filter feeders of the forest

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During my week at La Selva, I had a great time out in the river seeing my old friends the freshwater shrimps and discovering new ones. My part in the course was to lead a research project which explored the connections between aquatic and terrestrial systems. We examined the influence of stream habitat on riparian dwelling web-weaving spider density and web morphology. Many of the rivers at La Selva are pretty incised which leaves a lot of the stream channel exposed and available for spiders to build webs on to capture adult insects emerging from their larval stream-dwelling forms. Insects emerging from streams can make up the majority of riparian dwelling spiders’ diets. The diversity of methods these filter feeders of the forest used to trap their prey was impressive. Some spiders build Charlotte’s Web webs but other spiders build dome-shaped webs that they pull taught and release when a prey arrives, and others dangle individual strands of web onto the surface of the water to catch water striders. Just to name a few. Our project was fortuitous in that there was an Arachnid specialist course also happening at La Selva and a few of the students were also interested in spiders living near streams. This kind of cross-pollination is one of the reasons La Selva is a special and productive place in my opinion.

One afternoon the rain washed the spider webs away and we finished measuring earlier than planned. I took the unexpected free time (while the students were entering data and producing a film about the project) to visit the lab of the station manager Carlos. Carlos has worked his whole life with chironomids, the stream dwelling insects which serve as the base of the food chain in streams, rivers, and lakes through out the world. His office contains the world’s foremost collection of chironomid exuviae or shed exoskeletons. These exuviae can be used to identify chironomids to species and are the part of a chironomid stream-dwelling ecologists are most likely to find. Like many insect orders in the tropics, we have barely started identifying them to species. In his lab, Carlos had more than ten lifetimes of specimens for a taxonomist to spend identifying but there are only around four chironomid taxonomists left in the world. It left me wondering how it came to be that these stream dwelling invertebrates have not yet been identified. There is still so much left to discover. How are we going to get it all done?

dragonfly riparian spider snail eggs

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