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Why Are There More Anoles Here?

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On August 11, 2021

In All Posts, New Research

New Paper: Disentangling Controls on Animal Abundance: Prey Availability, Thermal Habitat, and Microhabitat Structure

DOI:  https://doi.org/10.1002/ece3.7930

Above: Male Anolis bicaorum, endemic to the island of Utila (photo credit Tom Brown).

Why are there more anoles in this plot? This is the question that we continually asked ourselves whilst setting up our 2018 survey plots on the small island of Utila, Honduras, home of the endemic Anolis bicaorum (pictured above). So in 2019 we set out from Heathrow airport, kitted up with A LOT of equipment, for our second field season, based at Kanahau Utila Research and Conservation Facility, with one of the goals being to look into just that (see previous Anole Annals posts on Utila and its anoles).

Above Left: Getting ready to leave Heathrow (photo: Adam Algar). Above Right: Miraculously all the field kit all safely arrived at Houston stopover.

We all know that such factors as the thermal environment, prey resources and structural habitat play important roles in the lives of our beloved anoles. And we also know that you can go to one spot and be overrun with anoles, but go to a seemingly similar spot nearby and find none (usually when the field season is drawing to a close and you still don’t have a large enough sample size). But how are these aspects of anole biology linked? Specifically what determines their abundance, and its variation, at fine scales? While ecological niche theory is well developed, empirical evidence for which factors are most important, and how they interact, is still rare for many taxa, including anoles. Given rapid environmental change, understanding the drivers and mechanisms governing abundance is now more important than ever.

We measured the abundance of the endemic Anolis bicaorum across thirteen 20x20m plots along a tropical habitat gradient, using standard mark-recapture methods, based on Heckel & Roughgarden (1979). Within these plots, we also measured factors relating to the thermal habitat suitability (using 3D printed models fitted with iButtons), structural habitat (perch surveys), canopy cover (leaf area index) and prey availability (arthropod biomass and diversity). We then used N-mixture models and path analysis to disentangle direct and indirect effects of these factors on anole abundance.

Above Left: Emma setting up 3D printed anole thermal models. Above Right: Tom out collecting 3D printed anole replica models (photo credits Adam Algar).

We first decided on several measures for each niche factor which could determine the suitability of the habitat for the anoles. For the thermal environment, we first determined the thermal preference (Tpref) range of A. bicaorum, following Battles and Kolbe (2018). We then calculated two indices to quantify the thermal habitat quality of each plot. The first was the percent of model hours that operative temperatures (from 3D models) were within the Tpref range over the 36-hour study period for each plot. The second was the total number of degrees (°C) that the models deviated from the Tpref range across all models throughout the survey period for each plot, which included the total degrees, the degrees above and degrees below the Tpref range.

Above: Many of the anoles were “side-eye” pros

As a measure of structural microhabitat quality we determined both perch availability by counting surveys and the plot basal area (a measure of stand density), across all tree trunks, palm stems and fence posts in the plot.

Above:  A. bicaorum predating on an unidentified spider (Araneae).

For prey availability, we measured arthropod biomass (g) and diversity (Simpson and Shannon’s) from a combination of leaf litter sieving and sweep-net samples taken in each plot. Sweep-net and leaf-litter samples were combined for plot level analyses.

We also measured mean leaf area index (LAI) in each plot using an Accupar LP80 ceptometer. LAI is the one-sided area of leaves per unit ground area and is a measure of canopy density; it is expected to influence thermal environment via the interception of solar radiation (Campbell & Normal 1998; Algar et al 2018).

After we determined reasonable measures of habitat suitability for each factor, we examined univariate relationships between A. bicaorum abundance and each of our habitat variables (percent of time within Tpref, deviation from Tpref, perch number, basal area, arthropod biomass, arthropod diversity and LAI) by including each predictor as a covariate in a multinomial-Poisson mixture model of abundance. The results of the most significant and strongest relationships can be seen in the figure below.

Above: Relationships between Anolis bicaorum abundance and individual niche metrics in forest plots across Utila, Honduras. Relationships were estimated using multinomial Poisson mixture models with a constant detection rate across plots. All variables are scaled to a mean of zero and unit variance; (a) reflects thermal habitat quality, (b) reflects structural habitat quality, (c) reflects prey availability and (d) reflects canopy cover.

