Ecosystem engineering in a changing environment: R-tipping and transients

Background/Question/Methods

Ecological interactions occur in a physical matrix created by the organisms themselves. Some easy to recognize examples include coral reefs, forests, burrows and associated burrow aprons. In particular, burrowing engineering that affects terrestrial soils and their properties is particularly likely to be long-lasting and have wide community impacts. Similar burrowing impacts in aquatic environments may, in contrast, have quite short persistence times. For example, arctic fox burrows are large structures can last up to hundreds of years, even while undergoing periodic abandonment. These burrows have impacts on the favoured prey, lemmings, where the prey species is attracted to the burrows of its predator because of beneficial alterations to vegetation and snow cover. Burrows in aquatic systems have also been shown to have important benefits for prey species. For example, larvae of endangered Hine's emerald dragonfly uses crayfish burrows during drought in wetlands. It is unclear how the persistence of these important structures, and the related predator-prey dynamics, will be altered with climate change. Impacts on factors that promote the degradation engineered structures are expected in some cases, through increases in soil temperatures, increased rainfall and decreased snow cover.

Results/Conclusions

We examine some simple nonautonomous models with an engineering predator and a prey species that can benefit from the engineered structure. We explore how changes to climate may impact the stability of the system through changes in the degradation rates of engineered structures. This degradation rate is a key parameter for determining the long-term dynamics. Low degradation rates can produce persistent structures which promote the coexistence of the predator with the prey at higher densities than if the predator was not in the system. At high levels of degradation, predators can drive the prey to extinction. The rate at which climate changes alters this degradation parameter can impact the expected outcome as well. Where change is slow, an large "banked" amount of engineered structures can build up, tracking a previous high density state, which effectively produces a long slow transient of decline in prey density. With fast rates of change, prey extinction can occur quite quickly, while a slow oscillatory increase in degradation rates produce transients of medium length. Understanding climate impacts on engineered structures, and in particular, how the rate of of climate change is impacting ecosystem dynamics, may allow for a useful triage of mitigation management efforts.