Where are the good groceries? Food web dynamics in the Warm Springs region, Moapa, NV

Authors: Adam B. StSaviour, Stanley V. Gregory, Matt Mesa, Gayton G. Scoppettone

Year: 2009 (xli)

Abstract

The headwaters of the Muddy River, known as the Warm Springs area, is home to a host of endemic vertebrate and invertebrate species. A tremendous effort is underway to conserve these species, especially Moapa dace, Moapa coriacea. M. coriacea is an endangered thermophilic minnow that primarily feeds on drift (Scoppettone et al. 1992, Great Basin Naturalist 52, no. 3: 216-225). To provide insight on food availability, drift was quantified at 20 sites throughout the thermally suitable habitat in the Warm Springs area. Stable isotope analyses were also conducted on the organisms from these sites to understand nutrient cycling and specific food resources for M. coriacea. Finally, a drift manipulation experiment was conducted to investigate if M. coriacea are rigid in their drift feeding strategy or if they can exhibit plasticity in a changing environment. Observations were recorded for 30 individual M. coriacea at five different treatment levels of drift. Observed trends indicate the highest diversity and abundance of drifting macroinvertebrates within close proximity to the head spring pools where temperatures are warmest and where the largest numbers of Moapa dace are found. Results are not yet available for stable isotope analysis, but I hypothesize that M. coriacea will exhibit an isotopic signature consistent with consumption of herbivorous macroinvertebrates that are most likely to actively drift. Smaller individual M. coriacea feed more frequently than larger individuals but are less successful, meaning that they reject a greater proportion of the food items that they take. Intraspecific competition occurs when drift is reduced to the lowest levels, but interspecific competition was not observed between M. coriacea and White River Springfish, Crenichthys baileyi. The implications of this study are to help us better understand how anthropogenic activities affecting the environment might affect Moapa dace, and how to steer habitat restoration efforts in a way that promote a productive food web for Moapa dace.