Statistical issues with using herbarium data for the estimation of invasion lag-phases
- 457 Downloads
Current methods for using herbarium data as time series, for example to estimate the length of the invasion lag phase, often make assumptions that are both statistically and logically inappropriate. We present an alternative statistical approach, estimating the lag phase based on annual rather than cumulative data, a generalized linear model incorporating a log link for overall collection effort, and piecewise linear splines. We demonstrate the method on two species representing good and poor data quality, then apply it to two data sets comprising 448 species/region combinations. Significant lags were detected in only 28 and 40 % of time series, a much lower level than the 95 and 77 % found in previous analyses of the same data. In a case with high quality data, a lag was concluded even though during the “lag” the locations of herbarium collections indicated that it was spreading rapidly at a continental scale. In species with few records, results were sensitive to the way in which zeroes were included. Overall, our method gives very good fit to the data, avoids unrealistic assumptions of other methods and gives more reliable estimates of confidence. However, given the poor representation of herbarium samples in the early stages of invasions and the fact that they do not constitute a structured survey of abundance, we warn against over-reliance on statistical analysis of such data to reach conclusions about the dynamics of invasions.
KeywordsLag phase Invasion Herbarium Statistical analysis
We thank Sami Aikio and Ines Schonberger for supplying data from the Allan Herbarium (CHR), Dan Larkin for his mid-west USA data and Alison Vaughan, National Herbarium of Victoria (MEL), for supplying data from Australia’s Virtual Herbarium. We also thank Rod Randall for supplying a list of invasive species for Australia. We appreciate comments on a previous version of this paper by Richard Duncan, Sami Aikio and Dan Larkin, although we have only incorporated some of their suggestions.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- Booth BD, Murphy SD, Swanton CJ (2011) Invasive plant ecology in natural and agricultural systems, 2nd edn. CABI, Cambridge, MassachusettsGoogle Scholar
- Davidson R, MacKinnon JG (2004) Econometric theory and methods. Oxford University Press, OxfordGoogle Scholar
- Dobson AJ (2008) An introduction to generalized linear models, 3rd edn. Chapman and Hall/CRC Press, Boca Raton, FloridaGoogle Scholar
- Dogra KS, Sood SK, Dobhal PK, Sharma S (2010) Alien plant invasion and their impact on indigenous species diversity at global scale: a review. J Ecol Nat Environ 2:175–186Google Scholar
- Holt RD, Barfield M, Gomlkiewicz R (2005) Theories of niche conservatism and evolution: could exotic species be potential tests? In: Sax DF, Stachowicz JJ, Gaines SD (eds) Species invasions: Insights into ecology, evolution, and biogeography. Sinauer, Sunderland, Massachusetts, pp 259–290Google Scholar
- Kowarik I (1995) Time lags in biological invasions with regard to the success and failure of alien species. In: Pyšek P, Prach K, Rejmánek M, Wade M (eds) Plant invasions—general aspects and special problems. SPB Academic Publishing, Amsterdam, pp 15–38Google Scholar
- The Council of Heads of Australasian Herbaria (1999) Australia’s Virtual Herbarium www.chah.gov.au/avh. Accessed 19 April 2013
- Webber BL, Yates CJ, Le Maitre DC, Scott JK, Kriticos DJ, Ota N, McNeill A, Le Roux JJ, Midgley GF (2011) Modelling horses for novel climate courses: insights from projecting potential distributions of native and alien Australian acacias with correlative and mechanistic models. Divers Distrib 17:978–1000CrossRefGoogle Scholar
- Wells MJ (1974) Nassella trichotoma (Nees) Hack in South Africa. In: Proceedings of 1st National Weeds Conference of South Africa, pp 125–137Google Scholar
- Wood SN (2006) Generalized additive models: an introduction with R. Chapman and Hall/CRC Press, Boca Raton, FloridaGoogle Scholar