Is species richness increasing or decreasing?

Posted by Richard B. Primack, Abraham J. Miller-Rushing, and Vincent Devictor

“It takes two to speak the truth, - one to speak, and another to hear.” 

-Thoreau in A Week on the Concord and Merrimack Rivers

Conservation biologists have argued that we need to protect local species richness (i.e. the number of species found locally) for its value in providing ecosystem services, such as clean water, flood control, and pollination. Yet in a recent editorial in Biological Conservation, we report that many long-term ecological studies have found the surprising result that the number of species at sites around the world has remained stable or is even increasing. We have similarly found that the number of wildflowers in Concord, MA has increased from Thoreau’s time to the present.

A diversity of wildflowers grow in this Romanian meadow

How could this be true when hundreds of species have gone extinct, and thousands more are declining and threatened with extinction? The answer seems to be that the loss of species at the local scale is often balanced by the arrival and establishment of new native or nonnative species.

These findings highlight the need for conservation biologists to avoid oversimplification when selecting management indicators, such as species richness. Targeting only species richness ignores the ethical, cultural, and aesthetic values of certain local species and ecological communities, such as monarch butterflies and redwood forests. These aspects of biodiversity can still be damaged or lost, even as species richness remains steady or increases.

Richard Primack is a professor in the BU Biology Department.
Abraham J. Miller Rushing works for the National Park Service at Acadia National Park (and received his PhD at BU).
Vincent Devictor is a professor at the University of Montpellier in France.
A version of this article was originally published in the journal Biological Conservation.

Candy-covered Science

Posted by Richard B. Primack

“There are innumerable avenues to a perception of the truth.”

-Thoreau in his Journal, 1851

The Biogeoscience program, which brings together researchers from BU's Biology and Earth & Environment Departments, recently held its Annual Symposium and Winterfest. The event featured short research talks, mostly by grad students, and afterwards grad students enjoyed designing replicas of their research projects using gingerbread, candy, frosting and sprinkles.

Sarabeth Buckley (Earth and Environment) describes her project on the ecosystem ecology of rooftop gardens. 

Mustafa Saifuddin (Biology) uses gingerbread to model fungi and root dynamics in forest soils.

I-Fang Hsieh (Biology) investigates how soil warming (black cable) and the elevation of CO2 levels (from yellow towers) will impact ecosystem processes in Minnesota peatlands. 

Here is a close-up of I-Fang’s project.

Our own Lucy Zipf (Biology) is developing citizen science methods to investigate how noise pollution impacts parks and cities, as shown by this candy-filled model of an iPhone app.

Nantucket faces a rising sea

Posted by Richard B. Primack

“The sea-shore is a sort of neutral ground, a most advantageous point from which to contemplate this world.” 

-Thoreau, in Cape Cod

Over the past half-century the mid-Atlantic coast, including Massachusetts, has experienced a sea level rise that is 3-4 times higher than the global average, according to a report by Sallenger and colleagues in Nature Climate Change. The effects of sea level rise are increasingly felt on Nantucket Island where powerful storm surges dramatically alter beaches and destroy houses.

A storm surge recently eroded the Nantucket coastline in Madaket, leaving this house isolated and vulnerable to being destroyed by the next storm

Homeowners are moving their houses further inland where possible, or building massive sea walls. Such efforts are understandable, but perhaps just delay the inevitable effects of climate change.

Near the town of Nantucket, homeowners build massive walls in front of their houses to keep back the rising sea

Because of its mild oceanic climate, Nantucket gardeners can grow cold-sensitive plants, such as camellias and crepe myrtles that cannot survive Boston winters. As the global climate warms, we will likely be able to grow these beautiful plants in Boston in coming decades.

Camellias are still flowering in early November in protected gardens

The efforts of Nantucket’s people to balance economic development and environmental protection faces new urgency because of rising sea levels and climate change. Some of these same issues have been described in the recent book A Meeting of Land and Sea: Nature and the Future of Martha’s Vineyard by the eminent Harvard Forest ecologist David Foster, that I reviewed for the journal Ecology.

