Aim A phylogeographic study of the endemic Mexican tulip poppy Hunnemannia fumariifolia (Papaveraceae) was conducted to determine: (1) the historical processes that influenced its geographical pattern of genetic variation; (2) whether isolation by distance was one of the main factors that caused genetic divergence in populations of this species; and (3) whether genetic flow still exists between populations from northern arid zones (Chihuahuan Desert and Sierra Madre Oriental) and those from southern arid zones (Tehuacán‐Cuicatlán Valley) – populations that are separated by the Transvolcanic Belt. Location Xerophytic vegetation in Mexico. Methods Chloroplast DNA (cpDNA) sequences of three regions, trnH‐psbA, rpl32‐trnL(UAG) and ndhF‐rpl32, were obtained for 85 individuals from 17 populations sampled in the field, covering the entire range of H. fumariifolia. The evolutionary history of these populations was investigated using a nested clade phylogeographic analysis and also by conducting various population genetic analyses. Results In total, 17 haplotypes were detected, 14 of which were found in the Sierra Madre Oriental. Differentiation among populations based on cpDNA variation (GST = 0.787, SE 0.0614) indicated population structure in H. fumariifolia, corroborated by a fixation index (FST) of 0.907. Results from analysis of molecular variance found that most of the total variation (90.71%, P <0.001) was explained by differences among populations. Three regions were determined based on geological correspondence – the Chihuahuan Desert, Sierra Madre Oriental and Tehuacán‐Cuicatlán Valley – and the variation between them was significant (43.39%, P <0.001). Results of a Mantel test showed a significant correlation between genetic and geographic distances (r =0.511; P =0.0001), suggesting a pattern of isolation by distance, which was corroborated by nested clade phylogeographic analysis. Mismatch distribution analysis indicated a sudden demographic expansion. Main conclusions Our study found that isolation by distance influenced genetic divergence in populations of H. fumariifolia. The finding that allopatric fragmentation influenced genetic divergence in populations in the Sierra Madre Oriental may be a reflection of the complex geology of the area. Our results suggest that the areas located in the north of the Sierra Madre Oriental acted as post‐glacial refugia for some populations. 相似文献
The Beckmann rearrangement of the syn and anti isomers of the spirocyclic oxime derived from a 16β,23:23,26-diepoxy-5β-cholestan-22-one was studied. Whereas the anti isomer always follows the Beckmann fragmentation course, the syn isomer, depending on the reaction conditions, follows the normal Beckmann rearrangement course and/or the isomerization to the anti isomer followed by the fragmentation course. 相似文献
ABSTRACT Roads can affect the persistence of wildlife populations, through posing mortality risks and acting as barriers. In many countries, transportation agencies attempt to counterbalance these negative impacts. Road mortality is a major threat for European wildcats (Felis silvestris); therefore, we tested the effectiveness of a newly developed wildcat-specific fence in preventing wildcat mortality along a new motorway. We hypothesized that such a fenced motorway would at the same time be a significant barrier to wildcats and may at worst result in 2 isolated populations. We used radiotracking data of 12 wildcats, resulting in 13,000 fixes, to investigate individual movement behavior during and after construction of a new motorway in southwestern Germany. The motorway was fenced with the wildcat-specific fence and included crossing structures, not especially constructed for wildlife. Additionally we collected road kills on stretches of the same motorway with various types of fencing. A rate of 0.4 wildcat kills/km/year on the motorway, which was traveled by 10,000 vehicles/day and fenced with a regular wildlife fence, was reduced by 83% on stretches with wildcat-specific fencing. Of the available crossing structures, wildcats preferred open-span viaducts. Road underpasses were used but hold a mortality risk themselves. As opposed to our expectations, the fenced motorway (fenced with wildcat fence) posed only a moderate barrier to wildcats. Individuals were hindered in their daily routine and some stopped crossing completely but others continued crossing regularly. The adaptation of spatial and temporal behavior to traffic volume and location of crossing structures has an energetic cost. Hence, we suggest that only a small number of major roads can be tolerated within a wildcat's home range. To meet the demands of the European Habitats Directive, we recommend installing the wildcat fence in wildcat core areas along motorways to reduce wildcat mortality. We suggest that fences should incorporate safe crossing structures every 1.5-2.5 km. Our findings in terms of fencing design and crossing structures can be used by transportation agencies for an effective reduction of road mortality and barrier effect for carnivores. 相似文献
We evaluated changes in levels of diversity of copro-necrophilous staphylinids attracted to piles of cattle dung and rat carrion
in four contrasting habitats (continuous oak forest, oak forest patches, savannah and ravines) in southeastern Mexico during
2005 and 2006. In total, 181 morpho-species (N = 9,875 individuals) of Staphylinidae were recorded, of which 40 were coprophiles, 98 were necrophiles, and 43 were present
in both substrates. Ten species accounted for 65% of the total number of individuals, 68 species were represented by singletons,
whereas 103 species registered intermediate abundances. Less disturbed habitats recorded higher levels of beetle diversity.
