Arid Biomes Research Articles

Spatial patterns of terrestrial vertebrates richness in Brazilian semiarid, Northeastern Brazil: Selecting hypotheses and revealing constraints

We tested the species-energy and environmental-stability hypotheses to evaluate if they explain the species richness patterns of terrestrial vertebrates in Caatinga, an arid biome in northeast Brazil. Furthermore, we determined which climate conditions constrain richness patterns in different taxonomic groups, taking into account their ecological and life-history characteristics. Amphibian richness and reptile richness were best explained by environmental instability and were constrained by the driest environmental conditions, whereas bird richness and mammal richness were driven by environmental energy and constrained by the hottest environmental conditions, highlighting their limited physiological budgets for handling high temperatures. Thus, our results revealed the primary climatic factors driving the species richness of vertebrates in this arid environment and determined, for each vertebrate group, which climate variable constrains its distribution. These findings can also be used to help improve conservation strategies in Caatinga by recognizing that the alteration of natural habitats for human dwellings, as well as changes in the global climate, could enhance desertification processes in this region and threaten the region’s biodiversity.

Molecular phylogenetics of the genus Gerbillus (Rodentia, Gerbillinae): Implications for systematics, taxonomy and chromosomal evolution

Although gerbils forms an important component of the mammalian fauna of arid and semi-arid area, the taxonomic and phylogenetic relationship within the species of the genus Gerbillus are still ambiguous. The present paper introduces findings based on the whole cytochrome b (1140 bp) mitochondrial genes of seven species ( Gerbillus campestris, G. latastei, G. nanus, G. tarabuli, G. gerbillus, G. simoni and G. nigeriae) six of which are present in Tunisia. Our results show that all the Gerbillus species are monophyletic. Moreover, molecular phylogeny rejects the genus rank for the taxon Dipodillus. Gebillus nanus, a species belonging to the subgenus Hendecapleura, early diverged from the other species which are divided into two clades: the subgenus Dipodillus, including G. campestris and G. simoni and the subgenus Gerbillus including G. gerbillus, G. nigeriae, G. tarabuli and G. latastei. These results are congruent with morphological and karyological evidences. According to molecular clock, the appearance of the genus Gerbillus coincides with the Miocene–Pliocene expansion of African arid biomes. Extensive intraspecific chromosomal changes evolved in a relatively narrow lapse of time, like in the case of G. latastei, allowing the fixations of different chromosomal variants due to pericentric inversion.

The evolution of sexual and parthenogeneticWarramaba: a window onto Plio–Pleistocene diversification processes in an arid biome

Environmental changes over the Plio-Pleistocene have been key drivers of speciation patterns and genetic diversification in high-latitude and mesic environments, yet comparatively little is known about the evolutionary history of species in arid environments. We applied phylogenetic and phylogeographic analyses to understand the evolutionary history of Warramaba grasshoppers from the Australian arid zone, a group including sexual and parthenogenetic lineages. Sequence data (mitochondrial COI) showed that the four major sexual lineages within Warramaba most likely diverged in the Pliocene, around 2-7 million years ago. All sexual lineages exhibited considerable phylogenetic structure. Detailed analyses of the hybrid parthenogenetic species W. virgo and its sexual progenitors showed a pattern of high phylogenetic diversity and phylogeographic structure in northern lineages, and low diversity and evidence for recent expansion in southern lineages. Northern sexual lineages persisted in localized refugia over the Pleistocene, with sustained barriers promoting divergence over this period. Southern parts of the present range became periodically unsuitable during the Pleistocene, and it is into this region that parthenogenetic lineages have expanded. Our results strongly parallel those for sexual and parthenogenetic lineages of the gecko Heteronotia from the same region, indicating a highly general effect of Plio-Pleistocene environmental change on diversification processes in arid Australia.

Overview of the geography of the Monte Desert biome (Argentina)

The compilation of published results on the geography of the Monte Desert biome of Argentina that we present here offers a review of its boundaries and ecotones, and of its biophysical and socio-economic characteristics. In relation to socio-ecological issues, the focus is on a case study in the province of Mendoza. An analysis is presented about the ecological-economic issues and the sustainable investment policies in rangelands of the Patagonian Monte. In addition, this biome is compared with other South American arid biomes and their North American counterparts. We identified some gaps in the current knowledge, especially at a mesoscale level, where studies on Monte borders are deemed necessary as well as explicit boundary criteria for ecosystem differentiation. Also the ecological-economic relations and feedbacks between livestock herbivory, soil erosion and market behaviour should be considered within the framework of wider socio-ecological research.

