Award Abstract # 0240265
Density vs. Trait-Mediated Interactions Between Predators and Prey: Their Influence on Rocky Shore Algal Diversity and Community Structure

NSF Org: OCE
Division Of Ocean Sciences
Recipient: NORTHEASTERN UNIVERSITY
Initial Amendment Date: February 4, 2003
Latest Amendment Date: May 24, 2005
Award Number: 0240265
Award Instrument: Standard Grant
Program Manager: Phillip R. Taylor
OCE
 Division Of Ocean Sciences
GEO
 Directorate for Geosciences
Start Date: March 1, 2003
End Date: February 28, 2007 (Estimated)
Total Intended Award Amount: $297,567.00
Total Awarded Amount to Date: $304,921.00
Funds Obligated to Date: FY 2003 = $297,567.00
FY 2005 = $7,354.00
History of Investigator:
  • Geoffrey Trussell (Principal Investigator)
    g.trussell@neu.edu
Recipient Sponsored Research Office: Northeastern University
360 HUNTINGTON AVE
BOSTON
MA  US  02115-5005
(617)373-5600
Sponsor Congressional District: 07
Primary Place of Performance: Northeastern University
360 HUNTINGTON AVE
BOSTON
MA  US  02115-5005
Primary Place of Performance
Congressional District:
07
Unique Entity Identifier (UEI): HLTMVS2JZBS6
Parent UEI:
NSF Program(s): BIOLOGICAL OCEANOGRAPHY
Primary Program Source: app-0105 
app-0103 
Program Reference Code(s): 9169, SMET, 9178, EGCH, 9251
Program Element Code(s): 165000
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.050

ABSTRACT

The trophic cascade concept has profoundly improved our understanding of how predator-prey interactions shape the structure and diversity of ecological communities. Trophic cascade studies typically focus on how predator effects on prey density propagate through food chains to shape species diversity and community structure (i.e., Density-Mediated Indirect Interactions). Recently, there has been growing interest in interaction modifications: the presence of a third species (predator) in the system alters the interaction between two other species (prey and their resource). Trait-Mediated Indirect Interactions (TMIIs) are those that occur because of predator effects on prey traits rather than prey density. For example, in aquatic systems water-borne predator risk cues can induce changes in prey behavior, such as feeding rates, thus altering the prey.s impact on lower trophic levels. Hence, TMIIs emphasize nonlethal predator effects in contrast to the more prevalent emphasis on lethal indirect effects (DMIIs).
Although ecologists are beginning to appreciate the importance of TMIIs, there is still a limited understanding of the factors governing the relative importance of density and trait-mediated predator effects and how they shape the diversity and structure of ecological communities. Classic work on the importance of herbivorous snails to the diversity and structure of macro-algal communities on rocky shores has left a lasting impression. Luchenco demonstrated that diversity and succession in these communities is closely tied to snail (Littorina
littorea) density and that the functional nature of this relationship differs between tidal pools and emergent substrata. Moreover, she hypothesized that green crab (Carcinus maenas) predation may exert an indirect influence on algal communities by regulating L. littorea density. This hypothesis is conceptually appealing, but over 20 years have passed without it being tested experimentally.
Recent data suggest that the suppression of snail grazing by green crab risk cues can have a significant effect on rocky shore algal communities. This research examines the relative importance of density and trait-mediated interactions between green crabs and L. littorea to patterns of algal diversity and structure on rocky shores by asking the following questions:
--I. What factors shape the relative importance of density and trait-mediated effects?
-- II. How may the relative importance of DMIIs and TMIIs influence long-term algal diversity and community structure on rocky intertidal shores?
-- III. Can habitat-specific differences in the relative importance of DMIIs and TMIIs explain differences in the functional relationship between algal diversity and snail density in two prominent rocky shore habitats: emergent substrata and tide pools?
This research will have broad implications to empirical and theoretical ecology by explicitly examining the role higher order interactions play in shaping long term community dynamics. By working in a system (a) widely held as a classic demonstration of the role of density-mediated effects and (b) that has contributed significantly to the development of modern ecology, the proposed research will provide a better understanding of the processes shaping diversity and structure in rocky shore and other communities. Because these food chains are relatively simple and easily manipulated, these habitats afford an excellent opportunity to explore these issues.

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