The invasive bullfrog <Emphasis Type="Italic">Lithobates catesbeianus</Emphasis> in oases of Baja California Sur,Mexico: potential effects in a fragile ecosystem

The American bullfrog (Lithobates catesbeianus), considered as one of the world’s worst invasive species because of its negative effects on native fauna, has been introduced into over 40 countries in four continents. The invasion status in Mexico is poorly known. The first known record for this species in the Peninsula of Baja California, northwestern Mexico is an individual collected 35 years ago. A great portion of the peninsula is an arid desert where the sources of freshwater are the spring-fed oasis and mountain arroyos that support rare and endemic species closely associated with wetland conditions. Humans, who have introduced alien species, inhabit many of those oases. The aim of this work was to document the presence of the exotic bullfrog in 40 oases and mountain arroyos in Baja California Sur state during 2006–2009. Bullfrogs were found in 25% of the oases sampled; 15% have confirmed records of breeding populations and five oases are new location records. Our results show a considerable increase (50%) in the number of oasis invaded by bullfrogs in only 8 years. The animal populations of rare or endemic species associated with oases would be threatened by the arrival of bullfrogs. Actions for their control and eradication are urgently needed.     

Metabarcoding reveals seasonal and spatial patterns of arthropod community assemblages in two contrasting habitats: Desert and oasis of the Baja California Peninsula,Mexico

Aim

Desert springs or oases are the only permanent mesic environments in highly water-limited arid regions. Oases have immense cultural, evolutionary and ecological importance for people and a high number of endemic and relic species. Nevertheless, they are also highly vulnerable ecosystems, with invasive species, overexploitation and climate change being the primary threats. We used the arthropod communities' spatiotemporal diversity and distribution patterns as a proxy to understand biodiversity dynamics in two geographically close but ecologically contrasting and highly threatened ecosystems: deserts and oases.

Location

Baja California Peninsula, Mexico.

Methods

Arthropod communities at five oases and surrounding desert scrub areas were sampled in two seasons. Using DNA metabarcoding and traditional taxonomic surveys, we tried to identify what biotic and abiotic characteristics of the habitat are important drivers of arthropod diversity and how these characteristics can change across spatial and temporal scales.

Results

Over 6200 individuals representing 23 orders were collected. In oasis samples, the community composition fluctuated more in space (i.e. among sites) than in time (i.e. seasons). Thus, seasonal changes did not affect oasis community diversity and composition, but the dissimilarity among sites increased with geographic distance. Moreover, anthropic activities negatively correlated with arthropod diversity in oases. On the other hand, the season, geography (e.g. latitude) and biotic characteristics of the habitat (e.g. sampled scrub species) significantly affected the diversity and composition of the desert arthropod communities.

Main Conclusions

Neutral dynamics (e.g. historical climatic events, dispersal limitation and spatial component) and human impact significantly influenced the biodiversity patterns of each oasis. In contrast, the habitat's seasonal variation and biotic characteristics were the most important variables influencing the diversity of the desert communities. Baja California oases harbour distinct invertebrate communities; therefore, each oasis should be conserved individually to preserve these unique assemblages.     

Possible Phytoplasma Disease in Papaya (Carica papaya L.) from Baja California Sur: Diagnosis by Scanning Electron Microscopy

The symptoms of possible phytoplasma infection in introduced and local varieties of papaya were first noted in the Mexican state of Baja California Sur (BCS) during field surveys in 2002–2003. Phytoplasma structures were observed using scanning electron microscopy (SEM) in phloem sieve elements in diseased papaya plants, but not in healthy plants. They were rounded structures 400–1600 nm in diameter. This is the first report of the possible association of phytoplasmas with diseased papaya plants in BCS. The use of SEM for the primary detection of disease aetiology is discussed.     

