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Gibson, Peter, M.
Seleccin de perchas para dormir en tres especies de lagartos Norops (Squamata Polychrotidae) en el Valle de San Luis, Puntarenas, Costa Rica
Sleep site selection in three species of Norops lizards (Squamata Polychrotidae) in the San Luis Valley, Puntarenas, Costa Rica
The sleeping patterns of animals are important factors in fully understanding their behavior. I studied the sleeping site
selection of three species of Norops lizards. I caught the lizards during the day, applied fluorescent powder, and tracked them to their eventual sleeping location at night using UV light. I measured multiple variables, including weather conditions, height, and level of protection provided by the site. Mean night heights of males and females, as well as among species, proved significantly different, thus maintaining daytime stratification. However, males and females were distributed opposite of that seen during the day, with females sleeping higher than males. Additionally, there were significant
differences in protection preference across sex and species divisions, as only males and one species showed no preference for protected sites. Weather effects, such as precipitation and temperature, failed to show significance. Therefore, it appears that sex and species differences are the strongest factors driving sleeping site selection. Males seem driven more by sleeping site height, while females demonstrated greater desire for protection. Overall, the lizards were found to have a preference for protected sites.
Para comprender todo sobre las acciones de un animal, es importante saber cmo duerme el animal. Yo estudi la seleccin de perchas para dormir en tres especies de Norops. Los atrapaba durante el da, les pona polvo fluorescente, y los segua por la noche con un foco de luz ultravioleta. Estudi algunos factores, incluyendo el tiempo, la altitud de percha, y el nivel de proteccin dado por la percha. Comparaciones de los promedios de las altitudes de los machos y las hembras y tambin entre las tres especies mostraron diferencias. Sin embargo, los machos y las hembras se distribuyeron diferentes de lo que se ve durante el da. Las hembras duermen ms arriba que los machos. Tambin, haba diferencias en las preferencias por perchas con ms proteccin entre los sexos y las especies; solo los machos y una especie no preferan las perchas protegidas. Los efectos del tiempo no eran significantes. Por eso, parece que las diferencias entre los sexos y las especies son los factores ms importantes para escoger perchas nocturnas. A los machos, les importa ms la altitud de la percha, pero las hembras necesitan perchas protegidas. En general todos prefieren las perchas con ms proteccin.
Text in English.
Sleep behavior in animals
Costa Rica--Puntarenas--Monteverde Zone--San Luis
Comportamiento de sueo en animales
Costa Rica--Puntarenas--Zona de Monteverde--San Luis
Tropical Ecology Spring 2010
Ecologa Tropical Primavera 2010
t Monteverde Institute : Tropical Ecology
1 Sleep Site Selection in Three Species of Norops Lizards (Squamata: Polychrotidae) in the San Luis Valley, Puntarenas, Costa Rica Peter M. Gilson Department of Biology, Point Loma Nazarene University ABSTRACT The sleeping patterns of animals are import ant factors in fully understanding their behavior. I studied the sleeping site selection of three species of Norops lizards. I caught the lizards during the day, applied fluorescent powder, and tracked them to their eventual sleeping location at night usin g UV light. I measured multiple variables, including weather conditions, height, and level of protection provided by the site. Mean night heights of males and females, as well as among species, proved significantly different, thus maintaining daytime strat ification. However, males and females were distributed opposite of that seen during the day, with females sleeping higher than males. Additionally, there were significant differences in protection preference across sex and species divisions, as only males and one species showed no preference for protected sites. Weather effects, such as precipitation and temperature, failed to show significance. Therefore, it appea rs that sex and species differences are the strongest factors driving sleeping site selection. Males seem driven more by sleeping site height, while females demonstrated greater desire for protection. Overall, the lizards were found to have a preference for protected sites. RESUMEN Para comprender todo sobre los acciones de un animal, es importan te saber como duerme el animal. Yo estudi la seleccin de perchas para dormir en tres especies de Norops Los atrapaba durante el da, les pona polvo florescente, y los segua por la noche con un foco de luz ultravioleta. Estudi algunos factores, incluy endo el tiempo, la altitud de percha, y el nivel de proteccin dado por la percha. Comparaciones de los promedios de los altitudes de los machos y las hembras y tambin entre las tres especies mostraron diferencias. Sin embargo, machos y hembras se distrib uyeron diferente de lo que se ve durante el da. Las