Coastal Desert Research Articles

A two-state, multi-criteria Markov chain model for stochastic solar generators

ABSTRACT This paper presents a method of building a two-state multi-criteria Markov chain for stochastic solar generators. The design is based on different criteria which are defined using some statistical thresholds such as quartiles and averages. These thresholds have been used for classifying the state of all individual data samples. The proposed model is analyzed via computer simulation on Matlab environment using the historical data recorded over a period of 29 years by three meteorological stations in Algeria (Tamanrasset, Ghardaïa, and Oran). In order to validate and compare the performance of our model, several statistical tests were performed. The root mean square error and mean absolute error range, respectively, from 0.18 to 0.26 h and −0.10 h to 0.16. The obtained results proved that the model is effective to predict the data. Moreover, this study can be applied in its methodology not only in Algeria sites but also in other countries of the world and can serve as a reference for different climates, which are Mediterranean coastal climate, desert climate, and Sahel climate. Hence, it is useful to the designers of solar energy systems.

WITHDRAWN: Prehistoric coastal fisheries on the Atacama Desert (Taltal, 25°S). A Trans-Holocene record of paleoceanographic and archaeological fish remains

Abstract The Humboldt Current System (HCS) is one of the most productive marine ecosystems on earth. Humans have inhabited the desert coast of Chile and Peru for the last 12,000 years and have consistently based their subsistence and economy on the marine resources obtained from this rich ecosystem. Archaeological evidence on prehistoric coastal fisheries from the southern coast of the Atacama Desert, shows a Trans-Holocene record on knowledgeable fishers that developed gear to catch species from a wide array of habitats. However, the Holocene was a period with important changes in climate and paleoceanographic conditions that should have played an important role modulating natural conditions of fish habitats. In addition, fishing gear used in the past along the Atacama Desert coast varied through time, providing us clues on changing fishing patterns through the Holocene. Hence, the objective of the study is to examine our understanding of prehistoric fisheries from the area of Taltal (25°S) together with our present knowledge of the environmental factors that modulated it. We present fish data from ten archaeological sites with occupations dated between 12,000 and 1500 cal yrs BP, and discuss patterns of fishing behavior and their relationship to paleoceanographic conditions and fishing gear throughout the Holocene. Our results suggest that fishing strategies used by past communities adapted and took advantage of the dynamics of marine and coastal habitats. Furthermore, Trachurus murphyi, a neritic species and a staple fishery, plays a key role to help us understanding changes in fishing activities throughout the Holocene.

Metabolomics analysis of annual killifish (Austrofundulus limnaeus) embryos during aerial dehydration stress.

The annual killifish, Austrofundulus limnaeus, survives in ephemeral ponds in the coastal deserts of Venezuela. Persistence through the dry season is dependent on drought-resistant eggs embedded in the pond sediments during the rainy season. The ability of these embryos to enter drastic metabolic dormancy (diapause) during normal development enables A. limnaeus to survive conditions lethal to most other aquatic vertebrates; critical to the survival of the species is the ability of embryos to survive months and perhaps years without access to liquid water. Little is known about the molecular mechanisms that aid in survival of the dry season. This study aims to gain insight into the mechanisms facilitating survival of dehydration stress due to aerial exposure by examining metabolite profiles of dormant and developing embryos. There is strong evidence for unique metabolic profiles based on developmental stage and length of aerial exposure. Actively developing embryos exhibit more robust changes; however, dormant embryos respond in an active manner and significantly alter their metabolic profile. A number of metabolites accumulate in aerial-exposed embryos that may play an important role in survival, including the identification of known antioxidants and neuroprotectants. In addition, a number of unique metabolites not yet discussed in the dehydration literature are identified, such as lanthionine and 2-hydroxyglutarate. Despite high oxygen availability, embryos accumulate the anaerobic end product lactate. This paper offers an overview of the metabolic changes occurring that may support embryonic survival during dehydration stress due to aerial incubation, which can be functionally tested using genetic and pharmacological approaches.

