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Natural History of the green anacondas in the Venezuelan llanos
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... Our understanding of the biology of adult Green Anacondas has improved in recent years. There have been comprehensive studies of their mating system (Rivas and Burghardt, 2001;Rivas et al., 2007a), general natural history (Rivas, 2000;Rivas et al., 2007b), conservation and sustainable use (Rivas, 2007(Rivas, , 2010, predation (Rivas et al., 1999Rivas and Owens, 2000), diseases (Calle et al., 1994, foraging (Rivas, 1998(Rivas, , 2004, and demography (Rivas and Corey, 2008), along with notes on field techniques (Rivas et al., 1995;Raphael et al., 1996;Rivas, 2008). Adult anacondas live in shallow, stagnant water that is often covered by aquatic vegetation (Rivas, 2000;Rivas et al., 2007b). ...
... There have been comprehensive studies of their mating system (Rivas and Burghardt, 2001;Rivas et al., 2007a), general natural history (Rivas, 2000;Rivas et al., 2007b), conservation and sustainable use (Rivas, 2007(Rivas, , 2010, predation (Rivas et al., 1999Rivas and Owens, 2000), diseases (Calle et al., 1994, foraging (Rivas, 1998(Rivas, , 2004, and demography (Rivas and Corey, 2008), along with notes on field techniques (Rivas et al., 1995;Raphael et al., 1996;Rivas, 2008). Adult anacondas live in shallow, stagnant water that is often covered by aquatic vegetation (Rivas, 2000;Rivas et al., 2007b). They are ambush hunters that may go for long periods without a meal, although when they do eat they can take quite large meals. ...
... We systematically searched all the bodies of water in the study area with water depths less than 50 cm. Search parties were anywhere between two to six people wading through the vegetation looking for snakes by feeling under the water and probing with sticks (see Rivas et al., 2007b for a complete description of search and capture). During the first six years (1992)(1993)(1994)(1995)(1996)(1997), we sampled for about six hours a day for 55 days per season. ...
Our knowledge of the biology of neonatal snakes has lagged behind that of adult animals, mostly due to the difficulty of finding and studying neonatal snakes in the wild. Traditional approaches view neonatal reptiles as miniature replicates of their adult counterparts. In this contribution, we present data on the natural history of neonatal Green Anacondas from opportunistic captures in the wild over a 17-year period, as well as from a brief study on captive-born radio-tagged individuals. Both approaches converge in presenting a picture of the ecology of neonatal anacondas showing many similarities between their natural history and that of adult anacondas in spite of the great size difference. The neonates' biology resembles that of adults, especially males, in their preference for birds in their diet, the relative prey size they choose, slow growth rates they experience, low feeding frequency, little mobility, and preference for similar habitats of stagnant, shallow water covered by aquatic vegetation. The conventional wisdom that neonatal reptiles are replicates of their adult counterparts seems to be largely on target in Green Anacondas. © 2016 by the American Society of Ichthyologists and Herpetologists.
... However, an "open farm system" may be possible. Large pregnant females can be found along the riverbanks (Rivas 2000, Rivas et al. 2007b, caught, kept in captivity, and released after they deliver. Due to high fertility (Rivas, 2000), a large number of individuals can be produced quickly. ...
... Due to high fertility (Rivas, 2000), a large number of individuals can be produced quickly. Neonates have a high natural mortality in the field (Rivas 2000, Rivas et al. 1999, 2007b. Releasing some percentage of individuals subjected to lower captive mortality rates would presumably equal the number that would have survived to that age in nature. ...
... Releasing some percentage of individuals subjected to lower captive mortality rates would presumably equal the number that would have survived to that age in nature. Neonates can grow quickly (Holmstrom 1982, Rivas et al. 2007b, and, after a relatively short period in captivity, could provide scar-free, small-scaled skins with high value on the legal market. ...
... Large aquatic snakes usually have a great dispersal capacity, so they are expected to explore large proportions of wetlands, or even use these environments as dispersal routes to reach adjacent habitats. For example, the giant South American Anaconda Eunectes murinus and the Australian Water Python Liasis fuscus can cross multiple wetlands connected by streams, lakes, or even dry lands (Pizzatto et al., 2009;Rivas et al., 2007). On the other hand, the smaller water snake Nerodia sipedon sipedon from North America rarely moves away from a single wetland. ...
