Plant-pollinator network dynamics of the Little Fork Shale Barren

Shale barrens are steep sloping mountainside ecosystems characterized by rocky Upper Devonian age shale substrate, high light, and low water availability. They form an array of biogeographical “islands” throughout Mid-Appalachia whose niche dynamics, response to disturbance, and pollination ecology remain to be investigated. Using network analysis, this project addresses three objectives to fill gaps in shale barren pollination ecology. (i) Compare vegetative species composition, richness, diversity, and evenness to a descriptive vegetation study completed at the same site 27 years prior. ii) Outline the topology of plant-pollinator networks including identifying phenologically accurate networks, the architecture of such networks, and identifying plant species network hubs and key pollinators groups. (iii) Examine the scale of within-season interaction variation, whether that variation is reflective of fluctuations in pollinator activity, and that variation’s relationship to changes in weather conditions. Plant and pollinator data were collected via pollinator observation and flowering inventory surveys conducted on within 10-day monitoring periods through the full growing season of Little Fork Shale Barren (Pendleton Co.,West Virginia). General vegetation surveys occurred in the late summer to late fall at the same site. Comparisons between the current vegetation community and results from a 1994 survey of the site show a significant increase in community species richness and diversity. Analysis of large scale interaction data revealed the presence of diverse interaction networks with degree distributions, connectances, and levels of nestedness comparable to networks in other ecosystems. Fine scale interaction data showed the system experiences high within-season interaction turnover dictated by interaction rewiring. Simulation models confirmed that species abundance and phenology constrain interaction turnover and interaction rewiring. Linear regression analysis of weather conditions and pollinator activity found median temperature to have the strongest relationship with higher pollinator activity at greater median temperatures. Our findings expose the depth and dynamics of biodiversity and ecological function present in a superficially understood “barren” ecosystem