Thomas Heatherly will defend his doctoral dissertation, "Flow Regime, Guppy Introduction and Light Manipulation Influence Invertebrate Assemblages in Trinidadian Streams," at 2 p.m., Tuesday, Nov. 13 in Hardin Hall room 901.
Abstract
This dissertation concerns natural and experimental influences on macroinvertebrate assemblage structure and stoichiometry in Trinidadian streams as well as a new data analysis protocol for the bioassessment of rivers and streams of Nebraska. In the second chapter, I present models that describe how aspects of the natural flow regime, especially flood frequency and recovery time, structure individual invertebrates as well as overall assemblage structure. Chapter 3 describes the influences of light manipulation and the introduction of guppies on macroinvertebrates. I describe the influences of phylogeny, allometry and environment on the C:N:P stoichiometry of Trinidadian invertebrates in Chapter 4. Finally, I present a data analysis protocol for assessing the biotic integrity of Nebraska’s streams and rivers that uses physical factors to compare ecologically similar systems. I found that almost all invertebrates in montane Trinidadian streams are predictable by flow regime, and that a sizeable number of invertebrates as well as diversity respond positively to hydrologic variability. I also found that increased light immediately and persistently stimulated invertebrate assemblages, and that large increases have the capability of stimulating multiple trophic levels and feeding groups. Guppies significantly reduced the abundance of invertebrates, but only after they had been introduced for two years. Phylogeny explained most of the variance in invertebrate stoichiometry, but allometric relationships were common and the stream sampled often explained as much variance as allometry. I also found widespread variation in carbon and nitrogen content, which contradicts previous findings of homeostasis of consumers for these elements. Finally, I found that stream size and temperature were the primary factors responsible for different assemblages in Nebraska reference streams. Utilizing stream size and temperature to compare test sites to reference conditions proved to be more realistic than using proximity-based ecoregional groupings. My results elucidated the important effects of flow and top down and bottom controls over invertebrates in Neotropical streams, and found a surprising amount of variability in the stoichiometry of these consumers. The application of ecological theory to bioassessment should also ensure that the streams and rivers of Nebraska are managed properly.