Foraging ecology of the Tokay gecko Gekko gecko in a residential area in Thailand PDF

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Amphibia-Reptilia 27 (2006): 491-503 Foraging ecology of the Tokay gecko, Gekko gecko in a residential area in Thailand Anchalee Aowphol1 , Kumthorn Thirakhupt1 , Jarujin Nabhitabhata2 , Harold K. Voris3 Abstract. The foraging behavior of Gekko gecko was observed at the visitor complex of the Khao K...

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Amphibia-Reptilia 27 (2006): 491-503

Foraging ecology of the Tokay gecko, Gekko gecko in a residential area in Thailand Anchalee Aowphol1 , Kumthorn Thirakhupt1 , Jarujin Nabhitabhata2 , Harold K. Voris3 Abstract. The foraging behavior of Gekko gecko was observed at the visitor complex of the Khao Khiao Open Zoo at the Khao Khiao-Khao Chomphu Wildlife Sanctuary in Chon Buri Province, Thailand. Foraging parameters of G. gecko (foraging period, time spent moving, foraging attempts, foraging success, prey size consumed, and foraging distance) did not vary significantly between males, females, and juveniles. Individuals foraged between 18:01 and 09:00 hrs. Peak emergence time was between 18:01 and 20:00 hrs. Peak retreat time was between 04:01 and 07:00 hrs. Major food items included insects of the orders Lepidoptera, Orthoptera, and Coleoptera. Prey sizes of males, females, and juveniles were not significantly different, indicating no prey size selection. This may have been due to low insect availability in the habitat. Gekko gecko tended to be a sit-and-wait forager spending most of the time waiting for active prey. However, it sometimes foraged more actively when insect abundance was relatively high. Foraging behavior of males tended to be more variable than females and juveniles. In addition, variation in foraging parameters among individuals was noted. Foraging strategies of G. gecko observed in this study are interpreted in the context of optimal foraging theory.

Introduction In general, animals spend a considerable amount of time gathering food. Successful foraging behavior is assumed to be adaptive because it increases survival and reproduction. Knowledge of animal foraging has developed over several decades (Emlen, 1966; MacArthur and Pianka, 1966; Schoener, 1971; Perry and Pianka, 1997) and optimal foraging theory has been introduced into foraging studies (e.g. Charnov, 1976; Krebs et al., 1977; Martín et al., 2003). This theory states that animals behave in ways that maximize net energy gain or benefit/cost ratio. For example, animals may attempt to procure more food in less time, catch larger rather than smaller prey in the same amount of time, or reduce various time and energy expenses while foraging.

1 - Department of Biology, Faculty of Science, Chulalongkorn University, Pathumwan, Bangkok, 10330 Thailand Corresponding author’s e-mail: [email protected] 2 - National Science Museum, Technopolis, Klong 5, Klong Luang, Patumthani, 12120 Thailand 3 - Division of Amphibians and Reptiles, Department of Zoology, Field Museum of Natural History, Chicago, Illinois 60605, USA

Many species of lizard have been used as models for studying foraging behavior in the field (Perry et al., 1990; Werner et al., 1997b; Cooper et al., 2001). Among lizards, two major modes of foraging behavior are recognized: active (wide) foraging and sit-and-wait (ambush) foraging (Pianka, 1966; Huey and Pianka, 1981; Cooper, 1994). Geckos have been considered sit-and-wait foragers (e.g., Ikeuchi et al., 2005). However, some authors report that they are also active predators (Vitt and Pianka, 1994; Werner et al., 1997a). Gekko gecko is widespread from northeastern India, southern China, and Indochina to the Indo-Australian Archipelago and the Philippines (Smith, 1935; Taylor, 1963; Zhao and Adler, 1993). It has been introduced into other areas such as the United States. It is the only species of the genus Gekko that is found throughout Thailand including the large cities. This species lives in man-made environments and in forests. Its broad geographic range and habitat use suggest that it may exhibit high variability in foraging behavior. Even though this species is well known, its foraging ecology is poorly studied. This study aimed to explore foraging behavior of G. gecko in a man-made environment. We also evaluate the results in light of

© Koninklijke Brill NV, Leiden, 2006. Also available online - www.brill.nl/amre

492 optimal foraging theory. Specifically, we test the hypothesis that the increase in prey density will lead to the increase in foraging period, movement, prey capture rate, foraging distance and prey size consumed.

Materials and methods Study site The study was conducted at the visitor complex of the Khao Khiao Open Zoo at the Khao Khiao–Khao Chomphu Wildlife Sanctuary in Chon Buri Province, Thailand. It is located at 101◦ 04 10.7 N and 13◦ 12 44.3 E. The area is approximately 1000 m2 and is partly surrounded by deciduous forest. The visitor complex is composed of four buildings in which the daytime retreats of G. gecko are located. Fluorescent lights around the buildings are always on overnight between 18:00 hrs. and 06:00 hrs. During the year of observation, total monthly rainfall ranged from 0.0 mm in December 2001 to 281.8 mm in October 2001. Mean monthly temperatures ranged from 26.4◦ C to 30.5◦ C and mean relative humidity varied from 63% in December 2001 to 82% in October 2001. The weather was dry from November through April and wet from May through October. Insect abundance reached a peak in August, decreasing to the lowest level in November, and slightly increasing again to a second peak in April. Methods Observations on foraging behavior were carried out for seven consecutive days each month during the one-year study period (July 2001 - June 2002). Geckos were caught by noose, sexed, measured for snout-vent length (SVL), weighed, and individually marked by toe-clipping and for a future DNA study. Geckos were marked with field numbers from #1 to #60 during the three month period before the observations began. Observations were made from dusk to dawn. Observers slowly walked through the study area using binoculars to locate geckos. Upon detecting a gecko, the observer stopped moving to minimize disturbance to the gecko. Whenever possible, observations were made from a minimum distance of 5 meters away from the gecko. Each gecko was observed continuously from the time it left its daytime retreat until it returned to its retreat. The following data were recorded on a tape recorder for each observation: foraging time, foraging period, time used for moving (or time spent moving), foraging attempts, foraging success, foraging distance, prey type and prey size. These parameters are defined as follows: Foraging time extended from the time of emergence from daytime retreats to the time of return to retreats. Foraging period was the number of hours each night that a gecko foraged. Movement of geckos included running, walking, crawling, and jumping. Time used for moving was recorded using electronic stopwatches. Foraging attempts were movements toward prey that were

