Foraging Behavior among the Chameleon Species - Report Example

Topic: A Report on the Foraging Behavior among the Chameleon Species A Report on the Foraging Behavior among the Chameleon Species Species Report Proposal The report focuses on the foraging behavior of chameleons. Chameleons are interesting creatures due to their ability to camouflage, their variation in size, their bulging eyes and a long curled tail. Chameleons are naturally found in forests and jungles across the Sub-Saharan Africa, Asia and some parts of Europe. Some chameleon species have also been introduced in certain habitats in America and other pats of the world. Chameleons belong to the class Reptilia, order Squamata, suborder Iguania and family Chameleonidae with two subfamilies; subfamily brookesiinae and subfamily chamaeleoninae (Chameleon forums.com) There are more than 200 known species with varying morphological and behavioral characteristics though most are considered to be under threat of extinction or endangered. Chameleons are predominantly omnivorous though some species exhibit more preference for carnivorous diet while others are more herbivorous. Some smaller species are preyed upon by some predators like birds and snake making them. Chameleons have a unique feeding strategy due to the wide variety of diets and foraging habit. Aerts Herrel, Meyers and Nishikawa observed that the retraction of the chameleon tongue pad creates suction on the prey and enhances adhesion of the tongue (3262). This report focuses on the foraging behavior of the chameleon. Objectives of the Report The specific objectives of this report are to; I. Provide an in-depth understanding of foraging mode exhibited by different chameleon species II. Examine the prey capturing mechanism in chameleons and how it is associated with the chameleon foraging mode III. Establish whether chameleons exhibit a unique prey capturing mechanism and foraging mode Characteristic Features of the Foraging Mode in Chameleons Foraging mode is one of the most crucial aspects in animal life. Foraging mode is used to describe the manner in which animals obtain food within its ecological habitat. Foraging is usually associated with other natural and behavioral traits like locomotive ability, energy utilization and reproduction among others. More importantly, foraging mode plays a critical role in determining prey-predator interactions among animal species. The chameleon’s feeding behavior is often defined in terms of foraging mode which has been mainly classified as either active or ambush (sit-and-wait) type (Hagey, Harmon and Losos 1). With regards to behavior, there are observable differences between active and ambush foragers. Active foragers exhibit a high frequency of movement, tend to prey on sedentary prey, use more energy and possess small clutch size (Butler 797). As a result of their highly motile behavior, active foraging chameleon species are likely to obtain their prey through encounter. On the other hand, the sit-and-wait foraging chameleons exhibit less movements, tend to remain still for longer periods and often run to the prey as they spot it. Active and ambush foraging is largely determined by other factors including morphological and behavioral characteristics, the type of prey and habitat use among others. It has been found that variations exist among active and ambush foragers in terms of activity levels, body temperatures and intake of calories. Most active foragers have higher levels of activity, high caloric intakes and higher body temperatures than their ambush counterparts (Hagey, Harmon and Losos 1-2). This phenomenon is true for chameleons as such differences have been observed among different chameleon species. Chameleons have unique morphological and behavioral characteristics which influences their foraging behavior. In a study aimed at investigating chameleon foraging mode in the dwarf chameleon (Bradypodium pumilum), Butler suggested that in addition to the usual active versus ambush foraging strategy in chameleons, some species have adapted an alternative cruise mode which is an amalgamation of the active and ambush mode (805). The unique foraging mode observed among this chameleon species is largely due to their extraordinarily low movement making it hard to survive within the active or ambush paradigm. Butler found that the Bradypodium pumilum exhibited variation in foraging mode which is not commonly observed in other foraging studies hence the justifying the classification of the chameleon species as a cruise forager as opposed to either active or ambush forager found in most literature (803). The findings suggest that chameleons are apparently different from sit-and-wait foragers which exhibit less variation in total movements. The study also established that chameleons did not qualify to be active foragers since they exhibit less movement compared to what is observed in active foraging species. Butler’s findings about the foraging mode in chameleons are corroborated by the study by Hagey, Harmon and Losos which involved a species in a different subfamily, chamaeleoninae jacksonii (5). The C. jacksonii species was found to have low movement frequency and low speed which is rarely seen in either active or sit-and-wait foragers. This indicates that chameleons have a unique foraging mode which is characterized as cruise foragers. Relationship