The author, Jelena Bujan, in the canopy of Pseudobombax septenatum, a deciduous tree with smooth green bark. Jelena is completing her third field season on Barro Colorado Island, in Panama.
In tropical forests, is frequently assumed that canopies are “deserts” in terms of their microclimate conditions when compared to the leaf litter far below. If indeed they are extremely hot and dry then animals living in the canopies must require a special suite of adaptations. But the truth is we don’t know to which extent tropical canopies and understory diverge in their microclimates. Temperature and relative humidity (RH) data measured across BCI’s canopy tower provide air measurements in a close proximity to the canopy. And while these data are incredibly valuable, they don’t capture the microclimates experienced by ants crawling on the canopy’s leaves and branches. Ants, only a couple of millimeters high, experience quite different environmental conditions from those measured by weather stations. To handle high temperature and low humidity they need to adapt. Desiccation resistance arises through a suite of mechanisms which may be variously costly, trading off against other aspects of organismal performance. My study focuses on desiccation resistance and the tradeoffs that ants potentially experience regarding regulation of water loss, thus tolerating low humidity levels, and their critical thermal maximum (CTmax) – two traits necessary for surviving hot and dry environments. I am testing these ideas this in a community of tropical ants experiencing two microclimates—the tropical canopy and the understory of Barro Colorado Island (BCI).
First I needed to quantify the differences in microclimates of different habitats. This field season I placed data loggers in the canopies of 5 different tree species on BCI. Since I was trying to capture as many microhabitat variations as possible, I placed them above and below the branch, in the epiphytes, in the leaf litter, on lianas etc. To see how temperature and humidity changes in correlation with the surface distance I stacked them up.
Data logger probes in different canopy microhabitats, and at different heights. Cephalotes atratus is here for scale.
The loggers are recording temperature and relative humidity (RH) every 10 min. After finding the loggers that will tolerate high humidity and deploying them, it turns out they are also interesting monkey toys. But they are also quite durable – so far they all still work (knock on wood).
Data logger’s base station after a monkey attack
And yes, we are finding that the canopy is hotter, and more variable in terms of both temperature and RH, but the desert comparison seem to be exaggerated. Still, compared to the tropical litter is saturated with water, I predict that an RH under 60% found regularly in the tropical canopy should still be stressful to its ants. One way to avoid this stress is to be desiccation resistant.
To test ant desiccation resistance, we are first measuring how long ant workers from different habitats can survive in a 0% humidity air. Then, to see to which extent ants are regulating their water loss, we are exposing live and dead workers to 0% humidity, and measured their water loss over the same time interval. I expect to find no difference in water loss between live and dead ants from the understory (that is, understory ants don’t actively regulate water loss), because they do not need to invest in water regulation since they are living in 100% RH. Canopy ants, in turn, should actively regulate water loss. As of the time of this blog entry, I’m finishing the last runs of these experiments, and the data entry awaits….
A few days ago, a good friend wrote to ask what was known about the response of tropical soil invertebrates to drought. My first response was “precious little”, and then I remembered a cool article by Diana Wheeler and Sally Levings. The back story was that Levings did here dissertation work on BCI over a span of time that included a pretty awful El Nino drought. Back then BCI had a far-sighted program of ecological monitoring which included extracting soil litter for invertebrates. Wheeler collaborated with Levings years later to write the attached paper (as of this post, cited 4 times).
Funny, if this was published today, in an era of climate change, it would doubtless have wound up in a more high profile venue than Advances in Myrmecology. It is the curse of our times that understanding how ecosystems respond to highly unusual climate events is gaining traction. I attach Wheeler and Levings (1988) and another fine paper from Levings dissertation work that deserves to be more widely known. Enjoy.
Wheeler, Diana E., and Sally C. Levings. “The impact of the 1983 El Nino drought on the litter arthropods of Barra Colorado Island, Panama.” Advances in myrmecology (1988): 309-326.
Levings, S. C., and D. M. Windsor. “Litter arthropod populations in a tropical deciduous forest: relationships between years and arthropod groups.” The Journal of Animal Ecology (1985): 61-69.
MacroEcologist extraordinaire Brian McGill visited the lab last week, visited with grad students, and gave two first rate seminars. The first laid out trends for the next 25 years of ecology. The second laid out a compelling framework for a top down theory of community organization. The most inspiring slide (out of many):
What controls S? Check. Climate limits? Check. Global abundance? Check-a-rooni. Clumping and Traits? Sounds like we’re on the right track.
A splendid time was had by all by a handful of Rosenzweig lab alums.
Pictured Michael Weiser, Mike Kaspari, and Brian McGill.
Kaspari Lab alum Natalie Clay will be joining the Biology faculty of Louisiana Tech University this September. Good going Natalie, and Go Bulldogs!
Debby and I had a lovely hike along the South Canadian River with pals Susan Dragoo (Debby’s writing partner on the Oklahoma Today piece on Nuttall) and Tim Ryan. These scenes are about 10 minutes from Campus.
Laws are like sausages, it is better not to see them being made.
I’ve known both quotes for a while, but as I just now looked them up, I discovered they have the same source, Otto Von Bismarck, Chancellor of the German Empire, 1871-1890.
I’ve been thinking a lot about politics these days. I recognize my political skills can best quantified with a negative (or imaginary) number. I also think that academics are often charmingly naive about what it takes to make and pass policy, or, at its most basic, convince people of something that they are predisposed to disbelieve.
Last night I was going through the big stack of magazines that accumulated while Debby and I were on sabbatical in Copenhagen. I came across an amazingly concise primer on what it takes to run for office, by Michael Ignatieff, in a recent New Republic . By all means, go read it. I have shamelessly quoted some of his elegant turns of phrase (e.g., “you’re right to get a hearing as the person you are”). But it is better in the original.
None-the-less, here are the lessons I learned, digested and modified by an ecologists intellectual microbiome.
So next time you are talking to a politician, of whatever stripe, note that they have a skill set, and a constitution, likely very different from your own. At the same time, if you want to get something done, in a committee, in a faculty meeting, at the city council, bear in mind Ignatieff’s wise council on the relative importance of facts vs standing, and growing a thick skin. And recall the nickname of one of the more influential legislators of the past century: Hubert Humphrey, the happy warrior.
I have always been fascinated by the civil war biography, and find Catton’s treatment of this part of U.S. Grant’s generalship both infinitely readable and as quotable as the General himself. Catton in the 1940’s and 50’s rehabilitated Grant from an undeserved reputation as a drunkard and a brute. He portrays Grant–like Lincoln, his fellow westerner and greatest protector–as someone who manuvered through the politics of the civil war (and isn’t civil war the ultimate political dustup?) via a combination of tenacity, clarity, and supreme self-knowledge. Grant was a “hard war man”, acknowledging that war was a bloody business that was only won by fighting. His battlefield directions, often written from horseback on a notepad he kept in his right front pocket, were the model of clean, understandable prose.
Speaking of which, here is Catton’s quote from a General Schofield “Grant was very far from being a modest man, as the word modest is generally understood. His just self-esteem was as far above modesty as it was above flattery … He knew his own merits as well as anybody, and he new his own imperfections. When his attention was called to a mistake he had committed he would see and admit it with a smile, which expressed the exact opposite of that feeling which most men are apt to show under like circumstances … His absolute confidence in his own judgement upon any subject which he had mastered added to his accurate estimate of his own ability.