Species distribution models (SDMs) have become a workhorse to explain, understand and predict distributions of birds. However, SDMs at broad scales are typically built using climatic variables, while ignoring the effects of biotic interactions. Although its role still remains controversial, the inclusion of biotic interactions into SDMs could confirm and/or provide new ecological insights of poorly‐known species. We modeled the distribution of the rare South American straight‐billed reedhaunter Limnoctites rectirostris (Furnariidae), a specialist of marshy areas linked to the spiny herb eryngo (Eryngium spp., Apiaceae), which provides the main food and nest resources. To do this, we first modeled the distribution of three eryngo species considered as the main biotic interactors (E. eburneum, E. horridum and E. pandanifolium) and included them into the straight‐billed reedhaunter SDM. Second, we analyzed niche overlap between the straight‐billed reedhaunter and eryngos in terms of environmental variables using dynamic range boxes, a novel approach to quantify size of n‐dimensional hypervolumes. The inclusion of biotic interactions improved model performance relative to a model with climatic variables only. Climatic suitability of E. eburneum and mean temperature of wettest quarter were the most important predictors. By contrast, E horridum and E. pandanifolium resulted in poor predictors, suggesting that the straight‐billed reedhaunter's relative dependence on each eryngo species is different. The three eryngo environmental spaces largely covered the environmental space of the straight‐billed reedhaunter, but the opposite was not true. Our findings suggest that biotic interactions play an important role in explaining and predicting the distribution of a rare bird at macro‐scales, and that the assessment of niche overlap between interactors may confirm or improve the autoecological understanding of rare and cryptic birds. We advocate the use of an integrative modeling approach including climate and biotic interactions into SDMs to enhance ecological knowledge on poorly‐known bird species.

AimsAnimals in search of fleshy fruits forage mostly according to the number of available fruits and then select individual fruits based on reward quality or advertised subtle traits. This hierarchical pattern of fruit choice would be translated into patterns of selection strength mediated by frugivores on fruit display traits. Thus, frugivores would exert higher selection pressures on fruit crop size and lower selection pressures on within-plant variation of phenotypic traits (infructescence, fruit and seed size). However, no attempt to link this behavioral mechanism of hierarchical trait selection to natural selection patterns has been made. Therefore, we sought to determine the relationship between the hierarchical decision-making process of fruit choice and patterns of natural selection on fruit traits. MethodsWe recorded bird visits and measured fruit-related traits (fruit crop size, fruit diameter and seed weight) in a natural population of Psychotria carthagenensis, a bird-dispersed treelet, in a Yungas forest from Argentina. To assess phenotypic selection patterns on fruit display traits, we performed multivariate selection analysis, and to explicitly identify a hierarchy of fruit trait choice we used a classification tree as a predictive model. Important FindingsSelection patterns on fruit display traits were in agreement with a hierarchical process of fruit choice made by birds. The strength of directional selection on the total number of fruits in a plant (i.e. fruit crop size) was nearly two times higher than on fruit size, and the classification tree analysis supported this hierarchical pattern. Our results support previous evidence that seed dispersers shape fruit crop size with higher intensity than subindividual fruit traits. Also, high levels of subindividual phenotypic variation of fruit display traits may be explained by relaxed selection pressures exerted by frugivores. Empirical studies also show that this pattern may constitute a general phenomenon among other plant-animal interactions.

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