Pedro G. Blendinger

Putting plant resistance traits on the map: a test of the idea that plants are better defended at lower latitudes

• It has long been believed that plant species from the tropics have higher levels of traits associated with resistance to herbivores than do species from higher latitudes. A meta-analysis recently showed that the published literature does not support this theory. However, the idea has never been tested using data gathered with consistent methods from a wide range of latitudes. • We quantified the relationship between latitude and a broad range of chemical and physical traits across 301 species from 75 sites world-wide. • Six putative resistance traits, including tannins, the concentration of lipids (an indicator of oils, waxes and resins), and leaf toughness were greater in high-latitude species. Six traits, including cyanide production and the presence of spines, were unrelated to latitude. Only ash content (an indicator of inorganic substances such as calcium oxalates and phytoliths) and the properties of species with delayed greening were higher in the tropics. • Our results do not support the hypothesis that tropical plants have higher levels of resistance traits than do plants from higher latitudes. If anything, plants have higher resistance toward the poles. The greater resistance traits of high-latitude species might be explained by the greater cost of losing a given amount of leaf tissue in low-productivity environments.

Fine‐tuning the fruit‐tracking hypothesis: spatiotemporal links between fruit availability and fruit consumption by birds in Andean mountain forests

1. The fruit-tracking hypothesis predicts spatiotemporal links between changes in the abundance of fruit-eating birds and the abundance of their fleshy-fruit resources. 2. While the spatial scale of plant-frugivore interactions has been explored to understand mismatches between observed and expected fruit-frugivore patterns, methodological issues such as the consequences of measuring fruit and frugivore abundance rather than fruit availability and fruit consumption have not been evaluated. 3. Here, we explored whether predicted fruit-frugivore spatiotemporal links can be captured with higher accuracy by proximate measurements of interaction strength. We used a 6-ha grided plot in an Andean subtropical forest to study the link between (i) fruit and fruit-eating bird abundances; (ii) fruit availability and frequency of fruit consumption; and (iii) covariation between frugivore abundance and frequency of frugivory. We evaluated these links for the entire frugivore assemblage and for the four most important species using data gathered bimonthly along a 2-year period. 4. Fleshy-fruit availability and abundance varied sharply temporally and were patchily distributed in mosaics that differed in fruit quantity. Fruit availability and abundance also varied along spatial gradients extended over the whole study plot. We found a strong response of the entire frugivorous bird assemblage to fruit availability over time, and a weakly significant relationship over space at the local scale. The main frugivore species widely differed in their responses to changes in fruit abundance in such a way that response at the assemblage level cannot be seen as the sum of individual responses of each species. Our results suggest that fruit tracking in frugivorous-insectivorous birds may be largely explained by species-specific responses to changes in the availability of fruits and alternative resources. 5. In agreement with our prediction, more accurate measurements of interaction strength described fruit-frugivore relationships better than traditional measurements. Moreover, we show that covariation between frugivore abundance, frequency of fruit consumption and fruit availability must be included in the fruit-tracking hypothesis framework to demonstrate (or reject) spatiotemporal fruit tracking. We propose that estimation of nutrient and energy availability in fruits could be a new frontier to understanding the forces driving foraging decisions that lead to fruit tracking.

Land-use and land-cover effects on regional biodiversity distribution in a subtropical dry forest: a hierarchical integrative multi-taxa study

Abstract Latin American subtropical dry ecosystems have experienced significant human impact for more than a century, mainly in the form of extensive livestock grazing, forest products extraction, and agriculture expansion. We assessed the regional-scale effect of land use and land cover (LULC) on patterns of richness distribution of trees, birds, amphibians, and mammals in the Northern Argentine Dry Chaco (NADC) over c. 19 million hectares. Using species distribution models in a hierarchical framework, we modeled the distributions of 138 species. First, we trained the models for the entire Argentinean Chaco with climatic and topographic variables. Second, we modeled the same species for the NADC including the biophysical variables identified as relevant in the first step plus four LULC-related variables: woody biomass, distance to crops, density of livestock-based rural settlements (puestos), and vegetation cover. Third, we constructed species richness maps by adding the models of individual species and considering two situations, with and without LULC variables. Four, richness maps were used for assessing differences when LULC variables are added and for determining the main drivers of current patterns of species richness. We found a marked decrease in species richness of the four groups as a consequence of inclusion of LULC variables in distribution models. The main factors associated with current richness distribution patterns (both negatively) were woody biomass and density of livestock puestos. Species richness in present-day Semiarid Chaco landscapes is strongly affected by LULC patterns, even in areas not transformed to agriculture. Regional-scale biodiversity planning should consider open habitats such as grasslands and savannas in addition to woodlands.

