Community ecology in a changing environment: Perspectives from the Quaternary

Blog Author: Devra Hock

Author:

Stephen T Jackson—Director of the Southwest Climate Adaption Science Center (SW CASC) also an adjunct professor in the University of Arizona’s Department of Geosciences and an adjunct research professor in the University of Arizona’s School of Natural Resources and the Environment. 

Previously at University of Wyoming as a professor of botany and founding director of the doctoral program in ecology. Before joining the University of Wyoming in 1995, Dr. Jackson held faculty positions at Indiana University, Idaho State University, and Northern Arizona University. He is past president of the American Quaternary Association and is on the governing board of the Ecological Society of America and the editorial boards of Ecosystems, Frontiers in Ecology & Environment, and Trends in Ecology and Evolution. 

His own research employs tree rings, fossil rodent middens, and sediments from lakes and bogs to investigate how past climatic changes and human activities have affected species distributions, biodiversity, and 

Jessica L. Blois—Assistant Professor at University of California Merced, School of Natural Sciences

            Previously Assistant Professor at UC Merced in Life and Environmental Sciences; Research Assistant at the UC Museum of Paleontology. PhD from Stanford in Biological Sciences

            The overarching focus of the Blois Paleoecology Lab is investigating the relationship between species, communities, and the environment, focusing on the past 21 thousand years of life on earth in order to inform the next one hundred years and beyond. We have diverse projects, but they are generally united by a focus on spatio-temporal processes. Our work also has a strong “Conservation Paleobiology” focus, trying to understand how we can use the fossil record to inform our conservation decisions for the future.

Summary/Main Points:

1. Main Question:

            Background—Community ecology and Quaternary paleoecology are both concerned with answering similar questions: understanding composition and structure of biotic assemblages, including patterns of spatial variation and dynamics in changing environments. In spite of this, community ecology and Quaternary paleoecology are disconnected and have very little interdisciplinary work. Community ecology focuses on modern, existing species assemblages and works to understand local species interactions and consequences. Quaternary paleoecology looks at properties of past communities and how they have changed at local and regional scales, from a few thousand to 2.6 million years ago. 

            Main Questions—Provide an overview of what Quaternary terrestrial records reveal about environmental and community changes, suggest some foundations for bridging between community ecology and Quaternary paleoecology, and identify topics where the two fields can engage to mutual benefit. 

2. Ecology and Time’s Environmental Texture

            -Community Ecology: Previous ecological thought has held time as a simple, uniform dimension where ecological processes unfold against a constant environmental backdrop. Essentially, time is treated as the independent variable and ecological properties are time-dependent in their change. And while the environment itself may change, that is only due to ecological processes changing or as a stochastic variable, fluctuating randomly about a constant mean. Only recently have environmental change and nonstationary variability been explicitly accounted for in ecological models. 

            -Quaternary Paleoecology: Time is textured by environmental change and variability, suggested by a broad and apparently continuous spectrum of climate variability and change in paleoclimate records. Climate variability is rarely stationary in nature, with climate means, variances, extremes, and modalities evolving through time. There is no “normal” climate. Environmental conditions do not necessarily repeat themselves. While there are cyclic or quasicyclic events, the magnitude, spatial extent, and duration are different with each occurrence. Climate change often involves changing combinations of seasonal temperature, seasonal precipitation and other factors. Climate change can be gradual and directional, but is more often punctuated by episodic events and rapid state transitions.

3. Communities Come, Communities Go: 

            -New ecological thought that an ecological community comprises a single place that happens to be occupied by an assemblage of species with overlapping distributions and environmental tolerances. Therefore, community concept should be replaced by the spatial distributions of populations. 

            -Paleoecological records support a parallel conception, though involving time. An ecological community can be viewed as a single point in a spatial framework of species distributions overlapping environmental gradients and responses to environmental change and variability over time. Spatial distributions evolve through time and contingent on temporal processes, while temporal patterns of occurrence and abundance at individual sites are contingent on spatial distributions, patterns, and processes. 

            -Illustrative example of changing compositions of forest communities in the records of the past 8,600 years at Tower Lake in Central Upper Michigan.  The modern forest community has only existed as it is for the past 1,400 years. Furthermore, no forest community has persisted there for longer than 1,500 years. Another example is the 86,000 year pollen record of Lake Peten-Itza in Guatemala. The community observed at any single point in time is ephemeral, rarely persisting for more than a few millennia before being replaced by something new. These same patterns apply to terrestrial insect and vertebrate communities, which show changes in species abundances, range shifts, extirpations and colonizations, and extinctions. 

4. What Governs Community Assembly and Disassembly?

            -Community Ecology: Three modal concepts that determine community structure and composition: interaction assembly, environmental assembly, and neutral assembly. Interaction assembly is deeply rooted in community ecology, emphasizing Eltonian niche, which considers communities to be structured primarily by strong interactions among species. Resource competition is considered a main interaction, though others include facilitation, mutualism, and trophic relationships. Environmental assembly consider communities to be structured primarily by species’ physiological and demographical responses to the physical environment. It is also niche based, but emphasizes the Grinnellian niche, which supports species’ having finite environmental requirements or tolerances. Neutral assembly considers communities to be structured by random processes, such as dispersal, recruitment, and mortality. 

            -Quaternary Paleoecology: Strongly supports environmental assembly, based on both theoretical and empirical foundations. Paleoecologists look towards environmental change, particularly climate change, as the main driver of community dynamics. Comparisons with paleoenvironmental records and paleoclimate simulations justify environmental assembly, and most paleoecologists do not look for any other drivers of community dynamics. 

            -Environmental change is powerful, and should be incorporated more explicitly into community ecology. 

-Species interactions govern the community outcome of environmental change and should be considered more explicitly in paleoecological explanation

5. Spanning the Missing Middle

            -The missing middle Quaternary of ecological history provides abundant opportunity for collaboration between paleoecologists and community ecologists. Paleoecologists must understand the ecological questions that they are applying to their data. On the flip side, ecologists must understand the nature of paleoecological data and inference. Particularly, careful consideration must be paid to scale and taphonomy. 

            -Identify a nonexhaustive set of themes, topics, and questions on which collaborations might be entered:

·     Community Assembly and Disassembly

·     Trait Based Community Patterns

·     Diversity Dynamics  Through Time

·     Ecological Rules in the Anthropocene

·     Dynamics of Regional Species Pools

·     Clocking Time-Dependent Processes

6. Conclusion

            -We live in a time of rapid environmental change, with novel communities and ecosystems already widespread and increasing globally. Integrating mechanisms of community ecology and empirical richness of paleoecology will advance the general field of ecology, but will also increase its capacity to contribute to climate change adaptation and minimize risks to biodiversity and ecological services. 

Questions/Comments:

             Overall, I liked the way the authors formatted this paper, discussing particular ecological concepts and comparing how modern community ecology and paleoecology tackle those different concepts. I especially appreciated their informative figures, (fig. 1, fig. 4), as I think both figures demonstrated and illustrated the concepts outlined in the text. I also liked the authors consideration for areas that would benefit from a better combination of paleoecology and community ecology. While I do think that the interdisciplinary research would lead to better understanding of how species and communities react to change, I think the grandiose statement at the end takes that a tiny bit too far, though that is standard for some papers. 

            Can you think of any research (modern or older) that does a good job combining modern community ecology with paleoecology? Does it fit within any of the themes suggested in this paper? 

            I also would have liked to see a few more examples with real data. The authors talk about how all of the ecological processes apply to terrestrial communities, inverts or verts, but do not show any clear examples of that.