hembras duermen ms arriba que los machos. Tambin, haban diferencias en las preferencias por perchas con ms proteccion entre los sexos y las especies; solo los machos y una especie no preferan percha s protegidas. Los efectos del tiempo no eran significantes. Por eso, parece que diferencias entre los sexos y especies son los factores ms importantes para escoger perchas nocturnas. A los machos, les importa ms la altitud de la percha, pero las hembras necesitan perchas protegidas. En general todos prefieren perchas con ms proteccin. INTRODUCTION The behavior of sleep is a very important aspect of the natural history of an animal both because it takes up a significant amount of their time and becaus e they are left extremely vulnerable as a result (Singhal et al. 2007). In order to fully understand the behavior and natural history of an organism, their sleeping patterns must be taken into account. The sleeping behavior of lizards, along with that of m any other taxa, has been poorly documented. Though the concept of sleeping site selection by lizards has not been studied in great detail, there are a few theories concerning the motivations behind their selection patterns. Some believe that predator avoi dance is a determining factor in sleeping site selection, while others report that many factors such as abundance of certain plants, thermoregulation, or species
2 differences are more important (Christian et al. 1984; Clark & Gillingham 1990; J. A. Pounds, pers. comm.). Christian et al. (1984) found that ambient temperature had a significant effect on the sleeping site selection of adult Galapagos land iguana ( Conolophus pallidus ), while juveniles selected sites based on greater protection. Clark & Gillingha m (1990) noted that Anolis lizards were most often found sleeping on the most common understory plant in their study site, suggesting selection simply based on vegetation abundance. Finally, in an unpublished study of Norops sleeping site preference, Alan Pounds (pers. comm.) noticed strong trends corresponding to species differences. Lizards from the genus Norops are small to medium size, primarily arboreal lizards, and are widespread throughout the Neotropics (Savage 2002). Past studies have demonstrated daytime perch height stratification across both sex and species differences in Norops lizards (Andrews 1983; Rummel & Roughgarden 1985). This stratification has been interpreted as resulting from inter species competition for resources as well as from int ra species dominance hierarchies, with dominant males perching higher than other individuals. Females are typically found on lower perches. It is also known that male Norops go to lower perch heights to hunt and forage during the day in order to avoid comp etitive encounters with other males (Andrews 1983). At night, they are often observed sleeping on leaf surfaces of understory forest plants, presumably in hopes that they would be awakened by the approach of a predator climbing up from below. Though this strategy appears common, few studies have investigated if significant numbers of Norops also sleep in other locations, or what factors are driving their sleeping site choices (Singhal et al. 2007, Prez 2008). This study aims to determine the particular f actors leading to sleeping site selection in three species of Norops from the San Luis Valley in Puntarenas, Costa Rica. The goal was to determine the strength of each variable in relation to its influence on sleeping site selection, in order to discover w hich factors drive the sleeping site selection of Norops lizards. MATERIALS AND METHODS Study Site My study site consisted of a large area of dairy farm pasture and adjacent roadside habitat in the San Luis Valley, Puntarenas, Costa Rica, within the Pre montane Wet Forest Holdridge Life Zone. The habitats consisted of pasture lands, with fence posts, small trees, and long grass, as well as roadside plant communities, which were mainly composed of rocks, small shrubs, and trees. The different sites provide d a diverse array of vegetation, creating many possible sleeping sites. Study Organisms Norops biporcatus N. cupreus and N. intermedius are the three most abundant species in the study area, and were the object of this study. N. biporcatus is a large an ole species (Mean SVL = 105.25 5.25 mm) found primarily in and around trees. N. intermedius is a small to medium size species (Mean SVL = 43.38 1.06 mm) commonly found in pasture habitat both on tree trunks and posts. N. cupreus the most prevalent spe cies in my study area (N cupreus = 43, N total = 56; 77%), is also a small to medium size anole (Mean SVL = 40 2.82 mm) that is common both on posts in pasture habitat and on rocks and sticks along the roadside. This study was completed by observing these lizards in their natural habitat and measuring a wide range of variables. These variables were the following: type of sleeping site (e.g. on top of a leaf, under wood), height of perch, weather conditions (e.g. temperature, precipitation), level of protec tion provided by the sleeping site, and the size, sex, and species of each individual.
