Spatial patterns of the Chaco vegetation of central Argentina: Integration of remote sensing and phytosociology

Abstract. In this study we report the first application of Landsat TM imagery to Chaco vegetation studies at a regional scale in Argentina. We produced a map showing 13 clearly differentiated land‐cover types, and described the composition and structure of the plant communities, in an area of almost 42002 km² in central Argentina. The land‐cover map obtained shows that the Chaco vegetation in central Argentina is highly disturbed. In the lowland part of the area the dominant land‐cover types are largely cultural landscapes and substitute shrublands, which have displaced the original Chaco forests, leaving only small isolated remnants generally confined to sites with some kind of constrain for agriculture. The use of TM images and the multivariate analysis of phytosociological data showed a qualified, high accuracy mapping capability for land‐cover types in the Chaco region (ca. 85% overall accuracy). Our results highlight the utility of TM and field data in a subtropical to warm‐temperate region, which is promising where other ancillary data are not available and a rapid acquisition of reliable vegetation data is required, so constituting a starting point for an imperative and more extensive classification and mapping of the endangered Chaco region.     

Plant functional traits and environmental filters at a regional scale

Abstract. Links between plant traits and the environment, i.e. sets of plant attributes consistently associated with certain environmental conditions, are the consequence of the filtering effect of climatic, disturbance and biotic conditions. These filters determine which components of a species pool are assembled into local communities. We aimed at testing for consistent association between plant traits and climatic conditions along a steep regional gradient, divided into 13 climatically homogeneous sectors, in central-western Argentina. We analyzed 19 vegetative and regeneration traits of the 100 most abundant species along the gradient. For each trait, we tested for homogeneity of frequencies of different categories between sectors and the regional species pool, using the χ² statistic. We rejected H₀ in 71% of the pair-wise comparisons, which strongly suggests a ‘filtering effect’ of climatic factors on key plant functions. Vegetative traits were filtered more often than regeneration traits. Specific leaf area, life span, ramification, canopy height, leaf weight ratio, carbon investment into support tissue and pollination mode were the traits showing differences in the largest number of pair-wise comparisons. This is probably the first attempt to detect, on a quantitative, statistically conservative basis, consistent linkages between climatic factors and numerous plant traits, over a broad spectrum of environmental conditions and plant growth forms. We discuss the advantages and limitations of this approach in predicting vegetation structure and functioning under present environmental conditions, and those expected for the next century as a consequence of global change.     

Conspecific alarm cues, but not predator cues alone, determine antipredator behavior of larval southern marbled newts, Triturus pygmaeus

Predation imposes selection on the ability of prey to recognize and respond to potential threats. Many prey species detect predators via chemoreception, particularly in aquatic environments. Also, chemical cues from injured prey are often perceived as an indication of predation risk. However, because antipredatory behavior can be costly, prey responses should depend on the current level of risk that each predator poses, which may depend on the type of chemical cues detected. We exposed larval newts, Triturus pygmaeus, to chemical cues from predator larval beetles or to alarm cues from conspecific larval newts and examined the behavioral changes of larval newts. Results showed that larval newts reduced activity levels when conspecific alarm cues were present but not when the predator cues alone were present. These results might suggest that larval newts are unable to recognize predator chemicals. To avoid costs of unnecessary antipredatory behaviors, larval newts may benefit by avoiding only predators that represent a current high level of threat, showing only antipredatory responses when they detect conspecific alarm cues indicating that an actual predatory attack has occurred.     

Intensity of official Futsal matches

The purpose of this study was to assess the intensity of official Futsal matches, expressed in different ways. Fourteen male professional Futsal players from a First Division Brazilian team volunteered to participate in this study. Maximal oxygen uptake (VO(2)max) and the heart hate (HR) and oxygen uptake (VO(2)) correlation were determined for each player. The match intensity was estimated from the players' average HR measured during 13 National Futsal League matches. The HR measurements were obtained while the players were in the court but the values recorded while the players were sitting on the bench were not considered. In addition, these HR values were used to estimate the intensity of the effort expressed as a percentage of the maximal HR (% HRmax), percentage of VO(2)max (% VO(2)max), kilocalories per minute (kcal·min(-1)), and total caloric expenditure. The mean intensity of the matches was 86.4 ± 3.8% HRmax, 79.2 ± 9.0% VO(2)max, 18.0 ± 2.2 kcal·min(-1), and 313 ± 9.3 kcal. It was concluded that official Futsal matches have high intensity when expressed in the different ways used in this study. The information provided by this research can be used for planning the athletes' workouts, diets, and resting periods.     

