm and >33  cm DBH) selected for foraging by juveniles than non-used areas. These results suggest that foraging conditions may drive, at least partly, habitat use decisions by juvenile birds. We also discuss the potential influence of intraspecific competition, the search for a future breeding territory in the early postfledging period and predation avoidance on habitat use decisions by juvenile birds. Contrary to previous studies on migrant forest birds, postfledging juvenile woodpeckers selected the same habitat as for the breeding adults (i.e. old oak forest), indicating that migrant and resident specialist avian species may require different conservation actions. Conservation strategies of woodpecker populations should consider the protection of old oak forests with high densities of large trees to provide suitable habitat to breeding adults and postfledging juveniles. The habitat improvement for this indicator and umbrella species would also favour other organisms that depend on characteristics of old-growth oak forests.     

Forest Stand Characteristics Altered by Restoration Affect Western Bluebird Habitat Quality

Forest managers are setting Ponderosa pine (Pinus ponderosa) forests in the southwestern United States on a trajectory toward a restored ecosystem by reducing tree densities and managing with prescribed fire. The process of restoration dramatically alters forest stands, and the effects of these changes on wildlife remain unclear. Our research evaluated which aspects of habitat alteration from restoration treatments may be affecting the habitat quality of Western Bluebird (Sialia mexicana), an insectivorous songbird whose populations are declining. Habitat loss resulting from fire‐suppression activities may be partially responsible for their population declines; thus, the bluebird is a good representative species for assessing how the reconstruction of presuppression forest conditions can affect wildlife. We measured habitat variables at 63 successful and 19 unsuccessful Western Bluebird nests in 1999–2001 and 2003. We compared habitat models that represented bluebird biology and habitat changes from restoration. Two models of nest success that included (1) an increased herbaceous and bare ground cover and (2) increased Gambel oak (Quercus gambelii) densities and reduced Ponderosa pine densities were most supported by the data. Increased herbaceous ground cover and Gambel oak density likely represent improved invertebrate assemblages and thus improved forage abundance for nesting bluebirds. Lower Ponderosa pine densities may provide bluebirds with open perches from which to hunt and thereby improve the availability of invertebrates as a food source. We also provide a landscape‐scale example of changes to bluebird habitat quality from treatments, which we recommend as a useful tool in restoration planning.     

Migration timing and routes,and wintering areas of Flammulated Owls

Determining patterns in annual movements of animals is an important component of population ecology, particularly for migratory birds where migration timing and routes, and wintering habitats have key bearing on population dynamics. From 2009 to 2011, we used light‐level geolocators to document the migratory movements of Flammulated Owls (Psiloscops flammeolus). Four males departed from breeding areas in Colorado for fall migration between ≤5 and 21 October, arrived in wintering areas in Mexico between 11 October and 3 November, departed from wintering areas from ≤6 to 21 April, and returned to Colorado between 15 and 21 May. Core wintering areas for three males were located in the Trans‐Mexican Volcanic Belt Mountains in the states of Jalisco, Michoacán, and Puebla in central and east‐central Mexico, and the core area for the other male was in the Sierra Madre Oriental Mountains in Tamaulipas. The mean distance from breeding to wintering centroids was 2057 ± 128 km (SE). During fall migration, two males took a southeastern path to eastern Mexico, and two males took a path due south to central Mexico. In contrast, during spring migration, all four males traveled north from Mexico along the Sierra Madre Oriental Mountains to the Rio Grande Valley and north through New Mexico. The first stopovers in fall and last stopovers in spring were the longest in duration for all males and located 300–400 km from breeding areas. Final spring stopovers may have allowed male Flammulated Owls to fine tune the timing of their return to high‐elevation breeding areas where late snows are not uncommon. One male tracked in both years had similar migration routes, timing, and wintering areas each year. Core wintering and final stopover areas were located primarily in coniferous forests and woodlands, particularly pine‐oak forests, suggesting that these are important habitats for Flammulated Owls throughout their annual cycle.     

Environmental suitability for Agrilus auroguttatus (Coleoptera: Buprestidae) in Mexico using MaxEnt and database records of four Quercus (Fagaceae) species

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