Aim: The main focus of this chapter is to provide a brief overview on global patterns of diversity and conservation of wetlands herpetofauna and discuss both ecological and morphological adaptations that facilitate life in such environments.
By treating Amazonian wetland amphibians and reptiles as our case studies, we examine their level of specificity to wetland use and current conservation status. Snakes are evaluated in more detail to illustrate reptile diversity thriving in wetlands, which is not necessarily composed of species strictly adapted to water.
Finally, both crocodilians and chelonians are considered as case studies to discuss how management initiatives have been linked to their current conservation status.
Main concepts covered
•
Ecological and morphological adaptations of herpetofauna to wetland life.
•
Global diversity and conservation status of wetland amphibians and reptiles.
•
Level of specificity of Amazonian amphibian and reptiles to wetlands use.
•
Sustainable management initiatives for crocodilians and chelonians.
Main methods covered: In this chapter, we present a thorough literature review of the current knowledge regarding the ecology and conservation of amphibians and reptiles occurring in wetlands. Overall, we use updated global IUCN Red List assessments to evaluate their global diversity and conservation status. Furthermore, we use more refined group-specific assessments when available (i.e. IUCN Tortoise and Freshwater Turtle Specialist Group (TFTSG) for chelonians; Rhodin et al., 2018; Meiri, 2018; Uetz et al., 2020 for lizards and snakes). To a great extent, we focus on Neotropical herpetofauna, and specifically on some Amazonian species as case studies to exemplify broad ecological and morphological patterns.
Conclusion/outlook: Most amphibian and reptile groups are well represented by wetland-dweller species and some groups show ecological and morphological adaptations to thrive in the water for at least some part of their lives.
Broad patterns on the diversity and conservation status of wetland herpetofauna suggest that these animal groups depend mostly on habitat integrity and availability.
... Green Iguanas are almost entirely herbivorous, with documented animal prey, mostly of juveniles, limited to terrestrial snails (Townsend et al. 2005), insects (Hirth 1963), bird eggs (Schwartz and Henderson 1991), and carrion (Loftin and Tyson 1965;Krysko et al. 2007). Despite their large size, adult Green Iguanas have numerous natural predators; these include wild cats (Chinchilla 1997;Loc-Barragán 2017), mustelids such as Tayras (Galef et al. 1976; Barrio-Amorós and Ojeda 2015) and otters (Pereira et al. 2020), coatis (Greene et al. 1978), snakes (Rivas et al. 2007;Ribeiro Sanches et al. 2018), crocodilians (Platt et al. 2006;Balaguera-Reina et al. 2018), and raptors (Greene et al. 1978), including owls (Filipiak et al. 2012). Juvenile Green Iguanas are susceptible to an even broader range of predators that include other lizards (Burghardt et al. 1977), birds such as herons (Engeman et al. 2005), cuckoos (Guedes Coutinho et al. 2014), toucans, anis, flycatchers, and icterids (Rivas et al. 1998;Savage 2002), raccoons (Smith et al. 2006) and monkeys (Rivas et al. 1998). ...
... Large aquatic snakes usually have a great dispersal capacity, so they are expected to explore large proportions of wetlands, or even use these environments as dispersal routes to reach adjacent habitats. For example, the giant South American Anaconda Eunectes murinus and the Australian Water Python Liasis fuscus can cross multiple wetlands connected by streams, lakes, or even dry lands (Pizzatto et al., 2009;Rivas et al., 2007). On the other hand, the smaller water snake Nerodia sipedon sipedon from North America rarely moves away from a single wetland. ...
Aim: The main focus of this chapter is to provide a brief overview on global patterns of diversity and conservation of wetlands herpetofauna and discuss both ecological and morphological adaptations that facilitate life in such environments.
By treating Amazonian wetland amphibians and reptiles as our case studies, we examine their level of specificity to wetland use and current conservation status. Snakes are evaluated in more detail to illustrate reptile diversity thriving in wetlands, which is not necessarily composed of species strictly adapted to water.
