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Grantee Research Project Results

NCER Grantee Research Project Results

The Food Web Consequences Of An Omnivorous Whelk In The New Zealand Marine Intertidal.

EPA Grant Number: F5E10969
Title: The Food Web Consequences Of An Omnivorous Whelk In The New Zealand Marine Intertidal.
Investigators: Novak, Mark
Institution: University of Chicago
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: September 1, 2005 through September 1, 2008
Project Amount: $111,172
RFA: STAR Graduate Fellowships (2005)
Research Category: Academic Fellowships

Description:

Objective:

The goal of my dissertation is to gain a better understanding of the mechanisms by which omnivores -- species that feed at multiple trophic levels -- influence the structure and dynamics of their food webs.

Approach:

My approach combines field surveys, stable isotope techniques, and both observational and manipulative experiments focused on understanding the omnivorous interactions of Haustrum haustorium, a whelk common to New Zealand's rocky shore marine intertidal. I am conducting my work across a number of sites situated within regions of the New Zealand coastline that are characterized by different upwelling regimes. I will thereby be able to assess how omnivorous feeding strategies change in response to differing levels of basal productivity.

Having previously established the topology of Haustrum's food (i.e. sink) web, I am estimating the per capita strength of both top-down and bottom-up species interactions in this system using an observational, non-manipulative approach. I am assessing the inaccuracies of my observational approach using a manipulative perturbation experiment, contrasting the actual effect of reducing the abundance of a given species to the effect that I would predict to see given my observational estimates of interaction strengths. By following the feeding activities of tagged Haustrum individuals through time, before and after this perturbation, I am also assessing the extent to which intraspecific feeding specializations affect, and are effected by, changes in the abundances of prey trophic levels.

I am also comparing my observational estimates of species-specific interaction strengths to the importance of species-specific interactions as inferred from stable isotopes. Stable isotopes are being increasingly used to obtain estimates of the relative magnitude of bottom-up food web linkages, especially in systems where other means of inferring feeding relationships are difficult or impossible to make. Their use, however, remains largely untested. Finally, I am evaluating the use of stable isotopes for inferring the prevalence of intraspecific feeding specializations.

Expected Results:

The manner in which omnivory affects the stability of food webs is poorly understood. Given the prevalence of omnivores in natural communities, this has important consequences for the mechanisms responsible for regulating the abundance, diversity, and invasibility of natural communities. Furthering our knowledge of such processes has the potential to contribute both to the conceptual and the applied goals of community ecology.

Supplemental Keywords:

Community ecology, marine biology, food webs, species interactions, predation, omnivory, productivity gradient, trophic levels, interaction strengths, intraspecific specialization, generalist, specialist, stable isotopes, marine temperate intertidal, gastropods, New Zealand,, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Aquatic Ecosystem, Monitoring/Modeling, Environmental Microbiology, marine food web, ominvores, biodiversity, ecosystem monitoring, stabe isotope monitoring techniques, food web changes, marine biology, aquatic food web, energy transfer model, aquatic ecosystems, hydrologic modeling

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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