It is a rare pleasure to have a scientific study covered by the popular media. We got lucky with a recent publications on leaf shrinkage and climate. Inside Science TV, an educational channel produced by the American Institute of Physics, sent a film crew to our lab earlier this year to talk with University of Arizona professor Brian Enquist and me about this study.
Doing TV is a challenge that our lab has faced before with different National Geographic and PBS programs (follow the links to see us in action). It’s hard to know which soundbites or footage will be best for the program’s producers, so we spend a long time with each crew to provide them many options. I am always embarrassed to see myself on video, but the piece looks great overall – check it out!
Walking on an unfamiliar city street, do you ever feel as though someone is looking at you, with eyes that are curious, desirous, suspicious, or otherwise? The feeling can be unsettling, but is a pale comparison to walking in a forest. The natural world is also full of eyes, but these eyes are hungry.
Tennyson once rightly called nature ‘red in tooth and claw’. Life in the natural world is a nasty business, filled with bright eyes keen on eating by whatever means possible. Walking an unfamiliar forest one feels the gazes of countless creatures, great and small, peering out at each other. Eyes looking for prey, and eyes looking for predators. In this photograph I am sure the kite was looking at me as much as I was looking at it.
I often feel myself to be an unwelcome interloper in these complex natural food webs, imagining how my presence changes the rules of the game played by these countless organisms. I feel looked at.
But not every organism walks so carefully, fearful of the eyes of others. Some protect themselves with bright warning colors and toxic chemicals, like these hairy stinging caterpillars.
This caterpillar I found on my trouser leg halfway through a lunch break, with no recollection of when it crawled on to me. But with its bright colors and fine long hairs, I was easily convinced to leave it alone.
These three caterpillars we found on the forest floor, eating their way through some leaves with no concern for our presence. I made the mistake of touching one and felt a soft burning in my finger for the rest of the afternoon. After that experience, I found that twig chopsticks were a better way to examine these insects.
The hunt is a game I am unaccustomed to play, since my food comes from agriculture, and I can readily exchange money for sustenance. I have never had to rely on my ability to find food, or had to worry about starvation. In this I am lucky, but looking at these animals’ hungry eyes makes me feel somehow lessened.
Sometimes ecologists don’t look like they’re working very hard. I had a day where the major accomplishment was collecting three leaves from the forest. But what if I told you that each leaf was thirty-four feet long? The scourge of our research project is the giant Attalea butyracea. We are measuring the average area of leaves for all the dominant species in our transects, and the American oil palm happens to be one of them.
Palms are evolutionarily very strange. They don’t develop wood in the same way as other species, relying instead on a diffuse growth of fibrous tissue to provide structural support (think of them as grasses gone bad). The woody structures you see above are actually enlarged leaf petioles, the usually flimsy bases of leaves that attach them to stems. The things that look like leaves are actually evolutionary equivalent to leaflets (pinnae) like you might see on a mesquite or ash tree.
The consequence of this evolutionary biology digression is simple: when we measure leaf area, we can’t just collect a single pinna and declare victory. We have to cut down the entire leaf and carry it back to our lab without damaging it. This is a bigger challenge than it appears. You may have seen landscaping crews trimming palm trees in parks – but they use mechanized lifts and power tools, and have complete freedom of movement because of roads. We have to hike all our equipment in and out, and often can’t see where we are cutting because of other trees and vines. These leaves weigh dozens of pounds, have sharp edges, and fall from thirty or forty feet in the air. How do we do it without getting hurt, and why does it take all day to collect three?
We use a chain saw to cut the leaves out of the canopy, like the one you see here. The main challenge is getting the saw blades on top of the leaf. To solve this problem, we attach the saw to a rope, the rope to a bean bag, and the bean bag to a long extensible metal pole. We then carefully raise the bag up into the canopy, get it stuck a few times, and eventually maneuver it over the leaf. Then with some more pole work we pull the bean bag down, and are ready to start cutting.
Cutting too hastily is a bad idea. Imagine a thirty-foot long heavy sharp stick crashing out of the sky, and imagine all the other things it might bring down with it. Sometimes the falling leaves catch on other trees and abruptly swing in another direction, which can be an unwelcome surprise for the field crew.