3 Daytime Every day I did visual encounter surveys around pasture areas and along the road. For each Norops I caught, I recorded its snout vent length (SVL), determined i ts sex and species, and described its perch site (e.g. tree trunk). I then drew two colored dots with Sharpie paint pens on the dorsal surface, just in front of the hind leg joint. I drew one dot on each side of the spine, with each color corresponding to a specific number (Johnson 2005; M. A. Johnson, pers. comm.). This was done in order to identify individuals when found at night and to avoid recaptures. I placed the individual into a plastic bag, to allow time for the paint marks to dry and to minimize handling time. Next, I measured the height to the ground directly below the perch. I also marked the capture location with flagging tape, labeled with the individual's ID number, in order to find the location when returning at night. I then removed the ind ividual from the bag, marked it with florescent tracking powder (procedure described below), and released it at the point of capture. Nighttime I returned at night to the capture sites in order to track each lizard and find its sleeping site. Using an ult raviolet flashlight, I followed the fluorescent powder trail of the lizard to its eventual sleeping site. Upon locating the individual, I described the type of site (e.g. tree branch) and measured the height as during the day. I also measured the ambient t emperature, and described the amount of precipitation as either rain, mist, or none. Finally, I ranked the sleeping site as either Protected or Unprotected in relation to how easily a predator would be able to detect and access the individual. These lizard s have a multitude of potential predators capable of attacking from above or below, such as snakes and birds. Therefore, it was necessary to take into account various avenues of attack and detection. Sleeping on a leaf within the canopy of a tree would the refore be considered protected due to the surrounding leaves, while sleeping on a leaf on a shrub would not. Though each might notify the lizard of a predator's approach from below, exposure to predation from above is greater for the lizard on the shrub. Florescent Powder Application Fluorescent powder pigments have increased in popularity in recent years and have been used for tracking the movements of many small mammals, amphibians, and reptiles (Mullican 1988; Fellers & Drost 1989; Kearney 2002; Birchf ield & Deters 2005). It has been shown by numerous studies that the powder has no negative effects on the study individuals, even amphibians, which have very delicate skin that is important for respiration (Rittenhouse et al. 2006; Orlofske et al. 2009). The powder used in this study was purchased from the Radiant Color Company (Richmond, CA), from the RADGLO JST Series; the two colors used were (JST 10 and JST 12). After frustrated attempts to implement the methodologies described in numerous publicati ons (Fellers & Drost 1991; Lindquist et al. 2007; Roe & Grayson 2008), I mixed alcohol based hand sanitizer gel with the powder to create a paste. I applied the mixture with a small paintbrush over all ventral surfaces, including hands, feet, and arms. The gel evaporates quickly, leaving behind just the powder, and making application faster, easier, and more effective at covering all the ventral surfaces of the individual. This new method led to much greater tracking success due to the more consistent, long er lasting trails left by the study individuals. It also provides benefits for the study animals; it ensures that no powder is blown into the eyes, nose, or mouth, and that none is placed on the dorsal surface, thereby not increasing their visibility to pr edators. Though there is a question of whether the hand sanitizer might harm the animals, each individual found at night exhibited no negative effects and appeared in prime condition. Due to their protective scales and the quick evaporation of the alcohol, it is probable that there would be no effect. However, this method would likely be hazardous to animals such as amphibians, and is not recommended.
