Rurik List

Rapid Decline of a Grassland System and Its Ecological and Conservation Implications

One of the most important conservation issues in ecology is the imperiled state of grassland ecosystems worldwide due to land conversion, desertification, and the loss of native populations and species. The Janos region of northwestern Mexico maintains one of the largest remaining black-tailed prairie dog (Cynomys ludovicianus) colony complexes in North America and supports a high diversity of threatened and endangered species. Yet, cattle grazing, agriculture, and drought have greatly impacted the region. We evaluated the impact of human activities on the Janos grasslands, comparing changes in the vertebrate community over the last two decades. Our results reveal profound, rapid changes in the Janos grassland community, demonstrating large declines in vertebrate abundance across all taxonomic groups. We also found that the 55,000 ha prairie dog colony complex has declined by 73% since 1988. The prairie dog complex has become increasingly fragmented, and their densities have shown a precipitous decline over the years, from an average density of 25 per ha in 1988 to 2 per ha in 2004. We demonstrated that prairie dogs strongly suppressed woody plant encroachment as well as created open grassland habitat by clearing woody vegetation, and found rapid invasion of shrubland once the prairie dogs disappeared from the grasslands. Comparison of grasslands and shrublands showed markedly different species compositions, with species richness being greatest when both habitats were considered together. Our data demonstrate the rapid decline of a grassland ecosystem, and documents the dramatic loss in biodiversity over a very short time period concomitant with anthropogenic grassland degradation and the decline of a keystone species.

Rapid Response of a Grassland Ecosystem to an Experimental Manipulation of a Keystone Rodent and Domestic Livestock

Megaherbivores and small burrowing mammals commonly coexist and play important functional roles in grassland ecosystems worldwide. The interactive effects of these two functional groups of herbivores in shaping the structure and function of grassland ecosystems are poorly understood. In North Americas central grasslands, domestic cattle (Bos taurus) have supplanted bison (Bison bison), and now coexist with prairie dogs (Cynomys spp.), a keystone burrowing rodent. Understanding the ecological relationships between cattle and prairie dogs and their independent and interactive effects is essential to understanding the ecology and important conservation issues affecting North American grassland ecosystems. To address these needs, we established a long-term manipulative experiment that separates the independent and interactive effects of prairie dogs and cattle using a 2 x 2 factorial design. Our study is located in the Janos-Casas Grandes region of northwestern Chihuahua, Mexico, which supports one of the largest remaining complexes of black-tailed prairie dogs (C. ludovicianus). Two years of posttreatment data show nearly twofold increases in prairie dog abundance on plots grazed by cattle compared to plots without cattle. This positive effect of cattle on prairie dogs resulted in synergistic impacts when they occurred together. Vegetation height was significantly lower on the plots where both species co-occurred compared to where either or both species was absent. The treatments also significantly affected abundance and composition of other grassland animal species, including grasshoppers and banner-tailed kangaroo rats (Dipodomys spectabilis). Our results demonstrate that two different functional groups of herbivorous mammals, burrowing mammals and domestic cattle, have distinctive and synergistic impacts in shaping the structure and function of grassland ecosystems.

Home range and habitat use of the kit fox (Vulpes macrotis) in a prairie dog (Cynomys ludovicianus) complex

The largest remaining black-tailed prairie dog Cynomys ludovicianus towns in North America are in Mexico, where they coexist with the kit fox Vulpes macrotis ,p roviding a unique opportunity to study the relationship between these threatened species. We hypothesized that the presence of prairie dogs would positively affect the kit fox population in our study area in north-western Mexico, and that these influences would be manifest in home-range size, density and habitat selection. We estimated fox densities fluctuating from 0.32/km 2 to 0.8/km 2 ,a nd radiotelemetry revealed minimum convex polygon home ranges averaging 11 km 2 .T hese values are within the bounds of estimates from study sites elsewhere. Foxes used mesquite scrub less than expected, but grassland more than expected in relation to availability. Other habitats, including prairie dog towns, were used at random. Most (65.1% of 43) fox dens were in grassland, and were enlarged kangaroo rat Dipodomys spp. (34.9%) or prairie dog (34.9%) burrows. That kit foxes seemed to select grasslands rather than prairie dog towns was unexpected, particularly as prairie dogs are known to be a major component of kit fox diet. Foxes may reduce the amount of time they spend in prairie dog towns to avoid coyotes, which can be responsible for significant swift fox mortality. In our study area, coyotes were more active in prairie dog towns than in the grassland, where they were regularly shot. However, grassland used by kit foxes is a short-lived product of prairie dog poisoning, which is quickly invaded by scrub, a habitat favoured by coyotes. We conclude that kit fox conservation initiatives in north-western Mexico should be closely linked to conservation of the prairie dog ecosystem.