We used these models to select a subset of these variables (one representing habitat structure, one prey availability, and one thermal quality) for subsequent path analysis; we also included LAI as the sole measure for canopy cover. We used the path analysis to evaluate the relative strength of direct and indirect effects on abundance. As we could not estimate indirect paths within a single multinomial-Poisson mixture model, we estimated abundance for the path analysis from a multinomial Poisson mixture model that included no environmental covariates, held detection rate constant, and permitted abundance to vary by plot. The results of the path analysis can be seen in the figure below.

Above: Direct and indirect effects of niche axes on A. bicaorum abundance. (a) Values are standardized path coefficients; line width is proportional to the strength of the effect, solid lines indicate statistically significant pathways. ε, unexplained variation. (b) The total effects of covariates on abundance. NP: number of perches; PB: prey biomass; LAI: mean leaf area index; TP: time within Tpref range.

Our results showed that thermal habitat quality and prey biomass both had positive direct effects on anole abundance. However, thermal habitat quality also influenced prey biomass, leading to a strong indirect effect on abundance. Thermal habitat quality was primarily a function of canopy density, measured as leaf area index (LAI). Despite having little direct effect on abundance, LAI had a strong overall effect mediated by thermal quality and prey biomass.

We have demonstrated the interconnectedness of abiotic and biotic components that determine habitat quality and animal abundance. Rather than identify a single strong control on abundance, we found key abiotic factors (canopy cover and thermal environment) affect abundance through multiple pathways and have effects that are mediated by biotic interactions and the niche of the focal species. In particular, our results suggest alignment of thermal niches across multiple trophic levels results in strong indirect effects of thermal environment on anole abundance. Losses of thermal habitat quality, particularly due to canopy loss, may thus have greater effects than appreciated when only direct effects are considered.

Our results demonstrate the role of multidimensional environments and niche interactions in determining animal abundance and highlight the need to consider interactions between thermal niches and trophic interactions to understand variation in abundance, rather than focusing solely on changes in the physical environment. Identifying the factors responsible for population change along habitat gradients will improve our understanding of how multidimensional environments and niches interact to determine population abundance. Which is more important than ever in this ever-changing world.

You can read the full paper here.

If you have any questions or just an interest in the work, please feel free to contact me emma.a.higgins@hotmail.com.

I would also just like to thank everyone again who was involved in this project, it was a lot of hard work, but great fun and it couldn’t have been done without the team effort.

Above: Part of the field team, helping process what is certainly not an anole, whilst setting up survey plots (photo credit Adam Algar).

 

References

Algar, A.C. et al. 2018. Remote sensing restores predictability of ectotherm body temperature in the world’s forests. – Glob. Ecol. Biogeogr. 27: 1412-1425. https://doi.org/10.1111/geb.12811

Campbell, G. S., and J. M. Norman. 1998. An introduction to environmental biophysics. 2nd edition. -Springer-Verlag, New York.

Battles, A.C. and Kolbe, J.J. 2018. Miami heat: Urban heat islands influence the thermal suitability of habitats for ectotherms. – Glob. Change Biol. 25: 562–576. https://doi.org/10.1111/gcb.14509

Heckel, D.G. and Roughgarden, J., 1979. A Technique For estimating the Size of Lizard Populations .Published by : Wiley on behalf of the Ecological Society of America Stable URL : http://www.jstor.org/stable/1936865 References Linked refere 60, 966–975.

 

Lizards with Sticky Toepads Rule the Trees

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On August 7, 2021

In All Posts

AUGUST 6TH, 2021 POSTED BY 

Lizards with sticky toepads have a greater clinging ability. Above, the tree canopy specialist American green anole (Anolis carolinensis). (Credit: Getty Images)

Data from 2,600 lizard species worldwide indicate that those with sticky toepads prevail.

Many lizards are phenomenal climbers. Their sharp, curved claws are ideal for clinging to tree trunks, rocks, and other rough surfaces. However, in the precarious world of tree tops—filled with slippery leaves and unstable branches—three peculiar groups of lizards possess the remarkable evolutionary accessory of sticky pads on their fingers and toes.

Sticky toepads have independently evolved in geckos, skinks, and Anolis lizards—producing tree acrobats specially adapted to life in the forest canopy. Scientists have long considered sticky toepads an “evolutionary key innovation” that allow arboreal lizards to interact with the environment in ways that many padless lizards cannot.