Distribución de Sinsontillo (Polioptila lembeyei) en el sur del oriente de Cuba, implicaciones para su conservación

El Sinsontillo (Polioptila lembeyei) es una especie endémica de Cuba que posee una distribución restringida y de la que se conoce poco de su historia natural. La presente investigación se desarrolló en el sur de Oriente Cubano donde la especie es relativamente abundante. En la actualidad se desconocen las características de su distribución, lo que dificulta implementar acciones de conservación efectivas. Se trabajó en una franja costera al sureste de Cuba de 377 km de largo entre Cabo Cruz y Punta de Maisí y 10 km de ancho máximo. Se muestrearon 141 localidades a partir del método de conteo por puntos con radio variable combinado con reclamos. Se obtuvo reportes de la especie en 85 localidades. Se comprobó la presencia de Sinsontillo cercano a los 400 m de altitud y a más de 8000 m de distancia de la línea costera. Se observó la especie en nueve formaciones vegetales, 88 % de las localidades con presencia de la especie se agruparon en el matorral espinoso semidesértico costero, el bosque siempreverde micrófilo costero y prepostero (monte seco), la maleza compacta sin espinas y hierbas y pastos artificiales. Se realizó un modelo deductivo basado en las observaciones de campo, la literatura publicada y la experiencia de expertos. Las zonas de presencia ocupan 1063 km2 y está fragmentado en 274 parches de hábitat idóneo. Los valores de validación de modelo fueron buenos para el estadístico Kappa y para True Skill Statistic (TSS). El modelo predijo la presencia de la especie en una extensión inferior a la considerada en la bibliografía. Los resultados indican que los parches de hábitat idóneo de poca extensión presentes en zonas del sureste de Cuba son vulnerables a transformaciones por efectos de incidencia humana y del cambio climático y podría interrumpir la conectividad entre los parches de hábitats adecuados más grandes.

Assessing biodiversity within the range of Heleobia chimbaensis (Caenogastropoda: Cochliopidae) on the Atacama Desert coast

Heleobia is the most specious genus in the family Cochliopidae, in which many species are morphologically similar. Here we used morphological, microstructural and phylogenetic criteria to investigate species delimitation within the Heleobia chimbaensis complex on the Atacama Desert coast. The range included subdivided populations of the species, the subspecies Heleobia chimbaensis conica, and the allopatric snails from Los Perales, first recognized as a population of H. chimbaensis and more recently considered a candidate species of the group. Traditional shell characters, morphometric analysis, operculum, and protoconch were either uninformative or ambiguous to separate taxa. However, the phylogenetic analysis identified H. chimbaensis, H. chimbaensis conica and four additional populations of the species as a monophyletic group while the population from Los Perales was recovered as a distantly evolutionary significant unit for which the name Heleobia peralensis sp. nov. is provided here. While the geographic isolation and limited dispersal seem to have influenced the diversification and current distribution of H. chimbaensis in Atacama, the origin of Heleobia peralensis sp. nov. remains unclear because of uncertain relationships. A conservation status assessment according to IUCN criteria and NatureServe methodology suggests that both H. chimbaensis and Heleobia peralensis sp. nov. face a high risk of extinction. http://www.zoobank.org:pub:91770DA4-B16F-46AD-A6D6-9638065ED899

Range extension of the poorly known and Critically Endangered freshwater snail, Heleobia transitoria (Biese, 1947) (Gastropoda, Cochliopidae), in the Atacama Desert, northern Chile

The range distribution of Heleobia transitoria (Biese, 1947) is confined only to its type locality, Quebrada Cachina, a ravine located on the Atacama Desert coast in the Antofagasta Region, northern Chile. The species is classified as “En Peligro Crítico” according to Ministry of the Environment of Chile, a category equivalent to Critically Endangered (CR) of the IUCN Red List of Threatened Species, in part for its restricted distribution. This paper reports the occurrence of H. transitoria in the Atacama Region, Chile, after the study of morphological characters using light and scanning electron microscopy. This new record highlights considering the limited distribution and current conservation status of the species.

