An Isotopic Study of Diet and Muscles of the Green Iguana (Iguana iguana) in Puerto Rico

Abstract

1 SummaryA study was conducted to examine the distribution, abundance patterns, and ecological and social impacts of the invasive green iguana (Iguana Iguana) in the San Juan Bay Estuary (SJBE) ecosystem. Censuses, experiments, and interviews were performed across the estuary to learn about ecological impacts, and people's interactions and attitudes towards iguanas. In censuses it was found that iguanas are not randomly distributed across the SJBE mangrove forests, but that are aggregated at two spatial scales. At the local scale, iguanas clump in mangrove trees, and at the landscape scale they aggregate in disturbed areas of the SJBE, especially near edges and urban settlements.This means that iguanas appear to be more numerous to people than they actually are in the ecosystem -and they impact the urban environment at ecosystem edges more severely than they do impact pristine areas of the ecosystem. Indeed, results show that pristine pure-stand mangrove forest away from edges had very few or no iguanas. Iguanas also fed nonrandomly on mangrove species, and clearly preferred black mangrove (Avicennia germinans) when available. Over 80% of black mangroves in the Caño Martín Peña were moderately or severely damaged by the reptiles. The combined effects of spatial clumping at the local and landscape scale resulted in a concentration of iguana herbivory in already disturbed mangrove stands, resulting in high defoliation and mortality rates for mangroves where iguanas aggregate near edges and urban settlements. An experiment using automatic cameras to test the capacity and frequency of nest predation by iguanas was performed in areas of high iguana density in the Caño Martín Peña. Despite interacting frequently and easily of the artificial nests and the fresh eggs, no nest predation was detected. In turn, rats were recorded predating the eggs in artificial nests a couple of times. This experiment shows that iguanas, if anything, are not commonly interested in feeding on eggs, even when found in unprotected nests. 2People have been observing and interacting with iguanas in the SJBE for at least two decades. SJBE residents and resource users' attitudes about green iguanas varied. For some, iguanas are a welcome and interesting part of the landscape and some do not welcome iguanas at all. Others have ambiguous opinions about the iguanas or recognize that iguanas bring both challenges and benefits to the ecosystem they interact with, including humans. Regardless of their opinions or worries about the iguanas, most interviewed people did not approve of systematic extermination of green iguanas as a control strategy. Almost unanimously, people expressed an interest in learning more about the iguanas and their impact in local ecosystems.This represents a good opportunity for outreach and ecological education with SBJE human communities. Freelisting exercises of people's perceptions of iguana diets revealed that SBJE residents and resource users have an accurate perception of iguana diets as herbivorous, paying attention to ...

Can green iguanas compensate for vanishing seed dispersers in the Atlantic forest fragments of north‐east Brazil?

“…Iguanas in this study swallowed seeds up to 9.2 mm wide, but fruits of up to 20 mm wide have been recorded being swallowed by green iguanas in previous studies (Swanson, ; Govender et al ., ). In fact, Swanson () found up to 79 seeds of these fruits, Spondias mombin , in the gut of a single animal, indicating a significant capacity to consume many large seeds.…”

“…The green iguana Iguana iguana has the widest geographical distribution among the neotropical lizards (Central America to southern Brazil and Paraguay) and occupies a variety of habitats (Vitt & Caldwell, 2009). Iguana iguana are arboreal, medium-sized lizards (6 kg; length: 1.7 m: Swanson, 1950), and, like most other species of Iguanines (Iguanidae, 8 genera, 29 species), feed on leaves, flowers and fruits (Lazell, 1973;Rand et al, 1990;Campbell, 1998;Godinez-Alvarez, 2004;Govender et al, 2012). Although I. iguana disperse seeds (Valido & Olesen, 2007;Govender et al, 2012), available information is scant.…”

Effects of invasive Green Iguanas (Iguana iguana) on seed germination and seed dispersal potential in southeastern Puerto Rico

“…Some studies have characterized the distribution, diet, and reproduction patterns of Green Iguanas in Puerto Rico (García-Quijano et al 2011;Govender et al 2012;López-Torres et al 2012), but no study has assessed effects on seed germination and the potential for seed dispersal by Green Iguanas. This species feeds primarily on vegetation, specifically leaves, flowers and fruits (Rand et al 1990;Lara-López and González-Romero 2002;Figueiredo-de-Andrade et al 2011;Govender et al 2012).…”

“…This species feeds primarily on vegetation, specifically leaves, flowers and fruits (Rand et al 1990;Lara-López and González-Romero 2002;Figueiredo-de-Andrade et al 2011;Govender et al 2012). Green Iguanas have a number of characteristics that should make them successful seed dispersers, including consumption of fruits, relatively long passage times, microbial activity in the intestinal tract, and the ability to swallow food in large portions, which allows them to process seeds without destroying them by chewing (Troyer 1984a,b;van Marken 1992;Schupp 1993).…”

“…Because Green Iguanas are the largest and most abundant vertebrate frugivore in Puerto Rican mangrove forests, their impact on seed germination may be important for plant community structure (Iverson 1985). Previous studies of Green Iguana diet in Puerto Rico have found they consume plant material from both native and nonnative species, including seeds of the highly invasive Brazilian pepper, Schinus terebinthifolius (Govender et al 2012). If Green Iguanas promote the germination of non-native species compared to native species, then they could pose a threat to native communities by facilitating the spread of potentially invasive species.…”