Functional mismatch in a bumble bee pollination mutualism under climate change

Abstract

Ecological partnerships, or mutualisms, are globally widespread, sustaining agriculture and biodiversity. Mutualisms evolve through the matching of functional traits between partners, such as tongue length of pollinators and flower tube depth of plants. Long-tongued pollinators specialize on flowers with deep corolla tubes, whereas shorter-tongued pollinators generalize across tube lengths. Losses of functional guilds because of shifts in global climate may disrupt mutualisms and threaten partner species. We found that in two alpine bumble bee species, decreases in tongue length have evolved over 40 years. Co-occurring flowers have not become shallower, nor are small-flowered plants more prolific. We argue that declining floral resources because of warmer summers have favored generalist foraging, leading to a mismatch between shorter-tongued bees and the longer-tubed plants they once pollinated.

Examining plant physiological responses to climate change through an evolutionary lens

“…For example, bee diversity in alpine ecosystems in Colorado has increased with the influx of lower elevation bee species over the past 40 years (Miller-Struttmann and Galen, 2014). Additionally, some alpine bee species evolved significantly shorter tongues, which allow these bees to forage on a wider variety of plant species (Miller-Struttmann et al, 2015). These changes in the pollinator community have led to a functional mismatch between alpine plants and their pollinators, since average flower size in this system has not changed with warming temperatures (Miller-Struttmann et al, 2015).…”

“…Additionally, some alpine bee species evolved significantly shorter tongues, which allow these bees to forage on a wider variety of plant species (Miller-Struttmann et al, 2015). These changes in the pollinator community have led to a functional mismatch between alpine plants and their pollinators, since average flower size in this system has not changed with warming temperatures (Miller-Struttmann et al, 2015). In this case, climateinduced shifts in the pollination network may have cascading effects on the evolution of plant traits.…”

Comparing two methods for estimating floral resource availability for insect pollinators in semi-natural habitats

“…Roger et al 2016), while others investigated long-term compositional changes and their impact on evolutionary processes (e.g. Miller-Struttmann et al 2015) or developed methods for estimating floral resource availability (e.g. Frankl et al 2005).…”

Low functional diversity promotes niche changes in natural island pollinator communities

“…Functional groupings of pollinators and flowers were based on proboscis and corolla tube lengths, respectively, because morphological matching between these traits can shape interactions in plant-pollinator networks [32,43]. Proboscis and corolla tube length were measured in millimetres.…”

“…Owing to the usually intimate associations between long-tongued pollinators and flowers with specialized floral organs, such as long corolla tube and spur ( [31,32]; figure 1), declines in long-tongued pollinators can lead to such plants becoming pollinator-limited [16,19,20,33]. However, few studies of natural ecosystems have investigated the impacts of long-tongued pollinator declines and the resulting niche changes on a whole flower community (but see Brosi & Briggs [17] and Kadoya & Ishii [22]).…”