Climate change, vulnerability, social conflicts and human displacement in the Andes: The case of Huaytapallana glacier

La región andina, en particular el Perú, ha sido clasificada como la tercera región más vulnerable al cambio climático en el mundo (Trigoso 2008); además, a pesar del crecimiento económico de los últimos quince años, más de un tercio de la población vive en la pobreza, lo que aumenta su vulnerabilidad a los diversos efectos del cambio climático, como el retroceso de los glaciares, la pérdida de diversidad biológica, la salud, la producción agrícola y la escasez de agua. En la actualidad, el 65 por ciento de los conflictos sociales están relacionados con cuestiones ambientales, según diversos estudios. En las últimas seis décadas, Perú, como país tropical, ha experimentado cambios significativos en los niveles de precipitaciones y temperaturas, lo que ha provocado un mayor retroceso de los glaciares e inundaciones (Foresight Report 2011). El aumento de los riesgos y peligros ambientales, si bien es de carácter mundial, tendrá más repercusiones locales, en particular en el desierto costero y en las comunidades campesinas andinas (Blaikie y Cannon 2003). En las zonas costeras y áridas, el 80 por ciento del agua dulce proviene de los glaciares, lagos y ríos andinos. Durante los últimos diez años en la costa, la agricultura de regadío ha aumentado, ya que la mayor parte de esta producción se destina a la exportación. Esta producción incluye frutas, flores, espárragos, etc., que requieren más agua que la producción ganadera. Últimamente, se ha informado sobre la escasez de agua y los consiguientes conflictos sociales entre los grandes, medianos y pequeños productores.

Morphometric Comparison Between Different Populations of Darkling Beetles “Pimilia nilotica (Coleoptera: Tenebrionidae)” In Egypt

Insects include almost 60% of the described eukaryotic animals worldwide. However, the morphological measurements and assessment of the effects of isolation and habitat still lack many insect groups. The current study aimed to compare the morphometric measurements of dissimilar populations of darkling beetles “Pimelia nilotica” in Egypt. A variable comparison of morphometric variations was taken by a threaded micrometer for six different eco-geographical regions from Egypt fall under the Western Mediterranean Coastal Desert, Western Desert Oases, El-Faiyum Depression, the Eastern Desert, Nile Delta, and South Sinai. Twenty-one morphometric measurements were taken in the currents study. Traits best reminiscent of the excellence of populations were distinguished by cluster analysis, and also by the principal component analysis. The primary and second discriminants scores (score 1 and score 2) recorded 76.4% and 23.8%, respectively, of the full variation in samples. Multiple discriminant analysis disclosed clear morphometric differences between Western Desert, Eastern Desert, El-Faiyum Depression, and South Sinai populations. Traits clarifying the maximum of the changeability among populations were those associated with the morphological estimations.

The Response of Two Halophytic Species to Crude Oil-Contaminated Soil in the Northern Western Region of Egypt

A site that covers over 20 acres of coastal saline depression in the western Mediterranean coastal desert of Egypt (El-Hamra station, the main crude oil pipeline terminal in Alamein) is contaminated with petroleum. This area, prior to contamination by crude oil was dominated by different common halophytes. Atriplex halimus (L) and Arthrocnemum macrostachyum (Moric.) are now the most dominant species growing in this site. These species adapt themselves through different growth parameters, physiological and biochemical changes. Crude oil affects significantly on soil fertility and increasing pH (8.4). Importance value (IV), height and canopy diameter of the two studied species exhibited an increase in the polluted site. Organic metabolites such as fatty acids, antioxidant compounds and protein fractions in shoots of studied species which collected from the oil-contaminated and non-contaminated sites were examined. Fatty acid fractions exhibited the opposite performance especially the content of saturated C: 16 (palmitic), mono and di-unsaturated C18:1 (oleic) and C18:2 (linoleic) fatty acids as well as poly-unsaturated C18: 3 and C20: 3 (Omega -3 fatty acids). Antioxidant activity and most examined phenolic compounds were increased in A. macrostachyum which grow in a contaminated site. Protein fractions in A.halimus attained with enormous variations therefore, a Genomic Templet Stability (GTS %) was lower than in A. macrostachyum under contamination. The biochemical and behavioral responses to oil pollution varied with the two different species may be according to the genetic make-up of individuals, which make the two studied species useful and effective tools for phytoremediation purposes.

