ESA 2015 Baltimore, MD

Limits to plant diversity: an experimental decoupling of local and regional control

Rachel M. Germain1, Sharon Y. Strauss2, and Benjamin Gilbert1

1. Dept. Ecology & Evolutionary Biology, University of Toronto; 2. Dept. Ecology & Evolution, UC Davis

A metacommunity perspective of diversity

diversity ~ local processes + regional processes + their interaction

Metacommunity diversity

Modified from Leibold et al. 2004 EcoLett

Species sorting Source-sinkDispersal limitation

Identifying the processes that structure metacommunity diversity is challenging, because different processes can lead to similar outcomes

dispersal

Manipulating dispersal in a natural system

Speciesmixer

? ?

? ?

Diversity responses to the removal of dispersal limitation

Species sorting

Loca

l div

ersit

y

small large

Loca

l div

ersit

y

small large

Spatial scale of mixing

Spec

ies-

envi

ronm

ent

rela

tions

hips

small large

Spatial scale of mixing

Spec

ies-

envi

ronm

ent

rela

tions

hips

small large

Source-sink

?

?

Dispersal limitation

Loca

l div

ersit

y

small large

Spatial scale of mixing

Spec

ies-

envi

ronm

ent

rela

tions

hips

small large

Research questions1. Which metacommunity process best explains

diversity patterns in natural communities?

2. How does removing dispersal limitation at multiple scales affect metacommunity diversity?

: McLaughlin

serpentine metacommunity ▪ water limited ▪ many annual species

Experimental design: seed vacuuming procedure

Vacuuming procedure modified from Coiffait-Gombault et al. 2010 Restor Ecol

Environmental parameters were measured concurrent to the community survey

% soil moisture

Experimental design: plot locations

1 m 5 m 100 m 5 km 10 km

Each plot in a block received seed that were mixed from plots at five different spatial scales (the other three plots were control plots)

30 serpentine sitesarranged in six clusters offive sites

Each site contained a block of eight 0.75 x 0.75 m plots

Spatially nested plot arrangement

1 m = essentially natural diversity patterns 10 km = dispersal limitation completely removed

1 m5 m100 m5 km10 km

1 m

Result 1: Plot-level species richness increased with the spatial scale of seed mixing

lmer(species richness ~ treatment + (1|site))

NS

NS

Result 2: Community composition shifted with the spatial scale of seed mixing

1 m5 m100 m

10 km5 km

Example of spatial scaling effects on diversity

1 m 10 km

Plantago erectaHemizonia congestaMicroseris douglasiiLepidium nitidium

Plantago erectaHemizonia congestaMicroseris douglasiiLepidium nitidium

Rigiopappus leptocladusLasthenia califoricaCollinsia sparsifloraLotus wranglianus

What can the effects of removing dispersal limitation reveal about the specific metacommunity class that structures diversity?

Result 3: Species-environment associations increase with the spatial scale of seed mixing

5 km

100 m

Result 4: Species composition shifts with % soil moisture

0.45 0.35 0.05 0.20 0.20 R2

1 m5 m

10 km

lmer(axis scores ~ % sm *treatment + (1|site))

5 km

Community level

Species- vs. community-level environmental associations

1 m5 m100 m

10 km5 km

1 m

Species level

P = 0.011

0%

Even in communities with strong environmental determinism, dispersal limitation can still be widespread

Summary of results

Diversity increases non-linearly with the spatial scale of removed dispersal

Species-environment associations increase with the scale of the species pool

x x

The shifting importance of metacommunity processes with spatial scale of dispersal removal

1 m 5 m 100 m 5 km 10 km

dispersal limitation source-sink species sorting

Figure modified from Bell & Lechowicz 1991 JEcol

x x

The shifting importance of metacommunity processes with spatial scale of dispersal removal

1 m 5 m 100 m 5 km 10 km

dispersal limitation source-sink species sorting

suitable

Figure modified from Bell & Lechowicz 1991 JEcol

AcknowledgementsThe Gilbert LabThe Strauss lab

Susan HarrisonCaprice LeeErica CaseStella CopelandBrian Anacker

Webpage: rgermain.wordpress.com Email: [email protected]

Paola ArenasLaurren SergisonKate LeCroy

Cathy Koehler