Biotic homogenization

Biotic homogenizationOyomoare Osazuwa-Peters

Graduate Seminar; Lost in SpaceOctober 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

• Multiple levels of biodiversity of organization– Genetic– Taxonomic– Functional

Identity of species dictates the outcome

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 similarityJ= a/(a + b + c)

J ranges from 0 to 1a 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 Pre-decline

Post-decline

• 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.