Papers

​Avolio, ML, La Pierre, KJ, Houseman, GR, Koerner, SE, Grman, E, Isbell, F, Johnson, DS, Wilcox, KR. 2015. A framework for quantifying the magnitude and variability of community responses to global change drivers. Ecosphere 6: art280.
  • Global change drivers (GCDs) can drastically affect plant community composition, with consequences for ecosystem function.
  • Typical methods to study community changes condense complex community changes to univariate measures and focus on mean differences among treatments.
  • We suggest studying changes in means and variability of replicates using multivatiate measures, such as dissimilarity metrics, which consider the entire community response to GCDs.
  • Additionally, we suggested using rank abundance curves (RACs) alongside measures of community dissimilarity to understand how the community changed.
  • In such a way, we can improve our ability to predict community responses to global change drivers across a wide variety of systems.
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Global change drivers alter abiotic or biotic conditions that influence a wide range of potential mechanisms that change communities. Using rank abundance curves in conjunction with community dissimilarity measures provides insight into the magnitude and predictability of community change.
Wilcox, KR,  Tredennick, AT, Koerner, SE, Grman, E, Hallett, LM, Avolio, ML, La Pierre, KJ, Houseman, GR, Isbell, F, Johnson, DS, Alatalo, JM, Baldwin, AH, Bork, EW, Boughton, EH, Bowman, WD, Britton, AJ, Cahill JF Jr., Collins, SL, Du, G,  Eskelinen, A, Gough, L, Jentsch, A, Kern, C, Klanderud, K, Knapp, AK, Kreyling, J,  Luo, Y, McLaren, JR, Megonigal, P, Onipchenko, V, Prevéy, J, Price, JN, Robinson, CH, Sala, OE, Smith MD, Soudzilovskaia, NA, Souza, L, Tilman, D, White, SR, Xu, Z, Yahdjian, L, Yu, Q, Zhang, P, Zhang, Y. 2016. Asynchrony among local communities stabilises ecosystem function of metacommunities.  Ecology Letters.  DOI:10.1111/ele.12861
  • Stability of ecosystems through time is important for predicting ecosystem services from year to year and for preventing ecosystems from crossing catastrophic thresholds under extreme environmental conditions, such as drought.
  • Stability of entire metacommunities (i.e., large mosaics of different local communities or patches) might be driven by two main factors: 1) how stable individual patches are through time, and 2) asynchrony among patches – or how out-of-sync local patches are with one other through time.
  • First, we found that the stability of metacommunities (gamma stability in the accompanying figure) was indeed strongly correlated with the stability of individual patches (alpha stability).
  • Second, we found very strong effects of patch asynchrony on meta-community stability. This asynchrony enhanced metacommunity stability by as much as 300%.
  • So, to maintain the stability of landscapes, we need to promote and conserve heterogeneity of physical and biotic characteristics. In other words: Patchiness matters!
Langley, AJ,  Chapman, SK, Avolio, ML, Bowman, WD, Johnson, DS, La Pierre, KJ, Isbell, F, Wilcox, KR, Foster, BL, Hovenden, MJ, Knapp, AK, Koerner,  SE, Lortie, C, IN , JP, Newton, P, Reich, PB, Smith, MD, Suttle, B, Tilman D. Ambient changes exceed treatment effects on plant species abundance in global change experiments. Global Change Biology (in press).
  • Global change experiments compare manipulated plots to ambient control plots to understand how plant communities will respond to environmental changes, but these responses have not been compared to plant community changes occurring the background.
  • We used plant species abundance data from 16 long-term experiments (>10 years) to compare the magnitude of treatment effects (CO2, N, P, water, warming) to the rate of change in unmanipulated, control plots (ambient change).
  • We found that the rate of long-term directional change in ambient plots through time is greater than the influence of the treatment on that rate of change for 57% of species.
  • Previous evidence suggests that ongoing environmental change is dramatically altering terrestrial plant communities. Our findings show that these changes may be strongly shifting the baseline by which we gauge conventional treatment effects, and should be considered in experimental design and interpretation. 