Genetic isolation and evolutionary history of oases populations of the Baja California killifish,Fundulus lima

The Baja California killifish, Fundulus lima, is found in six desert oases of the southern Baja California Peninsula, Mexico. The recent introduction of exotic fishes, particularly redbelly tilapia, have impacted the ecology of Fundulus lima such that it is now endangered. Plans of relocating F. lima to bodies of freshwater that are free of exotics have been proposed, however little is know about the genetic identity of the current populations. In this study, we examined the mitochondrial control region of F. lima samples from 4 oases, and in addition, compared these samples to their sister species, the California killifish F.␣parvipinnis. Using a combination of phylogenetic and coalescent approaches, we were able to determine that the two subspecies of the California killifish, F. p.␣brevis, and F. p. parvipinnis, and F. lima form an unresolved trichotomy that diverged between 200,000 years and 400,000 years ago. The one F. lima individual that we were able to collect in the southernmost oasis grouped with the southern subspecies of the California killifish, F. parvipinnis brevis. In contrast, we found that the 3 northern oases grouped together in a “Fundulus lima” clade. Each oasis is genetically distinct, yet there is no evidence of a␣marked genetic bottleneck in any populations (Haplotype diversity between 0.5 and 0.8). Future relocation plans will therefore need to be done cautiously to preserve the genetic identity of the original populations.     

Social-ecological Resilience Modeling: Water Stress Effects in the Bighorn Sheep Management System in Baja California Sur,Mexico

Bighorn sheep (Ovis canadensis) management involves ecological and socioeconomic aspects, creating a social-ecological system (SES). Social-ecological thresholds can be identified in the system to assess its specific resilience in response to climate stressors. Thus, the aim of this study is to build a dynamic model to assess whether this system is resilient to a particular stressor (water stress). In this study, the SES is considered resilient if the bighorn population is sufficiently large to provide economic revenue to landowners and promote conservation action. We validate and formalize this model by conducting semistructured interviews to Bonfil ejido landowners located in Baja California Sur (BCS), Mexico, and to experts in the field of recreational hunting and wildlife management. To explore the changes in specific resilience in this SES, we conduct simulations to assess the impact of rainfall variability patterns on the system. Our results indicate that rainfall variations with respect to the historical record have the potential to disrupt both the species and the local economy and that the lack of adaptive capacity in both harvest and conservation strategies may affect the dynamics of the whole SES. Finally, this paper explores how adaptive wildlife conservation management strategies can enhance the resilience of both subsystems in this SES.     

Mission and Modern Citrus Species Diversity of Baja California Peninsula Oases

The spring-fed mission oases of the Baja California peninsula, Mexico, hold several species, varieties and unique hybrids of heritage citrus, which may represent valuable genetic resources. Citrus species first arrived to the peninsula with the Jesuit missionaries (1697-1768), and new varieties were introduced during the colonial and rancho periods following the mission era. These heritage trees are grown in field and house gardens as ornamental, fruit and shade trees. Commercial citrus varieties introduced from the United States have become a strong source of economic revenue for peninsula agriculturalists. A few of the peninsula oases support commercial citrus groves, though these are primarily found in the broader valleys of the peninsula where groundwater is tapped for irrigation. The isolated environments of the mission oases and surrounding ranches have facilitated propagation of unique citrus types, and these have stabilized through integration into the cultural practices of the region. We identify and document citrus of the peninsula oases to serve as a baseline for those interested in the cultural ecology of citrus and citrus genetic resources.     

Phylogeography of Pseudacris regilla (Anura: Hylidae) in western North America, with a proposal for a new taxonomic rearrangement

The Baja California populations of Pseudacris regilla, a widespread species in Western North America ranging from British Columbia to southern Baja California, are characterized by extensive geographic fragmentation. We performed phylogeographic and historical demographic analyses on 609 bp of the cytochrome b mitochondrial gene of 110 individuals representing 28 populations to determine the relative influences of current and historical processes in shaping the present distribution of genetic diversity on the Baja California Peninsula. Haplotypes from this area were nested in a clade with three well-differentiated groups. Two of these groups are from Baja California Sur and another is from California and Baja California. The estimated date for the split of these groups, between 0.9-1 Ma, fits with previously proposed hypotheses of vicariance due to different transpeninsular seaways, although successive population fragmentation and expansion due to climatic oscillations during Pleistocene glaciations cannot be discarded. Historical demographic analyses detected signs of past population expansions, especially in the southernmost group. With respect to populations north of this region, two older clades were identified, one with haplotypes mainly distributed in central California, and the other corresponding to the northern half of the species range, in what apparently is a recurrent pattern in the Pacific coast of North America. Based on the concordance between mt-DNA and available allozyme data indicating that these species have a long independent evolutionary history, we propose to consider the three major clades as distinct species: P. regilla, P. pacifica, and P. hypochondriaca.     

