Semi-arid Biome Research Articles

Conidial fungi from the semi-arid Caatinga biome of Brazil. New species and new records of <I>Helicosporium</I>

Conidial fungi from the semi-arid Caatinga biome of Brazil. New species and new records of <I>Helicosporium</I>

Análise da degradação da caatinga no núcleo de desertificação do Seridó (RN/PB)

A condição de aridez associada à pressão antrópica resulta em áreas de degradação extrema, conhecidas como núcleos de desertificação. No núcleo do Seridó a antropização é caracterizada por queimadas, cultivo do algodão no passado, pastoreio e exploração de lenha, que alteraram a composição florística e a estrutura da vegetação potencial. Com este estudo se objetivou identificar níveis de degradação na caatinga arbóreo-arbustiva do Seridó, por meio de técnicas multivariadas que envolveram variáveis do ambiente físico, da florística, fitofisionomia e diversidade da vegetação. O inventário florístico e fitossociológico foi realizado em 16 fragmentos, pelo método Ponto-Quadrante, com a inclusão de plantas com diâmetros no nível do solo 1 cm e altura ≥ 1 m, totalizando 3472 indivíduos, que foram identificados em 15 famílias, 24 gêneros e 31 espécies. As famílias Euphorbiaceae, Mimosaceae, Apocynaceae e Caesalpinaceae apresentaram maiores VI, assim como as espécies Croton hemiargyreus, Aspidosperma pyrifolium, Mimosa hostilis, Caesalpinia pyramidalis e Jatropha mollissima. Os resultados mostraram que a degradação dos fragmentos está associada às condições ambientais mais favoráveis, o que indica causa antrópica da degradação.

Physiological basis for diurnal activity in dispersing juvenile Bufo granulosus in the Caatinga, a Brazilian semi-arid environment

Diurnal activity is characteristic of many toad species, including Bufo granulosus from the Brazilian semi-arid biome called the Caatinga. Because of their patterns of activity, juvenile toads are exposed to hot and dehydrating conditions. Our investigation focuses on temperature and water relationships, and is based on the prediction that anuran diurnal activity in a semi-arid environment must be associated with morphological, physiological and behavioral traits enhancing thermal tolerances, capacity for performance at high temperatures and water balance. To test specific hypothesis related with this prediction, we investigated postmetamorphic B. granulosus and collected data on thermal tolerances and preferences, thermal safety margins, thermal dependence of locomotor behavior, thermal and kinetic properties of citrate synthase (CS), and skin morphophysiology. This information was compared with additional data from adult conspecifics and adult toads from sympatric species or from species from more moderate environments. We found that juvenile B. granulosus exhibit the highest critical maximum temperature reported for toads (44.2 degrees C) and are well suited to move at high temperatures. However, and in contrast with juveniles of other Bufo species, they do not show thermal preferences in a gradient and appear to hydroregulate more than thermoregulate. The CS of adult and juvenile toads shows typical patterns of thermal sensibility, but the thermal stability of this enzyme is much higher in juveniles than in adult Bufo of any other species studied. The inguinal skin exhibits a complex folding pattern and seems highly specialized for capillary water uptake. Diurnal activity in juvenile B. granulosus is possible given high thermal tolerances, keen ability to detect and uptake water, and avoidance behaviors.

A preliminary assessment of anuran physiological and morphological adaptation to the Caatinga, a Brazilian semi-arid environment

Anuran amphibians exploit a variety of water-deprived environments, including the Caatinga, a semi-arid biome that is exclusive to Brazil. The Caatinga is characterized by seasonal but unpredictable rains and by droughts that might last from several months to more than a year, or various years with negligible rain. Despite expected ecophysiological challenges, the Caatinga is home to a significant anuran fauna represented by five families. Many species retain behaviors and ecological associations that are typical for their genera, and avoid the full challenge of the Caatinga climate by seasonal and opportunistic activity. Therefore, the ability to aestivate seems a requirement for the colonization of the Caatinga, but a deep dormant state might not be typical of all species, as the microecological conditions of the shelters might vary significantly. From the standpoint of the skin as barrier to evaporative water loss, Caatinga anurans range from species with reduced levels of water evaporation due to waxy secretions to species that favor water uptake and exhibit a fully permeable skin. Most species are seasonal and nocturnal, but the few diurnal species tolerate temperatures that would impair or kill typical tropical anurans. The Caatinga anuran community depends on diverse behaviors, ecological associations and physiological adaptations that vary from taxa to taxa.

Local and regional‐scale responses of ant diversity to a semiarid biome transition

The locations of biome transitions and ecotones are frequently defined by the rapid shift from one form of dominant vegetation to another. The composition of animal taxa is predicted to shift in parallel with that of dominant plants and species diversity is predicted to he greater in transitional zones than in adjacent areas. We asked whether ant species diversity and composition supported these predictions across a biome transition between shortgrass steppe and Chihuahuan desert vegetation. Neither species richness nor diversity was highest at the biome transition region as a whole, or within habitats in the biome transition. The biome transition region was not intermediate in ant species composition or in the representation of different faunal complexes. The community similarity between matched habitats shared between the biome transition zone and adjacent regions was less than that between distinct habitats occurring within regions. A zoogeographic transition for ants may occur to the north of the phytogeographic transition and may be coincident with the northern limits of monsoonal precipitation patterns. In contrast, the phytogeographic transition may be related to less extreme climatic variation within the monsoonal region occurring further south.

Local and regional-scale responses of ant diversity to a semiarid biome transition

Local and regional-scale responses of ant diversity to a semiarid biome transition

Der Kapitza-widerstand dei einem heliumfilm

Dung beetles (Scarabaeinae) interact with resources in different ways and are classified according to resource relocation guilds. Dichotomius geminatus (Coprini) and Deltochilum verruciferum (Canthonini) are two of the most abundant and ecologically important species of the semi-arid region of Brazil, and understanding their behaviour may facilitate the comprehension of strategies associated to competition for resources. The aim of the present study was to investigate the behavioural repertoire of D. geminatus (tunneler) and D. verruciferum (roller), in isolation and controlled setting in the Brazilian semi-arid biome, using carrion as a food resource. Our hypothesis was that, due to the distinct food relocation strategies presented by these species, distinct behaviours would occur involving resource utilization. We also compared the behaviour of the two species and investigated the period of diel activity. Both species were more active during the night, but D. geminatus presented a shorter peak of nocturnal activity when compared to D. verruciferum. Although there was activity during the day, feeding was only observed during the night, for both species. During the periods of inactivity, D. verruciferum commonly went underneath the carrion, remaining still. As the target species of the study are very abundant, the differences in behaviour associated with the distinct relocation guilds may indicate a strategy to avoid direct competition.