A version of this chapter was published as: Liss, W.J., G.L. Larson, E.A. Deimling, L.M. Ganio, R.L. Hoffman, and G.A. Lomnicky. 1998. Factors influencing the distribution and abundance of diaptomid copepods in high-elevation lakes in the Pacific Northwest, USA. Hydrobiologia 379:63-75.

ABSTRACT

We investigated the impact of abiotic factors and trout density on distribution and abundance of diaptomid copepods in high-elevation lakes in North Cascades National Park Service Complex (NOCA), Washington, USA. The most common large diaptomid, Diaptomus kenai (mean length = 1.88 mm), was able to persist over a wide range of abiotic factors, but the smaller herbivorous diaptomid, D. tyrrelli (mean length = 1.18 nun), was restricted to shallow lakes (maximum depth <= 10 m) with relatively high concentrations of total Kjeldahl nitrogen and total phosphorous. There was a significant negative relationship between the density of D. tyrrelli and the density of large diaptomids, which could imply interaction between large and small diaptomids. The abundance of large diaptomids was significantly lower in shallow lakes with high densities of reproducing trout (>250 fish ha^-1) than in fishless lakes, in deep lakes with reproducing trout, or in lakes where trout do not reproduce and are periodically stocked with fry at low densities (average 179 fry ha^-1). In lakes where nutrient concentrations were suitable for D. tyrrelli, the small diaptomid was often abundant when trout density was high and large diaptomids were either absent or in low abundance. Our research suggests that trout density, nutrient concentration, and lake depth influence food web interactions in high lakes in NOCA.