Facilitation of sap-feeding birds by the white-fronted woodpecker in the Monte Desert, Argentina

In the Monte desert of South America, the overall supply of water and food for birds decreases in the dry, cold season (June through September). During this period the White-fronted Woodpecker (Melanerpes cactorum) drills holes in the trunks and branches of Prosopis flexuosa and feeds on the exuded sap. Other bird species, diverse in ecological attributes and taxonomic affinities, take advantage of this resource which otherwise would be rarely available. Sap is a major constituent of the diet of the White-fronted Woodpecker and 11 other bird species, and sap feeding comprises between 16% to 83% of foraging observations made during June and July. Aggression by White-fronted Woodpeckers significantly reduced the time smaller bird species spent fecding on sap, indicating that White-fronted Woodpeckers actively compete for this resource. Other bird species profit from having access to a resource rich in water and sugar.

Effect of habitat and landscape structure on waterbird abundance in wetlands of central Argentina

Determining the response of birds to local habitat characteristics and landscape structure is essential to understanding habitat selection and its consequences for the distribution of species. This study identified the influence of environmental factors as determinants of the waterbird assemblage composition in 39 wetlands in the Pampas of central Argentina. Multivariate analysis allowed the identification of environmental factors affecting the use of habitat by waterbird species, whose variable numbers were explained by local and landscape environmental factors. Interspecific variation in responses to changes in environmental factors shows that habitat selection occurs at a species-specific level, although species with similar ecological requirements tend to respond similarly to environmental heterogeneity. Plovers and flamingos were mostly associated with high salinity and the presence of a muddy shoreline and temporary ponds; ducks, herons and ibises were associated with vegetation abundance and decrease in salinity; piscivores and carnivorous species were associated with water depth. The small degree of overlap of habitat requirements between some species suggests a high level of specialization within waterbird assemblages. This knowledge can be used for the design of appropriate conservation and management strategies in central Argentina, where the alarming loss of wetlands requires management strategies that ensure the permanence of the greatest diversity of waterbirds.

Foraging behaviour of birds in an arid sand-dune scrubland in Argentina

Abstract Studies of the foraging behaviour of birds allow exploration of the mechanisms that structure species assemblages. The major objective of this study was to describe relationships among various components of foraging behaviour and whether changes in those relationships reflected seasonal changes in assemblage structure of birds from an arid scrubland of the Monte Desert, Argentina. Foraging behaviour was described in terms of attack manoeuvres, food substrate (i.e. substrate from which food was taken), foraging site (i.e. the substrate and height from where birds launched the attack), and plant species used. Between-species differences in attack manoeuvres, food substrate and foraging site were interrelated, the association being strongest between foraging sites and food substrates. During the non-breeding season, foraging sites and food substrates differentiated species. The most important changes between seasons were related to the arrival in summer of aerial-foraging tyrant flycatchers, a functional group absent during the non-breeding season. Foraging sites explained most of the differences among species groups, suggesting that habitat heterogeneity and structural complexity of vegetation are important environmental variables that determine the avian assemblage structure. Moreover, temporal changes in food availability, mediated by strong seasonality in climate, were important factors that were correlated with compositional and structural variability in functional groups of birds (i.e. granivores-insectivores, surface insectivores and aerial insectivores).

Frugivory and seed dispersal role of the Yellow-striped Brush-Finch (Atlapetes citrinellus), an endemic emberizid of Argentina

Abstract The stability and dynamics of multispecies interactions often rely on a small core of species. We examine whether the Yellow-striped Brush-Finch (Atlapetes citrinellus), the only species of bird endemic to the Argentinean Yungas, is a core species for seed dispersal. Of 30 species of fleshy fruit consumed, 16 were dispersed through endozoochory. The Yellow-striped Brush-Finch mostly used the ‘cut or mash’ method of handling fruit, in which reasonably large seeds (>0.04 g) were discarded or swallowed equally. Medium-sized and small seeds were more often swallowed than discarded. Although the fruits consumed were mostly understorey species, there was no difference in the consumption of fruit from forest understorey or canopy when total fruit abundance in vertical strata was considered. By using interaction network metrics, we determined that the role of Yellow-striped Brush-Finches in seed dispersal during the rainy season was more important at higher altitudes and in the southern sector of its distribution. Our findings support the idea that the Yellow-striped Brush-Finch must be considered a core seed-disperser of understorey and canopy fruits. Use of network metrics is an effective way to assess the importance of individual species in a network, allowing restoration and conservation efforts to be focussed on environments in which these species occur.

