Movement Behavior is Habitat Dependent in Invasive Jackson's Chameleons in Hawaii
The Jackson's Chameleon (Trioceros jacksonii xantholophus) is a predatory, arboreal east African lizard that has become established in the forests of several Hawaiian Islands where they have been shown to prey upon rare endemic invertebrate taxa. In this study, we used radiotelemetry to assess movement behavior of T. j. xantholophus in three different habitats that varied in suitability for sustained persistence of chameleons. Landscape ecology theory holds that movement behavior tends to be relatively rapid and linear in unsuitable habitat, minimizing time spent in suboptimal areas, but more circuitous and less rapid in suitable habitat to optimize resource use. Therefore, we predicted that in Hawaii, chameleons released in unsuitable habitat will 1) move longer distances each day; 2) follow straighter paths; 3) move away from point of release continuously; and 4) cover larger areas, relative to those released in suitable habitat. Our results indicated that mean daily distance, total cumulative distance, total net displacement, and home range did not vary significantly among the three habitats. However, daily distances decreased and path tortuosity increased over time under suitable conditions, whereas the opposite pattern was seen under unsuitable conditions. Notably, daily net displacement did not increase over time, regardless of habitat type or suitability, and home range overlap was inversely correlated with habitat suitability. In general, Jackson's Chameleons traveled short distances with nonlinear paths, reflecting a sedentary life history. We propose that localized control and potential eradication in critical areas may be possible via manual removal.Abstract
Map showing locations of collection of Jackson's Chameleons in both the Waianae and the Koolau Mountain ranges on the island of Oahu. Radiotagged individuals were released at three sites in the Koolau Mountain Range: Tantalus (Tan, suitable habitat), Waahila Low (WaL, unsuitable habitat), and Waahila High (WaH, intermediate suitability habitat). Also shown on the map is the Waianae collection locality, indicated by a star symbol. Elevation of each release site is indicated under site labels. The square symbol indicates the location of the Tree Snail Conservation Laboratory at the University of Hawaii, Manoa.
Close-up of radiotransmitter device and adult male Jackson's Chameleon with transmitter affixed to rear flank via epoxy adhesive (photos by B. Holland).
Movement patterns of Jackson's Chameleons recorded at the three study sites, during 21-d per site trial period. (A) Pattern of daily distance traveled (log scale, solid lines) over time. Significant nonlinear trends were detected (generalized additive models [GAMs]) at Tantalus and Waahila High, whereas a significant linear trend (general linear regression [GLR] models) was detected at Waahila Low. (B) Mean weekly tortuosity ratios for chameleon paths over time. Trends are represented by the solid lines. Different lowercase letters indicate significant differences among weeks within sites, and the asterisk indicates significant differences in tortuosity between Tantalus and Waahila Low for week 1 (ANOVA, Tukey' test, P < 0.05). (C) Trends of net displacement (lo -scale, solid lines) of chameleons over time. Significant nonlinear trends (GAM) were detected at Tantalus and Waahila Low, whereas no trend (slope = 0) was detected at Waahila High. Dots represent mean values (Tantalus and Waahila Low, N = 5, Waahila High, N = 4), whiskers are SE, and dashed lines represent 99% confidence levels. Each week of the study is delimited by dashed vertical lines.
Home range overlap patterns for tagged Jackson's Chameleons released and tracked at three different sites: (A) Tantalus, (B) Waahila Low, and (C) Waahila High. Shaded polygons represent home range for each specimen released (i.e., area used during 21-d release period). Percentages indicate degree of overall home range overlap. Significant differences in home range overlap among sites are indicated by different lowercase letters (ANOVA, Tukey's test, P < 0.05). Note that patterns for only four animals are shown (C), because one male chameleon went missing during this trial, and the signal was not reacquired (see Materials and Methods for details).
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