Disentangling biotic and abiotic drivers of a neotropical mistletoe

Parasitic plants known as mistletoes are a key resource in ecosystems and form intricate networks of biotic interactions. Several mistletoe species exhibit specific associations with particular hosts and dispersers, such as Psittacanthus robustus, which is distributed across South America. Here, we assessed the climatic niche similarity between P. robustus, its host trees, and seed dispersers, and identified the main factors influencing the parasite's occurrence. We analyzed the spatial overlap among P. robustus, hosts, and seed dispersers using niche equivalence and similarity tests and assessed the importance of predictors through machine-learning classification. We detected higher climatic niche similarity between P. robustus and its host trees, while niche equivalence was absent in all comparisons. The spatial distribution of P. robustus was primarily shaped by the presence of host trees rather than climatic conditions or seed dispersers. These results highlight the impact of host trees on the spatial distribution of P. robustus, serving as ecological filters that influence mistletoe occurrence. The secondary role of climate and dispersers likely arises from interacting processes such as climatic predictability, mistletoe reproductive phenology, host vulnerability, and the asymmetric dependence of mutualist animals on mistletoe resources.