Invasive oaks escape pre‐dispersal insect seed predation and trap enemies in their seeds

Abstract

Species introduced to habitats outside their native range often escape control by their natural enemies. Besides competing with native species, an alien species might also affect the native herbivores by introducing a new source of different quality food. Here, we describe the case of northern red oak (Quercus rubra) invasion in Europe. We collected data on insect (moth Cydia spp. and weevil Curculio spp.) seed predation of northern red oak in its native (USA, North America) and invasive (Poland, Europe) range, as well as for sessile oaks (Quercus petrea) in Europe. We also evaluated the quality of acorns as hosts for weevil larvae by collecting infested acorns and measuring weevil developmental success, and quantifying acorn traits such as seed mass, tannins, lipids and protein concentration. We used DNA barcoding to identify insects to the species level. The predation by moths was similar and very low in both species and in both ranges. However, red oaks escape pre-dispersal seed predation by weevils in Europe. Weevil infestation rates of northern red oak acorns in their invasive range were 10 times lower than that of sessile oaks, and also 10 times lower than that of red oaks in North America. Furthermore, even when weevils oviposited into northern red oaks, the larvae failed to develop, suggesting that the exotic host created a trap for the insect. This phenomenon might gradually decrease the local abundance of the seed predator, and further aid the invasion.

Consumer‐mediated indirect interaction with a native plant lowers the fitness of an invasive competitor

“…In the absence of sensitivity to germination schedules, and without differences in tannin concentration (Bogdziewicz, Bonal, et al, ), mice may treat Q. rubra acorns like large Q. petraea , and this may help explain our results. Q. rubra was more likely than Q. petraea to escape predation when both species were presented in isolation (Figure ).…”

“…Both species are scatterhoarded by rodents (Bogdziewicz, Crone, Steele, & Zwolak, ; Jensen & Nielsen, ; Smallwood, Steele, & Faeth, ). In comparison with Q. petraea , Q. rubra acorns weigh twice as much, have shells that are twice as thick, and have higher lipid concentrations (Bogdziewicz, Bonal, et al, ). Although tannin concentrations in Q. rubra acorns from their native range are higher than those in Q. petraea , Q. rubra acorns in Europe show unusually low tannin concentrations for the species, and are similar to Q. petraea (Bogdziewicz, Bonal, et al, ).…”

“…In comparison with Q. petraea , Q. rubra acorns weigh twice as much, have shells that are twice as thick, and have higher lipid concentrations (Bogdziewicz, Bonal, et al, ). Although tannin concentrations in Q. rubra acorns from their native range are higher than those in Q. petraea , Q. rubra acorns in Europe show unusually low tannin concentrations for the species, and are similar to Q. petraea (Bogdziewicz, Bonal, et al, ). Finally, Q. petraea acorns germinate in autumn while Q. rubra acorns overwinter and germinate in the spring (Steele, ).…”

Responses of seedling growth and survival to post‐germination cotyledon removal: An investigation among seven oak species

“…The dispersal and establishment of seeds are regarded as one of the most vulnerable and limiting stages in the plant life cycle (Chen, Tomlinson, Cao, & Wang, ; Janzen, ; Zhang, Chu, & Zhang, 2017a; Urgoiti, Muñoz, Espelta, & Bonal, ). Successful seed survival and seedling establishment are often threatened by a variety of biotic and abiotic factors (Bogdziewicz et al, ; Canelo, Gaytán, Gonzálezbornay, & Bonal, ; Gómez, Puerta‐Piñero, & Schupp, ; Hou, Yi, Yang, & Liu, ; Wallertz & Petersson, ; Zhang, Wang, Liu, & Yi, 2017b). Among the biotic factors, seed predation by vertebrates (e.g.…”

Maladaptive host choice by an alien leaf miner Phyllonorycter leucographella (Lepidoptera: Gracillariidae) has the potential to limit its invasiveness

“…The ability of an insect to successfully colonize new hosts is also strongly determined by the plant's physical, chemical, and phenological traits (Coley & Barone, 1996;Loranger et al, 2013;Bogdziewicz et al, 2018). Notably, leaves with a high specifi c leaf area (SLA), i.e., high leaf area to leaf mass ratio, which usually have a higher photosynthetic capacity, higher leaf nitrogen concentration and water content, and lower investment in structural defenses (Reich et al, 1997;Cornelissen et al, 2003) are more palatable to herbivores than leaves with a low SLA (Coley & Barone, 1996;Hanley et al, 2007).…”