Comparison of Ecological Communities: The Problem of Sample Representativeness

Abstract

Obtaining an adequate, representative sample of ecological communities to make taxon richness (TR) or compositional comparisons among sites is a continuing challenge. Although randomization in the collection of sample units is often used to assure that sampling is representative, randomization does not convey the concept of how well samples represent the community or site from which they are drawn. In ecological surveys, how well a sample represents a community or site literally means the similarity in taxon composition and relative abundance between a sample and the community from which it is drawn. Using both field and simulated data, we show that the proportion of the total taxon richness at a site (%TTR) achieved with a fixed sample size varies across sites, which in turn causes changes in site-to-site differences in observed TR with sample size. This means that equal-sized samples may differentially represent the communities from which they are drawn. However, the similarity of a sample to the community from which it is drawn cannot be measured directly because the taxon composition and relative abundance of the community is usually unknown. We propose to estimate it by measuring the average similarity among replicate samples randomly drawn from a community, i.e., autosimilarity, which is measured with Jaccard Coefficient in this study. Using the same data sets, we found that:(1) samples of equal size from different sites or communities achieved different levels of autosimilarity, with lower levels achieved in taxon richer sites, indicating variation in how well samples of equal size represent their respective communities; (2) %TTR was positively and almost linearly correlated with autosimilarity, indicating that autosimilarity might be a good predictor of TTR; and (3) when samples were compared at the same level of autosimilarity, similar %TTRs across different sites were achieved (i.e., the relative differences in taxon richness among sites became independent of sample size). We conclude that standardization on autosimilarity, rather than on sample size, can improve the accuracy of taxon richness comparisons.

Estimating sample representativeness in a survey of stream caddisfly fauna

“…These were then pooled to generate increasing sample size (Cao et al 2002a). Accordingly, a sample can be characterized by its sample size (i.e.…”

“…In contrast, precision can be expressed by comparing repeated measurements of the same quality. It is the basic idea in the development of the term sample representativeness (Cao et al 2002a(Cao et al , 2002b, a term used to describe how well a sample represents the community. In order to measure representativeness, two samples are collected from the same community and a measure of the similarity (or autosimilarity Cao et al 2003) determined.…”

“…increasing sample size) in a riffle using the recently developed similarity-based approach of Cao et al (2002a). We also tested how sampling representativeness varies with the inclusion, or exclusion of rare species.…”

A comparison of phytoplankton assemblages generated by two sampling protocols in a German lowland catchment

“…To our knowledge, no published studies have determined the best way to sample a stream reach to represent its phytoplankton assemblage adequately. Several studies have demonstrated that the observed composition and richness of macroinvertebrate and fish assemblages changed as more subsamples were collected within a reach (e.g., Cao et al, 1997Cao et al, , 2002, but no well-developed method existed to determine how many subsamples were enough for representative. Samples' representativeness tended to increase with the number of samples collected, but the stabilization point varied among habitat types (Weilhoefer and Pan, 2007).…”

Analysis on the Relationship between Biological Indices and Survey Area of Benthic Macroinvertebrates Using Mathematical Model

“…일정수준 이하의 면적 에서 저서성 대형무척추동물의 군집지수 값은 조사면적에 따라 민감하게 반응할 수 있다고 알려져 있다 (Duggan and Collier, 2002;Kim et al, 2013;Vlek et al, 2006). 생태학 적 분석에서 나타날 수 있는 오류의 요인 중 표본크기는 가장 중요한 요인으로 작용할 수 있으며(Morin, 1997), 이 에 따라 종 다양성 및 풍부도와 유사성은 물론 먹이망 구 조에 대한 해석이 달라질 수 있다( (Bagon et al, 1986;Cao et al, 2002). 국외에서는 군집에 대한 대표성과 비용효율을 고려한 표 본크기의 연구 (Bartsch et al, 1993;Resh and Price, 1984) 를 비롯하여 개체수 (Duggan and Coller, 2002;Lorenz et al, 2004)와 채집면적 (Vlek et al, 2006) 기준의 표본크기 에 대한 연구가 이루어져 왔다.…”