BIOTIC RESPONSES TO SHIFTING ECOLOGICAL DRIVERS IN A DESERT COMMUNITY

S.K. Morgan Ernest

Dept of Biology & Ecology Center, Utah State University

@skmorgane

Static Mentality

Dynamic Reality

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

Shifting Drivers• Driver: Controls the state of an ecosystem

Eco

syst

em D

river

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 ShiftsGinger 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?

Driv

er S

hift

Mag

nitu

de

Number of shifting drivers

Case Study 2: Long-term Driver Shifts

Brown et al (1997) PNAS

19951977

Year

Num

ber

of s

hrub

s

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: 20-30 year cycle

• Warm Phase:• La Nina – average winter

precipitation• El Nino – higher than

average precipitation

• Cool Phase: • La Nina – drought• El Nino – average winter

precipitationGutzler et al. (2002); Flagstaff NWS Office: http://www.wrh.noaa.gov

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

Eco

syst

em S

tate

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