Moorish Wall Geckos in LA County

[RobertH]

Yesterday my dad and I found ourselves in San Pedro when we were going to the beach. We decided to quickly stop by the streets where the invasive Italian Wall Lizards live. I believe the population of wall lizards was established when somebody released a large quantity of them because he wanted them to live in his backyard, or something along those lines. Within thirty seconds of getting out of the car I spotted one. By the end of our neighborhood stroll, together we estimated we saw only a little under one hundred individuals, adults, sub-adults and juveniles. This did not come as a surprise to us since we had been to that area on multiple occasions before. However I was quite surprised when I spotted a gecko in a crack in the concrete. At first, naturally, I assumed Turkish house gecko but upon closer examination I realized this gecko was far to robust and spiny to be a Turkish house gecko. Quickly I remembered seeing the Moorish Wall Gecko (Tarentola mauritanica) on the California Herps website (http://www.californiaherps.com/lizards/ ... anica.html). At this point I am fairly certain that this gecko is a Moorish wall gecko however I wanted other opinions.

Moorish Wall Gecko full body by NicholasHess, on Flickr

Moorish Wall Gecko front half of body by NicholasHess, on Flickr

Moorish Wall Gecko back half of body by NicholasHess, on Flickr

Moorish Wall Gecko Head Shot by NicholasHess, on Flickr

Moorish Wall Gecko tail by NicholasHess, on Flickr

Points of interest: Bulging vertical pupil, toe-pads without claws, darker stripe running across side of head through eye, many large tubercles, anterior side of ear bordering large tubercles, Tail slightly ringed with more large tubercles. Full length: 4 in. SVL: 2 1/2 in.
Out of all the geckos that are known to live in California, I think Moorish wall gecko is the best match. I guess there is a chance that this is a completely different species of gecko I've never heard of too. There is also another species of gecko in the genus Tarentola which is the Ringed wall gecko T. annularis but that species seems to have less large tubercles. How this gecko got there is of course unknown but it is plausible that they were introduced by the same person who introduced the wall lizards (it happens that the two species of lizards ranges overlap in Italy). At the moment it is entered as a Moorish wall gecko in the Herp Database but will be corrected as needed. If this is indeed a Moorish wall gecko then that entry is a county record as well as a new species for the database. Please post your opinion, I hope you guys can help determine what this gecko is.

Thanks, Nicholas.

[Jeroen Speybroeck]

Although there's a bunch of other Tarentola species, I'd guess that's a correct ID. Just like Turkish gecko, they are notorious historical hitch-hikers in the Mediterranean as well.

[Fieldnotes]

WoW, that must have been an incredible surprise. Great pictures too, especially for being inside a crevice.

[mattg]

awesome find Nicholas

[RobertH]

Thanks for your kind replies to Nicholas.

In the meantime I contacted Greg Pauly, the curator of herpetology at the LA NHM (and also a member of this forum) and he confirmed the ID - it is in fact a Tarentola. Funny enough, he and his research group had discovered this new gecko population themselves earlier this year, in May, vouchering nine individuals of different ages in a single night. So, Nicholas did not quite discover this population, but it's still a new species for the HERP data base and a county record.

Robert

[Jimi]

Nice find, nice images. Thanks for sharing.

One minor quibble with some terminology:

invasive Italian Wall Lizards

I'll readily grant that the Podarcis are non-native. But invasive? They're also known from, what? Victoria, Long Island, Topeka, Cincinnati, and now LA? A population in Philly is thought to have gone extinct, and who knows how many have been released that failed to start a new population, but otherwise - sure, they're evidently persistent. Some of the non-native populations are expanding modestly in range and numbers, and some are not at all. It has been my impression that they behave much like most of the diverse non-native saurians in FL - they are essentially human commensals, occupying (sometimes thriving in) vacant niches, but not competing well with (to the point of exclusion by) natives in more wildland situations.