A. Aowphol et al. either landing or already on a wall. Foraging success was the percentage of successful foraging attempts. Foraging distance was visually estimated as the longest distance from the daytime retreat to the spot where a gecko foraged. Prey sizes were estimated visually and prey types were visually identified from a distance. Air temperature, relative humidity, and insect abundance were recorded every hour. Air temperature and relative humidity were recorded using a digital, pen-type thermo-hygrometer (VWR). Insect abundance was estimated visually in the 1 m2 lighted area around a fluorescent light and was divided into 6 categories as follows: 0 = none, no insects present; 1 = very low, less than 5 individuals/m2 ; 2 = low, 5-10 individuals/m2 ; 3 = medium, 11-20 individuals/m2 ; 4 = high, 21-30 individuals/m2 ; 5 = very high, more than 30 individuals/m2 . Data analysis Mean, standard deviation (SD), and coefficient of variation (CV) were computed for each foraging parameter for males, females, juveniles and individuals. The coefficient of variation is the standard deviation expressed as a percentage of the mean. Foraging data from each individual observed at least three times during the study period was analyzed for comparisons among males, females and juveniles and the variation between and within individuals using the Kruskal-Wallis test; χ 2 test was used to analyse the foraging time among groups. Hourly frequencies were pooled 3 periods for emergence time and 4 periods for retreat time in order to meet the assumption for a valid χ 2 test. The expected frequency in each class should exceed 2 and 80% of the classes should have expected frequencies greater than 5. A Kruskal-Wallis test was used to test for differences in SVL among males, females, and juveniles. Spearman’s coefficient of rank correlation was used to determine the relationship between G. gecko body size and prey size and the relationship between insect abundance, foraging parameters and meteorological data. Statistical analyses were performed by SPSS version 10.0. Food niche was determined in two ways; Shannon-Weiner’s diversity index and Levin’s niche breadth index. Shannon-Weiner’s index (H = −pi log2 pi ) was used to determine prey diversity in diet for each group. The symbol “pi ” was designated as the proportion of the prey items in category i. Levin’s index (B = 1/pj2 ) was used to determined niche breadth in prey size consumed. The symbol “pj ” = proportion of items in the diet that are of food category j .

Results Monthly sample sizes The numbers of individual males, females, and juveniles observed during the year were 13, 8, and 6, respectively and the number of geckos observed varied by month. Table 1 shows

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Gekko gecko foraging ecology

Table 1. Number of independent observations of Gekko gecko over one year at the Khao Khiao Open Zoo, Khao Khiao-Khao Chomphu Wildlife Sanctuary, Chon Buri. Jul-01 Aug-01 Sep-01 Oct-01 Nov-01 Dec-01 Jan-02 Feb-02 Mar-02 Apr-02 May-02 Jun-02

Total observations

Male Female Juvenile

7 5 2

4 5 4

6 3 4

8 2 2

5 1 2

7 3 1

3 5 0

4 3 0

7 2 1

6 4 0

7 3 2

4 3 3

68 39 21

Total

14

13

13

12

8

11

8

7

10

10

12

10

128

monthly sample sizes for observations. Individuals observed more than once during the year (number in parentheses) were as follows: 2 observations (n = 4), 3 observations (n = 4), 4 observations (n = 2), 5 observations (n = 1), and >6 observations (n = 10). Group comparison Foraging time. Foraging time ranged from 18:01 to 09:00 hrs. Times of emergence of males, females, and juveniles were not significantly different (male: n = 68; female: n = 39; juvenile: n = 21; χ 2 = 2.8; df = 4; P = 0.592). Times of retreat also did not differ among the groups (male: n = 68; female: n = 39; juvenile: n = 21; χ 2 = 2.3; df = 6; P = 0.886). Most geckos emerged in the early evening and did not retreat later than 07:00 hrs (fig. 1). However, a few males were found to forage until late morning. Peak emergence time was between 18:01 to 20:00 hrs, whereas peak retreat time was between 04:01 and 07:00 hrs. The foraging time of males ranged from 18:01 to 09:00 hrs and females and juveniles ranged from 18:01 to 07:00 hrs. Diet. Diet consisted of several insect orders including Odonata, Orthoptera, Hemiptera, Coleoptera, adult and larval Lepidoptera, Hymenoptera Apoidea, and Isoptera. The agamid lizard, Calotes versicolor, was also a prey item (fig. 2A). Some prey could not be identified and were listed as unknown. Lepidoptera (41.3%) were a common diet item throughout most of the year. However, in April, May, and June, Isoptera were the most common diet item due

to much greater abundance in the habitat at that time (table 2). The prey of males was very similar to that of females and juveniles. The main prey items in order of importance among males, females, and juveniles were slightly different. The prey of males in order of frequency were Lepidoptera (39.9%), Orthoptera (20.3%), and Coleoptera (7.8%) whereas the prey of females were Lepidoptera (33.1%), Isoptera (27.1%), and Orthoptera (9.0%). The main juvenile prey items were Isoptera (40.3%), Lepidoptera (30.9%), and Orthoptera (4.8%). The size of prey items ranged from...