Lyons et al. 2016 - K. Lyons

Holocene shifts in the assembly of plant and animal communities implicate human impacts

Blog by Kate Lyons

Authors:

S. Kathleen Lyons, Kathryn L. Amatangelo, Anna K. Behrensmeyer, Antoine Bercovici, Jessica L. Blois, Matt Davis, William A. DiMichele, Andrew Du, Jussi T. Eronen, J. Tyler Faith, Gary R. Graves,  Nathan Jud, Conrad Labandeira, Cindy V. Looy, Brian McGill, Joshua H. Miller, David Patterson, Silvia Pineda-Munoz, Richard Potts, Brett Riddle, Rebecca Terry, Anikó Tóth, Werner Ulrich, Amelia Villaseñor, Scott Wing, Heidi Anderson, John Anderson, Donald Waller & Nicholas J. Gotelli

This research demonstrates that there has been a fundamental shift in community structure due to human activity. We evaluated the co-occurrence structure of plant and mammal communities using both fossil and modern datasets. The relative proportions of significantly aggregated and segregated species pairs were stable for 300 million years before abruptly changing approximately 6000 years ago.  We tested this finding against several possible biases and found that none of them could explain our data.  The timing of the shift coincides with increasing human impacts such as increasing population size and the spread of agriculture. Our study thus indicates that the processes acting on ecological communities today may be unique in the history of land ecosystems.

These results are important because of the intensifying debate about global change and biodiversity loss.  Human activity is changing the world in myriad ways, and the deep time perspective represented by our research can heighten awareness of the magnitude of human ecological impact. Demonstrating that even humans without advanced technology were able to cause a fundamental change in the long-lasting (300 million years) co-occurrence structure of land plant and mammal communities is an important result to communicate to the public, many of whom continue to express skepticism about the effects of our current environmental impacts.

Dornelas et al. 2014 by K. Sullivan

Assemblage Time Series Reveal Biodiversity Change but Not Systematic Loss

Blog by: Kaitlyn Sullivan

Authors:

·       Marie Dornelas

“My research focuses on quantifying biodiversity and understanding the processes that shape it. I often work on tropical systems and specifically coral reefs, but I also work with tropical freshwater fish, mangrove crabs and plants for example, as I am more question-driven that organism-driven. I like to combine ecological theory, synthesis of existing data, and fieldwork (preferably in exotic places!) in my research, and most of the research questions I’m interested in fall under the disciplines of community ecology, macroecology and biogeography. I tend to work on intermediate spatio-temporal scales (that is communities and networks of communities over time-scales of years to tens of years).”

https://synergy.st-andrews.ac.uk/diversity/dr-maria-dornelas/

·       Nicholas J. Gotelli

“My research addresses basic questions about the organization of animal and plant communities. What are the forces that determine the species composition and abundance of natural assemblages? How do competition and predation affect local community structure? What are the biotic and abiotic factors that control population growth and the risk of extinction? Current research projects include enrichment and tipping points in aquatic ecosystems, effects of climate change on ant assemblages of eastern deciduous forests, and null model analyses of community structure and biodiversity.”

http://www.uvm.edu/~ngotelli/homepage.html

·       Brian McGill

“I study questions pertaining to biodiversity at large scales – large areas of space, long periods of time, many species. These questions have been deemphasized in ecology due to the difficulty in doing experiments, but are of high relevance to conservation and management questions. I have two broad research questions. One is developing the ability to predict how species ranges will respond to climate change. The other is finding ways to measure the impact of humans (especially land cover change) on community structure.”

https://sbe.umaine.edu/mcgill/

·       Hideyasu Shimadzu

“My general research interest is in the science of data, Data Science. Data and models - measurement and description of phenomena - they have been the foundation of modern sciences. For the last several years my research activities lie on the intersection of statistics and subject matter sciences, with a particular focus on environmental/ecological sciences. My research concerns how statistical consideration contributes to advancing our knowledge and understanding of phenomena of interest.”

http://shimadzu.datascience.jp/

·       Faye Moyes

Is currently a research assistant for the School of Biology at the University of St. Andrews.

·       Caya Sievers

Is currently a Seal Diet Technician for the School of Biology at the University of St. Andrews.

·       Anne E. Magurran

Is currently a Professor for the School of Biology at St. Andrews.  “I am interested in the measurement, evolution and conservation of biological diversity with particular emphasis on freshwater fish assemblages and currently have projects in Brazil, Trinidad, Mexico, India and Scotland.”

]https://risweb.st-andrews.ac.uk/portal/en/persons/anne-magurran(4b27832d-6f10-48f3-9fe8-ac4b8bec6958).html

Summary

                  Losses or reductions in biodiversity are likely the result of habitat destruction, pollution, overharvesting, invasive species, as well as changes in climate.  However, the degree to which changes in biodiversity has occurred overtime is poorly understood.  The main purpose of this paper is to address “how diversity within assemblages is changing through time”.  To better understand the extent to which global biodiversity is impacted by changes in local biodiversity assemblages, data collected between 1874 to present, consisting of 6.1 million species occurrence records (35,613 species) from 100 individual time series from biomes across the entire globe were analyzed.  To quantify patters of temporal diversity, α was used to measure changes in local diversity, while β was used to measure changes in community composition. 

