Research

My research program is guided by a critical question: how do the supply, flux and allocation of energy and matter constrain the structure and dynamics of ecological systems (i.e., food webs and ecosystems). To answer this question, my research uses a diversity of approaches including experiments, observation, data synthesis, and a variety of analytical tools (e.g., stable isotopes). I am particularly interested in how the theory of “ecological stoichiometry” (i.e., the balance of multiple chemical substances in ecological processes) and scaling principles (i.e., body size) can be applied to better understand the structure and function of ecological systems. The diversity of ways in which organisms uptake, store, and transfer energy and matter may have profound effects on the ability of ecological systems to respond to global environmental change.

Some current and future field projects in my lab include: (1) influence of habitat size on pools and fluxes of energy and matter within ecosystem; (2) Macro-stoichiometry; patterns, causes and consequences of organismal C, N and P contents variation; (3) human-driven nutrient inputs (nitrogen and phosphorus) effects on ecosystem functioning; (4) variation in the energetic and material cost and benefits of different spider web architectures, and between solitary and social spiders; and (5) the structure and dynamics of spider-prey ecological networks. See below if you are interested in reading more about each project.

(1) How does habitat size influence community structure and thereby nutrient dynamics within ecosystems? Understanding the direct effects of habitat size on community structure. Understanding the direct effects of habitat size on community structure provides only one piece of the puzzle of predicting organismal responses to resource availability. While populations may directly respond to habitat size and influence food web structure, such changes may ultimately affect the storage, processing, and cycling of nutrients within ecosystems. My ongoing research on the role of habitat size on ecosystem processes addresses the following question: what is the effect of ecosystem size on multiple nutrient pools and cycling? I am using as a model system aquatic insect food webs in tank bromeliads. Bromeliads trap both water and detritus, which support larvae of many insects that in turn are consumed by aquatic predators. Bromeliads also vary substantially in their size (i.e. volume of water). By merging community ecology (i.e., numerical abundance of species and their body sizes) with ecological stoichiometry (i.e., nutrient content of organisms), I am studying how the pools of nitrogen and phosphorus within detritivore and predator compartments scale along habitat size, which I am using as a proxy of ecosystem function.

(2) What are the large scale patterns, ecological and evolutionary determinants, and consequences of the stoichiometry of living organisms? Chemical elements, and the complexes they form, are the building blocks of living Uracis imbuta2organisms. Although all living organisms are composed of the same main chemical elements, they differ quite widely in the proportion of these elements in their biomass. Two questions are central in my research: are there major patterns of stoichiometric composition in organisms and what are the evolutionary and ecological mechanisms underlying these patterns? My on-going work examines these questions using (1) an unique model systems – tropical tank bromeliad food webs. Using invertebrate nutrient content data from five widely spread bromeliad locations across South-Central America (The Bromeliad Working Group), I am testing whether insect body size, phylogeny, and functional group drive organism stoichiometry or whether organisms reflect local availability of nutrients, and (2) using published data on invertebrate stoichiometry from all over the world. My goal is to understand the underlying biological mechanisms regulating the elemental stoichiometry of organisms across taxa and ecosystems at local, regional and global spatial scales.

(3) What are the ecological consequences of human-driven nutrient inputs (nitrogen and phosphorus) on ecosystem functioning? Human activities have increased the atmospheric deposition of nitrogen (N) and phosphorus (P) into the biosphere 1- to 4-fold over ambient levels. Future inputs are forecast to increase and will probably shift primary producers from N-limitation to P-limitation, particularly in aquatic ecosystems. We will use tropical tank-bromeliads and temperate pitcher plants as micro-ecosystems that support functional aquatic food webs. Leaves of these plants form traps that fill with rainwater, which is often enriched with atmospheric nutrient inputs. These traps capture arthropod prey and detritus, which forms the base of a “brown” food web. Upper trophic levels of arthropod filter feeders and top predators feed omnivorously on a diverse sub-web of detritivores, protozoa, and bacteria. Tank-bromeliads and pitcher plants are model systems for studying the impacts of nutrient deposition on an entire ecosystem, because we can easily manipulate nutrient inputs in realistic field experiments, and measure nutrient pools and fluxes on time scales of days, weeks and months.

