Category: Lizards

Global lizard trait database

29/8/2018

In a recent publication in Global Ecology and Biogeograpy, I present a vast dataset of over 20 body size, ecological, thermal biology, geographic, phylogenetic and life history traits for global lizards.

Over the past 12 years I have been collecting trait data on lizards to complement GARD’s geographic data and allow asking interesting ecological, evolutionary and biogeographic questions – as well as, hopefully, informing conservation decisions. To this end I've now published geographical, morphological, ecological, physiological and life history data for the 6,657 known species of lizards. In the data paper I present descriptive statistics regarding these traits and point to avenues for future research using the dataset.

Scincus scincus (Photo: Simon Jamison)

I hope these data will facilitate more study into the biology of these most fascinating of creatures, and that the database publication will encourage others to add yet more data and to correct errors I surely have made when assembling them.

Author: Shai Meiri

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Hiding in plain sight: rare lizards are more common than we think

23/11/2017

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In a recently published paper in Diversity and Distributions we try to illuminate aspects regarding the biology, and conservation of all narrow ranged lizard species, across the globe.

We defined lizard species with the smallest ranges as those only known from a single locality, with a maximum range extent no larger than 10 km. Surprisingly, more than 900 species, or roughly 1 in seven of all known lizard species, have such small ranges. Furthermore, about 750 of these species have never been seen again after their initial discovery, and more than 200 lizard species are only known to science from a single individual.

Enyailoides altotambo from Ecuador ( Photo: Omar Torres Carvajal)

When exploring different attributes of small ranged species we found that most of them inhabit relatively inaccessible places in tropical climates worldwide. Furthermore, they are mostly small bodied species; many of them are active at night; and live in rocky habitats. Among the different lizard groups geckos and skinks dominate with many rare species.

Riama yumborum from Ecuador (Photo: Omar Torres Carvajal)

Many of these species (such as those inhabiting small islands or caves) may truly have small ranges. However others may actually have larger ranges, and we are simply ignorant of the true extent of their distribution. This is especially true those found in remote, inaccessible places with no obvious barriers to their dispersal. Thus their small ranges are potentially only an artifact of our poor knowledge. Distinguishing between these two possibilities is both illuminating from an ecological and evolutionary perspective and extremely important from a conservation point of view.

This work could help better focus conservation efforts by pointing at the species, and places, that are in the greatest need of protection. Many of the species, especially those which have not been observed for decades, may well be already extinct. However, to-date only six of the species studied have been officially recognized as such. In order to examine the true extent of such extinctions, and try to prevent future ones, the study provides invaluable information for directing future research and conservation efforts.

Lizard species known only from their type localities. Circles: species not observed after 1967. Crosses: species observed after 1967.

Authors: Shai Meiri and Uri Roll

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The Hot Eurasian nightlife - How do different environmental forces affect nocturnality in lizards?

10/10/2017

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In a recent publication in Global Ecology and Biogeography we explored the prevalence of nocturnality amongst Eurasian lizard species and tried to understand what drives these patterns.

Most animals – at least those that live above ground – are active either during the day or during the night. Being active at either time of day carries with it unique benefits and challenges, and thus particular adaptations. Because of this being nocturnal or diurnal is a trait that is pretty rigid amongst closely related species.

Lizards as a group are thought to be ancestrally diurnal. Most of them remain so to this day. Furthermore, they are ectotherms and are predominantly small bodied tetrapods and could thus be particularly affected by the climatic differences between day and night. For this work we collected distribution range and activity time data for all 1,113 lizard species found throughout mainland Eurasia. We then looked at links between richness patterns of lizards with either temperature or productivity.

Cyrtodactylus trilatofasciatus (Photo: Lee Grismer)

We found that nocturnal lizards have the highest species richness in the tropics and in deserts, and their richness decreases when they get closer to the North Pole. Nocturnal lizards are precluded altogether from the coldest regions inhabited by lizards – in high mountains and the highest latitudes.

Stenodactylus sthenodactylus (Photo Uri Roll)

Ambient temperature has a strong influence on richness patterns of both diurnal and nocturnal lizards, where species numbers increase with an increase in temperature. Productivity was found to be more tightly related to the proportion of nocturnal species – again in a positive relationship.

We think that our results point towards the fact that low temperatures are a limiting factor for lizard activity period. It is possible that the year-round warm nights of tropic regions enabled lizards to move towards nocturnal activity. In hot deserts, perhaps the combination of hot days and aridity make diurnal activity less attractive, whereas nocturnal activity can provide shelter from these extreme conditions

Author: Enav Vidan

Stenodactylus doriae (Photo Uri Roll)

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Island life only works if you’re easy-going – uncovering predictions of the island syndrome for lizard clutch size variation

18/9/2017

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In a recent publication in the Journal of Biogeography we show that Insular lizards with variable clutch sizes follow the predictions of the island syndrome, while lizards with fixed clutches do not.

