Monday, January 5, 2015

Biodiversity Hotspots Hold the Key to New Species Discovery in the Southeast

New species are still being discovered with regularity. Nearly every week there are posts of newly discovered species on Facebook's Novataxa page of some recently found frog from the Congo or new plant from the Peruvian Amazon. The majority of new species are being discovered in remote tropical areas - places like Borneo, Laos, Brazil, and Madagascar -  that are still relatively understudied and have a considerable amount of unexplored territory. Most of these are from regions called global biodiversity hotspots. Worldwide, there are 35 global biodiversity hotspots recognized by Conservation International. Examples include the Atlantic forests of Brazil, the Caucasus Mountains of Eurasia, and the pine-oak woodlands of Mexico. For a region to be a hotspot it must meet strict criteria aside from just having a high number of species. First, It must contain at least 1,500 endemic plant species (endemic species are species restricted to an area that occur nowhere else). Secondly, at least 70% of the region must have suffered from habitat loss or significant degradation such that less than 30% of its original vegetation remains. These threatened hotspots support more than half of all known plant species and more than 40% of mammal, bird, reptile, and amphibian species, despite just making up 2.3% of the Earth's land surface (Conservation International 2015).

Fig. 1. Map of Global Biodiversity Hotspots

Smaller biodiversity hotspots can also occur on a regional scale. For example in the mountains of southwestern China - which is itself a global biodiversity hotspot - there are specific mountains or watersheds that harbor their own sets of narrow endemics that can be thought of as local or regional hotspots. 

A new paper by Reed Noss and colleagues, entitled How global biodiversity hotspots may go unrecognized: lessons from the North American Coastal Plain, published in 2014 proposes that the southeastern US, specifically the Coastal Plain province, which comprises approximately half of the area known to many as "The South," should be considered the 36th global biodiversity hotspot since it meets the criteria set by Conservation International. Within this newly proposed global biodiversity hotspot, there are also regional hotspots that were identified in 2001 by former University of Tennessee researchers, James Estill and Mitch Cruzan. Their study identified several "centers of endemism" within the South - particular regions that are biodiversity hotspots but on a small regional scale. Examples include the Appalachicola region of the Florida Panhandle, the Southern Appalachian Mountains, and the Central Basin of Tennessee. 

Their maps provide coarse resolution of hotspots and are a good start, but recent data suggests that there are small hotspots even within some of the ones Estill and Cruzan found. For example, the Southern Appalachians contains numerous hotspots of endemism, each likely to harbor undescribed species as well. There a few areas not identified as hotspots by Estill and Cruzan that may in fact be unidentified hotspots that need additional study. Such areas include the upper Cumberland River Valley of Tennessee and Kentucky and the Boston Mountains of Arkansas. 

Estill and Cruzan's (2001) map of southeastern U.S. "centers of endemism."
These can be thought of as biodiversity hotspots within the larger southeastern
U.S. global biodiversity hotspot proposed by Noss et al. (2014).

Given the Southeast's status as a global biodiversity hotspot, It should be no surprise that the region is still yielding many new species of plants and animals despite 350 years of intensive exploration and scientific study. Recent remarkable U.S. examples of new animals include the discovery of four new bass species from Alabama, a new turtle species in Mississippi, and a new giant crayfish in south-central Tennessee. Data compiled independently by Alan Weakley (Univ. of North Carolina, Chapel Hill) and myself reveals that there have been more than approximately 250 plant species described from the Southeast since 1970 and the rate of discovery continues to remain steady at an average of five per year. There may be a few hundred species left to describe from the Southeast.

Vascular plant species described in the southeastern U.S. between 1970-2010.

Now, perhaps more than ever, it is imperative that we find, describe, and study new species because what little remains of our natural habitat in the South is now faced with nearly constant threats stemming from increased population growth. The continued degradation of our Southern landscape has been especially obvious to members of the conservation communities who are now in their 80s and 90s. Dr. Robert Kral, retired Vanderbilt University botanist, relayed the erosion of our biodiversity to me in this way: "Dwayne, 18 out of every 20 sites I've visited over my career that were high quality sites are now gone or degraded beyond repair." Numerous factors are responsible for the degradation of our natural habitats including urban sprawl, habitat fragmentation, wetland destruction, conversion of woodlands to pine plantations, increased herbicide usage, fire suppression, and competition from invasive species. Coastal areas are also under threat from sea level rise due to global warming. The sad reality is that if we don't act fast many species will likely become extinct before we can ever describe them. Given these threats and the potentially great number of species left to find and describe, is there any way to expedite the discovery of the South's undescribed species?

