Dominant network interactions are not correlated with resource availability: a case study using mistletoe host interactions

Abstract

Network theory in ecology has been central to understanding species co‐occurrence patterns, specialization and community stability. However, network theory has traditionally focused on the ‘higher’ trophic level where exploitation of network ‘partners’ (i.e. individual interactions in response to resource availability) have remained underappreciated. In this study we tested how clumping and host availability influenced mistletoe–host interactions in a semi‐arid woodland, central Australia. We used a hierarchical approach that evaluated individual interactions by modifying the traditional randomization technique to simulate clumping and host exploitation. Using published literature we then compared our results with mistletoes from other genera. We found that mistletoes clump on fewer trees than predicted, even though interaction strength was no different from random expectations, and we found no evidence that common trees were heavily infected as predicted by the host availability hypothesis. The rate of host exploitation (measured as the proportion of trees infected) in semi‐arid Australia is similar to that for mistletoe genera in other parts of the world. We hypothesize that specific host trees act as a focal point for infection that facilitates the spread and overall population size of mistletoes. Overall our results indicate that resources, such as the number of trees in a mistletoe network, are less important than clumping of individual plants. We suggest that exploitation of available resources may play a similar role in other networks that extend beyond antagonistic relationships such as parasite or herbivore interactions.

Can UAV-Based Infrared Thermography Be Used to Study Plant-Parasite Interactions between Mistletoe and Eucalypt Trees?

“…The observation that bigger trees typically have a higher chance of becoming infected and are more severely infected agrees with observations in other studies [69,70]. The fact that the distribution of mistletoe within the sampled area is clumped is in agreement with other studies [59,66,70]. It is likely that at a larger scale (ha-level), mistletoe distribution is also not evenly distributed across the woodland, as Renchon et al [54] mentioned mistletoe infection in this woodland was most severe in the vicinity of the tower.…”

“…Although the infection in the majority of trees was not severe (classes 1 or 2), 69% of the E. fibrosa and 75% of the E. moluccana were infected, and this increased to nearly 100% for the biggest trees ( Figure 5). This is clearly higher than reported infection rates for other eucalypt forests in Australia [58][59][60][61][62] or for mistletoe infections outside Australia [50,[63][64][65][66]. The reason for this high infection rate cannot be identified from this study, as it is often a complex interaction of environmental factors [62,67], as well as consequence of forest management, fire regimes and natural growth cycles of mistletoe [60,68].…”

Communities and Attachment Networks Associated with Primary, Secondary and Alternative Foundation Species; A Case Study of Stressed and Disturbed Stands of Southern Bull Kelp

“…Most network analyses in ecology have focused on trophic species interactions [20] or mutualistic pollination and seed dispersal webs in terrestrial systems [21], and with marine examples for fish, sea anemones and shrimps [22][23][24][25]. Many studies have also analysed bipartite attachment networks between trees and epiphytes [26][27][28][29][30][31][32][33][34]. Similar host-epiphyte interactions are prevalent in marine ecosystems [9,13,14,35], but we are not aware of studies that have analysed these attachment-interactions with community-wide network metrics.…”

Species importance in a heterospecific foraging association network

“…While the network approach has largely been restricted to trophic interactions such as food webs and plant‐animal mutualisms (Ings et al 2008; although mutualistic networks also include indirect non‐trophic inter actions, e.g. pollinators linked through a shared host‐plant) and host–parasite interactions (Blick et al 2012), emphasis has been placed on incorporating direct non‐trophic inter actions (Kéfi et al 2012, Pocock et al 2012) in order to gain a more complete picture of community organization. A first step towards this is building and understanding direct non‐trophic interaction networks.…”