Mistletoe macroecology: spatial patterns in species diversity and host use across Australia

Abstract

Mistletoes are parasitic plants, the spatial distributions of which are poorly understood on macroecological scales. Because of their highly unusual life history, investigating mistletoe macroecology may provide new insight into broad‐scale patterns in species distributions. We collated data on the spatial distribution and host use of 65 species of Loranthaceous mistletoes across the continent of Australia, and tested two predictions. First, we predicted mistletoe diversity would be unrelated to productivity (i.e. evapotranspiration and precipitation), as the parasitic lifestyle might relax environmental constraints on their distributions. Second, we predicted that mistletoe host ranges (number of infected host species) would increase in areas with more potential host species. The basis of this prediction is that greater host generality is likely to evolve in regions with greater host diversity because of greater unpredictability in encounter rates with particular host species. Conversely, in regions with fewer potential hosts, randomly dispersing mistletoe propagules are likely to repeatedly encounter particular host species, thus favouring the evolution of host specialization. The results were generally consistent with these predictions. Mistletoe diversity across Australia was weakly associated with environmental conditions, whereas mistletoe host ranges increased significantly with total plant diversity. Macroecological patterns in mistletoes are unusual. In contrast to non‐parasitic plants, mistletoe diversity is poorly correlated with productivity. Host ranges varied predictably across Australia, providing the first quantitative support for the hypothesis that mistletoes in diverse regions tend to be host generalists, whereas mistletoes in depauperate regions tend to be host specialists. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 459–468.

Range‐wide ecological niche comparisons of parasite, hosts and dispersers in a vector‐borne plant parasite system

“…In a study of spatial distribution and host use across 65 mistletoe species in Australia, Kavanagh & Burns () found diversity to be unrelated to productivity, but that host ranges (i.e. number of infected host species) were broader in areas with more potential host species.…”

“…Although most studies have focused at local scales, some recent studies have examined influences of factors at multiple spatial scales (e.g. Rist et al ., ; Kavanagh & Burns, ; Lira‐Noriega et al ., ). Nonetheless, variation in host quality and specificity (Watson, ) and the effectiveness of seed dispersal by different vectors (Montaño‐Centellas, ) remain important factors.…”

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

“…Historical fire regimes has been an important factor to determinate the distribution and abundance of North American mistletoe, while effective suppression of wildfires has contributed to an increase the abundance of mistletoe population in these forests in North America [9]. In Australia, changes in fire regimes are affecting spatial patterns of mistletoe diversity and abundance [10]. In Brazilian savannas, Fadini & Lima (2102) showed that the fire effects on the population vary with the mistletoe species, even for sympatric ones [8].…”

Host specificity in parasitic plants—perspectives from mistletoes

“…The generalist mistletoes may encounter host species that vary in compatibility at different locality, thus may parasitize a subset of available host species at a given locality. This process could drive mistletoe specialization by selecting for host-specific adaptation at a local level (Norton and Carpenter 1998; Norton and de Lange 1999; Amico et al 2007; Blick et al 2012; Kavanagh and Burns 2012). …”

“…Mistletoes that are initially capable of utilizing several host species may also become restricted to a subset of available hosts within an area (Barlow and Wiens 1977; Amico et al 2007; Okubamichael et al 2011 a ; Kavanagh and Burns 2012, Lira-Noriega et al 2015; Lira-Noriega and Peterson 2014). Generalist mistletoe species are therefore often composed of distinct host-specific populations (e.g.…”