Secondary production and consumer energetics • The consumer energy budget • Determinants of energy flow • Ecological efficiencies • Definition of secondary production • Measurement of secondary production • Predicting secondary production – For individual populations – For guilds of consumers – For the entire community of consumers
Secondary production and consumer energetics. The consumer energy budget Determinants of energy flow Ecological efficiencies Definition of secondary production Measurement of secondary production Predicting secondary production For individual populations For guilds of consumers - PowerPoint PPT Presentation
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Secondary production and consumer energetics
• The consumer energy budget• Determinants of energy flow• Ecological efficiencies• Definition of secondary production• Measurement of secondary production• Predicting secondary production
– For individual populations– For guilds of consumers– For the entire community of consumers
What affects ecological efficiencies (partitioning of energy)?
Assimilation efficiency
depends on food quality
Valiela 1984
Bacterial growth efficiency depends on food quality
Del Giorgio andCole 1998
Bacterial growth efficiency depends on temperature
Rivkin and Legendre 2001
Introduction to secondary production
• “All non-photosynthetic production (growth), regardless of its fate”
• NOT the same as biomass accumulation
• NOT just the production of herbivores
• Much better studied than other parts of the consumer energy budget– Easier to measure– Historically considered more important
Secondary production is aquatic and empirical
• 167 papers published on subject in 2005• 52% marine or estuarine, 35% freshwater, 3% terrestrial• 55% microbial, 39% invertebrate, 7% vertebrate• Very little theoretical work• Are generalizations about secondary production
really generalizations about aquatic ecosystems?
How do we estimate secondary production?
• Tracer methods
• Demographic methods
• Turnover methods
• Empirical methods
How do we estimate secondary production?
Organism Method Data requirements Limitations
Bacteria tracers (radioactive nucleotides or amino acids)
uptake of label subject to large errors because of (i) critical assumptions about fate and use of label and non-radioactive analogues, which may be hard to test; (ii) uncertain conversion factors to get from uptake of label to carbon production
Predicting secondary production (or ingestion): (2) guilds
(Cebrian and Lartigue 2004)
Aquatic is white (left) or blue (center and right); terrestrial is black (left) or green (center and right)
Terrestrial/aquatic differences
• Herbivores ingest a higher proportion of NPP in aquatic systems (higher nutrient content of NPP)
• Herbivore production possibly much higher in aquatic systems (higher ingestion, higher assimilation efficiency?, less homeothermy so higher net growth efficiency)
Predicting secondary production of guilds
• Predictable (and linear?) from resource supply• Too imprecise to be very useful as a predictor• Maybe strong terrestrial/aquatic differences
arising from nutrient content of primary producers
• Nutrients as well as energy affect guild production
εa = assimilation efficiency, εng = net growth efficiency,S = net supply of organic matter, L = non-respiratory losses
Predicting secondary
production: (3) entire communities
Predicting secondary production of entire communities
• Secondary production is large compared to primary production (if NGE=30%, secondary production = 43% of NPP)
• Decomposers see a lot of consumer tissue (not just plant tissue)
• Secondary production is larger in systems dominated by heterotherms than in systems dominated by homeotherms
• Energy available for ingestion and assimilation by consumers is greater than primary production (if NGE=30% and AE = 20%, A=143% of NPP, I = 714% of NPP)
Conclusions
• It’s easier to predict the secondary production of an entire community than a single population
• Consumer activity is tightly linked with other processes that control the movement and fate of organic matter
• When considered at the community level, secondary production (maybe) is controlled by the same factors that control primary production: supply of energy and nutrients, and their retention