Paleoenvironmental evolution of southern South America during the Cenozoic

Southern South America (SSA) has today a high diversity of climates, environments, biomes, and biotas, as a result of the complex interaction through time of plants and animals with the geological forces (e.g. plate tectonics, sea-level changes, glaciations) that modulated the geography of the continent. Arid biomes are well represented in SSA today, but were arid biomes similarly important in the geologic past? How long in time can be found major arid biomes in SSA? With the aim of replaying these questions, in this paper we summarized the paleoenvironmental changes of SSA through Cenozoic, emphasizing the relationships between biomes and the geological forces that, through different climatic-environmental factors, have driven its evolution. We define SSA the south of the 15°S area. We prefer this geographical delimitation because with it we can see and follow the history of the biogeographic (historic and ecologic) relationships of Patagonian biota with the rest of the South American biota. Additionally, with this delimitation we possess the most complete Cenozoic South American land-mammal fossil record. We use biomes because biomes are taxon-free analytical units, and their pattern of change can be traced through time independently of the taxa present at different geological periods. Data on plate tectonics, volcanism, sea-level changes, marine paleotemperatures, and glaciations were taken from literature. To analyse the pattern of change of southern South American climates and environments through the Cenozoic, we used the fossil record of land-mammals as information source. When available, the record of vascular plants were used to contrast the inferences derived from land-mammals. Finally, we used standard geologic divisions (i.e. Epochs) as chronological units. The main conclusion of this paper is that from Early Paleocene to Late Pleistocene, southern South American climatic conditions changed from warm, wet, and non-seasonal, to colder, dryer, and seasonal. Concomitantly, biomes changed from tropical forest to steppes, across a sequence constituted by subtropical forests, woodland savanna, park-savanna, and grassland savanna. During the Quaternary, and as a consequence of glacial cycles, cold and dry conditions were interrupted by warmer and wet periods. Accordingly, several pulses of expansion and retraction of steppes (and, concomitantly, advances and retreats of the northern tropical forests) are recorded. This cyclic pattern of changes produced the provincialism that has characterized the South American biota from Early Pleistocene to the present.

What is NPP? Inconsistent accounting of respiratory fluxes in the definition of net primary production

Primary production represents a globally important flux of carbon between the atmosphere and the biosphere. From an ecological perspective, it measures the rate at which solar energy is stored by plants as organic matter, and is therefore a measure of the rate at which solar energy is captured and made available to the rest of the food chain (Odum 1971). From a biogeochemical perspective, primary production provides links between the biosphere and the climate system through the global cycling of C, water and nutrients (Roy et al . 2001). Gross primary production (GPP) is the total amount of C assimilated by plants within a given area over a specified timeframe. (Here GPP refers to the total C fixed by photosynthesis, minus the C lost by photorespiration. We have adopted the convention of specifying productivity in units of C mass per unit ground area per unit time, although we could have alternatively used units of total biomass, or energy: Odum 1971.) Net primary production (NPP) is GPP less the flux of autotrophic respiration of assimilate used for the plant’s own metabolism ( R ), therefore:

Photosynthetic activity of US biomes: responses to the spatial variability and seasonality of precipitation and temperature

AbstractWe examined the response of the normalized difference vegetation index, integrated over the growing season (gNDVI) to mean precipitation, maximum temperature (Tmax), and minimum temperature (Tmin) over an 11‐year period (1990–2000) for six biomes in the conterminous United States. We focused on within‐ and across‐biome variance in long‐term average gNDVI, emphasizing the degree to which this variance is explained by spatial gradients in long‐term average seasonal climate. Since direct measurements of ecosystem function are unavailable at the spatial and temporal scales studied, we used the satellite‐based gNDVI as a proxy for net photosynthetic activity.Forested and nonforested biomes differed sharply in their response to spatial gradients in temperature and precipitation. Gradients in mean spring and fall precipitation totals explained much of the variance in mean annual gNDVI within arid biomes. For forested biomes, mean annual gNDVI was positively associated with mean annual and seasonal Tmin and Tmax. These trends highlight the importance of the seasonal components of precipitation and temperature regimes in controlling productivity, and reflect the influence of these climatic components on water balance and growing‐season length. According to the International Panel on Climate Change (IPCC) (2001) increases in temperature minima and fall precipitation have contributed the dominant components of US increases in temperature and precipitation, respectively. Within the range of conditions observed over the study region, our results suggest that these trends have particularly significant consequences for above‐ground plant productivity, especially for Grassland, Open Shrubland, and Evergreen Needleleaf Forest. If historical climatic trends and the biotic responses suggested in this analysis continue to hold, we can anticipate further increases in productivity for both forested and nonforested ecoregions in the conterminous US, with associated implications for carbon budgets and woody proliferation.

