Biodiversity, Biotic Interactions & Environmental Change

Why does environmental change alter biodiversity within and across trophic levels?

Our group explores this question by investigating why changes in climate, disturbance, productivity, and resource availability alter biotic interactions and patterns of biodiversity, including: 1) mutualistic interactions among plants and pollinators, 2) antagonistic interactions among plants their natural enemies (e.g., herbivores, pathogens & seed predators), and 3) effects of dispersal on biodiversity.

Plant-pollinator interaction in the
Northern Rocky Mountains, Montana
(Photo credit: Laura Burkle)

1. Wildfire disturbance and productivity as drivers of plant-pollinator diversity and function across scales

Among the threats posed to biodiversity by global environmental change, changes in natural disturbance regimes and net-primary productivity are likely to have some of the most profound impacts on plants and animals and the ecosystem services they provide. Although ecologists have excelled at investigating how individual species and some local communities respond to disturbance and productivity, little is known about the way in which complex networks of species interactions respond to environmental change, nor the ways in which species-interaction networks assemble across different biogeographic regions. In collaboration with Laura Burkle (Montana State University) and Travis Belote (The Wilderness Society), we are investigating why changes in wildfire disturbance and productivity influence spatial and temporal variation in plant-pollinator community composition (β-diversity), mechanisms of plant-pollinator community assembly, variation in plant-pollinator interactions (interaction β-diversity), and ecosystem services (pollination). We are addressing these questions across a large-scale productivity gradient in the Northern Rocky Mountains, a biogeographically diverse region of critical conservation importance. A major goal of this project is to enhance mechanistic understanding of community assembly, mutualistic species interactions, and ecosystem services following disturbance at the large spatial scales most germane to conservation and management in naturally heterogeneous landscapes.

Key Findings & Research Highlights

  • We identified challenges in scaling-up studies of β-diversity within single trophic levels to species-interaction networks from local to biogeographic scales, outlined a conceptual model of ecological and evolutionary processes that determine site-to-site variation in plant–pollinator interaction networks (interaction β-diversity), and synthesized outstanding questions for studies of interaction β-diversity in ecology, evolution, and conservation (Burkle, Myers & Belote 2016, American Journal of Botany).
  • Mixed-severity wildfires promote higher β-diversity of herbaceous plants than high-severity wildfires, suggesting that historically prevalent, mixed-severity fire regimes increase biodiversity by promoting the persistence of different types of ecological communities across a diverse mosaic of habitats (Burkle, Myers & Belote 2015, Ecosphere).
  • Changes in net primary productivity mediate the effect of wildfire on species richness of herbaceous plants, such that wildfire increases species richness at low productivity but decreases species richness at high productivity (Burkle, Myers & Belote 2015, Ecosphere).

Field Sites

Our field sites in the Northern Rockies include: 1) low-productivity, ponderosa-pine dominated forests and woodlands in Helena, Montana; 2) medium productivity, lodgepole-pine and Douglas-fir forests in Paradise Valley, Montana; and 3) high-productivity, western-larch, lodgepole-pine and mixed-conifer forests in Whitefish, Montana.

Sites with contrasting wildfire histories replicated across a net-primary productivity (NPP) gradient in the Northern Rockies, Montana (Map credit: Travis Belote)

Fireweed (Chamerion angustifolium [Onagraceae]),
Yellowstone National Park, Montana

Disturbance, Productivity &
Plant-Pollinator Biodiversity Team,
Helena, Montana (May 2013)

This gallery (*coming soon*) includes images from:

  • Helena, Montana
  • Glacier National Park, Montana
  • Whitefish, Montana
  • Yellowstone National Park, Montana

Broader Impacts

Our research advances understanding of how and why wildfire affects conservation, land management, and restoration of forest ecosystems in the mountain West. Billions of dollars are spent annually to suppress wildfires and to protect the livelihoods of human societies within fire-prone landscapes. Simultaneously, huge investments are devoted to restoring fire without clear understanding of how it influences plant-pollinator interactions and pollination services. By sharing our findings with federal land managers across the region, we have contributed ecological science to management plans, with the dual aim of maintaining biodiversity of plants and pollinators while restoring environmental complexity representative of historical fire regimes. Our research team has also contributed to scientific outreach by teaching a course in fire ecology and organizing an R Basics Workshop for students and early-career scientists, participating in a special session of the Montana Forest Collaboration Network (MFCN), and mentoring Native American students through the Hopa Mountain Native Science Fellows Program.