Finally, both crocodilians and chelonians are considered as case studies to discuss how management initiatives have been linked to their current conservation status.
Main concepts covered
•Ecological and morphological adaptations of herpetofauna to wetland life.
•Global diversity and conservation status of wetland amphibians and reptiles.
•Level of specificity of Amazonian amphibian and reptiles to wetlands use.
•Sustainable management initiatives for crocodilians and chelonians.
Main methods covered: In this chapter, we present a thorough literature review of the current knowledge regarding the ecology and conservation of amphibians and reptiles occurring in wetlands. Overall, we use updated global IUCN Red List assessments to evaluate their global diversity and conservation status. Furthermore, we use more refined group-specific assessments when available (i.e. IUCN Tortoise and Freshwater Turtle Specialist Group (TFTSG) for chelonians; Rhodin et al., 2018; Meiri, 2018; Uetz et al., 2020 for lizards and snakes). To a great extent, we focus on Neotropical herpetofauna, and specifically on some Amazonian species as case studies to exemplify broad ecological and morphological patterns.
Conclusion/outlook: Most amphibian and reptile groups are well represented by wetland-dweller species and some groups show ecological and morphological adaptations to thrive in the water for at least some part of their lives.
Broad patterns on the diversity and conservation status of wetland herpetofauna suggest that these animal groups depend mostly on habitat integrity and availability.
... Inferring that such mediumsized to large mammals and some birds may have constituted important components in the diet of large Cuban Boas is reasonable. A comparable pattern can be observed today in areas where other living giant constrictors (e.g., Boa, Eunectes, Malayopython, Python) feed on large herons, storks, antelope, deer, monkeys, capybaras, porcupines, wild pigs, and others (Shine et al. 1998;Rivas et al. 2007; see the review of Reed and Rodda 2009). Boback (2003) developed what he called the "diet alteration hypothesis," which states that the size of available prey on islands is the main factor affecting body size in gape-limited predators like snakes. ...
On oceanic islands, where carnivorous mammals are frequently absent, the niches of large predators are often filled by raptors and reptiles. Cuban Boas (Chilabothrus angulifer), along with Cuban Crocodiles (Crocodylus rhombifer) and large birds of prey, were the top predators in the Cenozoic terrestrial ecosystems of Cuba until the arrival of Homo sapiens in the region about 6,000 years ago. This ecological scenario of large boas in the genus Chilabothrus functioning as top predators in terrestrial ecosystems is repeated on each of the largest islands of the Greater Antilles. The evolution of very large size in the Cuban Boa is best explained as phyletic giantism (Cope's Rule), although other paleo-ecological selective factors might have maintained or even accentuated the evolutionary trend toward large body size (insular giantism). However, this seems not to be the case for all species of Chilabothrus, since the evolution of a small body size is repeated in several lineages, a phenomenon that is best explained by autapomorphic nanism (Island Rule). Unfortunately, the negative effects of humans on natural populations of the Cuban Boa apparently have induced a dramatic reduction in maximum body size even during the relatively short period since the first reliable measurements were recorded in the 19th century. Such a reduction in body size is consistent with that reported for other West Indian reptiles and is probably indicative of rapid evolution in response to a highly modified environment with new selective pressures.
... ), Bellosa and Mössle (2009), Calle et. al. (1994), , Cope (1869), Gay (1993), Gilmore and Murphy (1993), Infante-Rivero et. al. (2008), Lamonica et. al. (2007), Müller (1970), Petzold (1983) Rivas (1998, 2000, Rivas and Corey (2008), Rivas and Burghardt (2001), Rivas and Owens (2000), Rivas et. al. (1995Rivas et. al. ( , 1999Rivas et. al. ( , 2001Rivas et. al. ( , 2007aRivas et. al. ( , 2007b, Schreitmüller (1924), Starace (1998), Strimple (1993, , Trutnau (1982) and Vaz-Silva (2007 forms have been consistently recognized, namely Green (Eunectes murinus) and Yellow (E. notaeus), with most authors not recognizing other described variants until the period post- dating year 2000(see McDiarmid et. al. 1999 ...
