­Environmental heterogeneity and functional redundancy drive spatial groundfish diversity patterns in the Gulf of Alaska

Rachael Blake, Colette Ward, Mary Hunsicker, Ole Shelton, Anne Hollowed

\(\star\) NOTE Final author list is yet to be determined. Alphabetical listing right now.

NOTE This is a work-in-progress. Do Not Cite.

Abstract

       The mechanisms structuring patterns of diversity and community composition can be difficult to identify, and much of our knowledge stems from study of local ecological systems.  Two candidate mechanisms include dispersal and environmental heterogeneity, which structure communities at local and larger scales by fostering species coexistence and niche partitioning, respectively.   It is important to understand these patterns and their drivers at larger scales, especially in the face of climate change and other perturbations. The Gulf of Alaska (GOA) has complex topography, climate-driven variability, and a well-studied groundfish community, making it an ideal study system.   We examined patterns of diversity and community composition in the groundfish community across 14 sites in the GOA using geostatistically modeled groundfish abundance and biomass from the Alaska Fisheries Science Center trawl survey data (1984 – 2015).  We found that species richness, and alpha, beta, and functional diversity varied little both within and between study areas, and were conserved across the central GOA.  Conversely, community composition varied significantly along a longitudinal gradient, with distinct groups of species in individual study areas.  These differences in community composition were driven by rare and lower-density species, while high-density species remained the same.   Thus, community structure was conserved despite variation in species identities.  Overall, environmental heterogeneity and community structure control groundfish diversity across the GOA large marine ecosystem.

Introduction

      The mechanisms driving ecosystem stability, patterns of biodiversity, and community structure remain important topics of ecological study, as demonstrated by the substantial efforts dedicated to understanding diversity-stability relationships and the processes underlying species co-existence.  However, our knowledge of these concepts stems mostly from study of local ecological systems.  Much less is known about what drives large-scale patterns of stability and diversity, especially in a spatial context. 


An unexpected property of FD (Rao’s Q) is that its value may decrease if species richness increases.   (Journal of Vegetation Science 16: 533-540, 2005)

- How do all of the above components of diversity in our system build on each other to collectively create the spatial diversity-stability result (re ideas in Wang & Loreau 2014 & 2016, and pulling in ideas re mechanisms from the few empirical spatial diversity-stability papers published to date).
- spatial portfolio effect: previously documented among metapopulations (eg Schindler); little work documenting this phenomenon at the whole-community level (eg Mellin et al. 2014, Wang & Loreau 2014)
ADD SOMETHING ABOUT THE PORTFOLIO EFFECT HERE.



      Spatial stability in ecosystem properties and processes can be dependent on patterns of biodiversity at different scales, from organisms to ecosystems (Gonzalez 2009, Leibold 2004, Wang 2014, Wang 2016).  Species richness is one of the most fundamental diversity metrics and measures the number of species in a given space (habitat, ecosystem, etc.).  In a more explicitly spatial context, the effects of biodiversity are can be examined within local scale communities (\(\alpha\) diversity), between local scale communities (\(\beta\) diversity), and within regional scale communities (\(\gamma\) diversity) (CITES,