Field-Based Radiographic Imaging of Marine Megafauna: Marine Iguanas (Amblyrhynchus cristatus) as a Case Study (original) (raw)

Evaluation of a photographic technique for estimating body size in lizards from a distance

2012

Body size is often an important factor in understanding an animal's ecology. In squamates, snout-to-vent length (SVL) is a primary metric for quantifying body size. Measuring SVL typically requires capture and handling of animals, which may be difficult due to a species' behavior or its presence in complex habitat. Here, we evaluated an alternative to the capture, handling, and direct measurement of lizards via the use of paired photographs of animals in situ and with a ruler positioned in place of the lizard. Paired digital images were processed using the freely available image analysis software ImageJ. We found that snout-to-hindlimb length (SHL) measured directly on an animal was highly correlated with its SVL. In turn, SHL estimated from images was highly correlated with SHL measured directly on the animals and had an average error of 19.4 ± 16.2% (1 SD) compared with measurements made on the animals themselves. Estimates of total length from images were also highly correlated with total length measurements made directly on the animals and had an average error of 14.8 ± 12.9% (1 SD). There was no correlation between image measurement error and the distance from which photographs were made. Our results identify that the use of digital photographs and image analyses can in some cases eliminate the need to capture and handle lizards to quantify body size.

Multidisciplinary and interdisciplinary uses and approaches to vertebrate biostratigraphy

Ciencias Da Terra, 2013

Vertebrate biostratigraphy is essential to characterizing both marine and terrestrial strata by their fossil content. Calibrating biostratigraphy is an iterative and multidisciplinary process that supplies numeric ages necessary for calculating rates of change in phylogenetic processes, refining studies of evolutionary adaptation to paleoenvironmental change, and constraining molecular clocks.

BODY SIZE, DEMOGRAPHY, AND BODY CONDITION IN UTILA SPINY-TAILED IGUANAS, CTENOSAURA BAKERI

Utila Spiny-tailed Iguanas, Ctenosaura bakeri, are listed as Critically Endangered by the IUCN Redlist Assessment and are listed under Appendix II of CITES. This species occupies a portion of Utila, a small continental island located off the northern coast of Honduras, in the Bay Islands chain. Habitat destruction and overharvesting for consumption and the pet trade are among the top threats facing this species. Though first described in 1901 (Stejneger) and currently the focus of a local conservation program, little is known concerning that basic biology of this species. Combining data from six years we examined body size, sexual size dimorphism, and changes in demography and body condition over the study period. Our results indicate that males are larger and heavier than females on average, and have a longer tail for a given snout-vent length, as is the case with most iguanas. Over the study period we found an increase in the ratio of males to females, suggesting that female biased hunting pressure is increasing. This is consistent with an increase in the human population size and a preference for consuming gravid females. The body condition of both males and females declined over the duration of the study, which is suggestive of a decrease in habitat quality. These results indicate that the situation for this endangered species is becoming increasingly threatening. Conservation measures should focus on alleviating these threats through increased law enforcement, outreach, and education.

Methods of sampling marine and estuarial reptiles

167 this chapter are working to develop novel sampling strategies or to improve existing ones. Without doubt, readers of this chapter will also develop new strategies. Whether reptiles live underwater, underground, high in a forest canopy, sheltered within a mountain of rock, or in some other seemingly inaccessible place, they can be repeatedly and successfully collected and/or detected with methods currently available.

A reference database of reptile images

bioRxiv (Cold Spring Harbor Laboratory), 2024

While there are millions of reptile images available online, they are not well organized and not easily findable, accessible, interoperable, or reproducible (FAIR). More importantly, they are not standardized and thus hardly comparable. Here we present a reference database of more than 14,000 standardized images of 1,045 reptile species (969 lizard and 76 snake species), that are based on preserved specimens in 20 different collections, including 533 type species of genera and type specimens of 72 species. All images were taken with standardized views, including dorsal and ventral body shots as well as dorsal, ventral, and lateral views of the heads and other body parts. Although only 11 out of the 20 collections are cross-referenced in Vertnet, some others are indexed in GBIF, and this fraction will certainly grow in the near future. The utility of this and similar image collections will further grow with additional material and further cross-referencing, e.g., to DNA sequence databases or citizen science projects. The images are searchable and freely available on Morphobank.org (Project 5121) and on Figshare.com.

Photographic identification in reptiles: a matter of scales

2010

Photographic identification is a promising marking technique alternative to the toe-clipping, since it is completely harmless, cheap, and it allows long time identification of individuals. Its application to ecological studies is mainly limited by the time consuming to compare pictures within large datasets and the huge variation of ornamentation patterns among different species, which prevent the possibility that a single algorithm can effectively work for more than few species. Scales of Reptiles offer an effective alternative to ornamentations for computer aided identification procedures, since both shape and size of scales are unique to each individual, thus acting as a fingerprint like ornamentation patterns do. We used the Interactive Individual Identification System (I 3 S) software to assess whether different individuals of two species of European lizards (Podarcis muralis and Lacerta bilineata) can be reliably photographically identified using the pattern of the intersections among pectoral scales as fingerprints. We found that I 3 S was able to identify different individuals among two samples of 21 individuals for each species independently from the error associated to the ability of the operators in collecting pictures and in digitizing the pattern of intersections among pectoral scales. In a database of 1043 images of P. muralis collected between 2007 and 2008, the software recognized 98% of recaptures within each year, and 99% of the recaptures between years. In addition, 99% and 96% of matches were ranked among the top five, and no more than 5 minutes were needed for digitizing and processing each image. The lepidosis of reptiles is a reliable alternative to ornamentation patterns in photographic identification of reptiles, which can be effectively analysed using the I 3 S software. This result represents a significant improvement in photographic identification of reptiles since (i) this procedure can be easily extended to most other species of reptiles, (ii) all kind of individuals within a species can be marked (i.e., young, subadults and adults) despite the differences in ornamentation patterns, and (iii) it is the only technique for species, like the western green lizard, which lack a clear ornamentation pattern.

Investigation of deaths in marine iguanas (Amblyrhynchus cristatus) on Galapagos

Journal of Comparative Pathology, 1987

Large numbers of marine iguanas (Amblyrhynchus cristatus Bell) died on the Galapagos between December 1982 and August 1983. Gross and histopathological examination of five of these animals and comparison with three 1984 individuals indicated that the former had died of starvation. This was attributed to an inability to digest new species of algae which had flourished in the sea because of a rise in temperature associated with the El Niño-Southern Oscillation event in 1982 to 83. In 1984 to 85, after El Niño, conditions on the islands returned to normal; the original algal flora began to predominate and the iguana population showed a marked recovery, with increased rates of growth, survival and reproduction.