Predicting the Native-Exotic Richness Relationship Using Native Beta Diversity Gabriela Nunez-Mir and Songlin Fei Department of Forestry and Natural Resources Purdue University Princess Tree (Paulownia tomentosa) Bill Johnson Nature Stock Photography, Inc - Abstract Expected Native-Exotic Diversity Patterns Preliminary Results Invasion paradox, a change of direction in native-exotic richness relationships (NERRs) within and across scales We hypothesize that the directional changes in NERRs can be explained by the degree of beta, which describes heterogeneity We used data from the Forest Inventory and Analysis (FIA) dataset to evaluate the relationship between regional beta diversity and the slope of the NERR for different units at multiple scales Strong, yet inconsistent, relationships were observed at the largest scale High heterogeneity areas: Small increases in extent result in increases in beta diversity that generate positive NERRs Adj R2= 0.006 P-value < 0.001 Adj R2= 0.027 P-value= 0.02 Adj R2= 0.17 P-value = 0.006 Research Problem Low heterogeneity areas: Larger increases in extent are required to increase beta diversity and generate positive NERRs. Contradicting relationships between native and exotic diversity complicate our understanding of the role of native diversity in invasiibility and hinder the development of generalizations. Contradicting relationships are observed: Across scale: fine scale versus broader scales Within scale: E.g., two studies on North American grasslands at the ≤1m2 scale The inconsistencies observed across and within scale suggest that other variables or perspectives to the study of these relationships remain underexplored Adj R2= 0.005 P-value= 0.03 Methods Only positive or nonsignificant native- exotic richness relationships found in Cleland et al. 2004 Only negative native-exotic richness relationships found in Davies et al. 2005 Adj R2= 0.008 P-value= 0.52 Adj R2= 0.08 P-value= 0.08 Native and exotic species richness data for FIA plots in the eastern US For each ecoregion at increasing levels of spatial scale: Obtained the slope of NERRs for plots within region Measured beta diversity: βt (Wilson and Shmida 1984) Regressed NERR slopes as a function of beta diversity Adj R2= 0.008 P-value= 0.21 Adj R2= 0.02 P-value= 0.7 Adj R2= 0.2 P-value= 0.05 Beta Diversity Many community processes are driven by heterogeneity Beta diversity describes biotic heterogeneity by measuring the amount of variation in species assemblages in an area Are the inconsistencies observed across spatial scales in NERRs resolved along a biotic heterogeneity (beta diversity) gradient? Biotic heterogeneity generates positive NERRs by enhancing coexistence mechanisms and masking patterns generated by local processes, such as competitive exclusion. Conclusions Strong relationships between beta diversity and the slope of native-exotic richness relationship were only observed at the largest scale Inconsistent relationships  Possible evidence of aggregation bias Unclear whether beta diversity is able to explain inconsistencies. Aggregation bias might. Central Question Funded through NSF-Macrosystems Biology 1241932 Acknowledgements Hypothesis References Cleland, E. E., Smith, M. D., Andelman, S. J., Bowles, C., Carney, K. M., Claire Horner‐Devine, M., ... & Vandermast, D. B. (2004). Invasion in space and time: non‐native species richness and relative abundance respond to interannual variation in productivity and diversity. Ecology Letters, 7(10), 947-957. Davies, K. F., Chesson, P., Harrison, S., Inouye, B. D., Melbourne, B. A., & Rice, K. J. (2005). Spatial heterogeneity explains the scale dependence of the native-exotic diversity relationship. Ecology, 86(6), 1602-1610.