Over Under Sideways Down*: Inertia of a Transforming Food Weband Extinction Debt for Delta Smelt

* The Yardbirds, 1966

Bill Bennett Center for Watershed Sciences

Bodega Marine LaboratoryUC-Davis

J. Durand, 2015

Conceptual Model: Aquatic Food Web

Food Web & Extinction?

Alien food web rapidly transforming nativefood web.

A little Theory…Habitat loss, Hysteresis, and Extinction Debt

Evidence?

Is Extinction Inevitable?

Exotic SAV

Native SAV

Courtesy: Erin Hester,CSTARS, S. Ustin, UCD

Can “Flow” Alone Reverse the Regime?

Hysteresis – Muchharder to push system back!

Distribution of SAV June 2008

Boat samples withGPS referencing.

Exotic SAV primarily Brazilian waterweed.

1980 1990 2000 2010

0.0

0.1

0.2

0.3

0.4

0.5

0.6

De

lta

sm

elt

(g

m-3)

Delta smelt

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Largemouth bass

Bluegill sunfish

Redear sunfish

Ce

ntr

arc

hid

sp

p.

(g m

-3)

Inertia of Food Web Transformation

Egeria expansion:(Graph, S. Ustin 2016)

Centrarchid expansion:(Data, USFWS Beach seines)

Alien fishes: range expansion lags Egeria by

~ 10yrs.

Erkkila et al.1948-49

Historical Habitat Use

Historical Habitat Use

4,615

55%

1,570

19%

585

7%

409

5%

399

4.8%

324

4%

135

1.6%

0

0

00

0

Erkkila et al.1948-49

7

0.08%

26

0.30%

1

0.01%

135

1.6%

5

0.06%

0.64%

Historical Habitat Use

L. Radtke, 1966

Sampling 1963-64

Historical Habitat Use

MacCall’s (1990) Basin Model: Sardines -Individuals fill-up habitat of highest quality 1st, and then spill-over.

Errikla, 1940s

Hab

itat

Qu

ali

ty

Habitat Landscape

Depth indicates

optimal habitat.

Historical Habitat Use

MacCall’s (1990) Basin Model:

Mid-water Trawl > 2002

Hab

itat

Qu

ali

ty

Habitat Landscape

Historical Habitat Use

MacCall’s (1990) Basin Model:

Current

Hab

itat

Qu

ali

ty

Habitat Landscape

Historical Habitat Use

MacCall’s (1990) Basin Model:

Current

Hab

itat

Qu

ali

ty

Habitat LandscapeSuisun Bay

& Marsh

Cache Sl. &

Ship-channel

“The Alamo”

Sacramento R.

“ The Arc”

San Joaquin R.

& South Delta

Food Web & Extinction?

Habitat loss most important cause of extinction.

Most apparent for small-bodies species facedwith fragmented habitat.

Extinction Debt. Habitat has declined fasterthan ability to adapt. “You’re dead, but you don’t know that!” An extension of metapopulationtheory (Levins 1970, Tilman 1994).

Extinction Debt ?

Dynamic Regime Shift

Hysteresisreflects

Extinction Debt

-3 -2 -1 0 1 2-1

0

1

2

3

4

576

77

78

79

80

81

82

83

848586

8788 89909192 9394

95 969798 990001 02 0304 05060708 09

10 1112

131415

De

lta

sm

elt

(m

-3)

Water exports (m-3 sec)

0 5 10 15

0.0

0.2

0.4

0.6

Aut

ocor

rela

tion

lag

1

Years

P = 0.002, R2

= 0.53

System Behavior Indicates Regime Shift

Evidence for system dynamics slowing-downin years < 2001.

Points = autocorrelationcoefficients at lag 1, foryears before 2001.

Method: Dakos et al. 2008Proc. Nat. Acad. Sci.

Delta smelt biomass

Is Extinction Inevitable?

a. Delta region has fundamentally changed – since about 2000, it has undergoing a rapid transition to a new dynamic regime characterized by an alien food web.

b. Delta smelt disappearing, but historic optimal habitat hasn’t changed much; i.e., densities way down but optimal habitats still have highest densities.

c. Hysteresis associated with regime shift also reflects Extinction Debt.

d. Extinction is inevitable -UNLESS fundamental change occurs to halt the inertia of the alien food web.