A strong seasonality effect was recorded for necrophiles, but not for coprophiles. A beta diversity analysis suggested that
continuous oak forest registered the lowest fauna similarity when contrasted to other habitats; yet beetle composition among
oak forest patches, savannah and ravine remained comparable. Staphylinidae body size and trophic guilds differed significantly
among habitats. The results of this study suggest that key habitats such as ravines may represent a more permanent and predictable
habitat for beetles in highly seasonal landscapes, even at early stages, because this habitat is characterized by a slower
turnover of Staphylinidae species than in the case of tropical oak patches or savannah habitats. 相似文献
Aim We investigated the relative role of area, isolation, microhabitat diversity and number of individuals as explanatory factors defining the richness of waterbirds in wetland remnants. Location Freshwater marshes along the Atlantic coastal zone of South Brazil. (30°56′–30°22′S; 50°58–50°22′W; Fig. 1 ). Figure 1 Open in figure viewer PowerPoint The study area (dashed line), in the Atlantic coastal zone of Brazil, is characterized by a high concentration of remnant wetlands used by resident and migratory waterbirds. Waterbirds were surveyed monthly along 2003 in 42 randomly selected wetland remnants. 相似文献
Habitat fragmentation is a prevalent threat to biological diversity, and urbanization is a primary agent of fragmentation and a leading cause of species endangerment. Landscape biogeographic and local habitat characteristics can be important determinants of the distribution of species in habitat patches in urban landscapes. However, the specifics of which characteristics are most critical to maintaining biological diversity are not fully known for prairie ecosystems, especially in fragmented urban habitat. This study focuses on black-tailed prairie dogs along an urban gradient in Denver, CO. Prairie dogs have declined precipitously throughout the region and are an essential part of the prairie ecosystem, making them excellent study subjects. We identified a series of habitat fragments along a gradient of urbanization in the fully urbanized areas and south suburbs of Denver, CO, both containing and not containing prairie dogs. Local characteristics, including fragment slope and vegetative cover, and landscape characteristics, including fragment size, age and connectivity, were measured on each fragment. We used likelihood-based methods to explore which variables most accurately predicted prairie dog occurrence within our study area. Multiple factors influenced the distribution of prairie dogs in urban settings, with colony connectivity the strongest predictor of occupancy. Large and recently isolated fragments near other prairie dog colonies, flat areas and those with high graminoid cover were most likely to support prairie dog populations. Our study provides the first attempt to model prairie dog occurrence in highly fragmented urban habitat and has important implications for the management and conservation of prairie dogs. 相似文献
Disturbed communities are observed to be more susceptible to invasion by exotic species, suggesting that some attributes of
the invaders may interact with disturbance regime to facilitate invasion success. Alternanthera philoxeroides, endemic to South America, is an amphibious clonal weed invading worldwide. It tends to colonize disturbed habitats such
as riparian zones, floodplain wetlands and agricultural areas. We developed an analytical model to explore the interactive
effects of two types of physical disturbances, shoot mowing and root fragmentation, on biomass production dynamics of A. philoxeroides. The model is based on two major biological assumptions: (1) allometric growth of root (belowground) vs. shoot (aboveground)
biomass and (2) exponential regrowth of shoot biomass after mowing. The model analysis revealed that the interaction among
allometric growth pattern, shoot mowing frequency and root fragmentation intensity might lead to diverse plant ‘fates’. For
A. philoxeroides whose root allocation decreases with growing plant size, control by shoot mowing was faced with two dilemmas. (1) Shoot regrowth
can be effectively suppressed by frequent mowing. However, frequent shoot mowing led to higher biomass allocation to thick
storage roots, which enhanced the potential for faster future plant growth. (2) In the context of periodic shoot mowing, individual
shoot biomass converged to a stable equilibrium value which was independent of the root fragmentation intensity. However,
root fragmentation resulted in higher equilibrium population shoot biomass and higher frequency of shoot mowing required for
effective control. In conclusion, the interaction between allometric growth and physical disturbances may partially account
for the successful invasion of A. philoxeroides; improper mechanical control practices could function as disturbances and result in exacerbated invasion. 相似文献