Northern Prairie Wildlife Research Center
Ecologists need sampling devices and techniques that will function in aquatic habitats utilized by waterfowl. Sampling devices used for estimating standing crops of invertebrates (Swanson 1978a,b, 1983, and several devices described by Merritt and Cummins 1984) have been designed to sample water column or benthic invertebrates in lentic habitats. To adequately quantify wetland invertebrates, information is needed on both water column and benthic invertebrates. However, there are no devices that simultaneously sample from both habitats. Pooling data from different sampling devices that estimate water column and benthic invertebrates separately can create bias because of the double sampling of organisms that are associated with the benthic-pelagic interface.
Spatial distribution of invertebrates compounds sampling problems because most taxa are contagiously distributed into aggregations of individuals (Elliott 1977, Resh 1979, Downing 1979). Data sets frequently contain a high proportion of zero observations and have large variances associated with a negative binomial sampling distribution (Elliott 1977). Because of large variance, the number of samples required to estimate means with nominal confidence is limited by available manpower. Sorting of invertebrates is also time consuming and often limits the level of precision attainable in specific investigations.
Sampling devices that minimize bias and provide precise estimates of invertebrate populations are needed. Herein, we describe a device that eliminates the bias related to oversampling because water column and benthic organisms are sampled simultaneously; has the statistical advantage of partitioning samples into 4 subsamples; and can be used to estimate within-sample variance of invertebrates in shallow wetlands.
We thank P. L. Hudson, C. E. Korschgen, and J. H. Selgeby for critical review of this manuscript. D. M. Mushet prepared the figure.