Víctor Sánchez-Cordero

Effects of global climate change on geographic distributions of Mexican Cracidae

Although climate change and its implications are a frequent subject of detailed study, the effects of these changes on species’ geographic distributions remain little explored. We present a first cross-species analysis of the effects of global climate change on the distributions of one bird family, the Cracidae, in Mexico, based on projecting models of ecological niches from present conditions to modeled future conditions taken from general circulation models of climate change. Based on two different scenarios of climate change and on three assumptions regarding species’ dispersal abilities, effects on species’ distributions range from drastic reduction to modest increases. These results illustrate the complex nature of species’ geographic responses to environmental change, and emphasize the need for detailed analysis of individual species’ ecological requirements.

Ecologic Niche Modeling and Potential Reservoirs for Chagas Disease, Mexico

Ecologic niche modeling may improve our understanding of epidemiologically relevant vector and parasite-reservoir distributions. We used this tool to identify host relationships of Triatoma species implicated in transmission of Chagas disease. Associations have been documented between the protracta complex (Triatoma: Triatominae: Reduviidae) with packrat species (Neotoma spp.), providing an excellent case study for the broader challenge of developing hypotheses of association. Species pairs that were identified coincided exactly with those in previous studies, suggesting that local interactions between Triatoma and Neotoma species and subspecies have implications at a geographic level. Nothing is known about sylvatic associates of T. barberi, which are considered the primary Chagas vector in Mexico; its geographic distribution coincided closely with that of N. mexicana, suggesting interaction. The presence of the species was confirmed in two regions where it had been predicted but not previously collected. This approach may help in identifying Chagas disease risk areas, planning vector-control strategies, and exploring parasite-reservoir associations for other emerging diseases.

Effectiveness of natural protected areas to prevent land use and land cover change in Mexico

This study evaluated the extent to which natural protected areas (NPAs) in Mexico have been effective for preventing land use/land cover change, considered as a major cause of other degradation processes. We developed an effectiveness index including NPA percentage of transformed areas (agriculture, induced vegetation, forestry plantations, and human settlements) in 2002, the rate and absolute extent of change in these areas (1993–2002), the comparison between rates of change observed inside the NPA and in an equivalent surrounding area, and between the NPA and the state(s) in which it is located. We chose 69 terrestrial federal NPAs, decreed before 1997, that were larger than 1,000 ha, not urban/reforested with non-native vegetation, not islands and not coastal strips, and estimated the extent of transformed areas using 1993 and 2002 land use/land cover maps. Over 54% of NPAs were effective, and were heterogeneously distributed by management categories: 65% of Biosphere Reserves, 53% of Flora and Fauna Protection Areas, and 45% of National Parks. 23% of NPAs were regarded as weakly effective, and the remaining 23% as non-effective. We recognize the importance of NPAs as a relevant conservation instrument, as half of NPAs analyzed (particularly biosphere reserves) prevented natural vegetation loss compared with their geographic context. Our results suggest that conservation based on NPAs in Mexico still faces significant challenges. Our approach can be expanded for evaluating the effectiveness of NPA in other regions, as land use/land cover maps are now available almost worldwide.

POSTDISPERSAL FRUIT AND SEED REMOVAL BY FOREST-DWELLING RODENTS IN A LOWLAND RAINFOREST IN MEXICO

This study examined whether postdispersal fruit and seed removal by terrestrial mammals of common plant species was affected by the type of item, item density (low, medium, high), and habitat (gap, mid-succession, mature). Fruits of Brosimum alicastrum and Ficusyoponensis (Moraceae), Astrocaryum mexicanum (Palmae), and Nectandra ambigens (Lauraceae), and seeds of Omphalea oleifera (Euphorbiaceae) and Cymbopetalum baillonii (Annonaceae) were tested at the Los Tuxtlas rainforest in Mexico. Item removal from 108 experimental patches (N= 2340 fruits or seeds for each plant species tested) after 5 d was lower for F. yoponensis (6.6%) than for N. ambigens (68.8%), B. alicastrum (67.8%) C. baillonii (64.0%) and A. mexicanum (60.0%). No seeds of 0. oleifera were removed. A higher fruit or seed removal was observed from high density than low density food patches in A. mexicanum, C. baillonii and N. ambigens, but not in B. alicastrum and Fyoponensis. A higher fruit or seed removal was observed from food patches in mature forest than in gaps in all plant species tested. Similar removal values between open (open to all terrestrial mammals) and caged (open to small rodents) fruit and seed patches, abundant rodent live-trapping, and a scarcity of large terrestrial mammals, indicated that forest-dwelling small rodents were the main postdis- persal removal agents. Differences in plant species seedling recruitment resulting from small rodent food choices can partially determine long-term forest floristic composition at the Los Tuxtlas rainforest. RESUMEN. Se determino si la remocion postdispersion de frutos y semillas de plantas comunes, por parte de los mamiferos terrestres, es afectada por la especie de planta, la densidad de los lotes de frutos o semillas y por el habitat (claro, sucesion secundaria y selva madura). Frutos de Brosimum alicastrum y Ficus yoponensis (Moraceae), Astrocaryum mexicanum (Palmae) y Nectandra ambigens (Lauraceae) y semillas de Omphalea oleifera (Euphorbiaceae) y Cymbopetalum baillonii

