Honey bees ensure the pollination of <i>Parkia biglobosa</i> in absence of bats

Abstract

One of the socio-economically important West African parkland trees, Parkia biglobosa yields pods consumed by people and animals. Being animal-pollinated, it is unknown how climate change will affect the species if the guild of pollinators changes. Here, we compare the pollinator guilds and the pod production at two climatically different study sites: the first site, Tiba was drier with lower tree density and fewer fruit bats, whereas the second site, Pinyiri was more humid, with higher tree density and more fruit bats. We carried out a pollinator exclusion trial with bags separating the flower-visitors and made observations of the flower-visitors. Furthermore, we calculated pollination distances based on paternity analysis of the seeds produced within the trial. The numbers of immature fruits were similar for the sites, but the drier site, Tiba experienced more abortion and decreased pod set. At both sites, exclusion of bats led to marginally reduced pod set, while exclusion of bats and honey bees led to significantly reduced pod set. We found a small effect of stingless bees and solitary bees but only at the more humid site, Pinyiri. Tiba experienced a higher level of self-pollination, fewer pollen donors per tree, and longer median distances of pollen flow, compared with Pinyiri. Implications of the results for management of the species and its pollinators in the face of climate change are discussed.

Fine‐scale spatial genetic structure, mating, and gene dispersal patterns in Parkia biglobosa populations with different levels of habitat fragmentation

“…Previous studies based on allozyme markers and a controlled pollination experiment showed that P. biglobosa is self-compatible with a selfing rate of 5% (Ouedraogo, 1995;Sina, 2006). It is worth noting that Lassen et al (2017) reported a selfing rate of 2% in a humid site with a population density of 1.23 trees/ha, similar to our lowest population density recorded in Vouza. However, a higher selfing rate (s ~21%) was found in a drier site with a tree population density 20 times lower than in our site with lowest tree density (0.26 trees/ha), which seems to suggest that selfing does not occur until a minimum threshold in population density is reached.…”

“…However, a higher selfing rate (s ~21%) was found in a drier site with a tree population density 20 times lower than in our site with lowest tree density (0.26 trees/ha), which seems to suggest that selfing does not occur until a minimum threshold in population density is reached. On the other hand, in a humid site previously studied, selfing increased from 2 to 19% when both bats and honey bees were excluded (Lassen et al, 2017), demonstrating the role of these species in supporting cross-pollination. In addition, our study estimated a number of pollen donors per maternal tree from 3 to 20 times higher than in the experiment by Lassen et al (2017).…”

“…On the other hand, in a humid site previously studied, selfing increased from 2 to 19% when both bats and honey bees were excluded (Lassen et al, 2017), demonstrating the role of these species in supporting cross-pollination. In addition, our study estimated a number of pollen donors per maternal tree from 3 to 20 times higher than in the experiment by Lassen et al (2017).…”

“…A controlled-pollination trial showed that self-pollination is possible, particularly through geitonogamy (Ouedraogo, 1995). The species is essentially animal-pollinated, with about 30 potential pollinating species visiting its flowers (Lompo et al, 2017); bats, honey bees, and stingless bees are the most effective pollinators (Ouedraogo, 1995;Lassen et al, 2017). In addition to humans, seed dispersers are mainly primates, such as chimpanzees, small mammals (rodents), and birds (Ouedraogo, 1995).…”

“…The similarity in mating system of CP and NCP suggests that use of pesticides does not cause a strong decline of pollination services, either because pollinating species are not sensitive to the pesticides used or because some mitigating mechanisms are in place by which a few pollinating species are able to effectively sustain pollination services. These are open questions that deserve further investigation, along the line of research conducted by Lassen et al (2017) on pollinator behavior.…”