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A recent advance infreshwater ecology:
Biodiversity and ecosystem function in tropical rivers
Michael DouglasTropical Rivers and Coastal Knowledge
Research Hub (TRaCK),Charles Darwin University
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My career history• 88 Honours at Monash University
– Species-Area Relationships (Sam Lake)• 89-90 ABC TV Natural History Unit• 91-99 PhD at Monash University
– Effects of fire on stream communities:CSIRO’s Kapalga Fire Experiment (Sam Lake)
• 95-06 Lecturer/Senior Lecturer at CDU– Floodplain weeds, Riparian grazing, Env. flows– Trophic interactions, Top-down control– TRaCK consortium
• 07 Director, TRaCK Research Hub
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What sort of ecology interests me?
• Theoretical ecology
• Management relevance
• Community/Ecosystem level
• Tropical streams and rivers
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Loss of a harvested fish speciesdisrupts Carbon flow in a diverse
tropical river
(2006) Taylor, B. W., Flecker, A.S. andHall, R. O. Science 313:833-836
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• Impacts of biodiversity loss• Long-running and contentious debate
– Elton (1927) “Diversity begets stability”– Ives and Carpenter (2007) “Diversity is just one factor”
• Unresolved, but some consensus(Lareau et al. 2005 Science)–Some minimum number of species
required under constant conditions–More species at lower trophic levels
imparts a degree of insurance–Changing environments
Biodiversity & ecosystem function
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• “Rudimentary understanding” (Schindler2007, Ives and Carpenter 2007)
• Largely based on simple, experimentalterrestrial systems (Hooper et al. 2005 Ecol.Monogr.)
• Poor understanding of:– species-rich natural systems (Srivastava et
al. 2005 Annual Review Ecol. Evol. Syst.)– which species have a significant impact
(Lareau et al. 2005)– freshwater systems (Lareua et al. 2005)
Biodiversity & ecosystem function
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Loss of fish biodiversity
• Fish are the most species rich vertebrates• Harvesting is a major cause of species loss
(Allan et al. 2005 BioScience)
• Tropical fish fauna particularly diverse butincreasingly under threat fromoverharvesting (Winemiller 2005)
• Limited understanding of the ecosystemconsequences of speceis loss (Wantzen et al.2006 JNABS, McIntyre et al 2007 PNAS)
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Photo: Brad Taylor
Prochilodus mariae
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Prochilodus mariae
Photo: Bob Hall
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B. W. Taylor et al., Science 313, 833 -836 (2006)
Harvesting Prochilodus mariae
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Photo: Bob Hall
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Prochilodus mariae feeding and feeding scars on rock
B. W. Taylor et al., Science 313, 833 -836 (2006)
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Prochilodus: an “ecosystem engineer”
– Small-scale cage experiments (4m2)
– Reduces benthic particulate matter (Flecker 1996Ecology)
– Changes benthos from diatoms and bacteria toN-fixing cayanobacteria (Flecker 1996 Ecology)
– Switch system to primary production independentof N-limitation (Flecker et al. 2002 Ecology)
– But….only small-scale, short-term experiments
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Loss of a harvested fish speciesdisrupts Carbon flow in a diverse
tropical river
(2006) Taylor, B. W., Flecker, A.S. andHall, R. O. Science 313:833-836
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Photo: Bob Hall
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B. W. Taylor et al., Science 313, 833 -836 (2006)
Fig. 1. Interannual variation in organic carbon flux
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B. W. Taylor et al., Science 313, 833 -836 (2006)
Fig. 2. Photographs of the split-stream removal experiment
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Fig. 3. Ecosystem properties in the treatment and reference area of the split-stream experiment beforeand after removal of P. mariae B. W. Taylor et al., Science 313, 833 -836 (2006)
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Fig. 3. Ecosystem properties in the treatment and reference area of the split-stream experiment beforeand after removal of P. mariae B. W. Taylor et al., Science 313, 833 -836 (2006)
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Contribution of Prochilodus (Prma)to nutrient recycling
McIntyre, P.B., Jones, L.E., Flecker, A.S. and Vanni, M. J. (2007) Proceedings of the NationalAcademy of Sciences 104: 4461-4466
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B. W. Taylor et al., Science 313, 833 -836 (2006)
Fig. 4. Time trends of body mass for the migratory fish P. mariae
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River ecology & management
• Prochilodus reduces spatial and temporalvariability in organic carbon flow andnutrient recycling
• Single species results in a more constantsupply of energy and materials at a criticaltime
• Shows potential ecosystem ramifications ofspecies loss
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Biodiversity & ecosystem function
• More species = degree of insurance
• Naturally diverse freshwater community(>80 species in 3km)
• But….low functional redundancy forfundamental processes (synthesis °radation of carbon, recycling ofnutrients)
• No evidence of compensation in othersystems where Prochilodus permanentlylost (Barbanio Duque et al. 1998 Env. Biol. Fishes)
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Future research• Need to identify which species rather than
just how many (Schindler 2007 PNAS)
• Selective experimental removals of speciesmost likely to be threatened by humanactivity (Taylor et al. 2006 Science)
• Likely to vary with different perturbations somay require study of each ecosystem on acase-by-case basis (Ives and Carpenter 2007 Science)
• Preserve as much diversity as possible!