4 Statistics In order to determine if individuals slept above or below their daytime perch height, I subtract ed the day perch height from the night perch height of a given individual (H N H D ). Any vales greater than one signified sleeping above (H N H D > 0), and any values less than one meant the individual slept below (H N H D < 0). I then analyzed the percentages o f each sex and species sleeping above or below their day height and compared each to a random distribution using Chi Square analysis. Here, the term random distribution refers to a 50/50 split that would be expected if the individuals had no preference in relation to the variable being analyzed. RESULTS Sleeping site selection seemed to be related mainly to two major factors: height of perch and level of protection provided by the site. For this reason, I will explain how variables of size, sex, and spec ies relate to these factors. Sleeping Site Height Individual SVL was significantly related to night height, with a moderate positive correlation (Fig. 1). Larger lizards prefer to sleep higher up than their smaller counterparts. Between the sexes, males and females displayed significantly different mean night height values ( 97.44 38.73 cm and 244.24 280.33 cm, respectively ) with females tending to sleep higher than males (Fig. 2). Among the three species, N. cupreus was found to sleep significantly lo wer (Mean = 44.61 38.68 cm) than the other two species (Fig. 3; Tukey Kramer, F = 23.0, p < 0.0001, DF = 2,43). FIGURE 1. Snout vent length of Norops spp. compared to sleeping site heights in the San Luis Valley Puntarenas, Costa Rica. The regression is positively significant (F = 6.84, p = 0.012, N = 44). In terms of sex, males and females displayed no difference in choosing to sleep above or below their day height (Fig. 4). However, when males were compared to a random distribution (i.e. 50% above, 50% below) they showed a significant difference, implying that they prefer to sleep below their 2 = 7.84, p = 0.0051, DF = 1). N. cupreus showed a significant difference from the other two speci es in sleeping below its day height (Fig. 5). Additionally, all three species individually displayed differences from a random distribution, suggesting that they each have a preference for either sleeping above or below their day height ( N. biporcatus 2 = 11.6, p = 0.0007, DF = 1; N. cupreus 2 =
5 31.4, p < 0.0001, DF = 1; N. intermedius 2 = 57.8, p < 0.0001, DF = 1). FIGURE 2. Mean night height comparison between male a nd female Norops spp. from the San Luis Valley, Puntarenas, Costa Rica. Male and female means were determined to be significantly different (t = 2.46, p = 0.018, DF = 44). Male N = 39, female N = 7. FIGURE 3. Mean night height comparison between Norops spe cies from the San Luis Valley, Puntarenas, Costa Rica. Bars with different letters determined to be significantly different (p < 0.05). N bip = 6, N cup = 32, N int = 8. Protection Preference Males differed from females in protection preference (Fig. 6). Females were never found sleeping in 2 = 1.0, p = 0.32, DF = 1). The three species also showed differences in their preference for protected sites, and N. biporcatus was never found in an unprotected site (Fig. 7). N. cupreus was the only species that did not 2 = 0.040, p = 0.84, DF = 1); N. intermedius strongly 2 = 57.8, p < 0.0001, DF = 1 ). Finally I compared the total percentage of protected sites to a random distribution. The observed results were significantly different than what would be expected at random, which suggests that Norops 2 = 3.92, p = 0.04 8, DF = 1). FIGURE 4. Percentage bars comparing the percent of individuals sleeping above or below their daytime perch height between male and female Norops spp. from the San Luis Valley, Puntarenas, Costa Rica. 2 = 2.26, p = 0.13, DF = 1). However, males were shown to significantly differ FIGURE 5. Perc entage bars comparing the percent of individuals sleeping above or below their daytime perch height among Norops species from the San Luis Valley, Puntarenas, Costa Rica. Differences 2 = 21.5, p < 0.0001, DF = 2). All species were also shown to significantly differ from a
