The effect of propagule size on the invasion of an alien insect
Article first published online: 6 DEC 2004
Journal of Animal Ecology
Volume 74, Issue 1, pages 50–62, January 2005
How to Cite
MEMMOTT, J., CRAZE, P. G., HARMAN, H. M., SYRETT, P. and FOWLER, S. V. (2005), The effect of propagule size on the invasion of an alien insect. Journal of Animal Ecology, 74: 50–62. doi: 10.1111/j.1365-2656.2004.00896.x
- Issue published online: 6 DEC 2004
- Article first published online: 6 DEC 2004
- Received 27 November 2003; accepted 17 May 2004
- lag period;
- release size
- 1The movement of species from their native ranges to alien environments is a serious threat to biological diversity. The number of individuals involved in an invasion provides a strong theoretical basis for determining the likelihood of establishment of an alien species.
- 2Here a field experiment was used to manipulate the critical first stages of the invasion of an alien insect, a psyllid weed biocontrol agent, Arytainilla spartiophila Förster, in New Zealand and to observe the progress of the invasion over the following 6 years.
- 3Fifty-five releases were made along a linear transect 135 km long: 10 releases of two, four, 10, 30 and 90 psyllids and five releases of 270 psyllids. Six years after their original release, psyllids were present in 22 of the 55 release sites. Analysis by logistic regression showed that the probability of establishment was significantly and positively related to initial release size, but that this effect was important only during the psyllids’ first year in the field.
- 4Although less likely to establish, some of the releases of two and four psyllids did survive 5 years in the field. Overall, releases that survived their first year had a 96% chance of surviving thereafter, providing the release site remained secure. The probability of colony loss due to site destruction remained the same throughout the experiment, whereas the probability of natural extinction reduced steeply over time.
- 5During the first year colonies were undergoing a process of establishment and, in most cases, population size decreased. After this first year, a period of exponential growth ensued.
- 6A lag period was observed before the populations increased dramatically in size. This was thought to be due to inherent lags caused by the nature of population growth, which causes the smaller releases to appear to have a longer lag period.