I’m going to talk about feedbacks, interactions, and regime shifts in social-ecological systems. And this is basically the idea of how ecosystems, or social-ecological systems, can go from being organized in one way to being organized in a very different way.

And this is a concept that’s been around for a long time in ecology, and is in many other fields under many different names. And the term I’m going to use is regime shifts, but this also can be talked about in terms of tipping points, alternate ecological states, or critical transitions.

And what I mean when I say a regime shift, I use the definition, which is focused on people and the way they interact with nature. So thinking about, some change in a social-ecological system where you go from getting one set of ecosystem services to a different set.

And this persists over a time that matters for people, so usually at least a couple of years. And there’s some kind of stickiness to this that makes it, not just go back to where it was before, but there’s something that keeps it in this new type of state. So this is showing in this figure where you’re going from one set of ecosystem services to another, and there’s some really, distinct change over time, which persists.

So, why is this important? Why is this a useful concept? Well, there are two reasons why it’s useful.

• One is that a lot of ways people think about the world are based on sort of gradual or linear change, when that isn’t always true, how things happen. So, it’s at least sometimes useful to think well, what happens when we have changes that are abrupt and persistent?
• The other one is that these types of changes often have much bigger impacts on people. If a fishery, so say like the Newfoundland cod fishery, ends up closing as the Newfoundland fishery’s been closed for 20 years, this has huge impacts on both individual fishermen, but also the ability of towns to survive. So, these impacts can have very big consequences. Also when these occur they’re not easy to reverse. So once you’ve gone over these thresholds it’s much harder to come back; both in terms of the amount of effort, and in terms of costs in human resources and money. Finally, one of the other things that’s very tricky about regime shifts is that they’re very difficult to predict, even when we know they can occur.

So say, for example, people who study lakes. We still don’t know when exactly they’re going to occur, because they are non-linear and difficult to predict. So this means we often need to think about managing things differently.

And this requires thinking about the context, the history, and the possibility of surprise rather than just trying to get things right or trying to adjust to some kind of thermostat or dial to get the optimal outcome. So it’s really quite a different way of thinking about things when regime shifts occur.

So, what is a real example of regime shift? Well, one of the best studied ones in the world is coral reefs. In coral reefs all over the world there’s been shifts from diverse coral reefs, which are: dominated by coral, have rich fish populations, often have ability to support lots of tourist industries and protect the coast from storms, to algae-dominated reefs where there’s much less fish often, much smaller fish, and not a diverse community of things. And this can have big impacts for both the ability of local people to persist, and on the conservation of nature.

But not all big changes that you see in nature are regime shifts. For example, stuff can change around a lot, but if it returns to where it was before it’s not really regime shifts. This figure is trying to show an example of this. If you have something changing over time and you get maybe a storm, or you get some invasion of a new species and the system changed in the response, that’s not a regime shift.

A regime shift is when you get a big shift, which doesn’t go back to where it was before. And so you can see evidence for these regime shifts in time series stayed over time, but you can also guess that often it can be quite ambiguous of actually whether you’ve got a regime shift of not. And it can take some time to resolve this. So often there’s some uncertainty about what’s going on with regime shifts.

But one of the key things of regime shifts is that they’re maintained by feedbacks. And this figure here is showing an example of one of the other classic types of regime shifts, which is the change of shallow lakes from being clear water to being turbid and full of algae.

And there’s feedbacks that maintain both of these regimes, and it’s the competition between these different types of feedback; between a benthic-dominated, clear water regime, and a pelagic-dominated murky water regime that controls how likely you are to have one of the regime shifts to occur. And when you have these regime shifts occur different feedback dominate. So to understand regime shifts requires understanding feedbacks.

A simple way of thinking about this is that these types of regime shifts are generic features that you can expect to occur in all types of complex self-organizing systems, where you have lots of different processes interacting with one another. That’s because a whole bunch of different feedback processes interact. And a way of simplifying this is these sort of ball and cup diagrams, representing a whole set of complex interactions as a ball, which is representing your system, or your ecosystem or social-ecological system, and a landscape where the shape of the landscape is determined by the interacting feedback loops.

So this is saying you can think about how regime shifts occur in two ways.

• One is where you have shocks, which cause the feedback process to be overwhelmed, and a system to shift from one state to another. For example, a big pulse of nutrients coming into a lake can cause a lake to shift from being clear water to being turbid water.
• The other less obvious one is changes in the feedback processes themselves that can reduce the resilience, or the ability to persist in one of the states. So this could be, for example, changes in the fish community of a lake could reduce the ability of the lake to cope with nutrient inputs.

So all these kind of inputs that formerly wouldn’t cause a shift in a lake start to be able to cause a shift in a lake, and maybe unexpectedly you get a big shift which you can’t go back to because the feedback processes have changed.

And this is often one of the key features of regime shifts, is this gradual erosion of resilience where shocks that previously could be coped with, can’t be coped with. And this is also one of the things that makes predicting regime shifts so difficult, because even if you fully understand these slow processes the actual triggers of the regime shifts are these very difficult to predict, or almost unpredictable, shocks. But often it’s quite difficult to understand these slow processes.

So just to kind of wrap up, what does this mean for management? Well, there’s basically three different ways you can kind of think about managing regime shifts, and this goes with thinking about the shocks and slow variables.

• The first one is to try and think well what are all these perturbations that are affecting a system and how can you reduce the ability, the exposure of the system to these perturbations? For example, reducing fishing can enhance the ability of coral reefs to persist, or reducing land processes that are putting nutrients into a coral reef can decrease these shocks.
• Similarly you can think about maintaining the feedback loops, or enhancing the feedback loops, that are managing these sort of slow variables that increase the resilience of a system to regime shifts by, for example, ensuring there’s a diverse set of fish, there’s lots of different types of coral structure.
• But finally, and especially something that’s really key to think about in the Anthropocene, as we’re changing processes all around the world, is: well, what are the possibilities of novel regimes, as new species enter a system, new types of human activities? What are novel types of regimes that we either want to really avoid, or we’d like to restore systems to?

So it’s sort of three different ways of thinking about both these fast and slow processes as more normal ways, and then for the Anthropocene trying to think about what are novel outcomes we want to, achieve or avoid.