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.     

Length–weight relationships of cryptic reef fishes from the southwestern Gulf of California, Mèxico

Length–weight relationships of 33 cryptic reef fishes from the southwestern Gulf of California were estimated. The most common families were Gobiidae (seven species), Labrisomidae (four), Pomacentridae (three), and Tripterygiidae (three). These are the first length–weight parameters reported for 32 of these species. Specimens were sampled during a comparative ecological study of community structure of fish assemblages associated with coral heads, rocky walls, and artificial reefs in Bahía de La Paz, Baja California Sur. The b values varied between 2.63 and 3.61. New maximum length records for five of the species were established in the study.     

Association between cacti and nurse perennials in a heterogeneous tropical dry forest in northwestern Mexico

Abstract. The Sierra de La Laguna, Baja California Sur harbors the only tropical dry forest of the Peninsula. An inventory of the perennial plants was carried out at the eastern part of this mountain range. Plant spatial distribution was analyzed considering the species composition and vertical stratification of plant clusters in a study plot of 2 500 m². A plant cluster was defined as a group of at least three individuals with a maximum distance between plants of 1 m. Soil physical-chemical characteristics and soil surface temperatures were compared between shade and sun conditions. The tropical dry forest of Baja California Sur presents a highly aggregated pattern of species distribution. Most of the perennial plants grow clumped, yet not all of the six cactus species recorded were significantly associated with them. Pattern analysis revealed that only Stenocereus thurberii and Ferocactus peninsulae were aggregated and associated to perennial plants. There is no replacement pattern between cacti and perennial plants. Nutrient content, including soil fertility, between shade and sun conditions does not seem to explain the patchy distribution of perennial plants, while the differences in solar radiation between these conditions appear to be restrictive and determinant of this spatial pattern of distribution.     

Regionalization of the avifauna of the Baja California Peninsula, Mexico: a parsimony analysis of endemicity and distributional modelling approach

Aim To analyse the distributional patterns of the Baja California Peninsula's resident avifauna, and to generate a regionalization based on a method that uses a parsimony analysis (parsimony analysis of endemicity, PAE) of point data and modelled potential distributions. Location The Baja California Peninsula, Mexico. Methods A data base was constructed containing records of 113 species of resident terrestrial birds present in the Baja California Peninsula. Records and localities were obtained from the literature and from specimens housed in scientific collections world‐wide. Raw data points and potential distribution maps obtained using the software Genetic Algorithms for Rule‐set Prediction (GARP), were analysed with PAE. Results The data base consisted of 4164 unique records (only one combination of species/locality) belonging to 113 terrestrial resident bird species, in a total of 809 localities. From the point distribution matrix, the analysis generated 500 equally parsimonious trees, from which a strict consensus cladogram with 967 steps was obtained. The cladogram shows a basal polytomy and some geographical correspondence of a few resolved groups obtained in the analysis. These results do not allow the recognition of areas defined by avifaunistic associations. From the potential distribution matrix, the analysis generated 501 equally parsimonious trees, and a strict consensus cladogram of 516 steps was obtained. The cladogram shows a higher resolution because of the number of resolved groups with better geographical correspondence and therefore regions are well‐defined. Main conclusions The correspondence of some groupings of species suggest their validity as areas with biogeographical (historical and/or ecological) meaning. This regionalization in the Baja California avifauna seems to be consistent with previous regionalizations for other groups. Hence, PAE is a useful tool for area categorization if reliable point records and prediction tools are available. Our results suggest that the geographical definition is much better using potential data generated by GARP, particularly when they are contrasted with the results from point data. Thus, this is an excellent alternative for developing biogeographical studies, as well as for improving the use of data from scientific collections and other sources of biodiversity information.     