In Preparation

Global changes systematically shift plant communities without driving local species loss 
Lead authors: Kimberly La Pierre, Meghan Avolio, Nate Lemoine, Forest Isbell, Emily Grman, Greg Houseman, David Johnson, Sally Koerner, Kevin Wilcox
  • Humans are currently imposing a wide variety of global change drivers (GCDs) on ecosystems, which could dramatically alter their structure and consequently the services they provide. Yet there are limited broad-scale experimental investigations of the effects of these GCDs on plant community structure.
  • In 412 experimental global change treatments around the world, we show that composition of treated plant communities steadily diverged from control communities through time regardless of the GCD imposed.

A comprehensive approach to analyzing community dynamics using rank abundance curves
Lead authors: Meghan Avolio, Ian Carroll, Scott Collins and Greg Houseman
  • Univariate and multivariate methods are commonly used to explore the spatial and temporal dynamics of ecological communities. Both, however, have limitations, including oversimplification or abstraction of communities. Rank abundance curves are potentially a key approach to integrating these existing methodologies.
  • We develop new methods for studying temporal changes and spatial differences in rank abundance curves and introduce these metrics as functions in an update to the R package library (“codyn”), alongside other new functions to calculate univariate and multivariate metrics of community dynamics. ​

Global change drivers alter the spatial and temporal variability of ANPP in herbaceous systems
Lead authors: Meghan Avolio, Kimberly La Pierre, Kevin Wilcox, Bill Bowman, Scott Collins, Alan Knapp, Sally Koerner, Nathan Lemoine, Melinda Smith
  • Global change drivers can change the variability of aboveground net primary production (ANPP) both over time and space.
  • Synthesizing 27 global change experiments we found that GCDs affect ANPP variability by making less variable sites more variable, and more variable sites less variable both spatially and temporally.  Further, sites with greater temporal variability are more responsive to GCDs. Lastly, we found that GCDs increase the sensitivity of ANPP to precipitation.

Investigating the underlying mechanisms of plant community responses to global change
Lead authors: Meghan Avolio, Kimberly La Pierre, Kevin Wilcox, Andrew Tredennick, Emily Grman, Sally Koerner.
  • We contend there are five important ways a community can change over time. There can be a change in evenness, ranks (reordering of species within the community) and species gains and losses, which often, but not necessarily co-occurs with a change in richness. 
  • Only 45% of the time (out of 233 control - treatment comparisons) did the composition of the plant community change - but when the community did change, all aspects of the community change. There were changes in richness, evenness ranks and gains and losses of species. Additionally, community composition is change occurs more often with with CO2 and N+P than other global change drivers.

Relating plant community responses to global change drivers to productivity responses
Lead authors: Kimberly La Pierre, Meghan Avolio, Kevin Wilcox, Forest Isbell, Alan Knapp, Sally Koerner, Melinda Smith, Andrew Tredennick
  •  We have previously found that plant communities respond systematically to global change drivers around the world, however the consequences for functional differences have yet to be investigated in a large-scale synthesis.
  • Here we find that productivity responses to experimental global change drivers are initially driven by physiological responses of the existing plant community, followed by reordering of species within a community, and finally species turnover (losses and immigration). This result provides support for the Hierarchical Response Framework (Smith et al 2009).

Guidance for improving herbaceous community dynamics in Earth System Models.
Lead authors: Kevin Wilcox, Kimberly La Pierre, Meghan Avolio
  • Earth system models (ESM) are powerful tools to predict ecosystem functioning. However, few ESMs incorporate vegetation change, and those that do, only capture coarse changes.
  • Here we demonstrate that current approaches of representing community change into Earth system models often do not match observations, particularly for grasslands, using an example from a long-term resource manipulation experiment in tallgrass prairie. We also discuss commonalities in empiricist and process-based modeler goals and differences in approaches to obtain these goals. Finally, we present a roadmap for better incorporation of occurrences and impacts of community changes into ESMs.