SOURCES OF PROTEIN IN TWO SPECIES OF PHYTOPHAGOUS BATS IN A SEASONAL DRY FOREST: EVIDENCE FROM STABLE-ISOTOPE ANALYSIS

Abstract The relative importance of plants and insects as sources of protein through the year was evaluated in 2 bat species in a seasonal forest in the neotropics using stable-isotope analysis of carbon and nitrogen. Artibeus jamaicensis, a frugivore, met almost all of its protein requirements from plants with no seasonal or sexual variation. In contrast, Glossophaga soricina, a nectarivore, relied mostly on insects, but in females, plants and insects were equally important in the early rainy season and in the mid dry season. Evidence of changes in food origin of protein associated with reproductive activity was not detected in either species.

Sources of assimilated protein in five species of New World frugivorous bats

Abstract. Fruits are N-poor items and their availability in the tropics varies throughout the year. Field and experimental studies debate whether frugivorous bats have to switch to N-rich sources of food during part of the year or if they are able to subsist on a fruit-only diet. Different strategies to meet their N requirements may influence the way in which frugivorous bats partition food resources allowing the coexistence of numerous species in tropical communities. We examined the extent to which five species of frugivorous bats relied on plant and insect sources of assimilated protein using stable-N isotope analysis. We assumed that bats only had access to fruits and insects in our analysis but we also collected fecal samples to examine the presence of other food items. We conducted the study during at least 1 full year depending on the species of bat in a tropical rain forest in southern Mexico. In the five species of bats examined, plant sources (i.e. fruits) provided most of the protein assimilated during the year, although there was a general trend for all species to show a decrease in relative plant contribution at the end of the rainy season and beginning of the dry season. In Artibeus jamaicensis, Uroderma bilobatum and Dermanura phaeotis, plants were still a major source of protein during this period, but in some individuals of Sturnira lilium and Carollia brevicauda insects represented an important contribution to their diet. Fecal samples of most bats presented fruit remains, and insects and pollen were found in small proportions. Bat reproductive activity was detected at the end of the dry season and in the middle of the rainy season, and plants were the major source of protein during this period with the exception of pregnant S. lilum and one pregnant D. phaeotis during the dry season. Our findings showed that frugivorous bats might differ in their strategies to satisfy their N demands with some species relying almost completely on fruits during most of the year and some species switching to insects when fruits were less abundant.

Ecology of North American Triatominae.

In all, 40 native triatomine species and subspecies occur in NA, belonging to six genera from the Triatomini (Triatoma, Paratriatoma, Panstrongylus, Dipetalogaster, Belminus, Eratyrus), and one genus from the Rhodniini (represented by one non-native species Rhodnius prolixus, formerly occurring exclusively in domestic habitats); 28 species are found exclusively in Mexico (and/or Central America), eight are shared between the United States (US) and Mexico, and four occur exclusively in the US. The genus Triatoma is the most diverse with 26 species belonging to the species groups protracta, including the species complexes protracta and lecticularia, and rubrofasciata, which includes the species complexes rubida, phyllosoma and dimidiata. Triatomine species richness declined both at higher (south US) and lower (south of the Istmus of Tehuantepec, Mexico) latitudes. Triatoma species are found predominantly in cropland, grassland, wooded grassland and woodland landscapes. Land cover types were most similar among the lecticularia, protracta, and rubida complexes, in contrast to the phyllosoma and dimidiata species complexes. The land cover types having highest suitability for most species were wooded grassland, followed by woodland for the phyllosoma and dimidiata species complexes, and open and closed shrubland and cropland for the remaining three species complexes. A principal component analysis was used to demonstrate differences in the potential range for use of environmental conditions: protracta and phyllosoma complexes occupy the broadest niches. The present study represents a primary stratification of potential triatomine dispersal areas, based on species and species complexes, and based on predicted niche, a method which has already proven to be highly significant epidemiologically.

Using biotic interaction networks for prediction in biodiversity and emerging diseases.

Networks offer a powerful tool for understanding and visualizing inter-species ecological and evolutionary interactions. Previously considered examples, such as trophic networks, are just representations of experimentally observed direct interactions. However, species interactions are so rich and complex it is not feasible to directly observe more than a small fraction. In this paper, using data mining techniques, we show how potential interactions can be inferred from geographic data, rather than by direct observation. An important application area for this methodology is that of emerging diseases, where, often, little is known about inter-species interactions, such as between vectors and reservoirs. Here, we show how using geographic data, biotic interaction networks that model statistical dependencies between species distributions can be used to infer and understand inter-species interactions. Furthermore, we show how such networks can be used to build prediction models. For example, for predicting the most important reservoirs of a disease, or the degree of disease risk associated with a geographical area. We illustrate the general methodology by considering an important emerging disease - Leishmaniasis. This data mining methodology allows for the use of geographic data to construct inferential biotic interaction networks which can then be used to build prediction models with a wide range of applications in ecology, biodiversity and emerging diseases.

Pollination ecology of Stenocereus queretaroensis (Cactaceae), a chiropterophilous columnar cactus, in a tropical dry forest of Mexico

Flowers of columnar cacti are animal-pollinated, often displaying a chiropterophylic syndrome. This study examined if the columnar cactus Stenocereus queretaroensis, a tropical species endemic to western Mexico, is bat-pollinated, by studying its pollination biology and the foraging behavior of potential pollinators. Flowers were produced in winter through spring, peaking in April. Anthesis was nocturnal, and stigma and anther turgidity began around 2200 hours. Production of nectar secretion and highest sugar concentration and energy supply were nocturnal, peaking between 2200 and 2400 hours. Manual auto-pollination and exclusion experiments showed that self-pollination yielded no fruits, while nocturnal pollinators resulted in high fruit set and seed set compared to diurnal pollination treatments. The nectar-feeding bat Leptonycteris curasoae (Phyllostomidae) was the main nocturnal pollinator with the highest effective pollination. Peak bat visitation coincided with peaks in nectar production. The high abundance of L. curasoae throughout the 4-yr study, suggests that it is a seasonally reliable pollinator for this columnar cactus. While pollination syndromes have been increasingly called into question in recent years, this study suggests that at least for this system, there is a fairly close fit between pollinator and pollination syndrome.

Projected future distributions of vectors of Trypanosoma cruzi in North America under climate change scenarios.

Background Chagas disease kills approximately 45 thousand people annually and affects 10 million people in Latin America and the southern United States. The parasite that causes the disease, Trypanosoma cruzi, can be transmitted by insects of the family Reduviidae, subfamily Triatominae. Any study that attempts to evaluate risk for Chagas disease must focus on the ecology and biogeography of these vectors. Expected distributional shifts of vector species due to climate change are likely to alter spatial patterns of risk of Chagas disease, presumably through northward expansion of high risk areas in North America. Methodology/Principal Findings We forecast the future (2050) distributions in North America of Triatoma gerstaeckeri and T. sanguisuga, two of the most common triatomine species and important vectors of Trypanosoma cruzi in the southern United States. Our aim was to analyze how climate change might affect the future shift of Chagas disease in North America using a maximum entropy algorithm to predict changes in suitable habitat based on vector occurrence points and predictive environmental variables. Projections based on three different general circulation models (CCCMA, CSIRO, and HADCM3) and two IPCC scenarios (A2 and B2) were analyzed. Twenty models were developed for each case and evaluated via cross-validation. The final model averages result from all twenty of these models. All models had AUC >0.90, which indicates that the models are robust. Our results predict a potential northern shift in the distribution of T. gerstaeckeri and a northern and southern distributional shift of T. sanguisuga from its current range due to climate change. Conclusions/Significance The results of this study provide baseline information for monitoring the northward shift of potential risk from Chagas disease in the face of climate change.