Validation of a randomization procedure to assess animal habitat preferences: microhabitat use of tiger sharks in a seagrass ecosystem
Article first published online: 29 MAR 2006
Journal of Animal Ecology
Volume 75, Issue 3, pages 666–676, May 2006
How to Cite
HEITHAUS, M. R., HAMILTON, I. M., WIRSING, A. J. and DILL, L. M. (2006), Validation of a randomization procedure to assess animal habitat preferences: microhabitat use of tiger sharks in a seagrass ecosystem. Journal of Animal Ecology, 75: 666–676. doi: 10.1111/j.1365-2656.2006.01087.x
- Issue published online: 29 MAR 2006
- Article first published online: 29 MAR 2006
- Received 8 November 2005; accepted 16 January 2006
- habitat availability;
- habitat use;
- predator–prey interactions;
- 1Tiger sharks Galeocerdo cuvier are important predators in a variety of nearshore communities, including the seagrass ecosystem of Shark Bay, Western Australia. Because tiger sharks are known to influence spatial distributions of multiple prey species, it is important to understand how they use habitats at a variety of spatial scales. We used a combination of catch rates and acoustic tracking to determine tiger shark microhabitat use in Shark Bay.
- 2Comparing habitat-use data from tracking against the null hypothesis of no habitat preference is hindered in Shark Bay, as elsewhere, by the difficulty of defining expected habitat use given random movement. We used randomization procedures to generate expected habitat use in the absence of habitat preference and expected habitat use differences among groups (e.g. males and females). We tested the performance of these protocols using simulated data sets with known habitat preferences.
- 3The technique correctly classified sets of simulated tracks as displaying a preference or not and was a conservative test for differences in habitat preferences between subgroups of tracks (e.g. males vs. females).
- 4Sharks preferred shallow habitats over deep ones, and preferred shallow edge microhabitats over shallow interior ones. The use of shallow edges likely increases encounter rates with potential prey and may have profound consequences for the dynamics of Shark Bay's seagrass ecosystem through indirect effects transmitted by grazers that are common prey of tiger sharks.
- 5Females showed a greater tendency to use shallow edge microhabitats than did males; this pattern was not detected by traditional analysis techniques.
- 6The randomization procedures presented here are applicable to many field studies that use tracking by allowing researchers both to determine overall habitat preferences and to identify differences in habitat use between groups within their sample.