Research

Food web linkages that bridge land & water

Pervasive environmental degradation has altered biodiversity at a global scale.  At smaller scales, species extirpations, invasions, and replacements have greatly influenced how ecosystems interact by affecting the exchanges of energy, materials, and organisms.  The movement of such materials from one ecosystem to another can greatly influence how food webs are structured and how they function.  Broadly speaking, we examine how environmental degradation, and associated species losses and gains, change the exchange of resources (materials or organisms) within and among ecosystems.  We mechanistically examine how changes within an ecosystem may trigger effects that propagate (e.g., directly, indirectly, and via feedbacks) across ecological boundaries into other ecosystems via exchanges of materials and organisms.  This work has been conducted in the context of the extirpation of Pacific salmon in the Pacific northwest, the introduction of Pacific salmon in the Great Lakes ecosystem, and the invasion of Bigheaded carp in the Mississippi River basin.  Collectively, this work has shown that the loss or addition of a fish species has both local effects as well as effects that propagate from aquatic to terrestrial ecosystems.  We are continuing to explore how human-mediated changes (i.e., habitat degradation; species introductions; climate change) alter resource exchanges and how such changes propagate among ecosystems.

 

Who-eats-whom and what-of-the-consumed? Combining community- and ecosystem-based approaches to the of study biological invasions

  Understanding the mechanisms through which biological invasions alter ecological processes (e.g., trophic dynamics, energy flows, nutrient recycling) should aid in predicting the range of direct, indirect, positive, and negative effects that occur within invaded habitats as well as in adjacent habitats connected through material exchanges.  Unraveling the complex processes that structure food webs has historically been addressed under two epistemological approaches: individualistic and community-based approaches or a holistic ecosystem-based approach concerned with the fluxes and exchanges of energy and materials. By integrating these approaches, food web ecologists have expanded the traditional adage, who-eats-whom, to further consider how species interactions influence the flows and fluxes of materials among ecosystems. So, what of the consumed?  Through a combination of manipulative experiments, diet analyses, and modeling exercises, our work demonstrated that invasive bighead carp can alter energy flow through planktonic habitats by efficiently exploiting prey production, as well as identified the functional consequences of such alterations. So, what-of-the-consumed material? We found that a large quantity of consumed resources (zooplankton, algae) was shunted to the sediment as egested fish waste (i.e., fish poop), which subsidized midge populations and enhanced emergence into terrestrial ecosystems.  By reducing densities of large suspension feeding zooplankton, and increasing densities of some rotifers, we also observed functional deficits in the filtering capacity of zooplankton assemblages.  Collectively, our work argues that the perception of invasive species should evolve from competitors for finite resources to mediators and processors of nutrients and energy within and across ecosystems.  Moving forward, we will continue to bridge community- and ecosystem-based approaches of scientific inquiry to answer basic questions in ecology.

 

Facilitated fishes: Examining the co-occurring positive and negative interspecific interactions among invasive and native species

Understanding the outcomes of species interactions has been fundamental in describing why certain organisms thrive while others falter.  Ecological theory has long recognized the importance of positive and negative species interactions as drivers of food web structure.  However, processes such as competition and predation typically receive more attention than others like facilitation, although this disparity is diminishing.  Because competitive and facilitative mechanisms can operate simultaneously through unique food web pathways, the balance of their combined effects often produces complex and variable responses.  Ecological phenomena like biological invasions typically evoke notions of negative effects on native communities.  Yet, negative effects within specific food web components can also have positive feedbacks that manifest elsewhere within the food web. Success or failure of a newly introduced species (or any organism) may depend on the suite of negative and positive interactions an invader experiences within a community and its associated habitat characteristics.  If competition for shared and limited resources sufficiently stresses one or many species, negative species interactions and attenuating effects on food web structure may produce complex feedbacks that result in positive effects for some organisms and additional negative effects for others.  Predicting indirect ecological effects can be difficult, and therefore, there is a poor mechanistic understanding of how species interactions might elicit feedbacks within prey communities that result in facilitation of one fish species by another.  Through a series of manipulative experiments, we have documented underlying mechanisms that promote facilitation between native and invasive fish species.

 

Assessing social-ecological dynamics of inland recreational fisheries

Recreational fisheries are spatially structured social-ecological systems where individual waterbodies are linked by the movements of anglers. The dynamics of recreational anglers and inland fish populations across the landscape are complex, yet most inland fisheries studies evaluate one or a handful of waterbodies within a small geographical area. It has been argued that the reduction or collapse of fish stocks should occur in areas near large aggregations of recreational anglers where fishing effort is presumed to be greatest. Because the number of cities are increasing across the globe, and because fish are an important food and recreational resource, this hypothesis is timely and woefully understudied. We approach the study of recreational fisheries from the landscape scale to understand the inter-dependencies of recreational angler and fish populations.