To Poach or Not to Poach an Endangered Species: Elucidating the Economic and Social Drivers Behind Illegal Sea Turtle Hunting in Baja California Sur,Mexico

Despite complete legal protection, improvements in infrastructure, and market conditions that provide easier access to other protein sources, illegal poaching of sea turtles for consumption in Baja California Sur (BCS), Mexico remains a major threat to their recovery. Few studies have focused on understanding the economic and social drivers behind this activity, which is fundamental to determining best practices for discouraging it. From June 2007 to April 2008 we conducted eight in-depth, semi-structured interviews with sea turtle poachers at five coastal communities in BCS to determine the drivers influencing them. The most prevalent reasons for illegal poaching were direct economic benefits, lack of law enforcement and ease of escape from or bribery of authorities, and strong family tradition. Our results suggest that to reduce illegal poaching it will be necessary to better enforce existing environmental laws, reduce social acceptance of sea turtle hunting throughout the region, educate fishers on the ecological importance of sea turtles, and show fishers direct economic benefits from non-consumptive use of sea turtles, such as ecotourism.     

Structure of Benthic Diatom Assemblages from a Mangrove Environment in a Mexican Subtropical Lagoon1

The taxonomic list and the structure of benthic diatom assemblages occurring in fine sediments (silt and sand) from the mangrove forest of the Balandra lagoon in Baja California Sur, Mexico was determined based on seasonal samplings for one year. Assemblage structure was analyzed using several ecological indices for estimating diversity (H'), dominance (REDI), equitability, and similarity. A total of 230 diatom taxa were identified and include 109 new records for the Baja California peninsula coast. Taxa representative of highly productive and hypersaline environments were common. Assemblages were characterized by a few abundant species and many uncommon or rare taxa. High diatom diversity estimates at all sampling sites during all seasons suggest that diatom assemblages in sediments of the Balandra lagoon represent a quasi-pristine environment.     

Biogeography and endemism of ants (Hymenoptera: Formicidae) in Baja California, Mexico: afirst overview

Abstract Aims Ants (Hymenoptera: Formicidae) of the Baja California peninsula are poorly known, with information based largely on scattered museum and literature records. We provide the first comprehensive account of ant species occurring on the peninsula, we examine distribution patterns, and we assess the ‘peninsular effect’ which predicts that species richness declines from the base to the tip of a peninsula. Location Peninsula of Baja California, Mexico. Methods Data collection involved examining, identifying and recording label data from c. 2350 series of ants. These records provide a provisional, if incomplete, species list. We applied the incidence‐based estimator, Chao‐2, to our data base of specimen records to estimate the total number of ant species on the peninsula. We assessed endemism by comparing our peninsular species list to those from adjacent states. The peninsular effect was tested by comparing genus and species level richness between the two states of Baja California, and across five latitudinal blocks. Results We document 170 native ant species in thirty‐three genera, plus six non‐native species, in Baja California. It seems likely that additional species remain to be discovered: the Chao‐2 estimator of species richness, at 206.0 species, is about 20% higher than our observed species richness. About 30% of the species and 20% of the genera are restricted within Baja California to the relatively mesic California Floristic Province of north‐western Baja California. Nearly all of these species also occur in California. Forty‐seven species (27.6%) are peninsula endemics. Using our entire data set, the peninsular effect appears to be strong, with about twice as many species in the northern state of Baja California than are recorded from the southern state of Baja California Sur; the ratio of genera is 33 to 24. However, this effect becomes weak at the species level and absent at the genus level when minimizing habitat effects by omitting species restricted to the California Floristic Province. At a finer scale, across latitudinal blocks of about 1.9°, the number of species declines towards central portions of the peninsula and then increases in the Cape Region. Nine ant species display strongly disjunct distributions, and these occur in two general patterns: peninsula disjuncts and peninsula–mainland disjuncts. Main conclusions The Baja California peninsula supports a diverse and distinctive ant fauna, with the proportion of endemic species similar to that displayed by plants. Patterns of species and genus richness across the five latitudinal blocks provide poor support for the peninsular effect. Moreover, habitat diversity, especially that related to topographic relief, appears to be the most important factor affecting the gradient of ant species richness in Baja California. Additional collections are needed to develop a more complete species list and to determine the boundaries and status of many species. Nevertheless, the present data base provides a useful starting point for understanding the evolution of ant assemblages in Baja California and for comparison with peninsular patterns in other taxa.     

