Epsilon Archive for Student Projects

Abstract

The red clover seed production systems are dependent on pollinators for increase in red clover seed yield and its stability. When compared to domesticated honey bees, the wild bumble bees are highly efficient in pollinating the red clover crop due to its relatively longer tongue length. Longer dependence on single pollinator species i.e., honey bees has proved that reliance on single pollinator population is highly inefficient especially when the highly managed systems are prone to ecological surprises like colony collapse disorder. Therefore, global agro-ecosystem management has begun to increase their efforts of harnessing the pollination potential from diverse wild pollinator communities like bumble bees and non-bee pollinators. However, the agricultural intensification led landscape and environmental homogenisation has caused the populations of the wild pollinators decline, resulting in reduced pollination service from wild bumble bee diversity, necessitating conservation of bumble bees.
Among bumble bees the long tongue (LT) bumble bees are highly efficient pollinators, whereas short tongue (ST) bumble bees are relatively least efficient or unproductive because of their short tongue length and their one third proportion engages in robbery of nectar without pollinating the flowers. However, ST bumble bees are highly mobile and highly populated generalist functional group, contrasting specialist LT species in red-clover production systems. To investigate the impact of declining evenness in this 10-species community comprising of 5 LT and 5 ST, the empirical proportional abundance data from historic field investigations (1940’s, 1960’s & 2010) were modelled as temporal replication scenarios for 100 years in a model called FunBumble prepared for this study using empirical parameter estimates. The early 1940’s & 1960’s scenarios had one dominant and 3 co-dominant identities and the contemporary 2010 scenarios had one dominant and co-dominant identity. Throughout since 1960’s to 2010, B. terrestris is the dominant species. Thus, the 10-species community comprised of totally 5 dominant species, these each dominance identities taken as scenarios were designed as nested evenness levels namely, high evenness, medium evenness and low evenness scenarios.
The FunBumble model investigation of these scenarios, showed that as community evenness increased the temporal seed yield stability too increased due to portfolio effect and species asynchrony in the presence high evenness. Whereas, the low magnitude increases or decreases of temporal productivity depended largely on sign of selection effect and contributions of co-dominance identities. For example, when unproductive ST species B. terrestris is dominant due to negative selection effect, the co-dominant highly productive LT species contributed positively resulting in over yielding of productivity and enhanced species co-existence causing positive influence on biodiversity. This mechanistic understanding of biodiversity, productivity and stability relationship of realistic B. terrestris dominance identity scenarios showed that the bumble bee community composition since 1940’s in red clover production system had acted as species co-existence promoting buffering mechanism under the presence of selection processes like landscape and environmental homogenisation due to agricultural intensification. Especially the contemporary (2010) least evenness scenario with no LT species as co-dominant illustrates the reasons for current decline in both stability and productivity of red clover seed yield. This necessitates, the need for local and landscape scale management measures for increasing relative abundance of LT species, through nesting and floral resource facilitation in crop production systems.