Jarrett Byrnes, Community Ecologist

BIODIVERSITY AND ECOSYSTEM FUNCTION
predator diversity and trophic cascades diversity-function feedbacks invasive species diversity

Overview

The diversity of species around the globe is declining. What will this mean for the way ecosystems function? Will they produce the same amount of plant and animal biomass? Will their ability to sequester carbon, recycle nutrients, filter water, and decompose the dead all remain the same? Can fewer species get the job done, or will something unexpected happen? We do not know the answers to these questions, and yet, as more and more species go extinct, their answers are of vital importance.

Beyond Species Diversity: The Consequences of Changes to Food Web Network Structure

Ecology is replete with examples of researchers asking superficially similar questions - e.g., How does species diversity influence herbivory? How does herbivory influence species diversity? - and arriving at relationships that seem in conflict with one another.

If diversity influences the intensity of disturbance experienced by a community, it can shift observed patterns between diversity and disturbance in nature. Figure after Hughes et al. 2007 Ecology Letters

Rather than conflict, I see researchers looking at two sides of the same coin. When one looks at just what each researcher is assuming to be the cause and response in a relationship, however, one finds that they are often looking at different points in time of a larger feedback relationship. This is not surprising given the number of feedbacks in ecology - e.g., predator-prey cycling, plant-soil feedbacks, etc.

Currently, I am examining feedbacks between species richness and herbivory in the kelp forests of Southern California. Within these forests, the primary source of food for sea urchins, the giant kelp Macrocystis, can be removed by large storms, which are predicted to increase in frequency due to climate change. I have been running experiments to explore the importance of sessile species diversity for mediating the impact of urchin grazing on sessile species cover. I then removed urchins and followed the trajectory of communities to examine how the amount of damage inflicted influences sessile species diversity in the following year.

Results show that diversity actually enhances urchin grazing at low urchin abundance. This may be due to urchins attempting to "balance" their diet and use multiple prey species to satisfy their nutritional needs. At high urchin abundance, diversity had no effect on the intense grazing of urchins. Plots did recover a great deal, with initial diversity and damage inflicted interacting to affect future diversity.

Relevant references
Byrnes, J. E. K., B. J. Cardinale, and D. C. Reed. 2013. Interactions between sea urchin grazing and prey diversity on temperate rocky reef communities. Ecology 94:1636-1646. [doi]

Hughes A.R., Byrnes J.E., Kimbro D.L. & Stachowicz J.J. 2007. Reciprocal relationships and potential feedbacks between biodiversity and disturbance. Ecology Letters. 10: 849-864.[doi] [pdf]

Beyond Species Diversity: The Consequences of Changes to Food Web Network Structure

The food web of California Kelp Forests. Nodes represent species and links represent feeding relationships. What does this structure mean for the movement of energy from algae up to predatory fish?

Over the past century, science has come to understand that for every process in the world - ecosystem productivity, gene regulation, information transfer, disease dynamics, etc. - there is complex system of interacting pieces. These systems are commonly represented as networks - think of the Internet, a map of neural connections in the brain, or a food web. One of the great challenge of the next few decades is to understand how the complexity of networks in nature influences their dynamics. My research seeks to understand how network structure influences the function of marine food webs.

As a postdoctoral fellow at the National Center for Ecological Analysis and Synthesis (NCEAS), I am concentrating on developing new theory that examines the linkages between food web complexity and productivity. Over the past decade, the field of biodiversity-ecosystem function research has sought to understand the consequences of declines in species diversity due to human activities. The field has yielded many robust conclusions regarding the consequences of plant species loss for primary production and nutrient cycling. It has not, however, arrived at many generalities regarding the consequences of species loss at higher trophic levels for the flow of energy and nutrients through food webs, even in the most simplified of experimental systems. Nor do we have a strong idea of the consequences of extinction in food webs of real-world complexity - webs high in diversity and replete with omnivory, intraguild interactions, multiple trophic levels, and real range of diet breadths. This lack of understanding is due to extinction altering not just the number of species in a food web, but also degrading the network structure of feeding connections between species.

I am working to unite biodiversity-ecosystem function research with food web network theory to better understand the consequences of species loss for the efficiency of trophic transfer within food webs. I am (1) developing a unified theoretical framework to examine the consequences of species loss in the context of food web network structure. I am then (2) challenging this framework to multiple long-term community data sets to determine its efficacy. Lastly, I am (3) comparing my predictions to the results of food web manipulations to examine how the topology of simplified experiments has influences the dynamics of resource use. The results of this research will fill a critical gap in predicting the consequences of predator and consumer extinction in nature.