Posts Tagged ‘Subspecies’

The Greater Sage Grouse is one of the iconic birds of the western U.S.  It is huge, dramatic, and has fascinating breeding behavior that has made it the focus of many, many studies.  It is also declining.  These birds need extensive expanses of sagebrush to survive, and such expanses are being reduced by everything from grazing to road building to invasive plant species to oil and gas drilling.  One particular population of the Greater Sage Grouse has just been listed as federally threatened under the Endangered Species Act.  It is a geographically isolated and genetically distinct population that lives on the boarder between central California and central Nevada, hence the name the Bi-State Sage Grouse.  Only six groups of this grouse still exist and four of them are in immediate danger of destruction.  Endangered Species Act listing will make it a federal crime to harm these animals or the habitat they rely on.  Specifically, the listing guidelines set aside 1.86 million acres along the California-Nevada board as Bi-State Sage Grouse habitat to be protected for their conservation.

This population is the most southwesterly population of the species.  As such it has the potential to be especially important to the species conservation in the face of climate change.  As temperatures warm, on a global scale, organisms that are adapted to colder climates will tend to move north, but they will have a harder and harder time finding suitable habitat.  The organisms that are adapted to warmer climates will also tend to move north, but they will have a higher likelihood of finding suitable habitat as they do so.  This means that the Bi-State Sage Grouse has a high potential of being able to move into the rest of the Sage Grouse range and prevent the species from going extinct.  This is one of many reasons why protecting subspecies and distinct population units is so important.  If this population is allowed to go extinct, it could greatly effect the overall extinction risk of the species in the future.

A decision on whether or not to list the Greater Sage Grouse as an endangered species throughout its range is expected in 2015.  It is considered likely that the whole species will be listed, so the rest of the species will also be protected at that point.

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I saw two male Orange-crowned Warblers (Oreothlypis celata) chasing one another through the yard this morning.  This is somewhat unusual at this time of year since these birds are in all likelihood wintering birds, and as such they should not be that interested in defending territory and such.  That will all start in about a month (at the earliest) here in central California when the earliest males will arrive for breeding in mid February and the bulk of the rest will arrive by mid March. So these males may have just been doing some practice competing.  Some halfhearted pursuing just to make sure they have not lost the edge they will need again soon.

Of the four subspecies that are widely agreed upon in this species, the one we have here is O. c. lutescens.  It is a coastal subspecies that breeds from Alaska to southern California and winters from northern California to Baja California.  That places central California in the happy position of being in the overlap where we can see Orange-cornwed Warblers all year long.  I hope that is the case here in my specific neighborhood.

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As my wife and I were driving out of Berkeley a few days ago, we saw a group of five Wild Turkeys walking down the side walk of one of the  major streets.  When we turned a corner at the next intersection we saw another group of five crossing the street in front of us.   Many people were stopping their cars or coming out onto their front porches to watch and photograph the birds as they sauntered by.  The turkeys were completely unfazed by the attention as they calmly walked through the neighborhood.  With the Thanksgiving holiday just past, and this encounter fresh in my mind, I thought it would be appropriate to post on the Wild Turkey population of California.

Wild Turkeys (Meleagris gallopavo) are native to North America, and there are six recognized subspecies.  In the late 1800s they were nearly driven to extinction by a combination of heavy hunting and habitat loss which reduced the continent wide population to around 30,000 individuals restricted to remote locations.  In the 1970s reintroduction programs began to successfully bring the Wild Turkey back to large portions of its historical range.  But, Wild Turkeys are not native to the west coast.  The first recorded introduction of Wild Turkeys to California was in 1877 on a ranch on Santa Cruz Island where they were released for the express purpose of hunting.  More introductions followed, especially from the 1950s to the 1970s, and now there is an estimated population of 240,000 birds in California alone and they are found across 54 of 58 counties.  The birds we have here are largely of the Rio Grande subspecies (M. g. intermedia).  This subspecies is particularly long legged, generally weighs between 20 and 25 pounds, have body feathers that have a coppery-green sheen, and tail feathers and upper tail coverts that are tipped with tan.

As the population of Wild Turkeys in California has grown, they have increasingly moved into suburban areas.  Like deer, turkeys can adapt to human dominated landscapes and learn to thrive there.  This has led to an increase in human-turkey interactions.  Some of these interactions come in the form of turkeys doing damage to gardens and landscaped areas.  Agriculturally, turkeys eat wine grapes and have become a nuisance in many vineyards. And while males can become aggressive during the breeding season, the vast majority of the interactions between Wild Turkeys and humans are completely benign; just don’t feed them.

As an interesting aside, the reason they are called Turkeys has always puzzled me since these birds are not found in the country of Turkey at all.  I recently learned that the when these birds were first being imported to Europe from the new world they all came through trade routes that stopped in Turkey before being distributed to the rest of the continent.  The name of the bird became entwined with the shipping location, and the name has stuck ever since.

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Subspecies are a fundamentally important unit of taxonomy.  They represent the diversity of adaptations that various groups can acquire as they respond their local environment.  In circumstances where barriers are long-lasting, they can represent the first steps in speciation.  When barriers are less permanent, they can tell us about the dynamics of how major features of a landscape can change through time.  Subspecies can also offer information in areas of mate choice and sexual selection, breeding behaviors, dispersal and gene flow, colonization events, and phenotypic plasticity.  With so much to offer, subspecies warrant a great deal of attention from biologists from a wide range of disciplines.

From a conservation point of view, protecting subspecies ensures that a wide range of the genetic, morphological, and behavioral variation within a species is preserved.  This leads to the preservation of the greatest possible adaptive potential for the species as a whole.  From a policy perspective, subspecies that are declining are protected by law under the endangered species act of 1973.  Therefore, proper identification is needed for decisions on listing and delisting designations and for the assignment of money and labor that result from such decisions.  From an evolutionary biology standpoint, subspecies can represent the transitory step of one species becoming many.  The process of observing and mapping such speciation events is one of the primary goals of evolutionary and population biology.

However, despite the importance and need for accuracy in subspecies designations there is little agreement or consistency with regard to how it is done.  Some of these inconsistencies arise from problems of definition.  Defining a species is a tricky task with different situations lending themselves to different criteria.  The biological species concept, the morphological species concept, the phylogenetic species concept and the rest all have their supporters, and each species definition leads to a different subspecies definition.

The biological species concept states that a species is a group of individuals that can breed and produce viable offspring with other members of the group, but not with individuals from outside the group.   This is the most widely used and accepted species definition in raptor biology.  The major difficulty with applying this definition to subspecies (a subspecies is a group of individuals which can breed and produce viable offspring with any other member of the group, but not with individuals from outside the group, but who usually breed with only a subset of the group) is that it is not easy, and sometime impossible, to trace movement and breeding patterns among different populations.  The morphological species concept is the oldest form of classification.  It states that a species is a group of individuals that all share a suite of physical characteristics with each other, but not with individuals from outside the group.  This concept is not well supported in modern biology; however it is the most frequently used as the method for designating subspecies.  The phylogenetic species concept states that a species is comprised of all of the descendants of a single common ancestor.  This idea is gaining strength as genetic techniques to determine descent become easier, faster, and cheaper.  However, this species concept does not have specific levels of separation that mark species and subspecies, so any such designations become much more subjective.

These different definitions lead to many problems.  Each of these definitions has areas of grey where disagreements can, and do, arise.  How much interbreeding is enough to consider two groups part of the same subspecies?  Which morphological characteristics are included in the diagnostic suite, and how different do they have to be?  How much genetic divergence is enough to warrant species or subspecies designation?  These are the questions that need to be settled when designating and naming subspecies.

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