Change in such systems is difficult to understand employing conventional analytic approaches alone, but require new thinking and analytical methods drawn from complex systems theory. The discontinuous character of the processes or variables makes their interaction intuitively improbable except for the mediating effect of 'cross-scale influences' as illustrated in Figure 2 . Examples include the eruption of Hantavirus in the American Southwest, thought be associated with weather events precipitated by El Nino Southern Oscillation. Storms events are similarly episodic, and represent a discontinuous form of variation transporting pathogens via flood waters in domestic and natural environments. On the other hand, massive environmental events, like the recent Southeast Asian tsunami, are potentially capable of producing epidemics across an entire region, and may episodically extinguish some zoonotic diseases by temporarily destroying reservoir and vector populations and habitat. The roles of resilience and vulnerability in determining the severity of such events, both in terms of social systems and ecological systems is another critical aspect of social-ecological systems behavior (8) .