Taxonomic diversity and community structure of insect pollinators in Shivapuri-Nagarjun National Park, Central Nepal
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Institute of Science and Technology, Zoology
Abstract
Insect pollinators are important agents mediating useful services for human and the
ecosystem. Large number of wild plants and agricultural crops depend on the
pollinators for their pollination. Global trend has shown decline of several taxa of
pollinators and indicating habitat loss as major driving factor. Several studies have been
done on pollinators in agricultural and natural areas however there are very few works
describing their distribution and diversity in protected area despite the fact that these
areas are globally important for preserving disturbance-intolerant pollinators.
Wild flowering plants of the park may play an important role for conservation of
pollinators. This study explored the taxonomic diversity and the community structure
of insect pollinators; bees, butterflies, and hoverflies of Shivapuri-Nagarjun National
Park (SNNP). Furthermore, five least collected wild bees during two years of survey
were used as model pollinators to check the distribution. The research also documented
plant-pollinators interaction to find out the key pollinators, plants that serve as hubs of
pollinators, and seasonal variations of pollinators.The survey was done in SNNP for
two consecutive years (2018–2019) in four different habitats; Open trail, Forest trail,
Managed habitat, and Grassland using both belt transect and colored pan traps methods
in three different elevations that ranges from 1,400m–2,700m. The results showed 42
and 34 species of bees and hoverflies respectively. Out of them, 11 species: Amegilla
candida, A. fallax, A.insularis, A. quadrifasciata, Elaphropoda impatiens, Ceratina
perforatrix, Colletes similis, Megachile conjuncta, Nomia iridescens, Xylocopa
collaris, and X. violacea are new country records of bee and Graptomyza nigripes,
Lycastris albipes, and Volucella trifasciata are new country records of hoverflies.
Likewise, community structure of pollinators presented a total of 167 different species;
the butterflies being the most dominant group (48.50%) followed by bees (29.94%) and
hoverflies (21.56%). Diversity indices in alpha level was analysed; the Open trail was
comparatively more diverse (4.85), followed by the Managed habitat (4.30). Whittaker
Beta diversity analyzed the high species turnover between Forest trail and Managed
habitat. Environmental variables like humidity, atmospheric temperature, and flower
resources in different elevation have a significant effect (p<0.05) on pollinating insects.
The species distribution model showed Nomada mutabilis, Thyreus decorus, T.
himalayensis, Megachile femorata, and X. violacea are spread out across a broad region
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in the park. The accuracy of model predictions for all five bees are statistically well
specified (AUC is greater than 0.07). The plant-pollinator interactions were complex
and asymmetrical showing Eristalis tenax, E. cerealis, and Pieris canidia as key
pollinators. Ageratina adenophora, Bidens pilosa, and Trifolium repens were observed
as the most visited plants by pollinators. Seasonal comparisons showed that there is
high species turnover of bees and hoverflies between spring and autumn seasons (
p<0.05).
Based on these results, it is clear that the park provides suitable habitats for many
species of pollinators. Open trials with a rich herb and shrub coverage can provide
foraging habitat to pollinators. High diversity and abundance of insects in Open trial
can aid good pollination service in this habitat. Other habitats like managed area,
grassland, and forest can be important determinants of wild bees resulting different
pollinator community. Frequent visits of pollinators in exotic plants compared to native
plants could alter the native plant- pollinator interaction in long term if former plants
are not managed.