Biotic homogenization - Phylodiversity Network

advertisement
Biotic homogenization
Oyomoare Osazuwa-Peters
Graduate Seminar; Lost in Space
October 12, 2011
Overview
• History of Biotic homogenization (BH)
• What exactly does BH mean?
• What is the evidence for BH?
History
• Episodic mixing of
biotas when physical
barriers are removed
– Formation of
Panamanian land bridge
between N and S
America
• Modern recognition of
concept by Charles
Elton
What is BH?
• Laliberte & Tylianakis (2010) refer to it as a
phenomenon that reduces variability and
uniquess of flora and fauna across regions.
• “A gradual increase in compositional similarity
among formerly distinct biological
communities” (Naaf and Wulf 2010)
• “A temporal increase in community similarity”
(McKinney & Lockwood 1999).
• “Biotic homogenization is the process by which
species invasions and extinctions increase the
genetic, taxonomic or functional similarity of two
or more locations over a specified time interval”
(Olden 2008).
• “Biotic homogenization is defined as an increase
in spatial similarity of a particular biological
variable over time” (Olden et al. 2004).
BH definition
•
•
•
•
Change in similarity
Space
Time
Main drivers
– Species invasions
– Species extinctions
Identity of
species dictates
the outcome
• Multiple levels of biodiversity of organization
– Genetic
– Taxonomic
– Functional
Olden 2008
Olden and Rooney 2006
EVIDENCE FOR BIOTIC
HOMOGENIZATION?
• Goal: compare patterns of species invasion,
dispersal and impacts on three Eurasian seas
• Ponto-Caspian= The Black Sea + Sea of Azov +
The Caspian Sea
• Low diversity low salinity temperate waters
• Black Sea has become an international
shipping destination
• Goal: to determine how floristic similarity is
affected by exotics on a continental scale
• Data: native and exotic flora of America North
of Mexico
• Measure: Jaccard index of similarity
J= a/(a + b + c)
J ranges from 0 to 1
a is the number of species shared between two localities
b and c are the numbers of species unique to either locality
• Result: Exotic floras differ more among
neighboring communities, but have a broader
and more uniform distribution.
• Goal: to quantify extent of functional and taxonomic
homogenization across Great Britain between 1978
and 1998
• Data: National ecological surveillance data for Great
Britain
• Scale: random sampling plots of 10 – 200 m2 within 1
km2 regions
• Functional traits: canopy height, specific leaf area,
dispersal vectors, seed bank longevity
Space
&
Time
Space
• Positive correlations between change in α
diversity and change in trait variation between
1978 and 1998
• Conclusion: Plant communities became
taxonomically less similar but functionally
similar
• Goal: to explore regional and elevational
patterns in site similarity throughout the
Holocene.
• Data: eight fossil pollen datasets from
Romania
• Method:
– They divided time into 250 years intervals from
11500 years BP till recent.
– Used PCA and Bray-Curtis similarity analysis.
• Conclusion:
– Biotic differentiation = anthropogenic activities + climate
change
– BH= biotic interactions as immigration and competition
– Most studies that do not account for time represent single
snapshots in time
• Goal: to understand the importance of
patterns of extinction at a regional scale
• Data: species list of amphibian species before
and after extirpations associated with a
pathogenic fungus
• Approach: null model
• Results
Predecline
Postdecline
• Conclusion: Non random extinctions resulted
in the decline of regional diversity of Central
American amphibians.
• Goal: to determine whether parasitoid host
networks can be homogenized across a
gradient of habitat simplification
• Data: 48 quantitative food webs
– parasitism events
– parasitoid and host composition
– unique parasitoid-host interactions
– Strength of interactions
Composition
and
frequencies
of
interactions
Host relative
abundances
Parasitoid
relative
abundances
• Goal: Explicitly test the effect of landscape
fragmentation and disturbance on functional
homogenization of birds in France
• Data: French Breeding Bird Survey
• Method: Community Specialization index (CSI)
• Results: Functional homogenization
Clavel et al. 2010: Worldwide decline of specialist
species: toward a global functional homogenization?
• Goal: to validate a theoretical model predicting
the outcome of distinct invasion and extinction
scenarios
• Data: freshwater fish faunas in the USA at three
spatial scales
– Country
– Provinces in California
– Watersheds within provinces
• Method:
– used regression analysis
– Seeded the model with empirical data
• Conclusion
– Fish communities homogenization was at different
scales was due to
• Introduction of ubiquitous species
• No extinctions
• Differential patterns of native species extinctions
Take home message
• There is evidence for BH at different scales
– Most BH studies focus on taxonomic
homogenization
– Neglect of temporal comparison
– Most studies are performed at continental scales
• What are the implications of BH?
– Disruption of potential for local adaptation
– Reduced resilience of ecosystems to disturbance
Papers for discussion
1. Olden et al. (2004) Ecological and evolutionary
consequences of biotic homogenization
2. Smith et al. (2009): Selecting for extinction:
nonrandom disease associated extinction
homogenizes amphibian biotas
3. Abadie et al. (2011): Landscape disturbance
causes small scale functional homogenization,
but limited taxonomic homogenization in plant
communities.
Download
Related flashcards

Biogeography

20 cards

Mesoamerican cultures

39 cards

Mexico City

17 cards

Coral reefs

44 cards

Biogeography

25 cards

Create Flashcards