Dr. Brian S. Cheng

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Project Title:  Species invasions across latitude: a comparative approach to understanding biotic resistance and propagule pressure in driving biogeographic patterns of invasion

Advisors:  Greg Ruiz, Mark Torchin, Andrew Altieri

Invasive species have resulted in substantial ecological and economic damage in terrestrial and marine ecosystems. A global pattern of marine invasion is emerging, suggesting high densities of invaders at mid-latitudes with declines towards the tropics and polar regions. It has been proposed that high biotic resistance (ability of native communities to suppress invasion) may be driving this pattern in the tropics as a result of high species diversity. However, propagule pressure (number and rate of recruit arrival) is also known to be a major determinant of invader establishment and available evidence suggests that this also varies along a latitudinal gradient. Therefore, it is unclear if this global pattern of invasion is the result of biotic resistance, propagule pressure, or their interaction. I propose to experimentally alter propagule pressure and biotic resistance at field sites within the Tennenbaum Marine Observatory Network in order to clarify the roles of both of these ecological processes in shaping biogeographic patterns of invasion. I will use the comparative-experimental approach, establishing identical replicated experimental assemblages of focal invaders (solitary and compound tunicates) among three regions of the observatory network (SERC, SMSFP, STRI) that span 29° of latitude.

This proposed research incorporates classic ecological concepts (latitudinal gradient in species richness, biotic interactions hypothesis, supply-side ecology) with applied problems (invasions) to advance our understanding of the relationship between marine biodiversity and anthropogenic processes. Furthermore, this work is of management importance because invasive species can incur significant economic costs and are a threat to native biodiversity.