A review of the taxonomy of the New World boids finds several genera as currently recognized to be paraphyletic. There are available genus names for those species within genera that have been found to be composite, should they be split to ensure monophyletic genera. The only potential exception to this is within the genus Eunectes Wagler, 1830 as currently recognized. There is a strong argument in favor of splitting the so-called Yellow Anacondas away from the so-called Green Anacondas, at the genus level as a result of clear and consistent differences between the relevant taxa. This paper formalizes this division by taking a conservative position and naming and defining a new subgenus, Maxhoserboa subgen. nov. for the Yellow Anaconda and related species.
... Capturing anacondas. To capture anacondas, we searched intensively (3-5 people simultaneously, totaling 324 researcher hours) in water bodies by wading through water, shuffling in water under vegetation, and probing vegetation and water with sticks (Rivas et al., 2007b). However, local people captured most (90%) of the animals as found opportunistically near homes. ...
Understanding of snake ecology has increased over the past two decades, but is still limited for many species. This is particularly true for the recently described Beni anaconda (Eunectes beniensis). We present the results of a radio-telemetry study of nine (3M:6F) adult E. beniensis, including home range, and habitat use. We located the snakes 242 times in wet season, and 255 in dry season. Mean wet season home range (MCP) was 25.81 ha (6.7 to 39.4 ha); while mean dry season home range was 0.29 ha (0.13 to 0.42 ha). We found no relationship between home range size and either snout-vent length, weight, or sex. Beni anacondas seem to prefer swamps, and patujusal, while avoiding forest, and rice fields. However, habitat use by individual snakes seems to vary based on the habitats available within their respective home range. Notably, rice fields were avoided by most snakes, which suggests that this type of habitat is unsuitable for anaconda management.
... Inferring that such mediumsized to large mammals and some birds may have constituted important components in the diet of large Cuban Boas is reasonable. A comparable pattern can be observed today in areas where other living giant constrictors (e.g., Boa, Eunectes, Malayopython, Python) feed on large herons, storks, antelope, deer, monkeys, capybaras, porcupines, wild pigs, and others (Shine et al. 1998;Rivas et al. 2007; see the review of Reed and Rodda 2009). Boback (2003) developed what he called the "diet alteration hypothesis," which states that the size of available prey on islands is the main factor affecting body size in gape-limited predators like snakes. ...
On oceanic islands, where carnivorous mammals are frequently absent, the niches of large predators are often filled by raptors and reptiles. Cuban Boas (Chilabothrus angulifer), along with Cuban Crocodiles (Crocodylus rhombifer) and large birds of prey, were the top predators in the Cenozoic terrestrial ecosystems of Cuba until the arrival of Homo sapiens in the region about 6,000 years ago. This ecological scenario of large boas in the genus Chilabothrus functioning as top predators in terrestrial ecosystems is repeated on each of the largest islands of the Greater Antilles. The evolution of very large size in the Cuban Boa is best explained as phyletic giantism (Cope’s Rule), although other paleo-ecological selective factors might have maintained or even accentuated the evolutionary trend toward large body size (insular giantism). However, this seems not to be the case for all species of Chilabothrus, since the evolution of a small body size is repeated in several lineages, a phenomenon that is best explained by autapomorphic nanism (Island Rule). Unfortunately, the negative effects of humans on natural populations of the Cuban Boa apparently have induced a dramatic
reduction in maximum body size even during the relatively short period since the first reliable measurements were recorded in the 19th century. Such a reduction in body size is consistent with that reported for other West Indian reptiles and is probably indicative of rapid evolution in response to a highly modified environment with new selective pressures.
... The Rainbow Boa, Epicrates cenchria (Linnaeus 1758), is indigenous to a widespread region of the Amazon Basin of South America, with a disjunct population in the Atlantic Forest of Brazil (Passos & Fernandes 2009), and it has been introduced to non-indigenous regions of Brazil and Chile (Eterovic & Duarte 2002;Kraus 2009 The Green Anaconda, Eunectes murinus (Linnaeus 1758), is widely distributed in South America, including most tropical, lowland habitats east of the Andes mountain range (Rivas et al. 2007 . This snake sought refuge inside a culvert leading to a pond, and it was believed to be the perpetrator in the disappearance of many non-indigenous Muscovy Ducks (Cairina moschata) in the area. ...