Distribution of aquatic and raptor birds in a freshwater artificial pond of Baja California Sur,Mexico

We determined the taxonomic composition and spatial-temporal distribution of aquatic and raptor birds in a freshwater artificial pond of El Centenario, Baja California Sur, México, during 24 biweekly censuses (April, 1998 to March, 1999). The pond is particularly attractive for birds because of its variety of food items. A total 25,563 records of 69 species were done, among them the first report of Chlidonias niger and Phalaropus tricolor for the region. Species richness and abundance were determined for the migrant component, mostly Anatidae (16 species and 55.6% of the total abundance) and shorebirds (18 species and 13.3%). The greater number of species and individuals was in C the deepest and more heterogeneous section of the pond. The most important species was Oxyura jamaicensis (30% of the total observed individuals), with highest abundance in the peninsula. The artificial pond presented an atypical and distinct ornithological composition because it is located in an arid region, and acts as a resting site for migrant birds. The site included species that usually live in freshwater and coastal areas, a characteristic reflected in their high richness. It contributes noticeably to the local avian biodiversity.     

A phytogeographical characterization of the vine flora of the Sonoran and Chihuahuan deserts

Aim This study presents a phytogeographical characterization of the vine flora of two lower North American desert regions as a biogeographical framework for further ecological inquiry into desert vines. Location The phytogeography of the vine flora of the Sonoran and Chihuahuan Deserts was c haracterized based on 263 known species. Methods Checklists of the vines of each desert were developed. Represented genera were then grouped into 10 phytogeographical elements based on worldwide distribution patterns. To compare the floristic composition of the desert floras, an index of species similarity was calculated. Results About a third more species of vines occur in the Sonoran Desert than in the Chihuahuan Desert. Based on the analysis, cosmopolitan genera are the only group more numerous in absolute terms in the Chihuahuan Desert than in the Sonoran Desert. Tropical elements are represented in about the same proportion in each desert as the number of species, however, nearly twice as many pantropical and neotropical genera are represented in the Sonoran Desert as in the Chihuahuan Desert. Proportionately, more genera of temperate elements occur in the Chihuahuan Desert than in the Sonoran desert, although the absolute number of genera is slightly higher in the latter. Main conclusions As these deserts are relatively recent ecological formations and as vines evolved in forest ecosystems, the composition of the desert vine floras is the result of the interaction between historical vegetation types, their constituent taxa and climatic and geological history. The main differences in the vining floras of the present‐day Sonoran and Chihuahuan Deserts appear to be the result of greater historical influence in the Sonoran Desert of (1) tropical vegetation types and (2) the emergence of the Gulf of California. The Chihuahuan Desert vine flora seems to be the result of (1) a more pronounced historical temperate vegetation, (2) the lack of an important isolating event, such as the creation of the Baja California peninsula, and (3) a cooler climate with shorter growing seasons.     

A checklist of helminth parasites of Elasmobranchii in Mexico

A comprehensive and updated summary of the literature and unpublished records contained in scientific collections on the helminth parasites of the elasmobranchs from Mexico is herein presented for the first time. At present, the helminth fauna associated with Elasmobranchii recorded in Mexico is composed of 132 (110 named species and 22 not assigned to species), which belong to 70 genera included in 27 families (plus 4 incertae sedis families of cestodes). These data represent 7.2% of the worldwide species richness. Platyhelminthes is the most widely represented, with 128 taxa: 94 of cestodes, 22 of monogeneans and 12 of trematodes; Nematoda and Annelida: Hirudinea are represented by only 2 taxa each. These records come from 54 localities, pertaining to 15 states; Baja California Sur (17 sampled localities) and Baja California (10), are the states with the highest species richness: 72 and 54 species, respectively. Up to now, 48 elasmobranch species have been recorded as hosts of helminths in Mexico; so, approximately 82% of sharks and 67% of rays distributed in Mexican waters lack helminthological studies. The present list provides the host, distribution (with geographical coordinates), site of infection, accession number in scientific collections, and references for the parasites. A host-parasite list is also provided.     

