Ecological disequilibrium drives insect pest and pathogen accumulation in non-native trees

Abstract

Non-native plant invasions represent ecological disequilibrium situations, that is, the immediate breakdown of historically co-evolved interactions once introduced into novel environments. Globalization has led to increased transfer in organisms between countries. Native enemies also undergo host expansions onto non-native plants. Ecological disequilibrium conditions can thus be expected to change unpredictably over time. By retrospectively analysing the insect pest and pathogen accumulation on established non-native trees in South Africa, we review the eco-evolutionary background that may help to explain and predict variation in ecological disequilibrium conditions in non-native trees.

Mycorrhizae, invasions, and the temporal dynamics of mutualism disruption

“…; Flory & Clay ; Crous et al . ). Depending on these alternative ecological and evolutionary scenarios, we would expect a relationship between invasion age and the impacts of allelopathy – but how this relationship changes depends on which mechanism predominates.…”

“…Lankau et al (2009) found that older populations of A. petiolata had evolved reduced production of glucosinolates, presumably due to a switch from interspecific to intraspecific plant competition. On the other hand, pressure from pathogens and herbivores could cause allelochemical production to increase over invasion age, where newer invasions may have reduced investment in defense compounds because of enemy release in their introduced range (Blossey & Notzold 1995), and older invasions may produce more defensive compounds because of accumulating pathogens and herbivores (Mitchell et al 2010;Flory & Clay 2013;Crous et al 2017). Depending on these alternative ecological and evolutionary scenarios, we would expect a relationship between invasion age and the impacts of allelopathybut how this relationship changes depends on which mechanism predominates.…”

Biotic Interactions as Mediators of Biological Invasions: Insights from South Africa

“…For widely established invasive plants, for example, interactions with resident and native herbivores and pathogens are expected to accumulate over time (e.g. Crous et al 2017;Stricker et al 2016), and the evolutionary component of such interactions has now been demonstrated in many cases (e.g. Strauss et al 2006).…”

Tree invasions and biosecurity: eco-evolutionary dynamics of hitchhiking fungi

“…For example, the best-known pathogens of plantation forestry trees in the SH belong to the Teratosphaeriaceae and Mycosphaerellaceae (Hunter et al 2011). They have been moved globally with their hosts or caught up after initial establishment (Crous et al 2016), and can often cause severe disease problems in plantations. Dothistroma needle blight of pines can be a devastating disease in SH plantations following introduction, but there is no evidence of host shifts onto native gymnosperms (Barnes et al 2004).…”

“…However, pathogens usually catch-up to their hosts over time (Crous et al 2016). Additionally, native pathogens can eventually move onto the introduced trees.…”