(Fred)erick's Matsen's notes

Niche conservatism: tendency for organisms to stay in the same niche

Why study?

• generates diversity (e.g. speciation)
• leads to extinction because species are not able to adapt

Climatic niche conservatism: niche conservatism with respect to climate.

What explains patterns of biodiversity? Two common misconceptions.

• strong relationships between richness and environmental variables (this might indicate that evolutionary processes such as niche conservatism are not important)
• can’t act at the local level.

The number of species in a habitat can only be changed by speciation, extinction and dispersal. Why do some habitats have more species? One possibility is that there is a direct effect of ecology, but another is that niche conservatism keeps things constant.

Species conservatism in terms of salamanders. Most diversity seen at elevated elevation. Why? Zone of highest richness is the oldest lineages. Appalachian salamanders: similar pattern. Freckleton et al 2008 Am Nat method, also BiSSE.

Now look at the Andes– more frogs than any other part of the world. 2X as many frog species as the Amazon Basin. Glassfrogs. Can look right through to their internals organs. Same setup: time tree, and similar conclusions– higher elevation lineages are older. No evidence for higher diversification rates in elevational zones with highest richness.

Aridity gradients on Phrynosomatids. Same story, but now drier = more diverse.

• Q: Level of diversity just a function of area?
• A: Again, it would have to act through speciation and extinction.
• Q: But population genetics– can get MRCA that is recent compared to colonization time.
• A: We aren’t doing population genetics.
• Q: do we see the opposite ever?
• A: yes, in France we see lots of old lineages without lots of diversity.

Next: niche conservatism and “evolutionary lag times” in adaptation to novel climates. For three of the four clades, arid conditions colonized in the last 10Myr (Lag time > 20 Myr) For a fourth clade, hyperarid conditions colonized in the last 2 million years. This implies that adaptation to human climate change is not going to be fast enough.

Next: niche conservatism and future climate change. How quickly does niche preference change evolve compared to climate change? Slow. Climate change is fast: faster, and by a whole lot.

People don’t typically talk about evolution in terms of extinction and climate change. Perhaps this is justified– everything happens on too fast of a time scale for evolution to act.

Next: how does climate change impact biodiversity? Metastudy: very few studies have documented direct causes of climate-related extinctions and declines. The most common way is loss of food.

• Q: What about finiteness of niche space.
• A: We should be able to see that sort of effect in local scale, but we don’t.