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Large initial body size and rapid early growth rate are important in many species, both because predation rates decline as individuals grow and because females that attain a larger adult body size are more fecund. To identify possible factors contributing to size and growth rate variation in hatchling green iguanas, we artificially incubated six clutches at three constant temperatures to test for effects of incubation temperature and/or clutch effects on initial size and growth rate. Higher incubation temperatures resulted in significantly shorter incubation periods but did not influence initial body size. There were significant differences among clutches in egg size, and also in initial hatchling body size, even after correcting for differences in egg size among clutches. A subset of hatchlings from each nest was reared in semi-natural conditions for four months, with individuals from the high incubation temperature condition exhibiting the slowest longer-term growth rates. No clutch effects were detected in the growth rate analyses. The observed variation in early growth rate of juvenile iguanas seems to be selectively important and this variation may be due in part to the conditions the eggs experience during incubation, but clutch effects in this study were limited to egg size and initial hatchling body size variation, but were not found for subsequent growth rates.

Few studies have been conducted on the population dynamics of crocodiles, especially in the Neotropics. This is the first study to provide data on the population dynamics of the threatened American crocodile (Crocodylus acutus (Cuvier, 1807)) in Paramillo National Natural Park. Twenty-four survey routes of 22km each were studied, and a total of 733 sightings was recorded. During the study period (from October 2014 to March 2016), the population remained stable and experienced slight growth (λ=1.049±0.428). Offspring production by the adults II stage was the most sensitive contribution (17.05), whereas the permanence of this adult stage was the demographic process that contributed the most to population growth (0.653). However, an 18% decrease in adults II would jeopardise long-term population viability and lead to a high probability of quasi-extinction, with under 300 individuals over the next 30 years. Thus, despite the apparent stability of this population, we suggest that it be considered a key target for future conservation efforts. Additionally, we recommend that this species continue to be listed as endangered in Colombia and not be modified in the CITES Appendix I.

ResumenSe determinó la ecología trófica de la lagartija Xenosaurus mendozai en Querétaro, México, identificando la importancia relativa de las presas consumidas y evaluando las diferencias intersexuales en la composición de la dieta, a lo largo de un año. Para ello, se calculó su valor de importancia (IX), se evaluó el nivel de especialización mediante el índice de Levins, así como el solapamiento mediante el índice de Pianka. Los análisis del contenido del tracto digestivo indican que son insectívoras y su dieta se basa principalmente en 12 órdenes, de los cuales las larvas de lepidópteros, los coleópteros y los ortópteros representan más del 60% de su dieta; por lo que la tendencia de esta población es hacia la especialización (BA=0.015), con un alto índice de solapamiento entre machos y hembras (OMH=0.946). En términos generales, la conformación de la dieta de esta especie es similar a lo registrado en otras especies del género, lo que puede estar determinado por el uso del microhábitat. Sin embargo, se requiere de estudio de disponibilidad de presas para describir con mayor precisión las preferencias alimentarias, así como para realizar pruebas experimentales que permitan determinar si existe preferencia por algún tipo particular de presas.AbstractThe feeding ecology of the knob-scaled lizard Xenosaurus mendozai from Querétaro, México, was studied in order to identify the relative importance of prey consumed, by evaluating the intersexual differences in the composition of their diet, throughout a year. Therefore, we calculated the importance value (IX) of each item, the trophic breadth by the standardized index of Levins’, and the dietary niche overlap using the Pianka's index. Our results indicate that these lizards are insectivorous and their diet is mainly based in at least 12 orders, of which Lepidoptera larvae, Coleoptera and Orthoptera represent over 60% of their diets; so the tendency of this population is towards specialization (BA=0.015), with a high overlap index between males and females (OMF=0.946). In general the diet of this species is similar to those reported in other species of the genus, which can be strongly influenced by microhabitat use. However, additional studies of prey availability are necessary to accurately describe food preferences, and experimental tests to determe whether there is a preference for a particular type of prey.

Flight initiation distance is defined as the distance between a prey and an approaching predator when the prey starts to flee. Escape theory predicts that the optimal flight initiation distance is the distance where predation risk rises to the point at which it equals the cost of fleeing. Therefore, staying close to refuge and occupying microhabitats with more abundant shelters (i.e., crevices or shrubs) may allow lizards to have shorter flight initiation distance. By simulating an approaching predator, we studied the effect of microhabitat structural complexity on escape behaviour, in particular, the distance fled before stopping and final distance (predator-prey distance when the prey stops fleeing), of a small diurnal tropical gecko, the yellow-headed geckoGonatodes albogularisinhabiting a tropical dry forest. The findings indicate that refuge abundance and distance to the nearest potential refuge influence escape behaviour ofG. albogularis. In addition, we found sex differences in escape behaviour which are not explained by microhabitat use. Females had longer flight initiation distance but shorter distance fled, and longer final distances than males.

