Diversity begets diversity...in white sands?

Thanks for the introduction Simone!

This is Kayla signing on, and I’d like to address some of the questions Simone brought up at the end of her last entry. Specifically, I want to talk about the idea that diversity begets diversity. Schluter introduces this idea, which was first suggested by Whittaker, in chapter four of his book. Basically Whittaker proposed the idea that the addition of new species to an area, through colonization or evolution, constitutes an addition of new resources to an area which other species in higher trophic levels can take advantage of. The increase in resources permits new predator species to evolve or colonize the area, which in turn decrease the numbers of prey species and allows for the introduction of new prey species…and so on.

This idea could be relevant to an increase in species diversity in white sands. Currently there are three lizard species inhabiting the area, and we are only aware of a few avian predators having much of an effect on their populations. The presence of the lizards could encourage the introduction of new predator species to the area; these species could reduce the population sizes of the three lizard species and create additional ecological opportunity for colonization or evolution of new lizards in the area.

But could this kind of predator-prey interaction lead to an adaptive radiation? Simone mentioned the fact that some classic adaptive radiations seem to have come to be through multiple colonization events. This type of interaction seems like it could increase the chances of multiple colonization events, or even encourage the evolution of new species in white sands.

Though the idea that diversity begets diversity may apply to white sands, there is still the problem of gene flow to think about. As Simone mentioned, the environment is dynamic with few physical barriers. The predator-prey interaction envisioned by Whittaker would not decrease the chances of gene flow in this system. Gene flow is likely a major obstacle to speciation of white sands lizards, but as we continue to read Schluter, maybe we can to gain more insight into this and the other questions Simone posed at the end of her entry. Tune in next week to find out!

ADAPTIVE RADIATION- how the heck does this relate to White Sands lizards.

This image of White Sands, NM is from google maps.

Simone- signing on.

So Schluter focused a lot on the definitions of Adaptive Radiation and other concepts surrounding the term. Let's see what he says.
On the first few pages of chapter 3, Schluter outlines the four main features of an adaptive radiation. Here they are in abbreviated form:
1. common ancestry of component species
2. phenotype-environment correlation
3. trait utility (certain traits have a fitness advantage in respective environments)
4. rapid speciation.

We're not by any means suggesting that adaptive radiation has or will occur in White Sands lizards. But the parallel colonization by the three lineages is interesting in this context because many believe (Lister, Wilson, Simpson etc.) that this invasion of open and new territory is a key component of the initial stages of an AR. We'll talk about this concept of Ecological Release in more detail later.

Why don't we think that AR wouldn't occur in White Sands lizards?
We discussed this a little when Kayla and I met last time. Well first of all, when we look at adaptive radiations on islands... well, see, that's the thing. Adaptive radiations are on islandS! Not just one! Hawaiian silverswords, fruitflies and honey creepers, Galapagos finches and Caribbean anoles- they all inhabit archipelagos. Even if we consider White Sands as a relatively isolated and recently formed island... it is just one. Even the subdivision of interdune areas by high uninhabitable dunes is only ever temporary. The dunes are always moving, changing the configuration of habitable, vegetated space. One might imagine that the populations of lizards in White Sands are quite dynamic. And an adaptive radiation in the face of that kind of gene flow? I think not!

But some adaptive radiations seem to be born from multiple colonizations of the same lineage in one 'island' (stickleback, cichlids, anoles...):

Could we get an adaptive radiation of lizards in White Sands due to several invasions from surrounding dark soils habitats?
What do population genetics tell us about the structure of populations in White Sands?
Would this be more common in certain lizard species? (i.e. Holbrookia populations outside White Sands are far more disjunct and they have no continuous distribution over the ecotone from dark soils to White Sands).
Is there enough distinctive niche space for lizards in White Sands? Or is niche space indeterminate, with diversity begetting diversity (Whittaker)?

Over to you, Kayla!

Introduction

Hello and welcome! This is Kayla Hardwick and Simone Des Roches signing on. We are two doctorate students at the University of Idaho studying evolutionary ecology, genetics and behaviour of lizards in White Sands, NM.

We are creating are own course which explores the awesomeness of ECOLOGY, ADAPTIVE RADIATION, SPECIATION & SPECIES DISTRIBUTION.

This semester, we are reading 3 monumental books on evolution:
"The ecology of adaptive radiation" by Dolph Schluter
"Speciation" by Jerry A. Coyne & H. Allen Orr
"Geographical ecology: patterns in the distribution of species" by Robert H. MacArthur

The next four months promise to be a great adventure into the minds of these great scientists and the progression of evolutionary theory. Because we both are studying lizards in White Sands, we will try to link the concepts in these three books to evolution and ecology in this system. Feel free to read along with us!