Treponematosis in a pre-Columbian hunter-gatherer male from Antofagasta (1830 ± 20 BP, Northern Coast of Chile)

ObjectiveThis paper reports a new case of treponemal disease in a pre-Columbian hunter-gatherer inhabiting the desert coast of South America. MaterialsA well-preserved adult male skeleton from the “Vertedero Municipal” archaeological cemetery, located near the city of Antofagasta (Northern Chile). MethodsThe skeleton was radiocarbon dated, and isotopic analyses were performed to assess diet and mobility. Lytic and proliferative lesions identified were evaluated macroscopically and radiologically. ResultsA radiocarbon date of 1830 ± 20 BP and isotopic values indicating a marine diet and coastal residence were obtained. The cranium shows reactive changes as focal superficial cavitation, radial scarring and nodular cavitation, while the ribs, sternum, clavicles, and scapulae exhibit multiple lytic and proliferative lesions. The right femur has a node while both tibiae show mild anterior cortical thickening with a narrowed medullary cavity. ConclusionsCranial lesions are pathognomonic for treponemal disease while postcranial changes are typical, and highly consistent with this pathology. SignificanceThe type, morphology, and pattern of lesions make this case a good candidate for venereal syphilis. The case is relevant to the origin of venereal syphilis due to the lifestyle, temporal and ecological context of the individual. LimitationsDiagnosis of venereal syphilis is based on skeletal lesions; thus, it must be confirmed by molecular analysis. Suggestions for Further ResearchA comprehensive review of cases of pre-Columbian treponemal disease in South America as well as molecular studies are needed to confirm the presence of venereal syphilis in the New World before European contact.

Fluvial activity in the Lomas de Lachay during the upper Pleistocene and Holocene

The Lomas de Lachay are the first ridges of the western slope of the Andes, about 100 km northward from Lima. This study examines the structure and age of fluvial terraces in the valleys of different orders. Accumulation of alluvium took place during the periods ca. 57 ka, 24–15 ka and likely the Late Glacial/Early Holocene. These periods correlate with pluvial Minchin, Tauca, and probably Coipasa (when fluvial activity in some Peruvian valleys was also noted). These alluviation phases were separated by erosion and terrace formation. The progressive aridization of the climate caused LGM aeolian covers to appear (21–18 ka) for the first time. Wind-blown sands fossilized older forms of relief and covered the valley slopes in the border zone between the lomas and desert. In the Holocene period, three types of geosystems developed in line with different morphogenetic activity: Coastal Desert (typified by a prevalence of aeolian processes); Lomas (very stable, with a prevalence of chemical weathering – tafones); and Mountain Desert (typified by very active fluvial and slope systems during El Nino events). Settlement phases in Lomas de Lachay were related to a high frequency of ENSO, and intensive grazing in recent centuries caused the creation of terracettes and buried soils on the slopes.

GABA metabolism is crucial for long-term survival of anoxia in annual killifish embryos.

In most vertebrates, a lack of oxygen quickly leads to irreparable damages to vital organs, such as the brain and heart. However, there are some vertebrates that have evolved mechanisms to survive periods of no oxygen (anoxia). The annual killifish (Austrofundulus limnaeus) survives in ephemeral ponds in the coastal deserts of Venezuela and their embryos have the remarkable ability to tolerate anoxia for months. When exposed to anoxia, embryos of A. limnaeus respond by producing significant amounts of γ-aminobutyric acid (GABA). This study aims to understand the role of GABA in supporting the metabolic response to anoxia. To explore this, we investigated four developmentally distinct stages of A. limnaeus embryos that vary in their anoxia tolerance. We measured GABA and lactate concentrations across development in response to anoxia and aerobic recovery. We then inhibited enzymes responsible for the production and degradation of GABA and observed GABA and lactate concentrations, as well as embryo mortality. Here, we show for the first time that GABA metabolism affects anoxia tolerance in A. limnaeus embryos. Inhibition of enzymes responsible for GABA production (glutamate decarboxylase) and degradation (GABA-transaminase and succinic acid semialdehyde dehydrogenase) led to increased mortality, supporting a role for GABA as an intermediate product and not a metabolic end-product. We propose multiple roles for GABA during anoxia and aerobic recovery in A. limnaeus embryos, serving as a neurotransmitter, an energy source, and an anti-oxidant.

