Impacts of habitat fragmentationon plant and insect communities:

beyond species richness!

• Part 1Using traits to understand impact of habitat fragmentation on plant communities: local vs. dispersal processes

Seminar outline

• Part 2Impact of habitat fragmentation on changes in relative abundance of flower-visiting insects

2. Selection of traits linked to clear ecological hypotheses:

Using traits...

1. Theoretical predictions

3. Test using large scale datasets

Environmental change

Change in trait Composition (e.g. weighted mean)

Environmental change

Trait group A(e.g. Mobile species)

Trait group B(e.g. Sedentary species)

Response

Change in species diversity

Change in species diversity

Response

How does the trait modify the response to the environmental change?

“Traditional approach”

“Our approach”

Test interactions between traits

Impact of habitat fragmentationon plant communities:

local vs. dispersal processes

Marini L., Bruun H.H., Heikkinen R.K., Helm A., Honnay O., Krauss J., Kühn I., Lindborg R., Pärtel M., Bommarco R. (in press) Traits related to species persistence and dispersal explain changes in plant communities subjected to habitat loss. Diversity and Distributions

Impact of grassland fragmentation on plants

Large number of studies testing area and connectivity effect onoverall plant species richness

Area ConnectivityPl

ant s

peci

es

richn

ess

Metapopulation ecology has mainly considered mobile animals and therefore stressed the importance of dispersal processes

However...

Local vs. dispersal processes

For plants, it is expected that species’ ability to both persist locally and disperse are critical in shaping communities

One approach to clarify this is to explore species richness responses to fragmentation for groups of species with shared life-history traits

Sourcepopulation

Occupied patch

Unoccupied patch

Dispersal processesLocal within patch processes

Local processes

Asymmetric competition for light Plant height (short vs. tall)

Increase dispersal success

Starting hypotheses

Asexual reproduction

Dispersal processes

Persistence in the seed bank

Traits

Clonal vs. annual

Persistent vs. transient

Animal (directional) vs. abiotic agent (random)

Seed number(low vs. high)

Processes favouring species robustness to habitat fragmentation

Careful to avoid collinearity between traits!

2. To use traits to understand the relative importance of local vs. dispersal processes

AIMS

1. To test for interactions between traits: do any combination of traits provide higher robustness to habitat fragmentation?

Data

Extinction debt mostly paid in all regions [Krauss et al. (2010) Ecol. Lett.]

Homogenization of taxonomy and plant life-history traits across regions

Orthogonal gradients in area and connectivity (Hanski connectivity index in all regions)

Methods: Mixed model approach in two steps

Species richness~ Trait*Area, random=~1|country/site

Species richness~ Trait A*Trait B*Area, random=~1|country/site

I. Testing ecologically meaningful interactions between traits

II. Testing interactions between single traits and area (or connectivity)

AreaSpec

ies r

ichn

ess

Tall

Short

ConnectivitySpec

ies r

ichn

ess

Annual

Clonal

...

?

Results

No interactions between traits

Negative effect of habitat loss but no effect of connectivity

The effect of area was modified by three traits:1. Plant height (short vs. tall species)2. Clonality (annual vs. clonal)3. Dispersal agent (abiotically- vs. animal-dispersed species)4. Seed bank5. Seed number

Area Connectivity

Spec

ies r

ichn

ess

Results: trait effect

Plant sensitivity to habitat fragmentation

Higher sensitivity to habitat loss for:

1. Small species (low competitive ability for light)

2. Perennial clonal (trade-off between clonality and dispersal?)

3. Abiotically-dispersed species (random vs. animal directional dispersal)

Plant sensitivity to habitat fragmentation

Results match well with other recent studies

Lindborg et al. (2012) Ecography

Plant sensitivity to habitat fragmentation

Results match well with other recent studies

Montoya et al. (2008) Science

Negative Ωj implies a negative response to habitat loss

Conclusions

Our trait-based analyses gain insights into the potential mechanisms leading to plant extinction due to habitat fragmentation

The importance of within-patch local processes have been probably underestimated in fragmentation research so far

The interaction between local persistence and dispersal shaped plant communities

What about changes in relative abundance?

