With or without you: Effects of the concurrent range expansion of an herbivore and its natural enemy on native species interactions

Abstract

Global climatic changes may lead to the arrival of multiple range-expanding species from different trophic levels into new habitats, either simultaneously or in quick succession, potentially causing the introduction of manifold novel interactions into native food webs. Unraveling the complex biotic interactions between native and range-expanding species is critical to understand the impact of climate change on community ecology, but experimental evidence is lacking. In a series of laboratory experiments that simulated direct and indirect species interactions, we investigated the effects of the concurrent arrival of a range-expanding insect herbivore in Europe, Spodoptera littoralis, and its associated parasitoid Microplitis rufiventris, on the native herbivore Mamestra brassicae, and its associated parasitoid Microplitis mediator, when co-occurring on a native plant, Brassica rapa. Overall, direct interactions between the herbivores were beneficial for the exotic herbivore (higher pupal weight than the native herbivore), and negative for the native herbivore (higher mortality than the exotic herbivore). At the third trophic level, both parasitoids were unable to parasitize the herbivore they did not coexist with, but the presence of the exotic parasitoid still negatively affected the native herbivore (increased mortality) and the native parasitoid (decreased parasitism rate), through failed parasitism attempts and interference effects. Our results suggest different interaction scenarios depending on whether S. littoralis and its parasitoid arrive to the native tritrophic system separately or concurrently, as the negative effects associated with the presence of the parasitoid were dependent on the presence of the exotic herbivore. These findings illustrate the complexity and interconnectedness of multitrophic changes resulting from concurrent species arrival to new environments, and the need for integrating the ecological effects of such arrivals into the general theoretical framework of global invasion patterns driven by climatic change.

Winners and losers over 35 years of dragonfly and damselfly distributional change in Germany

“…However, increasing populations for some species represent expansion into new regions; while for other species, increases rather reflect recovery to formerly occupied parts of the range. The former group may be regarded as 'neonatives' (Essl et al 2019) and contribute to the development of novel species interactions and assemblages (Carrasco et al 2018), with currently unclear repercussions for established/native species (Flenner & Sahlen 2008;Suhling & Suhling 2013). Decreasing populations of other species have led to a decline mean in species richness during the 2010s.…”

Getting confused: learning reduces parasitoid foraging efficiency in some environments with non-host-infested plants

“…This suggests that it may be relatively easy for parasitoids to distinguish between different types of herbivores, but difficult to discriminate between herbivores such as P. brassicae and M. brassicae that do not differ much in traits associated with feeding. It was indeed found that C. glomerata (Desurmont et al 2015 ), Cotesia rubecula (Geervliet et al 1996 ; Van Poecke et al 2003 ), Cotesia kariyai (Thanikkul et al 2017 ), Microplitis mediator (Carrasco et al 2017 ; Desurmont et al 2017 ) and Aphidius ervi (Du et al 1996 ) can distinguish between host and non-host HIPV blends if the herbivores differ in at least one of the traits mentioned above. Cotesia flavipes, however, was not able to distinguish between HIPVs induced by its stem-boring host and a chewing herbivore (Peñaflor et al 2017 ), while Cotesia plutella and Cardiochiles nigriceps preferred host-induced HIPVs over non-host-induced volatiles, despite strong similarities in herbivore traits (De Moraes et al 1998 ; Peñaflor et al 2017 ).…”

Longer photoperiods through range shifts and artificial light lead to a destabilizing increase in host–parasitoid interaction strength

“…Climate change has caused many species to shift their ranges poleward (Parmesan & Yohe, 2003), altering their interactions with other species (Carrasco et al, 2018;Ettinger & HilleRisLambers, 2017).…”

“…Climate change has caused many species to shift their ranges poleward (Parmesan & Yohe, 2003), altering their interactions with other species (Carrasco et al., 2018; Ettinger & HilleRisLambers, 2017). However, as species track their thermal niches, and move closer to the poles, they experience longer summer days.…”