Biotic homogenization - PowerPoint Presentation

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Biotic homogenization

Oyomoare

Osazuwa-PetersGraduate Seminar; Lost in SpaceOctober 12, 2011Slide2

OverviewHistory of Biotic homogenization (BH)What exactly does BH mean?What is the evidence for BH?Slide3

HistoryEpisodic mixing of biotas when physical barriers are removedFormation of Panamanian land bridge between N and S AmericaModern recognition of concept by Charles EltonSlide4

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).Slide5

“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).Slide6

BH definitionChange in similaritySpaceTimeMain driversSpecies invasionsSpecies extinctionsMultiple levels of biodiversity of organizationGenetic

TaxonomicFunctional

Identity of species dictates the outcomeSlide7

Olden 2008Slide8

Olden and Rooney 2006Slide9

Evidence for Biotic homogenization?Slide10

Goal: compare patterns of species invasion, dispersal and impacts on three Eurasian seasPonto-Caspian= The Black Sea + Sea of Azov + The Caspian SeaLow diversity low salinity temperate watersBlack Sea has become an international shipping destinationSlide11
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Goal: to determine how floristic similarity is affected by exotics on a continental scaleData: native and exotic flora of America North of MexicoMeasure: 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 localitySlide13

Result: Exotic floras differ more among neighboring communities, but have a broader and more uniform distribution. Slide14

Goal: to quantify extent of functional and taxonomic homogenization across Great Britain between 1978 and 1998Data: National ecological surveillance data for Great BritainScale: random sampling plots of 10 – 200 m2 within 1 km2 regions

Functional traits: canopy height, specific leaf area, dispersal vectors, seed bank longevitySlide15

Space

& Time

SpaceSlide16

Positive correlations between change in α diversity and change in trait variation between 1978 and 1998Conclusion: Plant communities became taxonomically less similar but functionally similar Slide17

Goal: to explore regional and elevational patterns in site similarity throughout the Holocene.Data: eight fossil pollen datasets from RomaniaMethod: They divided time into 250 years intervals from 11500 years BP till recent. Used PCA and Bray-Curtis similarity analysis.Slide18

Conclusion: Biotic differentiation = anthropogenic activities + climate changeBH= biotic interactions as immigration and competitionMost studies that do not account for time represent single snapshots in timeSlide19

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 fungusApproach: null model Slide20

Results

Pre-decline

Post-declineSlide21

Conclusion: Non random extinctions resulted in the decline of regional diversity of Central American amphibians.Slide22

Goal: to determine whether parasitoid host networks can be homogenized across a gradient of habitat simplificationData: 48 quantitative food websparasitism eventsparasitoid and host compositionunique parasitoid-host interactions Strength of interactionsSlide23

Composition and frequencies of interactions

Host relative abundances

Parasitoid relative abundancesSlide24

Goal: Explicitly test the effect of landscape fragmentation and disturbance on functional homogenization of birds in FranceData: French Breeding Bird SurveyMethod: Community Specialization index (CSI)Slide25

Results: Functional homogenization Slide26

Clavel et al. 2010: Worldwide decline of specialist species: toward a global functional homogenization?Slide27

Goal: to validate a theoretical model predicting the outcome of distinct invasion and extinction scenariosData: freshwater fish faunas in the USA at three spatial scalesCountryProvinces in CaliforniaWatersheds within provincesMethod: used regression analysis

Seeded the model with empirical dataSlide28
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ConclusionFish communities homogenization was at different scales was due toIntroduction of ubiquitous speciesNo extinctionsDifferential patterns of native species extinctionsSlide30

Take home messageThere is evidence for BH at different scalesMost BH studies focus on taxonomic homogenizationNeglect of temporal comparisonMost studies are performed at continental scalesWhat are the implications of BH?Disruption of potential for local adaptation

Reduced resilience of ecosystems to disturbanceSlide31

Papers for discussionOlden et al. (2004) Ecological and evolutionary consequences of biotic homogenizationSmith et al. (2009): Selecting for extinction: nonrandom disease associated extinction homogenizes amphibian biotasAbadie et al. (2011): Landscape disturbance causes small scale functional homogenization, but limited taxonomic homogenization in plant communities.