I’ve never seen this before: a few hundred riffle beetles, Elmidae, all gathered behind a boulder in Rio Java. The larva are common, and I’d rarely see individual adults—here, in the thin film of water cascading over the boulder, were hundreds.
I don’t know what this fly is or does, and it’s maggot must be phenomenally large (flies, like many other insects with complete or holometabolous metamorphosis, don’t “grow” as adult—little flies aren’t babies, they’re likely just different species). On top of it’s size, there were pseudoscorpians hitching a ride on its legs (phoretic dispersal), so when it landed on our current, they began to climb down and investigate their surroundings!
I’ve seen some phoretically dispersed mites on dung beetles (an Instagram post I can’t link) and tabanid flies before too.
Dasyprocta punctata is about the size of my dog, Amos, and many times faster. Still, I would love to see his reaction to such a big rodent—or even a paca!
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.
Zane, Ahmi and I pose as part of El Gente Del Río, 2019.
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, and Trichomycterus 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.