Nesting success is linked to breeding phenology for California's birds

Posted by Amanda Gallinat

Many birds around the world have responded to warming temperatures by advancing their breeding phenology, initiating and fledging nests earlier in warmer years. These shifts are primarily considered a means to maintain synchrony with insect availability in the spring. Meanwhile, poleward range shifts are thought to be the main mechanism by which birds track their optimal environmental conditions for survival and reproduction.

White-crowned Sparrow (Zonotrichia leucophrys) nestlings in California. Photo by Sam Roberts.

However, a study of bird communities in California that was recently published in PNAS suggests that phenology shifts can also serve to maintain environmental niches in the spring. The research team, led by Jacob Socolar, found that birds have advanced their breeding phenology between 5-12 days over the past century, essentially negating a 1 degree C temperature increase over the same time period. In other words, the birds have used phenological shifts to maintain a particular temperature niche, which may reduce the need for range shifts. Socolar's group also found that nesting success changes with temperature anomalies; in the warmer parts of a species' range, hot years are associated with low nesting success.

Socolar's team combined observations by Joseph Grinnell (pictured above, preparing specimens in the field) and other observers in the early 1900's with more recent observations, to examine phenology shifts over the past century. Photo from the Bancroft Library/University of California.

This study is an important step forward in understanding the mechanisms behind shifting phenology: birds that nest earlier encounter cooler temperatures and increase their nesting success. As Richard Primack pointed out in an Audubon article highlighting this study, the next important step is to identify the specific links between temperature and nesting success, which may include heat or drought stress, or even insect availability.

New Insights from Old Herbarium Specimens

Posted by Richard B. Primack (Boston University; primack@bu.edu) and Charles G. Willis (Harvard University; charleswillis@fas.harvard.edu)

“Live in each season as it passes - breathe the air, drink the drink, taste the fruit & resign yourself to the influence of each.” -Thoreau, in his Journal, 1835

Millions of herbarium specimens are being digitized every year and made available online. In the USA, this effort is being led by the iDigBio program, and involves hundreds of institutions in the USA, Europe, China, Australia, and elsewhere. These massive digital datasets allow scientists to carry out ecological, evolutionary, and climate change research far more quickly and easily than ever before. In three recent papers many scientists, including ourselves, have shown some of the opportunities and limitations of research using herbarium specimens.

Willis, C.G., E.R. Ellwood, R.B. Primack, C.C. Davis, K.D. Pearson, A.S. Gallinat, J.M. Yost, G. Nelson, S.J. Mazer, N.L. Rossington, T.H. Sparks, P.S. Soltis. 2017. Old plants, new tricks: Phenological research using herbarium specimens. Trends in Ecology and Evolution 32: 531-546.

Botanists have always known that herbarium specimens can be a valuable source of information on when plants flower and mature their fruits. In their review article, Willis et al. (2017) summarize the range of climate change projects that have used herbarium specimens to study phenology and climate change in contrast with long-term field studies. In two case studies, they demonstrate that herbarium specimens typically cover a broader geographic area and sample from a wider variety of climatic situations than field studies, and that herbarium specimens can be used to detect the effects of climate change on a wider range of phenological events, like the leafing out times of trees. The review also underscores the promise of integrating herbarium specimen data of flowering dates with other historical datasets of flowering times, such as field observations and dated photographs, to best characterize the impacts of climate change on plant phenology.

Figure 1. Phenology studies using herbarium specimens (blue-gray dots) are increasing in number and their geographical distribution, and this process is being facilitated in regions of the world with a high density of digitized herbarium specimens (yellow-to-red dots). (From Willis et al. 2017; Figure 1) 

Pearse, W.D., C.C. Davis, D. Inouye, R.B. Primack, T.J. Davies. 2017. Measuring the limits of phenology: estimating synchrony and variation in contemporary, historic, and citizen-science datasets. Nature Ecology and Evolution 1, 1876–1882.

Until recently, climate change researchers did not have a good method for combining first observations of flowering time in the field with dates of peak flowering obtained from herbarium specimens. To deal with this problem, Pearse et al. (2017) demonstrate a new, robust statistical method to estimate historical first flowering dates from herbarium specimens collected from around Massachusetts and then compare these dates to observations of first flowering from Concord, MA made by the famous environmental philosopher Henry David Thoreau in Concord in the 19th century. Pearse and colleagues also demonstrate that their approach can be applied to large citizen science datasets like those gathered by the National Phenology Network and the extensive flowering time records collected over decades at the Rocky Mountain Biological Lab. This new statistical method opens the way for an expanded role for herbarium specimens in climate change research that combines diverse types of phenological data.