Yet, some lizards without toepads have adopted the canopy lifestyle, an observation that has puzzled scientists for decades. Biologists Aryeh Miller and James Stroud at Washington University in St. Louis set out to find if lizards with toepads had an evolutionary advantage for life in the trees relative to their padless counterparts.

“Lizards with toepads have a greater ecological advantage in the arboreal environment,” says Miller, a graduate student in the evolution, ecology, and population biology program at Washington University in St. Louis and lead author of the study. “Toepads are essentially a biological superpower for lizards to access new resources that lizards without toepads cannot.”

“We found that lizards with sticky feet dominate the arboreal environment. Once adapted to life in the trees, they rarely leave,” says Stroud, a postdoctoral research associate and the senior author of the paper. “Conversely, lizards without sticky toepads frequently transition away from living in trees to living on the ground.”

The study appears in Systematic Biology.

ANATOMICAL EVOLUTION

“Scientists have long wondered about the role that the origin of key innovation plays in subsequent evolutionary diversification. Lizards are an excellent type of organism for such studies due to their exceptional species richness and the incredible extent of anatomical variation and habitat use,” says Jonathan Losos, professor of biology and director of the university’s Living Earth Collaborative.

Using a recently published database of habitat use for nearly every lizard species across the globe, the researchers were able to perform a comprehensive analysis of toepad evolution in the context of lizard habitat use—for the first time, the evolutionary relationships between which lizards live in trees and which do not became clear.

“Miller and Stroud have developed an elegant new approach to understand this diversity and the role that anatomical evolution plays in shaping the great diversity of lizard kind. This work will be a model for researchers working on many types of plants, animals, and microbes,” Losos adds.

TOEPADS LET LIZARDS STICK AROUND

Miller, who led the analysis, is the first to find that species have evolved for specialized life in trees at least 100 times in thousands of lizards. In other words, it is evolutionarily easy for a lizard to become a tree lizard.

What’s difficult is sticking around (pun intended!). Toepads don’t evolve until after lizards get into the trees, not before. And padless lizards will leave trees at a high frequency—much higher than padbearing lizards.

“There are hundreds of lizards living in the trees, but over evolutionary time many of those species end up leaving for life on the ground because, presumably, they interact with these padded lizards that have a greater advantage,” Stroud says.

The next step in this research is to find out exactly what padbearing lizards can do that their padless relatives can’t. Scientists can learn about this by watching the animals in their natural habitat.

“Analyzing evolutionary relationships can tell us a lot, but next we need to go out into nature—to see what parts of the environment the lizards use and why these evolutionary relationships exist,” Miller says.

Source: Washington University in St. Louis

Insectivorous Bird Eats Anole!

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On August 6, 2021

In All Posts, New Lit Abstracts, New Research

Dominican House Wren (Troglodytes aedon rufescens) holding a juvenile Puerto Rican crested anole (Anolis cristatellus). Photo by M.P. van den Burg.

New literature alert!

Predation on the nonnative Puerto Rican crested anole (Anolis cristatellus) by the Dominican House Wren (Troglodytes aedon rufescens) on the Commonwealth of Dominica

In The Wilson Journal of Ornithology

van den Burg & Brisbane

 

Abstract

Predation on vertebrate species by insect-eating birds is rarely recorded, with only one report for the House Wren (Troglodytes aedon). On 4 January 2019, we observed a Dominican House Wren (T. a. rufescens) consume a juvenile of the nonnative Puerto Rican crested anole (Anolis cristatellus) in Roseau, Commonwealth of Dominica. This observation suggests the Dominican House Wren could additionally prey on the endemic Dominican anole (Anolis oculatus). This record aids our understanding of the ecosystem-wide impact of the A. cristatellus invasion.

Read the full article here, available as First Cite.

Tear-feeding by Cockroaches: Reptile Tears to Increase Reproductive Output?

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On July 30, 2021

In All Posts, New Lit Abstracts

Cockroach positioned on head of Anolis fuscoauratus, on 29 March 2019 in the Ecuadorian Amazon. Photo by Javier Aznar González de Rueda

New literature alert!

Lachryphagy by cockroaches: reptile tears to increase reproductive output?

