Frugivorous Bird Guild Seasonal Patterns in Semiarid Chaco Forests are Linked to Habitat Seasonality but Reveal Phylogenetic Signature

DIANA E. MARCO; SERGIO A. PÁEZ; BOAGLIO, GABRIEL

Journal of Scientific Research & Reports

Luigi Rodino, Professor of Mathematical Analysis, Dipartimento di Matematica, Università di Torino, Italy.

Año: 2015

Aims: This work aims to explain seasonal changes in frugivorous bird species richness,abundance and diversity, addressing climatic and habitat variables (rainfall, PhotosyntheticallyActive Radiation as PPDF) and species´ trait factors (diet), while considering the effect ofphylogenetic constraints.Place and Duration of Study: Forest Reserve of Chancaní, Córdoba Province, Argentina (31 2´ Sand 65 25´ W), during 1995-1996.Methodology: In the study area two randomly located sampling points separated each other bytwo km were established. Phenological records for seven forest plant species producing fruits weretaken monthly, along with habitat and climatic variables (PPDF, rainfall). Bird sampling was donemonthly. Fourteen transects, each of 50 m long were permanently marked from randomly locatedpoints in N-S direction. While slowly walking along each transect, all bird sightings as well ashearings both to right and left sides were recorded. The bird species and the vegetation stratumwhere the sighting occurred were also recorded.Statistical Analysis: For all the bird species and for frugivorous species, bird species richness (S),species abundance as sightings, diversity (Shannon Index H´) and evenness (H´/lnS) werecalculated for each sampling date. Friedman test was used to test differences in species richnessand sightings among dates. For frugivorous bird data analysis, two approaches were used, onewith the species values taken as independent data points, and the other removing phylogeneticeffects by means of the analysis of independent contrasts. Categorical Principal ComponentAnalysis (CATPCA) was used to explore the relationships among species dates of sightinginitiation, duration of the sighting period and abundances at peak dates, using species values andindependent contrasts. CATPCA (with species values) was also used to explore the relationshipsamong frugivorous bird species richness, abundance and diversity, and climatic (rainfall) andhabitat (PPDF and fruit abundance) variables.Results: A total of 67 species were recorded during the sampling period. Richness rose in spring,peaked during summer and then declined smoothly to winter. In contrast, abundance maintainedfluctuating values during the sampling period, with a small peak in autumn. There were nosignificant differences in vegetation strata occupancy by different species of birds, although somegroups showed a degree of preference.Considering frugivorous birds, a total of 29 frugivorous species were recorded during the samplingperiod. The temporal trend of species richness and diversity was similar to the pattern showed byall the species, although abundance showed a bimodal trend. CATPCA using species values andindependent contrasts showed common overall results for the variables initiation and maximum offrugivorous species abundance, that were inversely or not correlated with duration of sightings,maximum abundance and total abundance along the sampling period. However, the behaviour ofthe variable Diet changed when independent contrasts were used. From a closer relationship withsighting initiation and peak and a greater importance with species values data, Diet showed a moredistant relationship with these sightings variables and a negligible value when independentcontrasts were used. Besides, using independent contrasts many species were differently relatedwith the variables and the dispersion of the species was greater in the ordination space.Regarding climatic and habitat variables, rainfall and PPDF showed an overall similar seasonalpattern, although PPFD began rising earlier during the dry season. Rainfall and PPDF weretemporally correlated. Fruits began appearing in spring, peaked during this season, and thendecreased sharply to disappear during winter. Fruit abundance was highly correlated with PPFDbut not with rainfall. CATPCA of climatic, habitat, and frugivorous bird variables (richness,abundance and diversity) separated spring, summer and autumn sampling dates from the lastautumn date and winter dates. PPDF and fruit abundance explained most of the variance in birdrichness and diversity but not in abundance. Rainfall did not explain the behaviour of any birdvariable.Conclusion: We conclude that habitat characteristics, mainly PPFD and fruit abundance, areshaping the seasonal species composition (richness and diversity), although not abundance, offrugivorous bird assemblages in semiarid Chaco forests. The importance of the frugivorous dietdiversification, as a species´ trait factor that could be contributing to shape the seasonalarrangement of frugivorous birds, was secondary and mainly related to the timing of appearance inthe favourable season. However, even this modest contribution of diet diminished when thephylogeny were taken into account, showing a strong phylogenetic signal.