We follow a biological invasion model that consists of a series of five consecutive obligatory stages, concluding with stages 4a and 5 (i.e., widespread = invasive species). The State of Florida is infamous for having the most introduced (stages 2-5) amphibians and reptiles in the United States. However, there is disagreement regarding their numbers as well as identification in some cases. Unverified claims of species being introduced (stage 2), or established (stages 3-5) without evidence (i.e., a voucher specimen or photograph) are prevalent in the literature. It is crucial to provide data on all known non-indigenous herpetofaunal species via vouchers to help keep numbers of species consistent, accurately identify species, document when and where a particular species is found, and identify the invasion pathway and current invasion stage of each species. In this study, we use vouchers to confirm interceptions and introductions of all known non-indigenous amphibians and reptiles in Florida from 1863 through 2010, provide a list of these species along with their invasion pathways and current ecological status (i.e., invasion stage), and provide a species account for each newly confirmed species. We include species that were previously reported in the literature but lacking an associated voucherand provide greater details on previously reported species and those species whose invasion stage has been upgraded to established (stages 3-5). Based on nearly two decades of field work along with examination of museum records and literature, we confirm three intercepted and 137 introduced amphibian and reptile taxa in Florida. Of these, 56 are established (i.e., reproducing; stages 3-5), including three frogs, four turtles, one crocodilian, 43 lizards, and five snakes. Of 149 total independent introduction pathways (i.e., including a different pathway one time only for each taxon) for the 140 total non-indigenous taxa above, two (1.34%) are related to the biological control pathway, four (2.68%) to the zoo pathway, 18 (12.08%) to the cargo pathway, and 125 (83.89%) to the pet trade pathway. Florida now ranks as having the largest number of established non-indigenous herpetofaunal species in the entire world. Despite current state laws that make it illegal to release any non-indigenous animal in Florida without first obtaining a permit from the Florida Fish and Wildlife Conservation Commission, enforcement is difficult, and no person has ever been prosecuted for the establishment of a non-indigenous animal species in Florida. Because current state and federal laws have not been effective in curtailing the ever-increasing number of illegal introductions, laws need to be modified and made enforceable. At the very least, those responsible for introductions should be held accountable for compensation to clean up (= extermination) of those species for which they are responsible. Lastly, we strongly support the creation of an Early Detection and Rapid Response program to quickly identify newly found introduced species for eradication attempts. This paper will also serve as a baseline to document future introductions.
The aim of this chapter is to encourage additional studies of prey size-snake size relations. The fascinating evolutionary vistas sketched by Green (1983), Mushinsky (1987), Pough and Groves (1983), and Voris and Voris (1983) have not been explored as assiduously as they might. In this chapter I focus on one tantalizing result from the recent literature on snake diets in the hope of encouraging more work. The result is that in many of the snake species studied so far, larger snakes drop small prey items out of their diet. The implication is that snakes pass over, perhaps even avoid, some of the smallest prey items they encounter. Foraging theory is used to devise some hypotheses to explain this apparently enigmatic result. In trying to use foraging theory to this end, I was constantly plagued by the lack of relevant data. However, the lack of data is undoubtedly a reflection of our failure to adapt theory to snake biology. Perhaps even a provisional application of theory to the problem will help break the logjam.
Reptiles can harbor pathogenic microorganisms asymptomatically and serve as potential reservoirs of infection for humans, domestic animals, and other reptiles. Infectious diseases are also problematic for free-ranging reptile populations and are an important consideration in reptile reintroduction and translocation projects. There have been limited serologic studies of free-ranging reptiles for evidence of exposure to potential pathogens. In the present study, serum or plasma samples from five male and five female free-ranging Venezuelan anacondas (Eunectes murinus) were screened for antibodies to eastern, western, and Venezuelan equine encephalitis viruses, vesicular stomatitis virus, ophidian paramyxovirus, 19 Leptospira interrogans serovars, and Cryptosporidium serpentes. Antibodies to these agents were not detected, or antibody titers were low and possibly nonspecific. These results for the limited number of anacondas surveyed suggest that they do not serve as significant reservoirs for these infectious agents at this location.
