Testing the keystone plant resource role of a flagship subtropical tree species (Araucaria angustifolia) in the Brazilian Atlantic Forest

Ecological attributes enable the identification of Keystone Plant Resources (KPRs), including their community-wide contribution to vertebrate consumers, which are often highly threatened in terrestrial ecosystems. KPRs have been defined by intersecting four ecological attributes that influence local communities of vertebrate frugivores: temporal redundancy (TR); degree of consumer specificity (CS); reliability (RR); and resource abundance (RA). The conifer Araucaria angustifolia (Bert.) O. Kuntze (Araucaria) is the main arborescent component of Araucaria Forests, within the subtropical Atlantic Forest of South America. The large Araucaria seeds (pinhão) are heavily consumed by local faunas, and consequently could be automatically defined as a KPR. However, no previous studies have conceptually assessed the pinhão as a KPR based on their ecological attributes and trophic interactions with vertebrates. Using empirical data and a comprehensive literature review, we examine the degree to which Araucaria trees can be formally defined as a KPR within the subtropical Atlantic Forest. Our results show for the first time that Araucaria is a KPR according to both its ecological attributes and community-wide importance. Araucaria cones exhibited low temporal redundancy, low consumer specificity, high resource reliability and high resource abundance, structuring the associated vertebrate consumers spatiotemporally. Our insights contribute to understanding the implications of historical Araucaria population declines through logging and deforestation, as well as ongoing vertebrate defaunation. Both of these processes can lead to changes in baseline ecological process (e.g. seed dispersal versus seed predation), forest regeneration, community reassembly, and potential evolutionary consequences such as seed downsizing.