The Race to Discover the South's Remaining Undesribed Species

I believe there is a way to speed up and focus our efforts to identify new species. First, we need to understand the likely characteristics of those species that are still out there. You might think of this as a sort of forensic profile. Here's a list of things to consider:

  1. A significant number of new species, perhaps 50-70%, are very rare and known only from a few populations - thus the reason they've escaped detection.
  2. A high percentage, perhaps 20-40%, are actually quite widespread and have escaped detection because they are cryptic or belong to groups that are taxonomically  or architecturally complex.
  3. Probably at least 75-90% of all species to be described from the Southeast have already been "found" by past botanists and collections likely exist in herbaria, but their distinctiveness has yet to be realized.
  4. Probably only a very small number of species to be discovered have never been collected previously by botanists.
  5. probably less than 25% are species that are immediately recognizable as new species - that is they are so distinct as to be easily separable at a glance. 
  6. The remaining 75% will likely require detailed scientific research involving statistical analyses of morphological variation and examination of DNA sequence data.
  7. More than 90% will have geographic ranges that are restricted to or centered on known biodiversity hotspots.

Since we know that biodiversity hotspots are the areas most likely to contain narrowly endemic species these are the same areas where we should focus our efforts to locate undescribed species. For example, an analysis of the new species described in the past 40 years reveals distinct patterns. Certain areas have routinely yielded new species. For example, there have recently been a number of new species described from the Cumberland Plateau of Alabama and Tennessee in the past few decades (e.g. Blephilia subnudaClematis morefieldiiPenstemon kraliiPolymnia johnbeckiiSolidago arenicola, and Stenanthium diffusum). Other regions that have consistently yielded new species include the West Gulf Coastal Plain of eastern Texas and western Louisiana, the southern Ridge and Valley of Alabama and Georgia, the Florida Panhandle, and the Blue Ridge Mountains. What is clear from these data is that some places just aren't as likely to harbor undescribed species, such as areas along the Mississippi River in eastern Arkansas or western Tennessee.

While it is true that many of the remaining species to be discovered are in remote areas, many, if not most of those left to find in the Southeast literally may be in our backyards, along our favorite hiking trails, or along the side of the busy roads we travel everyday. A 2000 publication by Barbara Ertter (Univ. of California, Berkeley) titled Floristic surprises in North America north of Mexico, described countless examples of new species that were discovered right under our noses. Recent examples of newly discovered species in Southern "backyards" include the endangered John Beck's Leafcup (Polymnia johnbeckii) and the Smoky Mountain Sedge (Carex fumosimontana). The leafcup was discovered in 2008 along the side of Interstate 24 just a few miles west of Chattanooga, Tennessee in the southern Cumberland Plateau ecoregion - an area identified on Estill and Cruzan's map as a hotspot. This new species has escaped detection by countless botanists and millions of passersby over several decades in spite of growing abundantly along rocky ledges within 30 feet of and in plain site of the interstate. The Smoky Mountain Sedge was discovered in another hotspot, the Southern Appalachians. It was found on eastern North America's second highest mountain, Clingman's Dome, in Great Smoky Mountains National Park and was the dominant ground cover beneath the  observatory tower, at what may very well be the single most heavily visited landmark in the US National Park system.

Polymnia johnbeckii (John Beck's Leafcup), a new species discovered D. Estes in 2008
known from two localities just west of Chattanooga, TN and nowhere else.

It is imperative that we continue to conduct, support, and fund inventories of our biodiversity. We also should not take it for granted that just because botanists have studied an area or a group of plants in the past that there's nothing left to do or discover. 

Unfortunately funding for describing species is almost non-existent. It is generally beyond the purview of large granting agencies such as the National Science Foundation. Federal and state agencies charged with environmental protection are also generally reluctant or unable to fund the description of undescribed species since they don't yet officially have a name. This is unfortunate given that most undescribed species that remain are likely the rarest of the rare and many would qualify as candidates for federal listing or at least being tracked as rare species at the state or provincial level. A related factor is lack of time. Many of the people who describe new species are affiliated with academic institutions and between balancing their responsibilities for teaching, advising, committee assignments and research, the meticulous work required to research and describe new species must be moved to the back burner. It often takes 2-5 years of research to do the work necessary to describe a species and prove its distinctiveness. When we couple this with how few researchers there are in the Southeast who are actively working on describing species, it is evident that it could take decades to describe all that are presently known. Many species don't have that kind of time and will face serious depletions in populations sizes, numbers of populations, and perhaps even extinction before we can get to them. 

To highlight just how large the problem is with the new species backlog, consider the figure below that shows numerous undescribed species and some recently described species found within the past few years.

Forty undescribed or recently described species from the Southeast. Twenty-five of the species photographed in this plate are putatively undescribed.