Archive for February, 2013

To be completely honest, this post is a bit of a tirade on my part.  I have been hearing some views of evolution that have really been annoying me lately.  I am not talking about people who do not think evolution happens or anything like that (that would be a bigger tirade, trust me).  No, these views come from biologist who should know better.  But first, some background.

As a graduate student, I serve as a teaching assistant each quarter.  The most common position I have held is teaching labs for one of the big introductory biology classes that pretty much everyone has to take in college.  Specifically, the labs I teach are part of the class on phylogenetics and biodiversity (BIS 2C for any U.C. Davis people reading this).  While teaching these labs, I have the opportunity to interact with lots of other people who work a U.C. Davis including members of the faculty, administrators, and staff.  Since the class covers the diversity of all life on earth, these people all come from very different academic backgrounds from spider phylogenetics to fungal biology to microbial diversity to botany.  This week we are finishing up plants for the quarter and as part of the plant labs there are several botanists who help the students out.

And here is where my trouble lies.  Several of the botanists have asked students some variation on the following question: why do ferns have fewer herbivores than flowering plants?  This is a perfectly reasonable question.  My complaint comes with the answer that they give which is some variant of: ferns have been around longer and so have had more time to evolve defenses against herbivory than flowering plants. I have so many problems with this answer, I am not even sure where to start!

Now it is true that ferns, which are Monilophytes, diverged from the rest of plants earlier than flowering plants, which are Angiosperms.  As such Monilophytes display more ancestral traits than the more modernly diverged Angiosperms.  However, this does not mean that they have had more time to evolve!  All life on earth can trace its lineage back to a universal common ancestor.  All life.  Since we all started at the same point, every organism that is alive today has been evolving for the same amount of time!  We humans classify different organisms into different group and arrange the formation of these groups into chronological order, but that only indicates that the lineages that make up those groups have changed more or less over the course of the last 3.6 billion years, not that some of them are shorter or longer.

Another reason why this answer gets me hot-under-the-collar is that is reenforces the mindset that some organisms are older than others and therefore more primitive, or less evolved.  Natural selection has been operating on all lineages all the time which means that every organism that is alive today is just as evolved as every other organism that is alive today.  It may sound crazy to say that a single-celled bacteria is just as evolved as a human, but it is true.  The bacteria simply found a strategy for surviving very early on, and that strategy has kept on working really well.  Our ancestors, on the other hand, have had to keep altering their strategy over time to the point where they now look very different from how they did when they started.  Remember that the starting point for both groups was at the same point something like 3.6 billion years ago.  All of phyogenetics basically boils down to tracking which genetic lineages have accumulated what changes over their 3.6 billion year history.  We are all equally evolved!  Or as Neal Stephenson wrote, “Like every other creature on the face of the earth, Godfrey was, by birthright, a stupendous badass, albeit in the somewhat technical sense that he could trace his ancestry back up a long line of slightly less evolved stupendous badasses to the first self-replicating gizmo – which, given the number and variety of its descendants, might justifiably be described as the most stupendous badass of all time.”

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This past weekend a friend, my wife, our 7 week old daughter, and I went birding in the Sacramento Bypass Wildlife Area.  It was a beautiful day with bright sunshine and just a little coolness in the air.  The Cattails (Typha spp.) in the central portion of the bypass were letting go of their fluffy seeds and the Mugwort (Artemisia spp.) were just starting to send up their spring growth, resprouting from their roots.  As we walked along the northern channel among the willows and oaks and cottonwoods I heard a flock of Bushtits.  Wanting get a look at them, and not wanting to miss any other birds foraging with them, I found the little flock of about 6 birds and started to sift my way through the group.  But, I stopped in my tracks when I got the first bird in my binoculars.  It was a small bird with a bright yellow belly.  At first my mind jumped to male Lesser Goldfinch, but it just as quickly rejected that option.  The bird I was looking at had a long tail and no dark patch on the forehead.  It looked like a Bushtit, but it was really, really yellow!  Is it a Yellow Warbler?  No.  Is it an Oragne-crowned Warbler?  No.  American Goldfinch?  No.  And then I see another one, and another, and another.  They are acting like Bushtits.  They sound like Bushtits.  But the whole flock is comprised of birds that are bright yellow!  Finally, I realize what is going on.  They are indeed Bushtits and they are foraging in a willow tree that is in full bloom.  Every time one of the birds jumps to a new twig to search for insects it is dowsed by the bright yellow pollen from the willow.  Since Bushtits are very active foragers and often hang upside down to find the insects they eat, even the bellies of these birds were coated in pollen.  They looked amazing!  Bright yellow Bushtits!  The flock finished searching through the willow tree and moved on to a nearby oak where they stood out even more.  Just goes to show you that when you see something odd, there is often a perfectly sensible explanation, just not one that anyone would guess.

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Fire suppression has been the standard policy for the U.S. Forest Service since the 1950s.  It was based on the idea that fire was a bad thing that destroyed habitat and commercially harvestable trees, and should therefore be excluded from forests as much as possible.  This has resulted in major changes to the forests of California, and other habitats as well.

Before the 1900s fires in California burned an average of 2.5 million acres each year.  These were largely ignited by lightening strikes and they burned uninhibited by humans.  In the  middle of the century, active fire suppression began and the annual average area that burned dropped to about 250,000 acres.  However, since the 1980s, the amount of area that burns each year has been increasing to the point where today about 7 million acres burn each year.  Further, most of these 7 million acres burn in very large fires.  This indicates that fire suppression was initially able to stop fires from burning, but the absents of fire resulted in the accumulation of fuels to the point where now fuel loads are so heavy that when a fire does start it is so large that it cannot be controlled.  This lack of control ability has not stopped the U.S. Forest Service from continuing to attempt to control them.  Today, the majority of the U.S. Forest Service budget goes not to habitat conservation or managing timber harvesting practices or to researching how forests work, but to firefighting.

Another effect of fire suppression is in tree mortality and germination.  Before 1900, many small fires that burned at low to moderate severity resulted in the trees within an area that were of a wide range of ages.  This was because many trees could survive the fires and get older, but a few trees would be killed.  The gap that resulted from these scattered moralities provided sites for seeds to germinate and young trees to grow.  However, since 1900, the large catastrophic, stand-replacing fires tend to kill all the trees in a large area.  this whole area is then covered with young trees that germinate from seeds that were already in the soil.  The forest that grows up in these areas are comprised of trees that are all the same age.  This homogeneity reduces the diversity of habitats and the the number of niches for species to occupy.

The forests that we can all go out and see today have not had their natural fire regimes for as much as a hundred years.  This absents have had profound and dangerous effects.  To counter act these effects, more prescribed fires are strongly recommended.  By introducing fire back into California’s ecosystems, more natural habitats can be restored.  This is a long and labor intensive process, but one that most assuredly needs to be pursued.

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