PARENT SESSION
Poster Session 39: Late Breaking and Newsworthy Posters
Friday, August 12, 8:30 AM - 10:30 AM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Food chain length: Patterns across lakes, rivers, oceans and estuaries.

Fetzer, William^*,1, Vander Zanden, Jake¹, ¹ Center for Limnology, Madison, WI, USA

ABSTRACT- The question of what determines food chain length has been debated by ecologists for more than 70 years. Traditional theories attempted to explain food chain lengths from a theoretical approach, proposing four hypotheses: productivity, design constraint, optimal foraging and dynamic stability. Recent work has focused on cross-system comparisons to test the correlation of food chain length and environmental factors, such as disturbance regime, ecosystem size and productive space. Our research examines patterns in food chain length across lakes, rivers, oceans and estuaries using ¹⁵N ratios. Food chain lengths were estimated from ¹⁵N values of the top predator and primary consumers from each system. We were able to estimate food chain lengths for 198 aquatic ecosystems. Our results showed a significant effect of system type on food chain length (ANOVA, F_(3,194)=11.6, p<.001), with oceans having the longest mean food chain length (4.00, n=32), followed by lakes (3.92, n=105), estuaries (3.91, n=15) and rivers (3.46, n=46). The variances of system types also differed: estuaries (²=.33), lakes (²=.25), oceans (²=.17) and rivers (²=.17). No significant relationships were found between food chain length and predictors such as ecosystem size or mean annual air temperature. Cross system differences are likely the result of attributes that are shared within system types but not across them. Further research should attempt to identify the processes and drivers causing these patterns.

Key words: food chain length, stable nitrogen isotopes, cross ecosystem patterns