John Sabo
Research Statement
I am a stream and riparian community ecologist. Typically I use experimental and comparative approaches in field settings to answer questions about how the land-water boundary in riparian zones mediates energy or water fluxes and between rivers and riparian habitats. I then examine how these fluxes alter species interactions in riparian food webs. More broadly, I am interested in advancing theory in community ecology by integrating insights from this field with tools and concepts from population biology and ecosystem ecology. I use large-scale experiments and stable isotopic tracers to understand connections between ecosystem level processes such as energy flow and water fluxes and the structure of food webs in rivers and riparian forests. Here I focus on two main questions: 1) Do riparian trees link subsurface aquifers to consumers in surface-dwelling food webs in riparian forests? And, 2) How do ecosystem size, resource availability and flow-related disturbance affect the length of food chains in stream ecosystems? In both of these endeavors I am supported by grants from the National Science Foundation. In addition to this empirical work, my theoretical work combines insights from population and community ecology to understand how to better manage the negative impacts of non-native predator invasions. Here I focus on one central question: 3) How does the stochastic variation of non-native species influence the viability of threatened native populations?
Theme 1: Connectivity between groundwater and riparian food webs
El Jefe" masters raking technique at the San Pedro litter removal plots.
Riparian zones are habitats of critical conservation concern as they have been shown to increase regional species richness across the globe by supporting unique faunas relative to upland habitats more distant from the river (Sabo et al. in press). The goal of my groups primary field research program is to understand how fluxes of energy (Candan Soykan and Beth Hagen), water (Kevin McCluney) and nutrients (Tamara Harms) from river ecosystems determine observed gradients in the abundance and diversity of vertebrate species along the river-upland transition in watersheds. For example, my dissertation research examined how aquatic insect fluxes from rivers altered the abundance of terrestrial predators (lizards) and their impacts on terrestrial arthropods (Sabo and Power 2002 a & b). More recently, my research program at ASU focuses on quantifying fluxes of groundwater through riparian food webs at the San Pedro River in southwestern Arizona. The San Pedro River watershed hosts over 300 species of birds, 80 species of mammals and 50 species of amphibians and reptiles. Here I am quantifying the degree to which riparian trees deliver groundwater to an abundant resource for these vertebrates in gallery forest food webs—leaf-litter dwelling arthropods. Large scale field experiments (Sabo et al. in prep #22 on CV) suggest that these arthropods depend on fresh, green, water-laden litter as an alternate water source during the dry season when surface water is limited (both in soils from rain and in the active channel of the river). Currently my group (Kevin McCluney) makes use of stable isotopes of hydrogen and oxygen to quantify water budgets for terrestrial food webs in desert environments and to evaluate the role of water fluxes in mediating key species interactions and species diversity in desert food webs. This research will have enormous influence on our understanding of how water use practices in desert environments impacts desert fauna and the potential sustainability of desert diversity in the face of the expansion of human population centers in the Desert Southwest.
Candan and John show the litter who is boss.
 Spiders may use leaf litter as structure to avoid predation, or for foraging. |
 Leaf litter quality may drive abundance of detritovores/herbivores, while providing other animals with refuge or foraging habitat. |
 Whiptail (Aspidoscelis [formerly Cnemidophorus] uniparens) |
Theme 2: Controls on food chain length in stream ecosystems
The San Pedro River (Arizona) in winter
Understanding ecological processes that control the length of food chains in natural ecosystems is key to understanding links between ecosystem processes and community structure. The length of food chains is also an important metric in the realm of human health, as potentially toxic heavy metals and pesticides concentrate as they move up the food chain through successive feeding events. My second empirical focus is on understanding the factors that control food chain length in river ecosystems. I am the project coordinator of a collaborative NSF project that seeks to quantify the relative effects of three ecosystem-level variables on food chain length—ecosystem size, resource availability and flow-related disturbance. This work is done in collaboration with Ted Kennedy, David Post and Jacques Finlay. Together, we are compiling a dataset consisting of our own primary and previously published data describing these three ecosystem properties in many of the continents largest river systems (Colorado, Mississippi, Yukon and Hudson). We will then use these to predict food chain length, estimated using stable isotopes of carbon and nitrogen. Over the next 3 years our goal is to advance innovative methods for quantifying energy flow, disturbance and food chain length. For example, we have developed a new statistical tool for decomposing seasonal variation and more stochastic anomalies in long-term flow records (Sabo and Post in prep.) to describe flow-related disturbance. The ultimate product of this project will be one of the first quantitative cross-system analyses of the relationships between key ecosystem attributes and food chains in rivers.
 Ted working on a highly modified "stream" in Albuquerque, NM |
 Metabolism measurement injection site, Paria River, Arizona |
 Ted bravely fording the Owens River, Bishop California |
The "Powell Route" into the Little Colorado River canyon, Arizona
Theme 3:Stochastic variation in the effects of non-native species
An attempt at predator control in New Zealand. The fence protects koala habitat from animals like the opossum.
Introduced predators threaten native prey populations worldwide. For example, commensal rats are found on nearly 90% of the worlds island groups and have caused extinctions of native birds, reptiles and mammals. Interestingly, while risk assessment tools for single species abound, very few of these (Population Viability Analyses, or PVA) include possible negative effects of other species. Theory from community ecology readily provides predictions about the persistence of two or more species but traditionally ignores environmental variability—a key component of any PVA. My recent research effectively fills this gap by incorporating empirical estimates of environmental variability (from Sabo et al. 2004) into more traditional (community) models of interactions between predators and their prey. My analysis suggests that the most effective means for recovering a threatened prey population may be to control the variability, not the abundance per se, of non-native predator populations. While this research is purely theoretical, I am currently recruiting graduate students to use empirical approaches to test many of the predictions from my models.
 Opossums were introduced to New Zealand for the fur trade, but are an agressive mesopredator and have decimated the native fauna, particularly the Kiwi |
 The ultimate irony...a Kiwi made with opossum fur. |
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