Once we’ve found a safe location, we use two people to pull on the saw, and wait for the loud cracking sound that indicates the triumph of gravity over leaf. The leaf is now on the ground, but we’re far from finished. We have to bring it home without damaging it. This leaf we cut more than two kilometers away from our laboratory, and the forest is full of trees and vines that make it difficult to navigate with a heavy object of this side.
Extra care needs to be taken before moving a leaf too far. There are some arboreal spiders that call the pinnae home, and they make unwelcome guests when a leaf is wrapped in one’s arms. This one was loathe to leave its home, but quickly found its way to another nearby tree once we had carefully dislodged it with a (very long) stick.
After the brief spider inspection, we begin the long and sweaty task of dragging each leaf home. This was the first time I ever had to make a K-turn outside of a vehicle!
Once we get the leaves back, we have to measure leaf area, which was the original goal of the entire adventure. The leaves are far too large to scan using normal office equipment, so we resort to taking photographs of leaf sections. Here you can see us removing pinnae (more than 200 in total) and placing them on a white background – a shower curtain – for photography with a scale bar.
Each leaf took up to sixteen photographs to completely image, and involves several other scientists gawking at our slow progress.
By sunset, we were able to finish three leaves, from start to finish. I don’t think any of us much like palms, but I hope you see how much work it takes to measure them.
It was a sunny morning late last week, and I had just ducked under a branch to reach our next transect. Standing up straight, I had a sudden feeling that there was something very large hanging off the back of my shirt, and walking up towards my neck. So I called over a friend on our field crew and asked, as calmly as possible, if there was something on me. His immediate response was unpublishable, which didn’t restore my confidence in the situation.
We see a lot of spiders in Panama. They are found on the ground, on trees, and in the water. Here is a Dolomedes sp. fishing spider, about four inches long, waiting to catch a frog and then kill it with a venom that causes liquefaction from the inside out. Generally having a spider on you is likely to end in anything from a neutral to a very unpleasant experience.
Orb-weaving spiders are also very common. Their bodies are colorful, perhaps as a warning to potential predators. Here are two individuals of different species, perhaps in the Argiope or Actinosoma genus (please comment if you know).
Walking into spiders and their webs is inevitable. My first thought was that I had entangled myself with a golden-orb weaver, whose webs span at least a meter in diameter. These spiders have been observed (Nyffeler et al. 2013) to successfully catch and eat bats. Here you can see one eating a Morpho sp. butterfly, with iridescent blue wings.
But I didn’t see a orb-weaver’s web, and the thing on me felt far too big to be one of these spiders – big enough to make my shirt sag. It kept walking, and I soon found myself with an insect of the Phasmatodea order on my neck. Fortunately these, the stick-insects, are very friendly and completely harmless – I had not seen it camouflaged against a tree and dislodged it from its perch. The relief was immediate. I do like spiders, but I like stick-insects more! This one was the largest I’d ever seen before – bigger than my outstretched hand by far.
There are many kinds of stick-insects, but this one might be Metriophasma iphicles. Please comment if you know any better. A frightening morning became a fun adventure playing with one of the largest and nicest insects I’d ever seen.
The insect wouldn’t stay still while it was on me, and was equally restless while walking all over Colby’s face. But as soon as we put it on a branch, it extended its left front leg parallel to its body, tucked in its antennae, and became quite still and stick-like.
I glanced in the other direction, and when I turned back, it had already disappeared back into the thousands of branches of our forest.
The rhythm of the forest changes as dusk approaches. The hot exhaustion of the late afternoon dissipates, and the forest comes alive again, loudening with the calls of birds and monkeys. A few mammals like the tamandua (ant-eater) and ocelot may make a brief appearance, and many insects begin to seek refuge for the night. When the darkness deepens the quiet returns, but the forest does not sleep. Imagine taking a trip into a lowland tropical forest by night. Imagine looking for eyes reflecting the faint glint of moonlight, and listening for a soft rustling in the leaf litter.
This crab, for example, hunts by night. I found it in a small stream in close proximity to a number of large crayfish. But evidently life is not completely easy – you can see this individual is missing one of its claws. (And it was keen on pinching me with the other!)
Lizards can also be found at night. Most seem to be resting in inconspicuous locations, but perhaps some are taking advantage of new predation opportunities. It’s difficult to tell the difference between a lizard that has been startled by an overly curious biologist and one that was already active!
Many invertebrates continue their activity at night. I found this snail carefully navigating across a leaf, in search of some unknown destination.