Potential distribution model of Leontochir ovallei using remote sensing data

<p>Predicting the potential distribution of short-lived species with a narrow natural distribution range is a difficult task, especially when there is limited field data. The possible distribution of <em>L. ovallei</em> was modeled using the maximum entropy approach. This species has a very restricted distribution along the hyperarid coastal desert in northern Chile. Our results showed that local and regional environmental factors define its distribution. Changes in altitude and microhabitat related to the landforms are of critical importance at the local scale, whereas cloud cover variations associated with coastal fog was the principal factor determining the presence <em>of L. ovallei</em> at the regional level. This study verified the value of the maximum entropy in understanding the factors that influence the distribution of plant species with restricted distribution ranges.</p>

Procurement of camelid fiber in the hyperarid Atacama Desert coast: Insights from stable isotopes

Pastoralism and camelid management are traditionally attributed to the sociopolitical, economic and cosmovision of Andean populations, rather than to lowland hunter gatherer societies, living on the Pacific coast where camelid hunting is considered a marginal activity, and husbandry is a difficult enterprise given the hyper-arid conditions of lowland terrestrial ecosystems. Contrary to this interpretative historical view, our stable isotope analyses applied to 48 camelid fiber samples, suggests this highly valued camelid byproduct was obtained from camelids sustained on lomas vegetation formations during the Archaic (ca. 6500-4000 cal yr BP), Formative (ca. 4000-1500 cal yr BP) and Late periods (ca. 660-480 cal yr BP).

Ash-bearing transgressive coastal dune on São Vincente (Cape Verde Islands): dune history and evidence of explosive volcanic activity around 35 ka

Climbing, transgressive dunes are developed at the relief-controlled narrow desert coast of Praia Grande on Sao Vicente (Cape Verde Islands) and this paper describes one of these spectacular coastal dunes. The dune was initiated during a low sea level in the Late Pleistocene; the dune migrated landwards presumably during the influence of persistent northeasterly trade winds and it reached the present coast of the island some time before 35 ka, when it was covered with volcanic ash. Volcanic activity in the Cape Verde archipelago is presently limited to the island of Fogo or is submarine. However, Late Pleistocene eruptions have been identified on many of the islands, but few eruptions younger than 100 ka have been absolutely dated. The revelation of a 35 ka pyroclastic deposit on Sao Vicente is evidence for the continued activity in the northern part of the archipelago. The Praia Grande ash is not readily reconciled with the young Strombolian or effusive Sao Vicente volcanism, which is also geochemically different. The geochemical composition of the fractionation corrected Praia Grande ash is compared to a large database for volcanic rocks of the northern part of the Cape Verde archipelago. Major and trace elements as well as incompatible element ratios in combination allow identification of the likely source for the Praia Grande ash as the Monte Gordo volcano at the island Sao Nicolau 70 km to the SE and the eruption possibly was of VEI ≥ 5.

Late Pleistocene alluvial fan evolution along the coastal Atacama Desert (N Chile)

Due to their sensitivity to both tectonic activity and climatic variations, coastal alluvial fans (CAF) along the western flank of the Coastal Cordillera in the Atacama Desert (northern Chile) are important geo-archives for unravelling Quaternary environmental change. Our study focuses on terrestrial and marine deposits of five CAF complexes between 20° and 25°S along the coastal zone of the Atacama to identify phases of alluvial fan activity during the Late Quaternary. Based on a combination of luminescence dating and 10Be cosmogenic nuclide exposure dating as well as existing chronological data in the area, insights into climatic variations along the hyper-arid coast are presented for the Late Pleistocene derived from CAF morphodynamics. Activity of alluvial fans could be documented during time spans 95–80 ka, 60–45 ka, 35–20 ka, as well as the Holocene. Numerical dating of marine terrace deposits gives insights into the tectonic uplift of the Coastal Plain in northern Chile during the Late Quaternary period, for which estimated uplift rates between ~0.06 and ~0.57 m/ka were derived. While tectonic activity induces base-level changes, long-term tectonic activity rather indirectly controls alluvial fan activity. We suggest that alluvial fan activity is mainly controlled by atmospheric changes from the Pacific Ocean. Based on our observations, CAF in the hyper-arid Atacama Desert serve as suitable geo-archives for reconstructing climate changes during the Quaternary. In particular, the usefulness of alluvial fan systems in a water-limited environment is important for understanding the palaeoenvironmental evolution in a coastal desert.

