Elser, J. J. Arizona State University, j.elser@asu.edu
O'Brien, J. J. University of Kansas,
Dobberfuhl, D. R. Arizona State University,

 
THE EVOLUTION OF TROPHIC DYNAMICS AND CONSUMER-DRIVEN NUTRIENT RECYCLING: ECOLOGICAL STOICHIOMETRY OF A KEYSTONE HERBIVORE AT TEMPERATE AND ARCTIC LATITUDES.
 
Differences in body C:N:P ratios in zooplankton taxa are now know to affect nutrient cycling and trophic dynamics in lakes and oceans, leading ecologists to wonder about the cellular and evolutionary causes of differences in body elemental composition among various taxa. We tested the hypothesis that variation in body C:N:P ratios in consumer taxa is driven by differential selection for body growth rate that necessitates allocation to cellular machinery constructed of elementally contrasting biomolecules (ribosomes built from P-rich RNA). We also assessed whether such responses had ecological consequences for consumer-driven nutrient cycling and trophic dynamics. We did so by quantifying the growth rates and body elemental composition of conspecific populations from the widespread crustacean Daphnia pulex species complex at the latitudinal extremes of its natural distribution where variation in duration of growing season places a premium on somatic growth rate. We also measured rates of N and P recycling by the animals as well as their trophic response to variation in food elemental composition. Our findings strongly support the growth rate hypothesis as arctic animals grew more rapidly and had more P-rich bodies than temperate animals. Arctic animals were also poor recyclers of P and suffered greater declines in production when fed poor quality food. These findings indicate significant differences in nutrient cycling and trophic dynamics in arctic and temperate populations of this keystone taxon, highlighting the importance of evolutionary context in determining the reciprocal relationships between single species and ecosystem processes.
 
Day: Tuesday, Feb. 2
Time: 03:45 - 04:00pm
Location: Sweeney Center
 
Code: SS49TU0345S