PARENT SESSION
Organized Oral Session 39: Consequences of dispersal and colonization: What happens when communities are opened?
Organizer(s): CG Guthrie and DA Yee
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 516 C, Level 5, Palais des congrès de Montréal

It's not easy being brown: Linking productivity, nutrients, and species richness across spatial scales in ephemeral aquatic detritus-based microcosms.

Yee, Donald^*,1, Juliano, Steven ¹, ¹ Department of Biological Sciences, Normal, Il, USA

ABSTRACT- Productivity is hypothesized to affect species richness, although the form of the relationship varies among systems and with spatial scale. Much of the current knowledge of productivity-richness relationships is derived from studies involving primary production, despite the fact that systems energetically dependent on decomposition are more common than are systems dependent directly on photosynthesis. Tree holes are water-holding cavities that contain food webs driven almost exclusively by allochthonous inputs of energy (detritus) from the surrounding environment. These microcosms are good candidates for examining relationships among detritus-derived nutrients, microorganism productivity, and macroinvertebrate richness. We collected data from tree holes from 6 sites across Illinois (n = 90 tree holes total), with two sites in southern, central, and northern zones (n = 30 per zone). This sampling design enabled us to look for patterns at 3 spatial scales: local (within site), regional (2 sites per zone), and state (all sites combined). At three times (May, July, September, 2004) we collected data on two measures of productivity (microorganism O₂ consumption rates, bacterial production quantified as Leucine incorporation), two nutrient measures (total Nitrogen, total Phosphorus), and richness and abundance of all macroinvertebrates present in each tree hole. We observed a variety of productivity-richness relationships across scales and with the productivity metric. Patterns at local scales were highly variable (e.g., unimodal, U-shaped, linear, none) with sampling date. At the regional scale, we found weak relationships between productivity and richness. We found weak but significant positive (May) and negative (September) linear relationships between productivity and richness at the state scale. Nutrients were highly correlated with measures of productivity and with each other, as in other aquatic systems. In addition, richness was quadratically related to total abundance at multiple spatial scales and across time. We conclude that productivity-richness relationships in our detritus-based microcosms are strongly dependent on the metric of productivity and the scale of observation.

Key words: detritus, tree hole, macroinvertebrates, phosphorus