Steve Ellner's seminar

What started as three men and a chemostat…

This is Part III of the talk – some of you were in elementary school for the first two, so here’s a reminder:

Consumer-resource interactions are prone to cycle: due to delayed negative feedbacks. (note prey peaks are 1/4-cycle shifted). Simulations, Larch Budmoth and parasitoids, (Kendall et. al. 1998)

Chaos should be common But it isn’t. we observe Stable : cycles : chaos 2 : 1 : $ $ Zimmer 1999 (Zimmer, 1999)

why? Darwin.

But theorists show systems can evolve to chaos, ’cause theorists are bright.

So, we decided we test in real organisms: Rotifer-algal chemostats and cycles.

Dilution rate is a bifurcation parameter. Fussman 2000. (Fussmann, 2000) Model works – but no! Period is three times too long, cycles exactly out of phase.

Looks like evolution. blocking evolution confirms it (Yoshida et. al. 2003)

These results have been replicated many times… starting in 1972! Short period gets longer and goes out of phase. Some mention their models stopped working, but didn’t recognize Darwin staring them in the face.

But how important is rapid evolution? (Relative importance is a central theme of ecological work) Monica Geber, Hairston 2005 (Hairston et. al. 2005)

$ = + $

Big changes in traits involve many changes in genes. Traits can do the same thing,but genes do very different things. open mystery…

Returning to ecology: Theory predicts dilution rate is a bifurcation parameter, as is amount of heritability.

So: how well does this work in real food webs? Different system. (wow, evolution happening on experiments within 180 days).

But wait, trait change isn’t necessarily genetic change. Then in about 2005 theortical ecology said “I can’t believe I forgot about the Price Eqn”

$ = Cov(m,z) + E(z)$

Should have been: $ = + (cov(m,z) + E(z) ) $

But needs the genotype at time t with environment at time t+1, and vice verca. How can we do that? N. Hairston’s Daphnia from lake Constance preserved each year in sentiment for decades. Hiarston 1999. (Hairston et. al. 1999) Ellner’s analysis of this is in press at Ecology Letters

Demonstrates a bit of evolutionary rescue, trait not needing to change as much. Hairston 2005 method gets it wrong (giving evolution a negative estimated effect in the data). Demonstrates evolutionary rescue more then compensating for fitness loss due to ecology in an example in Great Tits.

With more studies, we might have a meta-analysis of when evolution is important. We think we can formulate a preemptive theory that we could then test.

Conclusions: Mucrocosms are awesome. match data to model, no excuses about what you didn’t measure.
Rapid evolution occurs with real consequences.

Field studies shown substantial ecological impact, and we can quantify (can be larger than the ecological impact).

Evolution seems most important when it is the cause of stasis rather than change. An important buffer.

References