"Analizamos el crecimiento corporal de una nueva especie de lagartija endémica del género Xenosaurus Peters, ubicada en la Reser va de la Biósfera, Sierra Gorda - Querétaro, México. Se estimaron las tasas de crecimiento corporal y se analizaron a partir de los modelos de crecimiento de Von Bertalanffy, logístico por longitud y logístico por peso. Para describir el patrón de crecimiento de estas lagartijas, utilizamos el modelo logístico por longitud debido a que fue el modelo que tuvo el mejor ajuste a las tasas obser vadas de crecimiento corporal. No encontramos diferencias signifi cativas entre machos y hembras en el parámetro característico de crecimiento ni en la talla asintótica proyectada. Por lo tanto, se construyó una sola cur va de crecimiento para ambos sexos. Los machos alcanzan la madurez sexual a los 24 meses, mientras que las hembras lo hacen hasta los 37 meses. Las tasas de crecimiento independientes de la talla no fueron estadísticamente diferentes entre años (2001, 2002 y 2003), ni entre estaciones (estación húmeda y seca). Nuestros resultados sugieren que la variación en el crecimiento corporal de esta especie, no es causada exclusivamente por las variaciones ambientales, sino más bien por una compleja combinación de factores ambientales y bases genéticas."

The evolution of ecological and morphological traits to attract seed dispersal animals is common in many plant species. However, these traits can also attract seed predators. These selection pressures stimulate the generation of strategies to attract more dispersers than predators. Here, we describe a strategy used by the Astrocaryum malybo palm to avoid predation of unripe fruits using prickles as a structural defense. We use camera traps to monitor three individuals of the palm for five months. We analyzed 83 videos of two animal species interacting with the palms fruits (Central American Agouti, Dasyprocta punctata and Red-tailed Squirrel, Notosciurus granatensis). Of these, six correspond to an individual with unprotected unripe fruits and 77 to an individual with exposed ripe fruits. No interaction was recorded in the individual with protected unripe fruits. We suggest that A. malybo has developed these prickles as a structural defense strategy to protect its unripe fruits from vertebrate predators. We use camera traps that allow documentation of basic natural history information including such otherwise cryptic interactions. This type of information can be used in models of food web structure, revealing unknown details of the ecological and evolutionary processes of such species interactions.

Asynchronous reproduction is a common phenomenon in high-elevation populations of lizards from Central Mexico. Sperm storage in the reproductive tract of females is the mechanism for making oocyte fertilization pos- sible. Our study addresses questions related to functional oviductal sperm storage of females mating on different dates throughout the reproductive season. A population of Sceloporus mucronatus with copulation in the summer and ovula- tion in the fall was chosen for this experiment. Eleven females that copulated in the field during June and 13 females that copulated in captivity during August were maintained in the laboratory until parturition. The number of pregnant females and the litter sizes produced in each experimental group were indicative of the viability of the stored sperm. Sperm stored in the reproductive tract of females were able to fertilize eggs after 4 months. No significant differences were found in the number of pregnant females between the 2 experimental groups nor in the litter sizes that they pro- duced. We found that the amount of time sperm were held in the female reproductive tract (ca. 3 months) had no effect on the capacity of sperm to fertilize eggs. Histological examination of 8 oviducts collected before the mating season eliminated the possibility of sperm storage from one year to the next. In this system, sperm retention could have evolved as a response mechanism to deal with the asynchrony between sexes in the reproductive cycles. However, we cannot rule out alternative hypotheses.

We report on growth and demography of Sceloporus mucronatus mucronatus, a lizard subspecies endemic to central Mexico. We characterize the life history of this subspecies, provide quantitative information relevant to conservation, and add to the growing literature on the diversity of life histories in the genus Sceloporus. We calculated body growth rates and fitted them to the Von Bertalanffy, the logistic-by-length, and the logistic-by-weight growth models. The Von Bertalanffy model provided the best fit, and we used it to analyze the growth pattern. Growth rates were similar during the 1st year of life in both sexes, but after that point males grew faster and reached maturity earlier (20 months) than females (31 months). We used a population projection matrix to model population dynamics during 2003–2004 and found a positive population growth rate (λ= 1.769). However, based on the projected stable size-class vector (w), this population does not appear to have reached stability, and it might be currently experiencing considerable interannual fluctuations. Elasticity values showed that the transition from the juvenile stage to the 1st adult stage was the vital rate that contributes the most to population growth rate, followed by fecundity and stasis of the 1st reproductive category. While total elasticities for demographic processes were similar, elasticities per size class showed the relatively high importance of small adults in comparison to juveniles and large adults. The restriction of this endemic subspecies to central Mexico, where human activities and consequent habitat destruction are increasing, demands further quantitative evaluation and monitoring of populations, even though our results indicate a potential for population growth.

