Metapopulation Dynamics of the Mistletoe and Its Host in Savanna Areas with Different Fire Occurrence

Abstract

Mistletoes are aerial hemiparasitic plants which occupy patches of favorable habitat (host trees) surrounded by unfavorable habitat and may be possibly modeled as a metapopulation. A metapopulation is defined as a subdivided population that persists due to the balance between colonization and extinction in discrete habitat patches. Our aim was to evaluate the dynamics of the mistletoe Psittacanthus robustus and its host Vochysia thyrsoidea in three Brazilian savanna areas using a metapopulation approach. We also evaluated how the differences in terms of fire occurrence affected the dynamic of those populations (two areas burned during the study and one was fire protected). We monitored the populations at six-month intervals. P. robustus population structure and dynamics met the expected criteria for a metapopulation: i) the suitable habitats for the mistletoe occur in discrete patches; (ii) local populations went extinct during the study and (iii) colonization of previously non-occupied patches occurred. The ratio of occupied patches decreased in all areas with time. Local mistletoe populations went extinct due to two different causes: patch extinction in area with no fire and fire killing in the burned areas. In a burned area, the largest decrease of occupied patch ratios occurred due to a fire event that killed the parasites without, however, killing the host trees. The greatest mortality of V. thyrsoidea occurred in the area without fire. In this area, all the dead trees supported mistletoe individuals and no mortality was observed for parasite-free trees. Because P. robustus is a fire sensitive species and V. thyrsoidea is fire tolerant, P. robustus seems to increase host mortality, but its effect is lessened by periodic burning that reduces the parasite loads.

Mistletoe Infection in an Oak Forest Is Influenced by Competition and Host Size

“…Our finding that the probability of mistletoe infection increases with increasing tree size is in accordance with studies from other ecosystems [ 16 , 20 , 35 , 36 ]. Aukema and Martínez del Rio [ 16 ] have found that within one host species, the tallest trees were more likely to be infected because they received more mistletoe seeds than smaller trees due to a higher number of bird visits, which is also likely to be a reason for the higher probability of infection of larger trees in our study.…”

Host specificity and aggregation for a widespread mistletoe in Campo Rupestre vegetation

“…It is known to parasitize 12 host species of Vochysiaceae and two species of Melastomataceae throughout its geographic range (Monteiro et al, 1992;Teodoro et al, 2010;Scalon et al, 2013). Indeed, this species usually presents a clumped distribution on the vegetation and infects the uppermost portions of taller host trees (Teodoro et al, 2010), with the population dynamics directly affected by fire occurrence (Teodoro et al, 2013). This mistletoe is one of the most conspicuous parasitic plant in the landscapes encompassing Rupestrian Grasslands or campo rupestre (CR hereafter), the Brazilian old-growth montane fire-prone vegetation mosaics with remarkable plant diversity and endemism (Silveira et al, 2016).…”

Host specificity and experimental assessment of the early establishment of the mistletoe Phoradendron crassifolium (Pohl ex DC.) Eichler (Santalaceae) in a fragment of Atlantic Forest in southeast Brazil

“…Mistletoes may alter host growth, reproduction and physiology, decreasing its fitness (Mourão et al 2009;Bell & Adams 2011). Thin twigs (< 1 cm in diameter) often die when infected by mistletoes (Sargent 1995), as can highly infected hosts (Teodoro et al 2013).…”