Biotic homogenization

1. Biotic homogenization OyomoareOsazuwa-Peters Graduate Seminar; Lost in Space October 12, 2011

2. Overview • History of Biotic homogenization (BH) • What exactly does BH mean? • What is the evidence for BH?

3. 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

4. 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).

5. “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).

6. 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

7. Olden 2008

8. Olden and Rooney 2006

9. Evidence for Biotic homogenization?

10. 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

12. 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

13. Result: Exotic floras differ more among neighboring communities, but have a broader and more uniform distribution.

14. 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

15. Space & Time Space

16. 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

17. 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.

18. 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

19. 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

20. Pre-decline • Results Post-decline

21. Conclusion: Non random extinctions resulted in the decline of regional diversity of Central American amphibians.

22. 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

23. Composition and frequencies of interactions Host relative abundances Parasitoid relative abundances

24. 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)

25. Results: Functional homogenization

26. Clavel et al. 2010: Worldwide decline of specialist species: toward a global functional homogenization?

27. 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

29. Conclusion • Fish communities homogenization was at different scales was due to • Introduction of ubiquitous species • No extinctions • Differential patterns of native species extinctions

30. 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

31. Papers for discussion • Olden et al. (2004) Ecological and evolutionary consequences of biotic homogenization • Smith et al. (2009): Selecting for extinction: nonrandom disease associated extinction homogenizes amphibian biotas • Abadie et al. (2011): Landscape disturbance causes small scale functional homogenization, but limited taxonomic homogenization in plant communities.