6 (p < 0.05) from a random distribution. Male N = 39, female N = 7. random distribution (p < 0.05). N bip = 6, N cup = 32, N int = 8. FIGURE 6. Percentage bars comparing the pe rcent of individuals sleeping in protected or unprotected sites between male and female Norops spp. from the San Luis Valley, Puntarenas, Costa Rica. Males and females were shown to have different preferences for protected sites 2 = 6.17, p = 0.013, DF = 1). Females displayed non random preference for protected sites (p < 0.05). Male N = 40, female N = 10. FIGURE 7. Percentage bars comparing the percent of individuals sleeping in protected or unprotected sites among Norops species from the San Luis Valley, Puntarenas, Costa Rica. Significant differences were 2 = 8.26, p = 0.016, DF = 1). Only N. cupreus failed to demonstrate a significant preference for protection against a random distribution (p > 0.05). N bip = 7, N cup = 35, N int = 8. DISCUSSION Sleeping Site Height My data suggest the same trend for sleeping site selection as is seen in daytime stratification, since larger individuals are found in higher sleeping sites. This trend could be due to larger individuals maintaining their dominant position during the night, and thus, sleeping higher than smaller individu als. The results from sex comparisons suggest that the stratification seen during the daytime switches at night. Females were found in higher sites than males, which contradicts day perch trends. Males even chose to sleep below their daytime perches. In t erms of female trends, it appears that they go higher in order to find more protected sites, as all females were found in protected sites. However, the reason for males to seek out lower sleeping sites is difficult to explain. This trend among males of sle eping low may be related to their daytime competition avoidance behavior while foraging, allowing them a period of time without the stress of competition while searching for an ideal sleeping site. Size seems to be an important factor leading to nighttime stratification since the two similarly species, N. cupreus and N. intermedius demonstrated significantly different nocturnal heights. N. biporcatus and N. intermedius showed no difference in mean night height, but because of their difference in size, the y would be less likely to be competing for the same resources and would not require height stratification. This sleeping site height stratification among sympatric anole species has been noted before (Goto & Osborne 1989; Molina Zuluaga & Gutierrez Cardena s 2007) but the fact that each species displayed non random selection of sites either above or below their day heights is further evidence. It also suggests that nocturnal site selection is more than just a consequence of their daytime perch height; that they choose to further stratify at night. Protection Preference Norops lizards are often encountered sleeping on leaves of understory plants, and it has been
7 demonstrated that they prefer these relatively exposed sleeping sites in forest habitat (Singhal et al. 2007; Prez 2008). However, the trends displayed here seem to show that there are many variables that work in concert to affect protection preference. Both sex and species divisions displayed significant differences in protection preference, sugge sting that level of protection provided by a sleeping site is an important factor between males and females, and among species. Females and members of N. biporcatus were always found in protected sites and obviously have a strong preference for being prote cted. Two groups, males and N. cupreus did not show preference for protection; it is possible that selection within these groups is driven by other factors, such as height of sleeping site. Ultimately, male sleeping site selection appears to be more dri ven by height, while females seem to choose based on protection provided by the site. Species differences