Ray Huey giving the first talk of the symposium, illustrating that present day temperatures are more suitable for A. cristatellus than A. gundlachi at the El Verde Field Station (the red circles show average temperature through the day now; the gray circles are for corresponding temperatures 40 years ago).

Ray Huey giving the first talk of the symposium, illustrating that present day temperatures are more suitable for A. cristatellus than A. gundlachi at the El Verde Field Station (the red circles show average temperature through the day now; the gray circles are for corresponding temperatures 40 years ago).

This is part II of my report on the the symposium “The Biological Impacts of Tropical Climate Warming for Ectothermic Animals,” which was recently (Aug. 1-3) held in San Juan Puerto. Previously I discussed several of the talks that focused on anoles; today I summarize the rest of the symposium (the program is listed here).

Symposium co-organizer Ray Huey kicked off the symposium with opening remarks, including some important background. The symposium was funded as part of a grant headlined by Huey to investigate the effect of global warming on Puerto Rican reptiles. Huey joined forces with Paul Hertz, George Gorman, and Brad Lister, all of whom had studied Puerto Rican anoles in the 1960’s and 70’s. The goal of the proposal was to revisit their study sites to see how things had changed in the intervening time, as the climate had warmed, including as much as 2 degree  C at the El Verde Field Station. A particular species of focal interest was the forest interior montane anole, A. gundlachi. This species is adapted to low temperatures, whereas its close relative, A. cristatellus, thrives at warmer temperatures. Huey and colleagues speculated that as the forest warmed, it would become more suitable for cristatellus and less for gundlachi, resulting in a forest invasion by the former and the disappearance by gundlachi from lower elevation forests.

Imagine their surprise, then, when they found not only that cristatellus had made no inroads into the forest at El Verde, but that gundlachi, previously found only at higher elevations, could now be found at sea-level! Exactly the opposite of what had been predicted–what a conundrum!

Noted forest science Ariel Lugo explained this result clearly in the next talk. It turns out that Puerto Rico has experienced massive reforestation in the last 50 years. Consequently, even if the world is getting warmer, it is also getting more tree-covered, at least in Puerto Rico, and this latter effect has had a greater impact on gundlachi’s distribution, allowing it to occupy newly re-emerged forests at lower temperatures. An important lesson that warming is not the only thing going on in the world today and that we must consider other factors as well.

Barry Sinervo showing the grim news for lizard populations worldwide

Barry Sinervo showing the grim news for lizard populations worldwide

Much of the rest of the day was pretty gloomy, with projections of massive ectotherm disappearance in the tropics as global temperatures rise (turtles, as well as lizards, as Barry Sinervo showed), the reason being that tropical species are often closer to their upper thermal limits, and so relatively small increases in temperature may push them over the edge. Michael Kearney’s talk was particularly notable in taking an extremely detailed mechanistic analysis of how increased temperatures affect all aspects of ectotherm biology through their entire life cycle. Such studies, though very elaborate, promise particularly rich insight into the specifics of how changing temperatures will affect ectotherms. One finding of particular interest is that the amount of shade available in a habitat will be critical: more shade = good; less shade = bad. In many cases, Kearney argued, it is not the warming per se, but the effect on vegetative cover that may be most significant in effecting species like lizards.

All of the talks were fascinating and I can’t discuss them all: a few particular points stick in my head: Mike Kaspari showing that the boundary layer of air around a surface is particularly important for small animals such as ants, that may experience temperatures as much as 10 degrees C higher than the air temperature a few centimers above the surface; symposium co-organizer Patricia Burrowes showing that changes in seasonality are extremely important, particularly with regard to host-pathogen dynamics; Carlos Navas discussing the relative importance of temperature and water availability for amphibians; Ana Carnival examining geographic patterns of genetic variation to understand responses to climate change in the past; and Brad Lister showing that anoles and almost everything else at his study site in the Luquillo Mountains have declined greatly in abundance in the last 40 years.

Have this many anole biologists ever been in the field together previously? And who are they?

Have this many anole biologists ever been in the field together previously? And who are they? This photo was taken at the El Verde Field Station, site of James Stroud’s observations on rock-using canopy anoles.

Jonathan Losos
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