Urban to Agro Ecosystems: Effects of Land Use on Pollinators and Ecosystem Services

Abstract

We are now living in the Anthropocene, a new epoch characterized by unprecedented levels of anthropogenic impact on earth systems. This epoch has seen a dramatic decline in biodiversity and, consequently, poses a great challenge to humanity, as we encounter diminished provisioning of ecosystem services, vital for our survival. My dissertation examines the ecological impact of land-use change, driven by agriculture and urbanization on the provisioning of ecosystem services, mainly pollination, and the pollinators that provide this ecosystem service. I investigate these questions at the level of the landscape within both the agricultural and urban matrix, and at the level of the farm scale in the agricultural matrix. In chapter 2, I evaluate the suitability of three habitats (organic shaded coffee farm, sun coffee farm, forest fragment) in supporting populations of Scaptotrigona mexicana, a stingless bee species that is native to Mexico and of great cultural significance. I find that stingless bee colony growth, survival and pollen-diet richness are comparable in the shaded coffee farm and the forest fragment. In contrast, I find that the sun coffee farm is inhospitable for stingless bee colonies likely due to use of agrochemicals and low floral resources. In chapters 3-4, I investigate the effects of nitrogen-fixing shade tree management on the interactions of two ecosystem services – pest control and pollination – in an organic shaded coffee farm in Mexico. I examine the effects of pollinators and ants as agents of pollination and pest control on Coffea arabica. I find that there is no trade-off between pest control and pollination services despite the deterrence of pollinators by the dominant and aggressive ant species, Azteca sericeasur, which also controls the coffee berry borer, a major pest of Coffea arabica. I find additive effects of pest-control and pollination on early fruit set and fruit weight, and that nitrogen-fixing shade trees only has indirect effects on pest-control via the reduction of Azteca ant activity on the coffee bushes. In chapter 5, I study the pollination ecology of green cardamom, Elleteria cardamomum. I examine the relative contributions of common pollinator species visiting cardamom using single-visit pollen deposition and fruit set in an organic shaded coffee plantation. I find that cardamom has both legitimate visitors and nectar-robbers. However, the nectar-robbers also collect pollen from the flowers, thereby pollinating the plant despite robbing its nectar. The most effective pollinator of E. cardamomum in its introduced range is a native stingless nectar-robbing bee species, Scaptotrigona mexicana, highlighting the need to examine the activity of visitors that on the face of it appear to only “rob” plants but may turn out to be the most effective pollinators. I discuss the implications of this finding by laying out conditions under which cardamom may adapt to its most effective pollinator, if at all. In chapter 6, I investigate the influence of roads on pollinator movement and pollination by examining patterns of pigment transfer. I find that plants across a road from a pigment-added plant receive significantly less pigment than plants on the same side of the road and this effect is mediated by the size of the pollinators. I show that roads pose substantial barriers to bee movement, reducing pollen flow between plants located across roadways from one another. Finally in chapter 7, I discuss the implications of my studies and future directions.