A basal aquatic-terrestrial trophic link in rivers: algal subsidies via shore-dwelling grasshoppers.

Rivers provide important resources for riparian consumers, especially in arid or seasonally arid biomes. Pygmy grasshoppers (Paratettix aztecus and P. mexicanus; Tetrigidae) graze river algae stranded along shorelines of the South Fork Eel River in northern California (39°44'N, 123°39'W) as the river recedes during the summer drought. Densities of tetrigids during the mid to late summer were highest (1individual/m2 in July) within 1m of the river margin, and declined to near zero at 4m from the margin, especially during peak temperatures in the afternoon. These observations suggested that the distribution of tetrigids was determined by the availability of algae, water, or both. We manipulated the presence/absence of water and beached algae (Cladophora glomerata) in a 2×2 factorial design. All treatments were positioned 2m upslope from the river's edge (about 30cm above the water table), where the cobble bar was naturally dry and devoid of algae and densities of tetrigids were lower than at the river margin (0.4 individuals/m2 in July). Tetrigids responded only to the wet Cladophora treatment, which had 30× higher densities than other treatments. Stable isotopic signatures (δ13C) of tetrigids (-19.7‰) collected from the same cobble bars were more similar to those of epilithic algae (-20.4‰) than terrestrial plants (-28.2‰), and higher than those of acridid grasshoppers (-27.9‰) from the same habitats. Mixing models suggest that 88-100% of the C in tetrigid grasshoppers at our study site is derived from riverine algae. A preliminary analysis suggests that tetrigids ingested sufficient quantities of algae to easily meet their energetic demands during the summer. This study supports the idea that algae, produced in stream systems, can determine the distribution and relative abundance of a common terrestrial scavenger and provide an additional pathway for energy exchange between rivers and riparian food webs.

Food Web Implications of δ13C and δ15N Variability over 370 km of the Regulated Colorado River USA

Dual stable isotope analysis in the regulated Colorado River through Grand Canyon National Park, USA, revealed a food web that varied spatially through this arid biome. Down-river enrichment of δ13C data was detected across three trophic levels resulting in shifted food webs. Humpack chub δ13C and δ15N values from muscle plugs and fin clips did not differ significantly. Humpback chub and rainbow trout trophic position is positively correlated with standard length indicating an increase in piscivory by larger fishes. Recovery of the aquatic community from impoundment by Glen Canyon Dam and collecting refinements for stable isotope analysis within large rivers are discussed.

THE DIURNAL ACTIVITY OF BRANTS' WHISTLING RAT (PAROTOMYS BRANTSII): THE EFFECT OF SEASONAL AND PHYSICAL CONDITIONS

SUMMARY Brants' whistling rat, Parotomys brantsii, is a gregarious rodent indigenous to the south-west arid biome of southern Africa. However, P. brantsii portrays few physiological adaptations to its semi-arid environment. Consequently behavioural considerations such as use of refuges, diet selection and activity patterns are probably critical to its survival. This field study, based on direct observations of individuals. examines the diurnal activity pattern of these rodents. Despite the negative effect of increasing windspeed on winter activity, ambient temperature did not limit diurnal activity. In contrast, during summer, individuals fed and foraged for shorter period!, than in winter, and spent a greater proportion of their time underground on hotter days. These limitations to ambient environmental conditions suggest that P. brantsii is probably better adapted, due to its physiological limitations, to winter rainfall areas such as Namaqualand and the Little Karoo, than summer rainfall areas such as the southern Kalahari and central Karoo.

Comparison of Channel and Hyporheic Invertebrate Communities in a Southwestern USA Desert Stream

ABSTRACT We collected invertebrates seasonally from the channel surface and hyporheic zone of a perennial desert stream in central Arizona, U.S.A. Channel collections were made with a Hess sampler and hyporheic collections were taken with a vacuum bilge pump and sand-point probe. Diptera, Plecoptera, Nematoda and Cyclopoida comprised 86% of total annual abundance in the hyporheic zone, while Diptera and Trichoptera made up 85% of the total annual abundance in the channel. Pot samplers with two substratum sizes and chamber depths were also buried in the channel during the summer for comparison with Hess and sand-point probe collections. Densities of invertebrates in the channel surface were higher (3,400 animals/m2) than those of subchannel pots (528 animals/m2); however, pots collected 71 animals/L compared to 1.3 animals/L for sand-point probe collections with no significant difference (p >0.20) in selection for substratum size and depth. Hyporheic communities may be restricted in arid biomes and/or in r...