The effect of insect herbivory on seed production of Lupinus nootkatensis, an introduced species in Iceland

Abstract

Lupinus nootkatensis is an exotic plant species that has been used for large‐scale sowing all around Iceland for land reclamation of eroded surfaces protected from livestock grazing. Until the early 1990s, L. nootkatensis was free from any significant arthropod herbivory in Iceland, whereas, after 1991, many outbreaks of native insect species, primarily Ceramica pisi and Eupithecia satyrata, have been recorded. These outbreaks have caused repeated total defoliation of extensive areas of L. nootkatensis, although the effects on its development are mostly unknown. We studied the effect of: (i) reduced herbivory; (ii) increased herbivory; and (iii) simulated increased herbivory, compared with (iv) unmanipulated herbivory, on defoliation and seed production of L. nootkatensis in a 3‐year field study within two sites at contrasting ages and successional stages. The results obtained showed that: (i) seed production across all treatments was negatively related to defoliation; (ii) reduced herbivory had a positive effect on the number of flowering stems and seed yield; and (iii) these effects depended on age and/or the successional stage because they were only significant in the older L. nootkatensis site. These findings indicate that arthropod herbivory may affect the invasiveness of L. nootkatensis in Iceland by reducing the seed production and the spatial distribution rate of late successional lupin communities.

Take me for a ride: Herbivores can facilitate plant reinvasions

“…In accordance with existing theory, we find that in many syndromes herbivores slow spreading speed, primarily through impacts on plant demography (Fagan et al, 2005; Fagan & Bishop, 2000; Holt & Barfield, 2009; Owen & Lewis, 2001; Radny & Meyer, 2018). Empirical evidence demonstrates that herbivores either consume plant tissue that subsequently decreases seed production (Foster & Ackerman, 2021; Hrafnkelsdottir et al, 2020; Miller et al, 2009; Schultz et al, 2017), or fully consume adult plants (Auberson‐Lavoie & Vellend, 2020; Kuijper et al, 2004; Rivest & Vellend, 2018), both which in turn slow spatial spread. Our findings that stage‐specific consumption by herbivores can cause different effects on plant spread rate fits with the broad literature using structured models (Caswell, 2000) to target certain stages for the conservation of endangered species (e.g., alterations to adult stages are often the most critical; Crouse et al, 1987) and control of invasive species (Buckley et al, 2005).…”

“…Insects native to Iceland ( Ceramica pisi , Eupithecia satyrata ) defoliate lupines ( Lupinus nootkatensis ) which reduce the number of flowering stems and seed production. Thus, seed production is negatively related to herbivory pressure (Hrafnkelsdottir et al, 2020). Lepidopteran larvae consume fig fruits from the Sonoran Desert rock fig ( Ficus petiolaris ), which can lead to the loss of entire fruit crops (Piatscheck et al, 2018).…”