Tuesday, September 25, 2007

Farming Good for Wetland Birds

The media loves a freak show so this deformed frog story is getting some distribution today. The source is a University of Colorado Boulder press release about experimental work done in large part in central Wisconsin.

Nutrient Pollution Drives Frog Deformities: The study showed increased levels of nitrogen and phosphorus cause sharp hikes in the abundance and reproduction of a snail species that hosts microscopic parasites known as trematodes. … The nutrients stimulate algae growth, increasing snail populations and the number of infectious parasites released by snails into ponds and lakes. The parasites subsequently form cysts in the developing limbs of tadpoles causing missing limbs, extra limbs and other severe malformations.

The trematode has a complex life cycle that involves three host species, he said. In addition to the infectious stage in snails and the cyst stage in frogs, the parasites rely on predators including wading birds to complete their life cycle by consuming infected frogs and spreading the parasite back into the ecosystem through defecation.

An alternative headline would be abundant nutrition yields increasing food supply for wetland birds, but that lacks the damnation of human activity implied in the word pollution. I would be less suspicious of political bias in this report except for this assertion: "Since most human diseases involve multiple hosts, understanding how increased nutrient pollution affects freshwater and marine food webs to influence disease is an emerging frontier in ecological research." Most? Uhhh - No. That statement is an example of the overgeneralization of limited results corrupting scientific reporting.

Host and parasite interactions are extremely complex co-survival adaptations evolved over hundreds of thousands of years, and it is not surprising that blooms of parasites produce surges of parasitic infections. What is important is not the increase in diseased amphibians but their percentage of all amphibians. The press release fails to include any hard data about the fortunes of the healthy froggy survivors in the waters of abundant nutrition. I suppose any good news would be bad news for the people are bad crowd.