Summing up, "invasive" implies "major problem, DO something". Does anyone think that's the case with Podarcis in North America? Personally, given available information, I'm more inclined to think of them as neutral. And not deserving the effort required for exclusion or eradication. They seem to contain themselves, more or less.

I'm genuinely curious, and/but also seeking to gently curtail "scope creep" in a word, and in its associated management imperatives and potentials. If that makes sense...

cheers

[RobertH]

Jimi,

The best person to answer this question is Greg Pauly himself. In personal communications to me he indicated that he is VERY concerned about the spread of the IWLs here in the Southland. The population in SP, he told me, has spread tremendously over the last year and he's concerned that collectors may, inadvertently or intentionally, spread IWLs to other locations around CA an beyond. This is not far-fetched, unfortunately. I, personally, was contacted by a collector (another FHF member) about two years ago, who wanted to collect a few IWLs for his personal collection. So, to those of you who happen to know the SP location of IWLs, please do not divulge it to anyone you don't know or can't trust.

As to the label "invasive": True, no one, including Greg, knows at this point how well - or badly - IWLs would do outside of an urban environment, e.g., in the local chaparral. But we do know that they have several breeding cycles per year and easily and quickly out-compete local fence lizard and alligator populations in a suburban environment. Given that their native habitat includes southern Italy, including the island of Sicily, which is similar in climate to Southern California, though Sicily receives annual rainfall of 23 inches, more like the Bay Area than SoCal, I don't think it's safe to assume that IWLs pose no threat to native lizards in the wild. Even if IWLs reproduced only half or a third as fast in the wild as they do in suburbia, they would still be a formidable threat. And even if this were not the case here in SoCal, it may well be the case for less arid Central California and Northern California (where they might be released by collectors one day if they are no eradicated soon here in LA). As such, non-native IWLs are very different from non-native geckos, which as far we can tell pose no threat to native herps, so that the label "invasive" seems justified, at least until someone shows that IWLs pose no threat. Practically, that'll, of course, be very difficult or impossible to accomplish.

Robert

[Jimi]

Ah, thanks Robert, for the time and the polite reply. These things can elicit strong emotions with odious behaviors not far behind...hopefully none of our resident trolls dogpile in on this pleasant chat. And hopefully your local herper community is able to weather this issue without too much corrosion and strife. Under the dictum "show me 3 people and I'll show you 5 opinions", I'm sure there are some with divergent sentiments on the presence of this population. E.g. they add a pleasant variety to the local suburban fauna, etc etc etc.

Anyway, I suspect someone is attempting a more formal risk assessment (risk = probability * consequences). Hopefully they do a creditable job of it. Many of your points touch on important aspects or dimensions of risk assessment; there are others as well, of course, some ecological, others not.

Just by way of disclosure, I have some background in invasive squamates and practical wildlife management - I'm not being flippant or offhand, just...realistic, I guess is how I think of it. "No threat" is a high, perhaps unreasonably high bar, and we live in a triage world. I suppose time will tell what humans attempt and lizards achieve. Simply occupying numerous small private parcels greatly elevates the likelihood this population can resist whatever active managers might attempt to throw at it. And, the human attention span is just pitiful; eradication frequently surpasses our grasp.

I need to call Greg on another matter, perhaps this will come up too.

Meanwhile, happy herping to man & boy.

Cheers

[RobertH]

Likewise, Jimi, I too enjoyed our pleasant chat. I'd like to think that it was more an exchange of facts than opinions. Whether or non-native IWLS are a threat to the local herp fauna is a question of fact, nothing else.

To learn more details about what is actually being done in terms of monitoring and eradication efforts/plans, it would indeed be best if you talked directly to Greg. I didn't realize you already knew him.

Best,

Robert

[Jimi]

I didn't realize you already knew him.

Only by phone & e-mail. I've been working on a somewhat delicate, multi-party "specimen destination problem" for about the last 3 years and think things have finally come to a resolution agreeable to all. I'm thinking I will finally get to meet him in person, when I deliver a bunch of tissue specimens to him this winter.

