Pollination success following loss of a frequent pollinator: the role of compensatory visitation by other effective pollinators

Abstract

Sudden declines of frequent and effective pollinators are often assumed to reduce pollination success. Yet this assumption has rarely been tested experimentally and may depend upon responses of other pollinators in the community. We temporarily excluded bumble bees in populations of the milkweed Asclepias verticillata, and quantified pollinator visitation rates and pollen receipt in both control and bumble bee exclusion plots. Asclepias pollination success did not decline following bee exclusion due to a nearly three-fold increase in wasp visitation. This highlights the importance of studies that explore the effectiveness and compensatory responses of other pollinator species in the community.

Complex long‐term dynamics of pollinator abundance in undisturbed Mediterranean montane habitats over two decades

“…) are likely to occur, and failure of some pollinators should be followed by pollination decline less often than in depauperate habitats (Pauw , Hallett et al. ). In habitats with diverse pollinator communities, therefore, indices of pollinator abundance that are not directly linked to their pollinating activity at flowers (e.g., pan trap or Malaise trap captures; Nielsen et al.…”

“…Wasps, for example, have been shown experimentally to replace bumble bees as efficient pollinators of Asclepias flowers (Hallett et al. ), and invasive bumble bees may replace advantageously the pollination services of declining native species (Madjidian et al. ).…”

“…"Pollinator decline," however, is not necessarily synonymous with "pollination decline" (Thomson 2001). Failure of keystone pollinators may not cause a decay in pollination success if it is followed by shifts in the composition and abundance of remaining pollinators that eventually compensate for the loss (Pauw 2007, Hudewenz and Klein 2015, Hallett et al 2017. Pollinator and pollination declines are expected to be tightly correlated in depauperate habitats with low overall diversity such as agroecosystems, where compensatory shifts by other species are unlikely to follow the decay of key pollinators (Kremen et al 2002).…”

“…Pollinator and pollination declines are expected to be tightly correlated in depauperate habitats with low overall diversity such as agroecosystems, where compensatory shifts by other species are unlikely to follow the decay of key pollinators (Kremen et al 2002). In wild habitats still harboring diverse pollinator communities, however, compensatory shifts and complementarity effects (Albrecht et al 2012, Fr€ und et al 2013) are likely to occur, and failure of some pollinators should be followed by pollination decline less often than in depauperate habitats (Pauw 2007, Hallett et al 2017. In habitats with diverse pollinator communities, therefore, indices of pollinator abundance that are not directly linked to their pollinating activity at flowers (e.g., pan trap or Malaise trap captures; Nielsen et al 2011, Hallmann et al 2017, Hall 2018) are prone to be weakly correlated across years with measurements of pollinator service based on flower visitation or pollination success.…”

Pollinator Diversity: Distribution, Ecological Function, and Conservation

“…Pollen limitation can have many causes (Knight et al 2005) and lower pollinator diversity in some populations of a species is certainly one of them, as Gómez et al (2010) Polistes wasps that were just as effective as pollinators (Hallett et al 2017) -an example of ecological redundancy within the system (see section 5.1). In contrast, Brosi and Briggs (2013) found that removing a single bumblebee species from localised patches reduced the reproductive success of Delphinium barbeyi (Ranunculaceae), even though alternative pollinators were present.…”