Conservation challenges for the austral and neotropical America section.

The Austral and Neotropical America (ANA) section of the Society for Conservation Biology includes a vast territory with some of the largest relatively pristine ecosystems in the world. With more than 573 million people, the economic growth of the region still depends strongly on natural resource exploitation and still has high rates of environmental degradation and biodiversity loss. A survey among the ANA section membership, with more than 700 members, including most of the sections prominent ecologists and conservationists, indicates that lack of capacity building for conservation, corruption, and threats such as deforestation and illegal trade of species, are among the most urgent problems that need to be addressed to improve conservation in the region. There are, however, strong universities and ecology groups taking the lead in environmental research and conservation, a most important issue to enhance the ability of the region to solve conservation and development conflicts.

Faecal marking behaviour in ringtails (Bassariscus astutus) during the non-breeding period: spatial characteristics of latrines and single faeces

Summary.Scent signals are the main source of information transmission in carnivores, being particularly important for those with nocturnal habits like the ringtail (Bassariscus astutus), a Procyonid widely distributed in Mexico. However, faecal marking behaviour of free-ranging ringtails has not been described previously. The aims of this study were to describe the use of latrines in ringtails and to test if single faeces and latrines have a marking function, based on the spatial characterisation of the defecation places and revisits to these sites. The study was conducted at an urban reserve within Mexico City in 2003, where 80 defecation points were analysed. The results showed that ringtails deposit faeces repeatedly in the same sites (latrines), which contain a variable number of faeces (between 2 and 19). The spatial distribution of latrines was not random, but a selection of substrates and zones that enhanced the effectiveness as faecal marks was observed. Latrines were preferentially placed on objects above ground level and at road margins. Latrines and single faeces that were in inconspicuous zones were generally deposited on conspicuous substrates and latrines and single faeces that were in conspicuous zones were deposited more frequently on inconspicuous substrates.

Historic Distribution and Challenges to Bison Recovery in the Northern Chihuahuan Desert

Ecologists and conservationists have long assumed that large grazers, including bison (Bison bison), did not occur in post-Pleistocene southwestern North America. This perception has been influential in framing the debate over conservation and land use in the northern Chihuahuan Desert. The lack of an evolutionary history of large grazers is being used to challenge the validity of ranching as a conservation strategy and to limit the protection and reintroduction of bison as a significant component of desert grassland ecosystems. Archeological records and historical accounts from Mexican archives from AD 700 to the 19th century document that the historic range of the bison included northern Mexico and adjoining areas in the United States. The Janos-Hidalgo bison herd, one of the few free-ranging bison herds in North America, has moved between Chihuahua, Mexico, and New Mexico, United States, since at least the 1920s. The persistence of this cross-border bison herd in Chihuahuan Desert grasslands and shrublands demonstrates that the species can persist in desert landscapes. Additional lines of evidence include the existence of grazing-adapted grasslands and the results of experimental studies that document declines in vegetation density and diversity following the removal of large grazers. The Janos-Hidalgo herd was formed with animals from various sources at the turn of the 19th century. Yet the future of the herd is compromised by differing perceptions of the ecological and evolutionary role of bison in the Desert Grasslands of North America. In Mexico they are considered native and are protected by federal law, whereas in New Mexico, they are considered non-native livestock and therefore lack conservation status or federal protection. Evidence written in Spanish of the presence of bison south of the accepted range and evidence from the disciplines of archaeology and history illustrate how differences in language and academic disciplines, in addition to international boundaries, have acted as barriers in shaping comprehensive approaches to conservation. Bison recovery in the region depends on binational cooperation.

Avian diversity in a priority area for conservation in North America: the Janos-Casas Grandes Prairie Dog Complex and adjacent habitats in northwestern Mexico

