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Determining trends in irruptive

desert species

Chris R. Dickman, Aaron C. Greenville and Glenda M. Wardle

Summary

Populations of many desert-dwelling organisms show ‘boom and bust’ dynamics,
irrupting brief ly following rain-driven pulses of productivity before collapsing
again to low numbers. Determining population trends for such organisms poses
unique challenges. This chapter describes population booms and busts in two
species of dasyurid marsupials monitored over 22–27 years at nine sites in arid
central Australia and uses these species to gain insight into how population trends
in irruptive species might be discerned. The brush-tailed mulgara Dasycercus
blythi increased predictably after heavy rainfall at all sites before again becoming
scarce, whereas the lesser hairy-footed dunnart Sminthopsis youngsoni fluctuated
asynchronously at all sites, with no population drivers identified. These disparate
patterns indicate that monitoring programs (survey timing, number and placement
of monitoring sites) should be designed with respect to the natural history of the
target species to reveal trends in their populations. Environmental factors and
known or putative threats to the target species also should be monitored, and