Decoupling the direct and indirect pathways of basal plant facilitation: A test of the double magnet hypothesis for pollinators.

PROGRESS REPORT – MARCH 2015

Ally Ruttan, MSc Candidate

Decoupling the direct and indirect pathways of basal plant facilitation: A test of the double magnet hypothesis for pollinators.

Positive interactions

Positive interactions

Magnet hypothesis

Magnet Hypothesis

Magnet (shrub)

+

+

-

Target

(annuals)

+

-

+

Net Outcome

Magnet (shrub)

+

+

-

Target

(annuals)

+

-

+

Net Outcome

Magnet Hypothesis

Magnet Hypothesis

Magnet (shrub)

+

+

-

Target

(annuals)

+

-

+

Net Outcome

+

O

O

+ –

+ + +

+

1

2

3

4 5

6

1. Facilitation of annuals by shrub indirectly provides resources for pollinators 2. Positive, bidirectional relationship between shrub and insect (pollination of shrub, food resource for pollinators) 3. Positive, indirect, bidirectional relationship between shrub and annuals for the attraction of pollinators 4. Shrub facilitates annuals directly through amelioration stress and access to resources 5. Bidirectional competition between shrub and annuals for resources (including pollinators) 6. Positive, bidirectional relationship between annuals and pollinators (pollination of annuals, food resource for pollinators)

A

B

1

1

2

2

Double magnet hypothesis

Chapter 1

A systematic review of the magnet species hypothesis for plant-pollinator interactions

Chapter 1 - Purpose

To determine the extent of study and methodologies applied to the magnet species hypothesis. 

Chapter 1 – Research Questions

What ecosystems are most commonly used to test the magnet hypothesis? What is the diversity of pollinators tested via the magnet hypothesis? What observational approached have been used in testing the magnet hypothesis (e.g. pan trapping, video, in-situ, etc.)? Are there specific focal species used as a magnet or many different ones? Are there underlying ecological theories explicitly associated with the magnet hypothesis?

Chapter 1 - Methods

(Magnet hypothesis OR magnet species OR pollinator facilitation OR co-flower) AND pollinat*

Chapter 1 - Methods

(Magnet hypothesis OR magnet species OR pollinator facilitation OR co-flower) AND pollinat*

228

Chapter 1 - Methods

Refined for relevance….

44

All visitors

(5)

All insects (27)

Bees (2)

Target bee

species (7)

Social bees (2)

Birds (1)

0

5

10

15

20

25

30

35

40

45

in situ collection proxy video

Freq

uenc

y

Observation method

Chapter 2

A survey examining the island effect of shrubs on understory plant pollination and reproductive patterns

Study site

Chapter 2 - Purpose

Test the capacity for entomophilous and anemophilous shrubs to act as magnets for the pollination of understory plants and the shrubs themselves.

Chapter 2 - Hypothesis

Shrubs (particularly entomophilous ones) act as resource islands/magnets that attract pollinators and increase the reproductive success of understory plants.

L. tridentata A. dumosa

Chapter 2 - Predictions

1.  Annuals under shrubs (especially L. tridentata, flowering magnet) will do better than in open microsites (abundance, pollen deposition, seed production).

2.  Lower annual density = increased seed set (competitor release)

3.  Seed set of L. tridentata (but not A. dumosa) will be positively correlated with annual floral density (assuming strict pollinator matching to floral densities, ignoring resource levels).

30 paired shrub/open sites 2 species

3 annuals x 3 species per site

1 flower per annual 1 seed head per annual

Chapter 3

The double magnet hypothesis: separating the direct and indirect effects of plant facilitation on pollinators

X Y Z

Chapter 3 - purpose

Contrast direct/indirect effects of shrubs and annual plants on desert pollinator communities and map important shrub traits onto extended community dynamics

Chapter 3 - Hypothesis

The floral resource island created by shrubs and the beneficiary annual plants will have positive non-additive effects on pollinator visitation rates.

Chapter 3 - Predictions

1. Annual plants under shrubs will have a higher frequency of pollinator visitations than annual plants in open microsites

2.  Shrubs with annuals in their understory will have a higher frequency of pollinator visitations than shrubs without annuals due to the concentration of floral resources

3.  Sites with both shrubs and annuals will have the highest frequency of pollinator visitations to both the shrubs and the annuals

Inse

ct V

isita

tion

Annuals Removed

Annuals Intact

shrub microsite open Microsite

A.

B.

C.

natural variation controlled variation phytometer

= shrub only

= annual first, then shrub

= annual only

= shrub first, then annual

*bonus experiment 1* – Fluroescent pollen dye

Timeline

Chapter 1: Data inputted/writing complete Sept 2015

Chapter 2: Survey mid-March to mid-April

Chapter 3: March: removals Late March – April (natural/controlled variation) April – early May (phytometer)

Thanks!