Diversity of <em>Myxomycetes</em> in arid zones of Peru part II: the cactus belt and transition zones

The results obtained from a second survey for Myxomycetes in the arid areas of Peru are reported. A total of 37 localities from the cactus belt (‘cardonal’), between 1500 and 3000 m a.s.l., were sampled over six years. This survey is based on 601 identifiable collections of myxomycetes, developed in the field under natural conditions or those that were recovered from moist chamber cultures. In total, 84 taxa representing 19 genera were recorded. One new species, Cribraria spinispora Lado & D.Wrigley sp. nov., is described, three species new to South America and 22 additional new species for Peru are reported as well. Endemic plants, expecially cacti, had a particular relevance as myxomycete substrates. The predominance of the order Physarales T.Macbr. in arid areas is reinforced. Comments are included on some collections, as well as SEM micrographs of several species. A statistical evaluation of the diversity of myxomycetes in the cardonal area and a comparison of this area with the dry coastal desert of Peru and other Neotropical xeric environments are also included. Results show that the arid areas are rich in myxomycetes, and that each area has a unique assemblage. The differences appear to be related to the host plants.

ASSESSMENT OF LAND USE AND LAND COVER CHANGE DETECTION BY USING REMOTE SENSING AND GIS TECHNIQUES IN THE COASTAL DESERTS, SOUTH OF IRAN

Abstract. Land use/land cover (LULC) changes have become a central issue in current global change and sustainability research. Due to the large expanse of land change detection by the traditional methods is not sufficient and efficient; therefore, using of new methods such as remote sensing technology is necessary and vital This study evaluates LULC change in chabahar and konarak Coastal deserts, located in south of sistan and baluchestan province from 1988 to 2018 using Landsat images. Maximum likelihood classification were used to develop LULC maps. The change detection was executed using post-classification comparison and GIS. Then, taking ground truth data, the classified maps accuracy were assessed by calculating the Kappa coefficient and overall accuracy. The results for the time period of 1988–2018 are presented. Based on the results of the 30-year time period, vegetation has been decreased in area while urban areas have been developed. The area of saline and sandy lands has also increased.

Tomopeas ravus (Chiroptera: Molossidae)

Abstract Tomopeas ravus Miller, 1900 is a bat commonly called Peruvian crevice-dwelling bat. It is the only representative of the subfamily Tomopeatinae and endemic to the coastal desert of Peru where it is associated with woody savanna ecosystems and narrow rock crevices. Globally, it is considered “Endangered” by the International Union for Conservation of Nature and Natural Resources, mostly due to the ongoing population reduction and small and fragmented geographic range.

Contributions to the natural history of Mormopterus kalinowskii (Chiroptera: Molossidae) in the southwest of Peru

Mormopterus kalinowskii, is an insectivorous species restricted to the Andean western slopes of Peru and Chile, it is rare and has very scarce available information. We evaluated sex ratio, roost use, and relationship between reproductive patterns and monthly seasonal variation throughout a 13-month period. In addition, we performed the first description and characterization of its echolocation calls. The study area was located in the Ite Valley, Tacna department (southwestern Peru) at the northernmost part of the Atacama Desert, one of the driest deserts in the world. Bats were caught using mist-nets. Sex ratio in the population was calculated from all individuals captured, and its difference with regard to a 1:1 ratio was assessed through a Binomial Coefficient Test. Roost use was assessed through observation and inspection of the study area. Pearson and Spearman correlation coefficients were calculated to establish the relationship between the number of captures and temperature and precipitation data. Echolocation calls were recorded using a Petterson D240x Ultrasound detector plugged to a digital recorder. Spectrogram displays of recorded calls allowed describing structural patterns within echolocation calls and to measure frequency and time parameters. 79 individuals of M. kalinowskii were captured; 30 males and 49 females. Sex ratio obtained, 1:1.63, evidenced more females in the study area. M. kalinowskii uses crevices as roosts and has a single reproductive cycle per year. Higher capture rates are correlated with temperature (r = 0.526), but not precipitation (r = 0.096). Calls in search phase exhibited long duration pulses and a descending quasi-constant frequency (QCF) component from 39 to 33 kHz, reducing length and increasing bandwidth when attempting to catch prey. The sex ratio, 1:1.63 (≈ 2), suggests that M. kalinowskii is a polygamous species, as occurs in the others molossids, whereas the single annual reproductive cycle shown by M. kalinowskii would indicate a seasonal monoestrous reproductive pattern. Echolocation calls share several traits observed in other molossids; however, the frequency values for M. kalinowskii search phase pulses could be the highest recorded among the molossid bats of the Pacific coastal desert, allowing them to detect smaller prey as a strategy to mitigate food competition among insectivorous bats in arid environments.