Factors affecting detection probability in plant distribution studies
Article first published online: 2 SEP 2009
© 2009 The Authors. Journal compilation © 2009 British Ecological Society
Journal of Ecology
Volume 97, Issue 6, pages 1383–1389, November 2009
How to Cite
Chen, G., Kéry, M., Zhang, J. and Ma, K. (2009), Factors affecting detection probability in plant distribution studies. Journal of Ecology, 97: 1383–1389. doi: 10.1111/j.1365-2745.2009.01560.x
- Issue published online: 13 OCT 2009
- Article first published online: 2 SEP 2009
- Received 21 March 2009; accepted 28 July 2009 Handling Editor: Pieter Zuidema
- detection probability;
- forest dynamic plot;
- generalized linear mixed model;
- plant distribution
1. Plant ecologists have been rather slow to appreciate the existence and the effects of imperfect detection probability in plants. Sources of heterogeneous detectability include differences in morphology or life-form, patch size, observers and survey effort. Understanding the relationship between such factors and detectability is crucial for the efficient design of new plant distribution studies and for the interpretation of existing ones.
2. We have studied the factors affecting detectability in a large permanent plot (24 ha) in East China where the true distribution of six shrub and tree species was known from a detailed earlier inventory. Two observers independently resurveyed and recorded detection and non-detection of each species in each 20 × 20 m sampling quadrat. A total of 288 quadrats were resurveyed (218 by observer A, 211 by observer B and 141 by both). We used generalized linear mixed modelling to study the relationships between detection and species, observer, survey effort and patch size.
3. Detectability of an occupied quadrat was remarkably low and ranged from 0.09 to 0.34 on average for the six shrub and tree species. Differences of detection among species were mainly as a result of distinctive morphology rather than life-form. There was no significant difference of overall detection probability between the two observers. Detectability increased to 0.95 as the survey path approached 20% area of the sampling quadrat and as a plant patch covered c. 19% of the area of the sampling quadrat.
4. Synthesis. Our results suggest that imperfect detection is much more widespread than currently acknowledged by most plant ecologists. We identify several sources of heterogeneity in detectability (species, survey effort and patch size) that ought to be considered when studying and modelling the distribution of plant species. Detectability should be accounted for in plant distribution studies to avoid spurious inferences.