In Neotropical Biodiversity

van den Burg & Aznar González de Rueda

 

Abstract

Lachryphagy, or tear-feeding, is generally considered as supplementary feeding by invertebrates with a long proboscis to acquire essential nutrients. Commonly reported vertebrate host species of lachrypaghic interactions are humans and birds, and in reptiles concern large species: turtles and crocodiles, with one report from an iguanid host. Here, we report tear-feeding by a cockroach, a species lacking a proboscis, on a small squamate species, Anolis fuscoauratus. We address how the nutritional needs for the reproductive cycle may force cockroaches to explore any dietary source with essential nutrients. In addition to birds, our report adds Anolis as invertebrate predators that are visited by lachryphagous invertebrates, interactions that may be restricted to nights to reduce predation risk for the feeding invertebrates. This report extends tear-feeding behavior to proboscis-lacking invertebrates, and to small squamate hosts, and demonstrates that lachryphagy on reptilian hosts is not restricted to diurnal occurrence. Overall, this observation suggests that similar interactions could be far more frequent.

Read the full paper here!

Owl Eats Anole!

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On July 28, 2021

In All Posts

Turns out that it happens more commonly than you might think! Here’s the latest report from The Bulletin of the Chicago Herpetological Society, a ferruginous pygmy-owl eating a clouded anole in Mexico.

NSF Grant to Study Niche Use in Anoles

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On July 27, 2021

In All Posts

From the University of Texas at Arlington press office:
SCIENTIST STUDIES ANOLE LIZARDS TO HELP CONSERVE VULNERABLE SPECIES
National Science Foundation funds UTA biologist’s investigation of islands’ reptile diversity

MONDAY, JUL 26, 2021 • LINSEY RETCOFSKY : CONTACT

 

Anole lizard

 

A biologist at The University of Texas at Arlington is studying the diversity of anole lizard species in the Caribbean islands to gain insight into why some species are common, while others are rare and possibly at risk for extinction.

The National Science Foundation awarded Luke Frishkoff, assistant professor of biology, a $1.1 million grant to investigate the reptile’s ecological niches, the set of conditions in which an organism can survive and reproduce.

Anoles with a broad niche thrive in a range of ecological conditions; those with a narrow niche are specialized to live in environments that meet their precise biological needs. Knowing the lizards’ niche characteristics will help scientists identify which species are in danger of dying out.

 

Luke Frishkoff, assistant professor of biology

 

“We are in the middle of an extinction crisis right now, and some species are more likely to go extinct in the next 100 years than others,” Frishkoff said. “Among researchers, there is a common assumption that specialization is a predicting factor for extinction. The narrower the niche, the less likely it is that a species could survive.”

Frishkoff will collaborate with Martha Muñoz, a thermal biologist at Yale University, and Luke Mahler, an evolutionary biologist at the University of Toronto, to examine three aspects of the animal’s niche: diet, where they live among vegetation and how they interact with temperature.

The team’s findings will inform researchers’ strategies to conserve vulnerable species. As a community ecologist fascinated by the question of why various types of animals choose to live where they do, Frishkoff has a driving ambition to preserve the world’s biological diversity.

“When we go hiking and observe the plants and animals that are assembled there, I feel a deep sense of mystery,” Frishkoff said. “For me, the deepest motivation is to understand the rules by which life exists in these complex ecosystems.”

Frishkoff said humans can learn a lot from anoles about how to sustain life on earth.

“These lizards are a treasure trove of knowledge about ecology and evolutionary history, and they are a great model for understanding the fundamental properties of life on earth,” Frishkoff said.

#DidYouAnole – Anolis stratulus

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On July 15, 2021

In All Posts


Photo: Chase G Mayers, iNaturalist

On the island of Puerto Rico this trunk-crown anole is locally called lagartijo manchando, but is also known as: the Puerto Rican spotted anole, spotted anole, banded anole, saddled anole, salmon lizard, barred anole, St. Thomas anole and chameleon.

They are possibly the most abundant anole in Puerto Rico but can also be found on the British Virgin Islands and US Virgin Islands. They can be spotted in a number of different habitats including urban environments, though they occupy buildings at a lower frequency than Anolis cristatellus. In Puerto Rico they can often be found in Tabonuco trees.


Photo: Steve Maldonado Silvestrini, iNaturalist

Spotted anoles are active foragers with an apparent preference for ants.

