Field Notes: Trinidadian guppies

For the last five years, I have studied the effects of human-induced land change on species interactions and behavior in freshwater streams in the Northern Range Mountains of Trinidad. As I put the finishing touches on my dissertation, this my first summer in four years when I’m not in the Northern Range Mountains of Trinidad doing fieldwork. I will miss it dearly – so this is a perfect opportunity to look back and muse about previous field forays.

Why Trinidad? First, Trinidad has an immensely biodiverse system of freshwater streams and rivers in a small geographic area that constitute three unique drainages: the Caroni, the Oropouche, and the Northern drainages. Comparing and contrasting processes in these three semi-independent drainages can allow us to make more generalizable conclusions about the ecology contained in these streams. Within each drainage (and especially within the Caroni and Oropouche), streams are topographically and structurally similar, further enhancing their comparability.

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Common guppy predators

Who are the players in these Trinidadian streams? The star of the show during field season is, of course, the Trinidadian guppy, a small but spunky fish that may be familiar to you as the forebear of colorful aquarium fish. This fish lives in streams throughout the island, but in many of the upstream reaches of Trinidad, is one of the only fish species. This means that, in lowland streams, guppies exist with lots of fish predators, but in high mountain reaches of streams, there are practically no predators. Guppies in these different reaches of the streams have thus evolved traits to match: guppies without predators are more brightly colored, produce larger but fewer young, and are less responsive to threats of predation.

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Examples of typical low- and high- predation streams and the common predators contained within

One of the joys of doing research in this system is that these differences between populations are observable every day in the field. Many of our experiments require catching fish in the field and taking them back to the lab to do lab-based behavioral observations. So, on days when we collect low-predation guppies, the going is easy. Unthreatened by predators, these fish are curious and abundant. The largest of their worries is competition from the many other guppies in the pool. Fishing for high-predation guppies, on the other hand, is tough. These guppies are experts at evasion; whole afternoons have been spent catching a pitifully small number of high-predation guppies. Differences in guppy traits not only affect guppy reproductive success but also the number of hours that hapless researchers spend foiled in their attempts to catch these fish!

After a day’s work in the streams and rivers of Trinidad, my field researchers and I hightail it back to the research station, an early 20th century family estate that was then purchased by the renowned explorer scientist William Beebe before being purchased by a local conservation organization. This old estate has a lot of character: partially digested by the surrounding forest Jumanji-style, it offers only limited protection from the beasts that buzz and bite—or, more pleasantly, from the myriad animal choirs that take their turns at serenade throughout the day. Therein lies part of the charm of the station. Staying there cultivates a sense of oneness with the forest and its creatures that would be diminished in a plush, climate-controlled modern building. And working at the station brings with it a sense of intellectual continuity—after work, my assistants and transcribe data, bent over the self-same desks that countless esteemed ecologists have work upon for more than half a century! After data entry and dinner, we wind down from a hard day, and a cool evening tropical breeze through the drafty estate feels earned. It’s not long till we’re falling asleep to the chirr of cicadas, readying ourselves for another hard but satisfying day of fieldwork in the unique Trinidadian streams.


Sean Ehlman is a sixth year PhD student in the Animal Behavior Graduate Group at UC Davis. When not dissertationing, he enjoys backpacking, yoga, and riding his tandem bicycle with friends around Davis. Sean will be graduating this summer and trading in his sunglasses and sandals for balaclavas and galoshes as he continues his research as an NSF Postdoctoral Fellow in Biology at the University of Minnesota. You can find him on twitter: @SeanEhlman.

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