Background: Caudal autotomy appears to be an adaptation strategy to reduce the risk of being preyed upon. In an encounter with a predator, the prey must reduce the risk of being preyed upon, and one of the strategies that has exerted a strong pressure on selection has been tail loss. In lizards, it has been demonstrated that tail loss reduces the probability of survival in the event of a second attack; therefore, they must resort to new escape strategies to reduce the risk of falling prey. In order to evaluate the effect of tail loss on the escape behavior of Gonatodes albogularis in natural conditions, we took samples from a forest interior population. We expected that individuals that had not lost their tails would allow the predator to get closer than those that had lost it. For each sample, we recorded the following: (1) escape behavior, measured through three distances (e.g., approach distance, escape distance, and final distance); (2) distance to shelter; and (3) length of tail. We included only males in the study since we did not record any females without a tail and far fewer with a regenerated tail. Results: We found that tail loss does have an effect on the escape behavior of G. albogularis. Males that have their tails intact allow the predator to come closer, and we found a negative correlation between the approach distance and the length of the tail. Conclusion: Our results support the escape behavior theory, in which G. albogularis males drop their tails when the risk of predation is much higher than the cost of fleeing., Facultad de Ciencias Naturales y Museo

La diversificacion fenotipica al interior de una especie en caracteristicas de dimensiones corporales relacionadas con la locomocion de los lagartos, se ha estudiado poco en especies de Anolis. Los datos de algunas especies de isla revelan patrones distintos de variacion geografica y sugieren que la adaptacion local, debida a la heterogeneidad del habitat, ocurre a este nivel. Los estudios de especies de continente son particularmente escasos y sugieren patrones distintos: un lagarto altoandino altamente variable y poblaciones poco diferenciadas en una especie amazonica. Caracterizamos la variacion inter poblacional en el tamano y forma del cuerpo del lagarto altoandino Anolis ventrimaculatus, especie endemica del Oeste de Colombia. Encontramos variacion geografica en el dimorfismo sexual en tamano y forma. El patron de variacion en las proporciones corporales entre poblaciones fue distinto en machos y en hembras, sugiriendo que las presiones de seleccion sexual o natural son diferentes en cada localidad. Dado que la especie exhibe una distribucion fragmentada en alta montana, la divergencia genetica entre poblaciones puede ser otro factor causal de la variacion observada. Datos ecologicos, etologicos y morfologicos adicionales, asi como informacion filogenetica puede contribuir al entendimiento de los procesos evolutivos responsables del patron de variacion geografica encontrado en esta especie.

We studied the demography and nesting ecology of two populations of Iguana iguana that face heavy exploitation and habitat modification in the Momposina Depression, Colombia. Lineal transect data was analyzed using the Fourier model to provide estimates of social group densities, which was found to differ both within and among populations (1.05-6.0 groups/ha). Mean group size and overall iguana density estimates varied between populations as well (1.5-13.7 iguanas/ha). The density estimates were far lower than those reported from more protected areas in Panama and Venezuela. Iguana densities were consistently higher in sites located along rivers (2.5 iguanas/group) than in sites along the margin of marshes, probably due to vegetational differences (1.5 iguanas/group). There was no correlation between density estimates and estimates of relative abundance (number of iguanas seen/hour/person) due to differing detectabilities of iguana groups among sites. The adult sex ratio (1:2.5 males:females) agreed well with other reports in the literature based upon observation of adult social groups, and probably results from the polygynous mating system in this species rather than a real demographic skew. Nesting in this population occurs from the end of January through March and hatching occurs between April and May. We monitored 34 nests, which suffered little vertebrate predation, perhaps due to the lack of a complete vertebrate fauna in this densely inhabited area, but nests suffered from inundation, cattle trampling, and infestation by phorid fly larvae. Clutch sizes in these populations were lower than all other published reports except for the iguana population on the highly xeric island of Curaçao, implying that adult females in our area are unusually small. We argue that this is more likely the result of the exploitation of these populations rather than an adaptive response to environmentally extreme conditions.