Overview
A species is but one part of a much larger food web. My research asks many basic questions about the structure and function of food webs in nature. What are the factors controlling the structure of a food web? What controls how energy and nutrients are channeled to different key players? Does the structure of a web itself influence its productivity and stability?
As global environmental change impacts life on earth, these questions are increasingly important. Human driven extinctions and invasions have and will continue to reshape the structure of food webs across the globe. By studying the emergent properties of food webs, I hope to be able to understand how human impacts will change the way they function in the future.
Global Change and Shifts in the Network Structure of Food Webs
The distribution of the types of species going extinct in the Wadden Sea versus the types of species likely to be invaders. Extinctions occur primarily at top trophic levels while invaders tend to be low-level primary consumers.
The distribution of the types of species going extinct in the Wadden Sea versus the types of species likely to be invaders. Extinctions occur primarily at top trophic levels while invaders tend to be low-level primary consumers.
Global environmental change is reshaping food webs through increased rates of extinction and invasion. But how? What kinds of species are winning, and what kinds are losing? How will climate change, overharvesting, habitat fragmentation, urbanization, and more interact to create the food webs of the future? I am interested in examining both global patterns of change to food webs as well as examining how environmental drivers shape food webs at local spatial scales.
In an analysis of global and regional trends, I have shown that most species driven extinct have been top predators whereas invasive species are primary consumers. This pattern is consistent both at the scale of a single ecosystem and across the globe. To think about it geometrically, extinctions and invasions are acting together to change the shape of food webs from classical pyramids down to squat boxes.
But what about the drivers of change to food web structure? At the Santa Barbara Coastal LTER, I examined how climate change driven increases in the annual frequency of intense storms in the Southern California could change structure of kelp forest food webs. Giant kelp acts as a foundation species, providing habitat and food for many species, as well as determining the balance between algae and sessile invertebrates by reducing light on rocky reefs. Through an analysis of long-term biological, oceanographic, and satellite data, I found that the loss of kelp by storm-driven waves increases algal diversity but decreases diversity at all other trophic levels. Simulating these results through time, I showed that annual large storms should ultimately simplify the network structure of kelp forest food webs. While these results were derived from structural equation models and simulations, they were still based on correlative evidence. I therefore verified these predictions using early results from a large-scale kelp removal experiment that we have set to run for the next decade. With the LTER, I am beginning to examine how this experimental kelp removal and concomitant changes in food web structure lead to shifts in the allocation of biomass between different compartments of the food web.
Relevant references
Byrnes, J.E., Reed, D.C., Cardinale, B.J., Cavanaugh, K.C., Holbrook, S.J., and Schmitt, R.J. 2011. Climate driven increases in storm frequency simplify kelp forest food webs. Global Change Biology. 17: 2513-2524. [doi] [pdf]
Byrnes, J.E., Reynolds, P.L., Stachowicz, J.J. 2007. Invasions and extinctions reshape coastal marine food webs. PLoS One. 2: e295. [doi] [pdf]
In an analysis of global and regional trends, I have shown that most species driven extinct have been top predators whereas invasive species are primary consumers. This pattern is consistent both at the scale of a single ecosystem and across the globe. To think about it geometrically, extinctions and invasions are acting together to change the shape of food webs from classical pyramids down to squat boxes.
 Kelp forests where no kelp was removed (top) versus two years of winter kelp removal (bottom). |
Relevant references
Byrnes, J.E., Reed, D.C., Cardinale, B.J., Cavanaugh, K.C., Holbrook, S.J., and Schmitt, R.J. 2011. Climate driven increases in storm frequency simplify kelp forest food webs. Global Change Biology. 17: 2513-2524. [doi] [pdf]
Byrnes, J.E., Reynolds, P.L., Stachowicz, J.J. 2007. Invasions and extinctions reshape coastal marine food webs. PLoS One. 2: e295. [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?
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.
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.
The Relative Contributions of Nutrients, Predation, and Recruitment in Nature
The forces that can influence the abundance of organisms in an ecosystem. All are important, but how strong is each?
The forces that can influence the abundance of organisms in an ecosystem. All are important, but how strong is each?
Ecologists have spent much of the last fifty years asking which of the following forces is driving the dynamics of food webs: top-down control by predation and herbivory or bottom-up control by nutrients and recruitment. I believe the question is not which forces drive food webs, but rather, what is the relative importance of each. Nor should these forces be viewed in isolation. We know, for example, that strong recruitment increases the importance of control by predation. Nutrient-rich plants increase herbivore growth rates.
In my research, I am interested in applying multivariate statistical models to experiments and long-term datasets to disentangle the effects of these different drivers of food web dynamics. Over the past few years I have been working with the National Park Service's Channel Islands Kelp Forest Monitoring Program. Working with colleagues, we constructed models of food web dynamics based in the natural history of these forests. Applying Structural Equation Modeling to the data, we have shown that kelp forests are driven by a combination of nutrient inputs and predation. Moreover, the impact of nutrients are masked by outbreaks of sea urchins. And some sessile species respond to neither nutrients nor herbivory, but rather shape subtidal communities through competitive and physical interactions with the species around them. It's a complex beautiful system.
In the future, I want to apply this approach to examining how the strength of top-down and bottom-up forces change due to climate change, urbanization, and habitat fragmentation.
Relevant references
Byrnes, J.E., Bowles, C.M., Bracken, M.E.S., Ferner, M.C., Grace, J.B., Gruner, D.S., Hays, C.G., Kushner, D. J., Nickols, K.J., Ram, K, Sorte, C.J.B., Williams, S.L. In Revision. Top-down and bottom-up forces jointly control kelp forest communities in the California Channel Islands.
Yang, L.J., Edwards, K.E., Byrnes, J.E., Baston, J.L., Wright, A.N., and Spence, K.O. In Press. A meta-analysis of resource pulse-consumer interactions. Ecological Monographs. 80: 125-151. [doi] [pdf]
 Which of these players is more important for kelp forests: predation by lobsters or upwelling-driven nutrient inputs |
In the future, I want to apply this approach to examining how the strength of top-down and bottom-up forces change due to climate change, urbanization, and habitat fragmentation.
Relevant references
Byrnes, J.E., Bowles, C.M., Bracken, M.E.S., Ferner, M.C., Grace, J.B., Gruner, D.S., Hays, C.G., Kushner, D. J., Nickols, K.J., Ram, K, Sorte, C.J.B., Williams, S.L. In Revision. Top-down and bottom-up forces jointly control kelp forest communities in the California Channel Islands.
Yang, L.J., Edwards, K.E., Byrnes, J.E., Baston, J.L., Wright, A.N., and Spence, K.O. In Press. A meta-analysis of resource pulse-consumer interactions. Ecological Monographs. 80: 125-151. [doi] [pdf]
Overview
A species is but one part of a much larger food web. My research asks many basic questions about the structure and function of food webs in nature. What are the factors controlling the structure of a food web? What controls how energy and nutrients are channeled to different key players? Does the structure of a web itself influence its productivity and stability?
As global environmental change impacts life on earth, these questions are increasingly important. Human driven extinctions and invasions have and will continue to reshape the structure of food webs across the globe. By studying the emergent properties of food webs, I hope to be able to understand how human impacts will change the way they function in the future.