Vegetation changes along a precipitation gradient in Central Argentina

Changes in vegetation along a precipitation gradient in Central Argentina were studied. Floristic samples were taken along an east-west transect of about 300 km. Correlation analysis between precipitation and ordination axes was used to provide an environmental interpretation of vegetation variability.Floristic analysis produced an ordination of plant communities from evergreen forests (precipitation >500 mm) to desert shrublands and therophyte communities (precipitation <200 mm). Results showed a trend of floristic and structural impoverishment towards the west. There is a replacement of species along the transect and a shift in dominant growth forms. The first ordination axis is significantly, negatively correlated with annual precipitation.     

Increased temperature disrupts chemical communication in some species but not others: The importance of local adaptation and distribution

Environmental conditions experienced by a species during its evolutionary history may shape the signals it uses for communication. Consequently, rapid environmental changes may lead to less effective signals, which interfere with communication between individuals, altering life history traits such as predator detection and mate searching. Increased temperature can reduce the efficacy of scent marks released by male lizards, but the extent to which this negative effect is related to specific biological traits and evolutionary histories across species and populations have not been explored. We experimentally tested how increased temperature affects the efficacy of chemical signals of high‐ and low‐altitude populations of three lizard species that differ in their ecological requirements and altitudinal distributions. We tested the behavioral chemosensory responses of males from each species and population to male scent marks that had been incubated at one of two temperatures (cold 16°C or hot 20°C). In high‐altitude populations of a mountain species (Iberolacerta monticola), the efficacy of chemical signals (i.e., latency time and number of tongue flicks) was lower after scent marks had been exposed to a hot temperature. The temperature that scent marks were incubated at did not affect the efficacy of chemical signals in a ubiquitous species (Podarcis muralis) or another mountain species (I. bonalli). Our results suggest that specific ecological traits arising through local adaptation to restricted distributions may be important in determining species vulnerability to climatic change.     

Chemistry and toughness predict leaf litter decomposition rates over a wide spectrum of functional types and taxa in central Argentina

Litter decomposition, a major determinant of ecosystem functioning, is strongly influenced by the litter quality of different species. We aimed at (1) relating interspecific variation in leaf litter decomposition rate to the functional types different species belong to; and (2) understanding the chemical and/or physical basis for such variation and its robustness to environmental factors. We selected 52 Angiosperms from a climatic gradient in central-western Argentina, representing the widest range of functional types and habitats published so far. Ten litter samples of each species were simultaneously buried for 9 weeks during the 1996 summer in an experimental decomposition bed. Decomposition rate was defined as the percentage of dry mass loss after incubation. Chemical litter quality was measured as carbon (C) content, nitrogen (N) content, and C-to-N ratio. Since tensile strength of litter and living leaves were strongly correlated, the latter was chosen as an indicator of physical litter quality. A subset of 15 species representing different functional types was also incubated in England for 15 weeks, following a similar experimental procedure. Litter C-to-N and leaf tensile strength of the leaves showed the strongest negative associations with decomposition rate, both at the species and at the functional-type level. Decomposition rates of the same species in Argentina and in England were strongly correlated. This reinforces previous evidence that species rankings in terms of litter decomposition rates are robust to methodological and environmental factors. This paper has shown new evidence of plant control over the turnover of organic matter through litter quality, and confirms, over a broad spectrum of functional types, general models of resource allocation. The strong correlations between leaf tensile strength – a trait that is easy and quick to measure in a large number of species – decomposition rate, and C-to-N ratio indicate that leaf tensile strength can be useful in linking plant quality to decomposition patterns at the ecosystem level. This revised version was published online in August 2006 with corrections to the Cover Date.