                  Due to undeniable changes in habitat and unusually high extinction rates, they hypothesized that “most assemblages would exhibit a decrease in α (local) diversity through time.  As for changes in community composition, they hypothesized that because of “long-term changes in species composition, we expect[ed] increasers in temporal β diversity”.

                  The results from the time series collectively indicate no such systematic change in temporal α diversity as was predicted.  However, as for temperate assemblages, the average trend in α diversity was positive, while the trend tended to be negative at the global scale.  The opposite is true of the trends regarding temporal β diversity, which increased relative to the baseline sample “across all climatic regions, realms, and taxonomic groups.”  They addressed these finding by stating that their “results suggest that local and regional assemblages are experiencing a substitution of their taxa, rather than a systematic loss.”

Barnosky et al. 2011 - by R. Kiat

Barnosky et al. 2011

Barnosky, A. D., Matzke, N., Tomiya, S., Wogan, G. O., Swartz, B., Quental, T. B., ... & Mersey, B. (2011). Has the Earth/'s sixth mass extinction already arrived?. Nature, 471(7336), 51-57.

blog by Rebecca Kiat

Paper Authors (Full list):

Anthony D. Barnosky, Nicholas Matzke, Susumu Tomiya, Guinevere O. U. Wogan, Brian Swartz, Tiago B. Quental, Charles Marshall, Jenny L. McGuire, Emily L. Lindsey, Kaitlin C. Maguire, Ben Mersey & Elizabeth A. Ferrer.

First three authors (info from personal websites):

Anthony D. Barnosky:

“Research revolves around calibrating past planetary changes and what they mean for understanding today’s global change. Current projects focus on the extinction crisis, climate change, the Anthropocene, and conservation biology, with the goal of understanding the state of the planet today and how we can guide it toward a future we want, rather than one that inadvertently happens to us.”

Nicholas Matzke:

“Biogeography is the study of where species live, and why. Traditionally, the "why" has been divided into "Ecological Biogeography" and "Historical Biogeography." Ecological Biogeography has focused on environmental and ecological controls on distribution, such as temperature and precipitation.  "Historical Biogeography" has focused on how geographic ranges evolve on geological timescales and across phylogenetic trees, primarily dealing with rare dispersal and vicariance events.

I believe that it is high time that these two traditions were re-integrated, not just in verbal models and interpretation, but with formal probabilistic models, using the computational tools of statistical phylogenetics. My work focuses on building these tools, and using them to answer Big Questions in evolution and biogeography.”

Susumu Tomiya:

"I study the fossil record of North American mammals, to understand how mammalian 'communities' are assembled and how they respond to major environmental changes at the macroevolutionary time scale of millions of years."

Press release in ScienceDaily:

https://www.sciencedaily.com/releases/2011/03/110302131844.htm

Paper Summary:

Barnosky et al. 2011 is a review paper that seeks to address the question: “Has the Earth’s sixth mass extinction already arrived?”.

“Thus, mass extinction, in the conservative paleontological sense, is when extinction rates accelerate relative to origination rates such that over 75% of species disappear within a geologically short interval—typically less than 2 million years, in some cases much less…”

The big five extinction events were distinct in having spiked levels of extinction rates (a decrease in origination rates for Devonian and Triassic events has also been suggested) compared to background extinction rates and in their magnitude (with over ~75% if species estimated to have been loss). It has been already suggested that humans might be driving a sixth mass extinction via e.g. fragmenting habitats, introducing non-native species, changing global climate etc.

In this paper, Barnosky et al. synthesize previous knowledge as well as the many issues and disparities in data and in analysis in attempting to answer this question using fossil data and modern data in order to evaluate comparative extinction rates accurately. For example, certain taxa, such bivalves, are better preserved and dominate the fossil record, but these species are poorly assessed or under-sampled today. Analyses of fossils are often done at genus level where similar morphologies are grouped together even if they may be distinct, while modern taxa are analyzed at the level of species. Extinction rates can also vary dramatically based upon the length of time measured – using a short time frame could yield a rate that is markedly faster or slower than the long-term average million-year rates. Barnosky et al. address these concerns and others in this paper (Box 1), along with possible comparative techniques that could help address these issues.

For their own approach, Barnosky et al. used a conservative approach in assessing extinction rates and in their comparisons (Table 2 for specifics). They found that recent extinctions according to their conservative analysis do not qualify (as of yet) for a mass extinction if using Big Five as a benchmark for a mass extinction (Fig 1. For comparative extinction rates depending on time intervals and Fig. 2 for comparative extinction magnitude). However, if species currently in the ‘threatened’ or in the ‘critically endangered’ categories as evaluated by IUCN went extinct within the next century and extinction rates remain the same, the sixth extinction event could be underway (Figure 3 – hypothetical; if extinction events were scaled to a length of 500 years).

Questions:

I was curious about current origination rates. If more recent research suggest that the Devonian and Triassic events were more a result of a decrease in origination rates, how is it taken into account here? (Note: This is mentioned in the notes for Table 2: diversification rates)