Figure 2. For each of seven orchid species in Massachusetts, the estimated date of first flowering (red dot) was calculated using the dates of herbarium specimens collected in full flower (black tick marks) and compared to the earliest first flowering date observed in the field by Thoreau and Hosmer (blue dot). (From Pearse et al. 2017; Figure 3, Credit: images of plant species Pogonia ophioglossoides, Platanthera lacera, Cypripedium acaule, Corallorhiza maculata and Arethusa bulbosa, Steven J. Baxter; Platanthera psycodes, Rob Routledge/Sault College; Platanthera grandifolia, Arnold T. Drooz/USDA Forest Service). 

Daru, B.H., D.S. Park, R.B. Primack, C.G. Willis, D.S. Barrington, T.J.S. Whitfeld, T.G. Seidler, P.W. Sweeney, D.R. Foster, A.M. Ellison, C.C. Davis. 2017. Widespread sampling biases in herbaria revealed from large-scale digitization. New Phytologist, doi: 10.1111/nph.14855

If ecologists, climate change biologists, and other researchers do not appreciate the biases of herbarium collections and other museum collections, this could lead to mistaken conclusions. In this study, Daru and his colleagues examined over 5 million digitized herbarium specimens from South Africa, Australia, and New England and determined that specimens were more frequently collected closer to roads and herbaria than other places, threatened species were collected less than other species, and collection efforts were disproportionately focused in some closely related groups. Also, a high percentage of specimens were collected by a small number of very active collectors, likely biasing collections toward the groups of plants these collectors preferred. Future studies using herbarium specimens for novel research projects, especially focused on diversity, distribution, and comparative evolution, will need to take these biases into account in order to avoid erroneous conclusions.

Figure 3. There is a strong geographical bias in collecting in Australia, South Africa and New England, with a greater density of collections nearer to herbaria, roads, and urban centers, with smaller, redder triangles expressing greater sampling effort and larger, blue triangles representing less sampling effort. (From Daru et al. 2017; Figure 1a, b, c.)

As these three papers demonstrate, there are many exciting new opportunities for ecological, evolutionary, and climate change studies using herbarium specimens, and the potential of these studies will greatly expand in coming years as millions more digitized herbarium specimens become available online.

Imagination and Reality: Thoreau’s journal and objects

Posted by Richard B. Primack

“I have as much property as I can command and use.” -Thoreau in his Journal

The Concord Museum has a new special exhibit that combines Henry David Thoreau’s journals and objects, highlighting many facets of his life, such as being an observer, a writer, a naturalist, a surveyor, and a writer. The exhibit reunites journals from the Morgan Library in New York with objects from the Concord Museum and elsewhere that are normally housed separately. The exhibit will continue until January 21, 2018.

Thoreau’s flute and one of his journals

A box of pencils from the Thoreau family business along with a journal

A yearly table made by Thoreau showing important weather events

A herbarium specimen of blue irises made by Thoreau; note that the specimen does not have a date or label, which limits its value for phenological research

Congratulations Dr. Amanda Gallinat!

Posted by Richard B. Primack

“If one advances confidently in the direction of [her] dreams, and endeavors to live the life in which [she] has imagined, [she] will meet with success unimagined in more common hours.”  -Thoreau, in Walden. 

Amanda during her final thesis seminar

Congratulations to Amanda Gallinat for the successful defense of her doctoral dissertation “Effects of climate change and species invasions on autumn phenology and bird-fruit interactions in Massachusetts, USA.” Amanda’s thesis was notable for the strong connections between successive chapters, and her large number of collaborators and co-authors both at BU and elsewhere in the USA and internationally. Also, the first chapter of the thesis, “Autumn, the neglected season in climate change research” has already been published in the high-impact journal Trends in Ecology and Evolution. And the second chapter on using herbarium specimens to monitor fruiting phenology was accepted for publication in the American Journal of Botany two hours before the defense; great timing!

Amanda with her committee members after her successful defense!