Males have an SVL of 40-44mm, and females an average of 46mm. They have large orange dewlaps that fade into yellow closer to the margins but female dewlaps are smaller and grey with orange near the throat. Spotted anoles are typically brown or pale gray with pale and dark coloured spots along its body. Unlike some of the anoles found in Puerto Rico, they don’t permanent crests but have a nuchal crest that they raise during antagonistic interactions and otherwise ridges down their backs. There is also a patch behind their eyes that darkens during these interactions as well, much like in Green anoles.


Photo: larsonek, iNaturalist

#DidYouAnole – Anolis sabanus

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On July 8, 2021

In All Posts


Photo: Delano Lewis, iNaturalist

This week’s anole, Anolis sabanus, can only be spotted on the island of Saba (Dutch W.I.).

Also called the Saban anole, this tan to pale grey coloured species is sexually dimorphic with males being covered with black spots/patches at an SVL of 29-72mm and females having a dorsal stripe and an SVL of 23-25mm. Their dewlaps are green or orange tinted.


Photo: Mark Yokoyama

In 2016, there was an introduction of the anole on the neighbouring island of Sint Eustatius. They belong to the bimaculatus series of anoles which includes other island endemics like Anolis oculatus (from my home island of Dominica).

Gina Zwicky, New Orleans based herper, is currently working on a study to see if there is a link between parasite pressure and the rise of immunity in generations of this anole, examining if evidence can be found of fluctuating selection in a natural population. Anoles are incredibly useful for research with their genomes being readily available for reference, how quickly they adapt and other factors. Island endemics especially are great research subjects due to their isolation which helps to eliminate certain other variables.


Photo: iNaturalist

#DidYouAnole – Anolis aeneus

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On July 1, 2021

In All Posts


Photo: Mikel2500, iNaturalist

Happy Thursday!

Today’s anole is the Bronze anole, Anolis aeneus! The Bronze anole can be found on most of the Grenadines (the small islands between St. Vincent and Grenada) and Grenada itself, and has been introduced to Trinidad & Tobago and Guyana.

Bronze anoles can be found in forests and some urban environments, and is one of many anole species that also feed on plant matter (Simmons et al., 2005), like nectar and seeds. Males have an SVL of 77mm while females are 55mm.


Photo: Mark Hulme, iNaturalist

Though called the Bronze anole, not all individuals are brown/bronze; some may be greyish brown or olive and their mottled pattern may be light or dark. The dewlap of the Bronze anole is pale white or green and spots of orange or yellow may be near the front edge. They spend a lot of time in a ‘survey posture’ sitting on tree trunks surveying the habitat for prey items that may come along.

Hybridisation between A. aeneus and A. trinitatis (St. Vincent bush anole) has been found to occur, with the possibility of fertile offspring (Losos, 2009).


Photo: Mike G Rutherford, iNaturalist

#DidYouAnole – Anolis cybotes

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On June 24, 2021

In All Posts


Photo: GotCritters, iNaturalist

Hello!

Thanks for sticking around while I did Black Birders Week planning, events and follow ups. I hope you were able to take part and check out the week. If not, we’ve archived the recordings and they all live somewhere on the internet which we’ve conveniently collected for you over on our website BlackAFinSTEM.com.

Now, for the anoles.

It’s funny how I accidentally did an anole this one is commonly mistaken for twice, but haven’t actually talked about it yet. But, Anolis cybotes is this week’s anole.

Commonly known as the large-headed/largehead anole because the males have really big heads (creative, I know), or the Hispaniolan stout anole, these lizards are native to Hispaniola and small neighbouring islands, but have been introduced to Suriname and everyone’s favourite state, Florida. Largehead anole males can have an SVL of ~65-70mm and females, ~52-60mm. Like many other stout brown patterned anoles, they’re also of the trunk-ground ecomorph and are territorial as adults.


Photo: Christian Nunes, iNaturalist

Male largehead anoles have a dirty white dewlap with no patterning, an easy way to tell them apart from the similarly coloured A. sagrei (red-orange dewlap), and A. cristatellus (yellow and orange dewlap). If you are able to take a closer look at its head in comparison with others, you should also be able to notice the blocky shape and size it got its name for.


Photo: GotCritters, iNaturalist

Anolis cybotes haa been studied with another similar sympatric anole, A. marcanoi, to see if anoles can recognise each other and other species by dewlap, which you can read here.

PS: It’s Pride Month and I am one of 23 scientists featured in the New Science Exhibit at Cal Academy; it’s also virtual so you can check it out here.

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