Study Area and Natural History
The study was conducted in Nahuel Huapi National Park and Llao Llao
Municipal Reserve in northwestern Patagonia, Argentina. The climate in
this region has a dry season in spring-summer and a humid season in
autumn-winter, with 1800 mm of average annual precipitation and 9°C of
average annual temperature. The forest is dominated by the evergreen
southern beech (Nothofagus dombeyi) and cordilleran cypress
(Austrocedrus chilensis ), with an understory layer dominated by
the shrub Aristotelia chilensis and bamboo Chusquea culeou(Mermoz & Martín 1986). Currently the non-native ungulates red deer
(Cervus elaphus ), dama deer (Dama dama ), and domestic
cattle (Bos taurus ) are the most abundant ungulates in these
forests (Jaksic 1998; Jaksic et al. 2002; Merino et al.2009) and occupy 56% of the area of Nahuel Huapi National Park
(Lauría-Sorge & Romero 1999).
In this study we took advantage of the contagious distribution of the
mistletoe populations (García et al. 2009) that allows us to
compare sites with high and low mistletoe density. We selected six 1-ha
native forest sites, separated by more than 2 km. Four sites were
located in intact forest lacking introduced ungulates: two sites with
high density of mistletoes (>400 reproductive individuals
per hectare) and the presence of A. chilensis , and two sites with
low density of mistletoes (<20 reproductive individuals per
hectare) and the presence of A. chilensis . Two additional sites
were located in forests that have been invaded by non-native ungulates.
We considered invaded sites those with records of non-native ungulates
over the last 100 years. Due to the herbivory pressure by non-native
ungulates, the abundance of the mistletoe and its host A.
chilensis is low and the hummingbird-mistletoe-marsupial interaction is
ecologically extinct (Rodriguez-Cabal et al. 2013). Each site was
chosen haphazardly from a pool of possible sites. Fieldwork and data
collection were carried out during two consecutive austral springs and
summers (2017-2018 and 2018-2019).