between prey capturing mechanism and foraging mode in chameleons Prey capturing mechanism is an important determinant of the manner in which animals obtain their prey. Prey capturing is in turn determined by morphological and behavioral factors like size and characteristics of the tongue, jaw movements and presence or absence of papillae among others. Among the lizard species under which the chameleons lie, prey capture occurs either through tongue prehension or jaw prehension. The commonly observed prey capturing mode among most lizard species is the tongue prehension. In tongue prehension, the prey adheres to the predators tongue through an adhesive/interlocking mechanism. This mechanism is highly dependent on the nature of the tongue. The chameleon tongue pad has been found to contain numerous epithelial glands and papillae that enable the prey to be interlocked into the irregular surfaces. It is believed that in addition to the interlocking mechanism, wet adhesion is also involved. Due to the unique morphological characteristics exhibited by its tongue, chameleons exhibit unique prey capturing technique in order to catch different sizes of prey. Though its tongue mainly classified as an adhesive system, studies have indicated that an additional mechanism that would make it possible for chameleons to capture large, smooth prey which would not easily be captured through the tongue prehension mechanism. In a study to investigate the mechanisms involved in prey prehension in chameleons, Aerts, Herrel, Meyers and Nishikawa established that in addition to tongue prehension, suction plays an important role in prey capturing (3255). The authors established that the suction mechanism is facilitated by the presence of powerful pouch retractor muscles in the tongue. It was established that once the chameleon tongue is laid open after coming into contact with the prey, the pouch retractor muscles are immediately activated hence creating a suction pressure that pulls the prey as the tongue retracts back to its usual position (Aerts, Herrel, Meyers and Nishikawa 3255). Figure 1. Illustration of prey capturing in chameleon (Chameleo oustaleti): the prey is almost completely engulfed by the tongue (Source Aerts, Herrel, Meyers and Nishikawa 3257). After examining chameleons of varying species and sizes using different techniques, it has been found that suction plays a major role in prey capturing among chameleons. A large proportion of the force generated by the chameleon tongue is usually as a result of suction which enables the chameleon to capture large prey estimated to be up to 15 % of the chameleon body mass (Aerts, Herrel, Meyers and Nishikawa 3262). Aerts Herrel, Meyers and Nishikawa also observed that the retraction of the chameleon tongue pad and the resulting pouch formation not only serves to create suction on the prey but also serves to enhance the adhesion mechanism of the tongue by increasing the surface area of contact and rearranging the tongue papillae hence increasing the interlocking activity (3262). Additionally, the retraction process of the retractor muscles contributes to the prey capturing and foraging mode of the chameleon. Conclusions Chameleons have a unique morphology and behavior that exhibits a high level of divergent from that of related species. It is highly likely that the difference in morphological and behavioral characteristics have necessitated the evolution of a unique foraging strategy that is not observed among other predators. As a result, chameleons can be best classified as cruise foragers since their movement patterns do not allow them to be classified as either active or sit-and-wait foragers. Prey capturing mechanism is important in determining the foraging mode. In addition to the tongue prehension mechanism which involves formation of adhesive bonds and interlocking activity common among many related species, chameleons have an additional prey capturing mechanism. This report established that chameleons have a unique prey capturing mechanism facilitated by the presence of a powerful pouch retractor muscles which are activated after the tongue gets into contact with the prey allowing immediate retraction of the tongue. The tongue retraction not only serves to create suction on the prey but also serves to enhance the adhesion mechanism of the tongue by increasing the surface area of contact and rearranging the tongue papillae which increases the interlocking activity. The tongue retraction process contributes to the unique prey capturing and foraging mode observed in the chameleon. Works Cited Aerts, Peter, Herrel Anthony, Meyers Jay and Nishikawa Kiisa. “The mechanics of prey apprehension in chameleons”. The Journal of Experimental Biology 203: 3255-3263, 2000. Butler, Marguerite. 2005. “Foraging mode of the chameleon, Bradypodium pumilum: a challenge to the sit-and-wait versus active forager paradigm?”Biological Journal of the Linnean Society, 84: 797-808. Chameleon forums. “Chameleon taxonomy”. [Online] www.chameleonforums.com/species/ Accessed 31 Jan. 2012. Hagey, Travis, Harmon Luke and Losos Jonathan. March 2010. “Cruise foraging of invasive chameleon (Chamaeleo jacksonii xantholophus) in Hawaii”. Breviora Museum of Comparative Zoology, 516: 1-7. [Online] www.oeb.harvard.edu/faculty/losos/jblosos/pdfs/Hagey Breviora 519 opy.pdf Accessed 31 Jan. 2012. Read More