Adriana Ruggiero

Latitudinal correlates of the sizes of mammalian geographical ranges in South America : Mainly Southern Hemisphere

The geographic distribution of 536 species of South American mammals was used to analyse latitudinal gradients in the north-south and east-west range of species, and to determine how they related to the width of the continent, the size of habitats, regional habitat heterogeneity, seasonality, and species richness. Taxonomic comparisons revealed differences in: (1) the adherence to Rapoports Rule (i.e. the progressive increase in the latitudinal extent of species with latitude), (2) the relationship between mean latitudinal range of species and seasonality, (3) the skewness of frequency distribution of geographical range sizes, and (4) the relationship between the size of geographical ranges and the number of species found at each latitude. However, all taxa showed that regional habitat heterogeneity is negatively correlated with the longitudinal fraction of the continent occupied by a species. Species with reduced area are clustered around the Andes and coasts, regardless of latitude. Species with the largest ranges are found north of 30°S. In spite of this, the shape of the continent does not prevent some taxa to conform to Rapoports Rule. This suggests that taxon-dependent factors (e.g. habitat-use, history legacy) could also account for empirical differences observed in the latitudinal variation of geographical ranges among distinct taxa. Thus, the utility of the Rapoport-rescue-hypothesis for understanding the latitudinal patterns in species diversity might be logically constrained. The present study leads to the prediction that some taxa might be more suitable than others when trying to test Rapoport-rescue-hypothesis

Phylogeny of Chuquiraga sect. Acanthophyllae (Asteraceae-Barnadesioideae), and the Evolution of its Leaf Morphology in Relation to Climate

Phylogenetic relationships among the 11 species and subspecies of the Andean-Patagonian Chuquiraga sect. Acanthophyllae were resolved by parsimony cladistic analysis using 22 morphological characters. The comparative method was used to test whether a reduction in leaf width occurred in species due to an adaptation to warmer desert climates. Mean values of annual precipitation, January (summer) temperature and July (winter) temperature were estimated for each taxon. Independent comparisons for leaf width and climatic variables were calculated at each node of the cladogram and a regression analysis of leaf variation versus climatic variation was performed. The probable ancestral geographic area for the group was determined using Bremers method. Results of these analyses suggest that marked involution and reduction in leaf width occurred twice independently in the evolution of the group. Reduction of leaf width was correlated with an increase in temperature. The Puna, Patagonia and the High Andes have the highest probability of having been part of the ancestral area of this section, which currently also extends to the Monte, Prepuna and Chilean Desert. This study suggests a relatively recent climatic effect on the evolution of leaf morphology.

Quality of basic data and method to identify shape affect richness–altitude relationships in meta-analysis

We compiled 109 species richness-altitude (SRA) relationships in arthropods to test the hypothesis that identification of shape and robustness of pattern are contingent on the selection of studies included in meta-analysis. We used attributes of their sampling design to distinguish three subsets of data according to stringent, intermediate, and lax selection criteria. We tested (1) whether uncertainty over identification of shape increases as the criteria of inclusion of studies relaxes and (2) whether studies that conform to stringent selection criteria show robustness in SRA patterns to variation in method used to identify shape. We identified the shape of each SRA relationship using statistical and visual methods; data sets that suggested several shapes as equally likely were sorted out by consensus. Arthropods suggested multiple forms in the SRA relationship, with predominance of hump-shaped patterns in the stringent subset. Uncertainty over identification of shape increased after application of intermediate and lax selection criteria. The method of analysis interacted with the quality of basic data to influence the relative distribution of patterns. We concluded that the gathering of large quantities of data is insufficient and that critical evaluation of literature is crucial to infer with confidence the general shape of ecological patterns in meta-analysis.

Cliffs Used as Communal Roosts by Andean Condors Protect the Birds from Weather and Predators

The quality and availability of resources influence the geographical distribution of species. Social species need safe places to rest, meet, exchange information and obtain thermoregulatory benefits, but those places may also serve other important functions that have been overlooked in research. We use a large soaring bird that roosts communally in cliffs, the Andean condor (Vultur gryphus), as a model species to elucidate whether roost locations serve as a refuge from adverse weather conditions (climatic refuge hypothesis, CRH), and/or from predators or anthropogenic disturbances (threats refuge hypothesis, TRH). The CRH predicts that communal roosts will face in the opposite direction from where storms originate, and will be located in climatically stable, low precipitation areas. The TRH predicts that communal roosts will be large, poorly accessible cliffs, located far from human-made constructions. We surveyed cliffs used as communal roosts by condors in northwestern Patagonia, and compared them with alternative non-roosting cliffs to test these predictions at local and regional scales. We conclude that communal roosting places provide refuge against climate and disturbances such as, for instance, the threats of predators (including humans). Thus, it is not only the benefits gained from being aggregated per se, but the characteristics of the place selected for roosting that may both be essential for the survival of the species. This should be considered in management and conservation plans given the current scenario of global climate change and the increase in environmental disturbances.

Richness-environment relationships in epigaeic ants across the Subantarctic-Patagonian transition zone

Abstract.  1. We analysed ant species richness‐environment relationships across the Subantartic‐Patagonian transition, in southern South America. We tested the predictions of the (i) thermal limitation hypothesis: temperature limits ant species richness, (ii) the productivity hypothesis: ant richness is driven by the indirect effect of climate (temperature and precipitation) mediated by changes in plant environment (plant cover and litter accumulation). We also evaluated the effects of (iii) plant species richness, and (iv) habitat use by cattle on richness.

