Abstract
Volcanic eruptions are large-scale natural disturbances, which can negatively affect insect fauna and the ecological interactions in which they are involved. The 2011 eruption of the volcanic complex Puyehue Cordon-Caulle (PCC) produced the deposition of 950 million tons of ash on Argentine Patagonia, creating an ash layer of varying thickness. Although experimental studies confirmed that PCC volcanic ash negatively affects survival and behavior in many insect taxa, including bees, the effects of ash deposition on the plant-pollinator interactions (PPI) of this group of insects in natural landscapes remained untested. We evaluated the effect of the gradient of increasing ash layer thickness (0-15cm) on: (1) number of wild bees visiting flowers and total bee richness in 16 raspberry fields after the eruption, (2) number of native ( Bombus dahlbomii) and invasive (B. terrestris and B. ruderatus) bumble bees foraging on wild flowers in 10 sites before and after the eruption, and (3) the proportion of flowers (i.e. papilionaceous flowers visited for first time by large bees) in 32 populations of the invasive shrub scotch broom (Cytisus scoparius), before and after the eruption. With the increase of ash deposition, we found a consistent and significant decrease in (1) the number of wild bees and total bee richness visiting raspberry flowers; (2) the number of bumble bees, particularly B. terrestris, visiting wild flowers; and (3) the proportion of triggered flowers of scotch broom. Thus, volcanic eruptions can exert a detrimental effect on bee fauna and concomitant PPI, with a potential cascade effect on the pollination service to crops, the spread of invasive bumble bees, and the pollination success of invasive plants. (Keywords: Bombus terrestris, bumble bees, large scale disturbance, pollination, Puyehue Cordon-Caulle Volcano, raspberry, scotch broom)
Highlights
Volcanic eruptions can be very intense and highly sporadic natural disturbances, sometimes with multiple, complex and longlasting consequences (Wilson et al 2010; Schowalter 2012)
We evaluated the effect of the gradient of increasing ash layer thickness (0-15cm) on: (1) number of wild bees visiting flowers and total bee richness in 16 raspberry fields after the eruption, (2) number of native (Bombus dahlbomii) and invasive (B. terrestris and B. ruderatus) bumble bees foraging on wild flowers in 10 sites before and after the eruption, and (3) the proportion of “triggered” flowers in 32 populations of the invasive shrub scotch broom (Cytisus scoparius), before and after the eruption
During the flowering season after the eruption, the number of B. terrestris and native bees visiting raspberry flowers decreased with increasing ash layer thickness, by 97 and 100 % from fields without ash to fields with approximately 10 cm of deposited ash, respectively (Figure 2a)
Summary
Volcanic eruptions can be very intense and highly sporadic natural disturbances, sometimes with multiple, complex and longlasting consequences (Wilson et al 2010; Schowalter 2012). Depending on ash characteristics (i.e. amount, particle size, physical and chemical components) volcanic events impose different intensities of stress on organisms and the ecological processes in which they are involved. Mechanisms underlying decreased survival are mostly related to the hygroscopic and abrasive nature of volcanic particles, which alters tissues and vital systems (Klostermeyer et al 1981) and processes such as respiration and digestion (Wille & Fuentes 1975)
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