Ecologically diverse clades dominate the oceans via extinction resistance

Ecologically diverse clades dominate the oceans via extinction resistance

Matthew L. Knope, Andrew M. Bush, Luke O. Frishkoff, Noel A. Heim, and Jonathan L. Payne

Summarized by Anna Geldert

What data were used? Researchers examined taxonomic data of marine organisms across 444 million years of geologic time. Taxonomic data relates to the level of biodiversity of organisms, and classifies them under different evolutionary categories (domain, kingdom, phylum, class, order, family, genus, and species). On the whole, this study examined 19,992 genera (species groups) from the fossil record and 30,074 genera of living marine species..

Methods: This study examined speciation (origination) and extinction rates of marine species over the past 444 million years. Speciation refers to the evolution of new species, while extinction occurs when a species dies out; both factors impact the overall level of biodiversity. Net diversification rates (i.e., the difference between speciation and extinction rates) were calculated for each period  of geologic time. Additionally, researchers graphed a relationship between the species richness and ecological diversity at different points in geological time. Species richness refers simply to the number of species in a group, while ecological diversity indicates the number of “modes of life” present, such as varying habitats, levels of mobility, and feeding methods.

Results: An examination of the fossil record found that a high biodiversity among species groups could be reached in two primary ways: firstly, by a relatively short period of high speciation, and secondly, by a gradual increase over time due to average speciation and low extinction. While the first category tended to reach high biodiversity faster, they were more vulnerable to mass extinctions than the second group. Most species groups alive today, therefore, evolved via the second route. With respect to the relationship between species richness and ecological diversity, this study found a positive correlation between the two factors, meaning that a variety of life modes can be tied to having more species. 

The figure compares ecological diversity and species richness over the past 444 million years of geologic time. Species richness is graphed as the log10 of the number of genera on the x-axis, while ecological diversity (in log10 of the number of modes of life) is on the x-axis. The x-axis spans from 0 to 4 in increments of 1, while the y-axis spans from 0.0 to 1.5 in increments of 0.5. Several slopes in different colors are shown, with a legend indicating the geologic time to which the slope corresponds. The geologic stages of time included are: Silurian to Devonian (443.4 to 358.9 million years ago), Carboniferous to Permian (358.9 to 252.2 mya), Triassic (252.2 to 201.3 mya), Jurassic to Cretaceous (201.3 to 66.0 mya), and Paleogene to Neogene (66.0 to 0.0117 mya). The slope of the modern relationship between species richness and ecological diversity is also shown. Slope values range from approximately 0.20 to 0.32 and appear generally to increase steadily over time, with some overlap between geologic stages. The modern slope is approximately 0.30, and lies in the middle of the range of slope values for the Paleogene to Neogene category.
Fig 1. Relationship between species richness and ecological diversity of marine species from 444 million years ago to present.

Why is this study important? The results from this study reveal that, in the long run, rapid diversification within a species group is not sustainable because the majority of this species group is likely to be wiped out during a mass extinction event. On the other hand, gradual diversification in species groups that are able to survive mass extinctions is a more probable explanation for modern levels of marine biodiversity. These species were most likely able to survive mass extinctions due to higher levels of ecological diversity, a theory which would also explain why ecological diversity has been increasing compared to species richness over more recent eras. This study is important because it calls into question an accepted theory that directly links ecological diversity to speciation rates. While the results from this study likewise recognizes a correlation between these factors, it also implies that the relationship between the two factors may be more complex. It is only because species groups with high ecological diversity were able to survive mass extinction events that this correlation is seen so clearly today.

The big picture: This study is important in the larger field of evolutionary ecology because it impacts our understanding of how species evolve and respond to extinction pressures over time. Researchers should not assume that the tight correlation between species richness and ecological biodiversity implies a direct causational relationship, because as this study reveals, in many cases the relationship is more complicated than that. Further research is needed to fully analyze the role that ecological diversity plays in survival of mass extinctions.

Citation: Knope, M. L., Bush, A. M., Frishkoff, L. O., Heim, N. A., & Payne, J. L. (2020). Ecologically diverse clades dominate the oceans via extinction resistance. Science, 367(6481), 1035–1038.


A data-driven evaluation of lichen climate change indicators in Central Europe

Matthew P. Nelson and H. Thorsten Lumbsch

Summarized by Anna Geldert

What data were used? For this study, researchers obtained collection data on 35 of the 45 lichen species designated as climate change indicators from the Global Biodiversity and Information Facility (GBIF). Data for this study focused on patterns found in Central Europe, and most specifically, Germany.

Methods: GBIF data on the lichen species were categorized into two age groups: before 1970, and 1970 to present. 1970 marked the year where reductions in the use of sulfur dioxide pollutants was implemented in Europe. Because pollution levels also play a role in the survival of lichen populations, it was important to create this distinction to separate this variable from other population changes due to climate change. Lichen species with fewer than 10 historical records were deemed unreliable and excluded from further analysis, leaving only 17 out of the 35 species. To determine the lichen’s preferred habitat, researchers combined historical distribution records of where the different species of lichen were found over time with a map of climate variables (temperature, humidity, soil composition, etc.). Using a computer model, they were able to predict the lichens’ preferred habitats with 95% accuracy, and generate a map to represent these predictions spatially. The map was compared to modern data to evaluate potential changes due to climate change.

