DECOUPLING THE MECHANISTIC PATHWAYS OF

INTERACTIONS BETWEEN SHRUBS AND ANNUAL

PLANTS IN SEMI-ARID AND ARID ECOSYSTEMS.

Alessandro Filazzola

MSc Candidate

Progress Report – March 19th

Nurse-protégé Dominant-Subordinate

Sensu Grime 1998

Plant Interactions

Novelty

Novelty

More than one dominant mechanism may operate at a time

Smit et al. 2009

Novelty

Herbivore Protection

Abiotic stress reduction

Increased Herbivory

Abiotic stress reduction

Herbivore protection

Resource competition

Novelty

Positive plant interactions change with plant life-stage

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10

Pla

nt

Tra

it

Distance from Dominant

Juvenile

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10

Pla

nt

Tra

it

Distance from Dominant

Juvenile

Adult

Adapted from Miriti 2006

FarNear

Novel contributions to ecological theory

Decouple plant interactions by life-stage

Decouple mechanistic pathways

Biotic(5)

Seed Germinant Adult Flowering Reproduction

Abiotic(3,5)

Factors

Dominant

Subordinate

Seed Trapping*(4)

*

*

Chpt Title Progress

1 A systematic review and conceptual framework for

the mechanistic pathways of dominant plants

Re-submitted to GEB March 10

2 A meta-analysis of benefactor plant mechanisms

based on beneficiary life-stage.

Papers compiled – Data needs to be

extracted.

3 Ontogenetic shifts from positive to negative

interactions between desert plants change on an

environmental gradient.

January to April 2014

4 Shrubs directly and indirectly increase seed

densities under canopy in arid environments.

Preliminary census 2013 complete

5 Experimental manipulations of micro-

environmental conditions and herbivory of shrubs

in an arid system.

To be set up – April 2014

6 Experimentally testing the importance of the shrub

(E. californica) as a tool for restoration of semi-

arid grasslands

Need to meet with local land managers

Chapter 3

Purpose: To determine how desert shrubs mediate

annual plant productivity to changes in drought

stress and subordinate progression through plant life-

stages.

H: The sign of net interactions between shrubs and

annuals changes with annual plant life stage and

water availability.

Chapter 3

2013 Measure shrub characteristics

2014 Artificial water gradient

2014 Ambient water gradient

RII S

oil

Mois

ture

Chapter 4

Purpose: To determine if facilitation of annual seeds

by shrubs is a dominant pathway responsible for

annual plant distribution in desert environments.

H: Shrubs act to increase seedbank densities for

annual plants in desert systems either directly or

indirectly.

Chapter 4

Seed Adult Reproduction

1) Compare Microsites Shrub > Open

2) Compare controls C > S

3) Compare seeds removed A > O

4) Compare effect size of 2 & 3 2-e+ > 3-e+

1) Compare Microsites Shrub > Open

2) Compare controls C > S

**Both shrubs and annuals increase seed arrival**

0

100

200

300

400

500

600

700

800

900

1000

Plants & Seeds Seeds only

Nu

mb

er

of

Se

ed

s

Treatment

Shrub

Open

0

50

100

150

200

250

300

350

400

450

No seeds & artifical plant No seeds

Nu

mb

er

of

Se

ed

s

Treatment

Shrub

Open

3) Compare seeds removed A ≠ O

4) Compare effect size of 2 & 3 2-e+ > 3-e+

**Annuals increase seed arrival through increased reproduction**

Chapter 5

Purpose: To decouple shrub-mediated herbivory

effects on annuals from micro-environmental effects.

H: The relative difference in annual plants between

shrub and open microsites decreases with

reductions in consumer pressure and drought stress

Measure subordinate response

Biotic

Seed Germinant Adult Flowering Reproduction

AbioticFactors

Dominant

Subordinate

Chapter 5

Chapt Title Short term goals Long Term goals Dates

3 Ontogenetic shifts from

positive to negative

interactions between desert

plants change on an

environmental gradient.

Repeat census, collect biomass

and seeds, environmental data

Paper submitted for August

2014

Jan-April

census

2014

4 Shrubs directly and indirectly

increase seed densities under

canopy in arid environments.

Repeat census, add new seed

capturing devices and

measurements

Decouple the direct and

indirect mechanisms of seed

facilitation

Jan-April

census

2014-2016

5 Experimental manipulations

of micro-environmental

conditions and herbivory of

shrubs in an arid system.

Set up herbivory exclosures Water additions in 2015 and

measure annual success.

Jan-April

census

2015-2016

Upcoming field work

Thank you!