Complex sentence: Folke et al state that the likelihood of sustaining development is raised by "Managing for resilience" whilst Perman et al propose that safeguarding the environment to "deliver a set of services" should be a "necessary condition for an economy to be sustainable".
Split into simpler sentences: Folke et al state that the likelihood of sustaining development is raised by "Managing for resilience". Whilst Perman et al propose that safeguarding the environment to "deliver a set of services" should be a "necessary condition for an economy to be sustainable".