liu.seSök publikationer i DiVA
Ändra sökning
RefereraExporteraLänk till posten
Permanent länk

Direktlänk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Resampling species-wise abundance data
Linköpings universitet, Filosofiska fakulteten. Linköpings universitet, Matematiska institutionen, Statistik.
2006 (Engelska)Ingår i: The 17th Annual Conference of The International Environmetrics Society (TIES), Kalmar, Sweden, 2006Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
Abstract [en]

 Monitoring the abundance of plant species in grasslands is time-consuming. Accordingly, sampling or inspection is usually sparse both in time and space. Typically, a grassland area is visited 1-2 times per decade, and each time 5-20 plots are inspected. For each plot (about one square meter) an inspection protocol, containing coverage data for up to 100 species, is established. The collected data can thus be characterized as high-dimensional and sparse. Moreover, it is not unusual that some of the monitored species are present in only a few of the investigated plots, i.e., the vectors of coverage data may contain numerous zeroes. The analysis of abundance data can be either multivariate or univariate. Canonical correlation analysis (CCA) and redundancy analysis (RDA) are widely used multivariate methods. Univariate analyses are usually applied to summary statistics, such as diversity indices or measures of evenness. In either case, the complexity of the data makes it difficult to use parametric models for inference about the whole grassland, and modest sample sizes prevents using asymptotic results. Due to this, nonparametric methods, such as permutation tests, are often used to assess trends in abundance data. However, the power of these tests may be low due to the small number of sampling occasions. Here, we propose a resampling technique that can be used to determine the distribution of arbitrary estimators or test statistics based on high-dimensional abundance data. The original idea of the bootstrap is to substitute the true (but unknown) cumulative distribution function (cdf) for an empirical cumulative distribution function (edf) calculated from a sample of observations. When the collected data can be regarded as a simple random sample, the bootstrap principle provides a convenient method to determine the distributions of a large number of moment-related statistics (e.g. Singh, 1981). Also, it has been demonstrated that regression or time series data can be resampled by first extracting residuals (or innovations) and then forming pseudo data by resampling these residuals (Wu, 1989; Kreiss & Franke, 1992). We propose high-dimensional abundance data be resampled by extracting residuals from a principal components factor analysis in which a small number of factors are retained. Furthermore, we handle point masses at zero (absent species) by using a truncated probit function to transform the original data prior to the principal components factor analysis, and to back-transform the pseudo data. The threshold and the number of factors retained are determined in such a way that the most important features of the resampled data are similar to those of the original observations in the most important resoe. In particular, the number of observed species should not differ too much. The latter is achieved by using a subsampling procedure, in which the number of zeros (i.e. non-observed species) in a subsample and in pseudo-data from that subsample are compared. Also, relative biases and coverage degrees of empirical confidence intervals are optimized. The performance of our procedure is illustrated by extensive simulations and a case study of temporal changes in Shannon entropy in a grassland in South West Sweden.

Ort, förlag, år, upplaga, sidor
2006.
Nationell ämneskategori
Matematik
Identifikatorer
URN: urn:nbn:se:liu:diva-37178Lokalt ID: 33869OAI: oai:DiVA.org:liu-37178DiVA, id: diva2:258027
Tillgänglig från: 2009-10-10 Skapad: 2009-10-10 Senast uppdaterad: 2010-09-28

Open Access i DiVA

Fulltext saknas i DiVA

Personposter BETA

Nordgaard, Anders

Sök vidare i DiVA

Av författaren/redaktören
Nordgaard, Anders
Av organisationen
Filosofiska fakultetenStatistik
Matematik

Sök vidare utanför DiVA

GoogleGoogle Scholar

urn-nbn

Altmetricpoäng

urn-nbn
Totalt: 30 träffar
RefereraExporteraLänk till posten
Permanent länk

Direktlänk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf