BIOTIC RESPONSES TO SHIFTING ECOLOGICAL DRIVERS IN A DESERT COMMUNITY S.K. Morgan Ernest Dept of Biology & Ecology Center, Utah State

Static Mentality

Dynamic Reality

Shifting Ecosystems: Regime Shifts e.g. Scheffer et al. (2001) Nature

Shifting Drivers Driver: Controls the state of an ecosystem Ecosystem Driver Time

Shifting Climate Driver

Biotic Responses

Shifting drivers, biotic responses Two case studies: Short-term driver shifts Eruption of an exotic species Long-term driver shift Increasing shrub cover

LTREB Portal Project - Background Initiated 1977 by Jim Brown and associates Monitor rodent and plant dynamics Diverse rodent & winter and summer annual communities Portal

Portal Project - Background Control plots, kangaroo rat exclosures, rodent exclosures Responses to climate and plant responses to granivory

Case Study 1: Short-term Driver Shifts Ginger Allington, David Koons, Morgan Ernest, Michelle Schutzenhofer, Thomas Valone State Change: Exotic species increase Exotic species: Erodium cicutarium Allington et al (2013) Ecology Letters Population increase

Short-term Driver Shifts Biotic Driver: When kangaroo rats or all rodents experimentally reduced, Erodium increases. Allington et al (2013) Ecology Letters Population increase

Short-term Driver Shifts Biotic Driver: Considerable variation in kangaroo rats and other rodents through time Allington et al (2013) Ecology Letters Population increase

Short-term Driver Shifts Abiotic Driver: No variation across site, but considerable temporal variation in precipitation. Allington et al (2013) Ecology Letters Population increase

Short-term Driver Shifts Biotic Driver: Extended drop in kangaroo rat consumption before eruption Allington et al (2013) Ecology Letters Population increase

Short-term Driver Shifts Abiotic Driver: Preferred levels of precipitation before kangaroo rats could recover Allington et al (2013) Ecology Letters

Best explanation: perfect storm Allington et al (2013) Ecology Letters

Niche Opportunities Driver shifts create niche opportunities (Shea & Chesson 2002) How many drivers and what magnitude to create niche opportunity? Driver Shift Magnitude Number of shifting drivers

Case Study 2: Long-term Driver Shifts Brown et al (1997) PNAS Year Number of shrubs The State Change: Arid Grassland to Shrubland

The Driver: Precipitation Long-term increase in winter precipitation Winter precipitation and shrub growth Brown et al (1997) PNAS

PDO and Southwest Precipitation Pacific Decadal Oscillation: year cycle Warm Phase: La Nina – average winter precipitation El Nino – higher than average precipitation Cool Phase: La Nina – drought El Nino – average winter precipitation Gutzler et al. (2002); Flagstaff NWS Office:

PDO Rain Shrubs Rodents Ernest et al 2008 Am Nat

What will tomorrow look like? ? end Cool cycle end Warm cycle end Cool cycle?

Long-term Driver Shifts & Reversals Multiple drivers and the problem of ‘reversing’ state changes Driver Condition 1 Driver Condition 2 Driver Condition 1 fire Ecosystem State: Single Driver Ecosystem State: Multiple Drivers

Regime Shift Theory Focused on non-linear state- driver relationships Multiple driver shifts Natural shifts & anthropogenic shifts Ecosystem Driver Ecosystem State

What will tomorrow look like? ?

Acknowledgments Portal Project: Hundred of volunteers, postdocs, graduate and undergraduate students Alan Ernest Funded by NSF for almost 35 years Most recently by NSF LTREB & Utah State University