(4) What are the energetic and material costs and benefits of different spider web architectures as well as solitary, sub-social, and social spiders? Eriophora_Araneidae2The flux and allocation of energy and matter (i.e., chemical elements) fundamentally constrains all living organisms. A major factor affecting energy use and biomass construction in living organisms is body size, and metabolic scaling explicitly predicts a size-dependence of many biological and ecological processes for multicellular organisms. Energetic and material constraints may also limit the rate at which social organisms uptake, process and allocate chemical substances to biological functions. A major cost for a web-building spider is the energetic and material investment into a functional web. As web construction, affect individual spider metabolism and resource uptake but also depend on group size, social web construction and maintenance costs might follow principles from economy of scale. This is, larger webs might be less costly in terms of energy and material, and at the same time increase the likelihood to capture more and larger prey than smaller webs, and therefore, living in a group may confer energetic benefits to spiders. In collaboration with Leticia Avilés (University of British Columbia) we are investigating the energetic and material costs of several types of web architectures (bi-dimensional, tangle, three-dimensional without sheet, three-dimensional with sheet), and social lifestyles.

(5) How do spider web architecture influence network structure? Food webs or antagonisticEriophora sp_Araneidae ecological networks represent descriptors of trophic interactions in a community. A recent advance in ecological network analysis is the integration of both energy and nutrient fluxes within ecosystems. Chemical constraints on predator-prey interactions may play a key role on food web structure. Web-building spiders are outstanding model systems for the study of predator-prey interactions and network structure because actual predator-prey interactions are relatively easy to quantify. We are combining energetic and stoichiometric approaches to explicitly examine the structure of quantitative spider-prey food webs on the basis of prey biomass and flows of C, N, and P.

 

 

 Some other research interests/projects are:

tb-Egeria-densa-01How do stoichiometric constraints affect the dynamics of species invasiveness and the invasibility of communities?
Biological invasions represent one of the major drivers of environmental change and a strong threat to biodiversity and ecosystem functioning worldwide. Several mechanisms for biological invasions have been proposed; yet, to date there is no common framework that can broadly explain patterns of invasion success among ecosystems with different resource availabilities. Beginning with a working group that I led in 2009 in Japan as part of “Woodstoich” (a workshop on ecological stoichiometry), I combined conceptual modeling and cross-system meta-analyses to propose how energy and nutrients constrain key physiological and ecological processes and ultimately determine the success of invasive organisms. I am particularly interested in the integration of metabolic theory, ecological stoichiometry, and stable isotopes techniques to the understanding of the causes of biological invasions as well as their impact on nutrient pools and fluxes within ecosystems.

AtacamaHow do ecosystems respond to spatio-temporal variation in water and nutrient availability?
For my doctoral dissertation, I conducted research in fog-dependent ecosystems of the hyper-arid Atacama Desert, Chile. By integrating natural and experimental manipulation, I sought to understand the role of nutrient inputs from fog on ecosystem structure and functioning, considering multiple organisms and trophic levels. My results showed that local nutrient supply, structural differences in material allocation, trophic level and phylogeny can all contribute to variation in the stoichiometry of plants and animals, and they indicate that the elemental composition of animals can be useful information for identifying broad-scale linkages between nutrient cycling and trophic interactions in terrestrial food webs. Elemental mismatches between the nutrient requirements of consumers and that of their resources have shown to be powerful drivers of ecosystem functioning (i.e., affecting plant productivity and biomass accumulation within trophic levels). My longer-term goal is to understand how abiotic (water, nutrients) and biotic (species interactions) forces interact to affect food webs and ecosystems.

DSC_0088_cWorldwide, wetland ecosystems are being altered and reduced at an increasing rate by human activities. Growing recognition of wetlands as important environments for birds, due to their habitat diversity and high productivity, have led to increasing concern about the impact of their loss. I have done additional research on the spatial and temporal dynamics of populations and community structure of waterbirds in freshwater ecosystems. I am broadly interested in the role of habitat structure in determining the use of wetlands by waterbirds In fact, my professional career began with a focus on birds and wetland ecology, and I am still actively involved in aquatic bird ecology research.

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