Connectivity refers to the structure and strength with which resources, species or actors disperse, migrate or interact across patches, habitats or social domains in a social-ecological system. Consider, for example, patches of forests connected in a landscape: the forest landscape is the system, the forest patches are parts of the system. How they are linked together determines how easy it is for an organism to move from one patch to another. In every system, connectivity refers to the nature and strength of the interactions between the various components. From a social network perspective, people are individual actors within a system embedded in a web of connections.
Connectivity can influence the resilience of ecosystem services in a range of ways. It may safeguard ecosystem services against a disturbance either by facilitating recovery or preventing a disturbance from spreading. The effect on recovery is demonstrated in coral reefs. Closely situated reef habitats with no physical barriers enhance recolonisation of species that may have been lost after disturbances such as storms. The basic mechanism is that connections to areas that serve as refuges can accelerate the restoration of disturbed areas, thus ensuring the maintenance of functions needed to sustain the reef and their associated ecosystem services.
Perhaps the most positive effect of landscape connectivity is that it can contribute to the maintenance of biodiversity. This is because among well-connected habitat patches local species extinctions may be compensated by the inflow of species from the surroundings. Reduced connectivity caused by anthropo-genic fragmentation, like road or dams, has a negative effect on population viability, particularly among large mammal popula-tions. The Yellowstone-to-Yukon (y2y.net) project in North America is an example of conservation planning that reconnects large habitat patches by re-establishing wildlife corridors. Through a variety of collaborative initiatives with diverse stakeholder groups, Y2Y’s primary objective is to connect eight priority areas that function as either core wildlife habitat or key corridors in an area spanning 1.3 million square kilometres.
However, too much connectivity can also be a problem. Limited connectivity can sometimes boost the resilience of an ecosystem service by acting as a barrier to the spread of disturbances such as a forest fire. On the other hand, an overly connected system may reduce the probability of population survival when all populations are affected by the same disturbance, for instance a fire or disease.
In human social networks, connectivity can build resilience of ecosystem services through enhanced and improved governance opportunities. High levels of connectivity between different social groups can increase information sharing and help build trust and reciprocity. Certain actors can serve as connectors to other actors and bring in outside perspectives and new ideas to local issues. However, just as high landscape connectivity can increase the risk for simultaneous exposure to a disturbance, well-connected actors with similar types of knowledge, and preferences for immediate gains over longterm resilience, can lead to negative outcomes. Studies show that when homogenisation of norms occurs, the explorative ability of social actors drops, leading to a situation where the network members all think in the same way and may believe they are doing well while they are actually heading towards unsustainable pathways. How can we manage connectivity?
As with all principles, putting them into practice is inevitably context dependent. To operationalise connectivity is an ambitious endeavour, but a few guidelines include:
Map connectivity. In order to understand the effect of connectivity on the resilience of an ecosystem service, the first step is to identify the relevant parts, their scale, their interactions and strength of connections. Once this is done, visualisation and network analysis tools can help reveal the structure of the network.
Identify important elements and interactions. To guide possible interventions and optimise connectivity, it is important to identify central nodes or isolated patches in the system. This helps to identify vulnerable and resilient parts of the system.
Restore connectivity. This involves the conservation, creation or elimination of nodes. One example is the Monteregie Connection project in southern Quebec, Canada. Here, forests and people are connected to make the landscape and its ecosystem services more resilient to environmental change.
Optimise current connectivity patterns. In some cases, it may be useful to reduce or structurally change the connectivity of a system (e.g. by making it more modular) to increase the resilience of a system. For instance, the loss of electricity across the eastern USA and Canada in 2003, which affected some 50 million people, is an example of a network where local failures in a highly connected system eventually led to a total, systemic collapse.