What happens when connectivity can vary over time?

In some ecological systems, individuals are only able to move between populations given a specific event, such as butterflies that require fires to clear old-growth forest and connect populations in open meadows. Such disturbances and other intermittent events can create “transient connectivity windows” – which we define as a limited period of time during which the conditions between habitat patches increase the probability that one or more individuals will move successfully between those patches. Other examples of such systems include populations of fish species on separate branches of a river that are only connected following major floods, mosses that require the presence of flies to carry spores between habitat patches on dung piles, and marine species that are only connected by atypical oceanic currents following an El Nino period. Little is known about the implications of dynamic changes in connectivity, and, to our knowledge, there are few tools that can explicitly consider intermittent changes in connectivity between habitat patches. In this paper, we examined the literature to better understand the consequences of variability in connectivity and to highlight knowledge gaps on this topic. We describe how connectivity can vary along a temporal gradient, from systems where connectivity windows only open after rare events (e.g., a 500 year flood) to systems where those windows open seasonally (e.g., such as following the seasonal flooding that occurs in the Florida Everglades and connects a variety of wetland habitats). We also examine how variability in connectivity is important for the survival of populations. This research is particularly relevant given that climate change, which is altering precipitation, temperature, and disturbance patterns, will likely impact how frequently and for how long connectivity windows will open between populations.