1. In many animal species, dietary habits shift with body size, and differ between the sexes. However, the intraspecific range of body sizes is usually low, making it difficult to quantify size-associated trophic shifts, or to determine the degree to which sex differences in diet are due to body-size differences. Large snakes are ideal for such a study, because they provide a vast range of body sizes within a single population.
2. More than 1000 Reticulated Pythons (Python reticulatus) from southern Sumatra were examined, with specimens from 1·5 to > 6 m in snout–vent length, and from 1 to 75 kg in mass. Females attained much larger body sizes than did conspecific males (maxima of 20 vs 75 kg, 5 vs 7 m), but had similar head lengths at the same body lengths.
3. Prey sizes, feeding frequencies and numbers of stomach parasites (ascarid nematodes) increased with body size in both sexes, and dietary composition changed ontogenetically. Small snakes fed mostly on rats, but shifted to larger mammalian taxa (e.g. pangolins, porcupines, monkeys, wild pigs, mouse deer) at 3–4-m body length.
4. Adult males and females showed strong ecological divergence. For some traits, this divergence was entirely caused by the strong allometry (combined with sexual size dimorphism), but in other cases (e.g. feeding frequency, dietary composition), the sexes followed different allometric trajectories. For example, females shifted from rats to larger mammals at a smaller body size than did conspecific males, and feeding frequencies increased more rapidly with body size in females than in males. These allometric divergences enhanced the degree of sex difference in trophic ecology induced by sexual size dimorphism.
Habituation of defensive attacks directed toward a threatening stimulus was investigated in neonatal garter snakes. The focus of the experiments was on differential effects of a simple experimental process in relation to species, litter, sex, and individual. In Experiment 1 newborn Thamnophis melanogaster from four liters and newborn Thamnophis butleri from three liters were given daily tests in which snakes were confronted with a nonmoving and moving human hand. Over five successive test days the T melanogaster neonates showed a decline in number of strikes directed toward the stimuli. When retested 10-13 days later the animals showed significant response recovery. Although some of the T? butleri newborns demonstrated significant habituation, there was no overall habituation of strike scores in this species. The T? melanogaster had high strike scores, more rapid habituation to moving than nonmoving stimuli, and significant liter differences in habituation rates. The T? melanogaster, but not the T? butleri neonates, showed significant habituation of flight responses over the five tests. In T? butleri, but not T? melanogaster, males were more prone to attack than were females. In both species there were large differences in both overall strike scores and habituation rates of individual newborn animals. In Experiment 2, T? melanogaster 2-months old, were tested for short-term habituation to either a moving or nonmoving stimulus for 10 successive tests on one day. Habituation of strikes was similar to both stimuli, but more animals confronted with the moving stimulus showed an initial increase in strikes, lending support to the dual-process theory of habituation. As in Experiment 1, there were large individual differences in habituation rates. The results are discussed in terms of the ecological and methodological implications for developmental studies.
The relatively large meal sizes consumed by sit-and-wait-foraging snake species make them favorable for investigating specific dynamic action, the rise in metabolic rate associated with digestion. Hence, we measured O2 consumption rates (VO2) before and up to 20 d after Burmese pythons (Python molurus) either had only constricted and killed rodent meals or had also been allowed to consume meals ranging in size from 5% to 111% of their body mass. Postprandial VO2 peaked within 2 d at a value that increased with meal size, up to 44 times standard metabolic rate for the largest meals. In addition to being the largest known magnitude of postprandial metabolic response, this also exceeds the factorial increase in VO2 during peak physical activity for all studied animals except perhaps racehorses. Specific dynamic action, calculated from the extra VO2 above standard metabolic rate over the duration of digestion, increased with meal size and equaled 32% of ingested meal energy. The allometric exponent for body mass was 0.68 for standard metabolic rate, 0.90 for peak postprandial VO2, and 1.01 for specific dynamic action. Specific dynamic action is higher, and standard metabolic rate is lower, in sit-and-wait-foraging snake species than in actively foraging snake species. This suggests that sit-and-wait-foraging snakes, which consume large meals at long and unpredictable intervals, reduce standard metabolic rate by allowing the energetically expensive small intestine and other associated organs to atrophy between meals but thereby incur a large specific dynamic action while rebuilding those organs upon feeding.