Spatial analysis of sap consumption by birds in the Chaco dry forests from Argentina

Abstract Sap is a resource of high energy content that is usually inaccessible to birds, although woodpeckers have the ability to drill into living trees to obtain sap. Because spatial patterns of resource availability influence avian abundance, we explored how spatial patterns of sap availability determine the spatial distribution of two sap-feeding species in the semiarid Chaco of Argentina. We studied the White-fronted Woodpecker (Melanerpes cactorum), which obtains sap by drilling holes into tree trunks, and the Glittering-bellied Emerald (Chlorostilbon aureoventris), which can obtain sap only from active woodpecker holes; 12 other bird species also exploited the sap flows from holes drilled by White-fronted Woodpeckers. The abundance of tree species used for sap feeding did not explain the spatial patterns of territorial groups of White-fronted Woodpeckers. However, within each territory, the abundance of Woodpeckers was centred on a single tree from which sap was obtained. The abundance of the Emeralds was strongly associated with the availability of trees with active sap-holes. During the dry season, sap is a major component in the diet of White-fronted Woodpeckers and Glittering-bellied Emeralds. However, the spatial distribution of these two consumers in relation to the availability of sap was species-specific. This species-specific response was closely related to the ecology and life history of each species. The abundance of woodpeckers could be determined by local mechanisms, such as location of a single sap tree in their small territories, whereas non-territorial hummingbirds would be able to track sap wells at a larger scale than the territory of a single territorial group of Woodpeckers. Our results show the importance of spatial analysis in identifying the ecological determinant of habitat selection and niche differentiation within species.

The role of trait combination in the conspicuousness of fruit display among bird‐dispersed plants

Summary In visually-driven seed dispersal mutualisms, natural selection should promote plant strategies that maximize fruit visibility to dispersers. Plants might increase seed dispersal profitability by increasing conspicuousness of fruit display, understood as a plant strategy to maximize fruit detectability by seed dispersers. The role of different plant traits in fruit choice and consumption by seed dispersers has been broadly studied. However, there is no clear evidence about the importance of the traits that increase conspicuousness of fruit display. Because strategies to maximize conspicuousness of fruit display are diverse, and usually are expected to be costly, we would expect that individual plant species will produce an efficient combination of traits. We explored this prediction with 62 fleshy-fruited plant species of a subtropical Andean forest (Southern Yungas), and using a large dataset of fruit consumption by birds (4,476 records). Conspicuousness of fruit display was characterized by both fruit and plant traits including chromatic contrast, size, exposure, aggregation, and crop size of fruits. We also considered phylogenetic effects on phenotypic variation. Fruit consumption was explained by fruit chromatic contrast depending on fruit crop size. These traits revealed low phylogenetic effects, with the exception of four plant clades at different levels in the phylogenetic tree. Negative correlations between pairs of traits support our assumption that fruit display traits are costly, suggesting natural selection favours parsimonious evolutionary pathways. Plant species seem to rely on conspicuousness of fruit display by a combination of traits that might minimize costs of fruit display. This appears adaptively relevant to improve communication with mutualistic animals, to increase fruit consumption in a community context and, ultimately, to enhance the profitability of seed dispersal. This article is protected by copyright. All rights reserved.

Trophic ecology of the Ringed Warbling-Finch (Poospiza torquata) in Neotropical semi- arid scrublands

Abstract Seed-eating birds in temperate deserts must cope with great variation in the availability of their food resources. We studied the trophic ecology of Ringed Warbling-Finches (Poospiza torquata) in semi-arid scrublands of the Monte Desert, Argentina. We assessed seasonality in the availability of seed and in the consumption of arthropods and seeds at a regional scale, and evaluated the composition of the granivorous component of the diet and the seed dietary breadth. Ringed Warbling-Finches had a granivorous-insectivorous diet consisting largely of arthropods in summer and seeds and arthropods in winter. The granivorous component of the diet consisted mainly of grass seeds, but with low breadth of the winter seed diet. To deal with seasonal variation in the availability of food resources, Ringed Warbling-Finches switched opportunistically between different resources, exploiting alternating seasonal patterns of food abundance. This seasonal switching is a well-established strategy in the behaviour of the species and was observed in all Ringed Warbling-Finch populations studied across the Monte Desert. Our results show the flexibility of foraging strategies of Ringed Warbling-Finches, an opportunist species that adjusts their relative consumption of seeds and arthropods in response to the spatial and temporal variations in these food resources.