Carolina buckthorn (Frangula caroliniana) & flowering dogwood (Cornus florida) fruits, Tyson Research Center, Missouri

2. Negative density dependence and diversity-environment relationships from local to global scales

Distance- or density-dependent specialist pathogens and predators are thought to maintain biodiversity by limiting abundances of dominant species, a process known as negative density dependence. This process was originally hypothesized to explain why there are so many more tree species in tropical latitudes compared to temperate latitudes. Despite decades of interest in negative density dependence, surprisingly little is known about the relative importance of negative density dependence in creating and maintaining biodiversity at different spatial scales, the ecological factors that mediate the strength of negative density dependence through space or time, and the ways in which negative density dependence interacts with processes at larger scales to determine biodiversity and community assembly. We are investigating these questions by exploring the role of negative density dependence in determining patterns of tree species richness, variation in tree community composition (β-diversity), and diversity-environment relationships at local, continental, and global scales.

Key Findings & Research Highlights

  • The latitudinal-gradient in tree-species diversity reflects not only stronger local biotic interactions (conspecific negative density dependence) at tropical versus temperate latitudes, but also a latitudinal shift in the strength of biotic interactions among common and rare species, suggesting that global patterns of biodiversity cannot be understood without considering the interplay of local biotic interactions and regional processes across temperate and tropical latitudes (LaManna et al. 2017, Science).
  • Using US Forest Service Forest Inventory and Analysis (FIA) data comprising over a quarter of a million trees in 9,592 plots that span 18 ecoregions in western North America, we found that changes in the strength of negative density dependence within and among tree species explain changes in β-diversity across a subcontinental-productivity gradient. Stronger conspecific relative to heterospecific negative density dependence in more productive regions was associated with higher local diversity, weaker habitat partitioning (less species sorting), and homogenization of community composition among sites (lower β-diversity), suggesting a key role for local biotic interactions in determining diversity-productivity relationships at multiple scales (LaManna et al. 2017, Nature Ecology & Evolution).
  • In a temperate forest, we found that the strength of conspecific negative density dependence increases with soil-resource availability and appears to reduce diversity when stronger for rare than common species during seedling recruitment, but increase diversity when stronger for common species during sapling recruitment, suggesting that negative density dependence is stronger in resource-rich environments and can either decrease or maintain diversity depending on its relative strength among common and rare species (LaManna et al. 2016, Ecology Letters).

Field Sites

Our field sites include: a long-term, 25-ha temperate-forest dynamics plot at Washington University’s Tyson Research Center (see the Tyson Research Center Plot page), which is part of the Smithsonian Center for Tropical Forest Science-Forest Global Earth Observatory (CTFS-ForestGEO), the largest, systematically studied network of forest-ecology plots in the world (Anderson-Teixeira et al. 2015).

Smithsonian CTFS-ForestGEO Network of 63 Forest-Dynamics Plots in 24 countries (left) & 25-ha Tyson Forest Dynamics Plot, Missouri (right). Each circle in the plot is an individual tree, scaled to its diameter.

Acknowledgements & Collaborators

Principal collaborators include Laura Burkle (Montana State University), Travis Belote (The Wilderness Society), and more than 100 collaborators from CTFS-ForestGEO. We thank the Montana Forest Collaboration Network (MFCN), Tyson Research Center, the International Center for Energy, Environment and Sustainability (InCEES) at Washington University in St. Louis, CTFS-ForestGEO, the CTFS-ForestGEO Grants Program, and the National Science Foundation (DEB 1256788, DEB 1256819 & DEB 1557094) for supporting our research.