Artificial Streams

We constructed 16 artificial streams alongside a natural stream in Trinidad.  We diverted the flow from a natural spring into a holding tank, then gravity feed the water into the channels. The water then flows into the natural stream that was the original recipient of the spring outflow.  With this arrangement, we can set up replicated, factorial experiments in streams that are a good facsimile of natural streams.  These experiments are all parameterized on what we know to be naturally occurring population densities of guppies. We also monitor guppy growth rate so that we can confirm that the performance of guppies in these streams falls within the range of values that we see in natural streams. In other ways we can confirm that the streams accurately represent nature. 

Catching guppies at the mesocosms

Differences in algal communities with and without guppies.

​We have shown that guppies do indeed have a significant impact on the structure of their ecosystem.  Furthermore, we have found that high and low predation guppies differ in their impact on the ecosystem, largely because of their different diets (Bassar, Marshall et al. 2010).  Guppies from high predation environments prey selectively on high quality invertebrate prey (Zandonà, Auer et al. 2011).  Those from low predation environments instead consume invertebrates, algae and detritus in an unselective fashion.  These results represent the first part of the interaction between ecology and evolution; guppies change their ecosystem, both in these artificial streams and the focal streams.  The second part of the cycle requires proving that the evolution of the low predation phenotype is at least in part driven by the way guppies change the ecosystem.

Tumbasson Falls, Trinidad