Community structure and association of waterbirds with spatial heterogeneity in the Bahia Magdalena-Almejas wetland complex, Baja California Sur, Mexico

Community structure and association of waterbirds with spatial heterogeneity in the Bahia Magdalena-Almejas wetland complex, Baja California Sur, Mexico. To test the hypothesis that spatial heterogeneity determines waterbird diversity in a coastal wetland, we compared waterbird density, diversity, and species composition among various habitats and landscapes units in Bahia Magdalena-Almejas, Baja California Sur, Mexico. Based on diversity patterns and bird distribution, we assessed the effect of coastal development on the waterbird community structure. To gather information on habitat features and waterbird populations we conducted waterbird censuses in 329 habitat segments along the internal coastline of the study area, from February 2002 to February 2003. We performed non-parametric analyses to test the null hypothesis of no diference on waterbird density, and diversity among landscape units and seasons. The species composition was evaluated using ordination techniques. Waterbird density was higher in winter and autumn in the three lagoons of the study area, particularly in the insular coast, sandy beach and dunes; it was higher in the few segments of antropic sustrate. Diversity was significantly higher in mangrove habitat along the peninsular coast, and in mangrove-dunes association on the insular coast. Although modification of coastal natural habitat and boat transit disturbance had no influence on waterbird density or diversity, the highest richness of waterbirds occurred in well preserved areas. Species composition analysis showed differences between Santo Domingo Channel and Magdalena Bay. Pelagic and mangrove habitat had a species composition difference higher than those associations in other habitats. Such differences in species assemblages by habitat and landscape units suggest that communities are structured according to the range of available natural resources in structurally complex habitats, and that dominant piscivorous waterbird species were favored in this community.     

Contemporary genetic structure of Xantus's Hummingbird (Basilinna xantusii) in the Baja California peninsula

Genetic structure and phylogeographic patterns of natural populations are of great importance in assessing the conservation status of species. These population properties can be estimated using molecular markers of either mitochondrial DNA (mtDNA) or nuclear DNA (nDNA) to understand the historical, ecological and dispersal patterns that influence genetic exchange within and between populations. Basilinna xantusii is a sexually dimorphic hummingbird endemic to the Baja California Peninsula (BCP). It comprises three ancestral mitochondrial lineages linked to vicariant events, late Pleistocene climate changes and the geographical distribution of oases. This study aimed to determine and understand the current population genetic structure of this hummingbird. The genotypes of 16 microsatellite loci from 100 individuals collected across the geographical range of this species were compared with mtDNA sequences previously published. Cluster analyses identified five populations, two with almost no genetic admixture in the northern part of the BCP and three others with varying levels of admixed ancestry across the BCP. In San José de Magdalena, at the northernmost end of the range of Xantus's Hummingbird, 40% of individuals collected belong to one genetic cluster and the remaining 60% to another, both genetic clusters showing very little admixed ancestry. We hypothesize that, despite being in sympatry, these individuals do not interbreed, unlike the other populations where individuals showed ancestry coefficients of the other genetic groups. The philopatric behaviour of males and the long-range dispersal capacity of females probably determine the observed genetic differentiation pattern. The mito-nuclear discordance detected could be due to the molecular markers used and to female-biased dispersal. Gene flow is asymmetric in this species, being greater from north to south than vice versa, which is probably related to differences in the seasonality of precipitation across the BCP and to urbanization of the oases.     

Louse flies on birds of Baja California

Louse flies were collected from 401 birds of 32 species captured in autumn of 1996 in Baja California Sur (Mexico). Only one louse fly species (Microlynchia pusilla) was found. It occurred in four of the 164 common ground doves (Columbina passerina) collected. This is a new a host species for this louse fly.