Flowering phenology influences butterfly nectar foraging on non‐native plants in an oak savanna

Abstract

The negative impacts of non‐native species have been well documented, but some non‐natives can play a positive role in native ecosystems. One way that non‐native plants can positively interact with native butterflies is by provisioning nectar. Relatively little is known about the role of phenology in determining native butterfly visitation to non‐native plants for nectar, yet flowering time directly controls nectar availability. Here we investigate the phenological patterns of flowering by native and non‐native plants and nectar foraging by native butterflies in an oak savanna on Vancouver Island, British Columbia, Canada. We also test whether native butterflies select nectar sources in proportion to their availability. We found that non‐native plants were well integrated into butterfly nectar diets (83% of foraging observations) and that visitation to non‐natives increased later in the season when native plants were no longer flowering. We also found that butterflies selected non‐native flowers more often than expected based on their availability, suggesting that these plants represent a potentially valuable resource. Our study shows that non‐native species have the potential to drive key species interactions in seasonal ecosystems. Management regimes focused on eradicating non‐native species may need to reconsider their aims and evaluate resources that non‐natives provide.

Shifting the paradigm: The role of introduced plants in the resiliency of terrestrial ecosystems to climate change

“…Differences in phenology between native and introduced plants have also had implications for pollinators. A recent study found that introduced plants flowered later than natives in an endangered savanna ecosystem, likely because of the increased drought‐tolerance of the introduced relative to the natives (Rivest et al., 2023). As a result, the native butterflies were entirely dependent on the nectar provided by introduced plants at the end of the season (Rivest et al., 2023).…”

“…A recent study found that introduced plants flowered later than natives in an endangered savanna ecosystem, likely because of the increased drought‐tolerance of the introduced relative to the natives (Rivest et al., 2023). As a result, the native butterflies were entirely dependent on the nectar provided by introduced plants at the end of the season (Rivest et al., 2023). Given a lack of historical data, it is unclear whether the introduced plants have extended (i.e., provided new resources) or maintained the length of the season (i.e., replacing native resources) in this ecosystem (Rivest et al., 2023).…”

“…As a result, the native butterflies were entirely dependent on the nectar provided by introduced plants at the end of the season (Rivest et al., 2023). Given a lack of historical data, it is unclear whether the introduced plants have extended (i.e., provided new resources) or maintained the length of the season (i.e., replacing native resources) in this ecosystem (Rivest et al., 2023). There have been similar reports from other ecosystems where introduced plants have extended the season where nectar is available for pollinators (Frankie et al., 2019; Staab et al., 2020; Table 1).…”

“…As evidence continues to accumulate of introduced plants providing alternative hosts and refuge for insects, determining when these shifts are maladaptive is a crucial next step (Braga, 2023; Rivest et al., 2023; Steward et al., 2022; Yoon & Read, 2016). One of the best‐known examples where introduced plants provided a new resource to insects is from populations and sub‐species of Edith's checkerspot butterfly ( Euphydryas editha ; Severns & Warren, 2008; Singer & Parmesan, 2018).…”

The Impact of Urbanization on Taxonomic Diversity and Functional Similarity among Butterfly Communities in Waterfront Green Spaces

“…The main limitations of this study are as follows: (1) Data were collected solely from urban waterfront green spaces, and the limited types of urbanization studied may only represent part of the urban butterfly community; (2) This study focused only on the overall impact of urbanization on butterfly diversity, without fully considering factors such as climate change, land cover type [58], ecological corridor connectivity [59], nectar plants [60], host plants [61,62], predators, and competitors [63]. (3) This study primarily concentrated on the summer season, potentially missing out on capturing seasonal and annual changes in butterfly populations.…”