Whether or non-native IWLS are a threat to the local herp fauna is a question of fact, nothing else.

Well, sure, in a strictly logical sense. But practical reality - i.e., the world as it actually is - intrudes here. Broadly, nature often doesn't give up her secrets cheaply or easily. Determining "the actual occupied state of a vacant fact box" (sorry, not super articulate or clear at present) can be vastly harder than it's worth attempting. A common human work-around is to fall back on "expert opinion". Refer back to my dictum...this work-around can be highly unsatisfying. More narrowly, determining the threat, a priori, that one species poses to another is challenged by the set of tools at our disposal, and their data requirements. Particularly if one wishes to remain in the realm of facts and not opinions. The principal trouble lies in forecasting, specifically 1) the eventual degree of distributional overlap, and 2) the severity of impact within that area of overlap.

Cutting to the chase, I think it would be easier to just eradicate the population than to answer "is it a threat" factually. And I do not think eradication will prove easy, if that is the chosen path. I also think about opportunity costs - what won't get done because people are working on this. Capacity is painfully finite...

Anyway, I hope that helps clarify where I'm coming from. I always enjoy your family's posts, I didn't mean this interchange to detract from one of them. Hopefully it has enhanced it.

cheers

[RobertH]

Hopefully it has enhanced it.

It absolutely has, Jimi. Your professional opinion, and eloquent explanations, are always appreciated, as I think most if not all people on this forum would agree.

You are right, of course, that as a practical matter, determining whether the IWLs in SP are in fact a threat to native herp populations in the wild would be next to impossible and probably is not worth spending the resources it would take. Someone is just going to have make a call, one way or another. And, I suppose, that would require an opinion, after all.

Personally, I am simply more interested in the factual question - whether the IWLs in SP are or could be a threat and why - than I am in what is ultimately done about the IWLs. Pragmatic solutions are necessary, but always a bit a boring to me. It's a good thing I am not in charge of anything important. I would think about and research solutions forever and never make a decision.

Take care,

Robert

[Jeroen Speybroeck]

As ever so often with alien species, they hang around at harmless numbers within a small range ('lag' phase) before they enter an exponential growth phase and become invasive. Yes, it is tough, as many may just as well maintain steady-state levels and/or crumble and disappear, but IF you can, it never hurts to act while it's still manageable. But most likely this is nothing new to any of you.

You might want to know that Podarcis siculus did some serious damage to populations of (admittedly much closer related) lizard species in Europe. The most clear example is how they outcompeted the Aeolian wall lizard, Podarcis raffonei, which is nowadays restricted to very few populations, all but one living on tiny islets where siculus wasn't introduced to (yet). In other areas, not unlike what I get from the CA situation description, they have occupied the more lush, cultivated, man-made, lowland, ... habitats, but did not really whipe the other species out (Podarcis tiliguerta on the Tyrrhenian islands (Corsica and Sardinia) and Podarcis melisellensis along the Eastern Adriatic Coast).

Maybe I was a bit surprised why you would deem siculus more of a (potential) threat to native biota than Tarentola. But, of course, there's much more insight to be gained from US herp invasions than those from Europe, as most species fail to thrive in our climate. While we do have a bunch of ancient introductions, dating back to Roman times etc. (chameleons, tortoises, geckoes, snakes, ...), the number of widespread, recent and troublesome species is fairly limited - Xenopus laevis, Lithobates catesbeianus and Trachemys scripta elegans. California king snakes are a problem on the Canary Islands, but from a biogeographical and climatological perspective those are not really European. You don't have to spend a lot of time herping in Florida to realise that things can be very, very different in a frost-free climate.

