Effects of biodiveristy on ecosystem functioning John Bruno

What is biodiversity? Genetic Species & species richness (#/unit area) Higher taxonomic level Functional group What is ecosystem functioning? Primary production (g/m 2 ) Primary productivity (g/m 2 /hour) Secondary production Resource use efficiency Resistance and resiliance, stability Invasibility

Why ask about the role of biodiversity?

CARNIVORES HERBIVORES PLANTS

CARNIVORES HERBIVORES PLANTS

Tilman’s study of the effect of plant diversity on productivity Manipulated plant diversity (0 to 16 species) by adding seeds and extensive weeding Measured productivity as biomass (above and below ground)

Plant species richness Total biomass (kg/m 2 ) Tilman et al. 2001

Plant diversity has strong positive effects on primary production Transgressive overyielding is common Selection effects are positive and partially drive biodiversity effects The most productive species dominate polycultures “Plant biodiversity paradigm”

General experimental approach Mixture (9 species)Monoculture

Mesocosm growth experiments- IMS, Morehead City, NC

Field growth experiments Beaufort, NC Jamaica

Jamaica photosynthesis measurements Temperature: 27-28ºC Flow: 4-8 cm/s Salinity: 35 ppt Light: uE

red algaegreen algae brown algae Sample size: 10 Duration: 10 days (January 2003) Starting wet weight: 60g P < 0.001P = 0.35

Effect size

Monoculture performance Negative selection effects

Plant diversity effects are relatively weak and frequently undetectable Compositional effects are much stronger Transgressive overyielding is rare Selection effects are often negative and reduce net biodiversity effects The most productive species rarely dominate polycultures Englehardt and Richie 2002 Hector et al other BIODEPTH papers Callaway et al Hooper and Dukes 2004 Fridley 2002 Downing 2004 Bruno et al “New Consensus”

CARNIVORES HERBIVORES PLANTS

Duffy and Hay’s amphipod study From Duffy and Hay Ecological Monographs 10: Dr. Emmett Duffy

Duffy and Hay’s amphipod study From Duffy and Hay Ecological Monographs 10:

Duffy’s test of the herbivore diversity hypothesis Manipulated micrograzer diversity (0-6 species) Used outdoor mesocosms at VIMS Measured effects on a variety of ecosystem parameters (algal biomass, sediment organic content, benthic diversity)

No grazers Idotea only Erichsonella only All six species Duffy’s test of the herbivore diversity hypothesis

Main findings: 1)Most of the herbivores specialized on one or a few types of algae 2) Increasing micrograzer diversity reduced primary production 3) The mechanism appears to be diet complimentarity Duffy’s test of the herbivore diversity hypothesis Duffy et al Ecology Letters

CARNIVORES HERBIVORES PLANTS

Predicted effects of increasing predator diversity on herbivores and plants, categorized as mechanisms that increase or decrease plant biomass – Herbivory, + Plant biomass 1) dietary complementarity 2) facilitation among predators 3) selection of a keystone predator 4) reduction of intraspecific competition 5) change in prey behavior (a TMII) + Herbivory, – Plant biomass 1) intraguild predation 2) cannibalism 3) predator emigration 4) change in predator behavior 5) omnivory

Omnivorous fish Omnivorous crab Carnivorous shrimp

Bruno and O’Connor 2005, Ecology Letters

Byrnes et al. In press, Ecology Letters

Byrnes et al. In press, Ecology Letters

Byrnes et al. In press, Ecology Letters Kelp crab urchin

Finke and Denno In press, Ecology Letters