also exert a significant effect on these preferences. As a whole, individuals displayed a non random preference for protection, which contradicts comm only observed trends. At least in this disturbed habitat, protection is an important driving factor in sleeping site selection. ACKNOWLEDGEMENTS I would like to thank the entire Leitn family for letting me use their farm as my study site. A special than ks to Eduardo Leitn, my unofficial field assistant, for his help in finding, catching, and tracking many Norops Also, to Dr. John Cossel for providing both the fluorescent powder I used in this study and many helpful thoughts before and during the projec t. Finally, thank you to Genieva Ozuna, Pablo Allen, and Hannah Findlay for reviewing this manuscript and providing helpful and insightful comments. LITERATURE CITED Andrews, R. M. 1983. Norops polylepis (Lagartija, Anole, Anolis Lizard). In: Costa Ric an Natural History D. H. Janzen, ed. University of Chicago Press, Chicago, IL, pp. 409 410. Birchfield, G. L. and J. E. Deters. 2005. Movement Paths of Displaced Northern Green Frogs ( Rana clamitans melanota ). Southeastern Naturalist 4: 63 76. Christian, K. A., C. R. Tracy, and W. P. Porter. 1984. Physiological and Ecological Consequences of Sleeping Site Selection by the Galapagos Land Iguana ( Conolophus pallidus ). Ecology 65: 752 758. Clark, D. L. and J. C. Gillingham. 1990. Sleep site fidelity in two Puerto Rican lizards. Animal Behaviour 39: 1138 1148. Fellers, G. M. and C. A. Drost. 1 989. Fluorescent powder A method for tracking reptiles. Herpetological Review 20:91 92. ----------a nd ----------. 1991. Ecology of the Island Night Lizard, Xantusia riversiana on Santa Barbara Island, California. Herpetological Monographs 5: 28 78. Goto, M. M. and M. A. Osborne. 1989. Nocturnal Microhabitats of Two Puerto Rican Grass Lizards, Anolis pulchellus and Anolis krugi Journal of Herpetology 23: 79 81. Johnson, M. A. 2005. A new method of temporarily marking lizards. Herpetological Review 36:277 279. Kearney, M. 2002. Hot rocks and much too hot rocks: seasonal patterns of retreat site selecti on by a nocturnal ectotherm. Journal of Thermal Biology 27: 205 218. Lindquist, E. D., S. A. Sapoznick, E. J. Griffith Rodriguez, P. B. Johantgen, and J. M. Criswell. 2007. Nocturnal position in the Panamanian Golden Frog, Atelopus zeteki (Anura, Bufonidae ), with notes on fluorescent pigment tracking. Phyllomedusa 6: 37 44. Molina Zuluaga, C. and P. D. A. Gutierrez Cardenas. 2007. Uso nocturno de perchas en dos especies de Anolis (Squamata: Polychrotidae) en un bosque Andino de Colombia. Papis Avulsos de Z oologia 47: 273 281. Mullican, T. R. 1988. Radio Telemetry and Fluorescent Pigments: A Comparison of Techniques. Journal of Wildlife Management 52: 627 631. Orlofske, S. A., K. L. Grayson, and W. A. Hopkins. 2009. The Effects of Fluorescent Tracking Powder on Oxygen Consumption in Salamanders Using Either Cutaneous or Bimodal Respiration. Copeia 3: 623 627. Prez, F. J. T. 2008. Hbitat Estructural Nocturno y Fidelidal al Dormidero en Anolis cristatellus Y Anolis krugi. MS Thesis. Universidad de Puerto Rico Recinto Universitario de Mayaguez., Department of Biology, 2008.
8 Rittenhouse, T. A. G., T. T. Altnether, and R. D. Semlitsch. 2006. Fluorescent Powder Pigments as a Harmless Tracking Method for Ambystomatids and Ranids. Herpetological Review 37: 188 191. Roe, A. W. and K. L. Grayson. 2008. Terrestrial Movements and Habitat Use of Juvenile and Emigrating Adult Eastern Red Spotted Newts, Notophthalamus viridescens Journal of Herpetology 42: 23 30. Rummel, J. D. and J. Roughgarden.1985. Effects of Reduced P erch Height Separation on Competition between Two Anolis Lizards. Ecology 66: 430 444. Savage, J. M. 2002. Genus Norops In: The Amphibians and Reptiles of Costa Rica The University of Chicago Press, Chicago, IL, pp. 457 458. Singhal, S., M. A. Johnson, a nd J. T. Ladner. 2007. The behavioral ecology of sleep: Natural sleeping site choice in three Anolis lizard species. Behaviour 144: 1033 1052.