A few years ago, a NAPIRE student of mine, Jerry, investigated predation risk of crabs in and away from leaf litter. He found substantial predation in the assay, and, this year, Zane is picking up the idea again (more to come).
The crabs are fairly abundant in the streams, but their densities can vary greatly, and, overall, the density is lower in the larger reaches of Rio Java (greater discharge) and those crabs that we do find in the river have a larger carapace width—big crabs in the big river. Perhaps predation is driving this pattern! And look, here’s a pile of dead crabs, partially eaten, probably by a mammal adjacent to a small backwater pool within the river.
I think my first encounter with Rana (or Lithobates) warszewitshii was in RBAMB over a decade ago, but I don’t know that I’ve ever posted a photograph other than their tadpoles.
One of my two students for this year’s LSAMP REU is sampling and documenting the fish communities within the rivers at Las Cruces as an extension of a previous student of mine’s project (David’s). David had discovered four species, Bryconamericanus terrabensis, Brachyrhaphis terrabensis, Rhamdia laticauda, andTrichomycterus striatus, and he had presented his work at AFS. Interestingly, at Bry. terrabensis and T. striatus, have not been reported as occurring above 1,000 meter above sea level in the literature, and he thought this could be due to (1) undersampling and reporting and/or (2) recent changes in the distribution of these fishes, possibly due to climate change. One way to find out—continued monitoring. And, hence, Ahmi’s interest.
Ahmi may be employing three survey methods (visual surveys via snorkeling, seining, and minnow trapping) and sample along the entire elevational gradient within the Las Cruces property (1,000 – 1,400 masl).
Here, Ahmi practices visual surveys—a 5-10 minute zig-zag, calling out letters that represent the most likely fishes. The water is cool and turbid, making it difficult to complete, unlike some of the rivers, like Rio Madrígal, Rio Claro and Rio Nuevo, I surveyed using similar methods years ago on the Osa Penninsula.
Next, Ahmi and Zane practice seining the same pool; the current and steep, slippery banks present some difficulty, but they do catch a few.
Seining is hard work!
Some catch from the sample, including Bry. terrabensis.
I think this might be the only salamander I’ve seen in Costa Rica—probably a plethodontid, lungless salamander in the genus Bolitoglossa. Found in a small stream pool on Cerro De La Muerte. (Yep, a few dead things today…).
