Mating Knight anoles (Anolis equestris) at FTBG

This morning Ken and I witnessed mating Knight anoles (Anolis equestris), a non-native lizard species introduced to south Florida from Cuba, in the rainforest section of Fairchild Tropical Botanical Gardens. They were positioned ~2.5m from the ground.

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Have you seen them yet? They are in this box somewhere…

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Here is a close up – still difficult to spot!

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Aside from being a pretty rare observation, this is interesting for a couple of reasons; i) relatively little is known about this species’ ecology in south Florida, so records of breeding activity and location are important, ii) this species is naturally highly arboreal – they are morphologically adapted to life at the top of the trees possessing larger toepads and shorter limbs relative to more terrestrial Anolis sp. Therefore observing an breeding pair in action, potentially representing an individual’s most vulnerable activity to either competitors or predators, outside of their preferred habitat range is interesting! Why is this occurring there?

Of course, this could just be a fluke. The majority of breeding attempts may occur in their preferred habitat location in tree crowns outside of our detection. Either way, a nice piece of lizard behaviour for a Friday morning!

Anolis lizard predation in south Florida

A common concept in ecology is that predators have a strong influence on the behaviour of prey species. Anolis lizards have been used as a classic model system to investigate the effect of predator presence on the behavioural response of prey species. On small experimental islands in the Bahamas the manipulated introduction of curly-tailed lizards (Leiocephalus carinatus), a large terrestrial anole-predator, has resulted in brown anoles (Anolis sagrei) shifting higher up in the vegetation, presumably in an understandable effort to avoid being eaten (1, 2, 3). However, predator-prey interactions such as these which may shape community structure are often difficult to observe.

Here in Miami FL we have a rich and diverse, although largely non-native, lizard community. There are two species of “crown-giant” anoles, the Cuban knight anole (A. equestris) and the Jamaican giant anole (A. garmani), that could be potential predators of smaller anoles in the canopy of trees and upper half of tree trunks (although see Giery et al. 2013 for an empirical analysis that suggests this may not be the case). Additionally, there are several large, terrestrial lizards present which may be filling a similar role to curly-tails in the Bahamas.

Potential lizard predators in south Florida:

– *Red-headed agama (Agama agama)
– *Cuban knight anole (Anolis equestris)
– Jamaican giant anole (Anolis garmani)
– *Brown basilisk (Basiliscus vittatus)
– Spiny tailed iguana (Ctenosaura similis)
– Curly-tail lizard (Leiocephalus carinatus)
– Giant day gecko (Phelsuma grandis)
– Black and white tegu (Tupinambis merianae)

Earlier this afternoon, while taking a break from my office at Fairchild Tropical Botanical Gardens (a hot spot for any anologist visiting Miami; 1, 2, 3, 4) in a typical graduate student effort to put off work that I should be doing instead, fellow lab member Evan Rehm and I noticed some scuffling in a nearby bush. At around 2.5m, and admittedly on relatively precarious branches by this stage, sat an adult female African red-headed agama (A. agama) around 30cm from an adamantly motionless adult male Cuban brown anole (A. sagrei)! As we moved towards the bush the agama was quick to ungraciously thump itself to the floor, while the brown anole remained still. On closer inspection, it soon became apparent why both lizards were so high.

Adult male Cuban brown anole (A. sagrei) found ~2.5m high in Miami FL, supposedly following a predation attempt from an African red-headed agama (A. agama) – JStroud

The significance of tail loss/damage in a population is still debated. The classical view argues that high proportions of tail damage indicates high predation pressure, therefore prey populations are under high predation stress (1). Alternatively, high proportions of tail damage could indicate low predator efficiency, which would suggest prey populations are experiencing low predation stress (1, 2). But the debate doesn’t stop there! Having already lost a tail, a lizard may experience either a resulting increase or decrease in predation depending on the predator species and its associated foraging tactic (1).