From February 1994 to January 2004, we studied the avifauna of a 25,000-ha area centered on the Janos-Casas Grandes Prairie Dog Complex of Northwestern Chihuahua, Mexico. Avian diversity totalled 227 species, of which 86 (38%) were residents, 78 (35%) winter migrants, 30 (14%) summer migrants, 27 (11%) transients, and 6 (2%) accidental vagrants. Around 84 (38%) species were observed in at least two habitat types, with riparian areas supporting the highest observed diversity of birds (112 species). Of the 143 species observed in only one habitat type, 44 (30%) occurred in riparian areas, 35 (26%) in association with ponds and aquatic vegetation, 28 (20%) in grasslands, 16 (11%) in the oak woodland–grassland ecotone, 12 (9%) in mesquite scrubland, 5 (3%) around human settlements, and 3 (2%) in crop fields. In particular, summer rains influenced the abundance and/or distribution of several species in grasslands such as the long-billed curlew (Numenius americanus). The present study, which was part of a larger effort to document the merits of establishing a large biosphere reserve in the area, confirmed the importance of the prairie dog complex and grasslands to many species of conservation concern, including the threatened mountain plover (Charadrius montanus), a winter resident. With the␣higher-elevation habitats yet to be surveyed, the local diversity of bird species here already places the proposed reserve among the most important protected areas in all of Mexico. The establishment of the reserve is urgently needed, especially for the protection of grasslands and their associated fauna.

Consensus on criteria for potential areas for wolf reintroduction in Mexico.

Given the conflict with human interests that in many cases results in the extirpation of large carnivores, acceptance of their reintroduction is a considerable challenge. By the 1980s Mexican wolves (Canis lupus) were extinct in the wild. In 1998 a population was reintroduced in the Blue Range Mountains of New Mexico (U.S.A.). Efforts to reintroduce the species in Mexico have been ongoing since the late 1980s. Four teams working independently identified 6 areas in northern Mexico in the historic range of Mexican wolves, where reintroductions could potentially be successful. Each team used different methods and criteria to identify the areas, which makes it difficult to prioritize among these areas. Therefore, members of the different teams worked together to devise criteria for use in identifying priority areas. They identified areas with high, intermediate, and low potential levels of conflict between wolves and humans. Areas with low potential conflict had larger buffers (i.e., distance from human settlement to areas suitable for wolves) around human settlements than high- and intermediate-conflict areas and thus were thought most appropriate for the first reintroduction. High-conflict areas contained habitat associated with wolf presence, but were closer to human activity. The first reintroduction of Mexican wolves to Mexico occurred in October 2011 in one of the identified low-conflict areas. The identification of suitable areas for reintroduction represents a crucial step in the process toward the restoration of large carnivores. Choice of the first reintroduction area can determine whether the reintroduction is successful or fails. A failure may preclude future reintroduction efforts in a region or country.

Genetic divergence of Microtus pennsylvanicus chihuahuensis and conservation implications of marginal population extinctions

Abstract Microtus pennsylvanicus is represented in Mexico only by the Chihuahuan meadow vole (M. p. chihuahuensis), known from only 1 disjunct population in a small and isolated marsh in the arid lands of northern Chihuahua. Livetrapping conducted between 2000 and 2004 provided no specimens of M. p. chihuahuensis, nor was any sign of this vole observed. By the end of this study the marsh providing water had been drained, thereby destroying the voles habitat. Surveys of other marshes in northern Chihuahua also failed to produce evidence of the species. We therefore conclude that M. p. chihuahuensis has been extirpated from its only known locality. Using “ancient” DNA from museum specimens we evaluated genetic divergence between museum specimens of M. p. chihuahuensis and 46 extant Microtus species and subspecies. Our results support the subspecific status of M. p. chihuahuensis. The loss of this subspecies is an example of population extinction, a very severe form of biodiversity loss. Until recently such losses have been mostly neglected.

The Role of Spatial Distribution of Faeces in Coyote Scent Marking Behaviour

SUMMARY: Scats are important for chemical communication in many canids, however, little is known about the faecal marking behaviour in coyotes. In this study we tested if faeces have a function as visual and scent marks during the non-breeding period, analyzing the spatial characteristics of defecation places. We predicted that if faeces are used as chemical signals, these should be deposited in substrates and/or zones that enhance their detection by conspecifics as it happens in other canid species. The study was conducted in native grasslands at the NW limit of the Chihuahuan Desert. Results showed that the proportion of faeces in conspicuous zones (91.3%) was significantly higher than those on inconspicuous zones (8.7%). However, the number of faeces deposited on inconspicuous substrates (92.1%) was significantly higher than on conspicuous substrates (7.9%). Most faeces were on the ground (99.2%) and only 0.8% where raised. 35% of faeces were deposited in crossroads, being these strategic zones repeatedly marked by the coyotes. We observed a significant negative correlation between the number of faeces in crossroads and the distance of faeces to the centre of the crossroad. A high number of scats were found in the proximity of livestock carcasses (21%). In addition, a selection of certain road sections (track and lateral) was observed. Our results suggest that the scats have an important function as scent-marks in coyotes, using specific defecation patterns that appear to correspond to the habitat characteristics in the study area.