Delineating limits: Confronting predicted climatic suitability to field performance in mistletoe populations

Abstract

1. Biotic stressors such as hemiparasites have a profound impact on forest functioning. However, predicting the future incidence of these stressors on forests remains challenging because climate-based distribution does not consider tree-hemiparasite interactions or the impacts of extreme climate events on stressors' performance.2. We use species distribution models (SDMs) and ecophysiological and demographic field data to assess whether climatic suitability is a proxy for the performance of the hemiparasite mistletoe (Viscum album) in two forests with contrasting climatic conditions. Two host tree species representing wet-cold (Scots pine) and drywarm (Aleppo pine) conditions were selected. We fitted SDMs based on climate variables, and measured different ecophysiological variables capturing cold-(photoinhibition) and drought tolerance (intrinsic water-use efficiency, iWUE). We also assessed demographic variables related to seed germination and establishment rates of mistletoe through a translocation experiment.3. Species distribution models showed a high climatic suitability of mistletoe in both forests. Mistletoes living in the Scots pines site presented a higher cold tolerance, while those inhabiting the Aleppo pine site showed a higher iWUE. Seedlings coming from local seeds showed a lower mortality than seedlings coming from translocated seeds. Germination and seedling establishment showed temporal mismatches when comparing local and translocated seeds. 4. Synthesis. Habitat suitability predicted by SDMs based on climate data and field performance were related in this mistletoe species. However, ecophysiological and demographic variables indicated a lower fitness of mistletoe in the drywarm site associated with drought stress. In conclusion, predicted climate suitability based on SDMs forecasts should be refined using field data on actual performance and considering plant-to-plant interactions and extreme climate events. K E Y W O R D S cold tolerance, establishment, germination, hemiparasitic plant, Species Distribution Models, Viscum album, water-use efficiency | 2219 Journal of Ecology SANGÜESA-BARREDA Et Al.

Association of putatively adaptive genetic variation with climatic variables differs between a parasite and its host

“…While these patterns of genome‐wide variation are consistent with local adaptation, further validation of the role of temperature is needed. Experimental work in other host–parasite systems have found temperature to influence local adaptation (Laine, 2007 , 2008 ) and the performance of mistletoe populations (Sangüesa‐Barreda et al, 2018 ).…”

Individual fitness is decoupled from coarse‐scale probability of occurrence in North American trees

“…The fitness-centre hypothesis has been detected for certain species in previous studies (Nagaraju et al 2013, Wittmann et al 2016, Sangüesa-Barreda et al 2018, Mammola et al 2019 but not in others (Larson et al 2010, Barela et al 2020, Chardon et al 2020. However, these studies show three main methodological limitations (which we will discuss in detail below).…”

“…Previous studies using SDMs to address the fitness-centre hypothesis used various functional traits as surrogates of individual fitness in both animals (Larson et al 2010, Pellissier et al 2013, Wittmann et al 2016, Mammola et al 2019, Barela et al 2020) and plants (Elmendorf and Moore 2008, Thuiller et al 2010, Sangüesa-Barreda et al 2018, Chardon et al 2020) and overall reported heterogeneous results. These studies generally tested the hypothesis on single species (but see Thuiller et al 2010) or normally used few observations of trait data collected in the field (but see Chardon et al 2020), possibly due to the rarity of the species under consideration (Mammola et al 2019) or because sampling functional traits at the intraspecific level over large areas is time-consuming and expensive.…”

Ecological consequences of parasite host shifts under changing environments: More than a change of partner

“…In either case, parasitism can determine the dominance of the plant community over the long term, introducing fundamental changes in the configuration of the future forest. Growing evidence points to altitudinal and latitudinal distributional changes of V. album across other European regions (Dobbertin et al, ; Sangüesa‐Barreda et al, ; Varga et al, ). In this context, it would be useful to detect whether host switching is occurring and to identify the ecological consequences that this change in host might have.…”