Life-histories of insular species are hypothesized to slow down, a phenomenon known as the "island syndrome". Insular individuals are thus expected to lay smaller clutches of larger eggs compared with individuals belonging to closely related mainland species. Most lizards have variable clutch sizes and can lay any number between one egg and a species-specific maximum, which can be well over 50 eggs. Many lizards, such as geckos and anoles, however, lay invariant small clutches of one or two eggs, and may thus be unable to manifest some aspects of the island syndrome. We tested whether insular species with either variable or invariant clutch sizes respond to insularity differently by analyzing egg, clutch, hatchling and female sizes and brood frequencies of 2,511 lizard species.

Mediodactylus kotschyi (photo Rachel Schwarz)

Pafilis & Rachel, Kalogria region NW Peloponnes (photo Shai Meiri)

We found that insular species with variable clutch sizes lay smaller clutches of larger eggs, from which larger hatchlings emerge, compared with mainland species, as expected by the island syndrome. Lizards with invariant clutch sizes, however, lay smaller clutches on islands and increase clutch frequency, compared with mainland species, perhaps because of limitations set by the female body cavity and pelvic opening. This may result from lower seasonality of tropical islands, leading to a greater spread of reproductive effort, or as a result from fluctuations in population densities caused by tropical storms. Our results also emphasize the importance of taking differences in life-history traits into account while studying lizard reproductive traits on large phylogenetic scales.

Kampana islet (photo: Rachel Schwarz)

Author: Rachel Schwarz

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The latitudinal diversity gradient and interspecific competition: no global relationship between lizard dietary niche breadth and species richness

27/1/2017

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In a 2017 publication in Global Ecology and Biogeography, we collated a novel quantitative volumetric dietary dataset for 308 lizard species worldwide from the field and literature. This novel dataset enabled us to test seven competing hypotheses posited to explain dietary niche breadth, focusing on those that are thought to either cause, or be influenced by, the latitudinal diversity gradient.

Notomabuya frenata (photo Alison Gainsbury)

A species’ niche breadth is defined as the suite of environments or resources that the species can inhabit or use. Niche breadth is often invoked to explain the latitudinal diversity gradient. The latitudinal diversity gradient is the increase in species richness or biodiversity that occurs from the poles to the tropics. Despite this pattern having been recognized for over 200 years, the processes that drive and maintain the latitudinal diversity gradient remain unclear. We investigated which processes are important drivers of global lizard dietary niche breadth patterns, focusing on the relationship between niche breadth and species richness.

A major tenant explaining greater species richness in the tropics is interspecific competition. Dietary niche breadth has long been hypothesized to decrease from the poles toward the tropics, as the numbers of competitors increase. Geographical variation in niche breadth is also hypothesized to be linked to high ambient energy levels, water availability, productivity and climate stability – reflecting an increased number of available prey taxa. Range size and body size are also hypothesized to be strongly and positively associated with niche breadth. We sought to determine which of these factors is associated with geographical variation in niche breadth across broad spatial scales and thus potentially drive the latitudinal diversity gradient.

Overall, our findings are consistent with the notion that climate is an important predictor of dietary specialization, with both less rainfall and more stable temperatures associated with narrower dietary niches. Trophic interactions between lizard species and their arthropod prey are sensitive to climate. It is likely that climatic conditions not only affect these interactions but also alter the functional role of other vertebrate predators in terrestrial ecosystems. The sensitivity of dietary niche breadth to climate has important implications for essential ecosystem functions that maintain increased species richness in the tropics, such as food web stability and energy flow.

Norops meridionalis (photo: Alison Gainsbury)

The synergistic effects of a narrow dietary niche and small range size augments the vulnerability of species to habitat loss and climate change. Based on our findings, the ‘competitionist’s paradigm’ seems to be the exception rather than the rule in explaining the latitudinal diversity gradient.

Author: Alison Gainsbury

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Global lizard trait database

Hiding in plain sight: rare lizards are more common than we think

The Hot Eurasian nightlife - How do different environmental forces affect nocturnality in lizards?

Island life only works if you’re easy-going – uncovering predictions of the island syndrome for lizard clutch size variation

The latitudinal diversity gradient and interspecific competition: no global relationship between lizard dietary niche breadth and species richness

Author

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Global lizard trait database

Hiding in plain sight: rare lizards are more common than we think

The Hot Eurasian nightlife - How do different environmental forces af﻿fect nocturnality in lizards?

Island life only works if you’re easy-going – uncovering predictions of the island syndrome for lizard clutch size variation

The latitudinal diversity gradient and interspecific competition: no global relationship between lizard dietary niche breadth and species richness

Author

Archives

Categories

The Hot Eurasian nightlife - How do different environmental forces affect nocturnality in lizards?