CSI Luquillo: Cold Case or Hot Pursuit? Is Climate Change Affecting Puerto Rican Lizards?

Three years ago I received a message from Ray Huey asking me if I’d be interested in collaborating on an NSF grant to return to Puerto Rico and replicate the studies on Anolis thermal biology and ecology that we had conducted during the 1970s.   The idea was to have the original investigators, including Ray, myself, and Paul Hertz, work in the same study areas, utilize the same techniques,  and document   changes that had occurred over the past 35-40 years.  Our ultimate goal was to understand the impact of climate warming on Anolis populations over a range of habitats, from the Luquillo rainforest in northeastern Puerto Rico to the Guanica dry forest in the southwestern corner of the island.

We eventually received NSF funding for the project,  and to date I have carried out field work in Luquillo and Guanica during July  2011 and January 2012.  Andres Garcia, my long term colleague from the National Autonomous University of Mexico, joined me in Puerto Rico as a co-investigator on the grant.   At the Luquillo study site, we successfully repeated all phases of the research I conducted in July 1976 and January 1977 (Lister, B. C. 1981. Seasonal niche relationships of rainforest anoles. Ecology 62(6):1548-1560).  The major components of this study were (1) a July and January census of forest dwelling anoles (A. gundlachi, A. evermanni, and A. stratulus) (2) measurements of perch heights, perch diameters, and perch site insolation (3) recording of body temperatures for all forest species (4) sweep samples of the forest understory during both the winter and summer seasons (5) collection of male and female A. gundlachi for subsequent scoring of reproductive condition and stomach content analysis.

Comparison of our results with those of my previous study indicate significant changes in all of the above areas.  (1) The total density of anoles within the 15mx15m census quadrat is 50% lower,  and biomass over 25% lower. The density of A. evermanni in the study area, formerly an abundant species along the edges and interior of the forest,  has dropped 10-20 fold. A. gundlachi abundances are down by about 25%. We did not see any A. stratulus within the study area, or in other areas of the interior forest at Luquillo.  Commonly observed along edges and more open areas in the 1970s, A. stratulus is now very rare in these habitats. (2) Within the study area, both male and female A. gundlachi have greatly expanded the range of perch heights and diameters  they utilize. (3) Compared to 1976 and 1977, body temperatures of male and female A. gundlachi were somewhat higher (~.50 C) during July and January. Interestingly, perch site insolation of males and females was substantially lower during July-January 2011-2012  than in July-January 1976-1977. (4) Our sweep samples indicate  that arthropod abundance  is now 10-15 fold less, and arthropod biomass 5-10 fold lower, than in July-January 1976-1977. (5) In July 2012, only 58% of female A. gundlachi were gravid (one or two oviducal eggs) vs. 92% in July 1976.

In conclusion, I am pleased to report that we have decisively disproved the null hypothesis of no change in the ecology of Luquillo anoles over the past three and a half decades!  But what about climate warming?  Our analyses of weather data from the El Verde station (1972-2011) indicate that mean rainfall has remained virtually unchanged, while average air temperature has increased by 20 C.  This is substantial, particularly for a tropical location.  So there’s a smoking gun right smack dab in the middle of our crime scene investigation. Let’s book the suspect!  But wait.  We’re faced with the usual problem in historical sciences  like ecology and evolution  that deal with complex, adaptive systems: a myriad number of alternative hypotheses present themselves. Perhaps, for currently obscure reasons, a sudden, critical transition occurred in the Luquillo ecosystem over the past 35 years, shifting the forest and it’s resident anoles into an alternative stable state. If this scenario actually occurred, we’re faced with the even more difficult task of cracking the proverbial  “cold case”.  Or, maybe 2011-2012 was just an anomaly and the lizards will return to the same basin of attraction they occupied in the 1970s.  Then again, it’s possible that we really are hot on the trail of the historical and ongoing effects of climate change.

Especially for all of us who love anoles, the stakes are high. The prospect of documenting the extinction of these most beautiful and wonderful species over  the coming decades is a dismal one to say the least.  We’ll be back in Puerto Rico next July to gather more data and begin transplant experiments that may give us deeper insight into the effects of climate warming.  I’ll keep you updated on our results via the Anole Annals blog.




7 thoughts on “CSI Luquillo: Cold Case or Hot Pursuit? Is Climate Change Affecting Puerto Rican Lizards?

  1. Brad, thanks for this interesting work! I look forward to your updates.

    I don’t have any good population size estimates from my work with A. carolinensis and A. sagrei in Florida but my gut feeling is that population sizes were much lower in July 2011 than July 2010. The lizards were just much harder to find last summer in places where the summer before they were abundant and easily found. For some reason, the anoles had a bad year in 2011. I’ll be interested to see your surveys from next summer. Perhaps the populations will bounce back.

  2. Hi Malcolm,

    I’m just finishing up analyzing the data from our January trip to Luquillo and
    Guanica. Andres and I would like to submit an article on the Luquillo comparisons/changes by May. We found some interesting and unexpected patterns in the Luquillo Anolis populations, as well as in the gundlachi population at the top of El Yunque, and I’m afraid I’ve taken a detour from the main goals of the project to research what might be going on.


  3. Thanks, Yoel. Interesting to know that your Florida populations had a downturn in 2011. I hope you’re right and that the Puerto Rican anoles had a similarly bad year and will rebound soon. As we now know, climate can synchronize populations over extensive geographic areas, but I guess the central question is whether there is a general negative trend along with the inevitable ups and downs. Long term changes in the abundances of Costa Rican reptiles and amphibians, not to mention lizard populations in Mexico, aren’t very encouraging. Hopefully, we can keep tracking the Puerto Rican populations. If the negative trends continue, your posting raises the question as to how widespread, and how ultimately devastating, the impacts of climate warming might be on Anolis populations throughout the Caribbean.

    1. Hey Brad,
      Just found your reply. I agree. Even if it was a down year and the populations rebound next season, the overall trends aren’t looking good. Long term data like the ones you’re collecting are key and unfortunately too rare!

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