Evenness refers to the relative contribution of each species to the total biomass or number of individuals

Background

Abundance-based measures:-Evenness-Dominance-Species composition-Functional diversity...

Species diversity

Species richness

Species evenness

Evenness

Impact of fragmentation on evenness of flower-visiting insect communities

Marini L. , Öckinger E., Bergman K.-O. , Krauss J., Kuussaari M., Jauker B., Pöyry J., Smith H.G, Steffan-Dewenter I., Bommarco R. (in prep.) Contrasting effect of habitat area and connectivity on evenness of flower-visiting insect communities

Species evenness has been used more often as a driver of ecosystem functioning rather than as a community response

AimsEv

enne

ss

Which are the effects of habitat fragmentation on abundance patterns of flower-visiting insects?

Fragmentation

?

Problems with evenness definition

Looseness of the mathematical definition of evenness: several indexes with different sensitivity to changes in rare or dominant species

The choice of the metric is central in the interpretation of the ecological relationships between environmental drivers and evenness

The most important property is the independence from species richness

Evenness profile

0 0.25 0.5 1 2 4 8 Inf

-2.0

-1.5

-1.0

-0.5

0.0

alpha

E-alpha

Baz1

Baz1

Baz2

Baz2

Baz3

Baz3

Baz4

Baz4

Baz5

Baz5

Baz1Baz2Baz3Baz4Baz5

Increasing importance of changes in dominant species

From the diversity Rényi profile we derived an evenness profile

Diversity profile: Community A is more diverse than a community B if the diversity profile for community A is everywhere above the diversity profile for community B.

Background: General predictionsEv

enne

ss

Connectivity

Local processes promoting evenness:-Larger habitat diversity in large patches-Lower inter-specific competition in large patchesEv

enne

ss

Area

Dispersal processes promoting evenness:-Larger exchange of individuals between patches

Aim: to test these predictions using a large empirical data set

Data

Ten grassland networks(7 for butterflies and 3 for wild bees)

Habitat area

Habi

tat c

onne

ctivi

ty

Orthogonal gradients in area and connectivity

Transect countsProportional sampling

Patch

Results

Increasing importance of changes in dominant species

Spec

ies e

venn

ess

Area

Increasing area

Slope ±CI 95%

Results

Increasing importance of changes in dominant species

Connectivity

Spec

ies

even

ness

Slope ±CI 95%

Increasing connectivity

Weaker effect for bees than for butterflies

Which are the underlying mechanisms?

Fragmentation modifies the specialization distribution

Area

% G

ener

alist

spp.

Area

% G

ener

alist

spp.

Area and specialization

Butterflies Bees (Central foragers)

P<0.01 P<0.01

% M

obile

spp.

Area Area%

Mob

ile sp

p.

Area and mobility

Same patterns for species mobility (body size)

Small patches host less sedentary species than large patches

P<0.01 P<0.01

What about connectivity?

% G

ener

alist

spp.

Connectivity

% M

obile

spp.

Connectivity-evenness relationship

No patterns for bees

P<0.01 P<0.01

Connectivity

% M

obile

spp.

Connectivity

% G

ener

alist

spp.

Negative relationship for butterflies

Interpaly of local and dispersal processes

Local processes:Inter-specific competition (nesting sites, plant resources etc.)

Different local population growth

Dispersal processes:Inter-patch movements

Sedentary and specialists

Mobile and generalists

Increasing importance of dispersal processes

Small patches are dominated by generalist immigrants, no viable local populations: minimum area threshold?

Increasing importance of local processes

Increasing connectivity may reduce species dominance by favoring inter-patch dispersal of sedentary and specialist species

Interpaly of local and dispersal processes

Combinations of species exhibiting true metapopulation dynamics with species with frequent inter-patch movements

Only large patches sustain populations that can be locally dominant

Highly complex processes underpinning abundance patterns

Interpaly of local and dispersal processes

Conclusions

Pollinators are expected to show drastic changes in evenness (dominance) due to several environmental pressures other than fragmentation

We need to evaluate multiple drivers and their interactions on pollinator evenness!

Pollinator evenness is expected to be strongly related to pollination service