Think of an isolated lake, located in the middle of proverbial Nowhere - doesn't matter exactly where. Surrounded by miles of forest, taiga, prairie, desert, savannah - whatever.
No river leads into it, no river drains from it; there is no underground spring connected to a larger aquifer. The water is replenished by rainfall and snowmelt.
And it has little fish in it. How did they get there? Naturalists and biologists have speculated about this for ages, but the Ecological Society of America has now published the first scientific proof of a plausible mechanism, as explained at Hakai magazine:
This idea that birds transport fish eggs became embedded in scientific knowledge. But as recently as 2018, whenever researchers searched the peer-reviewed literature for solid data supporting the hypothesis, they came up short. Except for a few anecdotal accounts, they could not find any evidence of birds carrying fish eggs.
But this long-lived hypothesis, so recently put to bed, has been given a second chance thanks to Giliandro G. Silva, a doctoral student at the University of the Sinos Valley in Brazil. In 2017, Silva inadvertently found a single killifish egg in the droppings of a wild coscoroba swan. “I was not looking for a fish egg. I was looking for other groups, like plants and invertebrates,” Silva says. That serendipitous discovery sparked a deeper investigation.
To definitively determine whether killifish eggs can survive digestion by birds, Silva and his colleagues fed eggs from two killifish species mixed in corn feed to captive-born coscoroba swans. Rummaging through the birds’ poop, they recovered five live killifish eggs. While four succumbed to fungal infections in the lab, one hatched into a tiny fish after 49 days. This egg had survived 30 hours inside a swan...
“If you just want a proof of concept, then one egg is enough,” says Benedikt Schmidt, an evolutionary biologist at the University of Zurich in Switzerland who was not involved in the study. Other life forms, including snails and aquatic leaf beetle eggs, are known to survive being eaten by waterfowl. Now, Schmidt says, we have evidence that a fish egg can do the same.
Provided just for anecdotal reasons: When I was a kid we lived in a very low area in southeast Texas. Occasionally we would get a tropical storm or some weather event that would dump enough rain that would pool in our yard for several days. We would get tiny fish in our yard. It took just a few days, not weeks or months.
ReplyDeleteThere was a pond near my house that was less than half an acre in size and at most six feet deep. It was unconnected to any other water source and only seemed to have formed because it was in a low lying area. People laughed when I told them I'd seen large fish in it. They stopped laughing when I pulled out a three and a half pound bass.
ReplyDeleteSurprisingly big fish can turn up in small ponds.
Some fishermen stock small ponds with minnows in order to have ready access to free bait.
Deleteor fishermen dumping out their minnow buckets - that could explain minnows in brook pools that are so far from the lake?
DeleteI-)