1. Multiscale regime shifts and planetary boundaries Hughes et al (2013) Kimberly Duong January 6, 2016

2. Regime Shifts Loosely defined by authors as “major changes in ecosystems” that occur when the climate or biosphere surpasses a tipping point In resilience theory, the stability landscape is characterized by peaks and valleys Interacting causal networks of slow and fast processes erode the resilience of a system Anthropogenic activities change shape and depth of valleys and influence the tendency towards or away from regime shifts

3. Tipping point Nonlinear relation between driver (or cause) of a regime shift and the eventual state of an ecosystem in equilibrium Slope of relation becomes steeper if positive feedback loops are present Smooth, slow or incremental ecological change over time may be the lagged transient response of ecosystem that has passed the tipping point

4. Slow responses Regional and planetary scale responses can occur slowly during regime shifts – Example: response to global warming after last ice age took 1000s of years to happen Important: transgressing global tipping points is unlikely to manifest as sudden The speed of transition is not important, but the presence or absence of tipping points is

5. Dinosaurs Dinosaur extinction at the end of the Cretaceous prompted mammals to expand in population This is an irreversible transition, a planetary- scale regime shift At the end of the Cretaceous, multiple cycles of climatic cooling stressed Cretaceous ecosystems, bringing it closer to a global tipping point that occurred in the form of a meteor impact

6. Drivers of change Major regional/global drivers of ecological regime shifts – Climate change – Land-use change and harvesting – Direct manipulation of biogeochemical cycles – Toxin release – Invasive species Important to distinguish external drivers from internal responses – (ex) Habitat fragmentation is not a driver of change. It’s an internal response to overharvesting (the driver)

7. Conclusion 1) Don’t confuse rate of change (may be fast or slow) with presence of absence of tipping point. A slow rate of change or lagged response doesn’t indicate absence of tipping point. 2) Don’t confuse internal responses for external drivers. – Anthropogenic drivers = climate change, overharvesting – Internal responses = habitat fragmentation, biodiversity loss, emergent diseases

8. Source Hughes, T. P., Carpenter, S., Rockström, J., Scheffer, M., & Walker, B. (2013). Multiscale regime shifts and planetary boundaries. Trends in Ecology & Evolution, 28(7), 389-395.