[Carl Brune]

FWIW, the Italian Wall Lizards are expanding their range in the Cincinnati area, albeit rather slowly. There's an interesting popular write up here: http://srel.uga.edu/outreach/ecoviews/ecoview140518.htm

[s_stocking]

As to the label "invasive": True, no one, including Greg, knows at this point how well - or badly - IWLs would do outside of an urban environment, e.g., in the local chaparral. But we do know that they have several breeding cycles per year and easily and quickly out-compete local fence lizard and alligator populations in a suburban environment. Given that their native habitat includes southern Italy, including the island of Sicily, which is similar in climate to Southern California, though Sicily receives annual rainfall of 23 inches, more like the Bay Area than SoCal, I don't think it's safe to assume that IWLs pose no threat to native lizards in the wild. Even if IWLs reproduced only half or a third as fast in the wild as they do in suburbia, they would still be a formidable threat. And even if this were not the case here in SoCal, it may well be the case for less arid Central California and Northern California (where they might be released by collectors one day if they are no eradicated soon here in LA). As such, non-native IWLs are very different from non-native geckos, which as far we can tell pose no threat to native herps, so that the label "invasive" seems justified, at least until someone shows that IWLs pose no threat. Practically, that'll, of course, be very difficult or impossible to accomplish.

Robert

This point of the exchange got me to thinking of Richard Hoyer's post and his concerns with the Precautionary Principle. This appears to be another case of the PP in action, right down to the point that we declare the lizard "invasive" because we don't know if is or if it has the potential to be, while also acknowledging that those skeptical of a PP claim will have to prove a negative - A level of proof that the proponents of the PP are not expected to achieve.

[RobertH]

Point well taken. You can't prove a negative.

However, consider this: We do know that in locations where non-native IWLs have become established in CA - and the places in Europe Jeroen mentioned above - they decisively and quickly do knock out competing, native lizard species. In the San Pedro neighborhood IWLs have essentially wiped out at least two native lizard species - fence lizards and alligator lizards. Surveys have detected none, and neighbors who remember seeing them in the past now say that they don't see them anymore. So, the question is not whether IWLs are invasive or have the potential of being invasive. They are and they do. The only question is how far and how quickly the invasion will spread if left unattended. Specifically, we don't know how well IWLs would do in non-urban settings of CA, e.g., chaparral. Data from IWLs invasions in Southern Europe may be instructive here, I don't know.

Since a definitive answer will be hard to come by (for the reasons we discussed above) and there is at least no ecological reason NOT to eradicate non-native IWLs, it seems that following the PP in this case makes good sense. As Jimi pointed out, though, eradication takes resources, perhaps resources the state of Ca simply doesn't have. But that is not really an argument against applying the PP. It just means that sometimes, and perhaps in this case, we can't afford to take the precautions we could and should take.

Robert

[Jeroen Speybroeck]

Interesting... I wonder how they would outcompete alligator lizard, because you'd think they occupy fairly different niches...

[RobertH]

Interesting... I wonder how they would outcompete alligator lizard, because you'd think they occupy fairly different niches...

I am not sure, of course, but it seems that at least in SP, the IWLs outcompete other lizards by sheer numbers: based on our own observations, the density of IWLs is at least twice that of what we normally see for fence lizards, e.g., in our own neighborhood. If you walk any given neighborhood in SoCal, you'll rarely see more than 2-3 fence lizards per front yard, given the right conditions. In the SP neighborhood, in contrast, we commonly see as many as 5, even 10, IWLs in the same front yard. Last time we were there, we counted at least 50 IWLs in just an hour or less and all on the same 2 blocks.

With that many additional lizards around - of any diurnal species, i.e., including fence lizards - juvenile alligator lizards are simply more likely to become prey than would normally be the case. In other words, if you doubled or tripled the density of fence lizards in any given area, the result would likely be the same. But there seem to be natural limitations on the density of fence lizards (e.g., clutch size, number of breeding cycles), limitations that apparently don't apply to IWLs in CA.

Robert

[Jimi]

Postscript to this chat - the latest Herp Review has a geographic note on P. sicula in San Marcos.