Wednesday, March 5, 2008

Rissler and Apodaca 2007

Rissler, L.J. and J.J. Apodaca. 2007. Adding more ecology into species delimitation: ecological niche models and phylogeography help define cryptic species in the black salamander (Aneides flavipunctatus). Syst. Biol. 56(6): 924-942.

In this paper, the authors combine ecological niche modeling, spatially explicit analyses of environmental data, and phylogenetics in species delimitation. They assess the relationships between genetic, environmental and geographic distance among populations. They use ecological niche models which take into account 11 climatic variables and point locality data. They found that patterns of genetic divergence are strongly associated with patterns of ecological niche divergence.

I think that it is great that they found a correlation but it makes me wonder if many animal species will show this. It would be interesting to find out how well this works for other animals because I have a feeling it is not so clear cut as this, but who knows.

"-environmental niche modelling = understanding how abiotic factors (e.g. temp., precip., seasonality) impact the geographic limits of lineages and species"

"-georeferenced data from specimens + environmental data + GIS = predicted presence on a map (i.e. identifies areas that are ecologically similar to regions where the point locality information was used to build the models)"

"-is the predicted region the actual or "fundamental" niche? The define fundamental niche as: the environmental space where fitness is greater than or equal to 1 in the absence of range-limiting biotic interactions and dispersal barriers. However, the ecological niche modeling is probably more equal to the "realized" niche."

"-historical biogeography and comparative phylogeography seek to explain patterns of geographic congruence in phylogenetic breaks across multiple taxa"

"-the process driving lineage divergence, speciation, and the buildup of biodiversity are many and include: 1) geographic factors
2) historical factors
3) environmental factors"

I understand factors 1 and 3, but what are some examples of 2?

"-understanding the mechanisms driving divergence can help in species delimitation"

"geographic distribution + ecological niche models + genetic information = species diagnosis"

I would be worried about environments that are known to rapidly change through time. How does this affect the ecological niche model?

The authors used the evolutionary species concept (ESC) and the general lineage species concept (GLC). I've heard of the ESC but I'm not sure I know what the GLC is. Their goal was to recognize historically distinct evolutionary lineages that are likely to remain distinct.

How can you really know if distinct lineages are "likely" to remain distinct. I'm going to create a mini theory on lineages that are kind-of distinct. I'm going to call it The Oscillating Non-Species Concept. This is based on my idea that one year a lineage may seem somewhat distinct, then the next year it is not, then the next year it is really distinct, but not distinct enough to be a species, then the next year it is somewhat distinct.....

"combining independent sets of data (ecological and genetic) = robust view of independent evolutionary lineages"

"ecological divergence is an important step in the process of speciation"

"info on ecological niche can be really important when genetic data are insufficient to determine whether the lineage in question is truly distinct". This is my problem exactly. If they are not truly genetically or morphologically distinct, only borderline, then is ecological data really going to help? It could just force the entire issue so you pick one or the other (species or not a species).

For bioclimatic modeling the authors used Maxent v. 2 to create ecological niche models.

"the extent of divergence across lineages is a result of either geographic or environmental isolation". One has to make sure that the difference in lineages is not due to clinal or ontogenetic factors.

"abiotic pressures -> natural selection -> divergence -> speciation"

"analysis of ecological divergence + phylogenetic diversity = insight into biodiversity patterns and processes"

"quantifying divergence in ecological niche should be an important part of current phylogeographic studies and useful for species delimitation"

"primary species concept = entities believed to be species,
secondary species concept = operational methods for the discovery of those entities"

All in all, I enjoyed reading this paper.