Large-scale patterns in morphological diversity and species assemblages in Neotropical Triatominae (Heteroptera: Reduviidae)

We analysed the spatial variation in morphological diversity (MDiv) and species richness (SR) for 91 species of Neotropical Triatominae to determine the ecological relationships between SR and MDiv and to explore the roles that climate, productivity, environmental heterogeneity and the presence of biomes and rivers may play in the structuring of species assemblages. For each 110 km x 110 km-cell on a grid map of America, we determined the number of species (SR) and estimated the mean Gower index (MDiv) based on 12 morphological attributes. We performed bootstrapping analyses of species assemblages to identify whether those assemblages were more similar or dissimilar in their morphology than expected by chance. We applied a multi-model selection procedure and spatial explicit analyses to account for the association of diversity-environment relationships. MDiv and SR both showed a latitudinal gradient, although each peaked at different locations and were thus not strictly spatially congruent. SR decreased with temperature variability and MDiv increased with mean temperature, suggesting a predominant role for ambient energy in determining Triatominae diversity. Species that were more similar than expected by chance co-occurred near the limits of the Triatominae distribution in association with changes in environmental variables. Environmental filtering may underlie the structuring of species assemblages near their distributional limits.

Ecological Diversity in South American Mammals: Their Geographical Distribution Shows Variable Associations with Phylogenetic Diversity and Does Not Follow the Latitudinal Richness Gradient

The extent to which the latitudinal gradient in species richness may be paralleled by a similar gradient of increasing functional or phylogenetic diversity is a matter of controversy. We evaluated whether taxonomic richness (TR) is informative in terms of ecological diversity (ED, an approximation to functional diversity) and phylogenetic diversity (AvPD) using data on 531 mammal species representing South American old autochthonous (marsupials, xenarthrans), mid-Cenozoic immigrants (hystricognaths, primates) and newcomers (carnivorans, artiodactyls). If closely related species are ecologically more similar than distantly related species, AvPD will be a strong predictor of ED; however, lower ED than predicted from AvPD may be due to species retaining most of their ancestral characters, suggesting niche conservatism. This pattern could occur in tropical rainforests for taxa of tropical affinity (old autochthonous and mid-Cenozoic immigrants) and in open and arid habitats for newcomers. In contrast, higher ED than expected from AvPD could occur, possibly in association with niche evolution, in arid and open habitats for taxa of tropical affinity and in forested habitats for newcomers. We found that TR was a poor predictor of ED and AvPD. After controlling for TR, there was considerable variability in the extent to which AvPD accounted for ED. Taxa of tropical affinity did not support the prediction of ED deficit within tropical rainforests, rather, they showed a mosaic of regions with an excess of ED interspersed with zones of ED deficit within the tropics; newcomers showed ED deficit in arid and open regions. Some taxa of tropical affinity showed excess of ED in tropical desert areas (hystricognaths) or temperate semideserts (xenarthrans); newcomers showed excess of ED at cold-temperate latitudes in the Northern Hemisphere. This result suggests that extreme climatic conditions at both temperate and tropical latitudes may have promoted niche evolution in mammals.

Altitudinal variation in the taxonomic composition of ground‐dwelling beetle assemblages in NW Patagonia, Argentina: environmental correlates at regional and local scales

Abstract.  1. Altitudinal gradients offer a unique scenario to elucidate how the increase in harsh climatic conditions towards the top of the mountain interacts with other environmental factors at regional and local scale to influence the spatial variation in local species composition and biodiversity maintenance. We analysed the altitudinal variation in the taxonomic composition of epigaeic beetle assemblages across five mountains in north‐western Patagonia (Argentina) to address whether substantial change in species composition was associated (i) at regional spatial scale, with changes in vegetation types, and the presence of dry and moist mountains, and (ii) at local spatial scale, with variation in temperature, plant cover and richness and several soil characteristics.

The latitudinal diversity gradient in South American mammals revisited using a regional analysis approach: The importance of climate at extra-tropical latitudes and history towards the tropics

The latitudinal diversity gradient has been considered a consequence of a shift in the impact of abiotic and biotic factors that limit species distributions from the poles to the equator, thus influencing species richness variation. It has also been considered the outcome of evolutionary processes that vary over geographical space. We used six South American mammal groups to test the association of environmental and evolutionary factors and the ecological structuring of mammal assemblages with spatial variation in taxonomic richness (TR), at a spatial resolution of 110 km x 110 km, at tropical and extra-tropical latitudes. Based on attributes that represent what mammal species do in ecosystems, we estimated ecological diversity (ED) as a mean pairwise ecological distance between all co-occurring taxa. The mean pairwise phylogenetic distance between all co-occurring taxa (AvPD) was used as an estimation of phylogenetic diversity. Geographically Weighted Regression analyses performed separately for each mammal group identified tropical and extra-tropical high R2 areas where environmental and evolutionary factors strongly accounted for richness variation. Temperature was the most important predictor of TR in high R2 areas outside the tropics, as was AvPD within the tropics. The proportion of TR variation accounted for by environment (either independently or combined with AvPD) was higher in tropical areas of high richness and low ecological diversity than in tropical areas of high richness and high ecological diversity. In conclusion, we confirmed a shift in the impact of environmental factors, mainly temperature, that best account for mammal richness variation in extra-tropical regions, whereas phylogenetic diversity best accounts for richness variation within the tropics. Environment in combination with evolutionary history explained the coexistence of a high number of ecologically similar species within the tropics. Consideration of the influence of contemporary environmental variables and evolutionary history is crucial to understanding of the latitudinal diversity gradient.