However, some insects do not fare so well. This scarab beetle was attracted to an artificial light source, mistaking it for a natural one. After a short flight, and a sudden collision, I found it upside-down on the ground, trying very unsuccessfully to right itself. I waited five minutes but it was no closer to a solution than at the beginning. Taking some pity, I righted it, only to see it fly into the light a few short seconds afterwards. Bright lights at night are not something these creatures are adapted to.
Walking slowly deep in the forest, I heard what sounded a lot like the footsteps of an animal trampling over leaves. It turned out to be not a mammal, but a spider – in this case, an enormous tarantula, probably six inches long. Being overly curious I pushed it with a stick, and felt it push back with its very strong legs. It was enough to convince me to leave it alone and keep walking.
But some night-time creatures are more amusing than scary. On the way home I stopped by the laboratory greenhouses, which are bordered by moat to keep out snails. In the water lives a species of frog that puffs up its body with air and floats, buoy-like, on the water’s surface. It reminded me of a balloon, and I was not disappointed to find out how it reacted to being touched!
It is difficult, as a human, to imagine what life would be like in the darkness, because our bodies are not adapted to these conditions. But for other species, being nocturnal has many advantages. Many predators are no longer present, and new sources of prey are available. Competition for resources is less strong. Finding other individuals of the same species to reproduce with is easier. Temperatures become more tolerable. These conditions have led to many species like the ones you saw here being well-adapted to these conditions, and in some cases strongly challenged when the darkness of their nights has been interrupted.
A final worthwhile note is that the darkness may not be as deep as we imagine. Many creatures can see quite well at night. Though a dark night may be 100 million times less bright than a sunny day, there are creatures with eyes suited to the challenge. Some nocturnal bees are active well past dusk, and dung beetles are capable of seeing by only the starlight of the Milky Way (Dacke et al., in Current Biology this year). Though these hikes can bring us closer to this hidden world, there is a whole night-time world we will never ever be able to see.
One of my images from last summer was just featured in the journal BMC Ecology, and was almost chosen for the cover . It is an honor to have a photograph recognized by a broad pool of judges. They noted,
we have selected a dazzling scene from Colorado of a subalpine flower meadow (Figure 2). Composing a photograph of this nature is surprisingly difficult, and Benjamin Blonder , a PhD student from University of Arizona, deserves congratulation for such a captivating portrayal of what it means to be biodiverse. The emphasis here is not on survival, but on reproduction: the dull but functional photosynthetic green seems an almost insignificant background compared to the waving of riotously coloured floral genitalia. Although it can be seen as a poster child for the beauty of our science, it is only when we force ourselves to view the picture through an ecologist’s eye that the true depths are revealed. What is it that allows such a diversity of forms and colours to coexist in an otherwise similar patch
Several of my other images are also featured in the contest, including some images of fieldwork in Puerto Rico and Panama. You can read more in a journal editorial: BMC Ecology image competition: the winning images. Be sure also to check out the winning image, which shows an impressive example of insect camouflage!
One week ago, the Panamanian forest was punctuated by bright yellow canopies interspersed high above the rest of the forest. You can see one of these dramatic trees behind a train of the Panama Canal Railway, but the view is even better from the forest floor.
This species, the guayacán (Tabebuia guayacan), drops its flowers in one large pulse. Standing underneath it, one experiences a steady rain of flowers that covers the forest floor in a radius of twenty or thirty meters downwind. The flowers have a softly sweet smell and a large trumpet shape characteristic of their family, Bignoniaceae. The flower density becomes high enough to paint all the leaf litter in bright yellow.
The pulse of flowering probably helps with reproduction – large floral shows attract lots of pollinators, and the synchrony of flowering between trees means that genetic material can be shared between far-away unrelated individuals, potentially increasing the fitness of any offspring growing from the resulting fruits. But the flowers are not just popular with pollinators – they also attract monkeys. Here you can see a mother and baby howler monkey (Alouatta palliata) sitting in a branch. We observed the monkeys playing in the flowers and throwing them down on us, but didn’t see them eating the flowers or looking for nectar. I’m not sure what the appeal for them is!
But if the monkeys were just playing, it wouldn’t surprise me. I too spent some time enjoying the bloom and sitting beneath one guayacán tree. Now the bloom is over and we will have to wait some months for the show to be repeated. Magical moments like these make long days of fieldwork worth it!