Variation of floral and extrafloral nectar resources in trees of the genus Inga (Fabaceae: Mimosoideae) in coffee agroforests

Background/Question/Methods

Floral and extrafloral nectar resources are important for arthropod communities in natural and managed systems. For nectar visitors, these resources can influence colonization and establishment and provide food in periods of prey scarcity. These resources, in particular extrafloral nectar can also drive insect-plant protective mutualisms. The variation of nectar in terms of concentration and composition across seasons, species and nectar structures can contribute to the structure and assemblage of arthropod communities and species coexistence through resource partitioning. In agricultural systems, management could also influence composition and ultimately impact consumers. In coffee agroforests, shade trees in the genus Inga (Fabaceae: Mimosoideae) provide sugar resources to a vast community of arthropods, although little is known about how their quantity and composition varies across species, agricultural management, seasons and nectar structures. Understanding how nectar resources vary is important to understand the ecology and function of tropical agroecosystems. In this work, we ask: Does Floral and EF nectar sugar composition and concentration vary across a) plant source (floral vs. EFN) b) season (dry and rainy), c) three species of the genus Inga, and d) two distinct coffee management systems? We collected nectar samples from flowers and EFNs in 76 trees across three Inga species distributed in conventional and organic coffee plots during the rainy and dry seasons. Nectaries were isolated using mesh bags for 24 hours and pooled samples were collected using filter paper. Nectar sample analysis (sugar composition) was performed using HPLC at UC Davis.

Results/Conclusions

We collected a total of 235 nectar samples, and we found 12 different types of sugars. Overall, we found that nectar concentrations and composition varied across groups. We found a significant interaction in total sugar concentrations between both EFN and Floral nectars, across species and between management regimes. Contrary to expected, seasonality did not drive differences in total sugar concentration. We also found significant sugar compositional differences between groups, except between seasons. However, there was a significant interaction in sugar composition between seasons, nectar structures and species. Collectively, our research suggests that management system, tree species and nectar source significantly drive differences in total nectar concentration and composition available in these coffee agroecosystems. Changes in management, tree species and source could scale up to create patchy nutritional landscapes with respect to sugar resources utilized by pollinators and natural enemies.