Artificial retreats are increasingly used to sample animal populations and in attempts to boost animal numbers in degraded habitats. Here, I test potential applications of artificial retreats for lizards inhabiting a coastal environment of high conservation value (Kaitorete Spit, New Zealand). I first conducted a pitfall-trapping survey examining the distribution and relative abundance of lizards in duneland, farmland and shrubland habitats, and tested the influence of trap placement on capture rates. Capture rates of the diurnal skinks Oligosoma maccanni (McCann�s skink) and O. nigriplantare polychroma (common skink) were highest in duneland and farmland, respectively, and were most sensitive to the distance separating traps from the nearest cover (the greater the distance, the lower the capture rate). Captures of O. lineoocellatum (spotted skink) and Hoplodactylus maculatus (common gecko) were rare.
Secondly, in separate chapters I test the utility of artificial retreats for monitoring: 1) a preference trial examining relative use of three types of artificial retreats by skinks (O. maccanni and O. n. polychroma) and geckos (H. maculatus); 2) a comparison of the effectiveness of artificial retreats relative to pitfall traps for detecting cryptic and primarily nocturnal geckos (H. maculatus) following translocation; and 3) capture-recapture estimation of population parameters (survival and abundance) of H. maculatus. I found that: 1) geckos strongly preferred retreats made of Onduline over corrugated iron and concrete tiles, whereas skinks exhibited no apparent preferences; 2) artificial retreats were more effective than pitfall traps for detecting geckos following translocation; and 3) monthly survival and recapture probabilities of geckos varied with age-class and over time. Estimated survival was unexpectedly low, possibly due to excessive trap spacing. I developed a new capture-recapture model specifically for population size estimation with data from artificial retreats, which gave estimates that were up to 50% greater than those predicted by conventional capture-recapture models. I caution that permanent placement of artificial retreats in long-term studies may be inappropriate for estimation of population parameters due to potential habitat-enhancement effects and/or altered predation risk.
Thirdly, I conducted a capture-recapture field experiment, using a replicated Before-After-Control-impact (BACI) design, to test the relative effects of habitat manipulation (artificial retreat addition) and partial predator removal (by fencing) on annual survival of duneland skink (O. maccanni) populations. Survival increased at sites with predator exclosures, but not at control sites or following the addition of artificial retreats, either alone or in combination with a predator exclosure. The magnitude of the increase in survival for the exclosure-only treatment was small, but sufficient to change the trajectory of an apparently stable population into an increasing one, suggesting that the population is limited by predators. Predator control, but not the addition of artificial retreats, is predicted to benefit O. maccanni.
To conclude, the Onduline design developed here appears to be particularly useful for sampling cryptic, terrestrial geckos; however, artificial retreats must be used appropriately to avoid bias arising from habitat-enhancing effects and/or altered predation risk. The restoration value of artificial retreats requires further testing on other species and in areas where natural retreat sites are limited.
| Identifer | oai:union.ndltd.org:ADTP/197594 |
| Date | January 2008 |
| Creators | Lettink, Marieke, n/a |
| Publisher | University of Otago. Department of Zoology |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Marieke Lettink |
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