The extent of tail damage is clearer in this photo. The lizard had autotomised the lower half of it’s tail however a secondary half-completed break is also evident – JStroud

African red-headed agamas (A. agama) are similar morphologically to curly-tailed lizards (L. carinatus), although are taxonomically distinct (Agamidae and Leiocephalidae, respectively). Predation of anoles by agamas in Miami has not previously been officially recorded, and the impact of these large predators remains unclear. Unlike in the Bahamas, there are multiple predators in the same geographic vicinity that anoles need to be aware of. For example, at Fairchild, brown anoles (A. sagrei) could be eaten from below by agamas, eaten at intermediate levels by basilisks and eaten from above by knight anoles!

South Florida is a tough place to be an anole!

Adult male African red-headed agama (A. agama) at Fairchild Tropical Botanical Gardens, Miami FL. The population of agamas is localised to the botanical gardens; the source remains unclear but is likely an introduction from the pet trade – JStroud

 

Why do we still know so little about common species?

South Florida is a wild place for lizards. And at the moment, as the region’s most abundant native lizard, life sucks for the American green anole Anolis carolinensis.

In the recent past a wealth of invasions have occurred from exotic Caribbean Anolis leading to the establishment of up to 10 non-native species around the Miami area, annually creeping further outwards towards the Everglades. The effect of congenerics on American green anoles has been well studied; the presence of an ecologically similar competitor – such as the now widespread Cuban brown anole Anolis sagrei (Fig. 2) – has forced them higher up into the trees and off the ground.

 

Fig 1. Range of the American green anole Anolis carolinensis in south-eastern United States. Different colours represent genetically distinct populations – from Campbell-Staton et. al. 2012.

However, the majority of these studies have been conducted in spatially explicit areas, that is to say on experimental islands. These have merits in themselves; it allows control of many assumptions which may skew your observations. For example, in continuous space one may expect species A to simply move away from species B if spatially out-competed, however islands offer the advantage of forced interactions meaning resource partitioning and habitat shifts may be more easily observed.

Figure 2. An adult male Cuban brown anole Anolis sagrei (Photo: J Stroud)

Isolated from all other Anolis since the pre-Pleistocene, the American green anole has had it pretty easy so far. They range from the southernmost tip of the USA, Key West, north to Tennessee, and west to mid-Texas (Fig 1). However the rapid range expansion of introduced species, pioneered by the previously mentioned Cuban brown anole, has caused the anecdotal decline of green anoles in the urban and suburban areas in south Florida. Whether this population decline is true, or a shift to arboreality has affected detection rates is unclear. What is clear is that the invasion by the exotic Anolis do not seem to be limited by habitat factors – yet.

Deep in the sawgrass plains of the Everglades the green anole still persists, for the time being at least, in allopatry. It’s ecology there is almost a complete mystery. Despite extensive research on the ecosystem, we know next to nothing about this species’ ecology here. Throughout the rest of its range a wealth of literature exists, however for populations in the Everglades we are still unclear on fundamental aspects of their ecology; habitat choice, diet, reproductive biology, sleeping sites or daily/seasonal activity patterns – all axes along which competitors may cause disruption.

And this is something that always puzzles me in ecological research – often we try to run before we can walk. Natural history is the basis of much of ecology, however in the present world of big science and meta-everything, this can often get overlooked.

 

Figure 3. For example, nectivory in American green anoles Anolis carolinensis is a relatively undocumented and still unstudied feeding behaviour whose implications are not well understood (photo: James Duquesnel, courtesy of: S. Koptur)

The potential ecological impacts of exotic anoles on the native green anole in the Everglades are unknown, and as it stands any hypothesis would be theoretical at best. However as scientists, we must remember that some of the greatest theories have arisen from natural observations. Where would evolution be without Darwin’s twitching?

Not only does the invasion expansion of Caribbean anoles present a native species conservation issue, but the potential for a large increase in terrestrial insectivores seems a topic of interest that should merit some thought for a wide range of ecologists. The Cuban brown anole is already present at every car park along the Everglades road to Flamingo, likely transported unwittingly via humans. How long we have before they begin to disperse may just be a question of time.

I encourage all of us that have the privilege to spend time outdoors in south Florida to collect as many field notes and natural history data as possible. In this world of change, the global scale effects of climatic events and warming remain unresolved, much like the more regionalised effects of human management. The importance of these data are clear, but often overlooked; they describe reality. So I return to my original question – with such a rich history of research in the Everglades why do we still know so little about the regions most charismatic lizard?