Results: The results of this study revealed that approximately half of the 17 primary species studied were found in significant numbers outside their historical range, while the other half still resides primarily in the same regions as they did prior to 1970. Species other than the primary 17 did not have sufficient historical data to recognize specific trends in geographic distribution. However, researchers noted that only one third of these additional species saw an increase in abundance in recent years, while the other two thirds saw equal or reduced numbers compared to the limited historical records.

The map shows the distribution of Opergrapha vermicellifera over time. The map spans 10° of latitude, from 45° North to 55° North, and 20° of longitude, from 5° East to 25° East. The map is divided into suitable and unsuitable habitat for Opegrapha vermicellifera, which are shaded in dark green and light green respectively. The suitable habitat makes up only about 10% of the image, and is composed of a narrow, uneven band running from 46° North, 5° East to 55° North, 14° East. Approximately 11 historical (before 1970s) records of lichen distribution are marked by yellow triangles on the map, and all are contained within or along the border of the area denoted as “suitable” habitat. Approximately 30 modern (1970 to present) records of lichen distribution are shown, and are marked with purple circles. While some modern lichen records lie within the “suitable” habitat, approximately two thirds lie in the “unsuitable” area; the majority of these points lie 5° to 10° East and a few degrees South of the “suitable” range.
Fig 1. Distribution of Opegrapha vermicellifera is shown as an example of one of the maps created to analyze changes in lichen distribution over time. The map compares historical records from prior to 1970 (orange triangles) and modern records from after 1970 (purple circles). Habitat deemed suitable/unsuitable was determined using a computer model of climate variables based on pre-1970 habitat. For Opegrapha vermicellifera, over 30% of modern records lie outside historically suitable habitat.

Why is this study important? This study calls into question the usefulness of lichen as climate change indicator species. For one, the study found that there is very little data, especially historical data, on these species and the habitat they lived in originally. Therefore, it is somewhat difficult to draw conclusions regarding the degree of the lichen’s response to climate change. The study also found that, even among species with sufficient data, only about half were found outside their historical range. If climate change was truly impacting lichen populations as much as was originally thought, researchers would expect to find all populations outside of this range because they would have migrated to better suit their traditional habitat. These results pose the question as to whether other factors may be impacting the distribution of lichen even more so than climate change. For example, the rise and fall of sulfur dioxide pollutants before and after 1970 may be more significant.

The big picture: This study serves as a warning for climate change scientists, who may tend to jump to conclusions regarding migration, geographic distribution, and local extinction of many species of lichen in recent years. For many species of lichen, there is not enough data to determine whether the geographic distribution of lichen has changed, as well as whether these changes were due to climate change instead of other factors. More research and collection of historical data is needed in order to confirm the usefulness of these species as climate change indicators in future studies.

Citation: Nelsen, M. P., & Lumbsch, H. T. (2020). A data-driven evaluation of lichen climate change indicators in Central Europe. Biodiversity and Conservation, 29(14), 3959–3971.

Anna Geldert (she/her), Geobiology Undergraduate Student

background: greenery with trees and leaves and grassy area. foreground: Anna hugging a tree trunk and smiling. Tell us a little bit about yourself. Hi! My name is Anna Geldert (she/her). I’m from Minnesota, but I’ve spent the past year living in Vermont where I’m working toward my undergraduate degree at Middlebury College. In my free time, I enjoy reading, writing, practicing music, and playing volleyball on my college’s club team. I’m also a huge outdoor enthusiast, and I always look forward to camping, hiking, canoeing, or skiing with friends and family. Spending so much time outdoors as a kid is one of the factors that sparked my interest in the natural sciences in the first place, and the main reason I am so passionate about sustainability today. 

What kind of scientist are you and what do you do? Currently, I’m working toward a joint undergraduate degree in Biology and Geology. I’m fascinated by the way Earth’s natural systems function, and how they’ve evolved around the world and across geologic time. While I’m not totally sure what direction I want to go in this field, I’m ultimately hoping to pursue a career doing field research in relation to ecosystem response to climate and other anthropogenic change. 

What is your favorite part about being a scientist, and how did you get interested in science? In many ways, my interest in science developed long before I took any classes or considered a career in the field. One of my biggest supporters is my dad, who is a physics teacher. Growing up, he always encouraged me to stay curious and frequently used me as a guinea pig for demonstrations he planned to do in class the following day. I also spent a lot of time camping and hiking as a kid, which sparked my interest in the natural sciences. My favorite part about science is that it allows me to spend time outside with lots of hands-on experiences. Seeing first-hand how something we learned in class presents itself in the real world is really gratifying and reminds me why I wanted to study science in the first place.

background: light blue sky with clouds and darker tree line. Foreground: Anna rowing a canoe on a calm lake

How does your work contribute to the betterment of society in general? I hope my work will be used to help human societies coexist with the Earth in a way that makes sense for both parties. For example, last year I studied the potential of using fungal mycelium as a sustainable option for treating acid mine drainage. I think Earth’s natural systems have a lot to offer, and studying them can help us better understand how to act sustainably in our own life. 

background: trail in a forest with bright green leaves and a brown trail. foreground: Anna dressed in hiking gear with binoculars.What advice do you have for up and coming scientists? Science can be whatever you want to make of it. It is such a broad field, and there are so many opportunities to tailor your education and research to something you’re passionate about. Personally, I wasn’t super interested in science until I was able to do more hands-on experiments and independent research.. That was when I realized I could apply interests I already had – such as sustainability and the outdoors – to actual scientific study in Geo-Biology. I would encourage future scientists to keep an open mind and use science as a means to explore whatever sparks their curiosity.